Citation
Production aspects of maize + sorghum intercropping systems in Central America

Material Information

Title:
Production aspects of maize + sorghum intercropping systems in Central America
Creator:
Arias Milla, Francisco Roberto, 1948-
Publication Date:
Language:
English
Physical Description:
vii, 238 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Agronomy thesis Ph. D
Corn -- Central America ( lcsh )
Dissertations, Academic -- Agronomy -- UF
Intercropping -- Nicaragua ( lcsh )
Sorghum -- Central America ( lcsh )
Corn ( jstor )
Crops ( jstor )
Dry matter accumulation ( jstor )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1985.
Bibliography:
Includes bibliographical references (leaves 223-237).
Additional Physical Form:
Also available online.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Francisco Roberto Arias Milla.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
021031350 ( ALEPH )
13991380 ( OCLC )

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Full Text
















PRODUCTION ASPECTS OF MAIZE + SORGHUM INTERCROPPING SYSTEMS
IN CENTRAL AMERICA











BY

FRANCISCO ROBERTO ARIAS MILLA


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1985




































TO

TINITA, BENERANDA, ROBERTO, LILIANA, AND VERONICA


AND IN MEMORY OF
MICAELA RETANA















ACKNOWLEDGMENTS


I express sincere gratitude to Dr. Raymond Gallaher, chairman of

the supervisory committee. His guidance, dedication, and continuous

encouragement were valuable throughout my graduate program. I also thank

Dr. Victor E. Green, Dr. Clift Taylor, Dr. Mary Collins, and Dr. Maxie

McGhee for their teachings and guidance in the preparation of this

manuscript.

My studies would have been impossible without the financial

assistance of the Centro Agronomico Tropical de Investigacion y

Ensenanza (CATIE) and the W. K. Kellogg Foundation, to the staff members

of which I express my sincere gratitude.

Thanks are also due to Mr. David Block for his assistance in the

statistical analysis of the data, and to Mr. Jacobo Reyes Palma for his

valuable assistance in conducting the field work. Acknowledgment is due

to Mrs Beneranda Arias and Mrs. Oliviethe Ortiz for their assistance in

the tissue analysis. Words of gratitude are expressed to Dr. Raul Moreno

for his encouragement, and friendship.

To my mother, for her never ending sacrifices, her love, and

prayers, I owe much gratitude. I also thank my brothers Julio, Marina,

and Guillermo who have also contributed greatly towards the fulfillment

of my goals in life. To my wife, Beneranda, I express my gratitude for

her moral support, patience, and encouragement. I thank Roberto,

Liliana, and Veronica, without whose motivation and love this task would

have been less bearable.

















TABLE OF CONTENTS


ACKNOWLEDGMENTS . . . . . . . . . . . . ..

ABSTRACT . . . . . . . ..............................

CHAPTER 1. INTRODUCTION . . . . . . . . . . .

CHAPTER 2. LITERATURE REVIEW . . . . . . . . . ..

Growth . . . . . . . . . . . ............
Crop Growth Rate . . . . . . . o . . . .
Factors That Affect Growth . . . . . . . . ..
Leaf Area Index . . . . . . . . . . . .
Dry Matter Accumulation . . . . . . .........

Forage Quality . . . . . . . . . . .........
Crop Residues . . . . . . . . . .........
Energy . . . . . . . . . . .............


Page

iii

vi

1

7

7
7
10
17
19


Nutrition . . . . . .. ....
Critical Levels . . . . .
Factors That Affect Concentration .
Nutrient Accumulation . . . .


Sulfur . . . . . . .
Importance of S . . . . .
Forms and Amount of S in the Soil
Sulfur Deficiency in Soils . .
Plant's Requirements and Content.
Absorption and Accumulation of S.
Effects of S Deficiency . . .
Interaction Between S and Other Nt
Crop Response to S Fertilizer .


* * *
* * *
* * *
* * *
* * *
* * *
* * *
itrients .
* * *


CHAPTER 3. MATERIALS AND METHODS . . . . . . . ..

Field Procedures . . . . . . . . . . . .
Fertility Trials . . . . . . . . . . .
Growth Analysis . . . . . . . . . . . .
Survey of Sulfur Deficiency in Maize . . . . . ..

Laboratory Procedures . . . . . . . . . . .
Soil Analysis Methods . . . . . . . . . .
Plant Analysis Methods . . . . . . . . ..








Page
CHAPTER 4. MAIZE + SORGHUM FARMING SYSTEMS IN CENTRAL AMERICA:
SITUATIONAL ANALYSIS . . . . . . . . .. 78

Introduction . . . . . . . . . . . .. 78
Materials and Methods . . . . . . . . . ... . 80
Results and Discussion . . . . . . . . . .. 81
Bio-Physical Environment . . . . . . . . .... 84
Socio-Economic Environment . . . . . . . ... 87
Crop/Animal Interactions . . . . . . . . ... 103
Constraints .. ..... . . . . . . . . . . 105
Research Opportunities . . . . . . . . ... 107
Interventions . . . . . . . . . . . .. 108

CHAPTER 5. DRY MATTER ACCUMULATION BY MAIZE + SORGHUM AND
MAIZE + MILLET INTERCROPPING SYSTEMS . . . . .. .109

Introduction . . . . . . . . . . . . .. 109
Materials and Methods . . . . . . . . . . .. II.I
Results and Discussion . . . . . . . . . .. 113
Percent Soil Moisture . . . . . . . . . .. 113
Dry Matter Accumulation . . . . . . . . .. 118
Leaf Area Index and Other Plant Characteristics . . .. .130

CHAPTER 6. NUTRIENT CONCENTRATION, IVOMD, AND METABOLIZABLE
ENERGY OF INTERCROPPED MAIZE + SORGHUM AND MAIZE
+ MILLET SYSTEMS . . . . . . . . . .. 131

Introduction . . . . . . . . . . . . . 131
Materials and Methods . . . . . . . . . ... 134
Field Procedures . . . . . . . . . . .. 134
Laboratory Procedures . . . . . . . . . .. 136
Results and Discussion . . . .. .................... 137
Percent Organic Matter, IVOMD, Metabolizable Energy,
and Nitrogen . . . . . . . . . . . .. 137
Phosphorus, K, Ca and Mg Accumulation . . . . . .. .157
Iron, Cu, Mn and Zn Accumulation and Distribution . . .. .174

CHAPTER 7. SURVEY OF SULFUR DEFICIENCY IN MAIZE . . . . .. .187

Introduction . . . . . . . . . . . . .. 187
Materials and Methods . . . . . . . . . ... 191
Field Methods . . . . . . . . . . . .. 191
Laboratory Procedures . . . . . . . . . .. 193
Results and Discussion . . . . . . . . . .. 195
Experiment I . . . . . . . . . . . . 195
Experiment 2 . . . . . . . . . . . .. 205

CHAPTER 8. SUMMARY AND CONCLUSIONS . . . . . . . ... 220

BIBLIOGRAPHY . . . . . . . . . . . . . .. 223

BIOGRAPHICAL SKETCH . . . . . . . . . . . ... 238
















Abstract of Dissertation Presented to the Graduate School of the
University of Florida in Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy

PRODUCTION ASPECTS OF MAIZE + SORGHUM INTERCROPPING SYSTEMS IN
CENTRAL AMERICA


By

Francisco Roberto Arias Milla

August 1985



Chairman: Raymond Noel Gallaher
Major Department: Agronomy


Farmers in the semi-arid areas of Central America have developed a

maize (Zea mays) + sorghum (Sorghum bicolor (L.) Moench)-animal mixed

production system in response to resource availability and family food

needs. The objectives of this study were to a) describe the maize + sor-

ghum system in its bio-physical and socio-economic environment, b) study

the relationship between soil moisture and dry matter accumulation, c)

describe dry matter, energy, and nutrient accumulation by the system,

and d) determine if S deficiency is a widespread problem in areas where

the system is used.

From a situational analysis it was found that marginal soils, ir-

regular rainfall pattern, lack of appropriate technology, and limited

resources are characteristics of farms in the areas where the system is

practiced. During a growing season a farmer on a 7 ha farm may invest up

to $200 (US), mainly on fertilizers (70% of the total cash investment)

and $45 (US) on animal feeds.









This research showed that late planting coupled with inadequate

soil moisture resulted in poor growth. Results suggest that grain yield

was more susceptible to water stress than total dry matter yield. The

highest crop growth rate observed (756 kg ha day ) was in maize plants

from the maize + millet system. Striking differences in dry matter

distribution were observed between the photosensitive and non-

photosensitive sorghums. At grain harvest, both sorghums had accumu-

lated similar amounts of dry matter (14.3 and 14.9 Mg ha respective-

ly). However, the distribution of the dry matter in the stems, leaves,

and heads of photosensitive sorghum and the non-photosensitive was 46,

37, 17 and 28, 17, and 55%, respectively.

Water stress affected IVOMD and nutrient concentration in all

crops. In the photosensitive sorghum, the stem had higher IVOMD than any

other plant component. In general, nutrient concentration declined with

maturity. However, leaf Ca increased with maturity. An imbalance between

K:Ca, K:Mg, and K:Ca+Mg was observed in maize plants from all systems.

Sulfur deficiency is a widespread problem in some areas of Nic-

aragua and Florida. Stunted chlorotic plants observed in both areas were

deficient in S and had a N:S and P:S imbalance. Sulfur deficiency appar-

ently caused maize leaves to be deficient in K, resulting in a K:Ca+Mg

imbalance, even though sufficient K was indicated in the whole plant

analysis.
















CHAPTER 1
INTRODUCTION


Historically, increases in production have been brought forth by

increasing the amount of land under cultivation or by increasing unit

yields of existing hectares through improved technology. These

constitute what Sanchez (1976) has called the area and space dimensions,

respectively. Except where limited by soil moisture supply or altitude,

the growing season in tropical latitudes is infinite and multiple

cropping systems have been used for centuries. Most low-income farmers

in the tropics practice cropping systems (i.e. intercropping, relay

and/or sequential cropping) that intensify production not only in space

but also in time.

Intercropping has been an important practice in many parts of the :

world, especially in the tropics, and there is little doubt that it will

remain so. It is only recently, however, that research has established

that intercropping can give higher yields than growing sole crops.

Wahua and Miller (1978a) explain why intercropping is popular among

small-scale farmers in tropical and sub-tropical environments. Some of

these reasons are built-in balanced nutritional supply of energy and

protein, profit and resource maximization, efficient water and light

utilization, inexpensive weed control, minimization of agricultural

risks, and improvement of soil fertility. Other authors (Mead and

Willey, 1980) consider that low-income farmers need to grow more than

one crop, whether intercropped or not, to spread labor peaks, to reduce

1










marketing risks, and to satisfy different dietary needs. Small-

scale farmers in Central America comprise the most important basic

food production group. They use production systems frequently referred

to as traditional in the literature (Rodriguez et al., 1977; Arias et

al., 1980; Rosales, 1980; Mateo et al., 1981). These systems have been

developed through the interaction of man and his environment, under

conditions involving high risk and restraints which limit crop

productivity.

Several cropping systems can be found in the dry areas of the

Isthmus. Maize (Zea mays L.) intercropped with sorghum (Sorghum bicolor

(L.) Moench) (maize + sorghum) with varying degrees of competition in

time and space, is the most widely practiced cropping system in Central

America (Hawkins et al., 1983; Larios et al., 1983). Other relevant

systems include mono or relay crops of maize, or bean (Phaseolus spp.)

or cowpea (Vigna spp.); sorghum intercropped with bean, sesame (Sesamum

indicum L.); or sisal (Agave spp.) intercropped with maize, sorghum,

and/or bean.

It is accepted (De Wit and Hollman, 1970; Quimby, 1974) that

sorghum was introduced to the western hemisphere by African slaves and

Portuguese sailors in the 16th century. According to Martin (1975) it

was not until the 19th century that sorghum gained importance in the

United States. It has not been documented in the literature when the

system was first used in Central America, but it cannot be more than 350

years ago.

Agricultural research in the tropics has been conditioned by the

cropping systems of more developed areas, the origin of most research

workers, and until recently, rather cursory attention has been paid to










indigenous systems. Baker (1979) emphasizes that attempts to improve

production in the tropics have failed not because of farmer conservatism

or the lack of extension programs, but because it has not been realized

that subsistence agriculture is a tropical agro-ecosystem geared for a

low level of production and not simply a collection of crops and

animals to which inputs can be applied indiscriminately to obtain

immediate results.

A lack of appreciation of the personal nature of the subsistence

farmers' farming systems has resulted in a tendency for research to

produce solutions to the wrong problems. For example, agricultural

research in Central America has traditionally been dedicated to export

crops such as banana (Musa spp.) and coffee (Coffea spp.), while most of

the available technology for increasing basic food crop productivity has

been adapted from temperate countries and thus has generally been

developed for sole cropping.

Mateo et al. (1981) and Larios et al.(1983) have pointed out that

in spite of the economic importance of the maize + sorghum this system

has received little attention in the work plans of local research

institutions. Reports in the literature (Arias et al., 1980; Mateo et

al., 1981; Fuentes and Salguero, 1983) indicate that of the total area

cultivated with sorghum in Guatemala, El Salvador, and Honduras, the

percentages intercropped with maize are, respectively, 80, 93 and 93.

Larios et al. (1983), concluded that knowledge of the process of

integrating component technologies into farming systems is lacking,

especially for small-scale farms. Due to the lack of available

technology adapted to conditions prevailing in the semi-arid regions of

Central America it is mandatory to conduct field experimentation that










will alleviate this deficiency. A summary of the scheme presented by

Arze et al. (1983) to accomplish this task follows:

1. Identify important cropping systems used in the semi-arid

regions of Central America.

2. Study the performance of the cropping patterns under different

environmental variables.

3. Determine the degree and form of relationship among these

variables.

4. Use the previous information to maintain, arrange or re-design

the system so that it operates optimally with respect to its objectives.

Several authors (Rodriguez et al., 1977, Arias et al., 1980; Mateo

et al., 1981; Guzman, 1982; Fuentes and Salguero, 1983; Hawkins et al.,

1983; Larios et al., 1983) have identified environmental stresses

limiting crop productivity in the semi-arid regions of Central America,

their listings including drought, nutrient deficiencies, particularly N,

P and S (CATIE, 1980, 1982a; Rico, 1982; Hawkins et al., 1983), and

water and wind erosion. These areas are primary sources of cereal

grains, oilseed crops, fruits, vegetables, table legumes, meats, and

dairy products for a large majority of the rural and urban population of

the Isthmus. Basic research projects to overcome environmental stress

limitations have been notably successful in many crops and can provide

data for future significant progress with adaptive research.

Maize + sorghum was selected as the subject of this research

project because of its importance in food production. The maize +

sorghum cropping system is predominant in semi-arid areas of Central

America at elevations below 1,000 m. The system apparently increases

the productivity and reduces risk of loss in areas with marginal










conditions for maize production. Shallow soils and variability of

rainfall make failure of the maize crop more common than failure of the

sorghum crop, which is of lower value to the farmer for both sale and

consumption.

Present fertilizer use is oriented toward maize production, while

sorghum mostly is dependent on native soil fertility and residual

fertilizers applied to the previous crop. Whether any of the fertilizer

applied to the maize reaches the sorghum will perhaps be clarified by

the present experiments. Presently, few farmers apply any fertilizer to

the sorghum, despite the fact that under climatic constraints in which

they are operating, sorghum or millet has as much or higher yield

potential than maize.

The general objectives of this research were 1) to provide basic

information, 2) to improve traditional cropping systems, 3) to develop

new systems adapted to prevalent bio-physical conditions, and 4) to

apply new discoveries that will increase net family income and that are

appropriate to the economic resources available to farmers of the

semi-arid regions of Central America.

The specific objectives of this study are 1) to describe the maize

+ sorghum system in its bio-physical and socio-economic environment in

Central America, 2) to describe the growth pattern of the maize +

sorghum system and of potential substitutes, 3) to describe the pattern

of energy and nutrient accumulation of the system and of potential

substitutes, 4) to determine if variation of other components of the

system, such as substituting the traditional photo-sensitive sorghum

with improved non-photosensitive cultivars or millet (Pennisetum

americanum (L.) Leeke), will increase productivity, and fertilizer and







6


water use efficiency; 5) to study the relation between gravimetric soil

moisture and dry matter accumulation by the maize + sorghum, maize +

millet systems; 6) to determine the existence of soil S deficiency in

areas where the system is practiced in Nicaragua.

















CHAPTER 2
LITERATURE REVIEW


Growth

Crop Growth Rate

Goldsworthy and Colegrove (1974) found that crop growth rates (CGR)

in maize (Zea mays L.) declined rapidly when grain growth commenced. As

grain growth increased towards a maximum, about 100-110 days after sowing,

CGR decreased to near zero values. There are two possible explanations

for this pattern of change in dry weight. First, it is possible that a

large part of grain dry matter is derived from assimilates which

accumulate in plant parts other than grain and are then translocated to

the grain. Second, if as reported by Allison and Watson (1966) and by

Palmer et al. (1973) the dry matter that fills the grain is derived from

current assimilation, then presumably the large loss in weight from other

parts of the plant, mainly the stem, represents respiration losses that

are not replaced by current assimilation.

The rates of dry-weight production (500 kg ha week ) per unit leaf

area reported by Goldsworthy and Colegrove (1974) were high at silking.

This, combined with the large leaf areas, accounted for the peak growth

rates observed. The rapid decline in CGR after silking was related to the

simultaneous and rapid decline in leaf area and net assimilation rate.








8

Vanderlip and Reeves (1972) have shown that during grain filling

there is a net reduction in stem weight, with grain accumulation occurring

at a greater rate than the rate of total dry matter accumulation.As the

grain approaches physiological maturity the stem again increases in

weight.

Goldsworthy (1970) concluded that a decrease in radiation and a

loss in dry weight from decay and detachment of dead sorghum (Sorghum

bicolor (L.) Moench) leaves were probably the most important of the

factors that contributed to the decrease in growth rate observed in the

middle of the season. Since net-assimilation rate is also dependent on

leaf area index (LAI), lower leaves were probably making little or no

contribution to dry weight increase at this time. A sharp decline in leaf

area and in net-assimilation rate accounts for the rapid fall in crop

growth rate of the non-photosensitive sorghum after heading, at the end of

September.

Goldsworthy (1970) reported that a large proportion of the increase

in total dry weight of sorghum 'Farafara' (a photosensitive cultivar)

after heading was as dry weight in the stems. During the 3 weeks before

harvest (22-25 weeks after sowing), stems lost weight, and the losses in

weight were similar to the weights gained after head emergence. In

contrast, virtually all of the dry weight increase by 'NK-300' (a

non-photosensitive cultivar) after head emergence was in the heads. In

the first year of his study the weight of stems of the 'NK-300' reached a

maximum at heading and then remained constant until harvest, whereas in

the second year the stems lost weight before harvest, and it is probable

that, with a smaller supply of assimilate, carbohydrate normally respired








9

in the stem was diverted to the head and that this accounts for the loss

in stem weight in this instance.

Apparent photosynthesis was closely correlated with dry matter

accumulation by the shoots during grain fill. Consequently, the progress

of photosynthate accumulation can probably be viewed as the progress of

dry matter accumulation. Translocation was less inhibited than dry matter

accumulation or apparent photosynthesis under dry conditions. As a

result, grain yield, while significantly inhibited, was probably less

inhibited than it would have been if the translocation of reserves had not

occurred.

Other authors have shown that maize stems often lose dry matter as

the grain matures (Johnson et al.,1966; Daynard et al., 1969; Hume and

Campbell, 1972), particularly when the environment becomes unfavorable

during grain fill. The dry weight appears to be soluble carbohydrates

that can be stored in the stem (Daynard et al., 1969; Hume and Campbell,

1972). This mobilization of stem reserves has not been observed in every

instance (Hanway, 1962a). This agrees with the conclusion by Duncan et

al. (1965) that even relatively short-term adjustment by stem reserves may

enable the maintenance of a high rate of grain filling while the

conditions for photosynthesis are temporarily unfavorable. Thus, in maize

stem, mobilization probably occurs when sink demand exceeds source

capacity.

It has been shown that the dry matter stored in the grain of

sorghum (Stickler et al., 1961b; Goldsworthy, 1970), in the grain of maize

(Allison and Watson, 1966), and in rice (Enyi, 1962) is derived mainly

from assimilates produced after head emergence so that grain yield is

directly related to leaf area after the ears emerge. However, McPherson








10

and Boyer (1977) concluded that since grain yield was in excess of the

photosynthesis occurring during grain development, yield must have

reflected the amount of photosynthate accumulated by the crop over a

larger portion of the growing season than the grain filling period alone.

This is generally interpreted to mean (Yoshida, 1972) that dry matter

accumulated by the shoots determines yield.

Factors That Affect Growth

Environmental factors

Maize plants, wherever they are grown, should progress through all

the stages of development described by Hanway (1963). However, the

length of time between the stages and the identifying characteristics may

differ for different hybrids and for different environmental conditions.

Shaw and Thorne (1951) reported that the elapsed time between plant

emergence, stage 0, and silking, stage 5, is variable, and Tyner (1946)

reported that the period from silking to physiological maturity appears to

be relatively constant for different hybrids and different environmental

conditions. The intervals between the intermediate stages of growth

differ for different hybrids and with differences in environmental

conditions, especially temperature and fertilization (Hanway, 1963).

Sivakumar et al. (1979) suggested that plant growth is the result

of an effective integration of many factors. Restriction of growth may

occur due to the limitation of any one factor; for example, water deficits

in plants generally lead to reduced leaf water potentials and stomatal

closure, as manifested from an increased leaf resistance to transpiration.

The effects of depletion and replenishment of soil water on transpiration

are of specific importance to water use and its efficiency in crop

production. The relative rates of absorption and transpiration determine







11

a plant's internal water balance, which directly affects the physiological

and biochemical process of plant growth.

Plant nutrition

Hanway (1962b) indicated that variations in light, moisture, and

many other factors cause fluctuations in the growth rate. The growth rate

of maize under N sufficient conditions was 250 kg ha-1 day while the

growth rate for maize on the extremely N-deficient continuous maize plot

was much less (84 kg haI day- ). The fertility differences did not

markedly alter the relative proportion of each plant part.

Goldsworthy and Colegrove (1974) found production of dry weight

after silking to be related to the amount and duration of leaf area after

silking and to the efficiency of the leaf area. The ratio of grain weight

to leaf-area duration per unit area of land after heading is an index of

the efficiency with which the leaf area present after heading produces dry

matter for the grain (Watson et al., 1963).

Hanway (1962a) observed that extreme N and K deficiencies result in

premature death of several lower leaves. This shortens the period over

which these leaves carry on photosynthesis. In any case, the primary

effect of nutrient deficiencies appears to be on the amount of leaves

produced rather than on the net assimilation rate (rate of increase of dry

weight per unit leaf area).

Data presented by Hanway (1962a) suggested that although N, P, and

K concentration of maize leaves at the beginning and end of the grain

formation period varied markedly, the chemical composition of the leaves

had very little effect upon the rate of photosynthesis in the leaves.

However, extreme N and K deficiencies were observed to result in premature

death of several lower leaves on some of these plants. Nutrient







12

deficiencies are reflected in both leaf area and the chemical composition

of the leaves. The chemical composition of the leaves at silking time can

indicate which nutrient elements are deficient and which deficiencies have

resulted or will result in a reduced leaf area and, thereby, a reduction

in grain yield. These leaf analyses are very valuable diagnostic tools,

but it appears that their interpretation should be based upon their

relation to leaf area and not to net assimilation rate.

According to Nelson (1956) many investigators have found high

positive correlation between the percentages of N, P, and K in maize

leaves at silking time and the yield of grain. Nutrient deficiencies are

reflected in both leaf area and in the chemical composition of the leaves.

Thus, while grain yield is primarily a function of leaf area, leaf area

is a function of the nutrient status of the plant which is reflected in

the chemical composition of the leaves.

Maize under low fertility generally silks later and forms the

black layer earlier, resulting in rather large differences in filling days

and filling degree-days. Peaslee et al. (1971) found that P may tend to

shorten the grain filling period by accelerating the development of the

grain to the maturity stage. This tendency was apparently counteracted by

the tendency of P to also accelerate development to the grain initiation

stage. Earlier silking and lower moisture contents of the grain at

harvest were associated with additions of P fertilizer. However, these

were cases in which the levels of P in the soil were low and plant growth

response to P was marked. Peaslee et al. (1971) concluded that either P

or K was directly responsible for early initiation of the ear and/or delay

of the black layer formation by some specific function or they indirectly







13

influence plant development through the quantity of soluble carbohydrates

present in plants and their transformation into grain.

Drought

Almost every plant process is affected directly or indirectly by

water deficits. Some processes are quite sensitive to water stress, but

others are relatively insensitive. When plants are subjected to water

stress there is a decrease in photosynthesis and cell enlargement. There

is also considerable retention of carbohydrates in photosynthetic tissues.

Although translocation proceeds, its rate is reduced. Translocation is

rarely mentioned as a factor in reduced plant growth under limited

moisture. Translocation could be one of the chief physiological factors

limiting growth under unfavorable moisture conditions.

Shaw (1974) found that experimental maize yields were highly

correlated with a plant moisture stress index which was based on

calculations of daily ratios of actual to potential evapotranspiration for

the period of 40 days before to 45 days after silking. Although soil

moisture strongly interacts with temperature in plant growth processes, it

is much less important in plant phasic development.

Sivakumar and Shaw (1978) reported that the major components of

sorghum yield which were significantly affected by drought in the case of

the nonirrigated plots were tertiary branches per secondaries, seed number

per panicle, and seed size. The reduction in these components was 46, 26,

and 28%, respectively. Data presented in this study bring out the

importance of the availability of a few additional cm of water to a

sorghum crop under water stress and the benefits that should accrue from

such water applications.








14

The depressive effect of water stress on photosynthate

translocation reported by Brevedan and Hodges (1973) is in agreement with

the observation of several other authors (Hartt, 1969; Plaut and Reinhold,

1965; Wardlaw, 1967). Wardlaw (1967) found a continued movement of

assimilates from the leaf to the developing wheat (Triticum aestivum L.)

grain under water stress conditions. He also observed a lower velocity of

sugar transport from leaves of stressed plants than from well-watered

plants.

Data presented by Denmead and Shaw (1960) suggested that lower

assimilation in plants subjected to stress is partly due to smaller leaf

area, as indicated by the size of the ear leaf, and partly due to the

metabolic activity of the plants at different growth stages. When

compared with the reduction in assimilation caused by stress at other

growth stages, the reduction in assimilation resulting from stress at

silking is larger than the reduction in leaf area could indicate. The

data also suggested that there may be a tendency for recurring periods of

stress to have less and less detrimental effect on assimilation and yield.

Stress applied while the plant is actively expanding retards enlargement

of plant parts. Recovery when the stress is removed is not immediate but

growth rate appears to return to normal after a few days.

McPherson and Boyer (1977) reported that the physiological

mechanisms responsible for yield losses under dry conditions are unknown,

especially for grain crops. Drought causes massive losses in the yield of

crops, but the physiological mechanisms responsible for decreased yields

are poorly understood. Most aspects of the physiological behavior of

plants are known to be altered by the onset of dry conditions (Boyer,

1973; Hsiao, 1973). But photosynthesis and translocation, which are








15

important in grain crops, are especially sensitive (Hsiao, 1973; Boyer and

McPherson, 1975; Boyer 1976).

It is generally accepted that optimized grain filling requires

continued dry matter production and translocation of the product to the

grain. However, Brevedan and Hodges (1973) concluded that translocation

was more sensitive than photosynthesis to drought. Wardlaw (1967) studied

desiccated wheat during the grain filling stage and found that movement of

assimilates into conducting tissue was delayed in wilted leaves, but the

velocity of translocation was relatively unaffected.

Barlow and Boersma (1976) found that the partitioning of the total

dry matter into grain was affected by desiccation. In the controls, the

grain dry matter was only 63 to 76% of the total dry matter accumulated by

the shoots during grain fill. In the desiccated plants, however, grain

dry matter was 50% larger than the total dry matter accumulated during

grain fill. Thus, in the desiccated plants, grain development must have

occurred at the expense of dry matter stored in other parts of the plants.

Jurgens et al. (1978) concluded that while grain fill was seriously

inhibited by desiccation (grain yield was reduced to 42% of the control),

it was clearly maintained above that expected from dry matter accumulation

during the grain filling period. This occurred because translocation to

the grain continued at a modest rate even when there was no net

accumulation of photosynthetic material by the desiccated plants. Thus,

under field conditions photosynthesis was more affected than translocation

during desiccation. It appears that grain crops having the opportunity to

accumulate reserves under favorable moisture conditions are able to

preserve grain development if conditions later become unfavorable.








16

Assimilation after ear emergence, both in the leaves and in the ear

itself, is primarily responsible for accumulation of material in the grain.

Early stress, then, has an indirect effect on yield of grain through

reducing the size of the assimilatory surface at the time of ear

development. Stress imposed after the ear has emerged has a more direct

effect through reducing assimilation in this critical period when daily

assimilation rates are high and most of the assimilates are being used for

grain production. The relatively small effect of stress during the ear

stage suggests that the critical period would not extend longer than about

3 weeks after 75% silking.

Jurgens et al. (1978) found that the induction of low leaf water

potentials in desiccated plants caused an almost immediate decrease in

viable LAI. At maturity it was evident that the prolonged drought

treatment had markedly affected grain components. Yield, kernel weight,

and percent oil were all substantially reduced by desiccation while

percent protein increased. Grain production was relatively closely tied

to the total dry matter production for the season. In the controls grain

production was 51% the total dry matter production, and in desiccated

plants it was 39%. The desiccated plants produced less dry matter and

exhibited a slower gain in grain dry weight than the controls.

Reddy and Willey (1981) reported that the total water use

(i.e.transpiration plus evaporation from the soil surface) by sole millet

and sole groundnut over their full growing periods were 30.3 and 36.8 cm,

respectively. The total water use of 40.6 cm by the intercrop was greater

than either sole crop but it was 11% less than the total water use

expected if each component had used water at its sole crop efficiency.

Thus, the 28% higher dry matter yield of the intercrop could only be








17

partly explained on the basis of greater total water use and it must have

been partly due to an increase in total water use efficiency.

In an irrigation study Sivakumar et al. (1979) found that the

non-irrigated sorghum crop used 213 mm of water to produce 510 kg ha1 of

dry matter, whereas, the irrigated sorghum used 321 mm of water to produce

930 kg haI of dry matter. Szeicz et al. (1973) observed that average

sorghum crops in Texas use approximately 320 mm of water throughout the
-i
growing season to produce around 0.8 kg dry matter m

Leaf Area Index

Dale et al. (1980) reported that growth and duration of green leaf

area of a crop determine the percentage of incident solar radiation

intercepted by the crop canopy and thereby influence canopy

photosynthesis, evapotranspiration, and final yields. Leaf area index is

defined as the ratio of the area of one side of the green leaves of a

plant to the area of soil surface allocated to the plant.

Shih et al. (1981) reported that LAI is often used as an indicator

of plant growth and for evaluating assimilation and transpiration rates in

plant physiological studies. This growth parameter is also frequently

used in agronomic studies to model yield and to make crop production

decisions. Ashley et al. (1965) found good correlation between LAI and

leaf dry weight of cotton (Gossypium hirsutum L.). Rhoads and Bloodworth

(1964) and Pearce et al. (1965) also found strong correlations between

leaf area and dry matter yield in cotton and orchard grass (Dactylis

glomerata L.).

According to Hanway (1963), the genetic characteristics of the

plant, day length and various environmental conditions prior to stage 1 of

growth, have determined the number of leaves that will develop on maize








18

plants. He also observed that except under very carefully controlled

conditions in fields or in experimental plots there will be differences in

growth between different plants that have received the same treatment.

The number of leaves per plant on plants of the same hybrid grown in the

same plot varied between 15 and 22 leaves per plant. All plants in a

given plot will develop at the same rate, so not all plants in a plot are

at the same stage of development at the same time (Hanway, 1963).

Hanway (1962a) suggested that the dry weight of the entire plant

and of the grain are directly related to and highly correlated with the

weights of the leaves in these plants. Since leaf growth in maize is

completed relatively early in the season, the linear rate of dry matter

accumulation over a major part of the growing season appears reasonable,

unless the net assimilation rate decreases with age of the leaves or

decreases with the seasonal trend in climatic conditions.

Hanway's (1962a) study of maize growth as related to soil fertility

showed that approximately 30% of the total leaf weight had been produced

45 days after planting and that during the following two weeks leaf growth

was very rapid and by 60 days after planting over 85% of the final leaf

weight had been produced. This would appear to be a critical stage in

leaf development when nutrient deficiencies might reduce the final weight

of leaves. Most of the grain was produced in a 30 to 35 day period. This

growth pattern was similar for plants from all the fertility levels except

that the silking and subsequent growth of the cob, shank, and grain was

delayed slightly in the N-deficient plants from the continuous maize plot.

Shih et al. (1981) reported that leaf area per stalk declined after

stalk length reached about 185 cm. This is consistent with the general








19

pattern of leaf area in sweet sorghum which starts declining after the

plant approaches 50% bloom.

Dry Matter Accumulation

Hanway (1962a) reported that the potential yield of maize grain

which is produced late in the season is determined by the leaf area, which

is always produced early in the season. However, less than this potential

yield of grain will actually be attained if a) the net assimilation rate

is decreased by any factor such as a moisture deficiency later in the

season or b) the leaf area is prematurely reduced by some factor that

results in premature death of leaves such as a nutrient deficiency or

insect, disease, or hail damage. If no other factor limits yield, one

would expect that increasing LAI should result in increased grain yield.

Data reported by Tollenaar and Daynard (1978) showed that grain

yield per plant was most affected by shading during the silking period,

indicating a sink limitation for grain yield in hot environments. A

source limitation in short-season regions may be the consequence of low

leaf area per plant.

Hanway and Russell (1969) reported relatively large differences

among maize hybrids in the length of the grain filling period. Daynard

and Duncan (1969) have observed such differences among hybrids and have

found a high correlation between the length of the grain filling period

and the yield.

The patterns of growth and dry matter distribution observed in

tropical cultivars grown in Mexico (Goldsworthy and Colegrove, 1974)

suggest that the capacity of the grain sink to accommodate assimilate can

limit grain production. Results of defoliation studies in Rhodesia

(Allison and Watson, 1966), which showed that a relatively large amount of







20

dry matter which could be translocated to the grain normally remains in

the stem, also indicate a sink limitation. Conversely, the decrease in

stem weight in the latter part of the grain-filling period, observed by

Daynard et al. (1969), seems to indicate that source may be limiting under

the environmental conditions prevailing in the northern periphery of the

maize-growing area of North America.

McPherson and Boyer (1977) pointed out that another potentially

more serious problem occurs if sink size has been affected by low leaf

water potential. If, for example, crop desiccation occurred during floral

development or pollination, irreversible loss of floral primordia (Moss

and Downey, 1971) or unsuccessful pollination could result. Thus, grain

yield would be limited more by the availability of developing grain than

by the availability of photosynthate (Denmead and Shaw, 1960; Classen and

Shaw, 1970), and prediction of yield based on photosynthesis would be in

error. Such a limitation would be less important where maize is grown for

silage, because shoot dry weight would reflect photosynthesis directly.

Moss (1962) and Allison and Watson (1966) have shown that when the

grain sink is missing, dry matter that would have passed to the grain

accumulates in the stem and husk. The presence of more barren plants

(Goldsworthy et al., 1974) probably explains why more dry weight

accumulated in the stems at Poza Rica than at Tlaltizapan, Mexico. It

would also account for the differences in the values for grain at the two

sites, since barren plants contribute to dry matter but not to grain

yield.

Goldsworthy et al. (1974) reported that dry weight also accumulated

in the stem of fertile plants and that the capacity of the ear to

accommodate the photosynthate produced was a further factor limiting








21

yield. Allison and Watson (1966) have shown that when the grain sink is

removed by preventing pollination the dry matter that would have passed to

the grain accumulates in the stover and that when the source of assimilate

is restricted by removing leaves, stem weight decreases as previously

stored dry matter moves to the grain.

Shih et al. (1981) found that the ratios between dry and fresh

phytomass were computed as 21.4, 35.1 and 35.4% for stalk, leaf, and

panicle, respectively. The ratios for leaves and panicles are similar,

but the ratio for stalks is lower. These ratios can be used to estimate

the dry weight yield based on the known fresh biomass, or vice versa.

Hanway (1962a) found that differences in soil fertility resulted in

different rates of dry matter accumulation but did not markedly influence

the relative proportions of the different parts. He reported crop growth

rates of maize of 250 kg ha dayI in N-sufficient plots. Hanway and

Russell (1969) found that the leaves, leaf sheaths, stalks, and husks of

maize attained their final mature weights at about stages 4.0, 4.5, 5.0,

and 5.5, respectively. All these plant parts continued to increase in

weight following these stages of development, but this continued increase

in weight was apparently an accumulation of materials which were later

translocated into the developing grain. At stage 6.5 the total

accumulated material in these plant parts was equivalent to about 20% of

the total mature dry weight of the nongrain parts of the plants. The cob

and ear shank attained their maximum dry weight at about stage 6.5 and

showed no later decrease in weight. An average of 42% of the total,

mature dry weights of the plants was grain and 58% was nongrain. However,

the relative proportions of grain and nongrain varied widely among the

different hybrids, years, and plant populations, with the grain varying








22

from 35 to 52% of the total plant weight. The rate of dry matter

accumulation in the grain was similar for all hybrids, years, and plant

populations varying from 163 to 181 kg ha day

Vanderlip and Arkin (1977) reported that on a daily basis, dry

matter in sorghum was allowed to be partitioned to the leaves up to 125%

of that neccesary for the leaf area developed that day. The same authors

found that at least 25% of the daily dry matter production was

partitioned to the roots, which under conditions of low photosynthate

production would cause an increase in specific leaf area.

Barlow and Boersma (1976) demonstrated that even grain dry matter

was only 63 to 76% of the total dry matter accumulated by the shoots

during grain fill. In the desiccated plants, however, grain dry matter

was 50% larger than the total dry matter accumulated and was accompanied

by a reduction in net photosynthate accumulation in the source leaf.

Goldsworthy (1970) reported that photosensitive sorghums sown at

the end of May formed from two to three times as much dry weight as 'NK

300' non-photosensitive which was sown 10 weeks later. The photosensitive

sorghum 'Farafara' had the largest total dry weight but the smallest

grain yield. About 70% of the total dry weight was in the stems and only

from 9 to 13% in the heads. In contrast, the dry weight of 'NK 300' was

only about one-third or one-half that of 'Farafara' but from 40 to 60% of

it was in the heads so that the grain yields were much larger than those

of 'Farafara'.

The reason, it seems, for the low grain yield of photosensitive

sorghum is that a substantial part of the assimilate formed after heading

accumulates in the stem, whereas most all of the dry matter produced

after heading in non-photosensitive moves to the head. The results of








23

these and of other experiments at Samaru suggest that the main reason for

the difference in yield between the photosensitive sorghum and

non-photosensitive sorghum is in the number of spikelets present at head

emergence; the number and/or potential size of the developing grains in

the photosensitive sorghum appears to be too small. Thus the dry weight

of the non-photosensitive sorghum 'NK 300' was much smaller than that of

the other sorghums mainly because of the inability of the head to accept

all the carbohydrate that the leaves can produce.

Goldsworthy (1970) observed that the heads of non-photosensitive

sorghum continued to gain weight 13 weeks before harvest, but those of

photosensitive sorghum did not and it is more probable that the loss in

weight from the stem was by respiration of labile carbohydrate that had

accumulated there. It may be that the developing head does not receive

the assimilate it needs before emergence and that it is unable to

accommodate all of the increased supply of assimilate from the leaves

after it emerges.

Blum (1970) concluded that when sorghum plants compete for water

the effect of competition on a photosensitive genotype is more severe

than on a non-photosensitive genotype, and that the highest yield is

obtained with an early maturing hybrid planted at relatively high plant

densities. Yielding potential was in direct relationship to duration of

growth under non-competitive conditions and in an inverse relationship

under extreme competition. This indicates that the importance ascribed to

a long duration of growth of cereals with respect to their yield

potentials does not hold under limited water supply. Blum (1970)

concluded that of his experiments demonstrated the superiority of an








24

early maturing hybrid under extreme plant competition for water is due,

at least partly, to advanced plant suppression by interplant competition.



Forage Quality

Many factors combine to determine the relative feeding value of

sorghum grain. Some of these are differences in tannin content, protein

content, amino acid composition, amount of floury and horny endosperm,

presence or absence of yellow endosperm, whether mixed with grain of

other species, whether processed in one or a number of ways such as

cooking, flaking, and/or steam rolling, whether weathered in the field

before being harvested, amount of damage of insects, presence of

aflatoxins or other molds, amount of rancidity of the oil, degree of

glume and other trash removal, presence of contaminants, and, most

important of all, degree of milling and type of animal to which it is to

be fed. Data presented by Hall et al. (1965) indicate that sorghum grain

is comparable to maize in digestibility of proximate components,

digestible energy, metabolizable energy, and nitrogen retention.

Eng et al. (1965) reported results which indicate wide variations

in the compositions and feeding values of sorghum grains. It appears that

such variations may be caused by geographical area, soil moisture, soil

fertility and variety of plants and might be important considerations in

the apparently divergent results which have been obtained by various

research workers when sorghum grain was compared to maize as an energy

source for fattening cattle. Further research work in this area is

needed.

Clark et al. (1965) found little difference in the carrying

capacity, milk production, or dry matter production of pearl millet and a







25

sorghum x sudangrass (Sorghum sudanense L.) hybrid when utilized as

pasture for lactating dairy cows. Johnson et al. (1966) studying changes

in dry matter and protein distribution in maize found that the protein

concentration of leaves declined rapidly and steadily until the final

mature stage. The protein concentration of the stalks was between 11 and

12% prior to tasseling, declined rapidly until 15 days after tasseling,

and declined only slightly throughout the remainder of ear growth and

maturation.

Johnson et al. (1966) observed that percent ash, cellulose and

crude protein were significantly decreased with increasing maturity.

Digestibility of dry matter and organic matter was significantly affected

by maturity, increasing to maximum at the dough-dent stage and decreasing

slightly thereafter. Dry matter digestibility was 68% at the earliest

maturity stage. Increasing maturity significantly decreased digestibility

of cellulose and protein throughout the harvest period.

Rendig and Broadbent (1979) observed that concentration of crude

protein ranged from about 6% in maize grain from plots that received no

added N or 90 kg N ha to nearly 10% in plots receiving 180 kg ha -1. The

concentrations in the grain protein of triptophane, lysine, glycine,

arginine, and threonine were decreased, and the concentrations of

analine, phenylalanine, tyrosine, glutamic acid, and leucine increased by

applications of N.

Schmid et al. (1975) observed that cell walls of maize cultivars

were considerably more digestible than those of the sorghum cultivars.

These results indicated that low cell wall digestibility was a major

factor limiting dry matter digestibility of sorghum silages. The same

authors reported that head IVDMD of short sorghum hybrids with high grain








26

ratios remained constant or increased with advancing maturity, while that

of the tall hybrids with lower grain ratios decreased with maturity. Stem

IVDMD of the tallest hybrids increased with maturity while the other

hybrids decreased with maturity.

Although maturity is a factor affecting sorghum silage nutritive

value, its influence varies depending on forage type in that a decline in

cellulose digestibility with maturity may be detrimental to total

digestibility of low-grain sorghums, but not for those with high-grain

content. Apparently, the rapid increase in the amount of a highly

digestible starch during maturation in the high-grain sorghums

compensates for the decline in cellulose digestion (Schmid et al., 1975).

Cummins (1970) in a two-year study observed that in general the in

vitro dry matter digestibility (IVDMD) of maize leaves decreased with

maturity, although some year-to-year variation occurred. The IVDMD was
2
negatively correlated with maturity (R =0.67 and 0.88, respectively).

Both IVDMD and carbohydrate content of the stalks were closely related to

the rainfall distribution during the maturity period.

Johnson and McClure (1966) found highest total dry matter yield per

hectare to be between the dent and glaze stage of kernel development.

Although ears constituted 60% of the dry matter of the mature maize

plant, they did not reach this proportion until the dent stage of

development. IVDMD of maize stem cellulose was quite constant during ear

development but digestibility of leaf cellulose declined steadily. The

soluble carbohydrate in maize stem tissue increased rapidly from

tasseling to a maximum in late August (milk stage) and thereafter

declined with maturity. Crude protein content declined steadily in maize

leaves but changed very little in maize stalks from milk stage to final








27

maturity (Johnson et al., 1966). Protein content in the whole plant

declined slowly during ear maturation.

The IVDMD for the stover silage reported by Colenbrander et al.

(1971) ranged from 41 to 50%. Results from this experiment indicated that

a low quality roughage such as maize stover silage can provide an

alternative source of nutrients for growing dairy heifers. Green (1973),

studying the yield and digestibility of bird-resistant grain sorghum,

observed that IVDMD varied from 79.8 to 50.5%. All of the NBR Varieties

had higher values. The correlation coefficient calculated to ascertain

the relationship between yield and IVDMD for the 41 varieties was low

(r=+0.52) and not significant, indicating they were not related. Schmid

et al. (1975) reported that IVDMD values at the 4-week growth stage

ranged from 71.7 to 84.2% for five brown midrib sorghum mutants compared

to 67.1 to 78.3% for their normal counterparts.

Crop Residues

Plant populations, row-spacings, and soil fertility affect not only

grain yields, but also the yields and quality of residues. Residue yields

from maize are normally greater than from grain sorghum but lower in

crude protein. Crude protein concentration of grain sorghum residues was

consistently higher than that of maize while IVDMD values were

consistently lower in grain sorghum.

Crop residues of grain sorghum and maize have attracted attention

as an alternate economical forage resource for livestock utilization.

There are few data available on agronomic production factors affecting

yield and quality of crop residues (Perry and Olson, 1975).

Perry and Olson (1975), studying the effects of N fertilization on

yield and quality of maize and sorghum residues, observed that grain N








28

concentration increased with N fertilization in both crops. Grain sorghum

N concentration was generally equal to or greater than that of maize.

Residue yields of both crops were increased significantly by 90 kg ha-

with no further increase at the higher N rate. Maize grain:stover ratios

increased with increasing N levels. Crude protein of grain sorghum

residues was consistently higher than that of maize while IVDMD values

were consistently lower in grain sorghum. Crude protein increased

significantly in grain sorghum residue with each increasing N level while

little increase occurred in maize.

Martin and Wedin (1974) reported that row-crop residues, although

present in great quantities in the midwestern United States, are often

considered to be of low quality. Consequently, grain sorghum stover on

millions of hectares is not utilized by livestock. Stover often remains

as a leafy, succulent, growing plant following grain harvest and should

be considered as a feed source for ruminants being maintained for

reproductive purposes.

Under Iowa conditions (Perry and Olson, 1975) grain sorghum

continues growth during the interval between grain harvest and killing

frost. This unique characteristic allows the ratoon crop to maintain and

perhaps improve its nutritional composition before utilization for winter

grazing or silage harvest. Burns et al. (1970) postulated that forage

sorghum produces photosynthate after maturation of seeds and until frost

and accumulates a reservoir of water-soluble carbohydrates in the pith of

the stalks.

Perry and Olson (1975) observed that maize dry matter yields

decline as much as 30% within 100 days of harvest. Any decline in crude

protein and digestibility following grain harvest of maize and grain







29

sorghum appears to be associated with environmental factors. Martin and

Wedin (1974) observed that grain sorghum stover lost 28.3% of its

original dry matter yield by 76 days after grain harvest. The leaves lost

dry matter more rapidly.

Any consideration of grain sorghum stover as a feed for ruminants

is dependent on meeting all or some of the animal's nutrient

requirements. For example, a 500-kg, dry pregnant beef cow consuming 7.6

kg of dry matter requires 5.9% crude protein and 50.0% total digestible

nutrients.

Using percentage IVDMD as roughly equivalent to percent TDN, data

presented by Perry and Olson (1975) indicate that IVDMD in stover before

frost is ample to maintain a pregnant beef cow or other ruminants.

Grazing grain sorghum stover must be reconciled with the high prussic

acid potential in sorghum species.

Energy

Net energy has become widely accepted in recent years for

expressing the value of a ration and the energy requirements for feedlot

cattle (Croka and Wagner, 1975). The energy value of livestock feeds can

be expressed as digestible or metabolizable energy or as the cultural

energy necessary to produce the feed. Livestock feeds are priced

essentially on their digestible energy content, except for high protein

feeds which are fed in supplemental amounts.

Energy reserves may be considered as organic accumulates

synthesized by the plant which are available for plant growth,

development and metabolism (Matches, 1969). Although soluble

carbohydrates are found throughout grass plants, their concentrations are

usually greater in the stubble than in the roots or leaves. Much of the








30

fructosan in grasses is accumulated in the first internode of the stem.

Within the stubble there may be a gradation in concentration of

carbohydrate reserves. In bromegrass (Bromus sp.) and timothy (Phleus

pratense) at anthesis concentrations of fructosans and total water-

soluble carbohydrates were greatest in the internode, leaf blade, and

sheath tissue closest to the stem base.

Bolsen et al. (1975) observed that sorghum stover and maize stalks

are energy-containing by-products of grain production. Both crop

residues make acceptable silage and both supply the energy needed in

maintenance rations for beef cows or ewes. Maize stalk silage can be

used in rations for growing dairy heifers if additional energy is

provided (Colenbrander et al., 1971).

On an energy basis, maize silage is especially valuable for milk

production. It has been reported that the energy value of maize silage

was closely related to total grain yield and proportion of ears to

stalks (Bryant et al., 1966). Sorghum has become increasingly important

in recent years as an energy source in high concentrate rations for

feedlot cattle in the southwest (Croka and Wagner, 1975b).

Crop residues have potential as fertilizer, as fuel, and as

livestock feed. Comparative values for these uses can be determined on

the basis of the amount of energy saved by substituting these materials

for conventional sources of feed, fertilizer, or fuel.

Goodrich et al. (1975) found that energy losses during the

ensiling process average 68% of dry matter losses, apparently because of

the loss of volatile energy-containing compounds during drying, which

inflated the dry matter loss values. Also, decarboxylation reactions

would result in greater losses of dry matter than energy. Energy losses








31

increased from 21.5 to 33.1%. The energy loss for maize ensiled at

33.1% moisture was greater (p=0.05) than that for maize ensiled at 21.5%

moisture. Energy loss was not significantly influenced by kernel

preparation (3.0 and 2.5% energy loss for whole kernel and rolled maize)

or by time of ensiling (2.9 and 2.6% energy loss for maize ensiled at

harvest and maize ensiled after drying and reconstitution).



Nutrition

Critical Levels

According to Bates (1970) the diagnosis of nutrient deficiencies

and the prediction of fertilizer requirements from plant analysis are

based on a critical concentration of a nutrient or nutrient fraction

within the plant or some plant part, below which growth or crop yield is

restricted.

In early studies by Macy (1936) the nutrient calibration curve

included the zones of minimum percentage, poverty adjustment, and luxury

consumption. He proposed a central concept stating that there is a

critical percentage of each nutrient in each kind of plant above which

there is luxury consumption and below which there is a poverty adjust-

ment which is almost proportional to the deficiency until a minimum

percentage is reached.

Ulrich (1952) defined critical nutrient concentration with respect

to plant growth in terms of 1) that which is just deficient for maximum

growth, 2) that which is just adequate for maximum growth, and 3) that

which separates the deficiency from the adequacy zones.










Factors That Affect Concentration

Bates (1970) reported that, next to the supply of elements, the

physiological age of tissue is probably the most important factor

affecting the mineral composition of a given species. There appears to

be general agreement with this statement. He further observed that the

pattern of nutrient content varies with the age of the species and with

the nutrient. Phosphorus concentration in a maize plant decreases with

age. This change in nutrient concentration with age is probably due to

both a changing nutrient content of a given tissue with age, the leaves

for example, and changing proportions of certain tissues with age, such

as an increasing proportion of stem and a decreasing proportion of leaf

tissue. Physiological age was particularly important for Ca and other

nutrients which are not readily translocated in the phloem. The

nutrient concentrations in plant samples can therefore be interpreted

only if the growth stage at sampling is defined.

Environmental and soil factors also influence the availability of

P and K and thus crop response to applied P and K. Volumetric water

content, soil bulk density, buffering capacity, concentration, counter

diffusing ions, and soil chemical reactions are important in determining

the amount of P and K that reach the root. These factors indicate

greater yield response to P and K applications in drier years. When

rates of K were split with application of P the response was dependent

on weather conditions (Reneau et al., 1983).

According to Bates (1970) although the concentration of nutrients

in plant tissue chosen to provide a constant physiological age changes

with the age of the plant, there is some question whether the critical

concentration changes with the age of the plant. It is commonly








33

accepted that critical concentrations vary from species to species

although it has been suggested that this may not be so for all

nutrients.

Nutrient Accumulation

Jacques et al. (1975) suggested that nutrient uptake precede dry

matter production because the nutrients are required for growth and dry

matter accumulation. More than half of the total nutrient uptake occurs

before maximum vegetative dry matter was produced. Nutrient

concentrations varied among sorghum plant parts and changed throughout

growth. Concentrations in most vegetative plant parts were highest

right after emergence, decreased until maximum vegetative dry weight had

been produced, and changed little, if at all, while grain developed.

Lockman (1972b), studying the mineral composition of sorghum,

found that N levels in plant samples were well correlated with yields at

all growth stages and in both years (1968-69). Dry weather during the

first year of his experiment decreased N levels slightly relative to the

normal moisture data from the same plots in the second year. Results

are quite convincing that the critical level for N will not drop below

3.0% even at late stages of growth.

Lockman (1972b) observed that P levels also were well correlated

with grain yields at all stages and in both years. Dry weather caused

higher P levels, which are considered to be simple accumulation effects

with less growth. Data presented by Lockman (1972b) indicated that K

levels were correlated with grain yield in only the seedling and

vegetative samples; K levels in grain sorghum plant samples decreased

almost linearly with age. Dry weather appreciably decreased relative K

levels in seedling samples in one year.








34

Lockman (1972b) reported that Ca levels were only moderately

correlated with yield, generally in a negative manner. Dry weather

samples had lower Ca levels at the seedling stage; however, Ca

accumulated in the later samples. Levels in grain sorghum were poorly

correlated with yield. Dry weather appeared to cause higher Mg levels

in late season samples.

Copper levels were not well correlated with yields. Higher Cu

levels were noted with later samples in the dry year. Iron levels in

grain sorghum samples generally were not well correlated with yield.

Whole-plant sample analyses indicate that the Fe:Mn ratio has to be

considered to accurately define Fe deficiency. Fe levels in bloom and

fruiting stage third-leaf samples were higher in a dry year in field

samples. Mn accumulated to relatively higher levels in the later

samples of the dry year. Zinc levels in grain sorghum plant samples

showed curvilinear correlation with grain yield. At low yield levels

the correlation was positive, but as yields increased beyond category,

the correlation became negative (Lockman, 1972b).

In their study of the efficiency of maize hybrids, Gallaher and

Jellum (1976) found that Mg deficiency in maize is a major problem in

many parts of the world because of widespread soil Mg deficiency.

Concentrations of K, Ca, and Mg in leaf tissue appeared to be positively

related to soil test.

Bates (1970) suggested that severe deficiency destroys the

potential for growth so that the plants stop growing completely but

continue to accumulate Zn. Plants usually resume growth when a nutrient

deficiency is corrected, but it is possible that a degree of deficiency

can be reached beyond which they are completely unable to recover.








35

From studies conducted to estimate the uptake of N, P, K, Ca, and

Mg by maize and grain sorghum harvested for silage Fribourg (1974)

concluded that the amounts contained in above-ground plant parts exhibit

considerable range: 34 to 220 kg ha- of N; 8 to 34 of P; 31 to 271 of

K; 8 to 55 of Ca; and 9 to 45 kg haI of Mg. This large range is not

unexpected, due to soil drainage and fertility.

According to Sayre (1948) the grain does not accumulate much K.

The maximum rate of accumulation and the time when the maximum amount

occurs in the leaves and stems is earlier than for N and P. There is a

small but consistent increase in the amount of K in the grain and a

rather marked loss from the other plant tissues, especially the stem.

Voss et al. (1970), studying factors that affect nutrient

concentration in maize, found that under nearly all combinations of

conditions the N:P ratio for these nutrient concentrations remained

nearly 10:1. Within the actual data for the individual plots, ratios

greater than this were observed, but there were few ratios smaller than

this, even under conditions of high applied and/or indigenous P and low

N levels. Thus, definite levels for leaf N and P at which maximum

predicted yields occurred could not be defined, but rather they varied

with soil. The authors concluded that nutrient levels of approximately

2.9% N and 0.28% P were predicted for 95% of maximum yields.

The maximum rate of P accumulation occurred at the same period as

nitrogen, but the total amount per plant continued to increase as long

as the plants were sampled. This shows that the plant continued to

absorb P from the soil all during the season, since the loss which

occurred from the leaves, stem, husks, and cob did not account for the

quantity which moved into the grain (Sayre, 1948). These data differ








36

from those of the other two elements in several ways. He also suggested

that N accumulation in the maize plant reached a maximum at silking time

and ceased about four weeks later in the season studied. Nitrogen

continued to move into the grain from other tissues until maturity.

There was an actual loss of potassium after that time, largely from the

leaves and stems of the plant. No marked accumulation of potassium

occurred in the grain.

Reneau et al. (1983) pointed out that interactions between P and K

(P:K) are vital information for obtaining maximum yields. The

literature in this area shows that limited progress had been made with

P:K so that viable interactions could not be proposed. They reported

that the concentrations of N, P, K, Ca, and Mg in forage sorghum were

influenced by either P or K application or both. Nitrogen, P, Ca, and

Mg concentrations were increased and K was decreased with P application.

Nitrogen, Ca, and Mg were decreased and K increased with increased K

application. This antagonistic effect of K on Ca and Mg uptake by

monocots is well documented (DeWit et al., 1963). Bar-Yosef (1971)

demonstrated that higher P concentration in solution would increase Ca

uptake. Conversely, Greenwood and Hallsworth (1960), with intact root

systems, reported no direct effect of P on Ca uptake and further

reported more severe deficiencies with high P levels. Although limited

data is available on the effect of P on Mg uptake, Truog et al. (1947)

reported a synergistic relationship between Mg and P in plants.

Several secondary reactions are shown by the data presented by

Lockman (1972a): decreased Mg with N deficiency; increased Zn with P

deficiency; Ca and Mg accumulation with K deficiency; increased P, Mn,

and Ca but less K with S deficiency; increased P with low Cu; increased








37

Mn, N, P, and Al with Fe deficiency; and N, P, and K accumulation with

Mn or Zn deficiency.

Average mineral composition of grain sorghum plant samples

reported by Lockman (1972a) was consistently affected by soil fertility

factors. Bloom and fruiting stage samples continued to reflect

fertilization practices for N and P, but not for K. The levels of Mg,

Fe, Mn, and Al were also affected by N-P-K fertilizers. Magnesium

levels were decreased in vegetative and later samples, which is likely

an antagonistic effect caused by K additions. Mn levels were increased

during the same periods, probably an effect of fertilizer acidity. Fe

and Al levels in seedling samples were higher without N-P-K fertilizers.

Limited nutrient criteria have been reported for grain sorghums.

Lockman (1972a) reported that in 1966, values of 1.90 to 2.37% N were

intermediate levels for second-leaf, bloom-stage grain sorghum samples.

Values of 1.60 to 1.76% N are cited as low, and a value of 1.57% N is

cited as deficient. Normal N level is 2.48% N for 42 day seedling

plants, with a value of 1.64% N being low for whole-plant N level. He
-I
listed 10 mg kg Zn as being an intermediate level for second-leaf,

bloom-stage sorghum samples. Intermediate levels of boron were listed
-l
as 16 to 138 mg kg in a mature leaf sample.

Locke et al. (1964), cited by Lockman (1972a) suggest that

critical levels for bloom-stage grain sorghum leaves are about 2% N and

between 0.17 and 0.21% P. He noted that 1.7% K is adequate, since no K

fertilizer responses were obtained with this level of K in bloom-stage

leaves.

Results presented by Lockman (1972a) indicate that seasons

appreciably affect nutrient levels in grain sorghums but not always in








38

the same manner and degree as in maize samples. The dry year, 1967,

caused increased P, Ca, Mn, Mg, Cu, Fe, and Al levels in grain sorghum

third-leaves, perhaps from lack of growth dilution. However, maize in

the dry year had reduced levels of N and K and increased levels of P,

Cu, Fe, and Mn in the ear-leaf samples. In a dry year maize did contain

less N than sorghum. With better moisture, maize leaves contained as

much N as the sorghum or more.

Comparisons of nutrient levels in sorghum and maize presented by

Bennett (1971) showed that N and P were generally higher in the grain

sorghum, whereas Ca and Mg were generally higher in the maize. There

were no consistent differences in the K content of the two crops. Baker

et al. (1970) reported growth response of maize hybrids to different

levels of P in the soil. In addition to showing more rapid growth,

hybrid 1 removed more P from the tagged band, contained more dry matter

after 29 days, but was not different from the other hybrids with respect

to grain sorghum in the Kansas survey but higher in maize in this study.

According to Jones and Wild (1975) P deficiency occurs widely in

the savanna zone. Kang and Osiname (1979) reported that crop responses

have been obtained with small P applications in the range of 4 to 10 kg

P ha In the forest zone the main response is to N application and

less to P application. This is contrary to the long-held belief that P

is the major problem in most tropical soils. The lesser P response may

be attributed to a combination of factors, such as a) higher P status of

forest soils due to better nutrient recycling, b) release of organic P

during cropping of newly cleared land, and c) large quantities of P made

available in the plant ash by traditional clearing and burning of

residue.








39

Olagunde and Sorensen (1982) reported that in spite of the

substantial decreases in Mg, Ca, and P concentrations in sorghum there

seemed to be no relationship between K/Mg ratio and dry matter yield.

This constant amount of cations in the plants might explain why there

was no substantial change in dry matter yield. The authors suggested

that K, Ca, and Mg carry out plant functions which can be performed by

one cation in the absence of another.

Shukla and Mukhi (1979) noted that applications of Zn to maize

resulted in increased shoot Mg at all levels of K and Na. The

increasing K levels decreased Mg and the decrease was more when Zn or Na

was not applied. The results thus showed that K and Zn had antagonistic

and synergistic relationships, respectively, with Mg. The results also

evidenced antagonism between K and Ca, K and Mg, and synergism between

Mg and Zn.

Gallaher and Jellum (1976) found that leaf concentrations of Zn

and Fe were influenced by planting date for maize hybrids but

interactions between hybrids and planting date were found only for K,

2+ -1
Ca, Mg concentrations and the sum of the mmol(M ) Ca+Mg kg the
2+ -1
mmol(M ) K+Ca+Mg kg and the K:Ca and K:Ca+Mg ratios.

Potassium content in maize tissue and its balance with Ca and Mg

has had widespread interest. Macy (1936) stated that a critical

percentage of each nutrient in each plant species existed, above which

there was luxury consumption and below which there was poverty
-l -l
adjustment. Critical concentrations of 2 mg K g and 200 mg Mg g on

a fresh weight basis were established for optimum photosynthesis in

maize.








40

Gallaher et al. (1975) defined the critical elemental K

concentrations in maize tissue at two sampling dates as the point at

which yields no longer give a statistically significant increase from

further applications of fertilizer K. Concentrations of K above those

critical levels would be in the luxury consumption category because

yields were not significantly increased beyond those concentrations.

Beyond those critical levels K might, in some instances, induce Ca or Mg

deficiencies because of the interaction among cations. Therefore the

critical levels of Ca and Mg are defined as being at the same point

where the critical level of K occurred. The optimum balance of the 3

cations should occur at the critical concentration for K.

Gallaher et al. (1975) reported critical mmol(M2+) of young maize

plants taken 38 days after planting to be 91 to 78 mmol(M2+ ) K kg -1, 31
2+ -1 2+ -1I
to 28 mmol(M2 ) Ca kg- and 40 to 39 mmol(M2 ) Mg kg-. The dilution or

age effect is evident from the critical levels of K at the thinning

stage compared to the ear leaf at the silking stage of growth. The
2+
critical mmol(M 2+) in the ear leaf 86 days after planting was 44 to 40
2+ 1 2+ 1 2+
mmol(M ) K kg 34 to 30 mmol(M2 ) Ca kgI, and 22 to 16 mmol(M2) Mg

kg The critical 44 to 40 mmol(M2) K kg-, in the ear leaf at the

silking stage of growth was in agreement with the critical percent of

1.75 for maize ear leaf tissue at the silking stage in the midwestern

United States.

Jacques et al. (1975) found Ca concentrations were much lower in

heads than in other plant parts both years and in the first year were

lower in grain than in threshed head parts. Calcium concentrations in

blades increased after maximum blade weight was reached. During grain

development Ca concentrations were higher in blades than in unformed








41

heads. Calcium utilized in calcium pectate formation in mature leaf

cells may have been responsible for the increased concentrations in

blades and culms. A greater percentage of the total Ca taken up in the

hybrids was accumulated in their blades than in the other plant parts.

Hanway (1962a) found that in maize, N accumulated in each plant

part as that part grew. He also observed that there was little

translocation from one plant part to another until after grain formation

began, and then N was translocated from all other plant parts to the

grain. Translocation of N from the cob, husk, and stalk appears to

precede that from the leaves. The leaves contained approximately 30% of

the N accumulated by the plant even though they constituted only about

13% of the final dry matter accumulation. At maturity the grain

contained approximately 66% of the total N in the plant. About 50% of

the N in the grain at maturity appeared to be N that had been lost

through translocation from other above-ground plant parts.

Jordan et al. (1950) observed a somewhat different pattern of N

uptake. In their study N fertilizer was side-dressed when the plants

were knee-high and the maximum rate of N absorption occurred immediately

following the application of N fertilizer. The pattern of N

accumulation by plants is undoubtedly influenced by the seasonal pattern

of N availability in the soil. K accumulation in this study continued

until a later stage of maturity and there was no loss of K from the

plants during the latter part of the season.

Hanway (1962a) suggested that continued mineral accumulation by

the plants later in the season is essential to prevent excessive loss

through translocation of N and K from the leaves which would result in

premature death of some of the leaves. Some loss of nutrients from the








42

leaves to the grain does not appear to be detrimental to the yield of

grain so long as this does not result in premature death of the leaves.

Jacques et al. (1975), comparing two sorghum hybrids, found that

Mg concentrations were lower in heads than in other plant parts.

Magnesium was evenly distributed in blades and sheaths of each hybrid.

For the two hybrids Mg accumulation in blades, sheaths, and culms was

similar to that of dry matter production. Both dry matter production

and evidence of translocation of Mg out of stems into the heads during

grain development was indicated, because the percentage of Mg decreased

in the stems and increased in the developing grain.

Jacques et al. (1975), studying nutrient uptake by different

sorghum hybrids, found that little difference between hybrids in Zn and

Cu uptakes occurred each year, but differences existed between hybrids

in Mn uptake. Stem tissue was initially high in Fe content but

decreased during both hybrids' vegetative growth. Concentrations in

head tissue and in head parts and grain were generally below 75 mg kg-

and relatively constant throughout the growing seasons, especially in

culm tissue. Differences were small among plant parts after vegetative

growth ceased, and concentrations in plant parts remained relatively

constant during grain development. Some translocation of Zn from

vegetative plant parts into the developing grain was suggested by a

decrease in Zn content in some cases, but for the most part Zn seemed to

be relatively immobile.








43

Sulfur

Importance of S

From the time of Liebig S has been known to be one of the elements

required for plant growth, but only recently has this element received

the attention it deserves as a plant nutrient. Despite this early

recognition, the importance of S as a limiting plant nutrient was

largely ignored until recently (Coleman, 1966; Caldwell et al., 1969).

In countries concerned with increasing food production, S is an

element that must not be overlooked. It is required not only for

increased total production, but what is probably far more important, it

is needed for increasing the quality of the protein present in the

foods that are produced (Coleman, 1966).

Allaway and Thompson (1966) indicated that the problem of

malnutrition due to deficiency and poor quality of protein in human

diets has been described by nutritionists and emphasized in the press.

The nutritional quality of a protein depends upon its amino acid

composition. Animals (including humans) must be supplied with the

S-containing amino acid methionine and the S-bearing vitamins biotin and

thiamine.

In areas where protein deficiency in human diets is a critical

problem, animal products are rarely consumed, and plants are the major

source of proteins. In addition, plants are frequently lower in total

protein than are animal products, so that the amounts of food required

to supply 1 g of S-amino acids are higher for plant products than for

animal products. The protein requirements of many areas will need to be

met by direct consumption of plant products. The appropriate ultimate

objective of S fertilization of soils is, therefore, to increase the








44

S-containing amino acid of human diets (Allaway and Thompson, 1966;

Coleman, 1966).

In a review article Coleman (1966) pointed out that S is needed in

crop production because certain plant functions require it for 1) the

synthesis of amino acids, cysteine, cystine, and methionine, and hence

for protein elaboration; 2) the activation of certain proteolytic

enzymes such as the papainases; 3) the synthesis of certain vitamins, of

glutathione, and of coenzyme A; 4) the formation of the glucoside oils

found in onion, garlic, and cruciferous plants; 5) the formation of

certain disulfide linkages that have been associated with the structural

characteristics of protoplasm; and 6) in some species the concentration

of sulfhydril (-SH) groups in plant tissue,which is related to an

increase in cold resistance.

The importance of S in animal nutrition has been summarized by

Allaway and Thompson (1966). They reported that the S-containing amino

acid requirement of chicks has been estimated at 0.8% of the total

ration when the ration is 23% protein. In the case of ruminant animals,

where synthesis of S-containing amino acids from inorganic S by rumen

microflora has been established, the total S content is normally used to

appraise S status of a ration. The optimum S level in lamb diets was

found to be approximately 0.17 dag kg-I S when methionine was used to

increase the S content of a low-S basal diet. The authors suggested a

N:S ratio of 15:1, or less, as an appropriate guide to the S adequacy of

a ration for dairy cows. A precise evaluation of the optimum N:S ratio

for ruminant animals is probably impossible, because ruminants adjust to

low levels of N and S through recycling processes.










Forms and Amount of S in the Soil

Tropical and temperate soils differ in both the total amount of S

and its form. Jordan and Reisenauer (1957) report average values of 540
-l
and 210 mg kg S for Mollisol and Alfisol surface soils from temperate

areas. Generally, the total S content of tropical soils is lower

because of their lower organic matter content, and adsorbed S is often

the major reserve of this element.

Sulfur is found in soils as a variable mixture of primary

minerals, sulfate ions in solution, adsorbed sulfate, ester sulfate, and

organic S compounds. Blair et al. (1980) summarized the differences

between the forms of S present in tropical and temperate soils.

Adsorbed S is generally higher in tropical soils, as in this state it

cannot be leached from the profile.

Neller (1959) showed that extractable sulfate-S increased with an

increase in the clay content in 14 Florida Ultisols. The subsurface

horizons contained considerably more sulfate-S than the surface

horizons. The increase in sulfate-S with horizon depth is associated

with S adsorption by Fe and Al hydroxides and oxyhydroxides and with an

increase in 1:1 clay minerals in the argillic horizons.

More recently Mitchell and Blue (1981) showed that most S in

Florida Spodosols and Entisols is associated with organic matter, and

sulfate-S accounted for less than 7% of the total soil S in the entire

profile of selected Florida Spodosols. Sulfate-S accounted for

approximately 15% of the total S in the C horizons of Florida Entisols,

and 44% of the total S in the B2t horizons of 10 Utisols. Extractable S

in the surface (A or A ) horizon (0-14 cm) ranged from 1 mg kg-I in a

Myakka fine sand (Aeric Haplaquod) from Alachua County to 8 mg kg-I in a








46

Leon fine sand (Aeric Haplaquod) from Duval County. Extractable

sulfate-S did not vary as much as total S in the soils. The mean total

S in the nine Spodosols varied from 104 mg kgI in the surface horizons

and 92 mg kg in the spodic (B2H) horizons to 17 mg kg in the A2

horizons.

Sulfur Deficiency in Soils

Blair et al. (1980) gathered information indicating that response

to S has been reported in 40 countries of the tropics. Coleman (1966)

and Spencer and Freney (1980) reported that S-deficient areas are rather

widespread throughout the world. For example, crop deficiencies of the

element have been reported from countries in Central and South Africa,

India, Brazil, Argentina, Central America, Europe, Australia, New

Zealand, Canada, and the United States.

Sulfur deficiency frequently occurs in soils derived from volcanic

parent-materials. In such soils, which are common in Central America

(Fritts 1970), the organic matter is closely associated with allophane

and the mineralization of the allophane-bound organic matter, i.e., the

rate of release of sulfate-S is very low. Plants on such soils are

often S deficient despite the fact that the soil is high in organic S.

According to Blair et al. (1980) the reasons for an S deficiency

in soils can be grouped broadly into three areas 1) inherently low

initial S status, 2) low availability of S-containing soil organic

matter, and 3) the result of agricultural practices. Sulfur deficiency

often develops in the tropics after a period of agricultural

exploitation. The major factors that contribute to its onset are crop

removal, organic matter losses, leaching and erosion losses, and

fertilizer use and management. The more intensive the cropping system,








47

the greater the product removal and S demand. For example S contents of

the rice grain vary from 0.034 dag kgI under deficiency conditions to

0.16 dag kg in a nonresponsive situation, and rice grain yields may

vary from 0.75 to 8 Mg ha -. A further factor to take into account when

considering the effect of crop removal on S demand is the zone of

removal in the soil.

The removal of crop residue contributes significantly to losses of

soil S in some situations (sorghum, millet). The recycling of S in crop

residues is important in livestock systems where the residue material is

used for animal feed or bedding. Since organic matter acts as a reserve

of S in soils, the losses have serious implications for the S-supplying

power of soils.

Coleman (1966) suggested that S deficiencies occur probably

because of a) the increased use of S-free fertilizers; b) the decreased

use of S as a fungicide and insecticide; and c) increased crop yields,

which means requirements of all of the essential plant nutrients in

larger amounts. Blair et al. (1980) indicated that the use of

non-S-containing phosphatic fertilizers may aggravate the S problem by

replacing adsorbed sulfate with phosphate. In this regard two aspects

of sulfate adsorption are important. First, phosphate ions will replace

sulfate ions. Bromfield (1974) estimated that sulfate ions are then

free in the soil solution and can be leached.

Adsorbed sulfate associated with the argillic horizons of Ultisols

is considered a primary source of plant-available S in soils of the

southeastern United States (Neller, 1959; Bardsley et al., 1964;).

Ensminger (1954) reported that in some areas S may leach out of the

surface horizons of coarse-textured soils but be retained by the lower








48

horizons. This is particularly true if the subsoil contains a large

amount of kaolinitic-type clays and of hydroxides of Fe and Al, and is

acid. Under such conditions plants may exhibit S deficiency during

early stages of growth. However, the plants will subsequently recover

when the roots enter the lower soil layers. The initial stunting of

growth caused by S shortage in the topsoil may, however, result in

reduced crop yields. Mitchell and Gallaher (1979) reported that deep

rooted plants are able to utilize adsorbed sulfate associated with the

clay in lower soil horizons, but seedlings may exhibit S-deficiency

symptoms when grown on sandy surface soils with no S fertilization.

These plants were definitely low in S with an average S concentration of
-l
0.12 dag kg Soil analyses indicated increasing extractable sulfate-S

with depth in the horizon. They further suggest that increased

mineralization of organic S later in the season may have also

contributed to the improved S status in the plants.

Sulfur present in soils as sulfate undergoes many reactions

similar to those of nitrate and phosphate, and its strength of

adsorption to surfaces is intermediate between that of the two anions.

In experiments by Pearson et al (1962), 90% of the water-soluble bases

were leached as sulfate from Latosol and Ultisol profiles; chlorides

and nitrates accounted for only about 6% and 1%.

Organic S and ester sulfate, which may be thought of as reserve S,

are generally lower in the tropical soils. Environmental conditions in

the tropics are generally conducive to a rapid mineralization of organic

matter, which leads to high turnover rates of S. An exception is the

volcanic soils (Andepts), in which adsorption of organic matter on the

particles of allophane retards mineralization (Blair et al.,1980).








49

In many parts of the tropics burning of plant matter, which is an

integral part of farming, can be an avenue for S loss. When carbon is

burned off by combustion there is a concentration of S in the ash.

Blair et al. (1980) and Bromfield (1974) showed that the S content in

ash can be 2 to 10 times higher than that in dried plant material. In

areas of prevailing winds S loss may be high, but in regions of variable

winds the gains may equal the losses. One additional consequence of

burning is that organic forms of S are converted to inorganic forms

which, at the beginning of the rainy season when fields are bare, are

susceptible to leaching losses.

Blair et al. (1980) reported that sulfate which was mineralized

from organic matter moved down the profile and accumulated at lower

depths. Since a large proportion of the S present in the soil is in the

organic matter and this is often accumulated on the soil surface, losses

from wind and water erosion may be high in some circumstances.

Plant's Requirements and Content

Tisdale and Nelson (1964) concluded that S is required by many

crop plants to about the same extent as is P. As a general rule of

thumb, grass and cereal crops generally require smaller amounts of S

than do legume and cruciferous crops. Ensminger and Freney (1966) list

the effect of age on S contents in several species. Because it is

necessary to select a plant part that has a relatively constant S

content, the effect of maturity on the S content of the plant parts)

should be examined to determine sensitivity to sampling time.

The critical concentration of S in young maize plants has been
-i
reported to be around 0.20 dag kg (Fox et al., 1964; Stewart and

Porter, 1969; Jones and Eck, 1973; Terman et al., 1973). Friedrich and








50

Schrader (1978) indicated that maize seedlings are not S-deficient

unless the concentration of S (dry weight basis) in the shoots is

approximately 0.10 dag kg-I or less. Blue et al. (1981), found that

maize plants without S fertilization were chlorotic and oven-dry herbage

contained only 0.10 dag kg total S; herbage from treatments with S
-1 -1
applied at 15 and 30 mg kg contained 0.19 and 0.23 dag kg ,

respectively. Oven-dry herbage yields were increased from 6.6 to 9.4 g
-i -
pot by the addition of 15 mg kg- of S, and there was no additional
-I
yield increase from the 30 mg kg S treatment. Mitchell and Gallaher

(1979) reported that seven harvested crops in a maize/grain system and
-I
the maize forage system removed an estimated 48 and 63 kg ha S,

respectively, during 2 years.

Fox et al (1977) have shown that the critical level of S in cowpea

varies between cultivars. In their solution culture experiment, the
-l
critical value varied between 0.032 dag kg total S in cultivar 'Sitao

Pole' and 0.064 dag kg-I in 'TVU76-2E'.

Published data for rice (Blair et al., 1979) show grain S contents
-l
varying from 0.134 dag kg under deficiency conditions up to 0.16 dag
-l
kg in a non-responsive situation. Rice grain yields may vary from 750

kg ha up to 8,000 kg haI which gives a S removal varying from 0.26 up

to 12.8 kg ha Rice straw may contain similar amounts of S.

Absorption and Accumulation of S

Coleman (1966) reported that in addition to the S they receive

from precipitation, plants and soils absorb sulfite and perhaps other

sulfurous gases directly from the atmosphere. It has been known for

many years that sulfite is absorbed directly by plant leaves. Work by

Olson (1957) showed that plants supplied with adequate sulfate in








51

solution still obtained about 30% of their S from the atmosphere. When

plants were grown in a S-deficient nutrient solution, they obtained up

to 90% of their S from the atmosphere, but the total amount absorbed was

insufficient for normal growth. There is considerable evidence that

sulfurous gases in the atmosphere may be absorbed directly by soil.

However, Blue et al. (1981) reported that S additions to soils through

the atmosphere and rainfall are inadequate for intensive production

systems.

Jones et al. (1979) estimated that an average of 8.4 kg ha yr-

of atmospheric S was absorbed directly by the soil in South Carolina

from 1973 to 1977. No data are available on the amount of S that may be

absorbed directly by the plant foliage as sulfite.

Sulfate is absorbed by plants with more difficulty than other

anions and it has been shown that the uptake proceeds even more slowly

in the presence of more mobile anions such as chloride and nitrate.

Usually S and N are absorbed in the form of sulfate and nitrate from the

soil and subsequently undergo metabolic conversion into organic S and N.

Any quantity above that needed to supply sulfate and nitrate to the

metabolic process is stored up provisionally as inorganic sulfate and

nitrate in the plant (Spencer and Freney, 1980).

Friedrich and Schrader (1978) suggested that N-reductase (NR), the

rate-limiting enzyme in nitrate-N assimilation, serves as a primary

regulatory coupling between nitrate and sulfate assimilation, while

Reuveny and Filner (1977) postulated that ATP-sulfurylase, the initial

enzyme in the pathway of sulfate assimilation, acts in synchrony with NR

to coordinate nitrate and sulfate assimilation in cultured cells.








52

However, Brunold and Schmidt (1976) proposed that adenosine-5'-

sulfotransferase, not ATP-sulfurylase, regulates sulfate assimilation in

chlorophyllous tissue.

Rabuffetti and Kamprath (1977) concluded that S accumulation in

maize grain is highly dependent upon the supply of N available for the

formation of amino acids. Sulfur accumulation in stover was enhanced by

both N and S application. On a Goldsboro soil, S application increased

S accumulation in the stover at all N rates. This occurred only at the

high N rates on the Wagram soil.

According to Friedrich and Schrader (1978) higher plants generally

accumulate N and S in amounts proportional to that incorporated into

protein. However, when plants are S-deficient, protein synthesis is

inhibited and nonprotein N is accumulated. Likewise, sulfate will often

accumulate in plants when the availability of N is limiting protein

synthesis. The observed interaction between N and S accumulation

suggests that nitrate and sulfate assimilation are closely linked

metabolically.

The pattern of remobilization of N and S reported by Friedrich and

Schrader (1979) is similar to the pattern of N redistribution observed

by previous researchers (Hanway, 1962c). The percentage of the labeled

N and S present at silking that was later remobilized was not constant

among fractions. The husk fraction remobilized more of its N and S than

did any other fraction.

Barrien and Wood (1939) studied the effects of N supply on the

amounts of protein-S and sulfate-S. The authors concluded that the most

striking feature of the curves for amount of protein-S plotted against

time is that they follow the trend of the curve for amount of dry








53

matter. An increase in N supply caused an increase in the amount of

protein-S. As in the case of protein-N, the highest N treatment caused

at first a depression in the amount of protein-S due to an effect of

treatment on growth rate.

Friedrich and Schrader (1979) reported that in maize a greater

proportion of N compared to S was remobilized from all fractions with

the exception of roots. This suggests that N is more mobile than S, at

least under the conditions of this experiment. The supply of S strongly

influences the efficiency of nitrate-N utilization in maize. Regardless

of the external supply of N during grain-filling, N and S absorbed prior

to silking will later comprise most of the N and S in the ear.

Sulfur absorbed by maize plants prior to silking was partitioned

more effectively into the ear than S absorbed after silking (49 vs.

23%). Although maize plants can absorb large quantities of S during

grain-filling, it is apparent that remobilization of S accumulated prior

to silking contributes more to ear development. Furthermore, the

remobilization of S is similar to N remobilization in that it occurs at

a constant rate that is not affected by N supply during grain-filling,

(Friedrich and Schrader, 1979)

Effects of S Deficiency

Sulfur affects not only the yield of crops, but in certain cases

the quality also. It is essential for the synthesis of methionine,

cystine, cysteine, and hence the elaboration of amino acids into a

high-quality protein. Methionine and cystine are indicators of protein

quality (Allaway and Thompson, 1966; Blair et al., 1980; Stewart and

Porter, 1969; Lancaster et al., 1971).








54

Friedrich and Schrader (1978) studied S deprivation and N

metabolism. In maize seedlings, leaf fresh weight was not affected by S

deficiency. However, stem fresh weight was reduced 24% compared to

normal plants. The authors concluded that it may be that S deficiency

was having a greater effect on the young, rapidly elongating culms and

unfurled leaves in the stem fraction than on the older leaf blades.

There are few data, however, that indicate to what degree yield and

quality are related.

According to Allaway and Thompson (1966) the importance to human

and non-ruminant animal nutrition of the S-containing amino acids cannot

be overstated. Many studies of the nutritive value of proteins have

shown that the lack of S-containing amino acids is the factor that

limits the biological value of the protein. The investigators making

this survey further concluded that a large segment of the world's

population is living on a diet that is strongly deficient in methionine.

If the animals are fed a ration low in total S, they will not make the

best utilization of the N in the diet. This means that meat, milk, or

wool production will be reduced.

Under conditions of S deficiency and high N fertilization, protein

synthesis is retarded by a lack of the S-containing amino acids,

cysteine and methionine, and this is reflected by marked accumulation of

unassimilated N in the plants as nitrate-N, amides, and free amino

acids. Such forage when fed to animals represents an unbalanced ration

in which N content may exceed requirement, which in turn can result in

nutritional disorders, especially in ruminants. High nitrate-N in

forage, for example, can cause nitrate poisoning and hypomagnesemia in

grazing dairy cattle. It arises from an inadequate absorption of Mg and








55

is probably associated with high ruminal ammonia (NH3) production.

Until recently, S had not been known to limit digestibility of inferior

quality standing pasture. It has since been shown that S fertilization

improved the intake and digestibility of inferior quality herbage.

Interaction Between S and Other Nutrients

According to Goh and Kee (1978) the total N (Nt):total S (St)

ratio in plants has been extensively studied because of its potential

use in assessing S deficiency in crops. Sulfur requirement is closely

associated with N metabolism, and high application of N fertilizer to

increase crop production may be detrimental and often wasteful if the

corresponding increase in S demand is not met. Stewart and Porter

(1969) found that to achieve maximum utilization of the added N, one

part of S must be added to 15 parts of N. Results presented by Goh and

Kee (1978) indicate 17 parts of N to one part of S.

Dijkshoorn et al. (1960) found that, on account of the ability of

grass to accumulate variable amounts of non-protein N-metabolites free

of S (such as glutamic and aspartic acid), the N:S ratio in the

non-protein organic substance is usually different from the protein

ratio Sp:Np and is subject to variation according to the nutritional

status of the plant. Therefore the ratio of organic S (So) to organic N

(No) in the total mass of forage So:No is also different from Sp:Np and

is some function of the nutritional status and the composition of the

plant.

In S-fertilization experiments in New Zealand, McNaught and

Christoffels (1961) reported N:S ratios of 17:18.5 for white clover and

11:12 in grasses at maximum yields. Pumphrey and Moore (1965) found

that a N:S ratio of 11 or less indicated an adequate S supply for








56

alfalfa. Stewart and Whitfield (1965) suggest a N:S ratio of 17 or less

in wheat clippings as indicative of adequate S nutrition. Thus, the N:S

ratios found desirable for optimum growth of plants are generally

slightly higher than the N:S ratio of 10:1 to 15:1 suggested by Allaway

and Thompson (1966) as optimum for ruminant animal nutrition. It would,

therefore, appear to be quite likely that certain forage plants may be

deficient in S for ruminant animals, even though the plants themselves

are growing at nearly maximum rates. When S is deficient, the ratio of

Nt:St will exceed the 15:1 required for protein synthesis, formation of

protein will diminish, and nonprotein N will accumulate.

The Np:Sp ratio has been reported to range from 11 for maize to 18

for legumes (Dijkshoorn and Van Wijk, 1960). Metson (1973) considered

the Np:Sp ratio to be more reliable than the total Nt:St ratio for

assessing the crop's N:S requirement because it is not influenced by the

accumulation of non-protein S and non-protein N. When S supply is

adequate the accumulation of non-protein S will cause the Nt:St ratio to

be lower than the Np:Sp ratio, whereas when S is deficient, non-protein

N will accumulate resulting in a higher Nt:St ratio.

Barrien and Wood (1939) observed a decline in the ratio of Np:Sp

in sudangrass leaves as the plants matured. They suggest that this

change might be due to the presence of a relatively stable S-rich

protein fraction that is not readily remobilized.

Under conditions of S deficiency the uptake of nitrate-N seems to

be affected less by a limited S supply than is the plant's capacity for

protein synthesis. Thus, because the ratio of Np:Sp in individual

proteins is fixed by the genetic code, nonprotein forms of N accumulate

when the availability of S limits protein synthesis. Similarly, sulfate








57

will accumulate in plants when the rate of uptake exceeds the amount

required for protein synthesis (Friedrich and Schrader, 1978).

The ratio of Nt:St in all vegetative fractions of maize plants

declined during grain-filling. Likewise, the Nt:St ratio was lower in

ears of N-deprived plants than in control plants; however, this ratio

was constant throughout grain-filling and was usually significantly

lower for N-deprived plants. Nitrogen supply had no effect on the

decline in Nt:St ratio in the leaves (Friedrich et al., 1979).

The accumulation of zein, a grain protein that is low in S-amino

acids, is known to be enhanced by increased N-fertilization. The ear

Nr:Sr ratios were much higher than the Nt:St ratios. This is due to the

larger proportion of ear S present as sulfate-S compared to the pro-

portion of total N present as nitrate-N (1 to 6 dag kg ). However,

this sulfate-S may have been in the cob, rather than in the grain.

Maize grain does not accumulate nitrate-N, (Friedrich and Schrader,

1978).

Goh and Kee (1978) found when N is added in high rates a reduction

in reducible S content occurred because of the incorporation of S into

plant proteins. In the high N low S treatments (N SO) over 95% of total
4
S in plants occurred as organic forms (total S, reducible S). Stewart

and Porter (1969) showed that when S is deficient nearly all the S

present in both herbage tops and roots occurred in the protein fraction.

Conversely, in the low N and high S treatments the reducible S fraction

consistently made up more than 20% of the total S.

Phosphorus-S interactions have been observed by Kamprath et al.

(1956) and Radet (1966). Caldwell et al. (1969) reported the S

treatments decreased the P content of the mature tissue. The S:P ratios








58

for second cutting alfalfa in 1966 ranged from 0.45:1 in untreated plots
-I
to 1.42:1 in alfalfa which received 112 kg ha of elemental S annually.

There was no effect of S on the P content of maize in 1962. Sulfur

increased the S content of the leaves from 0.22 to 0.26 dag kg .

Phosphorus content decreased from 0.45 dag kg without S to 0.38 dag
-1
kg when S was applied. Kamprath et al. (1957) reported that liming

and P fertilization reduced the retention of sulfate in the surface

horizons and as a result sulfate added to these soils would be leached

out of the plow layer into the B horizons, where it accumulates.

Work by Caldwell et al. (1969) demonstrated that the effect of S

on the K content of alfalfa varied. In one year increasing S resulted

in a decrease in the K content. In the second year the S-treated

alfalfa contained more K than the S controls. Apparently the healthier,

more vigorous plants on the treated plots were able to extract more K

from the soil than the weak, unthrifty, S-deficient plants.

Caldwell et al. (1969) found no discernible effects of S on the

Ca, Mg, and Fe content of alfalfa. Neither were there any significant

differences in the Cu, Zn, Al, and Sr contents of the alfalfa as a

result of the S fertilization. Average Cu content of the maize
-1
decreased from 10 to 8 mg kg with S (significant at the .05

probability level).

Mitchell and Blue (1981a, b) found that both total S and

extractable sulfate-S were significantly correlated with organic C and

total N in the surface horizons of Florida soils. Only total S was

highly correlated with organic C and total N in the spodic horizon.










Crop Response to S Fertilizer

Tisdale and Nelson (1964) reported that numerous crop species have

been found to respond to applications of S under the usual field

conditions. Some of these are lucerne clovers, pasture grasses, cotton,

maize, peanut (Arachis hypogea L.), rice, jute, banana, small grains,

apple, stone and citrus fruit, cruciferous crops, tea, and coffee. It is

to be suspected that this response would be found in every crop.

According to Jordan and Bardsley (1959), crop deficiencies of S

can be corrected by the application of numerous S compounds or elemental
-1
S. Normal superphosphate contains 11 to 13 dag kg S and ammonium
-I
sulfate contains 24 dag kg S. The intentional application of S as a

fertilizer nutrient has never received wide acceptance among growers.

It has been present in most fertilizer materials as an anion associated

with the other macro and micronutrients or as a by-product of the

manufacturing process.

Recent work with supplemental S by Gaines and Phatak (1982)

studied the effect of additional S on maize, soybean, cowpea, tomato,

cotton, and okra. This work showed that yields of maize, soybean,

cowpea, and tomato tops were significantly increased by rates of up to
-1
32 mg kg S, but yields of cotton and okra tops were unaffected by S

treatments. The results which were obtained by Rabuffetti and Kamprath

(1977) suggest that the addition of S to maize crops which were

adequately fertilized with N would be likely to improve the grain

quality of maize produced in Coastal Plain soils.

In a study testing the relation of S content of forage crops to

cattle fed on those forages, Lancaster et al. (1971) indicated that S

fertilization influenced rumen microbial activity when cattle were fed







60

four forage species but not in alfalfa. Gas production increased for

the grasses and decreased in the legumes with increased S application.

Total plant S and sulfate-S levels were increased with additional S

applied for all species; however, the percent protein decreased in the

grasses and increased in the legumes.

Lancaster et al. (1971) also found that the percentages of fiber

and lignin in the crops they studied were not influenced by S

fertilization, except for the second clipping of sudangrass and the 20
-I
and 40 mg kg levels applied to alfalfa. The critical level of S in
-l
these trials appears to be less than 10 mg kg S applied to the soil.

There were positive correlations between gas production and S

concentration for the grasses but there were negative correlations for

the legumes.

Caldwell et al. (1969) reported that the effect of S on the yield

of alfalfa was striking. Three times as much hay was produced by the

treated plots as by the check plots. The untreated alfalfa contained
-i
from 0.146 to 0.221 dag kg S. Lancaster et al. (1971) reported that

the dry matter production in the grass species they studied was

increased by the addition of S, but for the legumes this increase was

not significant.

Rabuffetti and Kamprath (1977) reported that S had little effect

at low N rates on N accumulation in maize stover. However, they found

that at N rates of 168 and 224 kg haI there was an increase in N

accumulation in stover with S rates of 44 and 66 kg ha-I on the

Goldsboro soil and 33 and 66 kg haI on the Wagram soil. Total S

accumulation in grain was found to be increased by N application at both

sites.








61

Work by Blue et al. (1981) showed that increasing rates of applied
-I.
S caused striking maize growth responses to S applied at 10 mg kg.

Yields from two soils were increased approximately fourfold. Herbage S

concentrations were only 0.06 dag kgI from each soil without S

fertilizer; interestingly, they were increased to only 0.09 and 0.07 dag
-!
kg respectively, from the Marion and Suwannee county soils fertilized

with 10 mg kgI of applied S. Stewart and Porter (1969) gave similar S

concentrations in maize plants of the same age with the additional point

that S requirement increased with increasing amounts of applied N.
-1
However, S content of herbage was increased from 2 and 3 mg pot for

soils from Marion and Suwannee counties without applied S to 11 and 14
-l -1
mg pot respectively, by application of 10 mg kg of S to the soils.

Mitchell and Gallaher (1979) found that applied S from non-Mg

sources had no significant effect on the final grain yield of two maize

cultivars. All of the S treatments increased the S concentration of the

tissue over that of the check, but did not affect yield of grain or

forage.

A grain yield response by rice to S application was obtained at

three sites by Blair et al. (1979); responses to S in three experiments

reported ranged from 47 dag kgI or 1837 kg grain ha at one site and

up to 231% or 2,146 kg grain ha- at another site.

From work reported by Wagner and Jones (1968) it is evident that S

fertilization affected the quality of annual grassland forage as

measured in terms of protein level. Evans and Davis (1966) reported

that addition of a dietary level of sulfate to an in vitro system

improved cellulose digestibility. Jung and Reid (1966) obtained a








62

correlation coefficient of 0.82 when in vivo digestible dry matter was

compared with in vitro cellulose digestibility.
















CHAPTER 3
MATERIALS AND METHODS


Field Procedures

Fertility Trials

Experiments involving three intercropping systems (Fig. 3-1) and

six fertilizer treatments (Table 3-1) were established at two sites in

Esteli, Nicaragua (Fig. 4-1) during the 1982-1983 growing season. Site 1

(Centro Experimental de Esteli) located 1 km north of the city of Esteli

on the Panamerican Highway at an elevation of 975 m. The average annual

precipitation is 1000 mm distributed in a bimodal pattern (CATIE,

1981a); the largest amounts fall during May, June, August, and September

(CATIE 1980, 1981). This rainfall pattern is the determining factor in

defining the growing season. The average annual temperature is 19C. The

soil may be classified as a Vertisol (CATIE, 1981). The field where the

experiment was established was previously planted to shade tobacco

(Nicotiana tabacum L.) but had been under fallow for the last 7 years.

Site 2 was a production cooperative (Sabana Larga) managed by 15

farmers and located 6 km southwest of the city of Esteli at an elevation

of 930 m. The average annual precipitation and temperature are 1247 mm

and 20.1 C, respectively (CATIE, 1980). The field had been under

continuous maize + beans (Phaseolus spp.) for the last 25 years.

There were 13 treatments with four replications in a randomized

complete block design at each site. The design incorporates all six

















Table 3-1. Fertilizer rates and times of application evaluated at two
sites in Northern Nicaragua.

Fertilization
TRT -Crop- Days after planting Cl 25 days after
# Cl C2 10 25 planting C2

P N N P N
-i
---------------------- kg ha --------------
1 M PS 30 0 0 0 0
2 M PS 30 30 40 0 0
3 M PS 30 0 35 0 0
4 M PS 30 0 70 0 0
5 M PS 30 30 40 0 35
6 M PS 30 30 40 30 35
7 M NS 30 30 40 0 0
8 M NS 30 30 40 0 35
9 M NS 30 30 40 30 35
10 M MI 30 0 0 0 0
11 M MI 30 30 40 0 0
12 M MI 30 30 40 0 0
13 M MI 30 30 40 0 0

M = maize, PS = photosensitive sorghum, NS = non-photosensitive sorgum,
MI = millet.














-80cmt-
PS PS PS

80cm M M M M M
I-- PS PS PS
1liPS
--- M M M M M

80cm PS PS PS
P- M M M M M

PS PS PS


50cm
PS PS PS

M M M M M

PS PS PS

M M M M M

PS PS PS

PM M M M

PS PS PS


80 cm Plants n-1
-NS---4 ---------------------------- NS
40cm M M M M M M M M M M M M
LNS ----------------------------------- NS
M+NS
NS ------------------------------------NS
F---M M 1` M M M M M M M M
I NS ------------------------------------- NS
80cm
INS------------------------------------ NS
M M M M M M M M M M M M
NS------------------------------------ NS

50cm 12 Plants m-
r-Ml- ---4-- ---------------------------- Mi
40cm M i M M M M M M M M M M
III--------------------------------------- MI
M+1M1
MI- M- I
i-I M nM M M MM K M M M 1
80cm
L MI- --i
-M M M M M M M MM M M M
-1------------------------------------- MI



Figure 3-1. Spatial arrangement of maize (M) + photosensitive
sorghum (PS), maize + non-photosensitive sorghum
(NS), and maize + millet (MI) intercropping
systems.


PS

M

PS
M

PS


MPS
PS







66

fertilizer treatments in the maize + photosensitive sorghum cropping

system, but only the high fertilizer treatments in the maize +

non-photosensitive sorghum and the maize + millet systems.

The individual plots were 9.8 by 10 m. Twelve rows of 'NB-3' maize

were planted no-tillage by hand in each plot (52,000 plants ha ) on 16

June. The second crops ('Criollo', photosensitive sorghum; 'Pioneer

895', non-photosensitive sorghum; and 'Gahi-3' millet) were interplanted

on 16 September according to the spatial arrangements depicted in Figure

3-1. The 'Criollo' was seeded between maize rows (40 cm from the maize

hills), in hills spaced 0.80 cm apart, and later thinned 24 days after
-l
seeding to six plants per hill to obtain 75,000 plants ha 'Pioneer

895' and 'Gahi-3' were seeded in double rows (20 cm from the maize).

Twenty four days after seeding the rows were thinned to have 120,000

plants haI.

One week prior to planting the experimental plots were sprayed with
-I
2 L ha of paraquat to kill the established weed population and

immediately after planting with a mixture of 1 L of atrazine + 0.75 L of

Lasso ha to prevent further weed infestations. Together with the seed

11 kg of carbofuran haI were incorporated in the soil to prevent damage

to the plants by soil insects. No further insect control was necessary

at either site. To simulate the conditions of the typical farmer all

other management activities were performed as described in Chapter 4.

The N, P, and K fertilizer applied at planting was incorporated

into the soil with a planting stick; later applications on N and P were

hand-drilled near the hills of the maize or photo-sensitive sorghum and

banded next to the rows of the non-photosensitive sorghum or millet and








67

covered with 3 to 5 cm of soil. The fertilizer treatments are described

in Table 3-1. No initial soil amendments were necessary.

Grain and stover were harvested from 8 m of the two central rows of

each plot. Grain moisture was measured with a Steinlite moisture meter

and yields calculated at 15.5% moisture content. The plant was separated

into components, and each part was then weighed. Dry matter yields were

calculated using subsamples dried to constant weight at 70C for 72

hours. All above ground plant material was removed from the plots,

separated into parts (leaf, stem, flower, ear, or head), and subsampled

for chemical analysis as described in the section of laboratory analysis

of this chapter.

One soil sample was collected from each plot prior to planting and

immediately after harvesting the last crop. All samples were air-dried,

sieved through a 2 mm stainless steel screen, and stored at ambient

temperatures until analyzed.

The following response variables were measured to determine the

effect of the fertilizer treatments on the systems under study: a) soil

pH (1:1) and extractable N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn

concentration at the beginning and end of the experiment, b) maize and

sorghum grain yield, c) Dry matter production of the different plant

parts, d) Concentration of N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn of the

different plant parts, e) combustible energy, f) percent organic matter,

and g) percent in vitro dry matter digestibility, (IVOMD). Statistical

analyses for these variables are presented in Tables 3-2, 3-3, 3-4, and

3-5.















Table 3-2. Stastistical analysis model for maize data. Factorial (3x3)
for treatments 2, 5, 6, 7, 8, 9, 11, 12, and 13.


Source df
Replications 3 (r-l)
Treatments 12 (T-l)
SPECIES EFFECT (2 sorghums + millet) 2 (E-1)
Treats (2, 5, 6, 7, 8) vs (11, 12, 13) 1
Treats (2, 5, 6) vs (7, 8, 9) 1
FERTILIZER RATES AND TIME OF APPLICATION EFFECT 2
Treats (2, 7, 11) vs (5, 6, 8, 9, 12, 13) 1
Treats (5, 8, 12) vs (6, 9, 13) 1
SPECIES X RATES-TIME 4
Treat 3 vs 4 1
Treats (1, 10) vs (3, 4) 1
Treat I vs 10 1
(LEFTOVER)* 1
ERROR 36 (r-1)
(t-1)
TOTAL 47 (RT-1)

* The degrees of freedom are not orthogonal.
















Table 3-3.


Statistical analysis model used for sorghum data. Factorial
(2x2) for treatments 1 through 9.


Source df


REPLICATIONS
TREATMENTS
GENOTYPE EFFECT
Treats (1, 2, 3, 4, 5, 6) vs (7, 8, 9)
FERTILIZER RATES AND TIME OF APPLICATION
Treats (2, 5, 6) vs (7, 8, 9)
GENOTYPES X RATES-TIME
LEFT OVER*
ERROR
TOTAL


(r-i)
(t-i)
(a-1)

(B-i)

(a-1) (b-1)

(r-i) (t-i)
(rt-i)


* Degrees of freedom are not orthogonal.


Table 3-4.


Statistical analysis model used for millet data. Randomized
complete block design.


Source df

REPLICATIONS 3 (r-1)
TREATMENTS 3 (T-I)
Treat (10) vs (11, 12, 13) 1
Treat (11) vs (12, 13) 1
ERROR 9 (r-1) (t-1)
TOTAL 15 (rt-1)

















Table 3-5.


Statistical analysis model used in the growth analysis. For
treatment 6, 9, and 13.


Source df

REPLICATIONS 3 (r-l)
TREATMENTS 12 (t-1)
ERRORS 36 (r-1) (t-l)
TOTAL 47 (rt-1)










Growth Analysis

To conduct an analysis of the growth of the systems under study in

the fertility trials, treatments 6, 9, and 13 were selected as

representatives of each system. Crop growth rate (CGR) of the 'NB-3' +

'Criollo', 'NB-3' + 'Pioneer 895', and 'NB-3' + 'Gahi-3' systems were

estimated on different phases of growth (Table 3-6). Total above-ground

growth was harvested from six hills of 'NB-3' and 'Criollo' and 1 m row

length from 'Pioneer 895' and 'Gahi-3' every sampling stage. Sampling

began when the crops were thinned, and at 21 and 24 days after seeding

for the first and second crops, respectively. At each sampling stage

plants were harvested, separated by components (leaf, stem, flower,

head, and/or ears) and weighed in the field. Subsamples were weighed and

oven dried at 70C for 72 hours (when constant weight was reached) then

weighed again to determine dry matter content. The change in average

plant dry weight on the nth (day n + t) day since the previous harvest

(on day t) was divided by n to estimate crop growth rate (CGR) expressed

in kg ha -dayI for each day in the period. Sub-samples were ground in a

Wiley mill to pass a 1 mm stainless steel screen, and stored in

air-tight bags until analyzed.

Green leaf area measurements were made at 50% bloom, soft-dough,

and at black-layer stages. All the leaves of the 12 maize plants from

each of the three plots were measured from base to tip and at the point

of maximum width. Leaf area was converted to leaf area indices (LAI) as

described by Dale et al (1980).

Daily precipitation data (Fig. 5-2) were obtained by averaging

readings from four rain gauges placed in the the four replications. Soil

samples from three 15-cm sections to a depth of 45 cm were taken on a

















Table 3-6. Sampling procedure for growth analysis.


Sampling Days after
Parts stage Cl planting

WP At thinning 21
L + S 1.0 m tall 65
L + S + F Full silk 73
L + S + F + E Soft-dough stage 99
L + S + F + E Black layer 120
L + S + F + E Harvest 160
L + S + 30 days after harvest 194


Sampling Days after
Parts stage PS NS MI

WP Thinning 24 24 24
L + S 0.75 m tall 45 45
L + S + H Full bloom 99 52 45
L + S + H Soft-dough stage 120 81
L + S + H Harvest 160 101 45/85
L + S 30 days after harvest 193 136

Cl = Maize, PS = 'Criollo', NS = 'Pioneer 895', MI = 'Gahi-3'.








73

weekly basis to determine percent soil moisture on a volumetric basis.

Soil from each increment was placed in a previously weighed can, then

weighed, oven dried at 105C for 24 hours, and weighed again. Assuming

constant weight, percent soil moisture was determined by difference.

Survey of Sulfur Deficiency in Maize

Experiment 1

Sixty day-old no-tillage maize was grown in a 65 ha field in

Alachua County, Florida. Plants showed various degrees of stunting and

ranged from dark green healthy plants to light green or yellowish

stunted plants. Plant height ranged from approximately 30 cm to 120 cm.

The stunted plants exhibited intervenal chlorosis, the degree of which

diminished as plant height increased. The hypothesis proposed stated

that the problem was likely associated with soil characteristics and the

solution could be obtained through soil-plant analysis.

A completely randomized experimental design was used that included

three replications of five maize treatments. Treatments included 30, 60,

75, 90, and 120 cm tall plants. Ten whole-plant samples were taken at

random for each replication, as well as the associated youngest mature

leaf. Soil samples were taken at several depths within 25 cm of the

treatment plants.

Plants and youngest mature leaves were washed in distilled water,

dried at 70C in a forced air oven, and ground in a Wiley mill to pass a

1 mm stainless steel screen. Soils were sampled in 15 cm increments to

45 cm, then later to 90 cm, air dried, ground by mortar and pestle, and

screened on a 2 mm stainless steel screen. Plant and soil samples were

analyzed as described in the section of laboratory procedures of this

chapter.


---'----- ___________________.....










Experiment 2

Eighteen maize fields in northern Nicaragua (Esteli and Matagalpa)

that were between 40 and 50 days old were selected as experimental

fields. A second criterion of selection was the ocurrence of S deficient

and sufficient healthy looking plants (based on the criteria established

in experiment 1).

Once inside the experimental field, four deficient and four

sufficient plants were selected. Each pair of plants within a field was

considered to form a replication of a randomized complete block design.

The youngest fully expanded mature leaf was collected from each plant,

described, and measured in length and width. The leaves were weighed,

oven dried, ground in a Wiley mill to pass a 1 mm stainless steel

screen, and stored in air-tight bags for analysis.

Four soil samples (from 0 to 30 cm depth) were taken within a 25 cm

circumference around each plant. The samples for each plant were mixed

to form one sample per plant per replication. Samples were air dried,

sieved to pass a 2 mm stainless steel screen and, stored for analysis.

Response variables measured in plants were a) plant height, b) leaf

length, c) leaf width at the widest point, d) dry weight per leaf, e)

leaf concentrations of S, N, P, K, Ca, Mg, Cu, Fe, Mn, Zn. Soil response

variables measured were concentration of the same nutrients measured in

the leaf tissue.



Laboratory Procedures

Soil Analysis Methods

For all experiments, N analysis employed a microKjeldahl procedure

(Bremner, 1960) as modified by Gallaher et al. (1976). A l.0-g sample








75

was placed in 100-ml digestion tube to which 3.2 g of catalyst (90%

anhydrous K SO4, 10% anhydrous CuSO 4), 10 ml concentrated H SO4 and 2 ml

of 30% H202 were added. Samples were then digested in an aluminum block

digester (Gallaher et al., 1976) for 2.5 hours at 375C. Upon cooling,

solutions were diluted to 75 ml with deionized water. Nitrogen

concentrations of these prepared solutions were determined using a

Technicon AutoAnalyzer II.

All soil P, K, Ca, Mg, Fe, Cu, Mn, and Zn analyses were conducted

using procedures recommended by the University of Florida's Soil Testing

Laboratory. Five grams of air-dried soil were extracted with 0.05 N HCl

+ 0.025 N H 2SO4 at a soil:solution ratio of 1 to 4 (W:V) for 5 minutes.

Soil P was then analyzed using colorimetry. Potassium was determined by

atomic emission spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were

determined by atomic absorption spectrophotometry. Soil pH was

determined using a 2:1 water:soil ratio.

Soil S was determined by the method described by Bardsley and

Lancaster (1965). Ten grams of 20-mesh soil were placed in a 50-ml

Erlenmeyer flask and extracted with 39 g of NH4 C2H302 diluted in one L

of 0.025 N acetic acid for 30 minutes, 0.25 g of washed activated

charcoal was added and extracted for 3 additional minutes. The soil

suspension was filtered using a sulfate-free Whatman No. 42 filter

paper. Ten milliliters of the filtrate were pipetted into a 50-ml

Erlenmeyer flask to which 1 ml of acid seed solution (6 N HCl + 20 mg
-l
kg of S as K 2SO 4) was added, swirled and 0.5 g of BaCl 22H 0 crystals

were added. This solution was left standing for 1 minute, then swirled

to dissolve all the crystals. Soil S concentration was then determined

using a Perkin-Elmer/Coleman 54 spectrophotometer.










Plant Analysis Methods

Nitrogen analysis of plant material employed the microKjeldahl

procedure modified by Gallaher et al. (1976). A 0.1-g sample was placed

in a 100-ml digestion tube to which two boiling chips, 3.2 g of catalyst

(90% anhydrous K 2SO4, 10% anhydrous CuSO4), 10 ml of concentrated H 2SO4

and 2 ml of H2 02 were added. Samples were then digested in an aluminum

block digester (Gallaher et al. (1976) for 2.5 hrs. Upon cooling,

solutions were diluted to 75 ml with deionized water. Nitrogen

concentration of these solutions were determined on a Technicon

AutoAnalyzer II.

Phosphorus, K, Ca, Mg, Fe, Cu, Mn, and Zn concentrations were

determined by a mineral analysis procedure in which 1.0 g samples were

placed in 50-ml pyrex beakers and ashed in a muffle furnace at 480C

for a minimum of 4 hrs. After cooling each was treated with 2 ml of

concentrated HC1 and heated to dryness on a hot plate. An additional 2

ml of concentrated HCl + water was added to the dry beakers followed by

reheating to boiling and then diluting to 100 ml volume with deionized

water. Solutions were analyzed for P using colorimetry on an

Autoanalyzer. Potassium was determined by atomic emission

spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were determined by

atomic absorption spectrophotometry.

IVOMD of plant material was determined by the Tilley and Terry

(1963) two-stage procedure adapted by Moore et al. (1972). For

measurements of combustible energy, approximately 0.5 g of sample was

pelleted in a cylinder press and weighed to the nearest 0.00001 g.

Samples were then placed in clean combustion boats. Combustible energy








77

values were obtained using a computerized Parr adiabatic calorimeter,

using standard ASTM methods (ASTM, 1979).

A sample of 0.3 g + 0.05 g of plant tissue was weighed in a clean

boat. The samples were spiked with 0.5 g of vanadium pentoxide (V2 0 5).

Sulfur concentrations were then determined using a Leco S Determinator

model SC132 at 540 nm.

















CHAPTER 4
MAIZE + SORGHUM FARMING SYSTEMS IN CENTRAL AMERICA: SITUATIONAL
ANALYSIS


Introduction

In Central America, sorghum (Sorghum bicolor (L.) Moench) is

generally cultivated in association or in sequence with maize (Zea mays

L.). These two cropping systems are used by low-income farmers on

marginal agricultural land located in the semi-arid regions. Farmers use

these systems to stabilize production, reduce the risk of maize yield

loss caused by irregularities in climate, and as a response to scarcity

of resources. Monocropping sorghum systems are found on excellent

agricultural land where mechanization is possible and are practiced by

farmers of bountiful resources.

These production schemes have different purposes. In multiple

cropping systems sorghum produced by low-income farmers serves as a

staple food for human and animal consumption, while monocropping systems

produce testa-colored sorghums, used only in animal feed or for forage.

Based on this differentiation, production problems can be grouped in two

categories: those of sequential and intercropping systems and those of

monocropping systems.

Available information to improve the maize + sorghum cropping

system is limited or has not been adequately diffused to low income

farmers. This scarcity exists because national research programs have

generally been designed with a reductionist philosophy (research by

78







79

product), making it difficult for scientists to analyze interactions or

competition within the system.

According to Arze et al. (1983), in a research scheme for sorghum

cropping systems it is necessary to analyze the problem in a series of

logical and sequential phases, beginning with broad aspects and ending

with specific matters. This analysis permits the hierarchic

identification of relations between components of the system and the

determination of restrictions to crop production. The identification of

these restrictions is a basic element for the successful design of

research; it will also enhance the possibilities of accomplishing

specific proposed objectives.

In a general way, and considering sequence, the phases designed by

Arze et al. (1983) can be summarized as follows: 1) definition of the

problem, 2) characterization and diagnosis, 3) design of the research,

4) implementation, 5) validation, and 6) diffusion.

Few attempts have been made in the area to describe the maize +

sorghum system. Some of the most recent attempts include those conducted

in different areas of El Salvador by Rodriguez et al. (1977), Guillen et

al. (1978); Alvarado et al. (1978), Alegria et al. (1979); and Arias et

al. (1980). Kass (1980) and Fuentes and Salguero (1983) give a brief

description of the system in Guatemala. In Honduras, Mateo et al. (1981)

described the system in some detail. Hawkins et al. (1983) and Larios et

al. (1983) have provided the only recent descriptions of what may be

considered the typical maize + sorghum cropping system in Central

America.

The objectives of this research were 1) to locate and describe the

maize + sorghum system in Central America, 2) to describe the relations








80

between the maize + sorghum systems and its bio-physical and

socio-economic environment, 3) to describe interactions with other

production systems, and 4) to identify constraints and research

opportunities to alleviate these constraints.



Materials and Methods

Between November 1981 and March 1983 several trips were made to

Guatemala, El Salvador, Honduras, and Nicaragua. During these visits the

primary areas of production in each country were visited to obtain first

hand observation of the bio-physical and socio-economic environments of

the system. Informal interviews were held with several randomly selected

farmers, with extension agents, and with research staff of each area.

These visits provided an opportunity to gather more secondary

information in each country.

Due to economic and time limitations the search of information to

meet the proposed objectives was limited to the topics listed in the

following outline:

I. Bio-physical characteristics.

A. Soil and climatic factors.

1. Edapho-climatic characterization.

2. Identify relations between climate and the

hydro-edaphocelations in the area.

B. Agro-biological factors.

1. Characterization of the maize + sorghum/animal system.

2. Analysis of constraints to the system.

C. Eco-physiological relations of the system.

1. Photoperiodism.








81

2. Rainfall and soil moisture.

3. Temperature.

II. Socio-economic Characteristics.

A. Social aspects.

1. Structure of the production system.

2. Social systems.

B. Economics.

1. Economic parameters of production.

2. Use of available resources.



Results and Discussion

In the semi-arid regions of Central America the owners of small and

medium size farms have developed a maize + sorghum/animal production

system (maize + sorghum/animal) in response to the predominant

environmental characteristics (Arias et al., 1980). Management of the

system and the structure of its components are based primarily on

environmental variations and economic parameters. Larios et al. (1983)

found few studies of the relationship among components in this system or

of the analysis of inputs and outputs. The search for technological

alternatives requires from the researcher an understanding of the system

and an analysis and selection of the alternatives within the farmer's

possibilities that will cause greater development.

The system described here has been generally called "Maize/sorghum

intercrop". A list of common names used in Central America follows:

NAME COUNTRY

Maiz y sorgo El Salvador and Guatemala (Arias et

al.,1980;Kass, 1980)








82

Maiz y maicillo El Salvador, Guatemala, and Honduras

(Arias et al., 1980; Rosales, 1980;

Mateo et al., 1981; Fuentes and

Salguero, 1983)

Maiz y million Nicaragua (CATIE, 1980; Pineda et al., 1979)

Although maize and sorghum are the most important food crops in the

semi-arid regions of Central America (Larios et al., 1983), other crops

such as bean (Phaseolus spp.) (Guillen et al., 1978), cowpea (Vigna

spp.) (Alegria et al., 1979), and fruits are important in specific

areas. Sesame (Sesamum indicum L.) (CATIE, 1982a) and flaxseed (Linum

usitatissimum L.) (CATIE, 1980) are widely cultivated and compete with

maize and sorghum for land and other resources.

Larios et al. (1983) reported that in the countries where the

system exists it interacts with animal production systems. Therefore, a

more complete and descriptive name should include its animal

componentss. A list of animal components of the systems found in these

areas follows:

SPECIES USES

Cattle (dual purpose) Meat, dairy, and power (Juarez

et al., 1979; Mateo et al., 1981

Swine Meat and lard (Rodriguez et al., 1977)

Poultry Meat and eggs (Guillen et al., 1978; Kass,

(1980)

Location

The maize + sorghum/animal production system is limited generally

to the foothills near the Pacific coastal plains, rolling lands and

valleys of the interior of Central America as depicted in Figure 4-1.
















































Figure 4-1.


Distribution of maize + sorghum systems in Central
America (Drawn with information from Arias et al.,
1980; Mateo et al., 1981; and Hawkins et al.,
1983).








84

Hawkins et al. (1983) identified northern El Salvador as the area where

the system is most widely cultivated (240,000 ha). Reports in the

literature (Arias et al., 1980; Mateo et al., 1981; Fuentes and

Salguero, 1983) indicated that of the total area cultivated with sorghum

in Guatemala, El Salvador, and Honduras, 80, 93, and 93%, respectively

are intercropped with maize.

Bio-Physical Environment

Climate

The Central American Isthmus extends from east to west with the

Caribbean Sea at the north and the Pacific Ocean at the south (Fig.

4-1). Hot humid lowlands predominate on the Atlantic coast. The interior

is composed of mountains and valleys. A wide belt of steppe conditions

is found in these areas where the maize + sorghum system is found.

Precipitation stays below 1,000 mm yrI in the interior valleys. This

dryness is probably caused by mountain valley winds rather than by the

shielding effect of the mountains. In the Pacific coastal foothills

annual rainfall may range from 1,400 to 2,000 mm (Alvarado et al., 1978;

CATIE, 1980), and in some areas, such as northern El Salvador it may be

greater than 2,000 mm (Guillen et al., 1978). Annual rainfall is

distributed in a bimodal pattern (CATIE, 1980; CATIE, 1982a). The dry

season begins in November and ends in April or May, and the wet season

is interrupted by a dry period called "canicula" in July or August

(Rodriguez et al., 1977; Guillen et al., 1978). Results of studies

conducted by CATIE, (1980); and Guzman (1982) indicate that potential

annual evapotranspiration is high. The observed range in some areas is

between 1,000 and 2,000 mm (Fig. 4-2). This results in a soil moisture

deficit through May and the depletion of soil reserve in July. In the



















700
'E
E 600
L-
0
E 500-

'- 400.
LLJ
S300

200

100-

0
No)


Figure 4-2.


S Jan Mar May Jul .Sep Nov


Water deficient periods. La Trompina, El
Salvador (CATIE, El Salvador, unpublished
data).








86

semi-humid areas an excess of water occurs in September, contributing to

an increase in the availability of residual moisture through December.

The number of months in a year with a moisture deficit in the semi-arid

and semi-humid regions ranges from 7 to 10 and from 5 to 6,

respectively.

Southeastern Guatemala, southern Honduras, northeastern El

Salvador, and northwestern Nicaragua correspond to what have been

described as semi-arid regions (Larios et al., 1983). The agroclimatic

characteristics of these regions are similar to other semi-arid regions

of the world. These are summarized by Larios et al. (1983) as follows:

1. The beginning of the rainy season is uncertain.

2. More than 90% of annual precipitation occurs during the wet

season, which lasts generally from four to seven months.

3. Precipitation during the wet season is often extremely variable,

not only from year to year but also within seasons.

4. Mean daily rainfall intensities are two to four times greater

than in many temperate regions. The short duration intensities

frequently exceed the water intake capacity of the soil.

Mateo et al., (1981) claimed that the areas where maize + sorghum

is found most frequently correspond to what Holdridge classified as 1)

Bh-S(c), humid sub-tropical forest with biotemperature above 24C, 2)

Bs-T, dry tropical forest with biotemperatures below 24C but with

annual average air temperatures above 24C, and 3) Bs-S, dry

subtropical forest. Arias et al. (1980) and Larios et al. (1983) agree

that the cultivation of sorghum is related to biotemperatures or air

average annual temperatures above 24C.










Predominant soil types

The soils where the maize + sorghum cropping system is cultivated

can be classified into one of the following orders: Alfisols, Entisols,

Inceptisols, Vertisols or Mollisols (CATIE, 1980; Kass 1980; CATIE

1982a; Rico, 1982). Figure 4-3 shows an environmental profile for the

association of maize and sorghum in El Salvador, Nicaragua, and

Honduras; considering annual rainfall, altitude, slope, and soil

fertility and depth. The typical landscape is made up of steep lands,

slopes up to 50%, shallow soils (30 cm maximum) with prevalence of loose

stone or shale. It is highly susceptible to erosion (Arias et al.,

1980; CATIE, 1980).

Socio-Economic Environment

Family composition

Larios et al. (1983) reported that the average farm family is

comprised of seven members, approximately 75% of whom are under 30 years

of age; in some areas the population is somewhat younger (40% under 12

years). Assuming the inputs of women and children are 0.7 and 0.5,

respectively, man's working day, the average farmer has a daily
-I
equivalent of 5 man days in his family.

Education

Education levels vary from country to country. In some literacy can

be higher than 80%; in others it may be lower than 60%. Among children

it is generally higher than in parental groups (Larios et al., 1983).

Capital

Farm size is considered to range from small to medium (0.25 to 70

ha.). Land tenure is unsatisfactory (Green, 1974). In some cases 75% of

the farmers occupy 25% of the land (Hawkins et al., 1983; Larios et al.,





























0 800 12001(





0 5001000





0.8 8.30 30





Very Moderate
* low low


0 10


Figure 4-3.


!000 2400 Annual ralnfoll,mm





2000 Alt Itudem


I Slope,%


ZU 4U I


Soil fertility




Soil depth cm


Environmental profile of the maize sorghum system
in three countries of Central America (El Salvador,
Nicaragua, Honduras) (Larios et al., 1983).








89

1983). This situation is rapidly changing through agrarian reform plans

(personal observation by the author).

Cash flow in and out of the farms is very difficult to quantify,

especially that spent on food and clothing. Farm expenses and farm

activities are closely related to farm size (Fig. 4-4). In crop

production, a low-income farmer on a 7 ha farm may invest up to $200

(US) mainly on fertilizers (70%) and other field supplies and about $45

(US) on animal feeds. Cash flow into the farms comes from activities on

and off the farm, as depicted in Figure 4-4. On small-scale farms most

of the income (approximately 75%) is obtained from the sale of excess

grains (maize and sorghum), dairy products, meat, and draft animals

(CATIE, El Salvador, unpublished data, 1982). In their characterization

studies Arias et al. (1980) and Larios et al. (1983) emphasize the

importance of the animal component in generating income increases as

farm size augments (Fig. 4-5). Cattle are more common on larger farms,

while swine and poultry can be important sources of income among the

smaller farms.

Facilities and equipment

The value of fixed capital (housing, storage, fencing, and animal

shelter) is affected also by farm size; on the average, farmers of these

areas report holdings worth approximately $830 (US) (CATIE, 1980).

Juarez et al. (1979) report that farm equipment is limited to sprayers,

hoes, shovels, and "macanas" or "bordones" (a handweeding instrument

used for planting beans and sorghum into stands of maize). The average

value of this equipment varies from $18 to 40 (US). Very few farmers

own transport facilities other than an oxcart.



















ANIMAL
PRODUCTION


L6 h' Il hoa


60 ho.


L CROP
80 ho. PRODUCTION


Figure 4-4. Percentage of income derived from farm activities
in different farm sizes (unpublished data, CATIE,
El Salvador).





















70- Cattle -
Annual Crops -
60 Rented Land

S50-

40-4

S30-

/o /
<20-, -

10-


0 7 14 21 2835 42 49 56
SIZE OF THE FARM (ha)

Figure 4-5. Variation of activities as farm size increases.
Tejutla, El Salvador (Unpublished data, CATIE,
El Salvador).










Farming systems

On small-scale farms crop production systems constitute the main

activities, since they are related to family subsistence. As farm size

increases the area dedicated to crop production is comparatively small,

about four or five hectares, the maximum surface which can be managed by

a farmer and his family (Larios et al., 1983). As farms become larger in

size, the areas dedicated to cattle activities tend to increase,

especially as related to crop production areas (Fig. 4-5).

On farms larger than 50 ha, crop production systems increase since

the owner rents part of the land to landless farmers to be planted with

maize and sorghum. In return the farm owner will receive cash, part of

the crop, different forms of labor, and/or combinations of these

arrangements. The cultivated areas managed directly by the farm owner

tend to diminish to a minimum level of subsistence.

Hawkins et al. (1983) and Larios et al. (1983) were able to

establish a direct relation between farm size and the availability of

soil moisture. Large farms are normally located in areas with less

available soil moisture whereas small-scale farms are concentrated in

areas where more soil moisture is available. In the low-income farmer's

production systems maize is the main crop, normally associated with

beans or sorghum. Pigs and poultry are the main income producing

animals. The increase in the hydric deficit modifies the cropping

patterns; maize is displaced in importance by sorghum, forage, pasture,

or sisal. Swine and poultry are kept on most farms, and the number of

cattle is increased. The relations among farm size, hydric deficit, and

farming systems are shown in Figure 4-6, all within a representative

area for the maize + sorghum/animal production system.










Crop production systems

Studies by Guzman (1982), Hawkins et al. (1983), and Larios et al.

(1983) indicated that the location of the cropping system (Fig. 4-1) is

very much related to the frequency of uncertain rainfall periods

interrupted by a "canicula" (Fig. 4-2). Those farmers who practice

sorghum-based cropping systems have adopted cropping patterns that

diminish risk but ensure food for their families (Clara et al., 1983).

Figure 4-7 depicts the relation between rainfall patterns and relative

growth of the maize + sorghum system. Arias et al. (1980), Mateo et al.

(1981), and Hawkins et al. (1983) identified four cropping patterns as

the most often used in the system (Fig. 4-7): a) maize and sorghum

planted simultaneously in May; b) maize planted in May, sorghum planted

25 to 30 days later (at sidedressing and hilling up of the maize); c)

maize planted in May, sorghum in July (during anthesis of maize); and d)

maize planted in May and sorghum in August (at bending-over of maize).

The patterns used are closely related to the cultivar and available soil

moisture in the area. The crop spacings found more frequently are a)

single rows of maize interplanted with sorghum, b) single rows of maize

and sorghum both sharing the same hill, and c) sorghum broadcast in

maize stands (Fig. 4-8).

The early maturing maize cultivars (46 days to tasseling and 80 to

harvest) have a greater probability of escaping the "canicula".

Cultivars such as 'Criollo' perform better when cultivated in

association with sorghum (Clara et al., 1983). Moreover, these varieties

can be seeded for grain and/or forage. Sorghum cultivars used are

day-length sensitive; when planted in May, they have a long vegetative

growth period. In August and afterwards the competition with maize is




Full Text
75
was placed in 100-ml digestion tube to which 3.2 g of catalyst (90%
anhydrous K^SO^, 10% anhydrous CuSO^), 10 ml concentrated H^SO^ and 2 ml
of 30% were added. Samples were then digested in an aluminum block
digester (Gallaher et al., 1976) for 2.5 hours at 375C. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen
concentrations of these prepared solutions were determined using a
Technicon AutoAnalyzer II.
All soil P, K, Ca, Mg, Fe, Cu, Mn, and Zn analyses were conducted
using procedures recommended by the University of Florida's Soil Testing
Laboratory. Five grams of air-dried soil were extracted with 0.05 N HC1
+ 0.025 N HS0. at a soil:solution ratio of 1 to 4 (W:V) for 5 minutes.
2 4
Soil P was then analyzed using colorimetry. Potassium was determined by
atomic emission spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were
determined by atomic absorption spectrophotometry. Soil pH was
determined using a 2:1 waterrsoil ratio.
Soil S was determined by the method described by Bards ley and
Lancaster (1965). Ten grams of 20-mesh soil were placed in a 50-ml
Erlenmeyer flask and extracted with 39 g of diluted in one L
of 0.025 acetic acid for 30 minutes, 0.25 g of washed activated
charcoal was added and extracted for 3 additional minutes. The soil
suspension was filtered using a sulfate-free Whatman No. 42 filter
paper. Ten milliliters of the filtrate were pipetted into a 50-ml
Erlenmeyer flask to which 1 ml of acid seed solution (6 N HC1 + 20 mg
kg of S as ^SO^) was added, swirled and 0.5 g of BaCl2*2H20 crystals
were added. This solution was left standing for 1 minute, then swirled
to dissolve all the crystals. Soil S concentration was then determined
using a Perkin-Elmer/Coleman 54 spectrophotometer.


77
values were obtained using a computerized Parr adiabatic calorimeter,
using standard ASTM methods (ASTM, 1979).
A sample of 0.3 g _+ 0.05 g of plant tissue was weighed in a clean
boat. The samples were spiked with 0.5 g of vanadium pentoxide
Sulfur concentrations were then determined using a Leco S Determinator
model SC132 at 540 nm.


204
Table 7-8.
Extractable
maize plant
cm soil).
nutrients
height in
in soil in relation
Florida (average top
to
45
Height
Nutrient
treatment
ph
P
K Ca
Mg
cm
-1
- mg kg
30
5.9
83
13 290
32
60
5.9
96
16 320
24
75
6.3
366
19 803
28
90
6.4
547
17 1680
45
120
6.7
1395
25 3480
79
r
+ .944
+ .925
+ .925
+ .916
+ .811
R2
.891
.831
.856
.839
.657
P
.044
.029
.0226
.0272
.095
Table 7-9.
Potassium,
leaf.
Ca, and Mg
concentration in maize
Height
Nutrient
Rat io
treatment
K
Ca
Mg
K/Ca+Mg
K/S
- dae kv_1 -
Kal 1.0
30
1.60
.73
.29
.68
17.8
60
1.56
.67
.24
.75
18.8
75
1.80
.61
.16
1.05
18.6
90
1.83
.63
.12
1.13
20.3
120
2.40
.67
.15
1.34
17.5
r
+ .944
+ .912
+ .925
+ .916
+ .811
R2
.891
.831
.856
.839
.657
P
.044
.029
.0226
.0272
.095


Table
5-2.
Crop
growth
rates
of 'NB
-3' in
three
intercropping
systems.
Days
Whole Plant
Stem
Leaf
Flower
Ear
M+PS
N+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
1
leg
0-21
2
2
2
22-44
77
59
92
32
25
37
44
34
49
45-65
277
267
326
216
181
209
8
37
62
53
49
55
66-99
113
116
136
-16
6
13
5
9
-22
-6
-8
-7
129
109
153
99-120
-62
-38
-93
-16
-23
-36
-44
-30
-37
-6
-1
-3
-3
17
-21
120-160
397
509
756
98
127
149
314
400
593
-2
-2
-2
-14
-15
-19
160-190
-157
-318
-671
-162
-192
-244
90
-47
-296
-1
-1
-2
M 3 maize, PS photosensitive sorghum, NS = non-photosensitive sorghum, and MI = millet
123


24
early maturing hybrid under extreme plant competition for water is due,
at least partly, to advanced plant suppression by interplant competition.
Forage Quality
Many factors combine to determine the relative feeding value of
sorghum grain. Some of these are differences in tannin content, protein
content, amino acid composition, amount of floury and horny endosperm,
presence or absence of yellow endosperm, whether mixed with grain of
other species, whether processed in one or a number of ways such as
cooking, flaking, and/or steam rolling, whether weathered in the field
before being harvested, amount of damage of insects, presence of
aflatoxins or other molds, amount of rancidity of the oil, degree of
glume and other trash removal, presence of contaminants, and, most
important of all, degree of milling and type of animal to which it is to
be fed. Data presented by Hall et al. (1965) indicate that sorghum grain
is comparable to maize in digestibility of proximate components,
digestible energy, metabolizable energy, and nitrogen retention.
Eng et al. (1965) reported results which indicate wide variations
in the compositions and feeding values of sorghum grains. It appears that
such variations may be caused by geographical area, soil moisture, soil
fertility and variety of plants and might be important considerations in
the apparently divergent results which have been obtained by various
research workers when sorghum grain was compared to maize as an energy
source for fattening cattle. Further research work in this area is
needed.
Clark et al. (1965) found little difference in the carrying
capacity, milk production, or dry matter production of pearl millet and a


186
Days After Planting Maize
Figure 6-36. Effect of the stage of maturity on
the Zn concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).


81
2. Rainfall and soil moisture.
3. Temperature.
II. Socio-economic Characteristics.
A. Social aspects.
1. Structure of the production system.
2. Social systems.
B. Economics.
1. Economic parameters of production.
2. Use of available resources.
Results and Discussion
In the semi-arid regions of Central America the owners of small and
medium size farms have developed a maize + sorghum/animal production
system (maize + sorghum/animal) in response to the predominant
environmental characteristics (Arias et al., 1980). Management of the
system and the structure of its components are based primarily on
enviromental variations and economic parameters. Larios et al. (1983)
found few studies of the relationship among components in this system or
of the analysis of inputs and outputs. The search for technological
alternatives requires from the researcher an understanding of the system
and an analysis and selection of the alternatives within the farmer's
possibilities that will cause greater development.
The system described here has been generally called "Maize/sorghum
intercrop". A list of common names used in Central America follows:
NAME COUNTRY
Maiz y sorgo El Salvador and Guatemala (Arias et
al.,1980;Kas s, 1980)


174
Iron, Cu, Mn and Zn Accumulation and Distribution
Iron (Figs. 6-25, 6-26, and 6-27), Cu (Figs. 6-28, 6-29, and 6-30),
Mn (Figs. 6-31, 6-32, and 6-33), and Zn (Figs. 6-34, 6-35, and 6-36)
concentrations did not differ among maize plants from the different
systems. Similar trends were observed for these nutrients in all crops,
with the exception of Fe. Iron presented a sharp decline at the
beginning of the season but maintained a constant concentration during
most of the growing season until black layer in maize, when it increased
markedly, returning to levels observed early in the season. In general,
Cu, Mn, and Zn concentrations decreased with maturity, and the leaves
contained higher concentrations than the stems.


125
respectively. No differences were observed among treatments, at the 0.05
level of probability.
Dry matter accumulation by 'Criollo', 'Pioneer 895', and 'Gahi-3' is
depicted in Figures 5-3b, 5-4b, and 5-5b, respectively. As expected, the
photosensitive 'Criollo' had the longest growing cycle of the three crops.
'Gahi-3' was harvested 45 days after planting, and a ratoon crop was
harvested 40 days after. The non-photosensitive sorghum was harvested 131
days after harvest. As in 'NB-3', a midseason loss in dry matter was
observed in the 'Criollo' and 'Pioneer 895', although, not as severe as in
'NB-3'. Goldsworthy (1970) reported similar losses, due to respiration
losses that are not replaced by assimilation.
In 'Criollo' at bloom the stem was accumulating dry matter at a rate
of 92gkg ha ^day ^(Table 5-3), while leaves lost weight from bloom to
milk-dough stage (10 kg ha ^day ^). Maximum dry matter accumulation (14.3
Mg ha \ Fig. 5-3b) occurred 162 days after planting (at grain harvest),
which coincided with the highest crop growth rate (134 kg ha ^day ^).
After head harvest, 'Criollo' lost dry matter rapidly; 190 days after
planting the rate of dry matter loss was 383 kg ha ^day ^
Distribution of dry matter as percent of total in 'Criollo' varied as
the growing season progressed (Table 5-5). Forty five days after planting
57 and 43% of the dry matter had accumulated in the leaves and stems,
respectively. As heads began to develop, assimilates moved out from the
leaves, while stems kept gaining weight. Head sink size was reduced by low
rainfall and soil water availability. Assimilates that were moving from
the leaves to the heads were shunted to the large sink in the stem. At
harvest 46, 37, and 17% of the dry matter had accumulated in the stems,


72
Table 3-6. Sampling procedure for growth analysis.
Sampling
Days after
Parts
stage Cl
planting
WP
At thinning
21
L + S
1.0 m tall
65
L + S + F
Full silk
73
L + S + F
+ E
Soft-dough stage
99
L + S + F
+ E
Black layer
120
L + S + F
+ E
Harvest
160
L + S +
30 days after harvest
194
Parts
Sampling
stage
PS
Days after
NS
MI
WP
Thinning
24
24
24
L +
S
0.75 m tall
45
45
L +
S
+
H
Full bloom
99
52
45
L +
S
+
H
Soft-dough stage
120
81
L +
S
+
H
Harvest
160
101
45/85
L +
s
30 days after harvest
193
136
Cl =
= Maize, PS =
'Criollo', NS = 'Pioneer 895'
ii
M
X
'Gahi-3'.


173
Table 6-1. Ratios among X, Ca, and Mg in maize
leaves as affected by maturity and
cropping system.
System
X: Ca
X:Mg
Ca:Mg
X:Ca+Mg
Thinning
M+PS*
10.7
20.9
2.0
7.1
M+NS
11.9
19.1
1.6
7.3
M+MI
11.1
19.5
1.8
7.1
75 cm Height
M+PS
12.7
19.3
1.5
7.7
N+NS
11.0
18.4
1.7
6.9
M+MI
9.0
17.6
2.0
6.0
Bloom
M+PS
10.9
18.8
1.7
6.9
M+NS
10.4
19.2
1.9
6.8
M+MI
10.7
20.4
1.9
7.0
Soft-Dough
M+PS
9.8
18.3
1.9
6.4
M+NS
13.8
20.4
1.5
8.3
M+MI
6.4
10.0
1.6
3.9
Black Layer
M+PS
6.8
11.7
1.7
4.3
M+NS
10.0
16.9
1.7
6.3
M+MI
5.7
8.0
1.4
3.3
Harvest
M+PS
7.8
13.2
1.7
4.9
M+NS
9.0
16.9
1.9
5.9
M+MI
4.0
6.3
1.6
2.5
30 Days After Harvest
M+PS
8.8
14.7
1.7
5.5
M+NS
6.2
9.6
1.6
3.8
M+MI
7.5
11.7
1.6
4.6
* M = maize,
PS =
photosensitive
sorghum
, NS =
non-photosens itive
sorghum, and
MI = millet.


102
Table 4-3.
Inputs and outputs per year in animal production subsystems
(Typical farm in Tejutla, El Salvador).
Inputs
Quantity/Farm
Quantity/Animal
Icc -1

SWINE SUBSYSTEM
Maize Grain
204
102
Sorghum Grain
612
306
POULTRY SUBSYSTEM
Sorghum Grain
57
29
CATTLE SUBSYSTEM
Concentrates
273
22
Cotton Seed Meal
273
26
Salt
91
9
Forage
?
?
OUTPUTS
Pigs (2)
135
kg
67
kg
Chickens (5)
4.5
kg
0.9
kg
Eggs
300
120
Calves (2)
360
kg
180
kg
Milk
909
kg
303
kg


93
Crop production systems
Studies by Guzman (1982), Hawkins et al. (1983), and Larios et al.
(1983) indicated that the location of the cropping system (Fig. 4-1) is
very much related to the frequency of uncertain rainfall periods
interrupted by a "canicula" (Fig. 4-2). Those farmers who practice
sorghum-based cropping systems have adopted cropping patterns that
diminish risk but ensure food for their families (Clara et al., 1983).
Figure 4-7 depicts the relation between rainfall patterns and relative
growth of the maize + sorghum system. Arias et al. (1980), Mateo et al.
(1981), and Hawkins et al. (1983) identified four cropping patterns as
the most often used in the system (Fig. 4-7): a) maize and sorghum
planted simultaneously in May; b) maize planted in May, sorghum planted
25 to 30 days later (at sidedressing and hilling up of the maize); c)
maize planted in May, sorghum in July (during anthesis of maize); and d)
maize planted in May and sorghum in August (at bending-over of maize).
The patterns used are closely related to the cultivar and available soil
moisture in the area. The crop spacings found more frequently are a)
single rows of maize interplanted with sorghum, b) single rows of maize
and sorghum both sharing the same hill, and c) sorghum broadcast in
maize stands (Fig. 4-8).
The early maturing maize cultivars (46 days to tasseling and 80 to
harvest) have a greater probability of escaping the "canicula".
Cultivars such as 'Criollo' perform better when cultivated in
association with sorghum (Clara et al., 1983). Moreover, these varieties
can be seeded for grain and/or forage. Sorghum cultivars used are
day-length sensitive; when planted in May, they have a long vegetative
growth period. In August and afterwards the competition with maize is


56
alfalfa. Stewart and Whitfield (1965) suggest a N:S ratio of 17 or less
in wheat clippings as indicative of adequate S nutrition. Thus, the N:S
ratios found desirable for optimum growth of plants are generally
slightly higher than the N:S ratio of 10:1 to 15:1 suggested by Allaway
and Thompson (1966) as optimum for ruminant animal nutrition. It would,
therefore, appear to be quite likely that certain forage plants may be
deficient in S for ruminant animals, even though the plants themselves
are growing at nearly maximum rates. When S is deficient, the ratio of
Nt:St will exceed the 15:1 required for protein synthesis, formation of
protein will diminish, and nonprotein N will accumulate.
The Np:Sp ratio has been reported to range from 11 for maize to 18
for legumes (Dijkshoorn and Van Wijk, 1960). Metson (1973) considered
the Np:Sp ratio to be more reliable than the total Nt:St ratio for
assessing the crop's N:S requirement because it is not influenced by the
accumulation of non-protein S and non-protein N. When S supply is
adequate the accumulation of non-protein S will cause the Nt:St ratio to
be lower than the Np:Sp ratio, whereas when S is deficient, non-protein
N will accumulate resulting in a higher Nt:St ratio.
Barrien and Wood (1939) observed a decline in the ratio of Np:Sp
in sudangrass leaves as the plants matured. They suggest that this
change might be due to the presence of a relatively stable S-rich
protein fraction that is not readily remobilized.
Under conditions of S deficiency the uptake of nitrate-N seems to
be affected less by a limited S supply than is the plant's capacity for
protein synthesis. Thus, because the ratio of Np:Sp in individual
proteins is fixed by the genetic code, nonprotein forms of N accumulate
when the availability of S limits protein synthesis. Similarly, sulfate


CHAPTER 5
DRY MATTER ACCUMULATION BY MAIZE + SORGHUM AND MAIZE + MILLET
INTERCROPPING SYSTEMS
Introduction
Dry matter accumulation (DMA) is a useful definition of growth. Crop
growth is more accurately estimated by measurement of DMA than by
measurements of fresh weight, which is strongly influenced by the
environment. However, DMA is not a completely satisfactory definition of
growth, because growth also includes germination during which dry matter
is lost. Cell multiplication and increase in volume both may represent
little change in DMA (Salisbury and Ross, 1969).
Dry matter accumulation has been described as a function of
physiological, phenological, and environmental factors. Dry matter
accumulation with time is usually characterized by a sigmoidal curve,
(Leopold and Kriedemann, 1975), in which three primary phases are
recognized: expanding, linear, and senescent (Richards, 1969). In the
expansion phase, the growth rate (dry matter accumulated per unit of time)
is initially slow, but the rate increases constantly as more dry weight is
added. Accumulation of dry matter is exponential until self-shading or
other conditions prevent the increasing leaf area from producing a
proportionate increase in the weight of the plant (Duncan et al. 1967).
The end of the expansion phase marks the beginning of the linear phase in
which DMA is continuous at a constant rate. The final, senescent phase is
characterized by a decrease in growth rate as the crop approaches maturity
109


80
between the maize + sorghum systems and its bio-physical and
socio-economic environment, 3) to describe interactions with other
production systems, and 4) to identify constraints and research
opportunities to alleviate these constraints.
Materials and Methods
Between November 1981 and March 1983 several trips were made to
Guatemala, El Salvador, Honduras, and Nicaragua. During these visits the
primary areas of production in each country were visited to obtain first
hand observation of the bio-physical and socio-economic environments of
the system. Informal interviews were held with several randomly selected
farmers, with extension agents, and with research staff of each area.
These visits provided an opportunity to gather more secondary
information in each country.
Due to economic and time limitations the search of information to
meet the proposed objectives was limited to the topics listed in the
following outline:
I. Bio-physical characteristics.
A.Soil and climatic factors.
1. Edapho-climatic characterization.
2. Identify relations between climate and the
hydro-edaphocelations in the area.
B. Agro-biological factors.
1. Characterization of the maize + sorghum/animal system.
2. Analysis of constraints to the system.
C. Eco-physiological relations of the system.
1. Photoperiod ism.


103
In many cases it not only includes material but also effective
relationships among man, his animals, and his land.
Crop/Animal Interactions
The interactions between crop and animal production systems within
the farm may be classified as positive or negative. Some important
interactions are:
Positive Interactions: a) animal sales provide capital for crop
production, b) animal production absorbs labor not utilized for crop
management, c) animals help complete the farmer's diet, d) animals
provide traction and manure for crops, e) the diversity in animal
species allows more efficient utilization of plant and animal products
or by-products, and f) poultry help to control insects.
Negative Interactions: a) cattle and crops compete for available
land, capital, and labor, b) swine and poultry compete with humans for
available grain, c) soil nutrients are carried off the field by cut and
carry crops "guateras" (maize or sorghum sown at extremely high
densities for green forage or hay), and d) cattle may compact soil and
cause erosion.
The schematic representation developed by Larios et al. (1983)
(Fig. 4-10) is a semiquantitative description of the maize +
sorghum/animal production system and the interactions between crops and
animals. The system is depicted as having six subsystems. The growing
of maize + sorghum demands high labor use at certain times, especially
during weeding, planting, and harvesting, while labor distribution in
the animal production systems is more or less constant during the year.
Family participation in labor is very important and it is used more
efficiently.


38
the same manner and degree as in maize samples. The dry year, 1967,
caused increased P, Ca, Mn, Mg, Cu, Fe, and A1 levels in grain sorghum
third-leaves, perhaps from lack of growth dilution. However, maize in
the dry year had reduced levels of N and K and increased levels of P,
Cu, Fe, and Mn in the ear-leaf samples. In a dry year maize did contain
less N than sorghum. With better moisture, maize leaves contained as
much N as the sorghum or more.
Comparisons of nutrient levels in sorghum and maize presented by
Bennett (1971) showed that N and P were generally higher in the grain
sorghum, whereas Ca and Mg were generally higher in the maize. There
were no consistent differences in the K content of the two crops. Baker
et al. (1970) reported growth response of maize hybrids to different
levels of P in the soil. In addition to showing more rapid growth,
hybrid 1 removed more P from the tagged band, contained more dry matter
after 29 days, but was not different from the other hybrids with respect
to grain sorghum in the Kansas survey but higher in maize in this study.
According to Jones and Wild (1975) P deficiency occurs widely in
the savanna zone. Kang and Osiname (1979) reported that crop responses
have been obtained with small P applications in the range of 4 to 10 kg
P ha In the forest zone the main response is to N application and
less to P application. This is contrary to the long-held belief that P
is the major problem in most tropical soils. The lesser P response may
be attributed to a combination of factors, such as a) higher P status of
forest soils due to better nutrient recycling, b) release of organic P
during cropping of newly cleared land, and c) large quantities of P made
available in the plant ash by traditional clearing and burning of
residue.


15
important in grain crops, are especially sensitive (Hsiao, 1973; Boyer and
McPherson, 1975; Boyer 1976).
It is generally accepted that optimized grain filling requires
continued dry matter production and translocation of the product to the
grain. However, Brevedan and Hodges (1973) concluded that translocation
was more sensitive than photosynthesis to drought. Wardlaw (1967) studied
desiccated wheat during the grain filling stage and found that movement of
assimilates into conducting tissue was delayed in wilted leaves, but the
velocity of translocation was relatively unaffected.
Barlow and Boersma (1976) found that the partitioning of the total
dry matter into grain was affected by desiccation. In the controls, the
grain dry matter was only 63 to 76% of the total dry matter accumulated by
the shoots during grain fill. In the desiccated plants, however, grain
dry matter was 50% larger than the total dry matter accumulated during
grain fill. Thus, in the desiccated plants, grain development must have
occurred at the expense of dry matter stored in other parts of the plants.
Jurgens et al. (1978) concluded that while grain fill was seriously
inhibited by desiccation (grain yield was reduced to 42% of the control),
it was clearly maintained above that expected from dry matter accumulation
during the grain filling period. This occurred because translocation to
the grain continued at a modest rate even when there was no net
accumulation of photosynthetic material by the desiccated plants. Thus,
under field conditions photosynthesis was more affected than translocation
during desiccation. It appears that grain crops having the opportunity to
accumulate reserves under favorable moisture conditions are able to
preserve grain development if conditions later become unfavorable.


92
Farming systems
On small-scale farms crop production systems constitute the main
activities, since they are related to family subsistence. As farm size
increases the area dedicated to crop production is comparatively small,
about four or five hectares, the maximum surface which can be managed by
a farmer and his family (Larios et al., 1983). As farms become larger in
size, the areas dedicated to cattle activities tend to increase,
especially as related to crop production areas (Fig. 4-5).
On farms larger than 50 ha, crop production systems increase since
the owner rents part of the land to landless farmers to be planted with
maize and sorghum. In return the farm owner will receive cash, part of
the crop, different forms of labor, and/or combinations of these
arrangements. The cultivated areas managed directly by the farm owner
tend to diminish to a minimum level of subsistence.
Hawkins et al. (1983) and Larios et al. (1983) were able to
establish a direct relation between farm size and the availability of
soil moisture. Large farms are normally located in areas with less
available soil moisture whereas small-scale farms are concentrated in
areas where more soil moisture is available. In the low-income farmer's
production systems maize is the main crop, normally associated with
beans or sorghum. Pigs and poultry are the main income producing
animals. The increase in the hydric deficit modifies the cropping
patterns; maize is displaced in importance by sorghum, forage, pasture,
or sisal. Swine and poultry are kept on most farms, and the number of
cattle is increased. The relations among farm size, hydric deficit, and
farming systems are shown in Figure 4-6, all within a representative
area for the maize + sorghum/animal production system.


162
Doys After Planting Maize
Figure 6-16. Effect of the stage of maturity on the
K concentration of 'NB-3' maize (a) and
'Criollo' sorghum (b).


59
Crop Response to S Fertilizer
Tisdale and Nelson (1964) reported that numerous crop species have
been found to respond to applications of S under the usual field
conditions. Some of these are lucerne clovers, pasture grasses, cotton,
maize, peanut (Arachis hypogea L.), rice, jute, banana, small grains,
apple, stone and citrus fruit, cruciferous crops, tea, and coffee. It is
to be suspected that this response would be found in every crop.
According to Jordan and Bardsley (1959), crop deficiencies of S
can be corrected by the application of numerous S compounds or elemental
S. Normal superphosphate contains 11 to 13 dag kg ^ S and ammonium
sulfate contains 24 dag kg ^ S. The intentional application of S as a
fertilizer nutrient has never received wide acceptance among growers.
It has been present in most fertilizer materials as an anion associated
with the other macro and micronutrients or as a by-product of the
manufacturing process.
Recent work with supplemental S by Gaines and Phatak (1982)
studied the effect of additional S on maize, soybean, cowpea, tomato,
cotton, and okra. This work showed that yields of maize, soybean,
cowpea, and tomato tops were significantly increased by rates of up to
32 mg kg ^ S, but yields of cotton and okra tops were unaffected by S
treatments. The results which were obtained by Rabuffetti and Kamprath
(1977) suggest that the addition of S to maize crops which were
adequately fertilized with N would be likely to improve the grain
quality of maize produced in Coastal Plain soils.
In a study testing the relation of S content of forage crops to
cattle fed on those forages, Lancaster et al. (1971) indicated that S
fertilization influenced rumen microbial activity when cattle were fed


224
Bardsley, C. E., and J. D. Lancaster. 1965. Sulfur. In C. A. Black,
(ed.) Methods of Soil Analysis. Am. Soc. of Agron. 9(2):1102-1116.
, R. F. Suman, and E. H. Stewart. 1964. The sulfur status
of South Carolina crops and soils. South Carolina Agr. Exp. Stn. Tech.
Bull. No. 1013. Clemson College. Clemson, S. C.
Barlow, E. W. R., and L. Boersma. 1976. Interaction between leaf
elongation, photosynthesis, and carbohydrate levels of water-stressed
corn seedlings. Agron. J. 68:923-926.
Barrien, B. S., and J. G. Wood. 1939. Studies on the sulphur metabolism
of plants. II. The effect of nitrogen supply on the amounts of protein
sulphur, sulphate sulphur and on the value of the ratio of protein
nitrogen to protein sulphur in leaves at different stages during the
life cycle of the plant. New Phyt. 38(3):257-264.
Bar-Yosef, B. 1971. Fluxes of P and Ca into intact corn roots and their
dependence on solution concentration and root age. Plant Soil.
35:589-600.
Bates, T. E. 1970. Factors affecting critical nutrient concentrations in
plants and their evaluation: A review. Soil Sci. 112:116-130.
Beaton, J. D. 1966. Sulfur requirements of cereals, tree fruits,
vegetables, and other crops. Soil Sci. 101:267-282.
Bennett, W. F. 1971. A comparison of the chemical composition of the
corn leaf and the grain sorghum leaf. Coram. Soil Sci. Plant Anal.
2(6 ):399-405 .
Blair, G. J., C. P. Maraaril, and M. Ismunadji. 1980. Sulfur deficiencies
in soils in the tropics as a constraint to food production. In
Priorities for alleviating soil-related constraint to food production in
the tropics. IRRI, Los Banos, Philippines.
, E. 0. Momuat, and C. P. Mamaril. 1979 Sulfur nutrition of
rice. II. Effect of source and rate of S on growth and yield under
flooded conditions. Agron. J. 71:477-80.
Blue, W. G., E. Jacorae, J. A. Perez, S. Brown, and D. W. Jones. 1981.
Sulfur and manganese deficiencies as causes of poor plant growth on
Florida's sandy soils. Soil and Crop Sci. Soc. of Florida Proc.
40:95-101.
Blum, A. 1970. Effects of plant density and growth duration on grain
sorghum yield under limited water supply. Agron. J. 62:333-336.
Bolsen, K. K., G. Q. Boyett, and J. G. Riley. 1975. Milo stover and
sources of supplemental nitrogen for growing beef heifers and lambs. J.
Anim. Sci. 40:306-312.
Boyer, J. S. 1973. Response of metabolism of low water potentials in
plants. Phytopathology 63:466-472.


CHAPTER 4
MAIZE + SORGHUM FARMING SYSTEMS IN CENTRAL AMERICA: SITUATIONAL
ANALYSIS
Introduction
In Central America, sorghum (Sorghum bicolor (L.) Moench) is
generally cultivated in association or in sequence with maize (Zea mays
L.). These two cropping systems are used by low-income farmers on
marginal agricultural land located in the semi-arid regions. Farmers use
these systems to stabilize production, reduce the risk of maize yield
loss caused by irregularities in climate, and as a response to scarcity
of resources. Monocropping sorghum systems are found on excellent
agricultural land where mechanization is possible and are practiced by
farmers of bountiful resources.
These production schemes have different purposes. In multiple
cropping systems sorghum produced by low-income farmers serves as a
staple food for human and animal consumption, while monocropping systems
produce testa-colored sorghums, used only in animal feed or for forage.
Based on this differentiation, production problems can be grouped in two
categories: those of sequential and intercropping systems and those of
monocropping systems.
Available information to improve the maize + sorghum cropping
system is limited or has not been adequately diffused to low income
farmers. This scarcity exists because national research programs have
generally been designed with a reductionist philosophy (research by
78


163
Doys Afler Plnnting Mnize
Figure 6-17. Effect of the stage of maturity on the
K concentration of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).


121
20 40 60 80 100 120 140 160 180 200
Days Afler Planting Maize
Dmis After Plnnttna Maize
Figure 5-5.
Total, stem,
and 'Gahi-3'
leaf, ear or head of 'NB-3' (a)
(b) intercropped.


46
Leon fine sand (Aerie Haplaquod) from Duval County. Extractable
sulfate-S did not vary as much as total S in the soils. The mean total
S in the nine Spodosols varied from 104 mg kg ^ in the surface horizons
and 92 mg kg ^ in the spodic (B2H) horizons to 17 mg kg ^ in the A2
horizons.
Sulfur Deficiency in Soils
Blair et al. (1980) gathered information indicating that response
to S has been reported in 40 countries of the tropics. Coleman (1966)
and Spencer and Freney (1980) reported that S-deficient areas are rather
widespread throughout the world. For example, crop deficiencies of the
element have been reported from countries in Central and South Africa,
India, Brazil, Argentina, Central America, Europe, Australia, New
Zealand, Canada, and the United States.
Sulfur deficiency frequently occurs in soils derived from volcanic
parent-materials. In such soils, which are common in Central America
(Fritts 1970), the organic matter is closely associated with allophane
and the mineralization of the allophane-bound organic matter, i.e., the
rate of release of sulfate-S is very low. Plants on such soils are
often S deficient despite the fact that the soil is high in organic S.
According to Blair et al. (1980) the reasons for an S deficiency
in soils can be grouped broadly into three areas 1 ) inherently low
initial S status, 2) low availability of S-containing soil organic
matter, and 3) the result of agricultural practices. Sulfur deficiency
often develops in the tropics after a period of agricultural
exploitation. The major factors that contribute to its onset are crop
removal, organic matter losses, leaching and erosion losses, and
fertili zer use and management. The more intensive the cropping system,


184
Doys Afler Planting Molze
Figure 6-34. Effect of the stage of maturity on
the Zn concentration of 'NB-3' maize
(a) and 'Criollo' sorghum (b).


236
Shukla, U. C., and A. K. Mukhi. 1979. Sodium potassium, and zinc
relationship in corn. Agron. J. 71:235-237.
Sivakumar, M. V., N. Seetharama, S. Singh, and F. R. Widinger. 1979.
Water relations, growth, and dry matter accumulation of sorghum under
post-rainy season conditions. Agron. J. 71:843-847.
Sivakumar, M. V., and R. H. Shaw. 1978. Leaf response to water deficits
in soybeans. Plant Physiol. 42:134-139.
Spencer, K., and J. R. Freney. 1980. Assessing the Sulfur status of
field-grown wheat by plant analysis. Agron. J. 72:469-472.
Stewart, B. A., and L. K. Porter. 1969. Nitrogen-Sulfur relationships in
wheat (Triticum aestiuum L.), corn (Zea mays), and beans (Phaseolus
vulgaris). Agron. J. 61:267-271.
Stewart, B. A., and C. J. Whitfield. 1965. Effect of crop residue, soil
temperature and sulfur on the growth of winter wheat. Agron J. 234-237.
Stickler, F. C., A. W. Pauli, H. H. Laude, H. D. Wilkins, and J. L.
Mings. 1961a. Row width and plant population studies with grain sorghum
at Manhattan, KA. Crop Sci. 1:297-300.
Stickler, F. C., S. Wearden, and A. W. Pauli. 1961b. Leaf area
determination in grain sorghum. Agron. J. 53:187-188.
Szeicz, G., C. H. M. Van Bauel, and S. Takami. 1973. Stomatal factor in
the water use and dry matter production by sorghum. Agrie. Meteorol
12:361-389.
Terman, J. L. S. E. Allen, and P. M. Giordano. 1973 Dry matter yield,
N and S concentration relationships, and ratios in young corn plants.
Agron. J. 65:633-636.
Terman, J. L., P. M. Giordano, and S. E. Allen. 1972a. Relationships
between dry matter yields and concentrations of Zn and P in young corn
plants. Agron. J. 64:684-687.
Terman, J. L., J. C. Noggle, and 0. P. Englestad. 1972b. Concentrations
of N and P in young corn plants, as affected by various growth limiting
factors. Agron. J. 64:384-388.
Tilley, J. M., and R. A. Terry. 1963. A two-stage technique for the in
vitro digestion of forage crops. J. Brit. Grassl. Soc. 18:104-111.
Tisdale, S. L., and W. L. Nelson. 1964. Soil fertility and fertilizers.
First Edition. The McMillan Co. New York.
Tollenaar, M., and T. B. Daynard. 1978 Relationship between assimilate
source and reproductive sink in maize grown in a short-season
environment. Agron. J. 70:219-222.


Table 7-11. Soil S, N, and P concentrations at 18 sites in Nicaragua
Site
S
N
P
D
SU
D
SU
D
SU
_1
mg kg
18
0.303a
0.318a
4.4 bede
6.1
ab
16
f
10 c
16
0.263ab
0.305a
5.0 abe
5.0
abed
7
f
12 c
17
0.228
be
0.223
be
5.4ab
6.0
ab
18
ef
5 c
14
0.225
be
0.253
b *
2.5 bede
4.2
abede
2
f
4 c
13
0.218
be
0.215
bed
4.9abc
3.3
abed
59
c
44 c
12
0.213
be
0.213
bed
7.8a
6.5
a
38
de
29 c
1
0.200
cd
0.200
bede
1.9 ede
1.9
ede
111 b
12 lab
11
0.193
ede
0.183
edef
3.8 bede
4.4
abede
21
ef
26 c
15
0.190
ede
0.208
bede
4.1 bede
5.3
abe
4
f
4 c
2
0.185
ede
0.198
ede
1.6 ede
1.3
e
3
f
7 c
10
0.180
ede
0.160
def
4.7abcd
5.2
abe
16
f
7 c
3
0.173
ede
0.210
bede *
1.5 de
0.9
e
3
f
2 c
5
0.153
def
0.170
edef
2.3 bede
2.7
bede
10
f
15 c
4
0.150
def
0.155
ef
1.3 e
5.3
abe
6
f
5 c
7
0.150
def
0.135
f
1.6 ede
1.4
de
52
cd
94 b
6
0.145
def
0.178
edef
2.4 bede
2.1
ede
5
f
16 c
9
0.135
ef
0.168
edef
4.4 bede
1.7
ede
22 b
102 b
8
0.115
f
0.155
ef *
1.9 ede *
5.8
ab *
161a
156a
Values in columns not followed by the same letter and rows within subheadings followed by an asterisk
are different at the 0.05 level of probability according to Duncan's new multiple range test and F test,
respectively.
209


61
Work by Blue et al. (1981) showed that increasing rates of applied
S caused striking maize growth responses to S applied at 10 mg kg *.
Yields from two soils were increased approximately fourfold. Herbage S
concentrations were only 0.06 dag kg from each soil without S
fertilizer; interestingly, they were increased to only 0.09 and 0.07 dag
kg *, respectively, from the Marion and Suwannee county soils fertilized
with 10 mg kg of applied S. Stewart and Porter (1969) gave similar S
concentrations in maize plants of the same age with the additional point
that S requirement increased with increasing amounts of applied N.
However, S content of herbage was increased from 2 and 3 mg pot for
soils from Marion and Suwannee counties without applied S to 11 and 14
mg pot respectively, by application of 10 mg kg of S to the soils.
Mitchell and Gallaher (1979) found that applied S from non-Mg
sources had no significant effect on the final grain yield of two maize
cultivars. All of the S treatments increased the S concentration of the
tissue over that of the check, but did not affect yield of grain or
forage.
A grain yield response by rice to S application was obtained at
three sites by Blair et al. (1979); responses to S in three experiments
reported ranged from 47 dag kg or 1837 kg grain ha 1 at one site and
up to 231% or 2,146 kg grain ha* at another site.
From work reported by Wagner and Jones (1968) it is evident that S
fertilization affected the quality of annual grassland forage as
measured in terms of protein level. Evans and Davis (1966) reported
that addition of a dietary level of sulfate to an in vitro system
improved cellulose digestibility. Jung and Reid (1966) obtained a


5
conditions for maize production. Shallow soils and variability of
rainfall make failure of the maize crop more common than failure of the
sorghum crop, which is of lower value to the farmer for both sale and
consumption.
Present fertilizer use is oriented toward maize production, while
sorghum mostly is dependent on native soil fertility and residual
fertilizers applied to the previous crop. Whether any of the fertilizer
applied to the maize reaches the sorghum will perhaps be clarified by
the present experiments. Presently, few farmers apply any fertilizer to
the sorghum, despite the fact that under climatic constraints in which
they are operating, sorghum or millet has as much or higher yield
potential than maize.
The general objectives of this research were 1) to provide basic
information, 2) to improve traditional cropping systems, 3) to develop
new systems adapted to prevalent bio-physical conditions, and 4) to
apply new discoveries that will increase net family income and that are
appropriate to the economic resources available to farmers of the
semi-arid regions of Central America.
The specific objectives of this study are 1) to describe the maize
+ sorghum system in its bio-physical and socio-economic environment in
Central America, 2) to describe the growth pattern of the maize +
sorghum system and of potential substitutes, 3) to describe the pattern
of energy and nutrient accumulation of the system and of potential
substitutes, 4) to determine if variation of other components of the
system, such as substituting the traditional photo-sensitive sorghum
with improved non-photosensitive cultivars or millet (Pennisetum
americanum (L. ) Leeke), will increase productivity, and fertilizer and


130
sorghums was leaf dry weight, while 'Criollo' lost dry matter more rapidly
(303 kg ha ^day ^).
The late planting affected 'Gahi-3' more than any of the other crops
(Fig. 5-5b). Between 25 and 45 days after planting, 'Gahi-3' was growing
at a rate of 135 kg ha ^day (Table 5-3). Stems and leaves were growing
at a rate of 55 and 43 kg ha ^day ^, respectively. During the ratoon
growth Gahi-3 grew at a much slower rate (25 kg ha *day ^).
Leaf Area Index and Other Plant Characteristics
Leaf area index and other plant characteristics are presented in
Table 5-5. No statistical differences were observed for plant height and
number of leaves per plant among maize plants in the three systems. In
general, plants from the M+MI system were taller and had more leaves.
Leaf area indices for all treatments were low when compared to values
reported by Eik and Hanway (1966) and Hoyt and Bradfield (1963) in similar
population stands. Another difference observed is that maximum LAI
occurred later in the season. Eik and Hanway (1966) observed maximum LAI
at 50% bloom. These results indicate that LAI was markedly affected by low
soil moisture. During soft-dough, differences between maize plants from
the systems were observed (Table 5-5). Plants from the M+PS and M+MI
system had larger LAI than plants from M+NS. This suggests that the
non-photosensitive sorghum was competing more intensely with maize.
Eik and Hanway (1966) reported that yield is affected not only by the
factors which affect plant growth early in the growing season but also by
leaf area duration. Leaf area did not decline after anthesis, as reported
in the literature (Eik and Hanway 1966; Dale et al., 1980). This explains,
in part, the pattern of growth observed in Figures 5-3a, 5-4a, and 5-5a.


212
SU-plants, although differences between treatments (p=0.05) were oberved
only at four sites. Leaf S concentration values for SU-plants (except
for sites 10 and 11) were above the critical levels (0.20 dag kg ^)
established by Fox et al. (1964) and fall within the sufficiency range
(0.15 to 0.50 dag kg ^) reported by Plank (1979). On the other hand,
only in a few sites were the leaf concentrations well above the critical
level in the leaves from D-plants.
Leaf S concentration was positively correlated to LAI (r=0.20) and
leaf N concentration (r=0.75). Interestingly, S concentration was
negatively correlated to leaf Ca and Mg concentration (r=-0.23 and
-0.14, respectively) but positively correlated to leaf K concentration
(r=0.30). Other correlation values are given in Tables 7-16 and 7-17.
Leaf N concentration for both treatments are low according to
criteria established by Plank (1979). Differences among sites within
each treatment were significant at p=0.05. Only at sites 14, 15, 5, and
6 were there differences (p=0.05) between treatments (Table 7-12). The
high soil N observed and low N concentration in the leaves suggest that
due to the low amount of available soil moisture, N fertilizer applied
had not been taken up by the plants, causing a N deficiency in the
plant. Further evidence is the low leaf N:S ratio observed (Friedrich
and Schrader, 1978), independent of site and treatment (Table 7-12).
Phosphorus concentration in the leaf and the P:S ratio are
presented in Table 7-13. Diferences among sites within treatments were
observed (p=0.05). Differences between treatments for leaf P
concentration were observed only at sites 11 and 15. According to
sufficiency levels (0.25 to 0.45 dag kg *) reported by Plank (1979),
most of the P concentration levels in the leaves of plants from either


37
Mn, N, P, and A1 with Fe deficiency; and N, P, and K accumulation with
Mn or Zn deficiency.
Average mineral composition of grain sorghum plant samples
reported by Lockman (1972a) was consistently affected by soil fertility
factors. Bloom and fruiting stage samples continued to reflect
fertilization practices for N and P, but not for K. The levels of Mg,
Fe, Mn, and Al were also affected by N-P-K fertilizers. Magnesium
levels were decreased in vegetative and later samples, which is likely
an antagonistic effect caused by K additions. Mn levels were increased
during the same periods, probably an effect of fertilizer acidity. Fe
and Al levels in seedling samples were higher without N-P-K fertilizers.
Limited nutrient criteria have been reported for grain sorghums.
Lockman (1972a) reported that in 1966, values of 1.90 to 2.37% N were
intermediate levels for second-leaf, bloom-stage grain sorghum samples.
Values of 1.60 to 1.76% N are cited as low, and a value of 1.57% N is
cited as deficient. Normal N level is 2.48% N for 42 day seedling
plants, with a value of 1.64% N being low for whole-plant N level. He
listed 10 mg kg Zn as being an intermediate level for second-leaf,
bloom-stage sorghum samples. Intermediate levels of boron were listed
as 16 to 138 mg kg in a mature leaf sample.
Locke et al. (1964), cited by Lockman (1972a) suggest that
critical levels for bloom-stage grain sorghum leaves are about 2% N and
between 0.17 and 0.21% P. He noted that 1.7% K is adequate, since no K
fertilizer responses were obtained with this level of K in bloom-stage
leaves .
Results presented by Lockman (1972a) indicate that seasons
appreciably affect nutrient levels in grain sorghums but not always in


108
Interventions
In the research scheme designed by Arze et al. (1983), the limiting
factors which should be studied are classified as follows:
Physical Characteristics: 1) Analysis of the variability of the
"canicula" and of the start and termination of the wet season, and 2)
analysis of water retention capacity of the soils in the regions where
the maize + sorghum/cattle system predominates.
Agrobiological Characteristics: 1) evaluate the "guatera" system,
2) evaluate the uses of the maize + sorghum system in animal and human
nutrition, 3) design spatial and chronological arrangements and
rotations that enhance the adaptability of the system to the
environmental conditions, and increase the availability of animal feed
during the dry season, 4) test varieties and/or species to improve the
quantitative and qualitative yield of the system, 5) genetically improve
the maize + sorghum system through a) incorporation of drought tolerance
or resistance, b) high nutritional yield, c) low fertilizer requirement,
and d) component substitution, 6) management and recovery of soils, 7)
identify and evaluate breeds, animal species, and management of the
traditional animal production system, emphasizing quantitative and
qualitative aspects, 8) identify and evaluate exotic forage species, 9)
evaluate (_in vitro and _in vivo) the components of the maize + sorghum
system, 10) quantify flow components within the system and establish
inputs and outputs of the whole system, and 11) study the animal
pasturing effects on land planted to maize and sorghum (soil compaction
and nutrient recycling).


118
low soil moisture availability. This may explain in part the low grain
yields observed. These findings support data reported by Sivakumar et al.
(1978). Classen and Shaw (1970) found that a stress at silking resulted in
marked increases in stem weight with a corresponding decrease in grain
yield. This effect was due to an increase in sugar accumulation because of
a reduction in ear sink size.
Soil moisture conditions during critical growth periods were
generally better for 'Pioneer 895' than for 'Criollo' and 'Gahi-3' (Fig.
5-2). Anthesis and grain fill coincided with a period of high soil
moisture availability. This may explain in part the considerable sorghum
grain yield observed (Fig. 5-4b). Alessi and Power (1976) found that water
depletion was greater during the early part of the growing season than
after midseason, making water use after midseason highly dependent on
rainfall. Olson (1971) reported high sorghum yields when rainfall
coincided with anthesis. 'Pioneer 895' was planted in double rows (Fig.
3-1). According to Blum (1970) this planting arrangement prompts plant
competition which causes a reduction of early plant growth and LAI. This
reduction in LAI is partially responsible for reduced soil moisture use
from early growth to heading, so that more water is available for the
grain filling period.
'Gahi-3' had relatively favorable moisture conditions during its
growth (Figures 5-1 and 5-2). Higher soil moisture was available and
higher yields were observed during the first vegetative growth and higher
yields (Fig. 5-5b) than in the ratoon crop.
Dry Matter Accumulation
Dry matter yields were measured throughout the growing season
(Figures 5-3, 5-4, and 5-5). Diffe fences for maize dry matter yield were


35
From studies conducted to estimate the uptake of N, P, K, Ca, and
Mg by maize and grain sorghum harvested for silage Fribourg (1974)
concluded that the amounts contained in above-ground plant parts exhibit
considerable range: 34 to 220 kg ha ^ of S; 8 to 34 of P; 31 to 271 of
K; 8 to 55 of Ca; and 9 to 45 kg ha ^ of Mg. This large range is not
unexpected, due to soil drainage and fertility.
According to Sayre (1948) the grain does not accumulate much K.
The maximum rate of accumulation and the time when the maximum amount
occurs in the leaves and stems is earlier than for N and P. There is a
small but consistent increase in the amount of K in the grain and a
rather marked loss from the other plant tissues, especially the stem.
Voss et al. (1970), studying factors that affect nutrient
concentration in maize, found that under nearly all combinations of
conditions the N:P ratio for these nutrient concentrations remained
nearly 10:1. Within the actual data for the individual plots, ratios
greater than this were observed, but there were few ratios smaller than
this, even under conditions of high applied and/or indigenous P and low
N levels. Thus, definite levels for leaf N and P at which maximum
predicted yields occurred could not be defined, but rather they varied
with soil. The authors concluded that nutrient levels of approxiamately
2.9% N and 0.28% P were predicted for 95% of maximum yields.
The maximum rate of P accumulation occurred at the same period as
nitrogen, but the total amount per plant continued to increase as long
as the plants were sampled. This shows that the plant continued to
absorb P from the soil all during the season, since the loss which
occurred from the leaves, stem, husks, and cob did not account for the
quantity which moved into the grain (Sayre, 1948). These data differ


144
Figure 6-5. Effect of the stage of maturity on the IVOMD
of 'NB-3' maize (a) and 'Pioneer 895' sorghum
(b).


48
horizons. This is particularly true if the subsoil contains a large
amount of kaolinitic-type clays and of hydroxides of Fe and Al, and is
acid. Under such conditions plants may exhibit S deficiency during
early stages of growth. However, the plants will subsequently recover
when the roots enter the lower soil layers. The initial stunting of
growth caused by S shortage in the topsoil may, however, result in
reduced crop yields. Mitchell and Gallaher (1979) reported that deep
rooted plants are able to utilize adsorbed sulfate associated with the
clay in lower soil horizons, but seedlings may exhibit S-deficiency
symptoms when grown on sandy surface soils with no S fertilization.
These plants were definitely low in S with an average S concentration of
0.12 dag kg Soil analyses indicated increasing extractable sulfate-S
with depth in the horizon. They further suggest that increased
mineralization of organic S later in the season may have also
contributed to the improved S status in the plants.
Sulfur present in soils as sulfate undergoes many reactions
similar to those of nitrate and phosphate, and its strength of
adsorption to surfaces is intermediate between that of the two anions.
In experiments by Pearson et al (1962), 90% of the water-soluble bases
were leached as sulfate from Latosol and Ultisol profiles; chlorides
and nitrates accounted for only about 6% and 1%.
Organic S and ester sulfate, which may be thought of as reserve S,
are generally lower in the tropical soils. Environmental conditions in
the tropics are generally conducive to a rapid mineralization of organic
matter, which leads to high turnover rates of S. An exception is the
volcanic soils (Andepts), in which adsorption of organic matter on the
particles of allophane retards mineralization (Blair et al.,1980).


208
10 of the sites differences (p=0.05) were detected among treatments.
Leaf dry weight ranged from a low of 4.9 g in site 6 for the D-plants to
a high of 20.2 g in site 10 for SU-plants. Generally, plants with
heavier leaves had the largest LAI (r=0.53); this implies a larger
photosynthetic capacity for SU-plants. Only a few sites (14, 15, 10, and
2) were nearing the point of maximum LAI. These results are congruent
with those observed in Florida. That is, taller plants have heavier
(r=0.60) and larger leaves (r=0.56).
Soils associated with D-plants were different among sites (p=0.05)
for S, N, and P concentration. Similar results were observed for soils
associated with SU-plants (Table 7-11). Soil test detected differences
for S concentration between soils associated with treatments in sites
14, 3, and 8. Nitrogen differences for treatments were detected at
p=0.05, only at site 8, and no differences between soils for P were
detected. Sulfur and P values are similar to those reported for Central
America. Nitrogen values may be considered high for the area (values
above 3 dag kg ^) Fassbender, (1980). In soils associated with the
D-plants S ranged from 0.115 to 0.303 dag kg in sites 8 and 18,
respectively. In soils associated with SU-plants the S concentration
ranged from 0.155 in site 8 to 0.318 dag kg in site 18. These S
concentrations fall into what may be the low range reported by Blair et
al. (1980). Soil S was positively correlated (r=0.20) with LAI and with
plant height (r=0.32). Soil N was correlated with LAI, plant height, and
LDW (r=0.23, 0.20, and 0.19, respectively).
The intensive rains prior to planting and the cropping system
practiced (maize + sorghum intercropped) may be the cause for this low
concentration of soil-S (Blair et al., 1980). Soil samples were taken


136
Laboratory Procedures
Soil analysis methods
Nitrogen analysis employed a microKjeldahl procedure (Bremner,
1960) as modified by Gallaher et al. (1976). A 1.0-g sample was placed
in a 100-ml digestion tube to which 3.2 g of catalyst (90% anhydrous
K^SO^, 10% anhydrous CuSO^), 10 ml concentrated ^02 and 2 ml 30%
were added. Samples were then digested in an aluminum block digester
(Gallaher et al., 1976) for 3.5 hours at 375C. Upon cooling, solutions
were diluted to 75 ml with deionized water. Nitrogen concentrations of
these prepared solutions were determined using a Technicon AutoAnalyzer
II.
All soil P, K, Ca, Mg, Fe, Cu, Mn, and Zn analyses were conducted
using procedures recommended by the University of Florida's Soil Testing
Laboratory. Five grams of air-dried soil were extracted with 0.05 N HC1
+ 0.025 N ^SO^ at a soil:solution ratio of 1 to 4 (W:V) for 5 minutes.
Soil P was then analyzed using colorimetry. Potassium was determined by
atomic emission spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were
determined by atomic absorption spectrophotometry. Soil pH was
determined using a 2:1 water:soil ratio.
Plant Analysis Methods
Nitrogen analysis of plant material employed the microKjeldahl
procedure modified by Gallaher et al. (1976). A 0.1-g sample was placed
in 100-ml digestion tubes to which two boiling chips, 3.2 g of catalyst
(90% anhydrous K SO., 10% anhydrous CuSO.), 10 ml of concentrated HS0.
z 4 4 2 4
and 2 ml of ^02 were added. Samples were then digested in an aluminum
block digester (Gallaher et al. (1976) for 3.5 hrs. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen


182
Figure 6-32. Effect of the stage of maturity on
the Mn concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).


66
fertilizer treatments in the maize + photosensitive sorghum cropping
system, but only the high fertilizer treatments in the maize +
non-photosensitive sorghum and the maize + millet systems.
The individual plots were 9.8 by 10 m. Twelve rows of 'NB-3' maize
were planted no-tillage by hand in each plot (52,000 plants ha on 16
June. The second crops ('Criollo', photosensitive sorghum; 'Pioneer
895', non-photosensitive sorghum; and 'Gahi-3' millet) were interplanted
on 16 September according to the spatial arrangements depicted in Figure
3-1. The 'Criollo' was seeded between maize rows (40 cm from the maize
hills), in hills spaced 0.80 cm apart, and later thinned 24 days after
seeding to six plants per hill to obtain 75,000 plants ha 'Pioneer
895' and 'Gahi-3' were seeded in double rows (20 cm from the maize).
Twenty four days after seeding the rows were thinned to have 120,000
plants ha
One week prior to planting the experimental plots were sprayed with
2 L ha ^ of paraquat to kill the established weed population and
immediately after planting with a mixture of 1 L of atrazine + 0.75 L of
Lasso ha to prevent further weed infestations. Together with the seed
11 kg of carbofuran ha were incorporated in the soil to prevent damage
to the plants by soil insects. No further insect control was necessary
at either site. To simulate the conditions of the typical farmer all
other management activities were performed as described in Chapter 4.
The N, P, and K fertilizer applied at planting was incorporated
into the soil with a planting stick; later applications on N and P were
hand-drilled near the hills of the maize or photo-sensitive sorghum and
banded next to the rows of the non-photosensitive sorghum or millet and


149
40 BO 120 160 200
Dnys After Planting Maize
17
16
15
14
13
130 170 210 250 290
Days After Planting Maize
Figure 6-8. Effect of the stage of maturity on the
amount of metabolizable energy of 'NB-3'
maize (a) and 'Pioneer 895' sorghum (b).


160
0.0
.*
- 0.6
i
en
.*
O)
o 0 4
T3
0.2
0 0
Figure 6-15. Effect of the stage of maturity on the
P concentration of 'NB-3' maize (a) and
'Gahi-3' millet (b).
I
_ (b)
T
r
r
o- Stem
o-Leaf
-
- Head
-
n
1 10
130
150
170 190
Days After Planting Maize


112
Crop growth rates of the 'NB-3' + 'Criollo', 'NB-3' + 'Pioneer 895',
and 'NB-3' + 'Gahi-3' systems were estimated at different periods of
growth (Table 3-6). Maize plants received 30 kg ha of N and P fertilizer
at planting and were sidedressed with 40 kg N ha 25 days later. Both
sorghums and the millet were sidedressed with 30 and 35 kg ha ^ of P and
N, respectively. Total above-ground growth was harvested from six hills of
'NB-3' and 'Criollo' and aim row length from 'Pioneer 895' and 'Gahi-3'
every sampling stage (Figures 5-3, 5-4, 5-5). Sampling began when the
crops were thinned at 21 and 24 days after seeding for the first and
second crops, respectively. At each sampling stage plants were harvested,
separated by components (leaf, stem, flower, head, and/or ears), and
weighed in the field. Subsamples were weighed and oven dried at 70C for
72 hours (when constant weight was reached), then weighed again to
determine dry matter content. The change in average plant dry weight on
the nt'1 (day n + t) day since the previous harvest (on day t) was divided
by n to estimate CGR expressed in kg ha ^day ^ for each day in the period.
Sub-samples were ground in a Wiley mill to pass a 1 ram stainless steel
screen, and stored in air-tight bags until analyzed.
Green leaf area measurements were made at 50% bloom, at soft-dough,
and at black layer stages. All the leaves of the 12 maize plants from each
of the three plots were measured from base to tip and at the point of
maximum width. Leaf area was converted to LAI as described by Dale et al.
(1980).
Daily precipitation data (Fig. 5-1) were obtained by averaging
readings from four rain gauges placed in the four replications. Soil
samples from three 15-cm sections to a depth of 45 cm were taken on a
weekly basis to determine percent soil moisture on a volumetric basis.


74
Experiment 2
Eighteen maize fields in northern Nicaragua (Esteli and Matagalpa)
that were between 40 and 50 days old were selected as experimental
fields. A second criterion of selection was the ocurrence of S deficient
and sufficient healthy looking plants (based on the criteria established
in experiment 1).
Once inside the experimental field, four deficient and four
sufficient plants were selected. Each pair of plants within a field was
considered to form a replication of a randomized complete block design.
The youngest fully expanded mature leaf was collected from each plant,
described, and measured in length and width. The leaves were weighed,
oven dried, ground in a Wiley mill to pass a 1 mm stainless steel
screen, and stored in air-tight bags for analysis.
Four soil samples (from 0 to 30 cm depth) were taken within a 25 cm
circumference around each plant. The samples for each plant were mixed
to form one sample per plant per replication. Samples were air dried,
sieved to pass a 2 mm stainless steel screen and, stored for analysis.
Response variables measured in plants were a) plant height, b) leaf
length, c) leaf width at the widest point, d) dry weight per leaf, e)
leaf concentrations of S, N, P, K, Ca, Mg, Cu, Fe, Mn, Zn. Soil response
variables measured were concentration of the same nutrients measured in
the leaf tissue.
Laboratory Procedures
Soil Analysis Methods
For all experiments, N analysis employed a microKjeldahl procedure
(Breraner, 1960) as modified by Gallaher et al. (1976). A 1.0-g sample


218
values observed for D-plants and some for SU-plants are well above this
critical ratio. These results suggest that the K:Ca+Mg imbalance may be
a limiting factor to increasing yields in this area.


62
correlation coefficient of 0.82 when _in vivo digestible dry matter was
compared with _in vitro cellulose digestibility.


Mn (mg kg'1) Mn (mg kg
181
Dogs After Plenting Moize
Figure &-31. Effect of the stage of maturity on
the Mn concentration of 'NB-3' maize
(a) and 'Criollo' sorghum (b).


34
Lockman (1972b) reported that Ca levels were only moderately
correlated with yield, generally in a negative manner. Dry weather
samples had lower Ca levels at the seedling stage; however, Ca
accumulated in the later samples. Levels in grain sorghum were poorly
correlated with yield. Dry weather appeared to cause higher Mg levels
in late season samples.
Copper levels were not well correlated with yields. Higher Cu
levels were noted with later samples in the dry year. Iron levels in
grain sorghum samples generally were not well correlated with yield.
Whole-plant sample analyses indicate that the Fe:Mn ratio has to be
considered to accurately define Fe deficiency. Fe levels in bloom and
fruiting stage third-leaf samples were higher in a dry year in field
samples. Mn accumulated to relatively higher levels in the later
samples of the dry year. Zinc levels in grain sorghum plant samples
showed curvilinear correlation with grain yield. At low yield levels
the correlation was positive, but as yields increased beyond category,
the correlation became negative (Lockman, 1972b).
In their study of the efficiency of maize hybrids, Gallaher and
Jellum (1976) found that Mg deficiency in maize is a major problem in
many parts of the world because of widespread soil Mg deficiency.
Concentrations of K, Ca, and Mg in leaf tissue appeared to be positively
related to soil test.
Bates (1970) suggested that severe deficiency destroys the
potential for growth so that the plants stop growing completely but
continue to accumulate Zn. Plants usually resume growth when a nutrient
deficiency is corrected, but it is possible that a degree of deficiency
can be reached beyond which they are completely unable to recover.


13
influence plant development through the quantity of soluble carbohydrates
present in plants and their transformation into grain.
Drought
Almost every plant process is affected directly or indirectly by
water deficits. Some processes are quite sensitive to water stress, but
others are relatively insensitive. When plants are subjected to water
stress there is a decrease in photosynthesis and cell enlargement. There
is also considerable retention of carbohydrates in photosynthetic tissues.
Although translocation proceeds, its rate is reduced. Translocation is
rarely mentioned as a factor in reduced plant growth under limited
moisture. Translocation could be one of the chief physiological factors
limiting growth under unfavorable moisture conditions.
Shaw (1974) found that experimental maize yields were highly
correlated with a plant moisture stress index which was based on
calculations of daily ratios of actual to potential evapotranspiration for
the period of 40 days before to 45 days after silking. Although soil
moisture strongly interacts with temperature in plant growth processes, it
is much less important in plant phasic development.
Sivakumar and Shaw (1978) reported that the major components of
sorghum yield which were significantly affected by drought in the case of
the nonirrigated plots were tertiary branches per secondaries, seed number
per panicle, and seed size. The reduction in these components was 46, 26,
and 28%, respectively. Data presented in this study bring out the
importance of the availability of a few additional cm of water to a
sorghum crop under water stress and the benefits that should accrue from
such water applications.


Fe (mg kg~ ') Fe (mg kg
176
Doys After Planting Maize
Figure 626. Effect of the stage of maturity on
the Fe concentration of 'NB-3' maize
(a) andPioneer 895' sorghum (b).


228
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between N and S accumulation. Agron. J. 71:466-472.
, and E. V. Nordheim. 1979. N derivation
in maize during grain-filling. I. Accumulation of dry matter, nitrate-N,
and sulfate-S. Agron. J. 71:461-465.
Fritts, J. W. 1970. Sulphur deficiency in Latin America. Sulphur Inst.
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Fuentes, J., and R. Salguero. 1983. Sistemas de cultivo practicados en
Guatemala para la produccin de maiz, frijol, y sorgo. _In Procs. The
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America. INTSORMIL/INIA/INCRISAT. El Batan, Mexico, pp. 230-243.
Gaines, T. P., and S. C. Phatak. 1982. Sulfur fertilization effects on
the constancy of the protein N:S ratio in low and high sulfur
accumulating crops. Agron. J. 74:415-418.
Gallaher, R. N., and M. D. Jellum. 1976. Influence of soils and planting
dates on mineral element efficiency of corn hybrids. Comm, in Soil Sci.
and Plant Anal. 7:665-676.
, W. L. Parks, and L. M. Josephson. 1975. Some factors
influencing yield and cation sum and ratios in corn. Commun. Soil. Sci.
and Plant Anal. 6:51-61.
, C. 0. Weldon, and F. C. Boswell. 1976. A semi-automated
procedure for total nitrogen in plant and soil samples. Soil Sci Soc.
Am. J. 40:887-889.
Gardner, B. R., B. L. Blad, R. E. Maurer, and D. G. Watts. 1981.
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Goh, K. M., and K. K. Kee. 1978. Effects of nitrogen and sulphur
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Goldsworthy, P. R. 1970. The growth and yield of tall and short sorghums
in Nigeria. J. Agrie. Sci. Camb. 75:109-122.
Goldsworthy, P. R., and M. Colegrove. 1974. Growth and yield of highland
maize in Mexico. J. Agrie. Sci. Camb. 83:213-221.
, A. F. Palmer, and D. W. Sperling. 1974. Growth and
yield of lowland tropical maize in Mexico. J. Agrie. Sci. Camb.
83:223-230.
Goodrich, R. D., F. M. Byers, and J. C. Meiske. 1975. Influence of
moisture content, processing and reconstitution on the fermentation of
corn grain. J. Anim. Sci. 41:876-881.


230
Hay, R. E., E. B. Earley, and E. E. de Turk. 1950. Concentration and
translocation of nitrogen compounds in the corn plant (Zea mays L.)
during grain development. Plant Physiol. 18:606-621.
Hoyt, P., and R. Bradfield. 1963. Effects of varying leaf area by
partial defoliation and plant density on dry matter production in corn.
Agron. J. 55:523-525.
Hsiao, T. C. 1973. Plant responses to water stress. Ann. Rev. Plant
Physiol. 24:519-570.
Hume, D. J., and D. K. Campbell. 1972. Accumulation and translocation of
soluble solids in corn stalks. Can. J. Plant Sci. 52:363-368.
Jacques, G. L., R. L. Vanderlip, and D. A. Whitney. 1975. Growth and
nutrient accumulation and distribution in grain sorghum. I. Dry matter
production and Ca and Mg uptake and distribution. Agron J. 67:607-611.
Johnson, R. R., and K. E. McClure. 1966. Corn plant maturity. IV.
Effects on digestibility of corn silage in sheep. J. Anim. Sci.
31 :535-539.
, L. J. Johnson, E. W. Klosterman, and G.
B. Triplett. 1966. Corn plant maturity. I. Changes in dry matter and
protein distribution in corn plants. Agron. J. 58:151-154.
Jones, J. B., and H. V. Eck. 1973. Plant analysis as an aid in
fertilizing corn and grain sorghum. Tn L. M. Walsh and J. D. Beaton
(ed.). Soil testing and plant analysis. Soil Sci. Soc. Am., Madison, WI.
Jones, M. B., and W. E. Martin. 1964. Sulfate-sulfur concentration as an
indicator of sulfur status in various California dryland species. Soil
Sci. Soc. Am. Proc. 28:539-541.
Jones, M. J. 1973. Time of application of N fertilizer to maize at
Samaru, Nigeria. Exp. Agrie. 9:113-120.
, and A. Wild. 1975. Soils of the West African Savanna.
Comm. Agrie. Bureaux. Tech. Comm. No. 55.
Jordan, H. V., and C. E. Bardsley. 1959. Sulfur content of rainwater and
atmosphere in the southern United States as related to crop needs. U.S.
Dep. Agrie. Tech. Bull. 1196.
, and L. E. Ensminger. 1958. The role of sulfur in soil
fertility. Advanc. in Agron. 10:408-433.
, R. D. Laird, and D. D. Ferguson. 1950. Growth rates and
nutrients uptake by corn in a fertilizer spacing experiment. Agron. J.
42:261-268.
, and H. M. Reisenauer. 1957. Sulphur and soil fertility.
In USDA. The yearbook of agriculture. U.S. Gov. Printing Office,
Washington D.C.


55
is probably associated with high ruminal ammonia (NH^) production.
Until recently, S had not been known to limit digestibility of inferior
quality standing pasture. It has since been shown that S fertilization
improved the intake and digestibility of inferior quality herbage.
Interaction Between S and Other Nutrients
According to Goh and Kee (1978) the total N (Nt):total S (St)
ratio in plants has been extensively studied because of its potential
use in assessing S deficiency in crops. Sulfur requirement is closely
associated with N metabolism, and high application of N fertilizer to
increase crop production may be detrimental and often wasteful if the
corresponding increase in S demand is not met. Stewart and Porter
(1969) found that to achieve maximum utilization of the added N, one
part of S must be added to 15 parts of N. Results presented by Goh and
Kee (1978) indicate 17 parts of N to one part of S.
Dijkshoorn et al. (1960) found that, on account of the ability of
grass to accumulate variable amounts of non-protein N-metabolites free
of S (such as glutamic and aspartic acid), the N:S ratio in the
non-protein organic substance is usually different from the protein
ratio Sp:Np and is subject to variation according to the nutritional
status of the plant. Therefore the ratio of organic S (So) to organic N
(No) in the total mass of forage So:No is also different from Sp:Np and
is some function of the nutritional status and the composition of the
plant.
In S-fertilization experiments in New Zealand, McNaught and
Christoffels (1961) reported N:S ratios of 17:18.5 for white clover and
11:12 in grasses at maximum yields. Pumphrey and Moore (1965) found
that a N:S ratio of 11 or less indicated an adequate S supply for


156
Hanway (1962a) reported similar findings. They attributed this
phenomenon to a dilution effect. The effect of the rains in early
September (Fig. 5-1) on N concentration was manifested by an increase in
the N concentration in the stem after black layer had formed in the
grain.
Lockman (1972b) suggested that the N critical level in maize is
near 3 dag kg ^, while Plank (1979) establishes the N sufficiency range
in maize ear leaves at bloom between 3.5 and 5 dag kg Values observed
throughout the growing season were well below these levels. At bloom the
N concentration in maize leaves was close to 1.35 dag kg ^. These
results suggest a constant N deficiency in the plant throughout the
growing season. Low soil moisture availability during the entire growing
season (Fig. 5-2) may have prevented the plants from absorbing N needed
for grain production. Hanway (1962a) observed that extreme N and K
deficiencies in maize result in premature death of several lower leaves.
This shortens the period over which these leaves carry on
photosynthesis.
This low N concentration observed affected quality as well as
yields. At bloom, leaves and stems contained approximately 8.5 and 2.5
dag kg of protein (dag kg ^ N x 6.25), respectively; well below the
12 dag kg ^ reported by Johnson and Me Clure (1966). However, grain
protein values at harvest (9.4 dag kg ^) compared well with values
reported by Rendig and Broadbent (1979). Jurgens et al. (1978) reported
that water stress caused an increase in percent protein in the grain.
The pattern of N distribution in different components of the plant
did not appear to differ appreciably for the different systems. Nitrogen
was lost from the stems and leaves just prior to bloom. There was little


32
Factors That Affect Concentration
Bates (1970) reported that, next to the supply of elements, the
physiological age of tissue is probably the most important factor
affecting the mineral composition of a given species. There appears to
be general agreement with this statement. He further observed that the
pattern of nutrient content varies with the age of the species and with
the nutrient. Phosphorus concentration in a maize plant decreases with
age. This change in nutrient concentration with age is probably due to
both a changing nutrient content of a given tissue with age, the leaves
for example, and changing proportions of certain tissues with age, such
as an increasing proportion of stem and a decreasing proportion of leaf
tissue. Physiological age was particularly important for Ca and other
nutrients which are not readily translocated in the phloem. The
nutrient concentrations in plant samples can therefore be interpreted
only if the growth stage at sampling is defined.
Environmental and soil factors also influence the availability of
P and K and thus crop response to applied P and K. Volumetric water
content, soil bulk density, buffering capacity, concentration, counter
diffusing ions, and soil chemical reactions are important in determining
the amount of P and K that reach the root. These factors indicate
greater yield response to P and K applications in drier years. When
rates of K were split with application of P the response was dependent
on weather conditions (Reneau et al., 1983).
According to Bates (1970) although the concentration of nutrients
in plant tissue chosen to provide a constant physiological age changes
with the age of the plant, there is some question whether the critical
concentration changes with the age of the plant. It is commonly


153
Days After Planting Maize
Figure 6-10. Effect of the stage of maturity on the N
concentration of 'NB-3' maize (a) and
'Criollo' sorghum (b).


134
organic accumulates synthesized by the plant which are available for
growth, development, and metabolism. Bolsen (1977) observed that sorghum
and maize stover are energy containing by-products of grain production.
Both crop residues make acceptable silage and both supply the energy in
maintanace rations for beef cows or ewes. On an energy basis, maize
silage is valuable for milk production.
Materials and Methods
Field Procedures
This experiment involving three intercropping systems (Fig. 5-1)
was conducted in Esteli, Nicaragua (Fig. 4-1) during the 1982-1983
growing season. The experimental site (Centro Experimental de Esteli)
was located 1 km north of the city of Esteli on the Panamerican Highway
at an elevation of 975 m. The average annual precipitation is 1000 mm
distributed in a bimodal pattern (CATIE, 1981a); the largest amounts
fall during May, June, August, and September (CATIE 1980, 1981). This
rainfall pattern is the determining factor in defining the growing
season. The average annual temperature is 19C. The soil classification
for the experimental site was not available but it may be classified as
a Vertisol (CATIE, 1981). Further classif ication has not been
determined. The experimental field was previously planted to shade
tobacco (Nicotiana tabacum L. ) but had been under fallow for the last
seven years.
Nutrient concentration, IVOMD, metabolizable energy, and percent
organic matter of the 'NB-3' + 'Criollo', 'NB-3' + 'Pioneer 895', and
'NB-3' + 'Gahi-3' systems were determined at different periods of growth
(Table 3-6). Total above-ground growth was harvested from six hills of


9
in the stem was diverted to the head and that this accounts for the loss
in stem weight in this instance.
Apparent photosynthesis was closely correlated with dry matter
accumulation by the shoots during grain fill. Consequently, the progress
of photosynthate accumulation can probably be viewed as the progress of
dry matter accumulation. Translocation was less inhibited than dry matter
accumulation or apparent photosynthesis under dry conditions. As a
result, grain yield, while significantly inhibited, was probably less
inhibited than it would have been if the translocation of reserves had not
occurred.
Other authors have shown that maize stems often lose dry matter as
the grain matures (Johnson et al.,1966; Daynard et al., 1969; Hume and
Campbell, 1972), particularly when the environment becomes unfavorable
during grain fill. The dry weight appears to be soluble carbohydrates
that can be stored in the stem (Daynard et al., 1969; Hume and Campbell,
1972). This mobilization of stem reserves has not been observed in every
instance (Hanway, 1962a). This agrees with the conclusion by Duncan et
al. (1965 ) that even relatively short-term adjustment by stem reserves may
enable the maintenance of a high rate of grain filling while the
conditions for photosynthesis are temporarily unfavorable. Thus, in maize
stem, mobilization probably occurs when sink demand exceeds source
capacity.
It has been shown that the dry matter stored in the grain of
sorghum (Stickler et al., 1961b; Goldsworthy, 1970), in the grain of maize
(Allison and Watson, 1966), and in rice (Enyi, 1962) is derived mainly
from assimilates produced after head emergence so that grain yield is
directly related to leaf area after the ears emerge. However, McPherson


175
Doys After Planting Maize
Figure 6-25. Effect of the stage of maturity on
the concentration of Fe of 'NB-3'
maize and 'Criollo' sorghum (b).


76
Plant Analysis Methods
Nitrogen analysis of plant material employed the microKjeldahl
procedure modified by Gallaher et al. (1976). A 0.1-g sample was placed
in a 100-ml digestion tube to which two boiling chips, 3.2 g of catalyst
(90% anhydrous K^SO^, 10% anhydrous CuSO^), 10 ml of concentrated
and 2 ml of were added. Samples were then digested in an aluminum
block digester (Gallaher et al. (1976) for 2.5 hrs. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen
concentration of these solutions were determined on a Technicon
AutoAnalyzer II.
Phosphorus, K, Ca, Mg, Fe, Cu, Mn, and Zn concentrations were
determined by a mineral analysis procedure in which 1.0 g samples were
placed in 50-ml pyrex beakers and ashed in a muffle furnace at 480C
for a minimum of 4 hrs. After cooling each was treated with 2 ml of
concentrated HC1 and heated to dryness on a hot plate. An additional 2
ml of concentrated HC1 + water was added to the dry beakers followed by
reheating to boiling and then diluting to 100 ml volume with deionized
water. Solutions were analyzed for P using colorimetry on an
Autoanalyzer. Potassium was determined by atomic emission
spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were determined by
atomic absorption spectrophotometry.
IVOMD of plant material was determined by the Tilley and Terry
(1963) two-stage procedure adapted by Moore et al. (1972). For
measurements of combustible energy, approximately 0.5 g of sample was
pelleted in a cylinder press and weighed to the nearest 0.00001 g.
Samples were then placed in clean combustion boats. Combustible energy


227
Dijkshoorn, W., J. E. Lampe, and P. F. Van Burg. 1960. A method of
diagnosing the sulphur nutrition status of herbage. Plant and Soil. 13
(3): 227-241.
Duncan, W. C., A. L. Hatfield, and J. L. Regland. 1965. The growth and
yield of corn. II. Daily growth of kernels. Agron. J. 57:221-223.
Duncan, W. G., R. S. Loomis, W. A. Williams, and R. Hanan. 1967. A model
for simulating photosynthesis in plant communities. Hilgardia.
38:181-205.
Eik, K., and J. J. Hanway. 1966. Leaf area in relation to yield of corn
grain. Agron. J. 58:16-19
Eng, K. S., B. E. Jeter, M. E. Riewe, and L. H. Brever. 1965.
Utilization of sorghum grain protein as affected by variety and
fertilization. J. Anim. Sci. 24:880. (Abstr.).
Ensminger, L. E. 1954. Some factors affecting the adsorption of sulfate
by Alabama soils. Soil Sci. Soc. Amer. Proc. 18:259-264
Ensminger, L. E., and J. R. Freney. 1966. Diagnostic techniques for
determining sulphur deficiencies in crops and soils. Soil Sci.
101 .-283-290.
Enyi, B. A. 1962. Comparative growth rates of upland and swamp rice
varieties. Ann. Bot. N. S. 26:467-487.
Evans, J. L., and G. K. Davis. 1966. Influence of sulfur, molybdenum,
phosphorus, and copper interrelationships in cattle upon cellulose
digestion in vivo and in vitro. J. Anim. Sci. 25:1014-1018.
Fassbender, H. W. 1980. Quimica de Suelos. Editorial IICA. 398 pp.
Fox, R. L., B. T. Kang, and D. Nangju. 1977. Sulfur requirements of
cowpea and implications for production in the tropics. Agron. J.
69:201-205.
, R. A. Olson, and H. F. Rhoades. 1964. Evaluating the sulfur
status of soils by plant and soil tests. Soil Sci. Soc. Am. Proc.
28:243-246.
Francis, C. A. 1983. Agronomic components of adaptation in sorghum. In
Procs. The plant breeding methods and approaches in sorghum. Workshop
for Latin America. INTSORMIL/INIA/INCRISAT. El Batan, Mexico, pp.
184-193.
Fribourg, H. A. 1974. Fertilization of summer annual grasses and silage
crops. _In D. A. Mays (ed.) Forage fertilization. Am. Soc. of Agron.
Madison, WI.
Friedrich, J. W., and L. E. Schrader. 1978. Sulfur deprivation and
nitrogen metabolism in maize seedlings. Plant Physiol. 61:900-903.


BIBLIOGRAPHY
Alegria, R. T. Walker, and A. Menjivar. 1979 Diagnostico sobre
sistemas de produccin agropecuarios del Cacerio la Trompina del
municipio de Jocoro, Depto. de Morazan, El Salvador. CENTA/MAG, El
Salvador. 62 pp.
Alessi, J., and F. Power. 1976. Water use by dryland corn as affected by
maturity class and plant spacing. Agron. J. 68:547-550.
Allaway, W. H., and J. F. Thompson. 1966. Sulfur in the nutrition of
plant and animals. Soil Sci. 101:240-247.
Allison, J. C. S., and D.J. Watson. 1966. The production and
distribution of dry matter in maize after flowering. Ann. Bot., N. S.
30: 356-81.
Alvarado, M., A. Chavez, and V. Rodriguez. 1978. Diagnostico de los
sistemas de produccin agropecuaria de la zona norte de Ahuachapan, El
Salvador. CENTA/MAG, El Salvador. 79 pp.
Archbold, H. K. 1945. Some factors concerned in the process of starch
storage in the barley grain. Nature, London. 156:70-3.
Arias, F. R., P. Estrada, and R. Martinez. 1980. Sistemas de produccin
de cultivos predominantes en el Salvador. Tn R. Moreno, (ed.) Reunion de
consulta sobre la localizacin de sistemas de produccin de cultivos en
Centroamerica. CATIE, Turrialba, Costa Rica. pp. 89-168.
Arze, J., F. R. Arias, and M. Smith. 1983. Esquema de investigacin en
sistemas de cultivo con sorgo: Propuesta para CLAIS. _In Proc. The plant
breeding methods and approaches in sorghum. Workshop for Latin America.
INTSORMIL/INIA/ICRISAT, El Batan, Mexico, pp. 196-206.
Ashley, D. A., B. D. Doss, and 0. L. Bennett. 1965. Relation of cotton
leaf area index to plant growth and fruiting. Agron. J. 57:61-64.
Baker, D. E., A. E. Jarrell, L. E. Marshall, and W. I. Thomas. 1970.
Phosphorus uptake from soils by corn hybrids selected for high and low
phosphorus accumulation. Agron. J. 62:103-106.
Baker, E. F. 1978. Mixed cropping in Northern Nigeria. I. Cereals and
ground-nuts. Exp. Agrie. 14(4): 293-298.
Baker, E. F. 1979. Mixed cropping in Northern Nigeria. III. Mixtures of
cereals. Expl. Agrie. 15:41-48.
223


101
Table 4-2. Management activities in animal subsystems.
Months
Activities JFMAMJJASOND
I CATTLE
Milking
Feeding
Maize residues
Sorghum residues
Grazing
Supplements, concentrates
Creara/butter/cheese process
Animal sales
II SWINE
Feeding
Grains
Crop residues
Milk residues
Live sale (2/year)
III POULTRY
Grain feeding maize/sorghum
Egg recollection
Live sale
IV "GUATERA CROPPING
XXX = Increased use or production
*** = Decreased use or production
**********XXXXXXXXX****
XXX** **XXX
XXXXXX **X
********XXXXXXXXXXXX***
xxxxxxx
**********XXXXXXXXXX***
XXX XXX
*****xxxxxxxxxxxx*****
xxxxx xxxxx
XXX XXX XXX
XXX XXX
**********************
**********************
XXX*** *xxxx
xxxx** **xxxx
*


221
Among the most relevant research needs are 1) evaluate the
"guatera" system, 2) evaluate the uses of the maize + sorghum system in
animal and human nutrition, 3) design spatial and chronological
arrangements and rotations that enhance the adaptability of the system
to the environmental conditions, and increase the availability of animal
feed during the dry season, 4) test varieties and/or species to improve
the quantitative and qualitative yield of the system, 5) soil
conservation and management, 6)identify and evaluate exotic forage
species, and 7) evaluate (in vitro and in vivo) the components of the
maize + sorghum system.
Results from the dry matter accumulation study showed that when ear
sink is reduced by water stress during bloom, dry matter will accumulate
in other plant components, particularly in the leaf. The ability of the
non-photosensitive sorghum to accumulate dry matter in the head explains
in part its high grain:stem ratio; conversely, photosensitive sorghums
accumulate more dry matter in the stem than in the head.
Non-photosensitive sorghums compare well to photosensitive sorghums in
dry matter production. Millet, 'Gahi-3' was not adapted to the growing
conditions in Nicaragua and was dramatically affected by water stress.
IVOMD decreased with maturity in the vegetative plant components
but increases in maize ears. Maize leaves had higher IVOMD than the
stems. The photosensitive sorghum maintained higher IVOMD values and for
longer periods of time than non-photosensitive sorghum. 'NB-3',
'Criollo', and 'Gahi-3' presented similar forage quality. Energy
accumulation in the different plant components varied little during the
growing season. Maize and sorghum stover have a potential as livestock
feed.


Page
CHAPTER 4. MAIZE + SORGHUM FARMING SYSTEMS IN CENTRAL AMERICA:
SITUATIONAL ANALYSIS 78
Introduction 78
Materials and Methods 80
Results and Discussion 81
Bio-Physical Environment 84
Socio-Economic Environment 87
Crop/Animal Interactions 103
Constraints 105
Research Opportunities 107
Interventions 108
CHAPTER 5. DRY MATTER ACCUMULATION BY MAIZE + SORGHUM AND
MAIZE + MILLET INTERCROPPING SYSTEMS 109
Introduction 109
Materials and Methods Ill
Results and Discussion 113
Percent Soil Moisture 113
Dry Matter Accumulation 118
Leaf Area Index and Other Plant Characteristics 130
CHAPTER 6. NUTRIENT CONCENTRATION, IVOMD, AND METABOLIZABLE
ENERGY OF INTERCROPPED MAIZE + SORGHUM AND MAIZE
+ MILLET SYSTEMS 131
Introduction 131
Materials and Methods 134
Field Procedures 134
Laboratory Procedures 136
Results and Discussion 137
Percent Organic Matter, IVOMD, Metabolizable Energy,
and Nitrogen 137
Phosphorus, K, Ca and Mg Accumulation 157
Iron, Cu, Mn and Zn Accumulation and Distribution ...... 174
CHAPTER 7. SURVEY OF SULFUR DEFICIENCY IN MAIZE 187
Introduction 187
Materials and Methods 191
Field Methods 191
Laboratory Procedures 193
Results and Discussion 195
Experiment 1 195
Experiment 2 205
CHAPTER 8. SUMMARY AND CONCLUSIONS 220
BIBLIOGRAPHY 223
BIOGRAPHICAL SKETCH 238
v


151
with maturity. Cummins (1970) reported that carbohydrate content in the
leaves was negatively correlated with maturity.
Conversely, energy in the stems increased with maturity. Apparently
carbohydrates accumulated in the stem even after grain harvest (Figs.
6-7a, 6-8a, and 6-9a). Data presented by Cummins (1970) supports this
observation. He reported a decline in carbohydrate content at midseason
and a rapid increase at the end of the season. These results also agree
in part with those presented by Johnson et al. (1966), who reported
increasing energy in the stem from tasseling to soft-dough, with a
slight decline thereafter. Energy values observed support dry matter
accumulation data reported in Chapter 5, which indicated a higher dry
matter accumulation in the stem than in any other plant component.
Cummins (1970) observed that rainfall during maturity decreased
carbohydrate content in the stem.
The patterns in energy contents observed in the PS, NS sorghums,
and in the millet differed somewhat from that observed in maize. Energy
content in the leaves from the PS sorghum (Fig. 6 7b) increased early in
the season, then declined at bloom, and remained fairly constant to the
end of the season. Stem energy increased rapidly from early growth to
bloom and thereafter it remained constant. Higher energy values were
observed in the stem than in the leaves towards the end of the season;
the inverse was true early in the growing season.
In general the NS sorghum had lower energy content in relation to
the PS sorghum (Fig. 6-8b). Both leaf and stem energy increased rapidly
from planting to bloom; however, leaf declined sharply soon after bloom.
Although stem energy contents were not as high as those observed in the
leaves, these did not decline after bloom. In fact energy content


193
Four soil samples (from 0 to 30 cm depth) were taken within a 25 cm
circumference around each plant. The samples for each plant were mixed
to form one sample per plant per replication. Samples were air dried,
sieved to pass a 2 mm stainless steel screen, and stored for analysis.
Response variables measured in plants were a) plant height, b) leaf
length, c) leaf width at the widest point, d) dry weight per leaf, e)
leaf concentrations of S, N, P, K, Ca, Mg, Cu, Fe, Mn, Zn. Soil response
variables measured were concentration of the same nutrients measured in
the leaf tissue.
Laboratory Procedures
Soil analysis methods
For both experiments N analysis employed a microKjeldahl procedure
(Bremner, 1960) as modified by Gallaher et al. (1976). A 2.0-g sample
was placed in a 100-ml digestion tube to which 3.2 g of catalyst (90%
anhydrous K^SO^, 10% anhydrous CuSO^), 10 ml concentrated H^SO^ and 2 ml
30% were added. Samples were then digested in an aluminum block
digester (Gallaher et al., 1976) for 2 1/2 hours at 375 C. Upon
cooling, solutions were diluted to 75 ml with deionized water. Nitrogen
concentrations of these prepared solutions were determined using a
Technicon AutoAnalyzer II.
All soil P, K, Ca, Mg, Fe, Cu, Mn, and Zn analyses were conducted
using procedures recommended by University of Florida's Soil Testing
Laboratory. Five grams of air-dried soil were extracted with 0.05 HC1
+ 0.025 H^SO^ at a soil: solution ratio of 1 to 4 (W:V) for 5 minutes
(Mehlich, 1953). Soil P was then analyzed using colorimetry. Potassium
was determined by atomic emission spectrophotometry. Calcium, Mg, Fe,


190
Friedrich and Schrader (1979) found that as plants reach maturity
the ratio of N:S in plant proteins tends to decrease. When leaf material
is used for analyses the amino acid N:S ratio is about 15:1 for a wide
variety of field crops.
Stewart and Porter (1969) observed that mass of maize roots was
greatly affected by applications of S-containing fertilizers. For
example, the mass of maize roots was increased from 2.9 g for the no-S
treatment to 6.7g for the 150-mg kg ^ level. They concluded that in
S-deficient soils the addition of 1 part S for every 15 parts of
fertilizer N will likely prevent S deficiencies.
Mitchell and Blue (1981a, 1981b) reported that millet responded
markedly to S applied to Florida Entisols. Rabufetti and Kamprath (1977)
found little response to S applications at low levels of N applications,
the opposite at higher N rates. Jones and Martin (1964) observed that
the application of S not only increased forage production, with changes
in relative growth rate of various species, but after S fertilization
the chemical composition of the forage was altered as well.
Objectives
Experiment 1
Sixty day-old no-tillage maize (DeKalb 'X L 395 A') was grown in a
65 ha center pivot irrigated field. Plants showed various degrees of
stunting and ranged from dark green healthy plants to very stunted
plants that were light green to yellow. Maize ranged in height from
about 30 to 120 cm. The small stunted plants exhibited intervenial
chlorosis, the degree of which diminished as height increased. The 120
cm plants looked normal and healthy. The hypothesis proposed stated that
the problem was likely associated with soil texture and the solution


49
In many parts of the tropics burning of plant matter, which is an
integral part of farming, can be an avenue for S loss. When carbon is
burned off by combustion there is a concentration of S in the ash.
Blair et al. (1980) and Bromfield (1974) showed that the S content in
ash can be 2 to 10 times higher than that in dried plant material. In
areas of prevailing winds S loss may be high, but in regions of variable
winds the gains may equal the losses. One additional consequence of
burning is that organic forms of S are converted to inorganic forms
which, at the beginning of the rainy season when fields are bare, are
susceptible to leaching losses.
Blair et al. (1980) reported that sulfate which was mineralized
from organic matter moved down the profile and accumulated at lower
depths. Since a large proportion of the S present in the soil is in the
organic matter and this is often accumulated on the soil surface, losses
from wind and water erosion may be high in some circumstances.
Plant's Requirements and Content
Tisdale and Nelson (1964) concluded that S is required by many
crop plants to about the same extent as is P. As a general rule of
thumb, grass and cereal crops generally require smaller amounts of S
than do legume and cruciferous crops. Ensminger and Freney (1966) list
the effect of age on S contents in several species. Because it is
necessary to select a plant part that has a relatively constant S
content, the effect of maturity on the S content of the plant part(s)
should be examined to determine sensitivity to sampling time.
The critical concentration of S in young maize plants has been
reported to be around 0.20 dag kg 1 (Fox et al., 1964; Stewart and
Porter, 1969; Jones and Eck, 1973; Terman et al., 1973). Friedrich and


203
Dijkshoorn et al. (1960) and Gaines and Phatak (1982) reported that
for maize, the N:S concentration ratio varies from 14 to 17. The N:S
ratio found in the leaves in plants from the 120-cm treatment is
adequate; not so for the other treatments. These high ratios (45, 37,
36, and 26) indicate that S concentration in relation to that of N is
low. Friedrich and Schrader (1978) reported that under S-deficient
conditions the plant's capacity to synthesize protein is affected and N
accumulates in non-protein forms in the plant. Similarly, sulfate will
accumulate in plants when the rate of uptake exceeds the amount required
for protein synthesis. Therefore, this imbalanced observed (N:S)
affected the growth of plants from all treatments, except those from the
120-cm treatment.
The P:S ratio is reported in Table 7-7. Values ranged from as high
as 5.3 to 1.3 for the 30 and 120-cm treatments, respectively. These high
ratios also indicate an inadequate S concentration. Phosphorus-sulfur
interactions have been observed by Kamprath et al. (1956) and Radet
(1966). Caldwell et al. (1969) observed that S applications decreased P
concentration in mature tissue. This could have been due to dilution; as
plants grow plant uptake of S and P concetration in the tissue will be
diluted.
Average extractable K, Ca, and Mg in the top 45 cm of soil in
relation to plant height is reported in Table 7-8. Blue et al. (1981)
reported similar values for two Florida Entisols. According to data
presented by Plank (1979), K is low and Ca high. In general, the trend
observed was that K, Ca, and Mg were higher in the soils related to the
120-cm treatment.


47
the greater the product removal and S demand. For example S contents of
the rice grain vary from 0.034 dag kg ^ under deficiency conditions to
0.16 dag kg ^ in a nonresponsive situation, and rice grain yields may
vary from 0.75 to 8 Mg ha *. A further factor to take into account when
considering the effect of crop removal on S demand is the zone of
removal in the soil.
The removal of crop residue contributes significantly to losses of
soil S in some situations (sorghum, millet). The recycling of S in crop
residues is important in livestock systems where the residue material is
used for animal feed or bedding. Since organic matter acts as a reserve
of S in soils, the losses have serious implications for the S-supplying
power of soils.
Coleman (1966) suggested that S deficiencies occur probably
because of a) the increased use of S-free fertilizers; b) the decreased
use of S as a fungicide and insecticide; and c) increased crop yields,
which means requirements of all of the essential plant nutrients in
larger amounts. Blair et al. (1980) indicated that the use of
non-S-containing phosphatic fertilizers may aggravate the S problem by
replacing adsorbed sulfate with phosphate. In this regard two aspects
of sulfate adsorption are important. First, phosphate ions will replace
sulfate ions. Bromfield (1974) estimated that sulfate ions are then
free in the soil solution and can be leached.
Adsorbed sulfate associated with the argillic horizons of Ultisols
is considered a primary source of piant-available S in soils of the
southeastern United States (Neller, 1959; Bardsley et al., 1964;).
Ensminger (1954) reported that in some areas S may leach out of the
surface horizons of coarse-textured soils but be retained by the lower


84
Hawkins et al. (1983) identified northern El Salvador as the area where
the system is most widely cultivated (240,000 ha). Reports in the
literature (Arias et al., 1980; Mateo et al., 1981; Fuentes and
Salguero, 1983) indicated that of the total area cultivated with sorghum
in Guatemala, El Salvador, and Honduras, 80, 93, and 93%, respectively
are intercropped with maize.
Bio-Physical Environment
Climate
The Central American Isthmus extends from east to west with the
Caribbean Sea at the north and the Pacific Ocean at the south (Fig.
4-1). Hot humid lowlands predominate on the Atlantic coast. The interior
is composed of mountains and valleys. A wide belt of steppe conditions
is found in these areas where the maize + sorghum system is found.
Precipitation stays below 1,000 mm yr ^ in the interior valleys. This
dryness is probably caused by mountain valley winds rather than by the
shielding effect of the mountains. In the Pacific coastal foothills
annual rainfall may range from 1,400 to 2,000 mm (Alvarado et al., 1978;
CATIE, 1980), and in some areas, such as northern El Salvador it may be
greater than 2,000 mm (Guillen et al., 1978). Annual rainfall is
distributed in a bimodal pattern (CATIE, 1980; CATIE, 1982a). The dry
season begins in November and ends in April or May, and the wet season
is interrupted by a dry period called "canicula" in July or August
(Rodriguez et al., 1977; Guillen et al., 1978). Results of studies
conducted by CATIE, (1980); and Guzman (1982) indicate that potential
annual evapotranspiration is high. The observed range in some areas is
between 1,000 and 2,000 mm (Fig. 4-2). This results in a soil moisture
deficit through May and the depletion of soil reserve in July. In the


58
for second cutting alfalfa in 1966 ranged from 0.45:1 in untreated plots
to 1.42:1 in alfalfa which received 112 kg ha ^ of elemental S annually.
There was no effect of S on the P content of maize in 1962. Sulfur
increased the S content of the leaves from 0.22 to 0.26 dag kg
Phosphorus content decreased from 0.45 dag kg without S to 0.38 dag
kg when S was applied. Kamprath et al. (1957) reported that liming
and P fertilization reduced the retention of sulfate in the surface
horizons and as a result sulfate added to these soils would be leached
out of the plow layer into the B horizons, where it accumulates.
Work by Caldwell et al. (1969) demonstrated that the effect of S
on the K content of alfalfa varied. In one year increasing S resulted
in a decrease in the K content. In the second year the S-treated
alfalfa contained more K than the S controls. Apparently the healthier,
more vigorous plants on the treated plots were able to extract more K
from the soil than the weak, unthrifty, S-deficient plants.
Caldwell et al. (1969) found no discernible effects of S on the
Ca, Mg, and Fe content of alfalfa. Neither were there any significant
differences in the Cu, Zn, Al, and Sr contents of the alfalfa as a
result of the S fertilization. Average Cu content of the maize
decreased from 10 to 8 mg kg ^ with S (significant at the .05
probability level).
Mitchell and Blue (1981a, b) found that both total S and
extractable sulfate-S were significantly correlated with organic C and
total N in the surface horizons of Florida soils. Only total S was
highly correlated with organic C and total N in the spodic horizon.


229
Green, V. E. 1973.
non-bird-resistant
33:13-16.
Yield and digestibility of bird resistant and
grain sorghum. Soil and Crop Sci. Soc. of Florida.
1974. Food crop production problems in Costa Rica and the
humid American tropics. World Crops. 26:250-255.
Greenwood, E. H. and E. G. Hallsworth. 1960. Studies on the nutrition
of forage legumes. II. Some interactions of calcium, phosphorus, copper,
and raolibdenum on the growth and chemical composition of Trifolium
subterraneum L. Plant Soil 12:97-127.
Guillen, N., J. Mayorga, J. Cortez, and R. Reyes. 1978. Diagnostico de
sistemas de produccin agropecuarios de Jocoatique, Morazan, El
Salvador. CENTA/MAG, El Salvador, p. 77.
Guzman, G. T. 1982. Conocimiento actual de la canicula en Centro
America. In J. F. Larios (ed.) Agricultura en zonas afectadas por
canicula interestival en El Salvador. MAG/CATIE, San Andres, El
Salvador, pp. 1-27.
Hall, G. A., C. W. Absher, R. Totusek, and A. D. Tillman. 1965. Net
energy of sorghum grain and corn for fattening cattle. J. Anim. Sci.
30:165-169.
Hanway, J. J. 1962a. Corn growth and composition in relation to soil
fertility: I. Growth of different plant parts and relation between leaf
weight and grain yield. Agron. J. 54:145-148.
1962b. Corn growth and composition in relation to soil
fertility: II. Uptake of N, P, and K and their distribution in different
plant parts during the growing season. Agron. J. 54:217-222.
1962c. Corn growth and composition in relation to soil
fertility:III Percentages of N, P, and K in different plants in relation
to stage of growth. Agron J. 54:222-229.
1963. Growth stages of corn (Zea mays L.). Agron. J.
55:487-491.
, and W. A. Russell. 1969. Dry-matter accumulations in corn
(Zea mays L.) plant: Comparisons among single-cross hybrids. Agron. J.
61:947-951.
Hartt, C. E. 1969. Effect of potassium deficiency upon translocation of
14c in attached blades and entire plants of sugarcane. Plant Physiol.
44:1461-1469.
Hawkins, R., M. Smith, and F. R. Arias. 1983. Sistemas de cultivo de
sorgo en Centroamerica: Importancia, localizacin y caracteristicas. _In
Procs. The plant breeding methods and approaches in sorghum. Workshop
for Latin America INTSORMIL/lNIA/INCRISAT/ El Batan Mexico, pp. 207-229.


192
75, 90, and 120 cm Call plants. Ten whole plant samples were taken at
random for each replication, as well as the associated youngest mature
leaf and soil samples. Soil samples were taken at several depths within
25 cm from the treatment plants.
Plants and youngest mature leaves were washed in distilled water,
dried at 70C in a forced air oven, and ground in a Wiley mill to pass a
1 mm stainless steel screen. Soils were sampled in 15 cm increments to
45 cm, then later to 90 cm, air dried, ground by mortar and pestle, and
screened in a 2 mm stainless steel screen. Plant and soil samples were
analyzed as described in the section on laboratory procedures of this
chapter.
Experiment 2
Eighteen maize fields in Northern Nicaragua (Esteli and Matagalpa)
that were between 40 and 50 days old were selected as experimental
fields. A second criterion of selection was the occurrence of S-
deficient and sufficient healthy-looking plants (based on the criteria
established in experiment 1). A description of the study area is given
in Table 3-7.
Once inside the experimental field, four deficient and four
sufficient plants were selected. Each pair of plants within a field was
considered to form a replication of a randomized complete block design.
Comparisons among fields were made through a split plot design; sites
were considered as main plots and plant phenotypes as split-plots. The
youngest fully expanded mature leaf was collected for each plant,
described, and measured in length and width. The leaves were weighed,
oven dried, ground in a Wiley mill to pass a 1 ram stainless steel
screen, and stored in air-tight bags for analysis.


87
Predominant soil types
The soils where the maize + sorghum cropping system is cultivated
can be classified into one of the following orders: Alfisols, Entisols,
Inceptisols, Vertisols or Mollisols (CATIE, 1980; Kass 1980; CATIE
1982a; Rico, 1982). Figure 4-3 shows an environmental profile for the
association of maize and sorghum in El Salvador, Nicaragua, and
Honduras; considering annual rainfall, altitude, slope, and soil
fertility and depth. The typical landscape is made up of steep lands,
slopes up to 50%, shallow soils (30 cm maximum) with prevalence of loose
stone or shale. It is highly susceptible to erosion (Arias et al.,
1980; CATIE, 1980).
Socio-Economic Environment
Family composition
Larios et al. (1983) reported that the average farm family is
comprised of seven members, approximately 75% of whom are under 30 years
of age; in some areas the population is somewhat younger (40% under 12
years). Assuming the inputs of women and children are 0.7 and 0.5,
respectively, man's working day, the average farmer has a daily
equivalent of 5 man days ^ in his family.
Education
Education levels vary from country to country. In some literacy can
be higher than 80%; in others it may be lower than 60%. Among children
it is generally higher than in parental groups (Larios et al., 1983).
Capital
Farm size is considered to range from small to medium (0.25 to 70
ha.). Land tenure is unsatisfactory (Green, 1974). In some cases 75% of
the farmers occupy 25% of the land (Hawkins et al., 1983; Larios et al.,


ACKNOWLEDGMENTS
I express sincere gratitude to Dr. Raymond Gallaher, chairman of
the supervisory committee. His guidance, dedication, and continuous
encouragement were valuable throughout my graduate program. I also thank
Dr. Victor E. Green, Dr. Clift Taylor, Dr. Mary Collins, and Dr. Maxie
McGhee for their teachings and guidance in the preparation of this
*
manuscript.
My studies would have been impossible without the financial
assistance of the Centro Agronmico Tropical de Investigacin y
Enseanza (CATIE) and the W. K. Kellogg Foundation, to the staff members
of which I express my sincere gratitude.
Thanks are also due to Mr. David Block for his assistance in the
statistical analysis of the data, and to Mr. Jacobo Reyes Palma for his
valuable assistance in conducting the field work. Acknowledgment is due
to Mrs Beneranda Arias and Mrs. Oliviethe Ortiz for their assistance in
the tissue analysis. Words of gratitude are expressed to Dr. Raul Moreno
for his encouragement, and friendship.
To ray mother, for her never ending sacrifices, her love, and
prayers, I owe much gratitude. I also thank my brothers Julio, Marina,
and Guillermo who have also contributed greatly towards the fulfillment
of my goals in life. To my wife, Beneranda, I express my gratitude for
her moral support, patience, and encouragement. I thank Roberto,
Liliana, and Veronica, without whose motivation and love this task would
have been less bearable.
m


107
al., 1983). Land availability may change in the area as a result of the
agrarian reform projects being carried out by some of the local
governments (personal observation by the author). Labor is limited
during short periods, especially at weeding times and when high-paying
off-farm jobs such as coffee, cotton, and/or sugar cane farms demand
labor. Low capital availability is identified by determining dates of
crop and animal sales, usually just after harvest. When grain prices are
low farmers will store the grains and sell animals; the cash generated
is used to buy commodities and as investment capital for the next
cropping season. From this fact arises the economic importance of having
cattle, swine, and poultry for sale when cash is needed.
Research Opportunities
Information on maize + sorghum/animal systems is relatively scarce.
The lack of quantitative as well as qualitative information on inputs,
outputs, flows, and components of the maize + sorghum/cattle system
makes it difficult to understand its structure and functions in time and
space. According to Arze et al. (1983) to find alternatives that improve
the system it is necessary to 1) delimit the system within a particular
farm or region, 2) identify the composition and ranges of crop
components, particularly forages, (autotropic) in the predominant farms,
3) study the composition of the animal production component
(heterotropic), 4) study the variability of the crop/animal relations in
the region and identify the interaction levels, 5) identify, by levels,
the use of human energy, (family and hired) used in the management of
the crop/cattle subsystem of the maize + sorghum /cattle system, and 6)
identify the bio-physical as well as socio-economic characteristics of
the region where the system is to be developed.


22
from 35 Co 52% of the total plant weight. The rate of dry matter
accumulation in the grain was similar for all hybrids, years, and plant
populations varying from 163 to 181 kg ha ^day
Vanderlip and Arkin (1977) reported that on a daily basis, dry
matter in sorghum was allowed to be partitioned to the leaves up to 125%
of that neccesary for the leaf area developed that day. The same authors
found that at least 25% of the daily dry matter production was
partitioned to the roots, which under conditions of low photosynthate
production would cause an increase in specific leaf area.
Barlow and Boersma (1976) demonstrated that even grain dry matter
was only 63 to 76% of the total dry matter accumulated by the shoots
during grain fill. In the desiccated plants, however, grain dry matter
was 50% larger than the total dry matter accumulated and was accompanied
by a reduction in net photosynthate accumulation in the source leaf.
Goldsworthy (1970) reported that photosensitive sorghums sown at
the end of May formed from two to three times as much dry weight as 'NK
300' non-photosensitive which was sown 10 weeks later. The photosensitive
sorghum 'Farafara' had the largest total dry weight but the smallest
grain yield. About 70% of the total dry weight was in the stems and only
from 9 to 13% in the heads. In contrast, the dry weight of 'NK 300' was
only about one-third or one-half that of 'Farafara' but from 40 to 60% of
it was in the heads so that the grain yields were much larger than those
of 'Farafara'.
The reason, it seems, for the low grain yield of photosensitive
sorghum is that a substantial part of the assimilate formed after heading
accumulates in the stem, whereas most all of the dry matter produced
after heading in non-photosensitive moves to the head. The results of


CHAPTER 8
SUMMARY AND CONCLUSIONS
During 1982-1983 studies were conducted in Florida and Nicaragua to
provide basic information needed to describe and improve the maize +
sorghum intercropping system. The plan of work included experiments to
a) identify limitations in crop productivity, b) study the relationship
between soil moisture and dry matter accumulation, c) evaluate quality,
dry matter accumulation, energy, and nutrient concentration in the crop
components of the maize + sorghum and maize + millet intercropping
systems, and d) determine if S deficiency is a widespread problem.
Results from the situational analysis showed that maize + sorghum
is the most important food-producing system in Central America.
Environmental stresses, especially drought, are the most important
limitations to crop production. This phenomenon occurs because of the
variability in the rainfall pattern and the "canicula", which in some
areas may last more than 30 days. Drought is accentuated by the existing
physiography, shallow soils, and heavy soil textures. In some areas
nutrient deficiency, particularly N, P, and S, may reduce crop
productivity and can be related to drought. Within the biological
constraints, the wide use of low-yielding cultivars, 'criollos' of both
maize and sorghum, is a limitation that reduces the possibility of
increasing grain crop yields. The primary constraints to the farm system
are the availability of land, labor, and/or capital.


30
fructosan in grasses is accumulated in the first internode of the stem.
Within the stubble there may be a gradation in concentration of
carbohydrate reserves. In bromegrass (Bromus sp.) and timothy (Phleus
pratense) at anthesis concentrations of fructosans and total water-
soluble carbohydrates were greatest in the internode, leaf blade, and
sheath tissue closest to the stem base.
Bolsen et al. (1975) observed that sorghum stover and maize stalks
are energy-containing by-products of grain production. Both crop
residues make acceptable silage and both supply the energy needed in
maintenance rations for beef cows or ewes. Maize stalk silage can be
used in rations for growing dairy heifers if additional energy is
provided (Colenbrander et al., 1971).
On an energy basis, maize silage is especially valuable for milk
production. It has been reported that the energy value of maize silage
was closely related to total grain yield and proportion of ears to
stalks (Bryant et al., 1966). Sorghum has become increasingly important
in recent years as an energy source in high concentrate rations for
feedlot cattle in the southwest (Croka and Wagner, 1975b).
Crop residues have potential as fertilizer, as fuel, and as
livestock feed. Comparative values for these uses can be determined on
the basis of the amount of energy saved by substituting these materials
for conventional sources of feed, fertilizer, or fuel.
Goodrich et al. (1975) found that energy losses during the
ensiling process average 68% of dry matter losses, apparently because of
the loss of volatile energy-containing compounds during drying, which
inflated the dry matter loss values. Also, decarboxylation reactions
would result in greater losses of dry matter than energy. Energy losses


52
However, BrunoLd and Schmidt (1976) proposed that adenosine-5'-
sulfotransferase, not ATP-sulfurylase, regulates sulfate assimilation in
chlorophyllous tissue.
Rabuffetti and Kamprath (1977) concluded that S accumulation in
maize grain is highly dependent upon the supply of N available for the
formation of amino acids. Sulfur accumulation in stover was enhanced by
both N and S application. On a Goldsboro soil, S application increased
S accumulation in the stover at all N rates. This occurred only at the
high N rates on the Wagram soil.
According to Friedrich and Schrader (1978) higher plants generally
accumulate N and S in amounts proportional to that incorporated into
protein. However, when plants are S-deficient, protein synthesis is
inhibited and nonprotein N is accumulated. Likewise, sulfate will often
accumulate in plants when the availability of N is limiting protein
synthesis. The observed interaction between N and S accumulation
suggests that nitrate and sulfate assimilation are closely linked
raetabolically.
The pattern of remobilization of N and S reported by Friedrich and
Schrader (1979) is similar to the pattern of N redistribution observed
by previous researchers (Hanway, 1962c). The percentage of the labeled
N and S present at silking that was later remobilized was not constant
among fractions. The husk fraction remobilized more of its N and S than
did any other fraction.
Barrien and Wood (1939) studied the effects of N supply on the
amounts of protein-S and sulfate-S. The authors concluded that the most
striking feature of the curves for amount of protein-S plotted against
time is that they follow the trend of the curve for amount of dry


188
Aquic Paleudult). Mitchell and Gallaher (1979), studying S fertilization
on an Arredondo fine sand (loamy, siliceous, hyperthermic Grossarenic
Paleudult), found that S content increased with soil depth, (2.2 and
16.4 mg kg ^ for the 0-15 and 60-80 cm depths, respectively). Soils of
temperate areas are generally richer in total S. Jordan and Reisenauer
(1957) reported values of 540 and 210 mg kg ^ for a Mollisol and an
Alfisol, respectively.
Coleman (1966) indicated that S is needed in crop production
because plants require it for 1) the synthesis of amino acids (cysteine,
cystine, and methionine) and hence for the elaboration of protein, 2)
the activation of certain proteolytic enzymes such as the papainases, 3)
the synthesis of certain vitamins, (glutathine and coenzyme A), 4) the
formation of the glucoside oils found in cruciferous plants, 5) the
formation of disulfide linkages that have been associated with the
structural characteristics of protoplasm, and 6) in some species the
concentration of sulhydril groups in plant tissue has also been
associated to increased cold resistance.
The problem of human and animal malnutrition due to deficiency and
poor quality of protein has been discussed by several authors (Barrien
and Wood, 1939; Allaway and Thompson, 1966; Coleman, 1966). The four
billion (4 X 10 ) people that inhabit the world require amino acids
containing over 40 Mg of S daily. The ultimate goal of S fertilization
of soils is, therefore, to increase the S-amino acid content of human
diets.
According to Caldwell et al. (1969) little attention has been given
to the effect of S on the availability of other macro and micro
nutrients. It is unfortunate that many workers studying the nutrient


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Raymond N. Gallaher, Chairman
Professor, Agronomy
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Victor E. Green
Professor, Agronomy
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Clifton L. Taylor
Associate Professor, Agricultural
and Extension Education
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
3?
Maxie 1$. McGhee
Associate Professor, Agr
and Extension Education
icultural


36
from those of the other two elements in several ways. He also suggested
that N accumulation in the maize plant reached a maximum at silking time
and ceased about four weeks later in the season studied. Nitrogen
continued to move into the grain from other tissues until maturity.
There was an actual loss of potassium after that time, largely from the
leaves and stems of the plant. No marked accumulation of potassium
occurred in the grain.
Reneau et al. (1983) pointed out that interactions between P and K
(P:K) are vital information for obtaining maximum yields. The
literature in this area shows that limited progress had been made with
P:K so that viable interactions could not be proposed. They reported
that the concentrations of N, P, K, Ca, and Mg in forage sorghum were
influenced by either P or K application or both. Nitrogen, P, Ca, and
Mg concentrations were increased and K was decreased with P application.
Nitrogen, Ca, and Mg were decreased and K increased with increased K
application. This antagonistic effect of K on Ca and Mg uptake by
monocots is well documented (DeWit et al., 1963). Bar-Yosef (1971)
demonstrated that higher P concentration in solution would increase Ca
uptake. Conversely, Greenwood and Hallsworth (1960), with intact root
systems, reported no direct effect of P on Ca uptake and further
reported more severe deficiencies with high P levels. Although limited
data is available on the effect of P on Mg uptake, Truog et al. (1947)
reported a synergistic relationship between Mg and P in plants.
Several secondary reactions are shown by the data presented by
Lockman (1972a): decreased Mg with N deficiency; increased Zn with P
deficiency; Ca and Mg accumulation with K deficiency; increased P, Mn,
and Ca but less K with S deficiency; increased P with low Cu; increased


137
concentration of these solutions were determined on a Technicon
AutoAnalyzer II.
Phosphorus, K, Ca, Mg, Fe, Cu, Mn, and Zn concentrations were
determined by a mineral analysis procedure in which 1.0 g samples were
placed in 50-ral pyrex beakers and ashed in a muffle furnace at 480C
for a minimum of 4 hrs. After cooling each was treated with 2 ml
concentrated HC1 and heated to dryness on a hot plate. An additional 2
ml of concentrated HC1 + water was added to the dry beakers followed by
reheating to boiling and then diluting to 100 ml volume with deionized
water. Solutions were analyzed for P using colorimetry on an
AutoAnalyzer. Potassium was determined by atomic emission
spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were determined by
atomic absorption spectrophotometry.
IVOMD of plant material was determined by the Tilley and Terry
(1963) two-stage procedure adapted by Moore et al. (1972). For
measurements of metabolizable energy approximately 0.5 g of sample was
pelleted in a cylinder press and weighed to the nearest 0.00001 g.
Samples were then placed in clean combustion boats. Combustible energy
values were obtained using a computerized Parr adiabatic calorimeter,
using standard ASTM methods.
, Results and Discussion
Percent Organic Matter, IVOMD, Metabolizable Energy, and Nitrogen
Percent organic matter percent OM for plant components for the
'NB-3' + 'Criollo' (M+PS), 'NB-3' + 'Pioneer 895' (M+NS), and 'NB-3' +
'Gahi-3' (M+Ml) is depicted in Figs. 6-1, 6-2, and 6-3. No differences
between maize components were observed among systems (p=0.05) for any


205
Leaf K, Ca, Mg concentrations are shown in Table 7-9. Critical
concentration of K in corn ear leaf tissue at silking was found to be
1.75 dag kg ^ (Gallaher et al., 1975). Plank (1979) sets the K
sufficiency range in ear leaf between 1.75 and 2.25 dag kg According
to these critical levels, K is deficient in the leaves from plants in
the 30 and 60 cm treatments and adequate in leaves from the 75, 90, and
120-cm treatments. Calcium concentration appears to be high in
comparison to the sufficiency range (0.25 to 0.50) reported by Plank
(1979). By the same standards, plants from all treatments had adequate
Mg concentrations. In general, the concentration of these nutrients
decreased as plant height increased.
Gallaher et al. (1975) reported that an adequate K:Ca+Mg ratio in
2+ -1
ear leaf is 11.7 to 13.1 mmol(M )kg 38 days after planting and 7.7 to
2+ -i .
8.7 mmol(M kg 86 days after planting. The K:Ca+Mg ratios reported in
Table 7-9 range from 0.68 to 1.34 in the 30 and 120-cm treatments. As
plant height increases the ratio becomes wider. This also implies that
as S concentration in the leaf increases, K concentration is also
increased. These results suggest a K x S interaction in the leaf.
Apparently S deficiency in the leaf accentuates a K deficiency, which in
turn affects growth directly, because the transport of photosynthates
from the leaf must be affected by the K deficiency. This is a possible
explanation for the stunted plants, reduced leaf dry weights, and K
deficiency symptoms observed in Tables 7-2 and 7-1, respectively.
Experiment 2
A representative weekly rainfall distribution for the 1982-1983
growing season in Nicaragua, Central America is depicted in Figure 5-1.
At the beginning of the rainy season intense rains caused a delay in


82
Maiz y maicillo El Salvador, Guatemala, and Honduras
(Arias et al., 1980; Rosales, 1980;
Mateo et al., 1981; Fuentes and
Salguero, 1983)
Maiz y milln Nicaragua (CATIE, 1980; Pineda et al., 1979)
Although maize and sorghum are the most important food crops in the
semi-arid regions of Central America (Larios et al., 1983), other crops
such as bean (Phaseolus spp.) (Guillen et al., 1978), cowpea (Vigna
spp.) (Alegria et al., 1979), and fruits are important in specific
areas. Sesame (Sesamum indicum L. ) (CATIE, 1982a) and flaxseed (Linum
usitatissimum L.) (CATIE, 1980) are widely cultivated and compete with
maize and sorghum for land and other resources.
Larios et al. (1983) reported that in the countries where the
system exists it interacts with animal production systems. Therefore, a
more complete and descriptive name should include its animal
component(s). A list of animal components of the systems found in these
areas follows:
SPECIES USES
Cattle (dual purpose) Meat, dairy, and power (Juarez
et al., 1979; Mateo et al., 1981
Swine Meat and lard (Rodriguez et al., 1977)
Poultry Meat and eggs (Guillen et al., 1978; Kass,
(1980)
Location
The maize + sorghum/animal production system is limited generally
to the foothills near the Pacific coastal plains, rolling lands and
valleys of the interior of Central America as depicted in Figure 4-1.


53
matter. An increase in N supply caused an increase in the amount of
protein-S. As in the case of protein-N, the highest N treatment caused
at first a depression in the amount of protein-S due to an effect of
treatment on growth rate.
Friedrich and Schrader (1979) reported that in maize a greater
proportion of N compared to S was remobilized from all fractions with
the exception of roots. This suggests that N is more mobile than S, at
least under the conditions of this experiment. The supply of S strongly
influences the efficiency of nitrate-N utilization in maize. Regardless
of the external supply of N during grain-filling, N and S absorbed prior
to silking will later comprise most of the N and S in the ear.
Sulfur absorbed by maize plants prior to silking was partitioned
more effectively into the ear than S absorbed after silking (49 vs.
23%). Although maize plants can absorb large quantities of S during
grain-filling, it is apparent that remobilization of S accumulated prior
to silking contributes more to ear development. Furthermore, the
remobilization of S is similar to N remobilization in that it occurs at
a constant rate that is not affected by N supply during grain-filling,
(Friedrich and Schrader, 1979)
Effects of S Deficiency
Sulfur affects not only the yield of crops, but in certain cases
the quality also. It is essential for the synthesis of methionine,
cystine, cysteine, and hence the elaboration of amino acids into a
high-quality protein. Methionine and cystine are indicators of protein
quality (Allaway and Thompson, 1966; Blair et al., 1980; Stewart and
Porter, 1969; Lancaster et al., 1971).


222
In general, nutrient concentration in plant tissue indicated that
growth was limited by nutrient deficiencies. Most nutrient concentration
declined with maturity, however, if growth was resumed by the plant,
nutrient concentration increased in the growing parts. Nitrogen
concentration and IVOMD were affected similarly by maturity. However, N
concentration in the ear increased with maturity. Very little P was
translocated from the leaf or stem to the head in the sorghums.
Potassium is lost from the plant soon after bloom. Cation imbalance
(K:Ca, K:Mg, and K:Ca+Mg) in plant tissue affected crop yields
adversely.
The S deficiency survey proved that S is a widespread problem in
the maize + sorghum growing areas of Nicaragua and in some areas in
Florida. The S study indicated that healthy plants were positively
correlated to higher cation exchange capacity and extractable bases.
Evidence indicated that stunted plants with intervenial chlorosis were
deficient in S and had a N:S and P:S imbalance. Sulfur deficiency
apparently caused maize leaves to be deficient in K and a K:Ca+Mg
imbalance, even though sufficient K was indicated by whole plant
analysis. Apparently K accumulated in the stems but was excluded from
the leaves as a result of S deficiency.


85
Figure 4-2. Water deficient periods. La Trompina, El
Salvador (CATIE, El Salvador, unpublished
data).


155
Days After Planting Maize
Figure 6-12. Effect of the stage of maturity on the N
concentration of 'NB-3' maize (a) and 'Gahi-3'
millet (b).


73
weekly basis to determine percent soil moisture on a volumetric basis.
Soil from each increment was placed in a previouly weighed can, then
weighed, oven dried at 105C for 24 hours, and weighed again. Assuming
constant weight, percent soil moisture was determined by difference.
Survey of Sulfur Deficiency in Maize
Experiment 1
Sixty day-old no-tillage maize was grown in a 65 ha field in
Alachua County, Florida. Plants showed various degrees of stunting and
ranged from dark green healthy plants to light green or yellowish
stunted plants. Plant height ranged from approximately 30 cm to 120 cm.
The stunted plants exhibited intervenal chlorosis, the degree of which
diminished as plant height increased. The hypothesis proposed stated
that the problem was likely associated with soil characteristics and the
solution could be obtained through soil-plant analysis.
A completely randomized experimental design was used that included
three replications of five maize treatments. Treatments included 30, 60,
75, 90, and 120 cm tall plants. Ten whole-plant samples were taken at
random for each replication, as well as the associated youngest mature
leaf. Soil samples were taken at several depths within 25 cm of the
treatment plants.
Plants and youngest mature leaves were washed in distilled water,
dried at 70C in a forced air oven, and ground in a Wiley mill to pass a
1 mm stainless steel screen. Soils were sampled in 15 cm increments to
45 cm, then later to 90 cm, air dried, ground by mortar and pestle, and
screened on a 2 mm stainless steel screen. Plant and soil samples were
analyzed as described in the section of laboratory procedures of this
chapter.


138
planting date. Maize leaves decreased with maturity; at thinning the
leaves were approximately 88 dag kg ^ OM, while at black layer the
leaves contained approximately 84 dag kg During the second period of
vegetative growth (Figs. 5-3a, 5-4a, and 5-5a) OM increased again to
nearly 88 dag kg Thirty days after grain harvest OM decreased to
levels near 84 dag kg (Figs. 6-la, 6-2a, and 6-3a).
Organic matter values for maize stems at thinning were
approximately 87 dag kg ^ and constantly increased to values of
approximately 96, 93, and 95 dag kg ^ for the M+PS, M+NS, and M+MI
systems, respectively. After bloom stem OM decreased to values below 90
dag kg 1 in the M+PS, and were constant in the other two systems (Figs.
6-la, 6-2a, and 6-3a). Ears and flowers followed opposite trends; ear OM
increased with maturity, while flower OM decreased.
The PS and NS followed a different trend than that observed in
maize. Organic matter values observed in sorghum were generally higher
than those observed in maize. Organic matter values in the leaves from
both sorghums increased with maturity. At bloom, OM values were
approximately 89 dag kg ^ for both sorghums (Figs. 6-lb and 6-2b). After
bloom OM in the leaf declined to approximately 84 dag kg Goldsworthy
(1970) postulated that sorghum stems are storage deposits for
photosynthates produced in the leaves; the results presented in Figs.
6-lb and 6-2b confirm this observation. In the PS sorghum OM increased
to a maximum 96 dag kg at soft-dough (Fig. 6-lb), from this stage to
harvest it maintained a constant OM value. In the NS sorghum the OM
increased to a maximum of 93 dag kg and from then on it declined
rapidly to approximately 88 dag kg ^, 30 days after grain harvest.
Organic matter in the head followed opposite patterns than those


67
covered with 3 to 5 cm of soil. The fertilizer treatments are described
in Table 3-1. No initial soil amendments were necessary.
Grain and stover were harvested from 8 m of the two central rows of
each plot. Grain moisture was measured with a Steinlite moisture meter
and yields calculated at 15.5% moisture content. The plant was separated
into components, and each part was then weighed. Dry matter yields were
calculated using subsamples dried to constant weight at 70C for 72
hours. All above ground plant material was removed from the plots,
separated into parts (leaf, stem, flower, ear, or head), and subsampled
for chemical analysis as described in the section of laboratory analysis
of this chapter.
One soil sample was collected from each plot prior to planting and
immediately after harvesting the last crop. All samples were air-dried,
sieved through a 2 mm stainless steel screen, and stored at ambient
temperatures until analyzed.
The following response variables were measured to determine the
effect of the fertilizer treatments on the systems under study: a) soil
pH (1:1) and extractable N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn
concentration at the beginning and end of the experiment, b) maize and
sorghum grain yield, c) Dry matter production of the different plant
parts, d) Concentration of N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn of the
different plant parts, e) combustible energy, f) percent organic matter,
and g) percent in vitro dry matter digestibility, (IVOMD). Statistical
analyses for these variables are presented in Tables 3-2, 3-3, 3-4, and
3-5.


124
the M+MI plots (756 kg ha ^day *). This compares well with the 500 kg
ha ^day ^ reported by Goldsworthy.
After ear harvest, leaves from the M+MI plots continued to gain
weight (90 kg ha ^day ^), but leaves from the M+NS and M+PS were losing
dry matter at rates of 296 and 47 kg ha ^day *, respectively (Figures
5-5a, 5-4a, and 5-3a, respectively). During this same period whole plants
were losing dry matter at rates of 157, 318, and 671 kg ha ^day ^,
respectively, for the M+PS, M+NS, and M+MI plots. Those plants with the
highest crop growth rates also had faster decreases.
Water stress during anthesis and grain fill reduced the size of the
maize ear sink considerably. Ears accumulated dry matter at similar rates
in all systems (129, 109, 153 kg ha ^day ^ for the M+PS, M+NS, and M+MI
plots, respectively (no differences were observed at the 0.05 level of
probability), as depicted in Figures 5-3a, 5-4a, and 5-5a. After
soft-dough, ears began to lose dry matter.
Sixty five days after planting (Table 5-2) more dry matter had
accumulated in the leaf than in the stem of maize (56 and 44%,
respectively). However, as flowers and ears began to develop, assimilates
moved out from the leaf into the ear. Barlow and Boersma (1976) reported
that in desiccated plants dry matter accumulation in the grain occurs at
the expense of dry matter stored in the leaves and stem. Once the effect
of water stress affected the size of the grain sink, assimilates began to
accumulate in the leaves and stem. McPherson and Boyer (1977) concluded
that translocation in maize was less inhibited than photosynthesis.
Conversely, Brevedan and Hodges (1973) reported that translocation was
more sensitive than photosynthesis. At harvest, approximately 63, 26, and
12% of the dry weight were distributed in the leaves, stem, and ears,


11
a plant's internal water balance, which directly affects the physiological
and biochemical process of plant growth.
Plant nutrition
Hanway (1962b) indicated that variations in light, moisture, and
many other factors cause fluctuations in the growth rate. The growth rate
of maize under N sufficient conditions was 250 kg ha day while the
growth rate for maize on the extremely N-deficient continuous maize plot
was much less (84 kg ha ^ day ^). The fertility differences did not
markedly alter the relative proportion of each plant part.
Goldsworthy and Colegrove (1974) found production of dry weight
after silking to be related to the amount and duration of leaf area after
silking and to the efficiency of the leaf area. The ratio of grain weight
to leaf-area duration per unit area of land after heading is an index of
the efficiency with which the leaf area present after heading produces dry
matter for the grain (Watson et al., 1963).
Hanway (1962a) observed that extreme N and K deficiencies result in
premature death of several lower leaves. This shortens the period over
which these leaves carry on photosynthesis. In any case, the primary
effect of nutrient deficiencies appears to be on the amount of leaves
produced rather than on the net assimilation rate (rate of increase of dry
weight per unit leaf area).
Data presented by Hanway (1962a) suggested that although N, P, and
K concentration of maize leaves at the beginning and end of the grain
formation period varied markedly, the chemical composition of the leaves
had very little effect upon the rate of photosynthesis in the leaves.
However, extreme N and K deficiencies were observed to result in premature
death of several lower leaves on some of these plants. Nutrient


97
reduced as days become shorter, a condition that favors the sorghum for
intensive growth (Fig. 4-9). When planted simultaneously before August,
there is strong competition between the crops since both have similar
growth patterns.
In their characterization of the maize + sorghum system Arias et
al. (1980) indicated that cropping activities begin early in the year
(Table 4-1) with slash and burning. After the first rains, maize is sown
and 10 days later fertilized with N and P; a second N application is
done between 25 and 30 days after planting. Amounts used vary from one
area to another and sorghum is seldom fertilized.
Weeding is one of the most time-consuming enterprises of the
system. A first weeding is done 15 to 21 days after seeding the maize;
the hilling up is also a weeding activity. The last weeding is done just
before the planting of sorghum and/or bending over of maize.
Maize is harvested between October and December; the complete ear
is removed from the field and hand-shelled near the house. Sorghum
panicles are cut at the base and carried from the field and spread to
facilitate final grain drying. Threshing is done by hand-beating the
panicles with a stick. Yields vary considerably from one area to
another (Table 4-1) depending on the duration and severity of the
"canicula", on the cultivar planted, on the soil type, and on the amount
of fertilizer applied.
Animal production systems
Patio management is primarily used for small animals. Usually
patio-farmers keep from two to eight pigs, from two to 12 hens. Only 2
to 3% of the farms raise turkeys and ducks (Guillen et al., 1978; Juarez
et al., 1979). According to DeLa Hoz (CATIE/Honduras, personal


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Mary fi^Collins
Collins
Assi^ant Professor, Soil Science
This dissertation was submitted to the Graduate Faculty of the College
of Agriculture and to the Graduate School and was accepted as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.
August 1985
^ 3as~/
liege of Agrigjilt
Dean,
ture
Dean, Graduate School


Organic Matter(dag kg
141
Days After Planting Maize
Figure 6-3. Effect of the stage of maturity on percent
organic matter of 'NB-3' maize (a) and
'Gahi-3' millet (b).


157
translocation from one plant part to another until after grain formation
began, and then N was translocated from the stem and leaves to the
grain. Translocation of N from the stem preceded that from the leaves.
Both sorghums and the millet followed a similar trend to that
observed in maize. Nitrogen concentration decreased with maturity (Figs.
6-10b, 6-llb, and 6-12b for the M+PS, M+NS, and N+MI systems,
respectively). Leaves and stems from the PS sorghum at bloom contained
approximately 1.4 and 0.48 dag kg ^, similar to the values observed for
maize. At the same stage of growth the NS sorghum leaves and stem
contained approximately 1.5 and 0.9 dag kg Head N concentration in
the NS sorghum decreased constantly to harvest. This may be attributed
to the dilution effect reported by Hanway (1962a). Millet (Fig. 6-12b)
exhibited N concentrations similar to those observed in the NS sorghum.
Lockman (1972a) reported that N concentrations of 1.57 dag kg in the
second leaf of grain sorghum at bloom may be considered deficient.
Phosphorus, K, Ca and Mg Accumulation
There were many similarities between the patterns of P distribution
in different maize plant parts as shown in Figs. 6-13a, 6-14a, and 6-15a
and those shown in Figs. 6-10a, 6-lla, and 6-12a for N. As with N, the
patterns for P did not vary markedly among systems. The amount of P in
the leaves and stems declined sharply between thinning and bloom and was
relatively constant from then until soft-dough, when concentration
increased again. Plank (1979) established the P sufficiency range in
maize ear leaf at bloom between 0.3 and 0.5 dag kg Values observed in
the leaves at bloom was 0.17, 0.20, and 0.18 dag kg ^ for the M+PS,
M+NS, and M+MI systems, respectively, which suggests a deficiency.


68
Table 3-2. Stastistical analysis model for maize data. Factorial (3x3)
for treatments 2, 5, 6, 7, 8, 9, 11, 12, and 13.
Source
df
Replications
3
(r-1)
Treatments
12
(T-l)
SPECIES EFFECT (2 sorghums + millet)
2
(E-l)
Treats (2, 5, 6, 7, 8) vs (11, 12, 13)
1
Treats (2, 5, 6) vs (7, 8, 9)
1
FERTILIZER RATES AND TIME OF APPLICATION EFFECT
2
Treats (2, 7, 11) vs (5, 6, 8, 9, 12, 13)
1
Treats (5, 8, 12) vs (6, 9, 13)
1
SPECIES X RATES-TIME
4
Treat 3 vs 4
1
Treats (1, 10) vs (3, 4)
1
Treat 1 vs 10
1
(LEFTOVER)*
1
ERROR
36
(r-1)
(t-l)
TOTAL
47
(RT-1)
* The degrees of freedom are not orthogonal.


45
Forms and Amount of S in the Soil
Tropical and temperate soils differ in both the total amount of S
and its form. Jordan and Reisenauer (1957) report average values of 540
and 210 rag kg ^ S for Mollisol and Alfisol surface soils from temperate
areas. Generally, the total S content of tropical soils is lower
because of their lower organic matter content, and adsorbed S is often
the major reserve of this element.
Sulfur is found in soils as a variable mixture of primary
minerals, sulfate ions in solution, adsorbed sulfate, ester sulfate, and
organic S compounds. Blair et al. (1980) summarized the differences
between the forms of S present in tropical and temperate soils.
Adsorbed S is generally higher in tropical soils, as in this state it
cannot be leached from the profile.
Neller (1959) showed that extractable sulfate-S increased with an
increase in the clay content in 14 Florida Ultisols. The subsurface
horizons contained considerably more sulfate-S than the surface
horizons. The increase in sulfate-S with horizon depth is associated
with S adsorption by Fe and Al hydroxides and oxyhydroxides and with an
increase in 1:1 clay minerals in the argillic horizons.
More recently Mitchell and Blue (1981) showed that most S in
Florida Spodosols and Entisols is associated with organic matter, and
sulfate-S accounted for less than 7% of the total soil S in the entire
profile of selected Florida Spodosols. Sulfate-S accounted for
approximately 15% of the total S in the C horizons of Florida Entisols,
and 44% of the total S in the B2t horizons of 10 Utisols. Extractable S
in the surface (A^ or A^) horizon (0-14 cm) ranged from 1 rag kg ^ in a
Myakka fine sand (Aerie Haplaquod) from Alachua County to 8 mg kg ^ in a


189
composition of plants fail to determine the S content. Tisdale and
Nelson (1964) found that S is required by many plants in about the same
amount as is P. Friedrich and Schrader (1978) and Rabufetti and
Kamprath (1977) found evidence suggesting a NxS fertilizer interaction
for S concentration in the grain.
The critical concentration of S in young maize plants has been
reported to be about 0.20 dag kg ^ (Fox et al., 1964; Stewart and
Porter, 1969; Jones and Eck, 1973; Terman et al., 1973). Mitchell and
Gallaher (1979) in their study of S fertilization of maize seedlings
found that 55-day old maize leaves contained from 0.18 to 0.25 dag kg ^
in the control compared to those plots fertilized with 10 kg CaSO^.2H^0
ha *. At harvest both treatments had 0.11 dag kg ^ S in the grain. Blue
et al. (1981) reported lower values (from .06 to 0.12 dag kg ^) for
35-day old maize herbage.
Dijkshoorn et al. (1960) concluded that the N:S concentration ratio
among species range from 14:1 to 17:1 for legumes. Gaines and Phatak
(1982) found that low S-accumulating crops; maize, soybean (Glycine max
(L. ) Merr.), and cowpea (Vigna Unguiculata (L.) Walp.); had higher and
constant protein N:S ratios than high S-accumulating crops; tomato
Lycopersicon esculentum (L.) Mil 1.), cotton (Gossypium hirsutum L.), and
okra (Abelmoschus esculentum (L.) Moench). This indicates that high
S-accumulating crops have a greater proportion of S-containing proteins
and need a higher S:N ratio than low S-accumulating crops. When S was
sufficient the ratio of protein N to S was 15 to 16 for maize, 20 for
soybean, 15 for cowpea, 12 for tomato, and 8 and 9 for cotton and okra,
respectively.


100
communication, 1983) the main characteristics of the typical animal
production systems interacting with maize + sorghum in the Central
American Pacific coast are as follows:
SYSTEM MAIN CHARACTERISTICS PRODUCTS
Cattle Pasturing, dual-purpose milk, cash, meat,
and butter
Swine Free and confined during cash, meat, lard
the wet season
goultry Free ranging eggs, cash, and
meat
Lar ios et al. (1983) stated that feeding of the animal is a primary
activity, consisting of obtaining and supplying crop residues. Other
activities include egg collection, processing and sale of dairy
products, and animals. Less frequent activities include the sale of
eggs, pigs, and poultry. Table 4-2 details such activities during the
course of the year, and Table 4-3 shows the input and outputs of a
typical farm with 10 ha of pasture.
Animal production systems also require a few specialized family
activities (Tables 4-2 and 4-3). The wife and children are usually in
charge of feeding the pigs and chickens; the children can also milk the
cows and move them from one pasture to another or tend them along
roadsides.
Farm animals consume almost all of the crop byproducts; the root
system is the only component that is not used. This finding, plus other
evidence shown in the following section, proves the high degree of
adjustment of the system to its physical and socio-economic environment.


CHAPTER 1
INTRODUCTION
Historically, increases in production have been brought forth by
increasing the amount of land under cultivation or by increasing unit
yields of existing hectares through improved technology. These
constitute what Sanchez (1976) has called the area and space dimensions,
respectively. Except where limited by soil moisture supply or altitude,
the growing season in tropical latitudes is infinite and multiple
cropping systems have been used for centuries. Most low-income farmers
in the tropics practice cropping systems (i.e. intercropping, relay
and/or sequential cropping) that intensify production not only in space
but also in time.
Intercropping has been an important practice in many parts of the
world, especially in the tropics, and there is little doubt that it will
remain so. It is only recently, however, that research has established
that intercropping can give higher yields than growing sole crops.
Wahua and Miller (1978a) explain why intercropping is popular among
small-scale farmers in tropical and sub-tropical environments. Some of
these reasons are built-in balanced nutritional supply of energy and
protein, profit and resource maximization, efficient water and light
utilization, inexpensive weed control, minimization of agricultural
risks, and improvement of soil fertility. Other authors (Mead and
Willey, 1980) consider that low-income farmers need to grow more than
one crop, whether intercropped or not, to spread labor peaks, to reduce
1


18
plants. He also observed that except under very carefully controlled
conditions in fields or in experimental plots there will be differences in
growth between different plants that have received the same treatment.
The number of leaves per plant on plants of the same hybrid grown in the
same plot varied between 15 and 22 leaves per plant. All plants in a
given plot will develop at the same rate, so not all plants in a plot are
at the same stage of development at the same time (Hanway, 1963).
Hanway (1962a) suggested that the dry weight of the entire plant
and of the grain are directly related to and highly correlated with the
weights of the leaves in these plants. Since leaf growth in maize is
completed relatively early in the season, the linear rate of dry matter
accumulation over a major part of the growing season appears reasonable,
unless the net assimilation rate decreases with age of the leaves or
decreases with the seasonal trend in climatic conditions.
Hanway's (1962a) study of maize growth as related to soil fertility
showed that approximately 30% of the total leaf weight had been produced
45 days after planting and that during the following two weeks leaf growth
was very rapid and by 60 days after planting over 85% of the final leaf
weight had been produced. This would appear to be a critical stage in
leaf development when nutrient deficiencies might reduce the final weight
of leaves. Most of the grain was produced in a 30 to 35 day period. This
growth pattern was similar for plants from all the fertility levels except
that the silking and subsequent growth of the cob, shank, and grain was
delayed slightly in the N-deficient plants from the continuous maize plot.
Shih et al. (1981) reported that leaf area per stalk declined after
stalk length reached about 185 cm. This is consistent with the general


226
Clara, R., R. Cordova, and H. Amaya. 1983. Formacin de variedades de
sorgo adaptables al asocio con raaiz. _In Procs. The plant breeding
methods and approaches in sorghum. Workshop for Latin America.
INTSORMIL/INIA/ICRISAT, El Batan, Mexico, pp. 244-255.
Clark, N. A., R. W. Hemken, and J. H. Vandersall. 1965. A comparison of
pearl millet, sudangrass, and sorghum-sudangrass hybrids as pasture for
lactating dairy cows. Agron. J. 57:266-269.
Classen, M. M., and R. H. Shaw. 1970. Water deficit effects on corn. II.
Grain components. Agron. J. 62:652-655.
Coleman, R. 1966. The importance of sulfur as a plant nutrient in world
crop production. Soil Sci. 101:230-239.
Colenbrander, V. F., L. D. Muller, J. A. Wasson, and M. D. Cunningham.
1971. Corn stover silage supplemented with varying increments of energy
for growing dairy heifers. J. Anim. Sci. 33:1306-1309.
Croka, D. C., and D. G. Wagner. 1975a. Micronized sorghum grain. II.
Influence on in vitro digestibility, in vitro gas production, and
gelatinization. J. Anim. Sci. 40:931-935.
Croka, D. C., and D. G. Wagner. 1975b. Micronized sorghum grain. III.
Energetic efficiency for feedlot cattle. J. Anim. Sci. 40:936-939.
Cummins, D. G. 1970. Quality and yield of corn plants and component
parts when harvested for silage at different maturity stages. Agron. J.
62:781-784.
Dale, R. F., D. T. Coelho, and K. P. Gallo. 1980. Prediction of daily
green leaf area index for corn. Agron. J. 72:999-1005.
Daynard, T. B., and W. G. Duncan. 1969. The black layer and grain
maturity in corn. Crop Sci. 9:473-476.
Daynard, T. B., J. W. Tanner, and D. J. Hume. 1969. Contribution of
stalk soluble carbohydrates to grain yield in corn (Zea mays L.). Crop
Sci. 9:831-834.
Denmead, 0. T., and R. H. Shaw. I960. The effects of soil moisture
stress at different stages of growth on the development and yield of
corn. Agron. J. 52:272-274.
De Wit, C. T., R. Brouwer, and F. W. Penning de Vries. 1970. The
simulation of photosynthetic systems. Tn Setlik (ed.) Prediction and
measurement of photosynthetic productivity. Pudoc, Wageningen,
Netherlands.
De Wit, C. T., W. Dijkshoorn, and J. C. Noggle. 1963. Ionic balance and
growth of plants. Versl. Landbouwkd. Onderz. 69:1-68.
De Wit, J. M. and J. R. Hollman. 1970. The origin and domestication of
sorghum bicolor. Economic Bot. 128-135.


Table 7-1.
Phenotypic characteristics
of maize plants
5 .
Plant
Height
Plants
Leaf
Deficiency
symtoms
Veins
Intervenial
Leaf
Mineral
cm
30
Uniformly
Green
Yellow
Chlorosis
in
older
K
Yellow
60
Uniformly
Green
Light Yellow
Chlorosis
in
older
K
Light Yellow
75
Uniformly
Green
Light Yellow
Chlorosis
in
older
N/A
Light Yellow
90
Green
Green
Green
Normal
N/A
120
Dark Green
Green
Green
Normal
N/A
N/A = None was apparent.


177
Days Afler Planting Maize
Figure 6-27. Effect of the stage of maturity on
the Fe concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).


40
Gallaher et al. (1975) defined the critical elemental K
concentrations in maize tissue at two sampling dates as the point at
which yields no longer give a statistically significant increase from
further applications of fertilizer K. Concentrations of K above those
critical levels would be in the luxury consumption category because
yields were not significantly increased beyond those concentrations.
Beyond those critical levels K might, in some instances, induce Ca or Mg
deficiencies because of the interaction among cations. Therefore the
critical levels of Ca and Mg are defined as being at the same point
where the critical level of K occurred. The optimum balance of the 3
cations should occur at the critical concentration for K.
Gallaher et al. (1975) reported critical mmol (m2 + ) of young maize
2+ -1
plants taken 38 days after planting to be 91 to 78 mmol(M ) K kg ,31
to 28 mmol(M^+) Ca kg and 40 to 39 mmol(M^+) Mg kg The dilution or
age effect is evident from the critical levels of K at the thinning
stage compared to the ear leaf at the silking stage of growth. The
2 +
critical mmol(M ) in the ear leaf 86 days after planting was 44 to 40
mmo1(M^+) K kg \ 34 to 30 mmol(M^+) Ca kg *, and 22 to 16 mmol(M^+) Mg
-1 2+ -1
kg The critical 44 to 40 mmol(M ) K kg in the ear leaf at the
silking stage of growth was in agreement with the critical percent of
1.75 for maize ear leaf tissue at the silking stage in the midwestern
United States.
Jacques et al. (1975) found Ca concentrations were much lower in
heads than in other plant parts both years and in the first year were
lower in grain than in threshed head parts. Calcium concentrations in
blades increased after maximum blade weight was reached. During grain
development Ca concentrations were higher in blades than in unformed


50
Schrader (1978) indicated that maize seedlings are not S-deficient
unless the concentration of S (dry weight basis) in the shoots is
approximately 0.10 dag kg 1 or less. Blue et al. (1981), found that
maize plants without S fertilization were chlorotic and oven-dry herbage
contained only 0.10 dag kg 1 total S; herbage from treatments with S
applied at 15 and 30 mg kg 1 contained 0.19 and 0.23 dag kg 1,
respectively. Oven-dry herbage yields were increased from 6.6 to 9.4 g
pot ^ by the addition of 15 mg kg 1 of S, and there was no additional
yield increase from the 30 mg kg 1 S treatment. Mitchell and Gallaher
(1979) reported that seven harvested crops in a maize/grain system and
the maize forage system removed an estimated 48 and 63 kg ha 1 S,
respectively, during 2 years.
Fox et al (1977) have shown that the critical level of S in cowpea
varies between cultivars. In their solution culture experiment, the
critical value varied between 0.032 dag kg 1 total S in cultivar 'Sitao
Pole' and 0.064 dag kg1 in 'TVU76-2E'.
Published data for rice (Blair et al., 1979) show grain S contents
varying from 0.134 dag kg 1 under deficiency conditions up to 0.16 dag
kg 1 in a non-responsive situation. Rice grain yields may vary from 750
kg ha up to 8,000 kg ha 1 which gives a S removal varying from 0.26 up
to 12.8 kg ha Rice straw may contain similar amounts of S.
Absorption and Accumulation of S
Coleman (1966) reported that in addition to the S they receive
from precipitation, plants and soils absorb sulfite and perhaps other
sulfurous gases directly from the atmosphere. It has been known for
many years that sulfite is absorbed directly by plant leaves. Work by
Olson (1957) showed that plants supplied with adequate sulfate in


PRODUCTION ASPECTS OF MAIZE + SORGHUM INTERCROPPING SYSTEMS
IN CENTRAL AMERICA
BY
FRANCISCO ROBERTO ARIAS MILLA
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1985


41
heads. Calcium utilized in calcium pectate formation in mature leaf
cells may have been responsible for the increased concentrations in
blades and culms. A greater percentage of the total Ca taken up in the
hybrids was accumulated in their blades than in the other plant parts.
Hanway (1962a) found that in maize, N accumulated in each plant
part as that part grew. He also observed that there was little
translocation from one plant part to another until after grain formation
began, and then N was translocated from all other plant parts to the
grain. Translocation of N from the cob, husk, and stalk appears to
precede that from the leaves. The leaves contained approximately 30% of
the N accumulated by the plant even though they constituted only about
13% of the final dry matter accumulation. At maturity the grain
contained approximately 66% of the total N in the plant. About 50% of
the N in the grain at maturity appeared to be N that had been lost
through translocation from other above-ground plant parts.
Jordan et al. (1950) observed a somewhat different pattern of N
uptake. In their study N fertilizer was side-dressed when the plants
were knee-high and the maximum rate of N absorption occurred immediately
following the application of N fertilizer. The pattern of N
accumulation by plants is undoubtedly influenced by the seasonal pattern
of N availability in the soil. K accumulation in this study continued
until a later stage of maturity and there was no loss of K from the
plants during the latter part of the season.
Hanway (1962a) suggested that continued mineral accumulation by
the plants later in the season is essential to prevent excessive loss
through translocation of N and K from the leaves which would result in
premature death of some of the leaves. Some loss of nutrients from the


Table
7-12. Leaf
content of
S and N
, concentration
of S
and N, and
the N:S
concentration
ratio.
Sice
S concent
N concent
S Concentration
N Concentration
N: S
D
su
D
su
D
su
D
su
D
SU
-
1
g
18
0.026a
0.034ab
0.40abcd
0.649abcd
0.296ab
0.27abcd
2.08a
2.32a
7.0
8.6
10
0.024ab
0.032abc *
0.63ab
1.090a
0.167
ef
0.17 e
0.74 g
1.06 f
4.4
6.2
14
0.023abc
0.031abcd
0.21 cd
0.492abcd
0.210
edef
0.28abc *
1.68abcd *
2.24ab *
8.0
8.0
16
0.022abc
0.039a *
0.41 abed
0.668abcd
0.265abcd
0.30a
2.03a
2.29ab
7.7
7.6
12
0.021abc
0.031abcd
0.78a
0.992ab
0.170
ef
0.21 de
0.73 g
1.42 def
4.3
6.8
17
0.021abc
0.035ab *
0.49abc
0.971abc
0.225
ede
0.26 bed
1.74abc
2.21 b
7.7
7.6
1
0.020abcd
0.034ab *
0.19 cd
0.345 cd
0.220
ede
0.29 b
1.40 edef
2.07 be
6.4
7.1
3
0.020abcd
0.024abcde
0.17 cd
0.102 d
0.217
edef
0.22 de
1.28 def
1.43 def
5.9
6.5
9
0.019abcd
0.030abcd
0.67ab
0.286 d
0.198
de f
0.23 bede
1.24 def
1.34 ef
5.4
5.8
11
0.017 bed
0.036ab *
0.35 bed
0.932abc
0.146
f
0.18 e*
1.00 fg 1.27 f
6.8
7.1
15
0.016 bed
0.036ab *
0.39abcd
0.951abc *
0.228
ede
0.29 b
1.53 bede*
2.25 b *
6.7
7.8
7
0.016 cd
0.014 e
0.17 cd
0.146 d
0.175
ef
0.21 de
1.17 ef
1.31 ef
6.7
6.2
13
0.015 cd
0.031abcd *
0.39abcd
0.476abcd
0.248
bed
0.22 ede
1.85ab
1.75 ede
7.5
8.0
2
0.013 de
0.033abc *
0.12 cd
0.226 d*
0.213
edef
0.29 b
1.46 bede
2. lOabc
6.9
7.2
5
0.008 e
0.024abcde*
0.12 cd
0.368 bed
0.27 7abc
0.29
1.45 bede*
2lOabc*
5.2
7.2
4
0.008 e
0.021 bede*
0.06 d
0,647abcd*
0.195
def
0.29 b *
1.54 bede
1.83 bed
7.9
6.3
6
0.007 e
0.019 ede
0.13 cd
0.243 d
0.175
ef
0.28ab *
1.20 ef*
1.74 ede*
6.9
6.2
8
0.007 e
0.017 de *
0.10 cd
0.669abcd*
0.319a
0.31a
2.08a
2.23ab
6.5
7.2
Values in columns noc followed by che same letter and rows within subheadings followed by an asterisk are different at the 0.05 level
of probability according to Duncan's new multiple range test and F test, respectively.
211


210
from the top 30 cm of soil. The rains probably leached the S from this
top layer and sorghum and maize stover removed from the field
continually mine the soil. In the area of study, burning plant material
is a popular practice. Therefore as pointed out by Bromfield (1974),
this may be a cause for the low S status of these soils. Fritts (1970)
reported that S deficiency occurs in soils derived from volcanic parent
material. In such soils, which are common in the area under study, the
organic matter is closely associated with allophane and mineralization
of the allophane-bound organic matter. Thus, the release of sulfate is
very low.
Plants with the largest leaves (Table 7-10) had larger S
concentration (Table 7-12). Leaves from SU-plants had consistently
higher S content than those from D-plants. Differences between
treatments (p=0.05) were observed in 11 of the 18 sites. Differences
among sites for both the D and SU-plants for S content were detected at
the 0.05 level. Leaf S content values for D-plants observed in sites 8,
6, 4, and 5 (0.007, 0.007, 0.008, and 0.008 g, respectively) were
considerably lower than the values observed at other sites.
Leaf N content was significantly different (p=0.05) among sites for
both D and SU plants. Differences between treatments were observed in
sites 15, 2, 4, and 8. A trend was observed for leaves from SU-plants to
have higher N content than D-plants. Values for N content in the leaves
from SU plants ranged from .102 to 1.09 g in sites 3 and 10,
respectively.
The trend observed for S concentration in the leaf was similar to
that observed for N content (Table 7-12). Only in sites 18 and 13 did
the leaf S concentration in D-plants surpass that reported for


42
leaves to the grain does not appear to be detrimental to the yield of
grain so long as this does not result in premature death of the leaves.
Jacques et al. (1975), comparing two sorghum hybrids, found that
Mg concentrations were lower in heads than in other plant parts.
Magnesium was evenly distributed in blades and sheaths of each hybrid.
For the two hybrids Mg accumulation in blades, sheaths, and culms was
similar to that of dry matter production. Both dry matter production
and evidence of translocation of Mg out of stems into the heads during
grain development was indicated, because the percentage of Mg decreased
in the stems and increased in the developing grain.
Jacques et al. (1975), studying nutrient uptake by different
sorghum hybrids, found that little difference between hybrids in Zn and
Cu uptakes occurred each year, but differences existed between hybrids
in Mn uptake. Stem tissue was initially high in Fe content but
decreased during both hybrids' vegetative growth. Concentrations in
head tissue and in head parts and grain were generally below 75 mg kg ^
and relatively constant throughout the growing seasons, especially in
culm tissue. Differences were small among plant parts after vegetative
growth ceased, and concentrations in plant parts remained relatively
constant during grain development. Some translocation of Zn from
vegetative plant parts into the developing grain was suggested by a
decrease in Zn content in some cases, but for the most part Zn seemed to
be relatively immobile.


31
increased from 21.5 to 33.1%. The energy loss for maize ensiled at
33.1% moisture was greater (p=0.05) than that for maize ensiled at 21.5%
moisture. Energy loss was not significantly influenced by kernel
preparation (3.0 and 2.5% energy loss for whole kernel and rolled maize)
or by time of ensiling (2.9 and 2.6% energy loss for maize ensiled at
harvest and maize ensiled after drying and reconstitution).
Nutrition
Critical Levels
According to Bates (1970) the diagnosis of nutrient deficiencies
and the prediction of fertilizer requirements from plant analysis are
based on a critical concentration of a nutrient or nutrient fraction
within the plant or some plant part, below which growth or crop yield is
restricted.
In early studies by Macy (1936) the nutrient calibration curve
included the zones of minimum percentage, poverty adjustment, and luxury
consumption. He proposed a central concept stating that there is a
critical percentage of each nutrient in each kind of plant above which
there is luxury consumption and below which there is a poverty adjust
ment which is almost proportional to the deficiency until a minimum
percentage is reached.
Ulrich (1952) defined critical nutrient concentration with respect
to plant growth in terms of 1) that which is just deficient for maximum
growth, 2) that which is just adequate for maximum growth, and 3) that
which separates the deficiency from the adequacy zones.


23
these and of other experiments at Samaru suggest that the main reason for
the difference in yield between the photosensitive sorghum and
non-photosensitive sorghum is in the number of spikelets present at head
emergence; the number and/or potential size of the developing grains in
the photosensitive sorghum appears to be too small. Thus the dry weight
of the non-photosensitive sorghum 1NK 300' was much smaller than that of
the other sorghums mainly because of the inability of the head to accept
all the carbohydrate that the leaves can produce.
Goldsworthy (1970) observed that the heads of non-photosensitive
sorghum continued to gain weight 13 weeks before harvest, but those of
photosensitive sorghum did not and it is more probable that the loss in
weight from the stem was by respiration of labile carbohydrate that had
accumulated there. It may be that the developing head does not receive
the assimilate it needs before emergence and that it is unable to
accommodate all of the increased supply of assimilate from the leaves
after it emerges .
Blum (1970) concluded that when sorghum plants compete for water
the effect of competition on a photosensitive genotype is more severe
than on a non-photosensitive genotype, and that the highest yield is
obtained with an early maturing hybrid planted at relatively high plant
densities. Yielding potential was in direct relationship to duration of
growth under non-competitive conditions and in an inverse relationship
under extreme competition. This indicates that the importance ascribed to
a long duration of growth of cereals with respect to their yield
potentials does not hold under limited water supply. Blum (1970)
concluded that of his experiments demonstrated the superiority of an


172
40 00 120 160 200
Days After Planting Maize
Days After Planting Maize
Figure 6-24. Effect of the stage of maturity on
the Mg concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).


122
not significant at the first sampling stage (thinning). However, a general
trend observed was that maize plants growing intercropped with 'Gahi-3'
(M+MI) generally produced higher dry matter yield than maize intercropped
with the photosensitive sorghum 'Criollo' (M+PS) or the non-photosensitive
'Pioneer 895' (M+NS). Maize plants from the M+PS and M+MI yielded higher
stem dry weight at bloom than those plants from the M+NS, at the 0.05
level of probability. No differences were observed between M+PS and M+MI.
Flower DMA was consistently higher in maize plants from the M+MI than
those from the other systems at p=0.05. No differences among systems were
detected for DMA in the leaf or ear at p=0.05.
Anthesis occurred 65 days after planting. Maize flowers gained weight
at rates of 55, 53, and 49 kg ha ^day ^, for M+MI, M+PS and M+NS,
respectively (Table 5-2). Thereafter, maize flowers decreased in weight at
low rates (6, 2, and 2 kg ha *day ^), for the M+PS, M+NS, and M+MI,
respectively.
Maize stem dry weight increased at a rate of 216, 209 and 181 kg
ha ^day ^for the M+PS, M+MI, and M+NS, respectively. At harvest, maize
plants from the M+MI system had accumulated more dry matter (38.5 Mg ha ^)
than maize in M+PS and M+NS systems.
Midseason losses of dry matter have been reported by Classen and Shaw
(1970) and Goldsworthy and Colegrove (1974). Results presented in Figures
5-3, 5-4, and 5-5 support these findings. The intense rains during the
second week of September triggered a second growth period for maize
(Figures 5-3a, 5-4a, and 5-5a). Since the drought had drastically reduced
the ear sink, dry matter accumulation occurred in the stem and leaves.
This ability to recover from water stress has been defined as tolerance to
drought. The highest crop growth rate was observed in maize plants from


Cu (mg kg ) Cu (mg kg~
179
40 80 120 160 200
Dnys After Planting Maize
Days After Planting Moize
Figure 6-29
Effect of the stage of maturity on
the concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).


CHAPTER 2
LITERATURE REVIEW
Growth
Crop Growth Rate
Goldsworthy and Colegrove (1974) found that crop growth rates (CGR)
in maize (Zea mays L.) declined rapidly when grain growth commenced. As
grain growth increased towards a maximum, about 100-110 days after sowing,
CGR decreased to near zero values. There are two possible explanations
for this pattern of change in dry weight. First, it is possible that a
large part of grain dry matter is derived from assimilates which
accumulate in plant parts other than grain and are then translocated to
the grain. Second, if as reported by Allison and Watson (1966) and by
Palmer et al. (1973) the dry matter that fills the grain is derived from
current assimilation, then presumably the large loss in weight from other
parts of the plant, mainly the stem, represents respiration losses that
are not replaced by current assimilation.
The rates of dry-weight production (500 kg ha *week *) per unit leaf
area reported by Goldsworthy and Colegrove (1974) were high at silking.
This, combined with the large leaf areas, accounted for the peak growth
rates observed. The rapid decline in CGR after silking was related to the
simultaneous and rapid decline in leaf area and net assimilation rate.
7


110
and begins to senesce (Salisbury and Ross, 1978). Crop growth rate (CGR)
is defined as dry matter accumulated per unit of land area per unit of
time. The mean CGR over a time period t^ to t^ is given by
CGR=W2~w^/t2~t^, where w^ and w^ designate the dry matter accumulated at
periods 1 and 2, respectively.
Sivakumar et al. (1979) suggested that plant growth is a result of an
effective integration of many factors. Hanway (1962a) found that
differences in soil fertility resulted in different rates of DMA, but the
relative proportion of the different parts was maintained. Goldsworthy and
Colegrove (1974) found production of dry matter to be related to the
amount and duration of leaf area after silking and to the efficiency of
the leaf area. Hsiao (1973) summarized the observed plant responses to
water stress, which include reductions in transpiration rates, CO^
assimilation rate, plant water potential, growth rate, and stomatal
aperture.
Shih et al. (1981) reported that LAI is often used as an indicator of
plant growth and for evaluating assimilation and transpiration rates in
plant physiological studies. Ashley et al. (1965) found good correlation
between LAI and leaf dry weight of cotton (Gossypium hirsutum L.). Hanway
(1962a) suggested that dry weight of the entire maize plant and of the
grain are directly related to and highly correlated to the weights of the
leaves in these plants.
The patterns of growth and dry matter distribution observed in
tropical maize (Goldsworthy and Colegrove, 1974) suggested that the
capacity of grain sink to accomodate assimilate can limit grain
production. McPherson and Boyer (1977) pointed out that another
potentially serious problem occurs if sink size has been affected by low


Ill
leaf water potential. Moss (1962) and Allison and Watson (1966) have shown
that when maize grain sink is missing, dry matter that would have passed
to the grain accumulates in the stem and husk.
Objectives
A series of experiments was conducted in Esteli, Nicaragua during
1982. The principal objectives of these studies were a) to describe the
DMA pattern of the maize + sorghum system and of potential substitutes; b)
to determine if variation of other components of the system, such as
substituting the traditional photosensitive sorghum with
non-photosensitive cultivars or with millet, will increase productivity of
the system; and c) to study the relation between gravimetric soil moisture
and DMA by the systems under study.
Materials and Methods
This experiment involving three intercropping systems (Fig. 5-1) was
conducted in Esteli, Nicaragua (Fig. 3-2) during the 1982-1983 growing
season. The experimental site (Centro Experimental de Esteli) was located
1 km north of the city of Esteli on the Panamerican Highway at an
elevation of 975 m. The average annual precipitation is 1,000 mm
distributed in a bimodal pattern (CATIE, 1981a); the largest amounts fall
during May, June, August, and September (CATIE 1980, 1981). This rainfall
pattern is the determining factor in defining the growing season. The
average annual temperature is 19C. The classification for the soil at
the experimental site was not available but it may be classified as a
Vertisol (CATIE, 1981). Further classification has not been determined.
The experimental field was previously planted to shade tobacco (Nicotiana
tabacum L.), but had been under fallow for the last 7 years.


16
Assimilation after ear emergence, both in the leaves and in the ear
itself, is primarly responsible for accumulation of material in the grain.
Early stress, then, has an indirect effect on yield of grain through
reducing the size of the assimilatory surface at the time of ear
development. Stress imposed after the ear has emerged has a more direct
effect through reducing assimilation in this critical period when daily
assimilation rates are high and most of the assimilates are being used for
grain production. The relatively small effect of stress during the ear
stage suggests that the critical period would not extend longer than about
3 weeks after 75% silking.
Jurgens et al. (1978) found that the induction of low leaf water
potentials in desiccated plants caused an almost immediate decrease in
viable LAI. At maturity it was evident that the prolonged drought
treatment had markedly affected grain components. Yield, kernel weight,
and percent oil were all substantially reduced by desiccation while
percent protein increased. Grain production was relatively closely tied
to the total dry matter production for the season. In the controls grain
production was 51% the total dry matter production, and in desiccated
plants it was 39%. The desiccated plants produced less dry matter and
exhibited a slower gain in grain dry weight than the controls.
Reddy and Willey (1981) reported that the total water use
(i.e.transpiration plus evaporation from the soil surface) by sole millet
and sole groundnut over their full growing periods were 30.3 and 36.8 cm,
respectively. The total water use of 40.6 cm by the intercrop was greater
than either sole crop but it was 11% less than the total water use
expected if each component had used water at its sole crop efficiency.
Thus, the 28% higher dry matter yield of the intercrop could only be


FREQUENCY
AREA OF THE SYSTEM
88
0 800 1200 1600 2000 2400 Annual ralnfall,mm
0 500 1000 1500 2000 Altitudes
0 10 20 40 I
Soil depth cm
Figure 4-3. Environmental profile of the maize sorghum system
in three countries of Central America (El Salvador,
Nicaragua, Honduras) (Larios et al., 1983).


200
treatment. In all cases 120-cm plants were growing in better nutrient
availability conditions than the deficient plant treatments (Table 7-4).
This explains in part differences observed in plant characteristics
(height, leaf length, width and weight) observed among treatments. Roots
of tall plants (120 cm) found higher nutrient concentrations at
shallower depths which caused higher growth rate than those of other
treatments. These findings agree with those reported by Rabuffetti and
Kamprath (1977)and Mitchell and Blue (1981a, 1981b).
Plant and leaf S concentrations (Table 7-5) in relation to plant
height were different among treatments (p=0.05). Whole plant S
concentrations varied from 0.09 to 0.14 dag kg in the 30 and 120-cm
treatments, respectively. Mitchell and Blue (1981a) reported similar
values for maize in different soils in Florida. Leaf S concentration was
generally higher than that of the whole plant. Taller plants (120 cm)
had higher (p=0.05) S concentrations than the other treatments.
According to Plank (1979) S sufficiency range for maize ear-leaf is from
0.15 to 0.50 dag kg This indicates that only those leaves from the
120-cm treatment (0.21 dag kg ^) were within the sufficiency of S level.
Those plants with the highest leaf-S concentration were those with the
highest values for the different phenotypic characteristics and dry
matter accumulation (Tables 7-2 and 7-3, respectively). Therefore, these
results indicate that low S concentration is limiting growth of the
deficient S-plants.
Soil-S concentration in relation to plant height is presented in
Table 7-6. A comparison of S concentration at three soil depths (0-15,
15-30, and 30-45) detected differences (p=0.05) for the 60, 75 and
120-cm treatments. In general, as soil depth increased S concentration


12
deficiencies are reflected in both leaf area and the chemical composition
of the leaves. The chemical composition of the leaves at silking time can
indicate which nutrient elements are deficient and which deficiencies have
resulted or will result in a reduced leaf area and, thereby, a reduction
in grain yield. These leaf analyses are very valuable diagnostic tools,
but it appears that their interpretation should be based upon their
relation to leaf area and not to net assimilation rate.
According to Nelson (1956) many investigators have found high
positive correlation between the percentages of N, P, and K in maize
leaves at silking time and the yield of grain. Nutrient deficiencies are
reflected in both leaf area and in the chemical composition of the leaves.
Thus, while grain yield is primarily a function of leaf area, leaf area
is a function of the nutrient status of the plant which is reflected in
the chemical composition of the leaves.
Maize under low fertility generally silks later and forms the
black layer earlier, resulting in rather large differences in filling days
and filling degree-days. Peaslee et al. (1971) found that P may tend to
shorten the grain filling period by accelerating the development of the
grain to the maturity stage. This tendency was apparently counteracted by
the tendency of P to also accelerate development to the grain initiation
stage. Earlier silking and lower moisture contents of the grain at
harvest were associated with additions of P fertilizer. However, these
were cases in which the levels of P in the soil were low and plant growth
response to P was marked. Peaslee et al. (1971) concluded that either P
or K was directly responsible for early initiation of the ear and/or delay
of the black layer formation by some specific function or they indirectly


126
Table 5-3. Crop growth rate of 'Criollo', 'Pioneer 895',
and 'Gahi-3' intercropped with maize.
Days
Whole
plant
Stem
Leaf
Head
-1
-1
rcg na
aay
Criollo
0-24
7
24-45
38
20
27
46-81
94
43
24
26
82-101
108
92
-10
26
102-162
134
48
68
18
163-193
-252
-141
-285
Pioneer 895
0-24
14
25-45
29
22
23
46-52
57
260
136
175
52-69
-37
0
105
11
69-101
341
50
57
234
101-136
-383
-32
-52
Gahi-3
0-24
7
25-45
135
55
43
29
46-85
25
10
3
10


10
and Boyer (1977) concluded that since grain yield was in excess of the
photosynthesis occurring during grain development, yield must have
reflected the amount of photosynthate accumulated by the crop over a
larger portion of the growing season than the grain filling period alone.
This is generally interpreted to mean (Yoshida, 1972) that dry matter
accumulated by the shoots determines yield.
Factors That Affect Growth
Environmental factors
Maize plants, wherever they are grown, should progress through all
the stages of development described by Hanway (1963). However, the
length of time between the stages and the identifying characteristics may
differ for different hybrids and for different environmental conditions.
Shaw and Thorne (1951) reported that the elapsed time between plant
emergence, stage 0, and silking, stage 5, is variable, and Tyner (1946)
reported that the period from silking to physiological maturity appears to
be relatively constant for different hybrids and different environmental
conditions. The intervals between the intermediate stages of growth
differ for different hybrids and with differences in environmental
conditions, especially temperature and fertilization (Hanway, 1963).
Sivakumar et al. (1979) suggested that plant growth is the result
of an effective integration of many factors. Restriction of growth may
occur due to the limitation of any one factor; for example, water deficits
in plants generally lead to reduced leaf water potentials and stomatal
closure, as manifested from an increased leaf resistance to transpiration.
The effects of depletion and replenishment of soil water on transpiration
are of specific importance to water use and its efficiency in crop
production. The relative rates of absorption and transpiration determine


25
sorghum x sudangrass (Sorghum sudanense L. ) hybrid when utilized as
pasture for lactating dairy cows. Johnson et al. (1966) studying changes
in dry matter and protein distribution in maize found that the protein
concentration of leaves declined rapidly and steadily until the final
mature stage. The protein concentration of the stalks was between 11 and
12% prior to tasseling, declined rapidly until 15 days after tasseling,
and declined only slightly throughout the remainder of ear growth and
maturation.
Johnson et al. (1966) observed that percent ash, cellulose and
crude protein were significantly decreased with increasing maturity.
Digestibility of dry matter and organic matter was significantly affected
by maturity, increasing to maximum at the dough-dent stage and decreasing
slightly thereafter. Dry matter digestibility was 68% at the earliest
maturity stage. Increasing maturity significantly decreased digestibility
of cellulose and protein throughout the harvest period.
Rendig and Broadbent (1979) observed that concentration of crude
protein ranged from about 6% in maize grain from plots that received no
added N or 90 kg N ha ^ to nearly 10% in plots receiving 180 kg ha The
concentrations in the grain protein of triptophane, lysine, glycine,
arginine, and threonine were decreased, and the concentrations of
analine, phenylalanine, tyrosine, glutamic acid, and leucine increased by
applications of N.
Schmid et al. (1975) observed that cell walls of maize cultivars
were considerably more digestible than those of the sorghum cultivars.
These results indicated that low cell wall digestibility was a major
factor limiting dry matter digestibility of sorghum silages. The same
authors reported that head IVDMD of short sorghum hybrids with high grain


195
block digester (Gallaher et al, 1976) for 2.5 hr. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen
concentration of these solutions were determined on a Technicon
AutoAnalyzer II.
Phosphorus, K, Ca, Mg, Fe, Cu, Mn, and Zn concentrations were
determined by a mineral analysis procedure in which 1.0 g samples were
placed in 50-ml pyrex beakers and ashed in a muffle furnace at 480C
for a minimum of 4 hours. After cooling each was treated with 2 ml
concentrated HC1 and heated to dryness on a hot plate. An additional 2
ml of concentrated HC1 + water was added to the dry beakers followed by
reheating to boiling and then diluting to 100 ml volume with deionized
water (this gave a solution containing about 0.10 _N HC1). Solutions were
analyzed for P using colorimetry on an AutoAnalyzer. Potassium was
determined by atomic emission spectrophotometry. Calcium, Mg, Fe, Cu,
Mn, and Zn were determined by atomic absorption spectrophotometry.
A sample of 0.3 g _+ 0.05 g of plant tissue was weighed in a clean
boat for total S concentration. The samples were spiked with 0.5 g of
vanadium pentoxide (V^O^). Sulfur concentrations were then determined
using a Leco S Determinator model SC132.
Results and Discussion
Experiment 1
Phenotypic characteristics of treatment plants are presented in
Table 7-1. Plants for the 30, 60, and 75 cm heights were uniformly light
yellow in appearance. Leaf veins were green, but intervenial spaces were
yellow, light yellow, and light yellow, respectively. Plants of the last
two height treatments (90 and 120 cm) had a vigorous appearance and were


132
concentration is reached. Ulrich (1952) defined the critical nutrient
concentration in relation to plant growth either in terms of the
concentration that is just deficient for maximum growth or that which is
just adequate for maximum growth, or the concentration separating the
deficiency zones from adequacy zones.
Brown and Jones (1977) concluded that plant species, genotypes, and
varieties differ in their nutrient requirements and tolerance to excess
mineral elements and poses the challenge of determining the nutrient
requirements of plants so that the plant and the soil can be made
compatible. Bates (1970) identified maturity, cultivar, and interaction
among nutrients and the environment as factors that affect nutrient
concentrations in plants. Among the environmental factors the most
relevant is available soil moisture supply. Because environmental
conditions do vary over short periods of time they will affect the
validity of the analysis. Peaslee and Moss (1966) postulated that since
it is widely known that K, Ca, and Mg interact in uptake, concentration,
and in many functions, discussing the cation sum and/or ratio efficiency
may be more appropriate than individual cations. This theory may be
applied to all cases where there is interaction between nutrients.
Green (1973) oberved that many factors combine to determine the
relative value of sorghum grain. Some of these are differences in tannin
content, protein content, amino acid composition, amount of floury and
horny endosperm, and field weathering. Johnson et al. (1966) concluded
that percent ash, cellulose and crude protein were significantly
decreased with maturity. Schmid et al. (1975) observed that cell walls
from maize cultivars were considerably more digestible with maturity
than those of sorghum cultivars. These results indicate that low cell


26
ratios remained constant or increased with advancing maturity, while that
of the tall hybrids with lower grain ratios decreased with maturity. Stem
IVDMD of the tallest hybrids increased with maturity while the other
hybrids decreased with maturity.
Although maturity is a factor affecting sorghum silage nutritive
value, its influence varies depending on forage type in that a decline in
cellulose digestibility with maturity may be detrimental to total
digestibility of low-grain sorghums, but not for those with high-grain
content. Apparently, the rapid increase in the amount of a highly
digestible starch during maturation in the high-grain sorghums
compensates for the decline in cellulose digestion (Schmid et al., 1975).
Cummins (1970) in a two-year study observed that in general the in
vitro dry matter digestibility (IVDMD) of maize leaves decreased with
maturity, although some year-to-year variation occurred. The IVDMD was
2
negatively correlated with maturity (R =0.67 and 0.88, respectively).
Both IVDMD and carbohydrate content of the stalks were closely related to
the rainfall distribution during the maturity period.
Johnson and McClure (1966) found highest total dry matter yield per
hectare to be between the dent and glaze stage of kernel development.
Although ears constituted 60% of the dry matter of the mature maize
plant, they did not reach this proportion until the dent stage of
development. IVDMD of maize stem cellulose was quite constant during ear
development but digestibility of leaf cellulose declined steadily. The
soluble carbohydrate in maize stem tissue increased rapidly from
tasseling to a maximum in late August (milk stage) and thereafter
declined with maturity. Crude protein content declined steadily in maize
leaves but changed very little in maize stalks from milk stage to final


237
Truog, E. G., C. Gerloft, R. J. Goates, and K. C. Berger. 1947.
Magnesium-phosphorus relationships in plant nutrition. Soil Sci.
63:19-25.
Tyner, E. H. 1946. The relation of corn yields to in-leaf nitrogen,
phosphorus, and potassium content. Soil Sci Soc. Amer. Proc. 11:317-323.
Ulrich, A. 1952. Physiological bases for assessing the nutritional
requirements of plants. Ann. Rev. Plant Physiol. 3:207-228.
Vanderlip, R. L., and G. F. Arkin. 1977. Simulating accumulation and
distribution of dry matter in grain sorghum. Agron. J. 69:917-922.
Vanderlip, R. L., and H. E. Reeves. 1972. Growth stages of sorghum
(Sorghum bicolor (L.)Moench.). Agron. J. 64:13-16.
Voss, R. £., J. J. Hanway, and L. C. Dumenil. 1970. Relationship between
grain yield and leaf N, P, and K concentrations for corn (Zea mays L.)
and the factors that influence this relationship. Agron. J. 62:726-728.
Wagner, R. E., and M. Jones. 1968. Fertilization of high yielding forage
crops. Changing patterns in fertilizer use. Soil Sci. Soc. Amer. Proc.
pp. 297-326.
Wahua, T. A., and D. A. Miller. 1978a. Effects of intercropping on
soybean N2-fixation and plant composition on associated sorghum and
soybeans. Agron. J. 70:292-295.
Wahua, T. A., and D. A. Miller. 1978b. Relative yield totals and yield
components of intercropped sorghum and soybeans. Agron. J. 70:287-291.
Wardlaw, I. F. 1967. The effect of water stress on translocation in
relation to photosynthesis and growth. I. Effect during grain
development. Aust. J. Biol. Sci. 20:2539.
Ware, G. 0., K. Ohki, and L. C. Moon. 1982. The Mitscherlich plant
growth model for determining critical nutrient deficiency levels. Agron.
J. 74:88-91 .
Watson, D. J. 1956. Leaf growth in relation to crop yield. Tn The growth
of leaves. F. L. Milthorpe (ed.). Butterworth Sci. Pub. London.
Watson, D. J., G. N. Thorne, and S. A. French. 1963. Analysis of growth
and yield of winter and spring wheats. Annals of Botany 27:1-22.
Wedin, W. F. 1970. Digestible dry matter, crude protein, and dry matter
yields of grazing-type sorghum cultivars as affected by harvest
frequency. Agron. J. 62:359-363.
Woodruff, J. R. and C. L. Parks. 1980. Topsoil and potassium calibration
with leaf potassium for fertility rating. Agron. J. 72:392-396.
Yoshida, S. 1972. Physiological aspects of grain yield. Ann. Rev. Plant
Physiol. 23:437-464.


113
Soil from each increment was placed in a previouly weighed can, then
weighed, oven dried at 105C for 24 hours, and weighed again. Assuming
constant weight, soil moisture was determined by difference.
Statistical analyses were conducted for the randomized complete block
design. Individual plots were 9.8 by 10 m. Twelve rows of 'NB-3' maize
were planted no-tillage by hand in each plot (52,000 plants ha on 16
June. The second crops ('Criollo', photosensitive sorghum; 'Pioneer 895',
non-photosensitive sorghum; and 'Gahi-3' millet) were interplanted on 16
September, according to the spatial arrangements depicted in Figure 3-3.
The 'Criollo' was seeded in-between maize rows (40 cm from the maize
hills), in hills spaced 0.80 cm apart, and later thinned 24 days after
seeding to six plants per hill to obtain 75,000 plants ha 'Pioneer 895'
and 'Gahi-3' were seeded in double rows (20 cm from the maize); 24 days
after seeding the rows were thinned to give 120,000 plants ha
Results and Discussion
Percent Soil Moisture
Late planting (delayed 3 weeks due to intense rains during the last
week of May and the first week of June (Fig. 5-1) together with a long and
intense "canicula") resulted in improper growing conditions for maize,
sorghum, and millet, in particular for maize. Rainfall in the area during
the growing season of the crops was less than 70% of the normal occurrence
(CATIE, 1981a). A long drought occurred between planting and and the
beginning of grain filling of 'NB-3'. Data presented by Gardner et al.
(1981) suggested that water stress during vegetative growth only had the
least damaging effects on yield, while stress during pollination and grain
filling stages had the greatest limiting effect on yield. Denmead and Shaw


Sorghum Dry Matter Yield (Mg ha ) Maize Dry Matter Yield (Mg ha
119
Days After Planting Maize
Figure 5-3. Total, stem, leaf, flower, ear, or head dry matter
accumulation for 'NB-3' (a) and 'Criollo' (b)
intercropped.


199
Table 7-4.
Selected soil
properties in relation to
maize
plant height
in Florida.
Height
Depth to
CEC
EB
treatment
20% clay
45 cm 90 cm
45 cm
90 cm
1
era-
30
120
2.6 1.9
2.3
1.3
60
90
3.3 4.2
2.2
2.9
75
75
2.2 7.0
1.7
4.5
90
45
5.8 21.6
4.9
18.0
120
15
15.0 70.7
14.5
19.3
CEC = cation exchange capacity, EB = extractable bases.
Table 7-5. Sulfur concentration in maize in relation to
plant height in Florida.
Height
treatment
Tissue
Plant Leaf
cm
dag kg
30
0.090 b
0.090 c
60
0.083 b
0.093 c
75
0.097 b
0.100 c
90
0.090 b
0.117 b
120
0.137 a
0.210 a
Values in columns not followed by the same letter are
different at the 0.05 level of probability according to
Duncan's new multiple range test.


159
130 170 210 250 290
Days After Plontlng Moize
Figure 6-14. Effect of the stage of maturity on the P
concentration of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).


19
pattern of leaf area in sweet sorghum which starts declining after the
plant approaches 50% bloom.
Dry Matter Accumulation
Hanway (1962a) reported that the potential yield of maize grain
which is produced late in the season is determined by the leaf area, which
is always produced early in the season. However, less than this potential
yield of grain will actually be attained if a) the net assimilation rate
is decreased by any factor such as a moisture deficiency later in the
season or b) the leaf area is prematurely reduced by some factor that
results in premature death of leaves such as a nutrient deficiency or
insect, disease, or hail damage. If no other factor limits yield, one
would expect that increasing LAI should result in increased grain yield.
Data reported by Tollenaar and Daynard (1978) showed that grain
yield per plant was most affected by shading during the silking period,
indicating a sink limitation for grain yield in hot environments. A
source limitation in short-season regions may be the consequence of low
leaf area per plant.
Hanway and Russell (1969) reported relatively large differences
among maize hybrids in the length of the grain filling period. Daynard
and Duncan (1969) have observed such differences among hybrids and have
found a high correlation between the length of the grain filling period
and the yield.
The patterns of growth and dry matter distribution observed in
tropical cultivars grown in Mexico (Goldsworthy and Colegrove, 1974)
suggest that the capacity of the grain sink to accomodate assimilate can
limit grain production. Results of defoliation studies in Rhodesia
(Allison and Watson, 1966), which showed that a relatively large amount of


198
Table 7-2. Plant characteristics of maize treatments in Florida.
Height First internode
treatment diameter
Dry weight
per plant
cm g
30
1.70 d
11.48 e
60
2.65 c
33.66 d
75
3.06 b
51.78 c
90
3.27a
61.15 b
120
3.18a
72.25a
Values in columns not followed by the same letter are different at
the 0.05 level of probability according to Duncan's new multiple
range test.
Table 7-3. Plant characteristics of maize treatments in Florida.
Height
treatment
Average/leaf
Length Width Weight
30
49.53 e
5.33 e
g
1.845
60
68.58 d
7.87 d
3.166
75
76.20 c
8.64 c
3.778
90
86.36 b
9.14 b
4.014 b
120
96.52a
9.53a
4.885a
Value in columns not followed by the same letter are different at
the 0.05 level of probability according to Duncan's new multiple
range test.


14
The depressive effect of water stress on photosynthate
translocation reported by Brevedan and Hodges (1973) is in agreement with
the observation of several other authors (Hartt, 1969; Plaut and Reinhold,
1965; Wardlaw, 1967). Wardlaw (1967) found a continued movement of
assimilates from the leaf to the developing wheat (Triticum aestivum L.)
grain under water stress conditions. He also observed a lower velocity of
sugar transport from leaves of stressed plants than from well-watered
plants.
Data presented by Denmead and Shaw (1960) suggested that lower
assimilation in plants subjected to stress is partly due to smaller leaf
area, as indicated by the size of the ear leaf, and partly due to the
metabolic activity of the plants at different growth stages. When
compared with the reduction in assimilation caused by stress at other
growth stages, the reduction in assimilation resulting from stress at
silking is larger than the reduction in leaf area could indicate. The
data also suggested that there may be a tendency for recurring periods of
stress to have less and less detrimental effect on assimilation and yield.
Stress applied while the plant is actively expanding retards enlargement
of plant parts. Recovery when the stress is removed is not immediate but
growth rate appears to return to normal after a few days.
McPherson and Boyer (1977) reported that the physiological
mechanisms responsible for yield losses under dry conditions are unknown,
especially for grain crops. Drought causes massive losses in the yield of
crops, but the physiological mechanisms responsible for decreased yields
are poorly understood. Most aspects of the physiological behavior of
plants are known to be altered by the onset of dry conditions (Boyer,
1973; Hsiao, 1973). But photosynthesis and translocation, which are


133
wall digestibility is a major factor limiting dry matter digestibility
of sorghum silage.
Data presented by Hall et al. (1965) indicated that sorghum grain
is comparable to maize grain in digestibility. Clark et al. (1965) found
no differences between millet (Pennisetum americanum (L.) Leeke) and
sorghum x sudangrass (Sorghum sudanense L.).
Crop residues of grain sorghum and maize have attracted attention
as alternate economical forage resource for livestock production (Perry
and Olson, 1975). However, Martin and Wedin (1974) reported that
thousands of hectares of sorghum residues are not used in the midwestern
United States because they are considered of poor quality. Ratoons often
remain as leafy and succulent growing plants following grain harvest and
should be considered as a feed source for farm animals.
Plant populations, row spacings, and soil fertility affect not only
grain yields but also the yields and quality of residues. Residue yield
from maize is normally greater from maize than from grain sorghum but
lower in crude protein. Perry and Olson (1975) observed that maize dry
matter yields decline as much as 30% within 100 days after grain
harvest. Martin and Wedin (1974) reported that sorghum lost
approximately 28% of its maximum yield by 76 days after grain harvest.
Crop residues have potential as fertilizer, as fuel, and as
livestock feed. Comparative values for these uses can be determined on
the basis of the amount energy saved by substituting these materials for
conventional sources of feed, fertilizer or fuel.
Croka and Wagner (1975) observed that net energy has become widely
accepted for expressing the value of a ration and the energy
requirements for feedlot cattle. Energy reserves may be considered as


166
Days After Planttng Maize
Figure 6 19. Effect of the stage of maturity on the
Ca concentration of 'NB-3' maize (a)
and 'Criollo' sorghum (b).


197
green and dark green, respectively. No intervenial chlorosis was
observed on the latter treatments. Older leaves of all treatments showed
some degree of chlorosis, but only on the leaves of the 30 and 60 cm
height plants were K-deficiency symptoms observed.
Results of measurements of the first internode of treatment plants
are presented in Table 7-2. Internode diameter increased with plant
height. Plants 30 cm tall had the smallest diameter, while those 90 cm
tall had the largest diameter. The results indicate no difference
(p=0.05) in internode diameter between plants 90 and 120 cm tall. Dry
weight per plant (Table 7-2) followed a trend similar to internode
diameter. As expected, taller plants had accumulated more dry matter
(p=0.05). Plants 120, and 30 cm tall had accumulated 72.3 and 11.5 g of
dry matter per plant, respectively.
Leaf length, width, and dry weight were different (p=0.05) for all
height treatments (Table 7-3). The 120 cm plant height presented the
largest values for all variables. In general, as plant height increased
leaves were longer and wider and had accumulated more dry matter. Leaf
length varied from 49.5 to 96 cm for the 30 and 120 heights,
respectively. Leaf width (at the widest point) varied from 5.33 to 9.53
cm in the 30 and 120 cm heights, respectively. The difference in leaf
weight between the 30 and 120 cm height was 3 g; this is a 100% increase
in leaf weight.
Soil depth to 20% clay varied among treatments (Table 7-4). Twenty
percent clay levels were shallower (15 cm) where 120 cm tall plants were
growing. Roots of the shortest plants would need to penetrate 120 cm or
more to reach cation-rich clays. Cation exchange capacity (CEC) and
extractable bases (EB) increased with depth, except for the 30-cm


201
Table 7-6. Sulfur concentration in soil in relation to
maize plant height in Florida
Height
treatment
Soil depth
0-15
15-30
30-45
cm
dac kc'1
30
3.17 b
2.83 e
4.00
b
60
2.00 b
3.00 e
4.17
b
75
2.83 b
3.67 b
4.33
b
90
3.00 b
4.33 be
4.50
b
120
4.50a
5.00a
18.67
b
Value in
columns not followed by the same letter
are
different
at the 0.50 level of probability according to
Duncan's
new multiple range test.
Table 7-7.
Nitrogen, P
, and S
concentration
in youngest
mature leaf
of maize in Florida.
Height
Nutrient
treatment
N
P
S
N: S
P: S
dag kg
1
30
4.08
.46
.090
45
5.1
60
3.44
.33
.093
37
3.6
75
3.61
.27
.100
36
2.7
90
2.99
.25
.117
26
2.1
120
2.96
.28
.210
14
1.3


Table
5-4. Dry matter
different
distribution as
cropping systems.
percent
of the total dry weight
of 'NB-3'
grown
in 3
Stem
Leaf
Flower
Ear
DAP
M+PS
N+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
dae ha"1
day 1-
65
42.2
42.8
46.3
57.8
57.2
53.7
73
56.2
54.0
53.3
36.3
37.9
40.1
7.5
8.1
6.6
99
32.3
35.1
38.1
25.3
26.1
20.7
3.2
2.3
2.7
39.2
36.5
38.5
120
34.2
32.1
38.4
17.5
20.0
16.2
2.2
2.2
2.2
46.1
45.7
42.9
160
27.6
26.7
23.6
60.1
63.6
65.1
0.3
0.3
0.3
12.0
9.4
11.0
193
5.6
5.8
6.3
94.2
94.0
93.6
0.2
0.2
0.1
M = maize, PS = photosensitive sorghum, NS = non-photosensitive sorghum, and MI = millet.
DAP = days after planting.
127


83
Figure 4-1. Distribution of maize + sorghum systems in Central
America (Drawn with information from Arias et al.,
1980; Mateo et al., 1981; and Hawkins et al.,
1983).


57
will accumulate in plants when the rate of uptake exceeds the amount
required for protein synthesis (Friedrich and Schrader, 1978).
The ratio of Nt:St in all vegetative fractions of maize plants
declined during grain-filling. Likewise, the Nt:St ratio was lower in
ears of N-deprived plants than in control plants; however, this ratio
was constant throughout grain-filling and was usually significantly
lower for N-deprived plants. Nitrogen supply had no effect on the
decline in Nt:St ratio in the leaves (Friedrich et al., 1979).
The accumulation of zein, a grain protein that is low in S-amino
acids, is known to be enhanced by increased N-fertilization. The ear
Nr:Sr ratios were much higher than the Nt:St ratios. This is due to the
larger proportion of ear S present as sulfate-S compared to the pro
portion of total N present as nitrate-N (1 to 6 dag kg ^). However,
this sulfate-S may have been in the cob, rather than in the grain.
Maize grain does not accumulate nitrate-N, (Friedrich and Schrader,
1978).
Goh and Kee (1978) found when N is added in high rates a reduction
in reducible S content occurred because of the incorporation of S into
plant proteins. In the high N low S treatments (N^SO) over 95% of total
S in plants occurred as organic forms (total S, reducible S). Stewart
and Porter (1969) showed that when S is deficient nearly all the S
present in both herbage tops and roots occurred in the protein fraction.
Conversely, in the low N and high S treatments the reducible S fraction
consistently made up more than 20% of the total S.
Phosphorus-S interactions have been observed by Kamprath et al.
(1956) and Radet (1966). Caldwell et al. (1969) reported the S
treatments decreased the P content of the mature tissue. The S:P ratios


225
. 1976. Water deficits and photosynthesis, pp. 153-190. Tn
T.T. Kozlowski (ed.) Water deficits and plant growth. Vol 4. Academic
Press, New York.
, and Me Pherson. 1975. Physiology of water deficits in
cereal crops. Adv. Agron. 27:1-23.
Bremner, J. M. 1960. Determination of nitrogen in soil by the Kjeldahl
method. J. Agrie. Sci. 55:11-33.
Brevedan, E. R., and H. F. Hodges. 1973. Effects of moisture deficits on
C translocation in corn (Zea mays L.). Plant Physiol. 52:436-439.
Bromfield, A. R. 1974. The deposition of sulphur in the rainwater of
northern Nigeria. Tellus 26:408-411.
Brown, J. C., and W. E. Jones. 1977. Fitting plants nutritionally to
soils. III. Sorghum. Agron. J. 69:410-414.
Brunold, C., and A. Schmidt. 1976. Regulation of adenosine-5'-
phosphosuIfate activity by in (Lemna mino L.). Planta 133:85-88.
Bryant, H. T., R. E. Blaser, R. C. Hammes, and J. T. Huber. 1966.
Evaluation of corn silage harvested at two stages of maturity. Agron. J.
58:253-255.
Burns, J. C., and W. F. Wedin. 1964. Yield and chemical composition of
sudangrass and forage sorghum under three systems of summer management
for late fall in situ utilization. Agron. J. 56:457-460.
Caldwell, A. C., E. C. Seim, and G. W. Rehm. 1969. Sulfur effects on the
elemental composition of alfalfa (Medicago sativa L.) and corn (Zea mays
L.). Agron. J. 61:632-634.
CATIE. 1980. Proyecto de desarrollo de sistemas de produccin agricola
para agricultores de escasos recursos en Nicaragua. CATIE, Nicaragua.
28 pp.
. 1981a. Informe de labores desarrolladas pro el programa de
cultivos anuales del CATIE en Nicaragua. CATIE, Nicaragua. 209 pp.
. 1981b. Informe final: Proyecto sistemas de cultivo, Nicaragua.
CATIE, Nicaragua. 32 pp.
. 1982a. Caracterizacin del area las fincas y sistemas de cultivo
practicados por los pequeos agricultores en Esteli, Nicaragua. CATIE,
Nicaragua. 126 pp.
. 1982b. Informe anual de labores desarrolladas por el departamento
de produccin vegetal del CATIE en Nicaragua, durante 1981. 143 pp.
Chapman, H. D. 1965 Cation exchange capacity. _In C. A. Black, D. D.
Evans, J. L. White, L. E. Ensminger, and S. E. Clark (ed. ) Methods of
soil analysis. Am. Soc. Agron., Madison, WI.


64
Table 3-1. Fertilizer rates and times of application evaluated at two
sites in Northern Nicaragua.
TRT
#
-Crop-
Cl C2
Fertilization
Days
10
after
planting Cl
25
25 days after
planting C2
P
N
N
P
N
-1
. K.g na
1
M
PS
30
0
0
0
0
2
M
PS
30
30
40
0
0
3
M
PS
30
0
35
0
0
4
M
PS
30
0
70
0
0
5
M
PS
30
30
40
0
35
6
M
PS
30
30
40
30
35
7
M
NS
30
30
40
0
0
8
M
NS
30
30
40
0
35
9
M
NS
30
30
40
30
35
10
M
MI
30
0
0
0
0
11
M
MI
30
30
40
0
0
12
M
MI
30
30
40
0
0
13
M
MI
30
30
40
0
0
M maize, PS = photosensitive sorghum, NS = non-photosensitive sorgum,
MI = millet.


Precipitntion (mm)
Time
Figure 5-1. Chronological arrangement of the three systems under study
and rainfall distribution during the growing season.
114


6
water use efficiency; 5) to study the relation between gravimetric
moisture and dry matter accumulation by the maize + sorghum, maize
millet systems; 6) to determine the existence of soil S deficiency
areas where the system is practiced in Nicaragua.
soil
+
in


ACTIVITY (ha)
91
Figure 4-5. Variation of activities as farm size increases.
Tejutla, El Salvador (Unpublished data, CATIE,
El Salvador).


194
Cu, Mn, and Zn were determined by atomic absorption spectrophotometry.
Soil pH was determined using a 2:1 water:soil ratio.
Soil S was determined by the method described by Bardsley and
Lancaster (1965). Ten grams of soil from a 20-mesh screen were placed in
a 50-ml Erlenmeyer flask and extracted with 39 g of NH^C2H^02 diluted in
one L of 0.025 N_ acetic acid for 30 minutes, 0.25 g of washed activated
charcoal was added and extracted for 3 additional minutes. The soil
suspension was filtered using a sulfate-free Whatman No. 42 filter
paper. Ten ml of the filtrate was pipetted into a 50-ml Erlenmeyer flask
to which 1 ml of acid seed solution (6 _N HC1 + 20 mg kg of S as i^SO^)
was added, swirled and 0.5 g of 83012*2^0 crystal was added. This
solution was left standing for 1 minute, then swirled to dissolve all
the crystals. Soil S concentration was then determined using a
Perkin-Elmer/Coleman 54 spectrophotometer set at 540 nm.
Cation exchange capacity (CEC) was determined by leaching the soil
with 1 M ammonium acetate (NH^OAc) at pH 7.0, followed by leaching with
95% ethyl alcohol to remove excess NH^+ and subsequently with acidified
NaCl to displace NH^+ which was then distilled (into boric acid) and
titrated with HC1 (Chapman, 1965). Soil pH was determined at 1:2 soil
solution ratio in deionized water using a glass electrode.
Plant analysis methods
Nitrogen analysis of plant material employed the microKjeldahl
procedure modified by Gallaher et al. (1976). A 100-mg sample was placed
in 100-ml digestion tubes to which two boiling chips, 3.2 g of catalyst
(90% anhydrous i^SO^, 10% anhydrous CuSO^), 10 ml of concentrated H2S4
and 2 ml of ^02 were added. Samples were then digested in an aluminum


191
could be obtained through soil-plant analysis. The objective of this
study was to determine the cause of maize leaf chlorosis and height
variability by analysis of plants and associated soils.
Experiment 2
In maize producing areas of Nicaragua it was apparent that
deficiency symptoms observed in Florida and Georgia were also visible in
these areas. To determine if the symptoms observed in Nicaragua were
also associated with S status in the plant, a study was conducted with
the following objectives: 1) to determine if S deficiency is a
widespread problem in Nicaragua, and if plants with deficiency symptoms
give the same plant analysis results as in Florida and Georgia, and 2)
to evaluate soil tests in relation to leaf analysis in assessing S
deficiency in maize.
Materials and Methods
Field Methods
Experiment 1
Sixty day-old no-tillage maize was grown in a 65 ha field in
Alachua County, Florida. Plants showed various degrees of stunting and
ranged from dark green healthy plants to light green or yellowish
stunted plants. Plant height ranged from approximately 30 cm to 120 cm.
The stunted plants exhibited intervenial chlorosis, the degree of which
diminished as plant height increased. The objective proposed stated that
the problem was likely associated with soil characteristics and the
identification could be obtained through soil-plant analysis.
A completely randomized experimental design was used that included
three replications of five maize treatments. Treatments included 30, 60,


TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS iii
ABSTRACT vi
CHAPTER 1. INTRODUCTION 1
CHAPTER 2. LITERATURE REVIEW 7
Growth
Crop Growth Rate 7
Factors That Affect Growth 10
Leaf Area Index 17
Dry Matter Accumulation 19
Forage Quality 24
Crop Residues 28
Energy 30
Nutrition 32
Critical Levels 32
Factors That Affect Concentration 32
Nutrient Accumulation 33
Sulfur 43
Importance of S 43
Forms and Amount of S in the Soil 45
Sulfur Deficiency in Soils 46
Plant's Requirements and Content. 50
Absorption and Accumulation of S 51
Effects of S Deficiency 54
Interaction Between S and Other Nutrients 55
Crop Response to S Fertilizer 59
CHAPTER 3. MATERIALS AND METHODS 63
Field Procedures 63
Fertility Trials 63
Growth Analysis 71
Survey of Sulfur Deficiency in Maize 73
Laboratory Procedures 74
Soil Analysis Methods 74
Plant Analysis Methods 76
xv


140
Days After Planting Maize
Figure 6-2. Effect of the stage of maturity on percent
organic matter of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).


Sorghum Dry Hotter Yield (Mg ha ) Maize Dry Matter Yield (Mg ha
120
Doys After Plnnting Maize
Figure 5-4. Total, stem, leaf, flower, ear, on head of 'NB-3'
maize (a) and 'Pioneer 895' sorghum (b) intercropped.


234
Pierre, W. H., L. Dumenil, and J. Henao. 1977 Relationship between corn
yield, expressed as a percentage of maximum, and the N percentage in the
grain. II. Diagnostic use. Agron. J. 69:221-226.
Pineda, L., G. Hernandez, R. Lemus, and E. Marin. 1979. Informe de
Nicaragua para la reunion de consulta para la localizacin de sistemas
de produccin de cultivos en el Istmo Centroamericano. _In R. Moreno,
(ed.) Reunion de consulta sobre la localizacin de sistemas de
produccin de cultivos en Centroamerica, CATIE, Turrialba, Costa Rica,
pp. 169-220.
Plank, 0. C. 1979. Plant analysis handbook for Georgia. Coop. Ext. Serv.
Univ. of Georgia Tech. Bull. 735. p. 68.
14
Plaut, Z., and L. Rernhold. 1965. The effect of water stress on C
sucrose transport in bean plants. Aust. J. Biol. Sci. 18:1143-1155.
Preston, R. L. 1975. Net energy evaluation of cattle finishing rations
containing varying proportions of corn grain and corn silage. J. Anim.
Sci. 41:622-624.
Pumphrey, F. V., and D. P. Moore. 1965. Diagnosing sulfur deficiency of
alfalfa (Medicago Sativa L.) from plant analysis. Agron. J. 57:364-366.
Quimby, J. R. 1974. Sorghum improvement and the genetics of growth.
Texas A & M Univ. Press, College Station, Texas.
Rabuffetti, A., and E. J. Kamprath. 1977. Yield, N, and S content of
corn as affected by N and S fertilization on coastal plain soils. Agron.
J. 69:785-788.
Radet, E. 1966. Sulfur requirements of various crops. Sulphur Inst.
2:11-15.
Rajat, R., S. Gupta, S. P. Singh, P. Mahendra, S. N. Singh, R. N.
Sharma, and S. K. Kaushik. 1978. Interplanting maize, sorghum and pearl
millet with short-duration grain legumes. Indian J. Agrie. Sci. 48(3)
132-137.
Reddy, M. S., and R. W. Willey. 1981. Growth and resource use studies in
an intercrop of pearl millet/groundnut. Field Crops Res. 4:13-24.
Rendig, V. V., and F. E. Broadbent. 1979. Proteins and amino acids in
grain of maize grown with various levels of applied N. Agron. J.
71 :509-512 .
Reneau, R. B., G. D. Jones, and J. B. Friedericks. Effect of P and K on
yield and chemical composition of forage sorghum. 1983. Agron. J.
75 :5-8.
Reuveny, Z., and P. Filner. 1977. Regulation of adenosine triphosphate
sulfurylase in culture tobacco cells. Effects of sulfur and nitrogen
sources on the formation and decay of the enzyme. J. Biol. Chem.
252:1858-1864.


169
Excessive production of oxalic acid by plants could result in Ca
deficiency, especially when Ca supply is limited.
Both sorghums and the millet presented patterns similar to those
observed in maize. Calcium concentration increased with maturity in the
leaf as it decreased in the stem. Only small amounts of Ca accumulated
in the head. Lockman (1972a) indicated that in dry years the Ca
concentration in the plant will increase.
Magnesium (Figs. 6-22, 6-23, and 6-24) presented a pattern of
accumulation and distribution very similar to that observed for Ca.
Higher concentrations were observed in the leaves of crops than in any
other plant component. Jacques et al. (1975) reported similar results.
However, their data suggest that leaf Mg remains constant through the
growing season, contrary to what was observed in this experiment.
Similar results were observed in millet (Fig. 6-24b).
Ratios among K, Ca, and Mg observed in maize leaves throughout the
growing season are presented in Table 6-1. Gallaher et al. (1975) showed
that when the K:Ca, K:Mg, and K:Ca+Mg ratios exceeded 3.5, 3.6, and 1.8,
respectively, Mg concentration in the leaves is close to the value that
has been found to reduce photosynthesis. Values presented in this
experiment indicate that Mg deficiency and an excess of K in relation to
the other two cations. The K:Ca, K:Mg, and K:Ca+Mg decreased with
maturity as a result of K losses from the plant and the increase in Ca
and Mg concentrations observed (Figs. 6-22, 6-23, and 6-24). This
imbalance observed among these cations may be limiting growth and
yields, as reported by Gallaher et al. (1975).


2
marketing risks, and to satisfy different dietary needs. Small-
scale farmers in Central America comprise the most important basic
food production group. They use production systems frequently referred
to as traditional in the literature (Rodriguez et al., 1977; Arias et
al., 1980; Rosales, 1980; Mateo et al., 1981). These systems have been
developed through the interaction of man and his environment, under
conditions involving high risk and restraints which limit crop
productivity.
Several cropping systems can be found in the dry areas of the
Isthmus. Maize (Zea mays L.) intercropped with sorghum (Sorghum bicolor
(L.) Moench) (maize + sorghum) with varying degrees of competition in
time and space, is the most widely practiced cropping system in Central
America (Hawkins et al., 1983; Larios et al., 1983). Other relevant
systems include mono or relay crops of maize, or bean (Phaseolus spp.)
or cowpea (Vigna spp.); sorghum intercropped with bean, sesame (Sesamum
indicum L.); or sisal (Agave spp.) intercropped with maize, sorghum,
and/or bean.
It is accepted (De Wit and Hollman, 1970; Quimby, 1974) that
sorghum was introduced to the western hemisphere by African slaves and
Portuguese sailors in the 16th century. According to Martin (1975) it
was not until the 19th century that sorghum gained importance in the
United States. It has not been documented in the literature when the
system was first used in Central America, but it cannot be more than 350
years ago.
Agricultural research in the tropics has been conditioned by the
cropping systems of more developed areas, the origin of most research
workers, and until recently, rather cursory attention has been paid to


69
Table 3-3. Statistical analysis model used for sorghum data. Factorial
(2x2) for treatments 1 through 9.
Source
df
REPLICATIONS
3
(r-1)
TREATMENTS
8
(t-l)
GENOTYPE EFFECT
1
(a-1)
Treats (1, 2, 3, 4, 5, 6) vs (7, 8, 9)
1
FERTILIZER RATES AND TIME OF APPLICATION
1
(B-l)
Treats (2, 5, 6) vs (7, 8, 9)
1
GENOTYPES X RATES-TIME
1
(a-1) (b-l)
LEFT OVER*
1
ERROR
27
(r-1) (t-l)
TOTAL
35
(rt-1)
* Degrees of freedom are not orthogonal.
Table 3-4. Statistical analysis model used for millet data. Randomized
complete block design.
Source
df
REPLICATIONS
TREATMENTS
Treat (10) vs (11, 12, 13)
Treat (11) vs (12, 13)
ERROR
TOTAL
3 (r-1)
3 (T-l)
1
1
9 (r-1) (t-l)
15 (rt-1)


115
(1960) found that grain yield was affected more than any other plant
characteristic by early stress.
A second period of intense rainfall occurred during the second week
of September which recharged the soil (Figure 5-2). In general, the 30-45
cm depth had a higher soil moisture percentage than the 0-15 cm depth.
Only during week 12 after planting maize did the superficial horizon
surpass the lower horizons in soil moisture content (Table 5-1). The
highest percentage observed (40.9) occurred in the 30-45 cm depth and
corresponded to the period immediately following black layer formation in
maize and prior to anthesis of the non-photosensitive sorghum. The lowest
value observed (10.4%) corresponded to the 0-15 cm depth and occurred
during grain filling of the photosensitive sorghum. Moisture stress was
frequently observed and was evident by dry curled leaves, short plants,
and barren stalks.
Even though water was available at deeper depths (Fig. 5-2), maize
from all cropping systems exhibited water stress (leaf wilt or firing)
before soft-dough. Generally there was less available moisture in the top
two depths for the 'NB-3', which caused pollen desiccation, therefore
limiting the size of the grain sink. Data reported by Moss (1962) and
Allison and Watson (1966) support these results. Percent soil moisture
increased between soft-dough and black layer, allowing a limited grain
fill. During this period dry matter accumulated in the stem and leaves due
to the lack of an adequate grain sink (Classen and Shaw, 1970; Goldsworthy
and Colegrove, 1974).
Soon after planting the second crops the shallow root system began to
draw available moisture, causing a depletion in all the depth intervals
(Fig. 5-2). 'Criollo' anthesis and grain fill occurred during a period of


3
indigenous systems. Baker (1979) emphasizes that attempts to improve
production in the tropics have failed not because of farmer conservatism
or the lack of extension programs, but because it has not been realized
that subsistence agriculture is a tropical agro-ecosystem geared for a
low level of production and not simply a collection of crops and
animals to which inputs can be applied indiscriminately to obtain
immediate results.
A lack of appreciation of the personal nature of the subsistence
farmers' farming systems has resulted in a tendency for research to
produce solutions to the wrong problems. For example, agricultural
research in Central America has traditionally been dedicated to export
crops such as banana (Musa spp. ) and coffee (Coffea spp. ), while most of
the available technology for increasing basic food crop productivity has
been adapted from temperate countries and thus has generally been
developed for sole cropping.
Mateo et al. (1981) and Larios et al.(1983) have pointed out that
in spite of the economic importance of the maize + sorghum this system
has received little attention in the work plans of local research
institutions. Reports in the literature (Arias et al., 1980; Mateo et
al., 1981; Fuentes and Salguero, 1983) indicate that of the total area
cultivated with sorghum in Guatemala, El Salvador, and Honduras, the
percentages intercropped with maize are, respectively, 80, 93 and 93.
Larios et al. (1983), concluded that knowledge of the process of
integrating component technologies into farming systems is lacking,
especially for small-scale farms. Due to the lack of available
technology adapted to conditions prevailing in the semi-arid regions of
Central America it is mandatory to conduct field experimentation that


232
Lockman, R. B. 1972a. Mineral composition of grain sorghum plant
samples. Part I: Comparative analysis with corn at various stages of
growth and under different environments. Comms. Soil Sci. and Plant
Anal. 3(4) :271-281 .
.. 1972b. Mineral composition of grain sorghum plant
samples. Part II: As affected by soil acidity, soil fertility, stage of
growth, variety, and climate factors. Ccmms. Soil Sci. and Plant Anal.
3(4):283-293.
Macy, Paul. 1936. The quantitative mineral nutrient requirements of
plants. Plant Physiol. 11:749-764.
Martin, J. H. 1975. Historia y clasificacin de los sorgos (Sorghum
bicolor (L. ) Moench). In Produccin y uso del sorgo. Ed. Hemisferio Sur.
Martin, N. P., and W. F. Wedin. 1974. Effects of fall weathering on
yield and composition of sorghum stover. Agron. J. 66:669-672.
Matches, A. G. 1969. Influence of cutting height in darkness on
measurement of energy reserves of tall fescue. Agron. J. 61:896-898.
Mateo, N., A. Diaz, and R. Nolasco. 1981. El Sistema maiz + maicillo en
Honduras. CATIE, Honduras, p. 20.
McNaught, K. J. and P. J. Kristoffels. 1961. Effect of sulfur deficiency
on sulfur and nitrogen levels in pasture and lucerne. New Zealand J.
Agr. Res. 4:177-196.
McPherson, H. G. and J. S. Boyer. 1977. Regulation of grain yield by
photosynthesis in maize subjected to a water deficiency. Agron. J.
69:714-718.
Mead, R. and R. W. Willey. 1980. The concept of a 'land equivalent
ratio' and advantages in yields from intercropping. Expl. Agrie.
16:217-228.
Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na and NH,. North
Carolina Soil Test Division (Mimeo, 1973). North Carolina State Univ.,
Raleigh, NC .
Metson, A. J. 1973. Sulphur in forage crops. Sulphur Inst. Tech. Bull.
20.
Miller, D. F. Composition of cereal grains and forages. Natl. Acad. Sci.
Pub. 1:585
Mitchell, C. C., and W. G. Blue. 1981a. The sulfur fertility status of
Florida soils. I. Sulfur distribution in Spodosols, Entisols, and
Utisols. Soil and Crop Sci. Soc of Fla. Proc. 40:71-76.


PRODUCTION ASPECTS OF MAIZE + SORGHUM INTERCROPPING SYSTEMS
IN CENTRAL AMERICA
BY
FRANCISCO ROBERTO ARIAS MILLA
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1985

TO
TINITA, BENERANDA, ROBERTO, LILIANA, AND VERONICA
AND IN MEMORY OF
MICAELA RETANA

ACKNOWLEDGMENTS
I express sincere gratitude to Dr. Raymond Gallaher, chairman of
the supervisory committee. His guidance, dedication, and continuous
encouragement were valuable throughout my graduate program. I also thank
Dr. Victor E. Green, Dr. Clift Taylor, Dr. Mary Collins, and Dr. Maxie
McGhee for their teachings and guidance in the preparation of this
*
manuscript.
My studies would have been impossible without the financial
assistance of the Centro Agronmico Tropical de Investigacin y
Enseanza (CATIE) and the W. K. Kellogg Foundation, to the staff members
of which I express my sincere gratitude.
Thanks are also due to Mr. David Block for his assistance in the
statistical analysis of the data, and to Mr. Jacobo Reyes Palma for his
valuable assistance in conducting the field work. Acknowledgment is due
to Mrs Beneranda Arias and Mrs. Oliviethe Ortiz for their assistance in
the tissue analysis. Words of gratitude are expressed to Dr. Raul Moreno
for his encouragement, and friendship.
To ray mother, for her never ending sacrifices, her love, and
prayers, I owe much gratitude. I also thank my brothers Julio, Marina,
and Guillermo who have also contributed greatly towards the fulfillment
of my goals in life. To my wife, Beneranda, I express my gratitude for
her moral support, patience, and encouragement. I thank Roberto,
Liliana, and Veronica, without whose motivation and love this task would
have been less bearable.
m

TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS iii
ABSTRACT vi
CHAPTER 1. INTRODUCTION 1
CHAPTER 2. LITERATURE REVIEW 7
Growth
Crop Growth Rate 7
Factors That Affect Growth 10
Leaf Area Index 17
Dry Matter Accumulation 19
Forage Quality 24
Crop Residues 28
Energy 30
Nutrition 32
Critical Levels 32
Factors That Affect Concentration 32
Nutrient Accumulation 33
Sulfur 43
Importance of S 43
Forms and Amount of S in the Soil 45
Sulfur Deficiency in Soils 46
Plant's Requirements and Content. 50
Absorption and Accumulation of S 51
Effects of S Deficiency 54
Interaction Between S and Other Nutrients 55
Crop Response to S Fertilizer 59
CHAPTER 3. MATERIALS AND METHODS 63
Field Procedures 63
Fertility Trials 63
Growth Analysis 71
Survey of Sulfur Deficiency in Maize 73
Laboratory Procedures 74
Soil Analysis Methods 74
Plant Analysis Methods 76
xv

Page
CHAPTER 4. MAIZE + SORGHUM FARMING SYSTEMS IN CENTRAL AMERICA:
SITUATIONAL ANALYSIS 78
Introduction 78
Materials and Methods 80
Results and Discussion 81
Bio-Physical Environment 84
Socio-Economic Environment 87
Crop/Animal Interactions 103
Constraints 105
Research Opportunities 107
Interventions 108
CHAPTER 5. DRY MATTER ACCUMULATION BY MAIZE + SORGHUM AND
MAIZE + MILLET INTERCROPPING SYSTEMS 109
Introduction 109
Materials and Methods Ill
Results and Discussion 113
Percent Soil Moisture 113
Dry Matter Accumulation 118
Leaf Area Index and Other Plant Characteristics 130
CHAPTER 6. NUTRIENT CONCENTRATION, IVOMD, AND METABOLIZABLE
ENERGY OF INTERCROPPED MAIZE + SORGHUM AND MAIZE
+ MILLET SYSTEMS 131
Introduction 131
Materials and Methods 134
Field Procedures 134
Laboratory Procedures 136
Results and Discussion 137
Percent Organic Matter, IVOMD, Metabolizable Energy,
and Nitrogen 137
Phosphorus, K, Ca and Mg Accumulation 157
Iron, Cu, Mn and Zn Accumulation and Distribution ...... 174
CHAPTER 7. SURVEY OF SULFUR DEFICIENCY IN MAIZE 187
Introduction 187
Materials and Methods 191
Field Methods 191
Laboratory Procedures 193
Results and Discussion 195
Experiment 1 195
Experiment 2 205
CHAPTER 8. SUMMARY AND CONCLUSIONS 220
BIBLIOGRAPHY 223
BIOGRAPHICAL SKETCH 238
v

Abstract of Dissertation Presented to the Graduate School of the
University of Florida in Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy
PRODUCTION ASPECTS OF MAIZE + SORGHUM INTERCROPPING SYSTEMS IN
CENTRAL AMERICA
By
Francisco Roberto Arias Milla
August 1985
Chairman: Raymond Noel Gallaher
Major Department: Agronomy
Farmers in the semi-arid areas of Central America have developed a
maize (Zea mays) + sorghum (Sorghum bicolor (L.) Moench)-animal mixed
production system in response to resource availability and family food
needs. The objectives of this study were to a) describe the maize + sor
ghum system in its bio-physical and socio-economic environment, b) study
the relationship between soil moisture and dry matter accumulation, c)
describe dry matter, energy, and nutrient accumulation by the system,
and d) determine if S deficiency is a widespread problem in areas where
the system is used.
From a situational analysis it was found that marginal soils, ir
regular rainfall pattern, lack of appropriate technology, and limited
resources are characteristics of farms in the areas where the system is
practiced. During a growing season a farmer on a 7 ha farm may invest up
to $200 (US), mainly on fertilizers (70% of the total cash investment)
and $45 (US) on animal feeds.
vi

This research showed that late planting coupled with inadequate
soil moisture resulted in poor growth. Results suggest that grain yield
was more susceptible to water stress than total dry matter yield. The
highest crop growth rate observed (756 kg ha ^day was in maize plants
from the maize + millet system. Striking differences in dry matter
distribution were observed between the photosensitive and non
photosensitive sorghums. At grain harvest, both sorghums had accumu
lated similar amounts of dry matter (14.3 and 14.9 Mg ha \ respective
ly). However, the distribution of the dry matter in the stems, leaves,
and heads of photosensitive sorghum and the non-photosensitive was 46,
37, 17 and 28, 17, and 55%, respectively.
Water stress affected IVOMD and nutrient concentration in all
crops. In the photosensitive sorghum, the stem had higher IVOMD than any
other plant component. In general, nutrient concentration declined with
maturity. However, leaf Ca increased with maturity. An imbalance between
K:Ca, K:Mg, and K:Ca+Mg was observed in maize plants from all systems.
Sulfur deficiency is a widespread problem in some areas of Nic
aragua and Florida. Stunted chlorotic plants observed in both areas were
deficient in S and had a N:S and P:S imbalance. Sulfur deficiency appar
ently caused maize leaves to be deficient in K, resulting in a K:Ca+Mg
imbalance, even though sufficient K was indicated in the whole plant
analysis.
Vll

CHAPTER 1
INTRODUCTION
Historically, increases in production have been brought forth by
increasing the amount of land under cultivation or by increasing unit
yields of existing hectares through improved technology. These
constitute what Sanchez (1976) has called the area and space dimensions,
respectively. Except where limited by soil moisture supply or altitude,
the growing season in tropical latitudes is infinite and multiple
cropping systems have been used for centuries. Most low-income farmers
in the tropics practice cropping systems (i.e. intercropping, relay
and/or sequential cropping) that intensify production not only in space
but also in time.
Intercropping has been an important practice in many parts of the
world, especially in the tropics, and there is little doubt that it will
remain so. It is only recently, however, that research has established
that intercropping can give higher yields than growing sole crops.
Wahua and Miller (1978a) explain why intercropping is popular among
small-scale farmers in tropical and sub-tropical environments. Some of
these reasons are built-in balanced nutritional supply of energy and
protein, profit and resource maximization, efficient water and light
utilization, inexpensive weed control, minimization of agricultural
risks, and improvement of soil fertility. Other authors (Mead and
Willey, 1980) consider that low-income farmers need to grow more than
one crop, whether intercropped or not, to spread labor peaks, to reduce
1

2
marketing risks, and to satisfy different dietary needs. Small-
scale farmers in Central America comprise the most important basic
food production group. They use production systems frequently referred
to as traditional in the literature (Rodriguez et al., 1977; Arias et
al., 1980; Rosales, 1980; Mateo et al., 1981). These systems have been
developed through the interaction of man and his environment, under
conditions involving high risk and restraints which limit crop
productivity.
Several cropping systems can be found in the dry areas of the
Isthmus. Maize (Zea mays L.) intercropped with sorghum (Sorghum bicolor
(L.) Moench) (maize + sorghum) with varying degrees of competition in
time and space, is the most widely practiced cropping system in Central
America (Hawkins et al., 1983; Larios et al., 1983). Other relevant
systems include mono or relay crops of maize, or bean (Phaseolus spp.)
or cowpea (Vigna spp.); sorghum intercropped with bean, sesame (Sesamum
indicum L.); or sisal (Agave spp.) intercropped with maize, sorghum,
and/or bean.
It is accepted (De Wit and Hollman, 1970; Quimby, 1974) that
sorghum was introduced to the western hemisphere by African slaves and
Portuguese sailors in the 16th century. According to Martin (1975) it
was not until the 19th century that sorghum gained importance in the
United States. It has not been documented in the literature when the
system was first used in Central America, but it cannot be more than 350
years ago.
Agricultural research in the tropics has been conditioned by the
cropping systems of more developed areas, the origin of most research
workers, and until recently, rather cursory attention has been paid to

3
indigenous systems. Baker (1979) emphasizes that attempts to improve
production in the tropics have failed not because of farmer conservatism
or the lack of extension programs, but because it has not been realized
that subsistence agriculture is a tropical agro-ecosystem geared for a
low level of production and not simply a collection of crops and
animals to which inputs can be applied indiscriminately to obtain
immediate results.
A lack of appreciation of the personal nature of the subsistence
farmers' farming systems has resulted in a tendency for research to
produce solutions to the wrong problems. For example, agricultural
research in Central America has traditionally been dedicated to export
crops such as banana (Musa spp. ) and coffee (Coffea spp. ), while most of
the available technology for increasing basic food crop productivity has
been adapted from temperate countries and thus has generally been
developed for sole cropping.
Mateo et al. (1981) and Larios et al.(1983) have pointed out that
in spite of the economic importance of the maize + sorghum this system
has received little attention in the work plans of local research
institutions. Reports in the literature (Arias et al., 1980; Mateo et
al., 1981; Fuentes and Salguero, 1983) indicate that of the total area
cultivated with sorghum in Guatemala, El Salvador, and Honduras, the
percentages intercropped with maize are, respectively, 80, 93 and 93.
Larios et al. (1983), concluded that knowledge of the process of
integrating component technologies into farming systems is lacking,
especially for small-scale farms. Due to the lack of available
technology adapted to conditions prevailing in the semi-arid regions of
Central America it is mandatory to conduct field experimentation that

4
will alleviate this deficiency. A summary of the scheme presented by
Arze et al. (1983) to accomplish this task follows:
1. Identify important cropping systems used in the semi-arid
regions of Central America.
2. Study the performance of the cropping patterns under different
environmental variables.
3. Determine the degree and form of relationship among these
variables.
4. Use the previous information to maintain, arrange or re-design
the system so that it operates optimally with respect to its objectives.
Several authors (Rodriguez et al., 1977, Arias et al., 1980; Mateo
et al., 1981; Guzman, 1982; Fuentes and Salguero, 1983; Hawkins et al.,
1983; Larios et al., 1983) have identified environmental stresses
limiting crop productivity in the semi-arid regions of Central America,
their listings including drought, nutrient deficiencies, particularly N,
P and S (CATIE, 1980, 1982a; Rico, 1982; Hawkins et al., 1983), and
water and wind erosion. These areas are primary sources of cereal
grains, oilseed crops, fruits, vegetables, table legumes, meats, and
dairy products for a large majority of the rural and urban population of
the Isthmus. Basic research projects to overcome environmental stress
limitations have been notably successful in many crops and can provide
data for future significant progress with adaptive research.
Maize + sorghum was selected as the subject of this research
project because of its importance in food production. The maize +
sorghum cropping system is predominant in semi-arid areas of Central
America at elevations below 1,000 m. The system apparently increases
the productivity and reduces risk of loss in areas with marginal

5
conditions for maize production. Shallow soils and variability of
rainfall make failure of the maize crop more common than failure of the
sorghum crop, which is of lower value to the farmer for both sale and
consumption.
Present fertilizer use is oriented toward maize production, while
sorghum mostly is dependent on native soil fertility and residual
fertilizers applied to the previous crop. Whether any of the fertilizer
applied to the maize reaches the sorghum will perhaps be clarified by
the present experiments. Presently, few farmers apply any fertilizer to
the sorghum, despite the fact that under climatic constraints in which
they are operating, sorghum or millet has as much or higher yield
potential than maize.
The general objectives of this research were 1) to provide basic
information, 2) to improve traditional cropping systems, 3) to develop
new systems adapted to prevalent bio-physical conditions, and 4) to
apply new discoveries that will increase net family income and that are
appropriate to the economic resources available to farmers of the
semi-arid regions of Central America.
The specific objectives of this study are 1) to describe the maize
+ sorghum system in its bio-physical and socio-economic environment in
Central America, 2) to describe the growth pattern of the maize +
sorghum system and of potential substitutes, 3) to describe the pattern
of energy and nutrient accumulation of the system and of potential
substitutes, 4) to determine if variation of other components of the
system, such as substituting the traditional photo-sensitive sorghum
with improved non-photosensitive cultivars or millet (Pennisetum
americanum (L. ) Leeke), will increase productivity, and fertilizer and

6
water use efficiency; 5) to study the relation between gravimetric
moisture and dry matter accumulation by the maize + sorghum, maize
millet systems; 6) to determine the existence of soil S deficiency
areas where the system is practiced in Nicaragua.
soil
+
in

CHAPTER 2
LITERATURE REVIEW
Growth
Crop Growth Rate
Goldsworthy and Colegrove (1974) found that crop growth rates (CGR)
in maize (Zea mays L.) declined rapidly when grain growth commenced. As
grain growth increased towards a maximum, about 100-110 days after sowing,
CGR decreased to near zero values. There are two possible explanations
for this pattern of change in dry weight. First, it is possible that a
large part of grain dry matter is derived from assimilates which
accumulate in plant parts other than grain and are then translocated to
the grain. Second, if as reported by Allison and Watson (1966) and by
Palmer et al. (1973) the dry matter that fills the grain is derived from
current assimilation, then presumably the large loss in weight from other
parts of the plant, mainly the stem, represents respiration losses that
are not replaced by current assimilation.
The rates of dry-weight production (500 kg ha *week *) per unit leaf
area reported by Goldsworthy and Colegrove (1974) were high at silking.
This, combined with the large leaf areas, accounted for the peak growth
rates observed. The rapid decline in CGR after silking was related to the
simultaneous and rapid decline in leaf area and net assimilation rate.
7

8
Vanderlip and Reeves (1972) have shown that during grain filling
there is a net reduction in stem weight, with grain accumulation occurring
at a greater rate than the rate of total dry matter accumulation.As the
grain approaches physiological maturity the stem again increases in
weight.
Goldsworthy (1970) concluded that a decrease in radiation and a
loss in dry weight from decay and detachment of dead sorghum (Sorghum
bicolor (L. ) Moench) leaves were probably the most important of the
factors that contributed to the decrease in growth rate observed in the
middle of the season. Since net-assimilation rate is also dependent on
leaf area index (LAI), lower leaves were probably making little or no
contribution to dry weight increase at this time. A sharp decline in leaf
area and in net-assimilation rate accounts for the rapid fall in crop
growth rate of the non-photosensitive sorghum after heading, at the end of
September.
Goldsworthy (1970) reported that a large proportion of the increase
in total dry weight of sorghum 'Farafara' (a photosensitive cultivar)
after heading was as dry weight in the stems. During the 3 weeks before
harvest (22-25 weeks after sowing), stems lost weight, and the losses in
weight were similar to the weights gained after head emergence. In
contrast, virtually all of the dry weight increase by 'NK-300' (a
non-photosensitive cultivar) after head emergence was in the heads. In
the first year of his study the weight of stems of the 'NK-3001 reached a
maximum at heading and then remained constant until harvest, whereas in
the second year the stems lost weight before harvest, and it is probable
that, with a smaller supply of assimilate, carbohydrate normally respired

9
in the stem was diverted to the head and that this accounts for the loss
in stem weight in this instance.
Apparent photosynthesis was closely correlated with dry matter
accumulation by the shoots during grain fill. Consequently, the progress
of photosynthate accumulation can probably be viewed as the progress of
dry matter accumulation. Translocation was less inhibited than dry matter
accumulation or apparent photosynthesis under dry conditions. As a
result, grain yield, while significantly inhibited, was probably less
inhibited than it would have been if the translocation of reserves had not
occurred.
Other authors have shown that maize stems often lose dry matter as
the grain matures (Johnson et al.,1966; Daynard et al., 1969; Hume and
Campbell, 1972), particularly when the environment becomes unfavorable
during grain fill. The dry weight appears to be soluble carbohydrates
that can be stored in the stem (Daynard et al., 1969; Hume and Campbell,
1972). This mobilization of stem reserves has not been observed in every
instance (Hanway, 1962a). This agrees with the conclusion by Duncan et
al. (1965 ) that even relatively short-term adjustment by stem reserves may
enable the maintenance of a high rate of grain filling while the
conditions for photosynthesis are temporarily unfavorable. Thus, in maize
stem, mobilization probably occurs when sink demand exceeds source
capacity.
It has been shown that the dry matter stored in the grain of
sorghum (Stickler et al., 1961b; Goldsworthy, 1970), in the grain of maize
(Allison and Watson, 1966), and in rice (Enyi, 1962) is derived mainly
from assimilates produced after head emergence so that grain yield is
directly related to leaf area after the ears emerge. However, McPherson

10
and Boyer (1977) concluded that since grain yield was in excess of the
photosynthesis occurring during grain development, yield must have
reflected the amount of photosynthate accumulated by the crop over a
larger portion of the growing season than the grain filling period alone.
This is generally interpreted to mean (Yoshida, 1972) that dry matter
accumulated by the shoots determines yield.
Factors That Affect Growth
Environmental factors
Maize plants, wherever they are grown, should progress through all
the stages of development described by Hanway (1963). However, the
length of time between the stages and the identifying characteristics may
differ for different hybrids and for different environmental conditions.
Shaw and Thorne (1951) reported that the elapsed time between plant
emergence, stage 0, and silking, stage 5, is variable, and Tyner (1946)
reported that the period from silking to physiological maturity appears to
be relatively constant for different hybrids and different environmental
conditions. The intervals between the intermediate stages of growth
differ for different hybrids and with differences in environmental
conditions, especially temperature and fertilization (Hanway, 1963).
Sivakumar et al. (1979) suggested that plant growth is the result
of an effective integration of many factors. Restriction of growth may
occur due to the limitation of any one factor; for example, water deficits
in plants generally lead to reduced leaf water potentials and stomatal
closure, as manifested from an increased leaf resistance to transpiration.
The effects of depletion and replenishment of soil water on transpiration
are of specific importance to water use and its efficiency in crop
production. The relative rates of absorption and transpiration determine

11
a plant's internal water balance, which directly affects the physiological
and biochemical process of plant growth.
Plant nutrition
Hanway (1962b) indicated that variations in light, moisture, and
many other factors cause fluctuations in the growth rate. The growth rate
of maize under N sufficient conditions was 250 kg ha day while the
growth rate for maize on the extremely N-deficient continuous maize plot
was much less (84 kg ha ^ day ^). The fertility differences did not
markedly alter the relative proportion of each plant part.
Goldsworthy and Colegrove (1974) found production of dry weight
after silking to be related to the amount and duration of leaf area after
silking and to the efficiency of the leaf area. The ratio of grain weight
to leaf-area duration per unit area of land after heading is an index of
the efficiency with which the leaf area present after heading produces dry
matter for the grain (Watson et al., 1963).
Hanway (1962a) observed that extreme N and K deficiencies result in
premature death of several lower leaves. This shortens the period over
which these leaves carry on photosynthesis. In any case, the primary
effect of nutrient deficiencies appears to be on the amount of leaves
produced rather than on the net assimilation rate (rate of increase of dry
weight per unit leaf area).
Data presented by Hanway (1962a) suggested that although N, P, and
K concentration of maize leaves at the beginning and end of the grain
formation period varied markedly, the chemical composition of the leaves
had very little effect upon the rate of photosynthesis in the leaves.
However, extreme N and K deficiencies were observed to result in premature
death of several lower leaves on some of these plants. Nutrient

12
deficiencies are reflected in both leaf area and the chemical composition
of the leaves. The chemical composition of the leaves at silking time can
indicate which nutrient elements are deficient and which deficiencies have
resulted or will result in a reduced leaf area and, thereby, a reduction
in grain yield. These leaf analyses are very valuable diagnostic tools,
but it appears that their interpretation should be based upon their
relation to leaf area and not to net assimilation rate.
According to Nelson (1956) many investigators have found high
positive correlation between the percentages of N, P, and K in maize
leaves at silking time and the yield of grain. Nutrient deficiencies are
reflected in both leaf area and in the chemical composition of the leaves.
Thus, while grain yield is primarily a function of leaf area, leaf area
is a function of the nutrient status of the plant which is reflected in
the chemical composition of the leaves.
Maize under low fertility generally silks later and forms the
black layer earlier, resulting in rather large differences in filling days
and filling degree-days. Peaslee et al. (1971) found that P may tend to
shorten the grain filling period by accelerating the development of the
grain to the maturity stage. This tendency was apparently counteracted by
the tendency of P to also accelerate development to the grain initiation
stage. Earlier silking and lower moisture contents of the grain at
harvest were associated with additions of P fertilizer. However, these
were cases in which the levels of P in the soil were low and plant growth
response to P was marked. Peaslee et al. (1971) concluded that either P
or K was directly responsible for early initiation of the ear and/or delay
of the black layer formation by some specific function or they indirectly

13
influence plant development through the quantity of soluble carbohydrates
present in plants and their transformation into grain.
Drought
Almost every plant process is affected directly or indirectly by
water deficits. Some processes are quite sensitive to water stress, but
others are relatively insensitive. When plants are subjected to water
stress there is a decrease in photosynthesis and cell enlargement. There
is also considerable retention of carbohydrates in photosynthetic tissues.
Although translocation proceeds, its rate is reduced. Translocation is
rarely mentioned as a factor in reduced plant growth under limited
moisture. Translocation could be one of the chief physiological factors
limiting growth under unfavorable moisture conditions.
Shaw (1974) found that experimental maize yields were highly
correlated with a plant moisture stress index which was based on
calculations of daily ratios of actual to potential evapotranspiration for
the period of 40 days before to 45 days after silking. Although soil
moisture strongly interacts with temperature in plant growth processes, it
is much less important in plant phasic development.
Sivakumar and Shaw (1978) reported that the major components of
sorghum yield which were significantly affected by drought in the case of
the nonirrigated plots were tertiary branches per secondaries, seed number
per panicle, and seed size. The reduction in these components was 46, 26,
and 28%, respectively. Data presented in this study bring out the
importance of the availability of a few additional cm of water to a
sorghum crop under water stress and the benefits that should accrue from
such water applications.

14
The depressive effect of water stress on photosynthate
translocation reported by Brevedan and Hodges (1973) is in agreement with
the observation of several other authors (Hartt, 1969; Plaut and Reinhold,
1965; Wardlaw, 1967). Wardlaw (1967) found a continued movement of
assimilates from the leaf to the developing wheat (Triticum aestivum L.)
grain under water stress conditions. He also observed a lower velocity of
sugar transport from leaves of stressed plants than from well-watered
plants.
Data presented by Denmead and Shaw (1960) suggested that lower
assimilation in plants subjected to stress is partly due to smaller leaf
area, as indicated by the size of the ear leaf, and partly due to the
metabolic activity of the plants at different growth stages. When
compared with the reduction in assimilation caused by stress at other
growth stages, the reduction in assimilation resulting from stress at
silking is larger than the reduction in leaf area could indicate. The
data also suggested that there may be a tendency for recurring periods of
stress to have less and less detrimental effect on assimilation and yield.
Stress applied while the plant is actively expanding retards enlargement
of plant parts. Recovery when the stress is removed is not immediate but
growth rate appears to return to normal after a few days.
McPherson and Boyer (1977) reported that the physiological
mechanisms responsible for yield losses under dry conditions are unknown,
especially for grain crops. Drought causes massive losses in the yield of
crops, but the physiological mechanisms responsible for decreased yields
are poorly understood. Most aspects of the physiological behavior of
plants are known to be altered by the onset of dry conditions (Boyer,
1973; Hsiao, 1973). But photosynthesis and translocation, which are

15
important in grain crops, are especially sensitive (Hsiao, 1973; Boyer and
McPherson, 1975; Boyer 1976).
It is generally accepted that optimized grain filling requires
continued dry matter production and translocation of the product to the
grain. However, Brevedan and Hodges (1973) concluded that translocation
was more sensitive than photosynthesis to drought. Wardlaw (1967) studied
desiccated wheat during the grain filling stage and found that movement of
assimilates into conducting tissue was delayed in wilted leaves, but the
velocity of translocation was relatively unaffected.
Barlow and Boersma (1976) found that the partitioning of the total
dry matter into grain was affected by desiccation. In the controls, the
grain dry matter was only 63 to 76% of the total dry matter accumulated by
the shoots during grain fill. In the desiccated plants, however, grain
dry matter was 50% larger than the total dry matter accumulated during
grain fill. Thus, in the desiccated plants, grain development must have
occurred at the expense of dry matter stored in other parts of the plants.
Jurgens et al. (1978) concluded that while grain fill was seriously
inhibited by desiccation (grain yield was reduced to 42% of the control),
it was clearly maintained above that expected from dry matter accumulation
during the grain filling period. This occurred because translocation to
the grain continued at a modest rate even when there was no net
accumulation of photosynthetic material by the desiccated plants. Thus,
under field conditions photosynthesis was more affected than translocation
during desiccation. It appears that grain crops having the opportunity to
accumulate reserves under favorable moisture conditions are able to
preserve grain development if conditions later become unfavorable.

16
Assimilation after ear emergence, both in the leaves and in the ear
itself, is primarly responsible for accumulation of material in the grain.
Early stress, then, has an indirect effect on yield of grain through
reducing the size of the assimilatory surface at the time of ear
development. Stress imposed after the ear has emerged has a more direct
effect through reducing assimilation in this critical period when daily
assimilation rates are high and most of the assimilates are being used for
grain production. The relatively small effect of stress during the ear
stage suggests that the critical period would not extend longer than about
3 weeks after 75% silking.
Jurgens et al. (1978) found that the induction of low leaf water
potentials in desiccated plants caused an almost immediate decrease in
viable LAI. At maturity it was evident that the prolonged drought
treatment had markedly affected grain components. Yield, kernel weight,
and percent oil were all substantially reduced by desiccation while
percent protein increased. Grain production was relatively closely tied
to the total dry matter production for the season. In the controls grain
production was 51% the total dry matter production, and in desiccated
plants it was 39%. The desiccated plants produced less dry matter and
exhibited a slower gain in grain dry weight than the controls.
Reddy and Willey (1981) reported that the total water use
(i.e.transpiration plus evaporation from the soil surface) by sole millet
and sole groundnut over their full growing periods were 30.3 and 36.8 cm,
respectively. The total water use of 40.6 cm by the intercrop was greater
than either sole crop but it was 11% less than the total water use
expected if each component had used water at its sole crop efficiency.
Thus, the 28% higher dry matter yield of the intercrop could only be

17
partly explained on the basis of greater total water use and it must have
been partly due to an increase in total water use efficiency.
In an irrigation study Sivakumar et al. (1979) found that the
non-irrigated sorghum crop used 213 mm of water to produce 510 kg ha ^ of
dry matter, whereas, the irrigated sorghum used 321 mm of water to produce
930 kg ha ^ of dry matter. Szeicz et al. (1973) observed that average
sorghum crops in Texas use approximately 320 mm of water throughout the
growing season to produce around 0.8 kg dry matter m
Leaf Area Index
Dale et al. (1980) reported that growth and duration of green leaf
area of a crop determine the percentage of incident solar radiation
intercepted by the crop canopy and thereby influence canopy
photosynthesis, evapotranspiration, and final yields. Leaf area index is
defined as the ratio of the area of one side of the green leaves of a
plant to the area of soil surface allocated to the plant.
Shih et al. (1981) reported that LAI is often used as an indicator
of plant growth and for evaluating assimilation and transpiration rates in
plant physiological studies. This growth parameter is also frequently
used in agronomic studies to model yield and to make crop production
decisions. Ashley et al. (1965) found good correlation between LAI and
leaf dry weight of cotton (Gossypium hirsutum L.). Rhoads and Bloodworth
(1964) and Pearce et al. (1965) also found strong correlations between
leaf area and dry matter yield in cotton and orchard grass (Dactylis
glomerata L.).
According to Hanway (1963), the genetic characteristics of the
plant, day length and various environmental conditions prior to stage 1 of
growth, have determined the number of leaves that will develop on maize

18
plants. He also observed that except under very carefully controlled
conditions in fields or in experimental plots there will be differences in
growth between different plants that have received the same treatment.
The number of leaves per plant on plants of the same hybrid grown in the
same plot varied between 15 and 22 leaves per plant. All plants in a
given plot will develop at the same rate, so not all plants in a plot are
at the same stage of development at the same time (Hanway, 1963).
Hanway (1962a) suggested that the dry weight of the entire plant
and of the grain are directly related to and highly correlated with the
weights of the leaves in these plants. Since leaf growth in maize is
completed relatively early in the season, the linear rate of dry matter
accumulation over a major part of the growing season appears reasonable,
unless the net assimilation rate decreases with age of the leaves or
decreases with the seasonal trend in climatic conditions.
Hanway's (1962a) study of maize growth as related to soil fertility
showed that approximately 30% of the total leaf weight had been produced
45 days after planting and that during the following two weeks leaf growth
was very rapid and by 60 days after planting over 85% of the final leaf
weight had been produced. This would appear to be a critical stage in
leaf development when nutrient deficiencies might reduce the final weight
of leaves. Most of the grain was produced in a 30 to 35 day period. This
growth pattern was similar for plants from all the fertility levels except
that the silking and subsequent growth of the cob, shank, and grain was
delayed slightly in the N-deficient plants from the continuous maize plot.
Shih et al. (1981) reported that leaf area per stalk declined after
stalk length reached about 185 cm. This is consistent with the general

19
pattern of leaf area in sweet sorghum which starts declining after the
plant approaches 50% bloom.
Dry Matter Accumulation
Hanway (1962a) reported that the potential yield of maize grain
which is produced late in the season is determined by the leaf area, which
is always produced early in the season. However, less than this potential
yield of grain will actually be attained if a) the net assimilation rate
is decreased by any factor such as a moisture deficiency later in the
season or b) the leaf area is prematurely reduced by some factor that
results in premature death of leaves such as a nutrient deficiency or
insect, disease, or hail damage. If no other factor limits yield, one
would expect that increasing LAI should result in increased grain yield.
Data reported by Tollenaar and Daynard (1978) showed that grain
yield per plant was most affected by shading during the silking period,
indicating a sink limitation for grain yield in hot environments. A
source limitation in short-season regions may be the consequence of low
leaf area per plant.
Hanway and Russell (1969) reported relatively large differences
among maize hybrids in the length of the grain filling period. Daynard
and Duncan (1969) have observed such differences among hybrids and have
found a high correlation between the length of the grain filling period
and the yield.
The patterns of growth and dry matter distribution observed in
tropical cultivars grown in Mexico (Goldsworthy and Colegrove, 1974)
suggest that the capacity of the grain sink to accomodate assimilate can
limit grain production. Results of defoliation studies in Rhodesia
(Allison and Watson, 1966), which showed that a relatively large amount of

20
dry matter which could be translocated to the grain normally remains in
the stem, also indicate a sink limitation. Conversely, the decrease in
stem weight in the latter part of the grain-filling period, observed by
Daynard et al. (1969), seems to indicate that source may be limiting under
the environmental conditions prevailing in the northern periphery of the
maize-growing area of North America.
McPherson and Boyer (1977) pointed out that another potentially
more serious problem occurs if sink size has been affected by low leaf
water potential. If, for example, crop desiccation occurred during floral
development or pollination, irreversible loss of floral primordia (Moss
and Downey, 1971) or unsuccesful pollination could result. Thus, grain
yield would be limited more by the availability of developing grain than
by the availability of photosynthate (Denmead and Shaw, 1960; Classen and
Shaw, 1970), and prediction of yield based on photosynthesis would be in
error. Such a limitation would be less important where maize is grown for
silage, because shoot dry weight would reflect photosynthesis directly.
Moss (1962) and Allison and Watson (1966) have shown that when the
grain sink is missing, dry matter that would have passed to the grain
accumulates in the stem and husk. The presence of more barren plants
(Goldsworthy et al., 1974) probably explains why more dry weight
accumulated in the stems at Poza Rica than at Tlaltizapan, Mexico. It
would also account for the differences in the values for grain at the two
sites, since barren plants contribute to dry matter but not to grain
yield.
Goldsworthy et al. (1974) reported that dry weight also accumulated
in the stem of fertile plants and that the capacity of the ear to
accommodate the photosynthate produced was a further factor limiting

21
yield. Allison and Watson (1966) have shown that when the grain sink is
removed by preventing pollination the dry matter that would have passed to
the grain accumulates in the stover and that when the source of assimilate
is restricted by removing leaves, stem weight decreases as previously
stored dry matter moves to the grain.
Shih et al. (1981) found that the ratios between dry and fresh
phytomass were computed as 21.4, 35.1 and 35.4% for stalk, leaf, and
panicle, respectively. The ratios for leaves and panicles are similar,
but the ratio for stalks is lower. These ratios can be used to estimate
the dry weight yield based on the known fresh biomass, or vice versa.
Hanway (1962a) found that differences in soil fertility resulted in
different rates of dry matter accumulation but did not markedly influence
the relative proportions of the different parts. He reported crop growth
rates of maize of 250 kg ha ^ day ^ in N-sufficient plots. Hanway and
Russell (1969) found that the leaves, leaf sheaths, stalks, and husks of
maize attained their final mature weights at about stages 4.0, 4.5, 5.0,
and 5.5, respectively. All these plant parts continued to increase in
weight following these stages of development, but this continued increase
in weight was apparently an accumulation of materials which were later
translocated into the developing grain. At stage 6.5 the total
accumulated material in these plant parts was equivalent to about 20% of
the total mature dry weight of the nongrain parts of the plants. The cob
and ear shank attained their maximum dry weight at about stage 6.5 and
showed no later decrease in weight. An average of 42% of the total,
mature dry weights of the plants was grain and 58% was nongrain. However,
the relative proportions of grain and nongrain varied widely among the
different hybrids, years, and plant populations, with the grain varying

22
from 35 Co 52% of the total plant weight. The rate of dry matter
accumulation in the grain was similar for all hybrids, years, and plant
populations varying from 163 to 181 kg ha ^day
Vanderlip and Arkin (1977) reported that on a daily basis, dry
matter in sorghum was allowed to be partitioned to the leaves up to 125%
of that neccesary for the leaf area developed that day. The same authors
found that at least 25% of the daily dry matter production was
partitioned to the roots, which under conditions of low photosynthate
production would cause an increase in specific leaf area.
Barlow and Boersma (1976) demonstrated that even grain dry matter
was only 63 to 76% of the total dry matter accumulated by the shoots
during grain fill. In the desiccated plants, however, grain dry matter
was 50% larger than the total dry matter accumulated and was accompanied
by a reduction in net photosynthate accumulation in the source leaf.
Goldsworthy (1970) reported that photosensitive sorghums sown at
the end of May formed from two to three times as much dry weight as 'NK
300' non-photosensitive which was sown 10 weeks later. The photosensitive
sorghum 'Farafara' had the largest total dry weight but the smallest
grain yield. About 70% of the total dry weight was in the stems and only
from 9 to 13% in the heads. In contrast, the dry weight of 'NK 300' was
only about one-third or one-half that of 'Farafara' but from 40 to 60% of
it was in the heads so that the grain yields were much larger than those
of 'Farafara'.
The reason, it seems, for the low grain yield of photosensitive
sorghum is that a substantial part of the assimilate formed after heading
accumulates in the stem, whereas most all of the dry matter produced
after heading in non-photosensitive moves to the head. The results of

23
these and of other experiments at Samaru suggest that the main reason for
the difference in yield between the photosensitive sorghum and
non-photosensitive sorghum is in the number of spikelets present at head
emergence; the number and/or potential size of the developing grains in
the photosensitive sorghum appears to be too small. Thus the dry weight
of the non-photosensitive sorghum 1NK 300' was much smaller than that of
the other sorghums mainly because of the inability of the head to accept
all the carbohydrate that the leaves can produce.
Goldsworthy (1970) observed that the heads of non-photosensitive
sorghum continued to gain weight 13 weeks before harvest, but those of
photosensitive sorghum did not and it is more probable that the loss in
weight from the stem was by respiration of labile carbohydrate that had
accumulated there. It may be that the developing head does not receive
the assimilate it needs before emergence and that it is unable to
accommodate all of the increased supply of assimilate from the leaves
after it emerges .
Blum (1970) concluded that when sorghum plants compete for water
the effect of competition on a photosensitive genotype is more severe
than on a non-photosensitive genotype, and that the highest yield is
obtained with an early maturing hybrid planted at relatively high plant
densities. Yielding potential was in direct relationship to duration of
growth under non-competitive conditions and in an inverse relationship
under extreme competition. This indicates that the importance ascribed to
a long duration of growth of cereals with respect to their yield
potentials does not hold under limited water supply. Blum (1970)
concluded that of his experiments demonstrated the superiority of an

24
early maturing hybrid under extreme plant competition for water is due,
at least partly, to advanced plant suppression by interplant competition.
Forage Quality
Many factors combine to determine the relative feeding value of
sorghum grain. Some of these are differences in tannin content, protein
content, amino acid composition, amount of floury and horny endosperm,
presence or absence of yellow endosperm, whether mixed with grain of
other species, whether processed in one or a number of ways such as
cooking, flaking, and/or steam rolling, whether weathered in the field
before being harvested, amount of damage of insects, presence of
aflatoxins or other molds, amount of rancidity of the oil, degree of
glume and other trash removal, presence of contaminants, and, most
important of all, degree of milling and type of animal to which it is to
be fed. Data presented by Hall et al. (1965) indicate that sorghum grain
is comparable to maize in digestibility of proximate components,
digestible energy, metabolizable energy, and nitrogen retention.
Eng et al. (1965) reported results which indicate wide variations
in the compositions and feeding values of sorghum grains. It appears that
such variations may be caused by geographical area, soil moisture, soil
fertility and variety of plants and might be important considerations in
the apparently divergent results which have been obtained by various
research workers when sorghum grain was compared to maize as an energy
source for fattening cattle. Further research work in this area is
needed.
Clark et al. (1965) found little difference in the carrying
capacity, milk production, or dry matter production of pearl millet and a

25
sorghum x sudangrass (Sorghum sudanense L. ) hybrid when utilized as
pasture for lactating dairy cows. Johnson et al. (1966) studying changes
in dry matter and protein distribution in maize found that the protein
concentration of leaves declined rapidly and steadily until the final
mature stage. The protein concentration of the stalks was between 11 and
12% prior to tasseling, declined rapidly until 15 days after tasseling,
and declined only slightly throughout the remainder of ear growth and
maturation.
Johnson et al. (1966) observed that percent ash, cellulose and
crude protein were significantly decreased with increasing maturity.
Digestibility of dry matter and organic matter was significantly affected
by maturity, increasing to maximum at the dough-dent stage and decreasing
slightly thereafter. Dry matter digestibility was 68% at the earliest
maturity stage. Increasing maturity significantly decreased digestibility
of cellulose and protein throughout the harvest period.
Rendig and Broadbent (1979) observed that concentration of crude
protein ranged from about 6% in maize grain from plots that received no
added N or 90 kg N ha ^ to nearly 10% in plots receiving 180 kg ha The
concentrations in the grain protein of triptophane, lysine, glycine,
arginine, and threonine were decreased, and the concentrations of
analine, phenylalanine, tyrosine, glutamic acid, and leucine increased by
applications of N.
Schmid et al. (1975) observed that cell walls of maize cultivars
were considerably more digestible than those of the sorghum cultivars.
These results indicated that low cell wall digestibility was a major
factor limiting dry matter digestibility of sorghum silages. The same
authors reported that head IVDMD of short sorghum hybrids with high grain

26
ratios remained constant or increased with advancing maturity, while that
of the tall hybrids with lower grain ratios decreased with maturity. Stem
IVDMD of the tallest hybrids increased with maturity while the other
hybrids decreased with maturity.
Although maturity is a factor affecting sorghum silage nutritive
value, its influence varies depending on forage type in that a decline in
cellulose digestibility with maturity may be detrimental to total
digestibility of low-grain sorghums, but not for those with high-grain
content. Apparently, the rapid increase in the amount of a highly
digestible starch during maturation in the high-grain sorghums
compensates for the decline in cellulose digestion (Schmid et al., 1975).
Cummins (1970) in a two-year study observed that in general the in
vitro dry matter digestibility (IVDMD) of maize leaves decreased with
maturity, although some year-to-year variation occurred. The IVDMD was
2
negatively correlated with maturity (R =0.67 and 0.88, respectively).
Both IVDMD and carbohydrate content of the stalks were closely related to
the rainfall distribution during the maturity period.
Johnson and McClure (1966) found highest total dry matter yield per
hectare to be between the dent and glaze stage of kernel development.
Although ears constituted 60% of the dry matter of the mature maize
plant, they did not reach this proportion until the dent stage of
development. IVDMD of maize stem cellulose was quite constant during ear
development but digestibility of leaf cellulose declined steadily. The
soluble carbohydrate in maize stem tissue increased rapidly from
tasseling to a maximum in late August (milk stage) and thereafter
declined with maturity. Crude protein content declined steadily in maize
leaves but changed very little in maize stalks from milk stage to final

27
maturity (Johnson et al., 1966). Protein content in the whole plant
declined slowly during ear maturation.
The IVDMD for the stover silage reported by Colenbrander et al.
(1971) ranged from 41 to 50%. Results from this experiment indicated that
a low quality roughage such as maize stover silage can provide an
alternative source of nutrients for growing dairy heifers. Green (1973),
studying the yield and digestibility of bird-resistant grain sorghum,
observed that IVDMD varied from 79.8 to 50.5%. All of the NBR varieties
had higher values. The correlation coefficient calculated to ascertain
the relationship between yield and IVDMD for the 41 varieties was low
(r=+0.52) and not significant, indicating they were not related. Schmid
et al. (1975 ) reported that IVDMD values at the 4-week growth stage
ranged from 71.7 to 84.2% for five brown midrib sorghum mutants compared
to 67.1 to 78.3% for their normal counterparts.
Crop Residues
Plant populations, row-spacings, and soil fertility affect not only
grain yields, but also the yields and quality of residues. Residue yields
from maize are normally greater than from grain sorghum but lower in
crude protein. Crude protein concentration of grain sorghum residues was
consistently higher than that of maize while IVDMD values were
consistently lower in grain sorghum.
Crop residues of grain sorghum and maize have attracted attention
as an alternate economical forage resource for livestock utilization.
There are few data available on agronomic production factors affecting
yield and quality of crop residues (Perry and Olson, 1975).
Perry and Olson (1975), studying the effects of N fertilization on
yield and quality of maize and sorghum residues, observed that grain N

28
concentration increased with N fertilization in both crops. Grain sorghum
N concentration was generally equal to or greater than that of maize.
Residue yields of both crops were increased significantly by 90 kg ha *
with no further increase at the higher N rate. Maize grain:stover ratios
increased with increasing N levels. Crude protein of grain sorghum
residues was consistently higher than that of maize while IVDMD values
were consistently lower in grain sorghum. Crude protein increased
significantly in grain sorghum residue with each increasing N level while
little increase occurred in maize.
Martin and Wed in (1974) reported that row-crop residues, although
present in great quantities in the midwestern United States, are often
considered to be of low quality. Consequently, grain sorghum stover on
millions of hectares is not utilized by livestock. Stover often remains
as a leafy, succulent, growing plant following grain harvest and should
be considered as a feed source for ruminants being maintained for
reproductive purposes.
Under Iowa conditions (Perry and Olson, 1975) grain sorghum
continues growth during the interval between grain harvest and killing
frost. This unique characteristic allows the ratoon crop to maintain and
perhaps improve its nutritional composition before utilization for winter
grazing or silage harvest. Burns et al. (1970) postulated that forage
sorghum produces photosynthate after maturation of seeds and until frost
and accumulates a reservoir of water-soluble carbohydrates in the pith of
the stalks.
Perry and Olson (1975) observed that maize dry matter yields
decline as much as 30% within 100 days of harvest. Any decline in crude
protein and digestibility following grain harvest of maize and grain

29
sorghum appears to be associated with environmental factors. Martin and
Wedin (1974) observed that grain sorghum stover lost 28.3% of its
original dry matter yield by 76 days after grain harvest. The leaves lost
dry matter more rapidly.
Any consideration of grain sorghum stover as a feed for ruminants
is dependent on meeting all or some of the animal's nutrient
requirements. For example, a 500-kg, dry pregnant beef cow consuming 7.6
kg of dry matter requires 5.9% crude protein and 50.0% total digestible
nutrients.
Using percentage IVDMD as roughly equivalent to percent TDN, data
presented by Perry and Olson (1975) indicate that IVDMD in stover before
frost is ample to maintain a pregnant beef cow or other ruminants.
Grazing grain sorghum stover must be reconciled with the high prussic
acid potential in sorghum species.
Energy
Net energy has become widely accepted in recent years for
expressing the value of a ration and the energy requirements for feedlot
cattle (Croka and Wagner, 1975). The energy value of livestock feeds can
be expressed as digestible or metabolizable energy or as the cultural
energy necessary to produce the feed. Livestock feeds are priced
essentially on their digestible energy content, except for high protein
feeds which are fed in supplemental amounts.
Energy reserves may be considered as organic accumulates
synthesized by the plant which are available for plant growth,
development and metabolism (Matches, 1969). Although soluble
carbohydrates are found throughout grass plants, their concentrations are
usually greater in the stubble than in the roots or leaves. Much of the

30
fructosan in grasses is accumulated in the first internode of the stem.
Within the stubble there may be a gradation in concentration of
carbohydrate reserves. In bromegrass (Bromus sp.) and timothy (Phleus
pratense) at anthesis concentrations of fructosans and total water-
soluble carbohydrates were greatest in the internode, leaf blade, and
sheath tissue closest to the stem base.
Bolsen et al. (1975) observed that sorghum stover and maize stalks
are energy-containing by-products of grain production. Both crop
residues make acceptable silage and both supply the energy needed in
maintenance rations for beef cows or ewes. Maize stalk silage can be
used in rations for growing dairy heifers if additional energy is
provided (Colenbrander et al., 1971).
On an energy basis, maize silage is especially valuable for milk
production. It has been reported that the energy value of maize silage
was closely related to total grain yield and proportion of ears to
stalks (Bryant et al., 1966). Sorghum has become increasingly important
in recent years as an energy source in high concentrate rations for
feedlot cattle in the southwest (Croka and Wagner, 1975b).
Crop residues have potential as fertilizer, as fuel, and as
livestock feed. Comparative values for these uses can be determined on
the basis of the amount of energy saved by substituting these materials
for conventional sources of feed, fertilizer, or fuel.
Goodrich et al. (1975) found that energy losses during the
ensiling process average 68% of dry matter losses, apparently because of
the loss of volatile energy-containing compounds during drying, which
inflated the dry matter loss values. Also, decarboxylation reactions
would result in greater losses of dry matter than energy. Energy losses

31
increased from 21.5 to 33.1%. The energy loss for maize ensiled at
33.1% moisture was greater (p=0.05) than that for maize ensiled at 21.5%
moisture. Energy loss was not significantly influenced by kernel
preparation (3.0 and 2.5% energy loss for whole kernel and rolled maize)
or by time of ensiling (2.9 and 2.6% energy loss for maize ensiled at
harvest and maize ensiled after drying and reconstitution).
Nutrition
Critical Levels
According to Bates (1970) the diagnosis of nutrient deficiencies
and the prediction of fertilizer requirements from plant analysis are
based on a critical concentration of a nutrient or nutrient fraction
within the plant or some plant part, below which growth or crop yield is
restricted.
In early studies by Macy (1936) the nutrient calibration curve
included the zones of minimum percentage, poverty adjustment, and luxury
consumption. He proposed a central concept stating that there is a
critical percentage of each nutrient in each kind of plant above which
there is luxury consumption and below which there is a poverty adjust
ment which is almost proportional to the deficiency until a minimum
percentage is reached.
Ulrich (1952) defined critical nutrient concentration with respect
to plant growth in terms of 1) that which is just deficient for maximum
growth, 2) that which is just adequate for maximum growth, and 3) that
which separates the deficiency from the adequacy zones.

32
Factors That Affect Concentration
Bates (1970) reported that, next to the supply of elements, the
physiological age of tissue is probably the most important factor
affecting the mineral composition of a given species. There appears to
be general agreement with this statement. He further observed that the
pattern of nutrient content varies with the age of the species and with
the nutrient. Phosphorus concentration in a maize plant decreases with
age. This change in nutrient concentration with age is probably due to
both a changing nutrient content of a given tissue with age, the leaves
for example, and changing proportions of certain tissues with age, such
as an increasing proportion of stem and a decreasing proportion of leaf
tissue. Physiological age was particularly important for Ca and other
nutrients which are not readily translocated in the phloem. The
nutrient concentrations in plant samples can therefore be interpreted
only if the growth stage at sampling is defined.
Environmental and soil factors also influence the availability of
P and K and thus crop response to applied P and K. Volumetric water
content, soil bulk density, buffering capacity, concentration, counter
diffusing ions, and soil chemical reactions are important in determining
the amount of P and K that reach the root. These factors indicate
greater yield response to P and K applications in drier years. When
rates of K were split with application of P the response was dependent
on weather conditions (Reneau et al., 1983).
According to Bates (1970) although the concentration of nutrients
in plant tissue chosen to provide a constant physiological age changes
with the age of the plant, there is some question whether the critical
concentration changes with the age of the plant. It is commonly

33
accepted that critical concentrations vary from species to species
although it has been suggested that this may not be so for all
nutrients.
Nutrient Accumulation
Jacques et al. (1975) suggested that nutrient uptake precede dry
matter production because the nutrients are required for growth and dry
matter accumulation. More than half of the total nutrient uptake occurs
before maximum vegetative dry matter was produced. Nutrient
concentrations varied among sorghum plant parts and changed throughout
growth. Concentrations in most vegetative plant parts were highest
right after emergence, decreased until maximum vegetative dry weight had
been produced, and changed little, if at all, while grain developed.
Lockman (1972b), studying the mineral composition of sorghum,
found that N levels in plant samples were well correlated with yields at
all growth stages and in both years (1968-69). Dry weather during the
first year of his experiment decreased N levels slightly relative to the
normal moisture data from the same plots in the second year. Results
are quite convincing that the critical level for N will not drop below
3.0% even at late stages of growth.
Lockman (1972b) observed that P levels also were well correlated
with grain yields at all stages and in both years. Dry weather caused
higher P levels, which are considered to be simple accumulation effects
with less growth. Data presented by Lockman (1972b) indicated that K
levels were correlated with grain yield in only the seedling and
vegetative samples; K levels in grain sorghum plant samples decreased
almost linearly with age. Dry weather appreciably decreased relative K
levels in seedling samples in one year.

34
Lockman (1972b) reported that Ca levels were only moderately
correlated with yield, generally in a negative manner. Dry weather
samples had lower Ca levels at the seedling stage; however, Ca
accumulated in the later samples. Levels in grain sorghum were poorly
correlated with yield. Dry weather appeared to cause higher Mg levels
in late season samples.
Copper levels were not well correlated with yields. Higher Cu
levels were noted with later samples in the dry year. Iron levels in
grain sorghum samples generally were not well correlated with yield.
Whole-plant sample analyses indicate that the Fe:Mn ratio has to be
considered to accurately define Fe deficiency. Fe levels in bloom and
fruiting stage third-leaf samples were higher in a dry year in field
samples. Mn accumulated to relatively higher levels in the later
samples of the dry year. Zinc levels in grain sorghum plant samples
showed curvilinear correlation with grain yield. At low yield levels
the correlation was positive, but as yields increased beyond category,
the correlation became negative (Lockman, 1972b).
In their study of the efficiency of maize hybrids, Gallaher and
Jellum (1976) found that Mg deficiency in maize is a major problem in
many parts of the world because of widespread soil Mg deficiency.
Concentrations of K, Ca, and Mg in leaf tissue appeared to be positively
related to soil test.
Bates (1970) suggested that severe deficiency destroys the
potential for growth so that the plants stop growing completely but
continue to accumulate Zn. Plants usually resume growth when a nutrient
deficiency is corrected, but it is possible that a degree of deficiency
can be reached beyond which they are completely unable to recover.

35
From studies conducted to estimate the uptake of N, P, K, Ca, and
Mg by maize and grain sorghum harvested for silage Fribourg (1974)
concluded that the amounts contained in above-ground plant parts exhibit
considerable range: 34 to 220 kg ha ^ of S; 8 to 34 of P; 31 to 271 of
K; 8 to 55 of Ca; and 9 to 45 kg ha ^ of Mg. This large range is not
unexpected, due to soil drainage and fertility.
According to Sayre (1948) the grain does not accumulate much K.
The maximum rate of accumulation and the time when the maximum amount
occurs in the leaves and stems is earlier than for N and P. There is a
small but consistent increase in the amount of K in the grain and a
rather marked loss from the other plant tissues, especially the stem.
Voss et al. (1970), studying factors that affect nutrient
concentration in maize, found that under nearly all combinations of
conditions the N:P ratio for these nutrient concentrations remained
nearly 10:1. Within the actual data for the individual plots, ratios
greater than this were observed, but there were few ratios smaller than
this, even under conditions of high applied and/or indigenous P and low
N levels. Thus, definite levels for leaf N and P at which maximum
predicted yields occurred could not be defined, but rather they varied
with soil. The authors concluded that nutrient levels of approxiamately
2.9% N and 0.28% P were predicted for 95% of maximum yields.
The maximum rate of P accumulation occurred at the same period as
nitrogen, but the total amount per plant continued to increase as long
as the plants were sampled. This shows that the plant continued to
absorb P from the soil all during the season, since the loss which
occurred from the leaves, stem, husks, and cob did not account for the
quantity which moved into the grain (Sayre, 1948). These data differ

36
from those of the other two elements in several ways. He also suggested
that N accumulation in the maize plant reached a maximum at silking time
and ceased about four weeks later in the season studied. Nitrogen
continued to move into the grain from other tissues until maturity.
There was an actual loss of potassium after that time, largely from the
leaves and stems of the plant. No marked accumulation of potassium
occurred in the grain.
Reneau et al. (1983) pointed out that interactions between P and K
(P:K) are vital information for obtaining maximum yields. The
literature in this area shows that limited progress had been made with
P:K so that viable interactions could not be proposed. They reported
that the concentrations of N, P, K, Ca, and Mg in forage sorghum were
influenced by either P or K application or both. Nitrogen, P, Ca, and
Mg concentrations were increased and K was decreased with P application.
Nitrogen, Ca, and Mg were decreased and K increased with increased K
application. This antagonistic effect of K on Ca and Mg uptake by
monocots is well documented (DeWit et al., 1963). Bar-Yosef (1971)
demonstrated that higher P concentration in solution would increase Ca
uptake. Conversely, Greenwood and Hallsworth (1960), with intact root
systems, reported no direct effect of P on Ca uptake and further
reported more severe deficiencies with high P levels. Although limited
data is available on the effect of P on Mg uptake, Truog et al. (1947)
reported a synergistic relationship between Mg and P in plants.
Several secondary reactions are shown by the data presented by
Lockman (1972a): decreased Mg with N deficiency; increased Zn with P
deficiency; Ca and Mg accumulation with K deficiency; increased P, Mn,
and Ca but less K with S deficiency; increased P with low Cu; increased

37
Mn, N, P, and A1 with Fe deficiency; and N, P, and K accumulation with
Mn or Zn deficiency.
Average mineral composition of grain sorghum plant samples
reported by Lockman (1972a) was consistently affected by soil fertility
factors. Bloom and fruiting stage samples continued to reflect
fertilization practices for N and P, but not for K. The levels of Mg,
Fe, Mn, and Al were also affected by N-P-K fertilizers. Magnesium
levels were decreased in vegetative and later samples, which is likely
an antagonistic effect caused by K additions. Mn levels were increased
during the same periods, probably an effect of fertilizer acidity. Fe
and Al levels in seedling samples were higher without N-P-K fertilizers.
Limited nutrient criteria have been reported for grain sorghums.
Lockman (1972a) reported that in 1966, values of 1.90 to 2.37% N were
intermediate levels for second-leaf, bloom-stage grain sorghum samples.
Values of 1.60 to 1.76% N are cited as low, and a value of 1.57% N is
cited as deficient. Normal N level is 2.48% N for 42 day seedling
plants, with a value of 1.64% N being low for whole-plant N level. He
listed 10 mg kg Zn as being an intermediate level for second-leaf,
bloom-stage sorghum samples. Intermediate levels of boron were listed
as 16 to 138 mg kg in a mature leaf sample.
Locke et al. (1964), cited by Lockman (1972a) suggest that
critical levels for bloom-stage grain sorghum leaves are about 2% N and
between 0.17 and 0.21% P. He noted that 1.7% K is adequate, since no K
fertilizer responses were obtained with this level of K in bloom-stage
leaves .
Results presented by Lockman (1972a) indicate that seasons
appreciably affect nutrient levels in grain sorghums but not always in

38
the same manner and degree as in maize samples. The dry year, 1967,
caused increased P, Ca, Mn, Mg, Cu, Fe, and A1 levels in grain sorghum
third-leaves, perhaps from lack of growth dilution. However, maize in
the dry year had reduced levels of N and K and increased levels of P,
Cu, Fe, and Mn in the ear-leaf samples. In a dry year maize did contain
less N than sorghum. With better moisture, maize leaves contained as
much N as the sorghum or more.
Comparisons of nutrient levels in sorghum and maize presented by
Bennett (1971) showed that N and P were generally higher in the grain
sorghum, whereas Ca and Mg were generally higher in the maize. There
were no consistent differences in the K content of the two crops. Baker
et al. (1970) reported growth response of maize hybrids to different
levels of P in the soil. In addition to showing more rapid growth,
hybrid 1 removed more P from the tagged band, contained more dry matter
after 29 days, but was not different from the other hybrids with respect
to grain sorghum in the Kansas survey but higher in maize in this study.
According to Jones and Wild (1975) P deficiency occurs widely in
the savanna zone. Kang and Osiname (1979) reported that crop responses
have been obtained with small P applications in the range of 4 to 10 kg
P ha In the forest zone the main response is to N application and
less to P application. This is contrary to the long-held belief that P
is the major problem in most tropical soils. The lesser P response may
be attributed to a combination of factors, such as a) higher P status of
forest soils due to better nutrient recycling, b) release of organic P
during cropping of newly cleared land, and c) large quantities of P made
available in the plant ash by traditional clearing and burning of
residue.

39
Olagunde and Sorensen (1982) reported that in spite of the
substantial decreases in Mg, Ca, and P concentrations in sorghum there
seemed to be no relationship between K/Mg ratio and dry matter yield.
This constant amount of cations in the plants might explain why there
was no substantial change in dry matter yield. The authors suggested
that K, Ca, and Mg carry out plant functions which can be performed by
one cation in the absence of another.
Shukla and Mukhi (1979) noted that applications of Zn to maize
resulted in increased shoot Mg at all levels of K and Na. The
increasing K levels decreased Mg and the decrease was more when Zn or Na
was not applied. The results thus showed that K and Zn had antagonistic
and synergistic relationships, respectively, with Mg. The results also
evidenced antagonism between K and Ca, K and Mg, and synergism between
Mg and Zn.
Gallaher and Jellum (1976) found that leaf concentrations of Zn
and Fe were influenced by planting date for maize hybrids but
interactions between hybrids and planting date were found only for K,
2+ -1
Ca, Mg concentrations and the sum of the mmol(M ) Ca+Mg kg the
2+ -1
mmol(M ) K+Ca+Mg kg and the K:Ca and K:Ca+Mg ratios.
Potassium content in maize tissue and its balance with Ca and Mg
has had widespread interest. Macy (1936) stated that a critical
percentage of each nutrient in each plant species existed, above which
there was luxury consumption and below which there was poverty
adjustment. Critical concentrations of 2 mg K g and 200 mg Mg g \ on
a fresh weight basis were established for optimum photosynthesis in
maize.

40
Gallaher et al. (1975) defined the critical elemental K
concentrations in maize tissue at two sampling dates as the point at
which yields no longer give a statistically significant increase from
further applications of fertilizer K. Concentrations of K above those
critical levels would be in the luxury consumption category because
yields were not significantly increased beyond those concentrations.
Beyond those critical levels K might, in some instances, induce Ca or Mg
deficiencies because of the interaction among cations. Therefore the
critical levels of Ca and Mg are defined as being at the same point
where the critical level of K occurred. The optimum balance of the 3
cations should occur at the critical concentration for K.
Gallaher et al. (1975) reported critical mmol (m2 + ) of young maize
2+ -1
plants taken 38 days after planting to be 91 to 78 mmol(M ) K kg ,31
to 28 mmol(M^+) Ca kg and 40 to 39 mmol(M^+) Mg kg The dilution or
age effect is evident from the critical levels of K at the thinning
stage compared to the ear leaf at the silking stage of growth. The
2 +
critical mmol(M ) in the ear leaf 86 days after planting was 44 to 40
mmo1(M^+) K kg \ 34 to 30 mmol(M^+) Ca kg *, and 22 to 16 mmol(M^+) Mg
-1 2+ -1
kg The critical 44 to 40 mmol(M ) K kg in the ear leaf at the
silking stage of growth was in agreement with the critical percent of
1.75 for maize ear leaf tissue at the silking stage in the midwestern
United States.
Jacques et al. (1975) found Ca concentrations were much lower in
heads than in other plant parts both years and in the first year were
lower in grain than in threshed head parts. Calcium concentrations in
blades increased after maximum blade weight was reached. During grain
development Ca concentrations were higher in blades than in unformed

41
heads. Calcium utilized in calcium pectate formation in mature leaf
cells may have been responsible for the increased concentrations in
blades and culms. A greater percentage of the total Ca taken up in the
hybrids was accumulated in their blades than in the other plant parts.
Hanway (1962a) found that in maize, N accumulated in each plant
part as that part grew. He also observed that there was little
translocation from one plant part to another until after grain formation
began, and then N was translocated from all other plant parts to the
grain. Translocation of N from the cob, husk, and stalk appears to
precede that from the leaves. The leaves contained approximately 30% of
the N accumulated by the plant even though they constituted only about
13% of the final dry matter accumulation. At maturity the grain
contained approximately 66% of the total N in the plant. About 50% of
the N in the grain at maturity appeared to be N that had been lost
through translocation from other above-ground plant parts.
Jordan et al. (1950) observed a somewhat different pattern of N
uptake. In their study N fertilizer was side-dressed when the plants
were knee-high and the maximum rate of N absorption occurred immediately
following the application of N fertilizer. The pattern of N
accumulation by plants is undoubtedly influenced by the seasonal pattern
of N availability in the soil. K accumulation in this study continued
until a later stage of maturity and there was no loss of K from the
plants during the latter part of the season.
Hanway (1962a) suggested that continued mineral accumulation by
the plants later in the season is essential to prevent excessive loss
through translocation of N and K from the leaves which would result in
premature death of some of the leaves. Some loss of nutrients from the

42
leaves to the grain does not appear to be detrimental to the yield of
grain so long as this does not result in premature death of the leaves.
Jacques et al. (1975), comparing two sorghum hybrids, found that
Mg concentrations were lower in heads than in other plant parts.
Magnesium was evenly distributed in blades and sheaths of each hybrid.
For the two hybrids Mg accumulation in blades, sheaths, and culms was
similar to that of dry matter production. Both dry matter production
and evidence of translocation of Mg out of stems into the heads during
grain development was indicated, because the percentage of Mg decreased
in the stems and increased in the developing grain.
Jacques et al. (1975), studying nutrient uptake by different
sorghum hybrids, found that little difference between hybrids in Zn and
Cu uptakes occurred each year, but differences existed between hybrids
in Mn uptake. Stem tissue was initially high in Fe content but
decreased during both hybrids' vegetative growth. Concentrations in
head tissue and in head parts and grain were generally below 75 mg kg ^
and relatively constant throughout the growing seasons, especially in
culm tissue. Differences were small among plant parts after vegetative
growth ceased, and concentrations in plant parts remained relatively
constant during grain development. Some translocation of Zn from
vegetative plant parts into the developing grain was suggested by a
decrease in Zn content in some cases, but for the most part Zn seemed to
be relatively immobile.

43
Sul fur
Importance of S
From the time of Liebig S has been known to be one of the elements
required for plant growth, but only recently has this element received
the attention it deserves as a plant nutrient. Despite this early
recognition, the importance of S as a limiting plant nutrient was
largely ignored until recently (Coleman, 1966; Caldwell et al., 1969).
In countries concerned with increasing food production, S is an
element that must not be overlooked. It is required not only for
increased total production, but what is probably far more important, it
is needed for increasing the quality of the protein present in the
foods that are produced (Coleman, 1966).
Allaway and Thompson (1966) indicated that the problem of
malnutrition due to deficiency and poor quality of protein in human
diets has been described by nutritionists and emphasized in the press.
The nutritional quality of a protein depends upon its amino acid
composition. Animals (including humans) must be supplied with the
S-containing amino acid methionine and the S-bearing vitamins biotin and
thiamine.
In areas where protein deficiency in human diets is a critical
problem, animal products are rarely consumed, and plants are the major
source of proteins. In addition, plants are frequently lower in total
protein than are animal products, so that the amounts of food required
to supply 1 g of S-amino acids are higher for plant products than for
animal products. The protein requirements of many areas will need to be
met by direct consumption of plant products. The appropriate ultimate
objective of S fertilization of soils is, therefore, to increase the

44
S-containing amino acid of human diets (Allaway and Thompson, 1966;
Coleman, 1966).
In a review article Coleman (1966) pointed out that S is needed in
crop production because certain plant functions require it for 1) the
synthesis of amino acids, cysteine, cystine, and methionine, and hence
for protein elaboration; 2) the activation of certain proteolytic
enzymes such as the papainases; 3) the synthesis of certain vitamins, of
glutathione, and of coenzyme A; 4) the formation of the glucoside oils
found in onion, garlic, and cruciferous plants; 5) the formation of
certain disulfide linkages that have been associated with the structural
characteristics of protoplasm; and 6) in some species the concentration
of sulfhydril (-SH) groups in plant tissue,which is related to an
increase in cold resistance.
The importance of S in animal nutrition has been summarized by
Allaway and Thompson (1966). They reported that the S-containing amino
acid requirement of chicks has been estimated at 0.8% of the total
ration when the ration is 23% protein. In the case of ruminant animals,
where synthesis of S-containing amino acids from inorganic S by rumen
microflora has been established, the total S content is normally used to
appraise S status of a ration. The optimum S level in lamb diets was
found to be approximately 0.17 dag kg ^ S when methionine was used to
increase the S content of a lowS basal diet. The authors suggested a
N:S ratio of 15:1, or less, as an appropriate guide to the S adequacy of
a ration for dairy cows. A precise evaluation of the optimum N:S ratio
for ruminant animals is probably impossible, because ruminants adjust to
low levels of N and S through recycling processes.

45
Forms and Amount of S in the Soil
Tropical and temperate soils differ in both the total amount of S
and its form. Jordan and Reisenauer (1957) report average values of 540
and 210 rag kg ^ S for Mollisol and Alfisol surface soils from temperate
areas. Generally, the total S content of tropical soils is lower
because of their lower organic matter content, and adsorbed S is often
the major reserve of this element.
Sulfur is found in soils as a variable mixture of primary
minerals, sulfate ions in solution, adsorbed sulfate, ester sulfate, and
organic S compounds. Blair et al. (1980) summarized the differences
between the forms of S present in tropical and temperate soils.
Adsorbed S is generally higher in tropical soils, as in this state it
cannot be leached from the profile.
Neller (1959) showed that extractable sulfate-S increased with an
increase in the clay content in 14 Florida Ultisols. The subsurface
horizons contained considerably more sulfate-S than the surface
horizons. The increase in sulfate-S with horizon depth is associated
with S adsorption by Fe and Al hydroxides and oxyhydroxides and with an
increase in 1:1 clay minerals in the argillic horizons.
More recently Mitchell and Blue (1981) showed that most S in
Florida Spodosols and Entisols is associated with organic matter, and
sulfate-S accounted for less than 7% of the total soil S in the entire
profile of selected Florida Spodosols. Sulfate-S accounted for
approximately 15% of the total S in the C horizons of Florida Entisols,
and 44% of the total S in the B2t horizons of 10 Utisols. Extractable S
in the surface (A^ or A^) horizon (0-14 cm) ranged from 1 rag kg ^ in a
Myakka fine sand (Aerie Haplaquod) from Alachua County to 8 mg kg ^ in a

46
Leon fine sand (Aerie Haplaquod) from Duval County. Extractable
sulfate-S did not vary as much as total S in the soils. The mean total
S in the nine Spodosols varied from 104 mg kg ^ in the surface horizons
and 92 mg kg ^ in the spodic (B2H) horizons to 17 mg kg ^ in the A2
horizons.
Sulfur Deficiency in Soils
Blair et al. (1980) gathered information indicating that response
to S has been reported in 40 countries of the tropics. Coleman (1966)
and Spencer and Freney (1980) reported that S-deficient areas are rather
widespread throughout the world. For example, crop deficiencies of the
element have been reported from countries in Central and South Africa,
India, Brazil, Argentina, Central America, Europe, Australia, New
Zealand, Canada, and the United States.
Sulfur deficiency frequently occurs in soils derived from volcanic
parent-materials. In such soils, which are common in Central America
(Fritts 1970), the organic matter is closely associated with allophane
and the mineralization of the allophane-bound organic matter, i.e., the
rate of release of sulfate-S is very low. Plants on such soils are
often S deficient despite the fact that the soil is high in organic S.
According to Blair et al. (1980) the reasons for an S deficiency
in soils can be grouped broadly into three areas 1 ) inherently low
initial S status, 2) low availability of S-containing soil organic
matter, and 3) the result of agricultural practices. Sulfur deficiency
often develops in the tropics after a period of agricultural
exploitation. The major factors that contribute to its onset are crop
removal, organic matter losses, leaching and erosion losses, and
fertili zer use and management. The more intensive the cropping system,

47
the greater the product removal and S demand. For example S contents of
the rice grain vary from 0.034 dag kg ^ under deficiency conditions to
0.16 dag kg ^ in a nonresponsive situation, and rice grain yields may
vary from 0.75 to 8 Mg ha *. A further factor to take into account when
considering the effect of crop removal on S demand is the zone of
removal in the soil.
The removal of crop residue contributes significantly to losses of
soil S in some situations (sorghum, millet). The recycling of S in crop
residues is important in livestock systems where the residue material is
used for animal feed or bedding. Since organic matter acts as a reserve
of S in soils, the losses have serious implications for the S-supplying
power of soils.
Coleman (1966) suggested that S deficiencies occur probably
because of a) the increased use of S-free fertilizers; b) the decreased
use of S as a fungicide and insecticide; and c) increased crop yields,
which means requirements of all of the essential plant nutrients in
larger amounts. Blair et al. (1980) indicated that the use of
non-S-containing phosphatic fertilizers may aggravate the S problem by
replacing adsorbed sulfate with phosphate. In this regard two aspects
of sulfate adsorption are important. First, phosphate ions will replace
sulfate ions. Bromfield (1974) estimated that sulfate ions are then
free in the soil solution and can be leached.
Adsorbed sulfate associated with the argillic horizons of Ultisols
is considered a primary source of piant-available S in soils of the
southeastern United States (Neller, 1959; Bardsley et al., 1964;).
Ensminger (1954) reported that in some areas S may leach out of the
surface horizons of coarse-textured soils but be retained by the lower

48
horizons. This is particularly true if the subsoil contains a large
amount of kaolinitic-type clays and of hydroxides of Fe and Al, and is
acid. Under such conditions plants may exhibit S deficiency during
early stages of growth. However, the plants will subsequently recover
when the roots enter the lower soil layers. The initial stunting of
growth caused by S shortage in the topsoil may, however, result in
reduced crop yields. Mitchell and Gallaher (1979) reported that deep
rooted plants are able to utilize adsorbed sulfate associated with the
clay in lower soil horizons, but seedlings may exhibit S-deficiency
symptoms when grown on sandy surface soils with no S fertilization.
These plants were definitely low in S with an average S concentration of
0.12 dag kg Soil analyses indicated increasing extractable sulfate-S
with depth in the horizon. They further suggest that increased
mineralization of organic S later in the season may have also
contributed to the improved S status in the plants.
Sulfur present in soils as sulfate undergoes many reactions
similar to those of nitrate and phosphate, and its strength of
adsorption to surfaces is intermediate between that of the two anions.
In experiments by Pearson et al (1962), 90% of the water-soluble bases
were leached as sulfate from Latosol and Ultisol profiles; chlorides
and nitrates accounted for only about 6% and 1%.
Organic S and ester sulfate, which may be thought of as reserve S,
are generally lower in the tropical soils. Environmental conditions in
the tropics are generally conducive to a rapid mineralization of organic
matter, which leads to high turnover rates of S. An exception is the
volcanic soils (Andepts), in which adsorption of organic matter on the
particles of allophane retards mineralization (Blair et al.,1980).

49
In many parts of the tropics burning of plant matter, which is an
integral part of farming, can be an avenue for S loss. When carbon is
burned off by combustion there is a concentration of S in the ash.
Blair et al. (1980) and Bromfield (1974) showed that the S content in
ash can be 2 to 10 times higher than that in dried plant material. In
areas of prevailing winds S loss may be high, but in regions of variable
winds the gains may equal the losses. One additional consequence of
burning is that organic forms of S are converted to inorganic forms
which, at the beginning of the rainy season when fields are bare, are
susceptible to leaching losses.
Blair et al. (1980) reported that sulfate which was mineralized
from organic matter moved down the profile and accumulated at lower
depths. Since a large proportion of the S present in the soil is in the
organic matter and this is often accumulated on the soil surface, losses
from wind and water erosion may be high in some circumstances.
Plant's Requirements and Content
Tisdale and Nelson (1964) concluded that S is required by many
crop plants to about the same extent as is P. As a general rule of
thumb, grass and cereal crops generally require smaller amounts of S
than do legume and cruciferous crops. Ensminger and Freney (1966) list
the effect of age on S contents in several species. Because it is
necessary to select a plant part that has a relatively constant S
content, the effect of maturity on the S content of the plant part(s)
should be examined to determine sensitivity to sampling time.
The critical concentration of S in young maize plants has been
reported to be around 0.20 dag kg 1 (Fox et al., 1964; Stewart and
Porter, 1969; Jones and Eck, 1973; Terman et al., 1973). Friedrich and

50
Schrader (1978) indicated that maize seedlings are not S-deficient
unless the concentration of S (dry weight basis) in the shoots is
approximately 0.10 dag kg 1 or less. Blue et al. (1981), found that
maize plants without S fertilization were chlorotic and oven-dry herbage
contained only 0.10 dag kg 1 total S; herbage from treatments with S
applied at 15 and 30 mg kg 1 contained 0.19 and 0.23 dag kg 1,
respectively. Oven-dry herbage yields were increased from 6.6 to 9.4 g
pot ^ by the addition of 15 mg kg 1 of S, and there was no additional
yield increase from the 30 mg kg 1 S treatment. Mitchell and Gallaher
(1979) reported that seven harvested crops in a maize/grain system and
the maize forage system removed an estimated 48 and 63 kg ha 1 S,
respectively, during 2 years.
Fox et al (1977) have shown that the critical level of S in cowpea
varies between cultivars. In their solution culture experiment, the
critical value varied between 0.032 dag kg 1 total S in cultivar 'Sitao
Pole' and 0.064 dag kg1 in 'TVU76-2E'.
Published data for rice (Blair et al., 1979) show grain S contents
varying from 0.134 dag kg 1 under deficiency conditions up to 0.16 dag
kg 1 in a non-responsive situation. Rice grain yields may vary from 750
kg ha up to 8,000 kg ha 1 which gives a S removal varying from 0.26 up
to 12.8 kg ha Rice straw may contain similar amounts of S.
Absorption and Accumulation of S
Coleman (1966) reported that in addition to the S they receive
from precipitation, plants and soils absorb sulfite and perhaps other
sulfurous gases directly from the atmosphere. It has been known for
many years that sulfite is absorbed directly by plant leaves. Work by
Olson (1957) showed that plants supplied with adequate sulfate in

51
solution still obtained about 30% of their S from the atmosphere. When
plants were grown in a S-deficient nutrient solution, they obtained up
to 90% of their S from the atmosphere, but the total amount absorbed was
insufficient for normal growth. There is considerable evidence that
sulfurous gases in the atmosphere may be absorbed directly by soil.
However, Blue et al. (1981) reported that S additions to soils through
the atmosphere and rainfall are inadequate for intensive production
systems.
Jones et al. (1979) estimated that an average of 8.4 kg ha ^yr ^
of atmospheric S was absorbed directly by the soil in South Carolina
from 1973 to 1977. No data are available on the amount of S that may be
absorbed directly by the plant foliage as sulfite.
Sulfate is absorbed by plants with more difficulty than other
anions and it has been shown that the uptake proceeds even more slowly
in the presence of more mobile anions such as chloride and nitrate.
Usually S and N are absorbed in the form of sulfate and nitrate from the
soil and subsequently undergo metabolic conversion into organic S and N.
Any quantity above that needed to supply sulfate and nitrate to the
metabolic process is stored up provisionally as inorganic sulfate and
nitrate in the plant (Spencer and Freney, 1980).
Friedrich and Schrader (1978) suggested that N-reductase (NR), the
rate-limiting enzyme in nitrate-N assimilation, serves as a primary
regulatory coupling between nitrate and sulfate assimilation, while
Reuveny and Filner (1977) postulated that ATP-suIfurylase, the initial
enzyme in the pathway of sulfate assimilation, acts in synchrony with NR
to coordinate nitrate and sulfate assimilation in cultured cells.

52
However, BrunoLd and Schmidt (1976) proposed that adenosine-5'-
sulfotransferase, not ATP-sulfurylase, regulates sulfate assimilation in
chlorophyllous tissue.
Rabuffetti and Kamprath (1977) concluded that S accumulation in
maize grain is highly dependent upon the supply of N available for the
formation of amino acids. Sulfur accumulation in stover was enhanced by
both N and S application. On a Goldsboro soil, S application increased
S accumulation in the stover at all N rates. This occurred only at the
high N rates on the Wagram soil.
According to Friedrich and Schrader (1978) higher plants generally
accumulate N and S in amounts proportional to that incorporated into
protein. However, when plants are S-deficient, protein synthesis is
inhibited and nonprotein N is accumulated. Likewise, sulfate will often
accumulate in plants when the availability of N is limiting protein
synthesis. The observed interaction between N and S accumulation
suggests that nitrate and sulfate assimilation are closely linked
raetabolically.
The pattern of remobilization of N and S reported by Friedrich and
Schrader (1979) is similar to the pattern of N redistribution observed
by previous researchers (Hanway, 1962c). The percentage of the labeled
N and S present at silking that was later remobilized was not constant
among fractions. The husk fraction remobilized more of its N and S than
did any other fraction.
Barrien and Wood (1939) studied the effects of N supply on the
amounts of protein-S and sulfate-S. The authors concluded that the most
striking feature of the curves for amount of protein-S plotted against
time is that they follow the trend of the curve for amount of dry

53
matter. An increase in N supply caused an increase in the amount of
protein-S. As in the case of protein-N, the highest N treatment caused
at first a depression in the amount of protein-S due to an effect of
treatment on growth rate.
Friedrich and Schrader (1979) reported that in maize a greater
proportion of N compared to S was remobilized from all fractions with
the exception of roots. This suggests that N is more mobile than S, at
least under the conditions of this experiment. The supply of S strongly
influences the efficiency of nitrate-N utilization in maize. Regardless
of the external supply of N during grain-filling, N and S absorbed prior
to silking will later comprise most of the N and S in the ear.
Sulfur absorbed by maize plants prior to silking was partitioned
more effectively into the ear than S absorbed after silking (49 vs.
23%). Although maize plants can absorb large quantities of S during
grain-filling, it is apparent that remobilization of S accumulated prior
to silking contributes more to ear development. Furthermore, the
remobilization of S is similar to N remobilization in that it occurs at
a constant rate that is not affected by N supply during grain-filling,
(Friedrich and Schrader, 1979)
Effects of S Deficiency
Sulfur affects not only the yield of crops, but in certain cases
the quality also. It is essential for the synthesis of methionine,
cystine, cysteine, and hence the elaboration of amino acids into a
high-quality protein. Methionine and cystine are indicators of protein
quality (Allaway and Thompson, 1966; Blair et al., 1980; Stewart and
Porter, 1969; Lancaster et al., 1971).

54
Friedrich and Schrader (1978) studied S deprivation and N
metabolism. In maize seedlings, leaf fresh weight was not affected by S
deficiency. However, stem fresh weight was reduced 24% compared to
normal plants. The authors concluded that it may be that S deficiency
was having a greater effect on the young, rapidly elongating culms and
unfurled leaves in the stem fraction than on the older leaf blades.
There are few data, however, that indicate to what degree yield and
quality are related.
According to Allaway and Thompson (1966) the importance to human
and non-ruminant animal nutrition of the S-containing amino acids cannot
be overstated. Many studies of the nutritive value of proteins have
shown that the lack of S-containing amino acids is the factor that
limits the biological value of the protein. The investigators making
this survey further concluded that a large segment of the world's
population is living on a diet that is strongly deficient in methionine.
If the animals are fed a ration low in total S, they will not make the
best utilization of the N in the diet. This means that meat, milk, or
wool production will be reduced.
Under conditions of S deficiency and high N fertilization, protein
synthesis is retarded by a lack of the S-containing amino acids,
cysteine and methionine, and this is reflected by marked accumulation of
unassimilated N in the plants as nitrate-N, amides, and free amino
acids. Such forage when fed to animals represents an unbalanced ration
in which N content may exceed requirement, which in turn can result in
nutritional disorders, especially in ruminants. High nitrate-N in
forage, for example, can cause nitrate poisoning and hypomagnesemia in
grazing dairy cattle. It arises from an inadequate absorption of Mg and

55
is probably associated with high ruminal ammonia (NH^) production.
Until recently, S had not been known to limit digestibility of inferior
quality standing pasture. It has since been shown that S fertilization
improved the intake and digestibility of inferior quality herbage.
Interaction Between S and Other Nutrients
According to Goh and Kee (1978) the total N (Nt):total S (St)
ratio in plants has been extensively studied because of its potential
use in assessing S deficiency in crops. Sulfur requirement is closely
associated with N metabolism, and high application of N fertilizer to
increase crop production may be detrimental and often wasteful if the
corresponding increase in S demand is not met. Stewart and Porter
(1969) found that to achieve maximum utilization of the added N, one
part of S must be added to 15 parts of N. Results presented by Goh and
Kee (1978) indicate 17 parts of N to one part of S.
Dijkshoorn et al. (1960) found that, on account of the ability of
grass to accumulate variable amounts of non-protein N-metabolites free
of S (such as glutamic and aspartic acid), the N:S ratio in the
non-protein organic substance is usually different from the protein
ratio Sp:Np and is subject to variation according to the nutritional
status of the plant. Therefore the ratio of organic S (So) to organic N
(No) in the total mass of forage So:No is also different from Sp:Np and
is some function of the nutritional status and the composition of the
plant.
In S-fertilization experiments in New Zealand, McNaught and
Christoffels (1961) reported N:S ratios of 17:18.5 for white clover and
11:12 in grasses at maximum yields. Pumphrey and Moore (1965) found
that a N:S ratio of 11 or less indicated an adequate S supply for

56
alfalfa. Stewart and Whitfield (1965) suggest a N:S ratio of 17 or less
in wheat clippings as indicative of adequate S nutrition. Thus, the N:S
ratios found desirable for optimum growth of plants are generally
slightly higher than the N:S ratio of 10:1 to 15:1 suggested by Allaway
and Thompson (1966) as optimum for ruminant animal nutrition. It would,
therefore, appear to be quite likely that certain forage plants may be
deficient in S for ruminant animals, even though the plants themselves
are growing at nearly maximum rates. When S is deficient, the ratio of
Nt:St will exceed the 15:1 required for protein synthesis, formation of
protein will diminish, and nonprotein N will accumulate.
The Np:Sp ratio has been reported to range from 11 for maize to 18
for legumes (Dijkshoorn and Van Wijk, 1960). Metson (1973) considered
the Np:Sp ratio to be more reliable than the total Nt:St ratio for
assessing the crop's N:S requirement because it is not influenced by the
accumulation of non-protein S and non-protein N. When S supply is
adequate the accumulation of non-protein S will cause the Nt:St ratio to
be lower than the Np:Sp ratio, whereas when S is deficient, non-protein
N will accumulate resulting in a higher Nt:St ratio.
Barrien and Wood (1939) observed a decline in the ratio of Np:Sp
in sudangrass leaves as the plants matured. They suggest that this
change might be due to the presence of a relatively stable S-rich
protein fraction that is not readily remobilized.
Under conditions of S deficiency the uptake of nitrate-N seems to
be affected less by a limited S supply than is the plant's capacity for
protein synthesis. Thus, because the ratio of Np:Sp in individual
proteins is fixed by the genetic code, nonprotein forms of N accumulate
when the availability of S limits protein synthesis. Similarly, sulfate

57
will accumulate in plants when the rate of uptake exceeds the amount
required for protein synthesis (Friedrich and Schrader, 1978).
The ratio of Nt:St in all vegetative fractions of maize plants
declined during grain-filling. Likewise, the Nt:St ratio was lower in
ears of N-deprived plants than in control plants; however, this ratio
was constant throughout grain-filling and was usually significantly
lower for N-deprived plants. Nitrogen supply had no effect on the
decline in Nt:St ratio in the leaves (Friedrich et al., 1979).
The accumulation of zein, a grain protein that is low in S-amino
acids, is known to be enhanced by increased N-fertilization. The ear
Nr:Sr ratios were much higher than the Nt:St ratios. This is due to the
larger proportion of ear S present as sulfate-S compared to the pro
portion of total N present as nitrate-N (1 to 6 dag kg ^). However,
this sulfate-S may have been in the cob, rather than in the grain.
Maize grain does not accumulate nitrate-N, (Friedrich and Schrader,
1978).
Goh and Kee (1978) found when N is added in high rates a reduction
in reducible S content occurred because of the incorporation of S into
plant proteins. In the high N low S treatments (N^SO) over 95% of total
S in plants occurred as organic forms (total S, reducible S). Stewart
and Porter (1969) showed that when S is deficient nearly all the S
present in both herbage tops and roots occurred in the protein fraction.
Conversely, in the low N and high S treatments the reducible S fraction
consistently made up more than 20% of the total S.
Phosphorus-S interactions have been observed by Kamprath et al.
(1956) and Radet (1966). Caldwell et al. (1969) reported the S
treatments decreased the P content of the mature tissue. The S:P ratios

58
for second cutting alfalfa in 1966 ranged from 0.45:1 in untreated plots
to 1.42:1 in alfalfa which received 112 kg ha ^ of elemental S annually.
There was no effect of S on the P content of maize in 1962. Sulfur
increased the S content of the leaves from 0.22 to 0.26 dag kg
Phosphorus content decreased from 0.45 dag kg without S to 0.38 dag
kg when S was applied. Kamprath et al. (1957) reported that liming
and P fertilization reduced the retention of sulfate in the surface
horizons and as a result sulfate added to these soils would be leached
out of the plow layer into the B horizons, where it accumulates.
Work by Caldwell et al. (1969) demonstrated that the effect of S
on the K content of alfalfa varied. In one year increasing S resulted
in a decrease in the K content. In the second year the S-treated
alfalfa contained more K than the S controls. Apparently the healthier,
more vigorous plants on the treated plots were able to extract more K
from the soil than the weak, unthrifty, S-deficient plants.
Caldwell et al. (1969) found no discernible effects of S on the
Ca, Mg, and Fe content of alfalfa. Neither were there any significant
differences in the Cu, Zn, Al, and Sr contents of the alfalfa as a
result of the S fertilization. Average Cu content of the maize
decreased from 10 to 8 mg kg ^ with S (significant at the .05
probability level).
Mitchell and Blue (1981a, b) found that both total S and
extractable sulfate-S were significantly correlated with organic C and
total N in the surface horizons of Florida soils. Only total S was
highly correlated with organic C and total N in the spodic horizon.

59
Crop Response to S Fertilizer
Tisdale and Nelson (1964) reported that numerous crop species have
been found to respond to applications of S under the usual field
conditions. Some of these are lucerne clovers, pasture grasses, cotton,
maize, peanut (Arachis hypogea L.), rice, jute, banana, small grains,
apple, stone and citrus fruit, cruciferous crops, tea, and coffee. It is
to be suspected that this response would be found in every crop.
According to Jordan and Bardsley (1959), crop deficiencies of S
can be corrected by the application of numerous S compounds or elemental
S. Normal superphosphate contains 11 to 13 dag kg ^ S and ammonium
sulfate contains 24 dag kg ^ S. The intentional application of S as a
fertilizer nutrient has never received wide acceptance among growers.
It has been present in most fertilizer materials as an anion associated
with the other macro and micronutrients or as a by-product of the
manufacturing process.
Recent work with supplemental S by Gaines and Phatak (1982)
studied the effect of additional S on maize, soybean, cowpea, tomato,
cotton, and okra. This work showed that yields of maize, soybean,
cowpea, and tomato tops were significantly increased by rates of up to
32 mg kg ^ S, but yields of cotton and okra tops were unaffected by S
treatments. The results which were obtained by Rabuffetti and Kamprath
(1977) suggest that the addition of S to maize crops which were
adequately fertilized with N would be likely to improve the grain
quality of maize produced in Coastal Plain soils.
In a study testing the relation of S content of forage crops to
cattle fed on those forages, Lancaster et al. (1971) indicated that S
fertilization influenced rumen microbial activity when cattle were fed

60
four forage species but not in alfalfa. Gas production increased for
the grasses and decreased in the legumes with increased S application.
Total plant S and sulfate-S levels were increased with additional S
applied for all species; however, the percent protein decreased in the
grasses and increased in the legumes.
Lancaster et al. (1971) also found that the percentages of fiber
and lignin in the crops they studied were not influenced by S
fertilization, except for the second clipping of sudangrass and the 20
and 40 mg kg ^ levels applied to alfalfa. The critical level of S in
these trials appears to be less than 10 rag kg ^ S applied to the soil.
There were positive correlations between gas production and S
concentration for the grasses but there were negative correlations for
the legumes.
Caldwell et al. (1969) reported that the effect of S on the yield
of alfalfa was striking. Three times as much hay was produced by the
treated plots as by the check plots. The untreated alfalfa contained
from 0.146 to 0.221 dag kg S. Lancaster et al. (1971) reported that
the dry matter production in the grass species they studied was
increased by the addition of S, but for the legumes this increase was
not significant.
Rabuffetti and Kamprath (1977) reported that S had little effect
at low N rates on N accumulation in maize stover. However, they found
that at N rates of 168 and 224 kg ha ^ there was an increase in N
accumulation in stover with S rates of 44 and 66 kg ha 1 on the
Goldsboro soil and 33 and 66 kg ha ^ on the Wagram soil. Total S
accumulation in grain was found to be increased by N application at both
sites .

61
Work by Blue et al. (1981) showed that increasing rates of applied
S caused striking maize growth responses to S applied at 10 mg kg *.
Yields from two soils were increased approximately fourfold. Herbage S
concentrations were only 0.06 dag kg from each soil without S
fertilizer; interestingly, they were increased to only 0.09 and 0.07 dag
kg *, respectively, from the Marion and Suwannee county soils fertilized
with 10 mg kg of applied S. Stewart and Porter (1969) gave similar S
concentrations in maize plants of the same age with the additional point
that S requirement increased with increasing amounts of applied N.
However, S content of herbage was increased from 2 and 3 mg pot for
soils from Marion and Suwannee counties without applied S to 11 and 14
mg pot respectively, by application of 10 mg kg of S to the soils.
Mitchell and Gallaher (1979) found that applied S from non-Mg
sources had no significant effect on the final grain yield of two maize
cultivars. All of the S treatments increased the S concentration of the
tissue over that of the check, but did not affect yield of grain or
forage.
A grain yield response by rice to S application was obtained at
three sites by Blair et al. (1979); responses to S in three experiments
reported ranged from 47 dag kg or 1837 kg grain ha 1 at one site and
up to 231% or 2,146 kg grain ha* at another site.
From work reported by Wagner and Jones (1968) it is evident that S
fertilization affected the quality of annual grassland forage as
measured in terms of protein level. Evans and Davis (1966) reported
that addition of a dietary level of sulfate to an in vitro system
improved cellulose digestibility. Jung and Reid (1966) obtained a

62
correlation coefficient of 0.82 when _in vivo digestible dry matter was
compared with _in vitro cellulose digestibility.

CHAPTER 3
MATERIALS AND METHODS
Field Procedures
Fertility Trials
Experiments involving three intercropping systems (Fig. 3-1) and
six fertilizer treatments (Table 3-1) were established at two sites in
Esteli, Nicaragua (Fig. 4-1) during the 1982-1983 growing season. Site 1
(Centro Experimental de Esteli) located 1 km north of the city of Esteli
on the Panamerican Highway at an elevation of 975 m. The average annual
precipitation is 1000 mm distributed in a bimodal pattern (CATIE,
1981a); the largest amounts fall during May, June, August, and September
(CATIE 1980, 1981). This rainfall pattern is the determining factor in
defining the growing season. The average annual temperature is 19C. The
soil may be classified as a Vertisol (CATIE, 1981). The field where the
experiment was established was previously planted to shade tobacco
(Nicotiana tabacum L.) but had been under fallow for the last 7 years.
Site 2 was a production cooperative (Sabana Larga) managed by 15
farmers and located 6 km southwest of the city of Esteli at an elevation
of 930 m. The average annual precipitation and temperature are 1247 mm
and 20.1 C, respectively (CATIE, 1980). The field had been under
continuous maize + beans (Phaseolus spp.) for the last 25 years.
There were 13 treatments with four replications in a randomized
complete block design at each site. The design incorporates all six
63

64
Table 3-1. Fertilizer rates and times of application evaluated at two
sites in Northern Nicaragua.
TRT
#
-Crop-
Cl C2
Fertilization
Days
10
after
planting Cl
25
25 days after
planting C2
P
N
N
P
N
-1
. K.g na
1
M
PS
30
0
0
0
0
2
M
PS
30
30
40
0
0
3
M
PS
30
0
35
0
0
4
M
PS
30
0
70
0
0
5
M
PS
30
30
40
0
35
6
M
PS
30
30
40
30
35
7
M
NS
30
30
40
0
0
8
M
NS
30
30
40
0
35
9
M
NS
30
30
40
30
35
10
M
MI
30
0
0
0
0
11
M
MI
30
30
40
0
0
12
M
MI
30
30
40
0
0
13
M
MI
30
30
40
0
0
M maize, PS = photosensitive sorghum, NS = non-photosensitive sorgum,
MI = millet.

65
Figure 3-1. Spatial arrangement of maize (M) + photosensitive
sorghum (PS), maize + non-photosensitive sorghum
(NS), and maize + millet (Ml) intercropping
systems.

66
fertilizer treatments in the maize + photosensitive sorghum cropping
system, but only the high fertilizer treatments in the maize +
non-photosensitive sorghum and the maize + millet systems.
The individual plots were 9.8 by 10 m. Twelve rows of 'NB-3' maize
were planted no-tillage by hand in each plot (52,000 plants ha on 16
June. The second crops ('Criollo', photosensitive sorghum; 'Pioneer
895', non-photosensitive sorghum; and 'Gahi-3' millet) were interplanted
on 16 September according to the spatial arrangements depicted in Figure
3-1. The 'Criollo' was seeded between maize rows (40 cm from the maize
hills), in hills spaced 0.80 cm apart, and later thinned 24 days after
seeding to six plants per hill to obtain 75,000 plants ha 'Pioneer
895' and 'Gahi-3' were seeded in double rows (20 cm from the maize).
Twenty four days after seeding the rows were thinned to have 120,000
plants ha
One week prior to planting the experimental plots were sprayed with
2 L ha ^ of paraquat to kill the established weed population and
immediately after planting with a mixture of 1 L of atrazine + 0.75 L of
Lasso ha to prevent further weed infestations. Together with the seed
11 kg of carbofuran ha were incorporated in the soil to prevent damage
to the plants by soil insects. No further insect control was necessary
at either site. To simulate the conditions of the typical farmer all
other management activities were performed as described in Chapter 4.
The N, P, and K fertilizer applied at planting was incorporated
into the soil with a planting stick; later applications on N and P were
hand-drilled near the hills of the maize or photo-sensitive sorghum and
banded next to the rows of the non-photosensitive sorghum or millet and

67
covered with 3 to 5 cm of soil. The fertilizer treatments are described
in Table 3-1. No initial soil amendments were necessary.
Grain and stover were harvested from 8 m of the two central rows of
each plot. Grain moisture was measured with a Steinlite moisture meter
and yields calculated at 15.5% moisture content. The plant was separated
into components, and each part was then weighed. Dry matter yields were
calculated using subsamples dried to constant weight at 70C for 72
hours. All above ground plant material was removed from the plots,
separated into parts (leaf, stem, flower, ear, or head), and subsampled
for chemical analysis as described in the section of laboratory analysis
of this chapter.
One soil sample was collected from each plot prior to planting and
immediately after harvesting the last crop. All samples were air-dried,
sieved through a 2 mm stainless steel screen, and stored at ambient
temperatures until analyzed.
The following response variables were measured to determine the
effect of the fertilizer treatments on the systems under study: a) soil
pH (1:1) and extractable N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn
concentration at the beginning and end of the experiment, b) maize and
sorghum grain yield, c) Dry matter production of the different plant
parts, d) Concentration of N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn of the
different plant parts, e) combustible energy, f) percent organic matter,
and g) percent in vitro dry matter digestibility, (IVOMD). Statistical
analyses for these variables are presented in Tables 3-2, 3-3, 3-4, and
3-5.

68
Table 3-2. Stastistical analysis model for maize data. Factorial (3x3)
for treatments 2, 5, 6, 7, 8, 9, 11, 12, and 13.
Source
df
Replications
3
(r-1)
Treatments
12
(T-l)
SPECIES EFFECT (2 sorghums + millet)
2
(E-l)
Treats (2, 5, 6, 7, 8) vs (11, 12, 13)
1
Treats (2, 5, 6) vs (7, 8, 9)
1
FERTILIZER RATES AND TIME OF APPLICATION EFFECT
2
Treats (2, 7, 11) vs (5, 6, 8, 9, 12, 13)
1
Treats (5, 8, 12) vs (6, 9, 13)
1
SPECIES X RATES-TIME
4
Treat 3 vs 4
1
Treats (1, 10) vs (3, 4)
1
Treat 1 vs 10
1
(LEFTOVER)*
1
ERROR
36
(r-1)
(t-l)
TOTAL
47
(RT-1)
* The degrees of freedom are not orthogonal.

69
Table 3-3. Statistical analysis model used for sorghum data. Factorial
(2x2) for treatments 1 through 9.
Source
df
REPLICATIONS
3
(r-1)
TREATMENTS
8
(t-l)
GENOTYPE EFFECT
1
(a-1)
Treats (1, 2, 3, 4, 5, 6) vs (7, 8, 9)
1
FERTILIZER RATES AND TIME OF APPLICATION
1
(B-l)
Treats (2, 5, 6) vs (7, 8, 9)
1
GENOTYPES X RATES-TIME
1
(a-1) (b-l)
LEFT OVER*
1
ERROR
27
(r-1) (t-l)
TOTAL
35
(rt-1)
* Degrees of freedom are not orthogonal.
Table 3-4. Statistical analysis model used for millet data. Randomized
complete block design.
Source
df
REPLICATIONS
TREATMENTS
Treat (10) vs (11, 12, 13)
Treat (11) vs (12, 13)
ERROR
TOTAL
3 (r-1)
3 (T-l)
1
1
9 (r-1) (t-l)
15 (rt-1)

70
Table 3-5. Statistical analysis model used in the growth analysis. For
treatment 6, 9, and 13.
Source
df
REPLICATIONS
3
(r-1)
TREATMENTS
12
(t-1)
ERRORS
36
(r-1) (t-1)
TOTAL
47
(rt-1)

71
Growth Analysis
To conduct an analysis of the growth of the systems under study in
the fertility trials, treatments 6, 9, and 13 were selected as
representatives of each system. Crop growth rate (CGR) of the 'NB-3' +
'Criollo', 'NB-3' + 'Pioneer 895', and 'NB-3' + 'Gahi-3' systems were
estimated on different phases of growth (Table 3-6). Total above-ground
growth was harvested from six hills of 'NB-3' and 'Criollo' and 1 m row
length from 'Pioneer 895' and 'Gahi-3' every sampling stage. Sampling
began when the crops were thinned, and at 21 and 24 days after seeding
for the first and second crops, respectively. At each sampling stage
plants were harvested, separated by components (leaf, stem, flower,
head, and/or ears) and weighed in the field. Subsamples were weighed and
oven dried at 70C for 72 hours (when constant weight was reached) then
weighed again to determine dry matter content. The change in average
plant dry weight on the n^ (day n + t) day since the previous harvest
(on day t) was divided by n to estimate crop growth rate (CGR) expressed
in kg ha ^day for each day in the period. Sub-samples were ground in a
Wiley mill to pass a 1 mm stainless steel screen, and stored in
air-tight bags until analyzed.
Green leaf area measurements were made at 50% bloom, soft-dough,
and at black-layer stages. All the leaves of the 12 maize plants from
each of the three plots were measured from base to tip and at the point
of maximum width. Leaf area was converted to leaf area indices (LAI) as
described by Dale et al (1980).
Daily precipitation data (Fig. 5-2) were obtained by averaging
readings from four rain gauges placed in the the four replications. Soil
samples from three 15-cm sections to a depth of 45 cm were taken on a

72
Table 3-6. Sampling procedure for growth analysis.
Sampling
Days after
Parts
stage Cl
planting
WP
At thinning
21
L + S
1.0 m tall
65
L + S + F
Full silk
73
L + S + F
+ E
Soft-dough stage
99
L + S + F
+ E
Black layer
120
L + S + F
+ E
Harvest
160
L + S +
30 days after harvest
194
Parts
Sampling
stage
PS
Days after
NS
MI
WP
Thinning
24
24
24
L +
S
0.75 m tall
45
45
L +
S
+
H
Full bloom
99
52
45
L +
S
+
H
Soft-dough stage
120
81
L +
S
+
H
Harvest
160
101
45/85
L +
s
30 days after harvest
193
136
Cl =
= Maize, PS =
'Criollo', NS = 'Pioneer 895'
ii
M
X
'Gahi-3'.

73
weekly basis to determine percent soil moisture on a volumetric basis.
Soil from each increment was placed in a previouly weighed can, then
weighed, oven dried at 105C for 24 hours, and weighed again. Assuming
constant weight, percent soil moisture was determined by difference.
Survey of Sulfur Deficiency in Maize
Experiment 1
Sixty day-old no-tillage maize was grown in a 65 ha field in
Alachua County, Florida. Plants showed various degrees of stunting and
ranged from dark green healthy plants to light green or yellowish
stunted plants. Plant height ranged from approximately 30 cm to 120 cm.
The stunted plants exhibited intervenal chlorosis, the degree of which
diminished as plant height increased. The hypothesis proposed stated
that the problem was likely associated with soil characteristics and the
solution could be obtained through soil-plant analysis.
A completely randomized experimental design was used that included
three replications of five maize treatments. Treatments included 30, 60,
75, 90, and 120 cm tall plants. Ten whole-plant samples were taken at
random for each replication, as well as the associated youngest mature
leaf. Soil samples were taken at several depths within 25 cm of the
treatment plants.
Plants and youngest mature leaves were washed in distilled water,
dried at 70C in a forced air oven, and ground in a Wiley mill to pass a
1 mm stainless steel screen. Soils were sampled in 15 cm increments to
45 cm, then later to 90 cm, air dried, ground by mortar and pestle, and
screened on a 2 mm stainless steel screen. Plant and soil samples were
analyzed as described in the section of laboratory procedures of this
chapter.

74
Experiment 2
Eighteen maize fields in northern Nicaragua (Esteli and Matagalpa)
that were between 40 and 50 days old were selected as experimental
fields. A second criterion of selection was the ocurrence of S deficient
and sufficient healthy looking plants (based on the criteria established
in experiment 1).
Once inside the experimental field, four deficient and four
sufficient plants were selected. Each pair of plants within a field was
considered to form a replication of a randomized complete block design.
The youngest fully expanded mature leaf was collected from each plant,
described, and measured in length and width. The leaves were weighed,
oven dried, ground in a Wiley mill to pass a 1 mm stainless steel
screen, and stored in air-tight bags for analysis.
Four soil samples (from 0 to 30 cm depth) were taken within a 25 cm
circumference around each plant. The samples for each plant were mixed
to form one sample per plant per replication. Samples were air dried,
sieved to pass a 2 mm stainless steel screen and, stored for analysis.
Response variables measured in plants were a) plant height, b) leaf
length, c) leaf width at the widest point, d) dry weight per leaf, e)
leaf concentrations of S, N, P, K, Ca, Mg, Cu, Fe, Mn, Zn. Soil response
variables measured were concentration of the same nutrients measured in
the leaf tissue.
Laboratory Procedures
Soil Analysis Methods
For all experiments, N analysis employed a microKjeldahl procedure
(Breraner, 1960) as modified by Gallaher et al. (1976). A 1.0-g sample

75
was placed in 100-ml digestion tube to which 3.2 g of catalyst (90%
anhydrous K^SO^, 10% anhydrous CuSO^), 10 ml concentrated H^SO^ and 2 ml
of 30% were added. Samples were then digested in an aluminum block
digester (Gallaher et al., 1976) for 2.5 hours at 375C. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen
concentrations of these prepared solutions were determined using a
Technicon AutoAnalyzer II.
All soil P, K, Ca, Mg, Fe, Cu, Mn, and Zn analyses were conducted
using procedures recommended by the University of Florida's Soil Testing
Laboratory. Five grams of air-dried soil were extracted with 0.05 N HC1
+ 0.025 N HS0. at a soil:solution ratio of 1 to 4 (W:V) for 5 minutes.
2 4
Soil P was then analyzed using colorimetry. Potassium was determined by
atomic emission spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were
determined by atomic absorption spectrophotometry. Soil pH was
determined using a 2:1 waterrsoil ratio.
Soil S was determined by the method described by Bards ley and
Lancaster (1965). Ten grams of 20-mesh soil were placed in a 50-ml
Erlenmeyer flask and extracted with 39 g of diluted in one L
of 0.025 acetic acid for 30 minutes, 0.25 g of washed activated
charcoal was added and extracted for 3 additional minutes. The soil
suspension was filtered using a sulfate-free Whatman No. 42 filter
paper. Ten milliliters of the filtrate were pipetted into a 50-ml
Erlenmeyer flask to which 1 ml of acid seed solution (6 N HC1 + 20 mg
kg of S as ^SO^) was added, swirled and 0.5 g of BaCl2*2H20 crystals
were added. This solution was left standing for 1 minute, then swirled
to dissolve all the crystals. Soil S concentration was then determined
using a Perkin-Elmer/Coleman 54 spectrophotometer.

76
Plant Analysis Methods
Nitrogen analysis of plant material employed the microKjeldahl
procedure modified by Gallaher et al. (1976). A 0.1-g sample was placed
in a 100-ml digestion tube to which two boiling chips, 3.2 g of catalyst
(90% anhydrous K^SO^, 10% anhydrous CuSO^), 10 ml of concentrated
and 2 ml of were added. Samples were then digested in an aluminum
block digester (Gallaher et al. (1976) for 2.5 hrs. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen
concentration of these solutions were determined on a Technicon
AutoAnalyzer II.
Phosphorus, K, Ca, Mg, Fe, Cu, Mn, and Zn concentrations were
determined by a mineral analysis procedure in which 1.0 g samples were
placed in 50-ml pyrex beakers and ashed in a muffle furnace at 480C
for a minimum of 4 hrs. After cooling each was treated with 2 ml of
concentrated HC1 and heated to dryness on a hot plate. An additional 2
ml of concentrated HC1 + water was added to the dry beakers followed by
reheating to boiling and then diluting to 100 ml volume with deionized
water. Solutions were analyzed for P using colorimetry on an
Autoanalyzer. Potassium was determined by atomic emission
spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were determined by
atomic absorption spectrophotometry.
IVOMD of plant material was determined by the Tilley and Terry
(1963) two-stage procedure adapted by Moore et al. (1972). For
measurements of combustible energy, approximately 0.5 g of sample was
pelleted in a cylinder press and weighed to the nearest 0.00001 g.
Samples were then placed in clean combustion boats. Combustible energy

77
values were obtained using a computerized Parr adiabatic calorimeter,
using standard ASTM methods (ASTM, 1979).
A sample of 0.3 g _+ 0.05 g of plant tissue was weighed in a clean
boat. The samples were spiked with 0.5 g of vanadium pentoxide
Sulfur concentrations were then determined using a Leco S Determinator
model SC132 at 540 nm.

CHAPTER 4
MAIZE + SORGHUM FARMING SYSTEMS IN CENTRAL AMERICA: SITUATIONAL
ANALYSIS
Introduction
In Central America, sorghum (Sorghum bicolor (L.) Moench) is
generally cultivated in association or in sequence with maize (Zea mays
L.). These two cropping systems are used by low-income farmers on
marginal agricultural land located in the semi-arid regions. Farmers use
these systems to stabilize production, reduce the risk of maize yield
loss caused by irregularities in climate, and as a response to scarcity
of resources. Monocropping sorghum systems are found on excellent
agricultural land where mechanization is possible and are practiced by
farmers of bountiful resources.
These production schemes have different purposes. In multiple
cropping systems sorghum produced by low-income farmers serves as a
staple food for human and animal consumption, while monocropping systems
produce testa-colored sorghums, used only in animal feed or for forage.
Based on this differentiation, production problems can be grouped in two
categories: those of sequential and intercropping systems and those of
monocropping systems.
Available information to improve the maize + sorghum cropping
system is limited or has not been adequately diffused to low income
farmers. This scarcity exists because national research programs have
generally been designed with a reductionist philosophy (research by
78

79
product), making it difficult for scientists to analyze interactions or
competition within the system.
According to Arze et al. (1983), in a research scheme for sorghum
cropping systems it is necessary to analyze the problem in a series of
logical and sequential phases, beginning with broad aspects and ending
with specific matters. This analysis permits the hierarchic
identification of relations between components of the system and the
determination of restrictions to crop production. The identification of
these restrictions is a basic element for the successful design of
research; it will also enhance the possibilities of accomplishing
specific proposed objectives.
In a general way, and considering sequence, the phases designed by
Arze et al. (1983) can be summarized as follows: 1) definition of the
problem, 2) characterization and diagnosis, 3) design of the research,
4) implementation, 5) validation, and 6) diffusion.
Few attempts have been made in the area to describe the maize +
sorghum system. Some of the most recent attempts include those conducted
in different areas of El Salvador by Rodriguez et al. (1977), Guillen et
al. (1978); Alvarado et al. (1978), Alegria et al. (1979); and Arias et
al. (1980). Kass (1980) and Fuentes and Salguero (1983) give a brief
description of the system in Guatemala. In Honduras, Mateo et al. (1981)
described the system in some detail. Hawkins et al. (1983) and Larios et
al. (1983) have provided the only recent descriptions of what may be
considered the typical maize + sorghum cropping system in Central
America.
The objectives of this research were 1) to locate and describe the
maize + sorghum system in Central America, 2) to describe the relations

80
between the maize + sorghum systems and its bio-physical and
socio-economic environment, 3) to describe interactions with other
production systems, and 4) to identify constraints and research
opportunities to alleviate these constraints.
Materials and Methods
Between November 1981 and March 1983 several trips were made to
Guatemala, El Salvador, Honduras, and Nicaragua. During these visits the
primary areas of production in each country were visited to obtain first
hand observation of the bio-physical and socio-economic environments of
the system. Informal interviews were held with several randomly selected
farmers, with extension agents, and with research staff of each area.
These visits provided an opportunity to gather more secondary
information in each country.
Due to economic and time limitations the search of information to
meet the proposed objectives was limited to the topics listed in the
following outline:
I. Bio-physical characteristics.
A.Soil and climatic factors.
1. Edapho-climatic characterization.
2. Identify relations between climate and the
hydro-edaphocelations in the area.
B. Agro-biological factors.
1. Characterization of the maize + sorghum/animal system.
2. Analysis of constraints to the system.
C. Eco-physiological relations of the system.
1. Photoperiod ism.

81
2. Rainfall and soil moisture.
3. Temperature.
II. Socio-economic Characteristics.
A. Social aspects.
1. Structure of the production system.
2. Social systems.
B. Economics.
1. Economic parameters of production.
2. Use of available resources.
Results and Discussion
In the semi-arid regions of Central America the owners of small and
medium size farms have developed a maize + sorghum/animal production
system (maize + sorghum/animal) in response to the predominant
environmental characteristics (Arias et al., 1980). Management of the
system and the structure of its components are based primarily on
enviromental variations and economic parameters. Larios et al. (1983)
found few studies of the relationship among components in this system or
of the analysis of inputs and outputs. The search for technological
alternatives requires from the researcher an understanding of the system
and an analysis and selection of the alternatives within the farmer's
possibilities that will cause greater development.
The system described here has been generally called "Maize/sorghum
intercrop". A list of common names used in Central America follows:
NAME COUNTRY
Maiz y sorgo El Salvador and Guatemala (Arias et
al.,1980;Kas s, 1980)

82
Maiz y maicillo El Salvador, Guatemala, and Honduras
(Arias et al., 1980; Rosales, 1980;
Mateo et al., 1981; Fuentes and
Salguero, 1983)
Maiz y milln Nicaragua (CATIE, 1980; Pineda et al., 1979)
Although maize and sorghum are the most important food crops in the
semi-arid regions of Central America (Larios et al., 1983), other crops
such as bean (Phaseolus spp.) (Guillen et al., 1978), cowpea (Vigna
spp.) (Alegria et al., 1979), and fruits are important in specific
areas. Sesame (Sesamum indicum L. ) (CATIE, 1982a) and flaxseed (Linum
usitatissimum L.) (CATIE, 1980) are widely cultivated and compete with
maize and sorghum for land and other resources.
Larios et al. (1983) reported that in the countries where the
system exists it interacts with animal production systems. Therefore, a
more complete and descriptive name should include its animal
component(s). A list of animal components of the systems found in these
areas follows:
SPECIES USES
Cattle (dual purpose) Meat, dairy, and power (Juarez
et al., 1979; Mateo et al., 1981
Swine Meat and lard (Rodriguez et al., 1977)
Poultry Meat and eggs (Guillen et al., 1978; Kass,
(1980)
Location
The maize + sorghum/animal production system is limited generally
to the foothills near the Pacific coastal plains, rolling lands and
valleys of the interior of Central America as depicted in Figure 4-1.

83
Figure 4-1. Distribution of maize + sorghum systems in Central
America (Drawn with information from Arias et al.,
1980; Mateo et al., 1981; and Hawkins et al.,
1983).

84
Hawkins et al. (1983) identified northern El Salvador as the area where
the system is most widely cultivated (240,000 ha). Reports in the
literature (Arias et al., 1980; Mateo et al., 1981; Fuentes and
Salguero, 1983) indicated that of the total area cultivated with sorghum
in Guatemala, El Salvador, and Honduras, 80, 93, and 93%, respectively
are intercropped with maize.
Bio-Physical Environment
Climate
The Central American Isthmus extends from east to west with the
Caribbean Sea at the north and the Pacific Ocean at the south (Fig.
4-1). Hot humid lowlands predominate on the Atlantic coast. The interior
is composed of mountains and valleys. A wide belt of steppe conditions
is found in these areas where the maize + sorghum system is found.
Precipitation stays below 1,000 mm yr ^ in the interior valleys. This
dryness is probably caused by mountain valley winds rather than by the
shielding effect of the mountains. In the Pacific coastal foothills
annual rainfall may range from 1,400 to 2,000 mm (Alvarado et al., 1978;
CATIE, 1980), and in some areas, such as northern El Salvador it may be
greater than 2,000 mm (Guillen et al., 1978). Annual rainfall is
distributed in a bimodal pattern (CATIE, 1980; CATIE, 1982a). The dry
season begins in November and ends in April or May, and the wet season
is interrupted by a dry period called "canicula" in July or August
(Rodriguez et al., 1977; Guillen et al., 1978). Results of studies
conducted by CATIE, (1980); and Guzman (1982) indicate that potential
annual evapotranspiration is high. The observed range in some areas is
between 1,000 and 2,000 mm (Fig. 4-2). This results in a soil moisture
deficit through May and the depletion of soil reserve in July. In the

85
Figure 4-2. Water deficient periods. La Trompina, El
Salvador (CATIE, El Salvador, unpublished
data).

86
semi-humid areas an excess of water occurs in September, contributing to
an increase in the availability of residual moisture through December.
The number of months in a year with a moisture deficit in the semi-arid
and semi-humid regions ranges from 7 to 10 and from 5 to 6,
respectively.
Southeastern Guatemala, southern Honduras, northeastern El
Salvador, and northwestern Nicaragua correspond to what have been
described as semi-arid regions (Larios et al., 1983). The agroclimatic
characteristics of these regions are similar to other semi-arid regions
of the world. These are summarized by Larios et al. (1983) as follows:
1. The beginning of the rainy season is uncertain.
2. More than 90% of annual precipitation occurs during the wet
season, which lasts generally from four to seven months.
3. Precipitation during the wet season is often extremely variable,
not only from year to year but also within seasons.
4. Mean daily rainfall intensities are two to four times greater
than in many temperate regions. The short duration intensities
frequently exceed the water intake capacity of the soil.
Mateo et al., (1981) claimed that the areas where maize + sorghum
is found most frequently correspond to what Holdridge classified as 1)
Bh-S(c), humid sub-tropical forest with biotemperature above 24C, 2)
Bs-T, dry tropical forest with biotemperatures below 24C but with
annual average air temperatures above 24C, and 3) Bs-S, dry
subtropical forest. Arias et al. (1980) and Larios et al. (1983) agree
that the cultivation of sorghum is related to biotemperatures or air
average annual temperatures above 24C.

87
Predominant soil types
The soils where the maize + sorghum cropping system is cultivated
can be classified into one of the following orders: Alfisols, Entisols,
Inceptisols, Vertisols or Mollisols (CATIE, 1980; Kass 1980; CATIE
1982a; Rico, 1982). Figure 4-3 shows an environmental profile for the
association of maize and sorghum in El Salvador, Nicaragua, and
Honduras; considering annual rainfall, altitude, slope, and soil
fertility and depth. The typical landscape is made up of steep lands,
slopes up to 50%, shallow soils (30 cm maximum) with prevalence of loose
stone or shale. It is highly susceptible to erosion (Arias et al.,
1980; CATIE, 1980).
Socio-Economic Environment
Family composition
Larios et al. (1983) reported that the average farm family is
comprised of seven members, approximately 75% of whom are under 30 years
of age; in some areas the population is somewhat younger (40% under 12
years). Assuming the inputs of women and children are 0.7 and 0.5,
respectively, man's working day, the average farmer has a daily
equivalent of 5 man days ^ in his family.
Education
Education levels vary from country to country. In some literacy can
be higher than 80%; in others it may be lower than 60%. Among children
it is generally higher than in parental groups (Larios et al., 1983).
Capital
Farm size is considered to range from small to medium (0.25 to 70
ha.). Land tenure is unsatisfactory (Green, 1974). In some cases 75% of
the farmers occupy 25% of the land (Hawkins et al., 1983; Larios et al.,

FREQUENCY
AREA OF THE SYSTEM
88
0 800 1200 1600 2000 2400 Annual ralnfall,mm
0 500 1000 1500 2000 Altitudes
0 10 20 40 I
Soil depth cm
Figure 4-3. Environmental profile of the maize sorghum system
in three countries of Central America (El Salvador,
Nicaragua, Honduras) (Larios et al., 1983).

89
1983). This situation is rapidly changing through agrarian reform plans
(personal observation by the author).
Cash flow in and out of the farms is very difficult to quantify,
especially that spent on food and clothing. Farm expenses and farm
activities are closely related to farm size (Fig. 4-4). In crop
production, a low-income farmer on a 7 ha farm may invest up to $200
(US) mainly on fertilizers (70%) and other field supplies and about $45
(US) on animal feeds. Cash flow into the farms comes from activities on
and off the farm, as depicted in Figure 4-4. On small-scale farms most
of the income (approximately 75%) is obtained from the sale of excess
grains (maize and sorghum), dairy products, meat, and draft animals
(CATIE, El Salvador, umpublished data, 1982). In their characterization
studies Arias et al. (1980) and Larios et al. (1983) emphasize the
importance of the animal component in generating income increases as
farm size augments (Fig. 4-5). Cattle are more common on larger farms,
while swine and poultry can be important sources of income among the
smaller farms.
Facilities and equipment
The value of fixed capital (housing, storage, fencing, and animal
shelter) is affected also by farm size; on the average, farmers of these
areas report holdings worth approximately $830 (US) (CATIE, 1980).
Juarez et al. (1979) report that farm equipment is limited to sprayers,
hoes, shovels, and "macanas" or "bordones" (a handweeding instrument
used for planting beans and sorghum into stands of maize). The average
value of this equipment varies from $18 to 40 (US). Very few farmers
own transport facilities other than an oxcart.

90
Figure 4-4. Percentage of income derived from farm activities
in different farm sizes (unpublished data, CATIE,
El Salvador).

ACTIVITY (ha)
91
Figure 4-5. Variation of activities as farm size increases.
Tejutla, El Salvador (Unpublished data, CATIE,
El Salvador).

92
Farming systems
On small-scale farms crop production systems constitute the main
activities, since they are related to family subsistence. As farm size
increases the area dedicated to crop production is comparatively small,
about four or five hectares, the maximum surface which can be managed by
a farmer and his family (Larios et al., 1983). As farms become larger in
size, the areas dedicated to cattle activities tend to increase,
especially as related to crop production areas (Fig. 4-5).
On farms larger than 50 ha, crop production systems increase since
the owner rents part of the land to landless farmers to be planted with
maize and sorghum. In return the farm owner will receive cash, part of
the crop, different forms of labor, and/or combinations of these
arrangements. The cultivated areas managed directly by the farm owner
tend to diminish to a minimum level of subsistence.
Hawkins et al. (1983) and Larios et al. (1983) were able to
establish a direct relation between farm size and the availability of
soil moisture. Large farms are normally located in areas with less
available soil moisture whereas small-scale farms are concentrated in
areas where more soil moisture is available. In the low-income farmer's
production systems maize is the main crop, normally associated with
beans or sorghum. Pigs and poultry are the main income producing
animals. The increase in the hydric deficit modifies the cropping
patterns; maize is displaced in importance by sorghum, forage, pasture,
or sisal. Swine and poultry are kept on most farms, and the number of
cattle is increased. The relations among farm size, hydric deficit, and
farming systems are shown in Figure 4-6, all within a representative
area for the maize + sorghum/animal production system.

93
Crop production systems
Studies by Guzman (1982), Hawkins et al. (1983), and Larios et al.
(1983) indicated that the location of the cropping system (Fig. 4-1) is
very much related to the frequency of uncertain rainfall periods
interrupted by a "canicula" (Fig. 4-2). Those farmers who practice
sorghum-based cropping systems have adopted cropping patterns that
diminish risk but ensure food for their families (Clara et al., 1983).
Figure 4-7 depicts the relation between rainfall patterns and relative
growth of the maize + sorghum system. Arias et al. (1980), Mateo et al.
(1981), and Hawkins et al. (1983) identified four cropping patterns as
the most often used in the system (Fig. 4-7): a) maize and sorghum
planted simultaneously in May; b) maize planted in May, sorghum planted
25 to 30 days later (at sidedressing and hilling up of the maize); c)
maize planted in May, sorghum in July (during anthesis of maize); and d)
maize planted in May and sorghum in August (at bending-over of maize).
The patterns used are closely related to the cultivar and available soil
moisture in the area. The crop spacings found more frequently are a)
single rows of maize interplanted with sorghum, b) single rows of maize
and sorghum both sharing the same hill, and c) sorghum broadcast in
maize stands (Fig. 4-8).
The early maturing maize cultivars (46 days to tasseling and 80 to
harvest) have a greater probability of escaping the "canicula".
Cultivars such as 'Criollo' perform better when cultivated in
association with sorghum (Clara et al., 1983). Moreover, these varieties
can be seeded for grain and/or forage. Sorghum cultivars used are
day-length sensitive; when planted in May, they have a long vegetative
growth period. In August and afterwards the competition with maize is

HYDRIC DEFICIT
Figure 4-6. Interrelationship among size of farms, hydric deficit, and
farming systems in small farms of East and North El Salvador.
(Unpublished data CATIE, El Salvador).
SIZE OF FARM (ho)

RELATIVE GROWTH
95
PERIOD (months)
Figure 4-7. Relation between chronological arrangements and
relative growth of the raaize/sorghum systems with
the rain distribution in El Salvador. (Personal
observation of the author, Mateo et al., 1981;
and Hawkins et al., 1983).

96
Figure 4-8. Spatial arrangements maize/sorghum cropping
systems.
a = Equidistant single rows,
b = single rows sorghum at foot of maize,
c = single rows of maize, sorghum broadcast
(Personal observation).

97
reduced as days become shorter, a condition that favors the sorghum for
intensive growth (Fig. 4-9). When planted simultaneously before August,
there is strong competition between the crops since both have similar
growth patterns.
In their characterization of the maize + sorghum system Arias et
al. (1980) indicated that cropping activities begin early in the year
(Table 4-1) with slash and burning. After the first rains, maize is sown
and 10 days later fertilized with N and P; a second N application is
done between 25 and 30 days after planting. Amounts used vary from one
area to another and sorghum is seldom fertilized.
Weeding is one of the most time-consuming enterprises of the
system. A first weeding is done 15 to 21 days after seeding the maize;
the hilling up is also a weeding activity. The last weeding is done just
before the planting of sorghum and/or bending over of maize.
Maize is harvested between October and December; the complete ear
is removed from the field and hand-shelled near the house. Sorghum
panicles are cut at the base and carried from the field and spread to
facilitate final grain drying. Threshing is done by hand-beating the
panicles with a stick. Yields vary considerably from one area to
another (Table 4-1) depending on the duration and severity of the
"canicula", on the cultivar planted, on the soil type, and on the amount
of fertilizer applied.
Animal production systems
Patio management is primarily used for small animals. Usually
patio-farmers keep from two to eight pigs, from two to 12 hens. Only 2
to 3% of the farms raise turkeys and ducks (Guillen et al., 1978; Juarez
et al., 1979). According to DeLa Hoz (CATIE/Honduras, personal

98
MAIZE GROWTH
SORGHUM GROWTH
. Relation between the sunrise, sunset and duration
of day length with variations in the relative
growth of the maize + sorghum system. (j. Arze,
CATIE, Costa Rica, unpublished data, 1983).
Figure 4-9
GROWTH (relative values)

99
Table 4-1. Typical management activities in cropping subsystems.
Activity
Man/
Days
Input
Output
Type
Quantity
Product
Quantity
Weeding
12.0
0 M
?
Burning
7.0
ashes
?
Herb. Applic.
3.0
Paraquat 2.4 1 ha
mulch
?
Planting
3.2
Seed
16*
Fert. Applic.
3.0
N-P
0 to 20-20
Weed (M)
3.6
0 M
1000*
Planting (S)
0.9
Seed
6-12*
Fert. Applic.
0.9
N
20*
Weeding (M)
5.0
0 M
?
Bend-over (M)
4.1
0 M
?
Weeding (S)
Harvesting (M)
ears
?
Shelling (M)
5.0
cobs
331*
grain
1700*
Harvesting (S)
6.0
forage
?
grain
57 0/1900*
(M) = maize, (S) = sorghum, 0 M = organic matter; *kg ha ; ** sorghum
planting date varies from 30 to 90 days after planting the maize.

100
communication, 1983) the main characteristics of the typical animal
production systems interacting with maize + sorghum in the Central
American Pacific coast are as follows:
SYSTEM MAIN CHARACTERISTICS PRODUCTS
Cattle Pasturing, dual-purpose milk, cash, meat,
and butter
Swine Free and confined during cash, meat, lard
the wet season
goultry Free ranging eggs, cash, and
meat
Lar ios et al. (1983) stated that feeding of the animal is a primary
activity, consisting of obtaining and supplying crop residues. Other
activities include egg collection, processing and sale of dairy
products, and animals. Less frequent activities include the sale of
eggs, pigs, and poultry. Table 4-2 details such activities during the
course of the year, and Table 4-3 shows the input and outputs of a
typical farm with 10 ha of pasture.
Animal production systems also require a few specialized family
activities (Tables 4-2 and 4-3). The wife and children are usually in
charge of feeding the pigs and chickens; the children can also milk the
cows and move them from one pasture to another or tend them along
roadsides.
Farm animals consume almost all of the crop byproducts; the root
system is the only component that is not used. This finding, plus other
evidence shown in the following section, proves the high degree of
adjustment of the system to its physical and socio-economic environment.

101
Table 4-2. Management activities in animal subsystems.
Months
Activities JFMAMJJASOND
I CATTLE
Milking
Feeding
Maize residues
Sorghum residues
Grazing
Supplements, concentrates
Creara/butter/cheese process
Animal sales
II SWINE
Feeding
Grains
Crop residues
Milk residues
Live sale (2/year)
III POULTRY
Grain feeding maize/sorghum
Egg recollection
Live sale
IV "GUATERA CROPPING
XXX = Increased use or production
*** = Decreased use or production
**********XXXXXXXXX****
XXX** **XXX
XXXXXX **X
********XXXXXXXXXXXX***
xxxxxxx
**********XXXXXXXXXX***
XXX XXX
*****xxxxxxxxxxxx*****
xxxxx xxxxx
XXX XXX XXX
XXX XXX
**********************
**********************
XXX*** *xxxx
xxxx** **xxxx
*

102
Table 4-3.
Inputs and outputs per year in animal production subsystems
(Typical farm in Tejutla, El Salvador).
Inputs
Quantity/Farm
Quantity/Animal
Icc -1

SWINE SUBSYSTEM
Maize Grain
204
102
Sorghum Grain
612
306
POULTRY SUBSYSTEM
Sorghum Grain
57
29
CATTLE SUBSYSTEM
Concentrates
273
22
Cotton Seed Meal
273
26
Salt
91
9
Forage
?
?
OUTPUTS
Pigs (2)
135
kg
67
kg
Chickens (5)
4.5
kg
0.9
kg
Eggs
300
120
Calves (2)
360
kg
180
kg
Milk
909
kg
303
kg

103
In many cases it not only includes material but also effective
relationships among man, his animals, and his land.
Crop/Animal Interactions
The interactions between crop and animal production systems within
the farm may be classified as positive or negative. Some important
interactions are:
Positive Interactions: a) animal sales provide capital for crop
production, b) animal production absorbs labor not utilized for crop
management, c) animals help complete the farmer's diet, d) animals
provide traction and manure for crops, e) the diversity in animal
species allows more efficient utilization of plant and animal products
or by-products, and f) poultry help to control insects.
Negative Interactions: a) cattle and crops compete for available
land, capital, and labor, b) swine and poultry compete with humans for
available grain, c) soil nutrients are carried off the field by cut and
carry crops "guateras" (maize or sorghum sown at extremely high
densities for green forage or hay), and d) cattle may compact soil and
cause erosion.
The schematic representation developed by Larios et al. (1983)
(Fig. 4-10) is a semiquantitative description of the maize +
sorghum/animal production system and the interactions between crops and
animals. The system is depicted as having six subsystems. The growing
of maize + sorghum demands high labor use at certain times, especially
during weeding, planting, and harvesting, while labor distribution in
the animal production systems is more or less constant during the year.
Family participation in labor is very important and it is used more
efficiently.

Passive ua
Energy srti
Recvc*ng
eceoior
360 Kg
o
p-
Figure 4-10. A serai-quantitative description of the maize + sorghum/animal
production system in Central America (Larios et al., 1983).

105
In the cropping subsystem, the association of maize and sorghum
requires products such as fertilizers, insecticides, herbicides and, in
some cases, seed from outside the farm. Production includes grains used
as food for the family and animals and the residues are sold or fed to
the cattle. Swine and poultry consume the damaged ears or grain that
falls in the field.
The "guatera" cropping system has not been studied in detail. The
farmer spends little time managing this system, especially in planting
and harvesting. Forage (from sorghum and occasionally maize) can be cut
and piled in the field or consumed directly by the animals.
Animals are produced for family consumption and for commercial
purposes, providing pork meat, milk, cheese, eggs, and live animals
(chicken, pigs, and calves). Ccmmon input expenses in animal production
are for salt and fish meal. Little is known about cash flow in this
production system.
Constraints
There are many constraints to crop production, animal, crop/animal,
and to farming systems. One of the main problems in discussing this
subject lies in delimiting the system to be analyzed. In the following
sections some of the most relevant will be discussed.
Crop production constraints
Arias et al. (1980), Guzman (1982), Francis (1983), and Hawkins et
al. (1983 ) agree that environmental stresses, especially drought, are
the most important limitations to crop production. This phenomenon
occurs because of the variability in the rainfall pattern and the
"canicula", which in some areas may last more than 30 days. Drought is
accentuated by the existing physiography, shallow soils, and heavy soil

106
textures. In some areas nutrient deficiency, particularly N, P, and S
(CATIE 1980, 1981a, 1981b, 1982a; Rico 1982; Hawkins et al., 1983), may
reduce crop productivity and can be related to drought.
Within the biological constraints, Arze et al. (1983) and Clara et
al. (1983) identified the wide use of low-yielding cultivars 'criollos'
of both maize and sorghum as a limitation that reduces the possibility
of increasing crop yields. Another disadvantage of these varieties is
that they are highly susceptible to downy mildew (Sclerospora spp. and
Sclerophthora spp.). Although a new disease (first reported in the area
in 1975, personal observation by the author), downy mildew has rapidly
gained importance in some regions of El Salvador, Honduras, and
Nicaragua. All the constraints for crop production activities also
affect animal yield directly.
Animal production constraints
Feed quality and availability are the primary constraints to animal
production (E. DeLa Hoz, CATIE/Honduras, personal communication 1983).
During the dry season maize and sorghum residues and "guateras" are the
only sources of feed, since pasture growth is limited to the rainy
season. The quality of the feed may be considered poor, protein intake
is low, and the low availability of feeds accentuates this constraint.
If feed availability were the main constraint to the animal production
system, then the most important constraint to the maize + sorghum/animal
system would be the same as those listed for crops; if more residues
were available, then more feed would be available.
Farming system constraints
The primary constraints to the farm system are the availability of
land, labor, or capital (Green (1974); Arias et al., 1980; Larios et

107
al., 1983). Land availability may change in the area as a result of the
agrarian reform projects being carried out by some of the local
governments (personal observation by the author). Labor is limited
during short periods, especially at weeding times and when high-paying
off-farm jobs such as coffee, cotton, and/or sugar cane farms demand
labor. Low capital availability is identified by determining dates of
crop and animal sales, usually just after harvest. When grain prices are
low farmers will store the grains and sell animals; the cash generated
is used to buy commodities and as investment capital for the next
cropping season. From this fact arises the economic importance of having
cattle, swine, and poultry for sale when cash is needed.
Research Opportunities
Information on maize + sorghum/animal systems is relatively scarce.
The lack of quantitative as well as qualitative information on inputs,
outputs, flows, and components of the maize + sorghum/cattle system
makes it difficult to understand its structure and functions in time and
space. According to Arze et al. (1983) to find alternatives that improve
the system it is necessary to 1) delimit the system within a particular
farm or region, 2) identify the composition and ranges of crop
components, particularly forages, (autotropic) in the predominant farms,
3) study the composition of the animal production component
(heterotropic), 4) study the variability of the crop/animal relations in
the region and identify the interaction levels, 5) identify, by levels,
the use of human energy, (family and hired) used in the management of
the crop/cattle subsystem of the maize + sorghum /cattle system, and 6)
identify the bio-physical as well as socio-economic characteristics of
the region where the system is to be developed.

108
Interventions
In the research scheme designed by Arze et al. (1983), the limiting
factors which should be studied are classified as follows:
Physical Characteristics: 1) Analysis of the variability of the
"canicula" and of the start and termination of the wet season, and 2)
analysis of water retention capacity of the soils in the regions where
the maize + sorghum/cattle system predominates.
Agrobiological Characteristics: 1) evaluate the "guatera" system,
2) evaluate the uses of the maize + sorghum system in animal and human
nutrition, 3) design spatial and chronological arrangements and
rotations that enhance the adaptability of the system to the
environmental conditions, and increase the availability of animal feed
during the dry season, 4) test varieties and/or species to improve the
quantitative and qualitative yield of the system, 5) genetically improve
the maize + sorghum system through a) incorporation of drought tolerance
or resistance, b) high nutritional yield, c) low fertilizer requirement,
and d) component substitution, 6) management and recovery of soils, 7)
identify and evaluate breeds, animal species, and management of the
traditional animal production system, emphasizing quantitative and
qualitative aspects, 8) identify and evaluate exotic forage species, 9)
evaluate (_in vitro and _in vivo) the components of the maize + sorghum
system, 10) quantify flow components within the system and establish
inputs and outputs of the whole system, and 11) study the animal
pasturing effects on land planted to maize and sorghum (soil compaction
and nutrient recycling).

CHAPTER 5
DRY MATTER ACCUMULATION BY MAIZE + SORGHUM AND MAIZE + MILLET
INTERCROPPING SYSTEMS
Introduction
Dry matter accumulation (DMA) is a useful definition of growth. Crop
growth is more accurately estimated by measurement of DMA than by
measurements of fresh weight, which is strongly influenced by the
environment. However, DMA is not a completely satisfactory definition of
growth, because growth also includes germination during which dry matter
is lost. Cell multiplication and increase in volume both may represent
little change in DMA (Salisbury and Ross, 1969).
Dry matter accumulation has been described as a function of
physiological, phenological, and environmental factors. Dry matter
accumulation with time is usually characterized by a sigmoidal curve,
(Leopold and Kriedemann, 1975), in which three primary phases are
recognized: expanding, linear, and senescent (Richards, 1969). In the
expansion phase, the growth rate (dry matter accumulated per unit of time)
is initially slow, but the rate increases constantly as more dry weight is
added. Accumulation of dry matter is exponential until self-shading or
other conditions prevent the increasing leaf area from producing a
proportionate increase in the weight of the plant (Duncan et al. 1967).
The end of the expansion phase marks the beginning of the linear phase in
which DMA is continuous at a constant rate. The final, senescent phase is
characterized by a decrease in growth rate as the crop approaches maturity
109

110
and begins to senesce (Salisbury and Ross, 1978). Crop growth rate (CGR)
is defined as dry matter accumulated per unit of land area per unit of
time. The mean CGR over a time period t^ to t^ is given by
CGR=W2~w^/t2~t^, where w^ and w^ designate the dry matter accumulated at
periods 1 and 2, respectively.
Sivakumar et al. (1979) suggested that plant growth is a result of an
effective integration of many factors. Hanway (1962a) found that
differences in soil fertility resulted in different rates of DMA, but the
relative proportion of the different parts was maintained. Goldsworthy and
Colegrove (1974) found production of dry matter to be related to the
amount and duration of leaf area after silking and to the efficiency of
the leaf area. Hsiao (1973) summarized the observed plant responses to
water stress, which include reductions in transpiration rates, CO^
assimilation rate, plant water potential, growth rate, and stomatal
aperture.
Shih et al. (1981) reported that LAI is often used as an indicator of
plant growth and for evaluating assimilation and transpiration rates in
plant physiological studies. Ashley et al. (1965) found good correlation
between LAI and leaf dry weight of cotton (Gossypium hirsutum L.). Hanway
(1962a) suggested that dry weight of the entire maize plant and of the
grain are directly related to and highly correlated to the weights of the
leaves in these plants.
The patterns of growth and dry matter distribution observed in
tropical maize (Goldsworthy and Colegrove, 1974) suggested that the
capacity of grain sink to accomodate assimilate can limit grain
production. McPherson and Boyer (1977) pointed out that another
potentially serious problem occurs if sink size has been affected by low

Ill
leaf water potential. Moss (1962) and Allison and Watson (1966) have shown
that when maize grain sink is missing, dry matter that would have passed
to the grain accumulates in the stem and husk.
Objectives
A series of experiments was conducted in Esteli, Nicaragua during
1982. The principal objectives of these studies were a) to describe the
DMA pattern of the maize + sorghum system and of potential substitutes; b)
to determine if variation of other components of the system, such as
substituting the traditional photosensitive sorghum with
non-photosensitive cultivars or with millet, will increase productivity of
the system; and c) to study the relation between gravimetric soil moisture
and DMA by the systems under study.
Materials and Methods
This experiment involving three intercropping systems (Fig. 5-1) was
conducted in Esteli, Nicaragua (Fig. 3-2) during the 1982-1983 growing
season. The experimental site (Centro Experimental de Esteli) was located
1 km north of the city of Esteli on the Panamerican Highway at an
elevation of 975 m. The average annual precipitation is 1,000 mm
distributed in a bimodal pattern (CATIE, 1981a); the largest amounts fall
during May, June, August, and September (CATIE 1980, 1981). This rainfall
pattern is the determining factor in defining the growing season. The
average annual temperature is 19C. The classification for the soil at
the experimental site was not available but it may be classified as a
Vertisol (CATIE, 1981). Further classification has not been determined.
The experimental field was previously planted to shade tobacco (Nicotiana
tabacum L.), but had been under fallow for the last 7 years.

112
Crop growth rates of the 'NB-3' + 'Criollo', 'NB-3' + 'Pioneer 895',
and 'NB-3' + 'Gahi-3' systems were estimated at different periods of
growth (Table 3-6). Maize plants received 30 kg ha of N and P fertilizer
at planting and were sidedressed with 40 kg N ha 25 days later. Both
sorghums and the millet were sidedressed with 30 and 35 kg ha ^ of P and
N, respectively. Total above-ground growth was harvested from six hills of
'NB-3' and 'Criollo' and aim row length from 'Pioneer 895' and 'Gahi-3'
every sampling stage (Figures 5-3, 5-4, 5-5). Sampling began when the
crops were thinned at 21 and 24 days after seeding for the first and
second crops, respectively. At each sampling stage plants were harvested,
separated by components (leaf, stem, flower, head, and/or ears), and
weighed in the field. Subsamples were weighed and oven dried at 70C for
72 hours (when constant weight was reached), then weighed again to
determine dry matter content. The change in average plant dry weight on
the nt'1 (day n + t) day since the previous harvest (on day t) was divided
by n to estimate CGR expressed in kg ha ^day ^ for each day in the period.
Sub-samples were ground in a Wiley mill to pass a 1 ram stainless steel
screen, and stored in air-tight bags until analyzed.
Green leaf area measurements were made at 50% bloom, at soft-dough,
and at black layer stages. All the leaves of the 12 maize plants from each
of the three plots were measured from base to tip and at the point of
maximum width. Leaf area was converted to LAI as described by Dale et al.
(1980).
Daily precipitation data (Fig. 5-1) were obtained by averaging
readings from four rain gauges placed in the four replications. Soil
samples from three 15-cm sections to a depth of 45 cm were taken on a
weekly basis to determine percent soil moisture on a volumetric basis.

113
Soil from each increment was placed in a previouly weighed can, then
weighed, oven dried at 105C for 24 hours, and weighed again. Assuming
constant weight, soil moisture was determined by difference.
Statistical analyses were conducted for the randomized complete block
design. Individual plots were 9.8 by 10 m. Twelve rows of 'NB-3' maize
were planted no-tillage by hand in each plot (52,000 plants ha on 16
June. The second crops ('Criollo', photosensitive sorghum; 'Pioneer 895',
non-photosensitive sorghum; and 'Gahi-3' millet) were interplanted on 16
September, according to the spatial arrangements depicted in Figure 3-3.
The 'Criollo' was seeded in-between maize rows (40 cm from the maize
hills), in hills spaced 0.80 cm apart, and later thinned 24 days after
seeding to six plants per hill to obtain 75,000 plants ha 'Pioneer 895'
and 'Gahi-3' were seeded in double rows (20 cm from the maize); 24 days
after seeding the rows were thinned to give 120,000 plants ha
Results and Discussion
Percent Soil Moisture
Late planting (delayed 3 weeks due to intense rains during the last
week of May and the first week of June (Fig. 5-1) together with a long and
intense "canicula") resulted in improper growing conditions for maize,
sorghum, and millet, in particular for maize. Rainfall in the area during
the growing season of the crops was less than 70% of the normal occurrence
(CATIE, 1981a). A long drought occurred between planting and and the
beginning of grain filling of 'NB-3'. Data presented by Gardner et al.
(1981) suggested that water stress during vegetative growth only had the
least damaging effects on yield, while stress during pollination and grain
filling stages had the greatest limiting effect on yield. Denmead and Shaw

Precipitntion (mm)
Time
Figure 5-1. Chronological arrangement of the three systems under study
and rainfall distribution during the growing season.
114

115
(1960) found that grain yield was affected more than any other plant
characteristic by early stress.
A second period of intense rainfall occurred during the second week
of September which recharged the soil (Figure 5-2). In general, the 30-45
cm depth had a higher soil moisture percentage than the 0-15 cm depth.
Only during week 12 after planting maize did the superficial horizon
surpass the lower horizons in soil moisture content (Table 5-1). The
highest percentage observed (40.9) occurred in the 30-45 cm depth and
corresponded to the period immediately following black layer formation in
maize and prior to anthesis of the non-photosensitive sorghum. The lowest
value observed (10.4%) corresponded to the 0-15 cm depth and occurred
during grain filling of the photosensitive sorghum. Moisture stress was
frequently observed and was evident by dry curled leaves, short plants,
and barren stalks.
Even though water was available at deeper depths (Fig. 5-2), maize
from all cropping systems exhibited water stress (leaf wilt or firing)
before soft-dough. Generally there was less available moisture in the top
two depths for the 'NB-3', which caused pollen desiccation, therefore
limiting the size of the grain sink. Data reported by Moss (1962) and
Allison and Watson (1966) support these results. Percent soil moisture
increased between soft-dough and black layer, allowing a limited grain
fill. During this period dry matter accumulated in the stem and leaves due
to the lack of an adequate grain sink (Classen and Shaw, 1970; Goldsworthy
and Colegrove, 1974).
Soon after planting the second crops the shallow root system began to
draw available moisture, causing a depletion in all the depth intervals
(Fig. 5-2). 'Criollo' anthesis and grain fill occurred during a period of

Figure 5-2. Percent soil moisture during 1982-1983 growing season in Esteli,
Nicaragua.
X Soil Moisture
n
i
o
*
w.
3
CQ
in
CO
a
w
o
fO OJ JkLnCTi^JCO^O
o oo oooooo
911

117
Table 5-1. Percent soil moisture at three soil
depths in Esteli, Nicaragua.
Weeks after Depths
planting
Maize 0-15 15-30 30-45
3 -3
m ra
1
25.3b*
31.0a
34.6a
2
27.3ab
30.3ab
35.3a
3
23.1b
26,6ab
28.7a
4
23.3c
28.5b
31.8a
5
22.3b
28.5a
30.5a
6
21.7b
29.2a
30.1a
7
22.8b
24.9a
26.2ab
8
39.2a
37.6ab
36.8ab
9
34.0b
36.9a
36.0a
10
34.5
39.0
36.5
11
29.1b
32.lab
40.9a
12
28.2b
32.lab
34.4a
13
25.3b
32.lab
34.4a
14
23.9c
27.5b
33.3a
15
31.9b
32.3a
34.2a
16
26.7b
30.0a
32.9a
17
21.2b
24.3a
26.2a
18
21.7
24.5
25.9
19
19.6b
27.8a
28.5a
20
21.4b
29.6a
31.4a
21
17.3b
26.5a
29.4a
22
18.5b
25.8a
26.5a
23
16.7c
23.5b
28.6a
24
16.7c
25.7b
30.1a
25
14.0c
19.5b
23.7a
26
12.4b
18.7a
20.0a
27
12.4b
15.8a
16.1a
28
11.4
18.0
14.1
29
11.2
14.3
14.7
30
10.4
13.4
14.4
Means within
a week not
followed by
the
same letter
are different
according
to Duncan's
new
multiple
range test at
the 0.05
level of probability.

118
low soil moisture availability. This may explain in part the low grain
yields observed. These findings support data reported by Sivakumar et al.
(1978). Classen and Shaw (1970) found that a stress at silking resulted in
marked increases in stem weight with a corresponding decrease in grain
yield. This effect was due to an increase in sugar accumulation because of
a reduction in ear sink size.
Soil moisture conditions during critical growth periods were
generally better for 'Pioneer 895' than for 'Criollo' and 'Gahi-3' (Fig.
5-2). Anthesis and grain fill coincided with a period of high soil
moisture availability. This may explain in part the considerable sorghum
grain yield observed (Fig. 5-4b). Alessi and Power (1976) found that water
depletion was greater during the early part of the growing season than
after midseason, making water use after midseason highly dependent on
rainfall. Olson (1971) reported high sorghum yields when rainfall
coincided with anthesis. 'Pioneer 895' was planted in double rows (Fig.
3-1). According to Blum (1970) this planting arrangement prompts plant
competition which causes a reduction of early plant growth and LAI. This
reduction in LAI is partially responsible for reduced soil moisture use
from early growth to heading, so that more water is available for the
grain filling period.
'Gahi-3' had relatively favorable moisture conditions during its
growth (Figures 5-1 and 5-2). Higher soil moisture was available and
higher yields were observed during the first vegetative growth and higher
yields (Fig. 5-5b) than in the ratoon crop.
Dry Matter Accumulation
Dry matter yields were measured throughout the growing season
(Figures 5-3, 5-4, and 5-5). Diffe fences for maize dry matter yield were

Sorghum Dry Matter Yield (Mg ha ) Maize Dry Matter Yield (Mg ha
119
Days After Planting Maize
Figure 5-3. Total, stem, leaf, flower, ear, or head dry matter
accumulation for 'NB-3' (a) and 'Criollo' (b)
intercropped.

Sorghum Dry Hotter Yield (Mg ha ) Maize Dry Matter Yield (Mg ha
120
Doys After Plnnting Maize
Figure 5-4. Total, stem, leaf, flower, ear, on head of 'NB-3'
maize (a) and 'Pioneer 895' sorghum (b) intercropped.

121
20 40 60 80 100 120 140 160 180 200
Days Afler Planting Maize
Dmis After Plnnttna Maize
Figure 5-5.
Total, stem,
and 'Gahi-3'
leaf, ear or head of 'NB-3' (a)
(b) intercropped.

122
not significant at the first sampling stage (thinning). However, a general
trend observed was that maize plants growing intercropped with 'Gahi-3'
(M+MI) generally produced higher dry matter yield than maize intercropped
with the photosensitive sorghum 'Criollo' (M+PS) or the non-photosensitive
'Pioneer 895' (M+NS). Maize plants from the M+PS and M+MI yielded higher
stem dry weight at bloom than those plants from the M+NS, at the 0.05
level of probability. No differences were observed between M+PS and M+MI.
Flower DMA was consistently higher in maize plants from the M+MI than
those from the other systems at p=0.05. No differences among systems were
detected for DMA in the leaf or ear at p=0.05.
Anthesis occurred 65 days after planting. Maize flowers gained weight
at rates of 55, 53, and 49 kg ha ^day ^, for M+MI, M+PS and M+NS,
respectively (Table 5-2). Thereafter, maize flowers decreased in weight at
low rates (6, 2, and 2 kg ha *day ^), for the M+PS, M+NS, and M+MI,
respectively.
Maize stem dry weight increased at a rate of 216, 209 and 181 kg
ha ^day ^for the M+PS, M+MI, and M+NS, respectively. At harvest, maize
plants from the M+MI system had accumulated more dry matter (38.5 Mg ha ^)
than maize in M+PS and M+NS systems.
Midseason losses of dry matter have been reported by Classen and Shaw
(1970) and Goldsworthy and Colegrove (1974). Results presented in Figures
5-3, 5-4, and 5-5 support these findings. The intense rains during the
second week of September triggered a second growth period for maize
(Figures 5-3a, 5-4a, and 5-5a). Since the drought had drastically reduced
the ear sink, dry matter accumulation occurred in the stem and leaves.
This ability to recover from water stress has been defined as tolerance to
drought. The highest crop growth rate was observed in maize plants from

Table
5-2.
Crop
growth
rates
of 'NB
-3' in
three
intercropping
systems.
Days
Whole Plant
Stem
Leaf
Flower
Ear
M+PS
N+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
1
leg
0-21
2
2
2
22-44
77
59
92
32
25
37
44
34
49
45-65
277
267
326
216
181
209
8
37
62
53
49
55
66-99
113
116
136
-16
6
13
5
9
-22
-6
-8
-7
129
109
153
99-120
-62
-38
-93
-16
-23
-36
-44
-30
-37
-6
-1
-3
-3
17
-21
120-160
397
509
756
98
127
149
314
400
593
-2
-2
-2
-14
-15
-19
160-190
-157
-318
-671
-162
-192
-244
90
-47
-296
-1
-1
-2
M 3 maize, PS photosensitive sorghum, NS = non-photosensitive sorghum, and MI = millet
123

124
the M+MI plots (756 kg ha ^day *). This compares well with the 500 kg
ha ^day ^ reported by Goldsworthy.
After ear harvest, leaves from the M+MI plots continued to gain
weight (90 kg ha ^day ^), but leaves from the M+NS and M+PS were losing
dry matter at rates of 296 and 47 kg ha ^day *, respectively (Figures
5-5a, 5-4a, and 5-3a, respectively). During this same period whole plants
were losing dry matter at rates of 157, 318, and 671 kg ha ^day ^,
respectively, for the M+PS, M+NS, and M+MI plots. Those plants with the
highest crop growth rates also had faster decreases.
Water stress during anthesis and grain fill reduced the size of the
maize ear sink considerably. Ears accumulated dry matter at similar rates
in all systems (129, 109, 153 kg ha ^day ^ for the M+PS, M+NS, and M+MI
plots, respectively (no differences were observed at the 0.05 level of
probability), as depicted in Figures 5-3a, 5-4a, and 5-5a. After
soft-dough, ears began to lose dry matter.
Sixty five days after planting (Table 5-2) more dry matter had
accumulated in the leaf than in the stem of maize (56 and 44%,
respectively). However, as flowers and ears began to develop, assimilates
moved out from the leaf into the ear. Barlow and Boersma (1976) reported
that in desiccated plants dry matter accumulation in the grain occurs at
the expense of dry matter stored in the leaves and stem. Once the effect
of water stress affected the size of the grain sink, assimilates began to
accumulate in the leaves and stem. McPherson and Boyer (1977) concluded
that translocation in maize was less inhibited than photosynthesis.
Conversely, Brevedan and Hodges (1973) reported that translocation was
more sensitive than photosynthesis. At harvest, approximately 63, 26, and
12% of the dry weight were distributed in the leaves, stem, and ears,

125
respectively. No differences were observed among treatments, at the 0.05
level of probability.
Dry matter accumulation by 'Criollo', 'Pioneer 895', and 'Gahi-3' is
depicted in Figures 5-3b, 5-4b, and 5-5b, respectively. As expected, the
photosensitive 'Criollo' had the longest growing cycle of the three crops.
'Gahi-3' was harvested 45 days after planting, and a ratoon crop was
harvested 40 days after. The non-photosensitive sorghum was harvested 131
days after harvest. As in 'NB-3', a midseason loss in dry matter was
observed in the 'Criollo' and 'Pioneer 895', although, not as severe as in
'NB-3'. Goldsworthy (1970) reported similar losses, due to respiration
losses that are not replaced by assimilation.
In 'Criollo' at bloom the stem was accumulating dry matter at a rate
of 92gkg ha ^day ^(Table 5-3), while leaves lost weight from bloom to
milk-dough stage (10 kg ha ^day ^). Maximum dry matter accumulation (14.3
Mg ha \ Fig. 5-3b) occurred 162 days after planting (at grain harvest),
which coincided with the highest crop growth rate (134 kg ha ^day ^).
After head harvest, 'Criollo' lost dry matter rapidly; 190 days after
planting the rate of dry matter loss was 383 kg ha ^day ^
Distribution of dry matter as percent of total in 'Criollo' varied as
the growing season progressed (Table 5-5). Forty five days after planting
57 and 43% of the dry matter had accumulated in the leaves and stems,
respectively. As heads began to develop, assimilates moved out from the
leaves, while stems kept gaining weight. Head sink size was reduced by low
rainfall and soil water availability. Assimilates that were moving from
the leaves to the heads were shunted to the large sink in the stem. At
harvest 46, 37, and 17% of the dry matter had accumulated in the stems,

126
Table 5-3. Crop growth rate of 'Criollo', 'Pioneer 895',
and 'Gahi-3' intercropped with maize.
Days
Whole
plant
Stem
Leaf
Head
-1
-1
rcg na
aay
Criollo
0-24
7
24-45
38
20
27
46-81
94
43
24
26
82-101
108
92
-10
26
102-162
134
48
68
18
163-193
-252
-141
-285
Pioneer 895
0-24
14
25-45
29
22
23
46-52
57
260
136
175
52-69
-37
0
105
11
69-101
341
50
57
234
101-136
-383
-32
-52
Gahi-3
0-24
7
25-45
135
55
43
29
46-85
25
10
3
10

Table
5-4. Dry matter
different
distribution as
cropping systems.
percent
of the total dry weight
of 'NB-3'
grown
in 3
Stem
Leaf
Flower
Ear
DAP
M+PS
N+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
M+PS
M+NS
M+MI
dae ha"1
day 1-
65
42.2
42.8
46.3
57.8
57.2
53.7
73
56.2
54.0
53.3
36.3
37.9
40.1
7.5
8.1
6.6
99
32.3
35.1
38.1
25.3
26.1
20.7
3.2
2.3
2.7
39.2
36.5
38.5
120
34.2
32.1
38.4
17.5
20.0
16.2
2.2
2.2
2.2
46.1
45.7
42.9
160
27.6
26.7
23.6
60.1
63.6
65.1
0.3
0.3
0.3
12.0
9.4
11.0
193
5.6
5.8
6.3
94.2
94.0
93.6
0.2
0.2
0.1
M = maize, PS = photosensitive sorghum, NS = non-photosensitive sorghum, and MI = millet.
DAP = days after planting.
127

Table 5-5. Dry matter distribution as percent of total dry weight of 'Criollo'
sorghum, 'Pioneer 895' sorghum, and 'Gahi-3' millet.
DAP
Criollo
DAP
Pioneer
895
DAP
Gahi-3
Stem Leaf
Head
Stem
Leaf
Head
Stem
Leaf
Head
-days-
dag kg
-days-
dag
kg
1
-days-
- dag kg 1
45
43
57
45
48
52
45
45
36
19
80
45
33
22
52
46
30
24
85
39
20
41
99
58
19
23
69
50
19
31
160
46
37
17
101
28
17
55
190
66
34
136
50
50
DAP = Days after planting

129
leaves, and head respectively. Thirty days after harvest, stems and leaves
represented 66 and 34% of total dry matter, respectively.
Dry matter accumulation by 'Pioneer 895' is depicted in Figure 5-4b.
It differed from that observed in the photosensitive 'Criollo' (Fig.
5-3b). At bloom 4.3 Mg ha ^ (approximately 25% of the total dry matter)
had accumulated. Leaves and stems represented 52 and 48% of the total,
respectively. Heads developed rapidly at the expense of leaf and stem dry
weight. Maximum dry matter accumulation (14.9 Mg ha *) occurred 101 days
after planting (grain harvest); heads, stems, and leaves had accumulated
55, 28, and 17%, respectively.
The most striking difference in the dry matter distribution patterns
between the photosensitive 'Criollo' and the non-photosensitive 'Pioneer
895' sorghum is the amount of accumulation by the head. Both sorghums
produced similar amounts of dry matter (14.3 and 14.9 Mg ha ^ for
'Criollo' and 'Pioneer 895', respectively). However, at harvest
non-photosensitive sorghum distributed 55% of the total dry matter
accumulated to the head, while the photosensitive sorghum had distributed
only 17%. Conversely, 'Criollo' accumulated 46% of the dry matter in the
stem while 'Pioneer 895' only allocated 28% of the total dry matter
accumulated in the stem. Goldsworthy (1970), comparing photosensitive and
non-photosensitive sorghums, reported similar results. His data suggest
that this difference can be explained in terms of the number of spikelets
present at heading. The number and/or potential size of the developing
grain in photosensitive sorghums appear to be too small to accept all the
assimilate produced. After head harvest, 'Pioneer 895' lost dry matter at
a rate of 156 kg ha *day ^(Table 5-3). Most of the loss in both the

130
sorghums was leaf dry weight, while 'Criollo' lost dry matter more rapidly
(303 kg ha ^day ^).
The late planting affected 'Gahi-3' more than any of the other crops
(Fig. 5-5b). Between 25 and 45 days after planting, 'Gahi-3' was growing
at a rate of 135 kg ha ^day (Table 5-3). Stems and leaves were growing
at a rate of 55 and 43 kg ha ^day ^, respectively. During the ratoon
growth Gahi-3 grew at a much slower rate (25 kg ha *day ^).
Leaf Area Index and Other Plant Characteristics
Leaf area index and other plant characteristics are presented in
Table 5-5. No statistical differences were observed for plant height and
number of leaves per plant among maize plants in the three systems. In
general, plants from the M+MI system were taller and had more leaves.
Leaf area indices for all treatments were low when compared to values
reported by Eik and Hanway (1966) and Hoyt and Bradfield (1963) in similar
population stands. Another difference observed is that maximum LAI
occurred later in the season. Eik and Hanway (1966) observed maximum LAI
at 50% bloom. These results indicate that LAI was markedly affected by low
soil moisture. During soft-dough, differences between maize plants from
the systems were observed (Table 5-5). Plants from the M+PS and M+MI
system had larger LAI than plants from M+NS. This suggests that the
non-photosensitive sorghum was competing more intensely with maize.
Eik and Hanway (1966) reported that yield is affected not only by the
factors which affect plant growth early in the growing season but also by
leaf area duration. Leaf area did not decline after anthesis, as reported
in the literature (Eik and Hanway 1966; Dale et al., 1980). This explains,
in part, the pattern of growth observed in Figures 5-3a, 5-4a, and 5-5a.

CHAPTER 6
NUTRIENT CONCENTRATION, IVOMD, AND METABOLIZABLE ENERGY OF
INTERCROPPED MAIZE + SORGHUM AND MAIZE + MILLET SYSTEMS
Introduction
Maize (Zea mays L.) + sorghum (Sorghum bicolor (L.) Moench)
intercropping systems are popular in the semi-arid regions of Central
America (Larios et al., 1983). This practice allows expansion of animal
feeding without additional capital investment by expanding the use of
land, facilities, and residues. In spite of the importance of the maize
+ sorghum system in procuring food and feed for the majority of the
population and animals in these regions there is little research
information upon which to base fertility or management decisions.
Information is needed concerning the accumulation of nutrients and
quality of the different plant components (Arze et al., 1983).
Plant analysis has long been used in various ways for diagnosing
plant nutrient adequacy and estimating fertilizer needs (Pierre et al.,
1977). According to Bates (1970) the diagnosis of nutrient deficiencies
and the prediction of fertilizer requirements from plant analysis are
based on a critical nutrient concentration or nutrient fraction within
the plant below which growth or yield is restricted. Macy (1936)
proposed a basic theory, the central concept of which is that there is a
critical concentration of each nutrient in each species, above which
there is luxury consumption and below which there is poverty adjustment
which is almost proportional to the deficiency until a minimum
131

132
concentration is reached. Ulrich (1952) defined the critical nutrient
concentration in relation to plant growth either in terms of the
concentration that is just deficient for maximum growth or that which is
just adequate for maximum growth, or the concentration separating the
deficiency zones from adequacy zones.
Brown and Jones (1977) concluded that plant species, genotypes, and
varieties differ in their nutrient requirements and tolerance to excess
mineral elements and poses the challenge of determining the nutrient
requirements of plants so that the plant and the soil can be made
compatible. Bates (1970) identified maturity, cultivar, and interaction
among nutrients and the environment as factors that affect nutrient
concentrations in plants. Among the environmental factors the most
relevant is available soil moisture supply. Because environmental
conditions do vary over short periods of time they will affect the
validity of the analysis. Peaslee and Moss (1966) postulated that since
it is widely known that K, Ca, and Mg interact in uptake, concentration,
and in many functions, discussing the cation sum and/or ratio efficiency
may be more appropriate than individual cations. This theory may be
applied to all cases where there is interaction between nutrients.
Green (1973) oberved that many factors combine to determine the
relative value of sorghum grain. Some of these are differences in tannin
content, protein content, amino acid composition, amount of floury and
horny endosperm, and field weathering. Johnson et al. (1966) concluded
that percent ash, cellulose and crude protein were significantly
decreased with maturity. Schmid et al. (1975) observed that cell walls
from maize cultivars were considerably more digestible with maturity
than those of sorghum cultivars. These results indicate that low cell

133
wall digestibility is a major factor limiting dry matter digestibility
of sorghum silage.
Data presented by Hall et al. (1965) indicated that sorghum grain
is comparable to maize grain in digestibility. Clark et al. (1965) found
no differences between millet (Pennisetum americanum (L.) Leeke) and
sorghum x sudangrass (Sorghum sudanense L.).
Crop residues of grain sorghum and maize have attracted attention
as alternate economical forage resource for livestock production (Perry
and Olson, 1975). However, Martin and Wedin (1974) reported that
thousands of hectares of sorghum residues are not used in the midwestern
United States because they are considered of poor quality. Ratoons often
remain as leafy and succulent growing plants following grain harvest and
should be considered as a feed source for farm animals.
Plant populations, row spacings, and soil fertility affect not only
grain yields but also the yields and quality of residues. Residue yield
from maize is normally greater from maize than from grain sorghum but
lower in crude protein. Perry and Olson (1975) observed that maize dry
matter yields decline as much as 30% within 100 days after grain
harvest. Martin and Wedin (1974) reported that sorghum lost
approximately 28% of its maximum yield by 76 days after grain harvest.
Crop residues have potential as fertilizer, as fuel, and as
livestock feed. Comparative values for these uses can be determined on
the basis of the amount energy saved by substituting these materials for
conventional sources of feed, fertilizer or fuel.
Croka and Wagner (1975) observed that net energy has become widely
accepted for expressing the value of a ration and the energy
requirements for feedlot cattle. Energy reserves may be considered as

134
organic accumulates synthesized by the plant which are available for
growth, development, and metabolism. Bolsen (1977) observed that sorghum
and maize stover are energy containing by-products of grain production.
Both crop residues make acceptable silage and both supply the energy in
maintanace rations for beef cows or ewes. On an energy basis, maize
silage is valuable for milk production.
Materials and Methods
Field Procedures
This experiment involving three intercropping systems (Fig. 5-1)
was conducted in Esteli, Nicaragua (Fig. 4-1) during the 1982-1983
growing season. The experimental site (Centro Experimental de Esteli)
was located 1 km north of the city of Esteli on the Panamerican Highway
at an elevation of 975 m. The average annual precipitation is 1000 mm
distributed in a bimodal pattern (CATIE, 1981a); the largest amounts
fall during May, June, August, and September (CATIE 1980, 1981). This
rainfall pattern is the determining factor in defining the growing
season. The average annual temperature is 19C. The soil classification
for the experimental site was not available but it may be classified as
a Vertisol (CATIE, 1981). Further classif ication has not been
determined. The experimental field was previously planted to shade
tobacco (Nicotiana tabacum L. ) but had been under fallow for the last
seven years.
Nutrient concentration, IVOMD, metabolizable energy, and percent
organic matter of the 'NB-3' + 'Criollo', 'NB-3' + 'Pioneer 895', and
'NB-3' + 'Gahi-3' systems were determined at different periods of growth
(Table 3-6). Total above-ground growth was harvested from six hills of

135
'NB 3' and 'Criollo' and aim row length from 'Pioneer 895' and
'Gahi-3' every sampling stage (Figs. 5-3, 5-4, 5-5). Sampling began when
the crops were thinned at 21 and 24 days after seeding for the first and
second crops, respectively. At each sampling stage plants were
harvested, separated by components (leaf, stem, flower, head, or ears),
and weighed in the field. Subsamples were weighed and oven dried at
70C for 72 hours (when constant weight was reached), then weighed
again to determine dry matter content. Sub-samples were ground in a
Wiley mill to pass a 1 mm stainless steel screen, and stored in
air-tight bags until analyzed. Soil samples were taken from each plot
before planting and after the last harvest.
Statistical analyses were conducted for the randomized complete
block design. Individual plots were 9.8 by 10 m. Twelve rows of 'NB-3'
maize were planted no-tillage by hand in each plot (52,000 plants ha ^)
on 16 June. The second crops ('Criollo', photosensitive sorghum;
'Pioneer 895', non-photosensitive sorghum; and 'Gahi-3', millet) were
interplanted on 16 September according to the spatial arrangements
depicted in Fig. 3-3. The 'Criollo' was seeded in-between maize rows
(40 cm from the maize hills) in hills spaced 0.80 cm apart and later
thinned 24 days after seeding to six plants per hill to obtain 75,000
plants ha 'Pioneer 895' and 'Gahi-3' were seeded in double rows (20
cm from the maize); 24 days after seeding the rows were thinned to give
120,000 plants ha Maize plants received 30 kg ha ^ of N and P
fertilizer at planting and were sidedressed with 40 kg N ha 25 days
later. Both sorghums and the millet were sidedressed with 30 and 35 kg
ha ^ of P and N, respectively.

136
Laboratory Procedures
Soil analysis methods
Nitrogen analysis employed a microKjeldahl procedure (Bremner,
1960) as modified by Gallaher et al. (1976). A 1.0-g sample was placed
in a 100-ml digestion tube to which 3.2 g of catalyst (90% anhydrous
K^SO^, 10% anhydrous CuSO^), 10 ml concentrated ^02 and 2 ml 30%
were added. Samples were then digested in an aluminum block digester
(Gallaher et al., 1976) for 3.5 hours at 375C. Upon cooling, solutions
were diluted to 75 ml with deionized water. Nitrogen concentrations of
these prepared solutions were determined using a Technicon AutoAnalyzer
II.
All soil P, K, Ca, Mg, Fe, Cu, Mn, and Zn analyses were conducted
using procedures recommended by the University of Florida's Soil Testing
Laboratory. Five grams of air-dried soil were extracted with 0.05 N HC1
+ 0.025 N ^SO^ at a soil:solution ratio of 1 to 4 (W:V) for 5 minutes.
Soil P was then analyzed using colorimetry. Potassium was determined by
atomic emission spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were
determined by atomic absorption spectrophotometry. Soil pH was
determined using a 2:1 water:soil ratio.
Plant Analysis Methods
Nitrogen analysis of plant material employed the microKjeldahl
procedure modified by Gallaher et al. (1976). A 0.1-g sample was placed
in 100-ml digestion tubes to which two boiling chips, 3.2 g of catalyst
(90% anhydrous K SO., 10% anhydrous CuSO.), 10 ml of concentrated HS0.
z 4 4 2 4
and 2 ml of ^02 were added. Samples were then digested in an aluminum
block digester (Gallaher et al. (1976) for 3.5 hrs. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen

137
concentration of these solutions were determined on a Technicon
AutoAnalyzer II.
Phosphorus, K, Ca, Mg, Fe, Cu, Mn, and Zn concentrations were
determined by a mineral analysis procedure in which 1.0 g samples were
placed in 50-ral pyrex beakers and ashed in a muffle furnace at 480C
for a minimum of 4 hrs. After cooling each was treated with 2 ml
concentrated HC1 and heated to dryness on a hot plate. An additional 2
ml of concentrated HC1 + water was added to the dry beakers followed by
reheating to boiling and then diluting to 100 ml volume with deionized
water. Solutions were analyzed for P using colorimetry on an
AutoAnalyzer. Potassium was determined by atomic emission
spectrophotometry. Calcium, Mg, Fe, Cu, Mn, and Zn were determined by
atomic absorption spectrophotometry.
IVOMD of plant material was determined by the Tilley and Terry
(1963) two-stage procedure adapted by Moore et al. (1972). For
measurements of metabolizable energy approximately 0.5 g of sample was
pelleted in a cylinder press and weighed to the nearest 0.00001 g.
Samples were then placed in clean combustion boats. Combustible energy
values were obtained using a computerized Parr adiabatic calorimeter,
using standard ASTM methods.
, Results and Discussion
Percent Organic Matter, IVOMD, Metabolizable Energy, and Nitrogen
Percent organic matter percent OM for plant components for the
'NB-3' + 'Criollo' (M+PS), 'NB-3' + 'Pioneer 895' (M+NS), and 'NB-3' +
'Gahi-3' (M+Ml) is depicted in Figs. 6-1, 6-2, and 6-3. No differences
between maize components were observed among systems (p=0.05) for any

138
planting date. Maize leaves decreased with maturity; at thinning the
leaves were approximately 88 dag kg ^ OM, while at black layer the
leaves contained approximately 84 dag kg During the second period of
vegetative growth (Figs. 5-3a, 5-4a, and 5-5a) OM increased again to
nearly 88 dag kg Thirty days after grain harvest OM decreased to
levels near 84 dag kg (Figs. 6-la, 6-2a, and 6-3a).
Organic matter values for maize stems at thinning were
approximately 87 dag kg ^ and constantly increased to values of
approximately 96, 93, and 95 dag kg ^ for the M+PS, M+NS, and M+MI
systems, respectively. After bloom stem OM decreased to values below 90
dag kg 1 in the M+PS, and were constant in the other two systems (Figs.
6-la, 6-2a, and 6-3a). Ears and flowers followed opposite trends; ear OM
increased with maturity, while flower OM decreased.
The PS and NS followed a different trend than that observed in
maize. Organic matter values observed in sorghum were generally higher
than those observed in maize. Organic matter values in the leaves from
both sorghums increased with maturity. At bloom, OM values were
approximately 89 dag kg ^ for both sorghums (Figs. 6-lb and 6-2b). After
bloom OM in the leaf declined to approximately 84 dag kg Goldsworthy
(1970) postulated that sorghum stems are storage deposits for
photosynthates produced in the leaves; the results presented in Figs.
6-lb and 6-2b confirm this observation. In the PS sorghum OM increased
to a maximum 96 dag kg at soft-dough (Fig. 6-lb), from this stage to
harvest it maintained a constant OM value. In the NS sorghum the OM
increased to a maximum of 93 dag kg and from then on it declined
rapidly to approximately 88 dag kg ^, 30 days after grain harvest.
Organic matter in the head followed opposite patterns than those

139
40 80 120 160 200
Days After Planting Maize
Doys After Planting Maize
Figure 6-1. Effect of the stage of maturity on percent
organic matter of 'NB-3' maize (a) and
'Criollo' sorghum (b).

140
Days After Planting Maize
Figure 6-2. Effect of the stage of maturity on percent
organic matter of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).

Organic Matter(dag kg
141
Days After Planting Maize
Figure 6-3. Effect of the stage of maturity on percent
organic matter of 'NB-3' maize (a) and
'Gahi-3' millet (b).

142
observed in the stems. As stem percent OM increased in the PS sorghum,
percent OM decreased in the head (Fig. 6-lb). The opposite occurred in
the NS sorghum (Fig. 6-2b); as dag kg 1 OM decreased in the stem dag
kg 1 OM in the head was increasing rapidly. These results support those
reported for dry matter accumulation discussed in Chapter 5 (Figs. 5-3b
and 5-4b).
Both leaves and stems from millet plants (Fig. 6-3b) increased in
dag kg ^ OM. Values observed in millet were generally lower than those
observed for sorghum. This is probably so because of the effect of the
late planting on the growth of millet. The data suggest that millet did
not reach the exponential growth stage.
Values for IVOMD are depicted in Figs. 6-4, 6-5, and 6-6 for the
M+PS, M+NS, and M+MI systems, respectively. In general, leaf, stem, and
flower digestibility decreased with maturity in all crops. While the
digestibility of the ear increased constantly until harvest, sorghum
heads increased to a maximum at soft-dough and thereafter decreased
until harvest. These results are similar to those reported by Cummins
(1970), Johnson et al. (1966), and Schmid et al. (1975).
IVOMD values observed in maize did not differ among components from
maize plants from the three systems at the 0.05 level of probability. In
general IVOMD was higher in the ear than in any other maize plant
component. There was no general trend in IVOMD differences between
leaves and stem, but higher values were observed in the leaves (Figs.
6-4a, 6-5a, and 6-6a). The low IVOMD values (less than 50%) observed
after soft-dough may have been caused by water stress and low available
soil moisture (Figs. 5-1 and 5-2, respectively); however, Cummins (1970)
observed similar IVDMD values. From soft-dough to harvest IVOMD in the

IVOMD (dag kg-1) IVOMD (dag kg
143
Days After Planting Maize
Figure 6-4. Effect of the stage of maturity on the
IVOMD of 'NB-3' maize (a) and 'Criollo'
sorghum (b).

144
Figure 6-5. Effect of the stage of maturity on the IVOMD
of 'NB-3' maize (a) and 'Pioneer 895' sorghum
(b).

145
100
00
O)
S 60
Q
> 40
(o)
20
o- Stem
o- Leaf
A- Ear
40 80 120 160 200
Days After Planting Maize
Days After Planting Maize
Figure 6-6. Effect of the stage of maturity on the
IVOMD of 'NB-3' maize (a) and 'Gahi-3'
millet (b).

146
leaves dropped from 52% to a low of 38% at harvest but increased later.
Martin and Wedin (1974) reported similar results for sorghum. Stem IVOMD
was high at thinning (approximately 73%)in the M+PS to less than 40% 30
days after grain harvest. Maize flower IVOMD decreased constantly until
reaching a minimum of approximately 20% at 30 days after harvest (Figs.
6-4a, 6-5a, and 6-6a).
Maturity affected IVOMD less dramatically in the PS sorghum (Fig.
6-4b) than that of the NS sorghum (Fig. 6-5b). Stem IVOMD in the PS
sorghum were generally higher than leaf IVOMD (Fig. 6-5b). After grain
harvest, leaf values decreased below 40%, while stem values were
maintained above 50%. Head IVOMD increased to a maximum of 68% at
soft-dough but decreased rapidly to near 40% by grain harvest. Again,
due to the lack of a well developed grain sink, photosynthates that
would have accumulated in the grain were shunted to the stem as reported
by Goldsworthy (1970) and Schmid et al. (1975), who observed that IVOMD
of stalks in tall sorghum hybrids increased with maturity. These results
also agree with the values for 41 sorghum varieties reported by Green
(1973 ).
Fig. 6-5b depicts the effects of maturity on the NS sorghum. IVOMD
in the leaves and stems declined rapidly from thinning to bloom stage
and was relatively stable thereafter. Schmid et al. (1975) reported
IVOMD values for grain sorghum 4 weeks after planting ranged from 67.1
to 78.3%, values which are similar to those found in this research at
thinning. At all sampling stages the leaves were more digestible than
the stem, contrary to what was observed in the PS sorghum. Head IVOMD
reached a maximum value of approximately 65% and then decreased to 57%
by harvest.

147
In general, IVOMD values observed in both sorghums compared well
with those observed in maize. Hall et al. (1965) reported similar
findings. However Schmid et al. (1975) concluded that lower cell wall
digestibility observed in low-grain-yielding sorghums (similar to the PS
sorghum in this study) was detrimental to total digestibility. In
high-grain-yielding sorghums the rapid increase in the amount of highly
digestible starch in the grain compensates for the decline in cellulose
digestion. In Chapter 5 it was reported that dry matter accumulation was
greater in the stem than in other plant components in the PS sorghum;
this may account for the higher IVOMD observed in the stem.
In millet, IVOMD was constantly higher in the leaf than in the stem
or head (Fig. 6-6b). Grain set in the head was low; therefore its
digestibility was low in relation to other plant components and to
sorghum heads. However, leaves and stems in millet reached similar
values to those observed in the sorghums and maize. These results are
supported by data presented by Clark et al. (1965), in which there were
no differences in the carrying capacity, milk production, or dry matter
production of millet and a sorghum x sudangrass hybrid.
Metabolizable energy as affected by maturity stage is depicted in
Figs. 6-7, 6-8, and 6-9 for M+PS, M+NS, and M+MI, respectively. No
differences among components were found from maize plants from the
different systems at the 0.05 level of probability. As expected, higher
energy values were observed in the ear and flowers than in the other
components. Flowers at 50% bloom contained 18.5 MJ kg ^dm and declined
to nearly 16.5 MJ kg ^ in all three systems (Figs. 6-7a, 6-8a, and
6-9a). Ears reached a maximum at soft-dough (18, 17 and 17 MJ kg *dm for
the M+PS, M+NS, and M+MI, respectively. Energy in the leaves declined

148
Figure 6-7.
Effect
amount
'NB-3'
of the stage of maturity on the
of metabolizable energy of maize
(a) and 'Criollo' sorghum (b).

149
40 BO 120 160 200
Dnys After Planting Maize
17
16
15
14
13
130 170 210 250 290
Days After Planting Maize
Figure 6-8. Effect of the stage of maturity on the
amount of metabolizable energy of 'NB-3'
maize (a) and 'Pioneer 895' sorghum (b).

150
Days After Planting Maize
Figure 6-9. Effect of the stage of maturity on the
amount of metabolizable energy of 'NB-31
maize (a) and 'Gahi-3' millet (b).

151
with maturity. Cummins (1970) reported that carbohydrate content in the
leaves was negatively correlated with maturity.
Conversely, energy in the stems increased with maturity. Apparently
carbohydrates accumulated in the stem even after grain harvest (Figs.
6-7a, 6-8a, and 6-9a). Data presented by Cummins (1970) supports this
observation. He reported a decline in carbohydrate content at midseason
and a rapid increase at the end of the season. These results also agree
in part with those presented by Johnson et al. (1966), who reported
increasing energy in the stem from tasseling to soft-dough, with a
slight decline thereafter. Energy values observed support dry matter
accumulation data reported in Chapter 5, which indicated a higher dry
matter accumulation in the stem than in any other plant component.
Cummins (1970) observed that rainfall during maturity decreased
carbohydrate content in the stem.
The patterns in energy contents observed in the PS, NS sorghums,
and in the millet differed somewhat from that observed in maize. Energy
content in the leaves from the PS sorghum (Fig. 6 7b) increased early in
the season, then declined at bloom, and remained fairly constant to the
end of the season. Stem energy increased rapidly from early growth to
bloom and thereafter it remained constant. Higher energy values were
observed in the stem than in the leaves towards the end of the season;
the inverse was true early in the growing season.
In general the NS sorghum had lower energy content in relation to
the PS sorghum (Fig. 6-8b). Both leaf and stem energy increased rapidly
from planting to bloom; however, leaf declined sharply soon after bloom.
Although stem energy contents were not as high as those observed in the
leaves, these did not decline after bloom. In fact energy content

152
increased slightly between bloom and soft-dough stages; it remained
constant thereafter. Head energy content was higher at bloom than at
grain harvest. This last finding does not agree with data presented by
Schmid et al. (1975 ).
The contrasting differences observed between the PS and NS sorghums
may explain in part the preference of the Central American farmers for
the PS sorghums. Besides accumulating higher energy, PS sorghum also
maintained a higher level of energy for a longer period of time after
grain harvest (Figs. 6-7b and 6-8b). This coupled with higher dry matter
accumulation in the stem and leaves by the PS sorghum makes it a first
choice for the semi-arid regions of Central America, where it is the
main source of feed for ruminants during the long dry season.
Energy values observed in millet are presented in Fig. 6-9b. Due to
the short duration of the growth period observed in millet, the
accumulation of carbohydrates did not reach its potential. In general,
lower values were observed in millet than in the sorghums or maize.
Leaves and stems followed similar patterns, increasing to bloom and then
declining. Heads maintained a constant amount of energy during the
growing season.
The distribution of N in the different plant parts of the maize
plants from the M+PS, M+NS, and M+MI systems throughout the season are
presented in Figs. 6-10a, 6-lla, and 6-12a, respectively. No differences
(p=0.05) were observed in N concentration among plant parts during any
stage of growth. Nitrogen concentration was affected by maturity in a
very similar manner as IVOMD. As maturity progressed N concentration
decreased in plant components with the exception of maize ears, in which
N concentration increased until harvested. Kumar and Awasthi (1977) and

153
Days After Planting Maize
Figure 6-10. Effect of the stage of maturity on the N
concentration of 'NB-3' maize (a) and
'Criollo' sorghum (b).

154
Figure 6-11. Effect of the stage of maturity on the N
concentration of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).

155
Days After Planting Maize
Figure 6-12. Effect of the stage of maturity on the N
concentration of 'NB-3' maize (a) and 'Gahi-3'
millet (b).

156
Hanway (1962a) reported similar findings. They attributed this
phenomenon to a dilution effect. The effect of the rains in early
September (Fig. 5-1) on N concentration was manifested by an increase in
the N concentration in the stem after black layer had formed in the
grain.
Lockman (1972b) suggested that the N critical level in maize is
near 3 dag kg ^, while Plank (1979) establishes the N sufficiency range
in maize ear leaves at bloom between 3.5 and 5 dag kg Values observed
throughout the growing season were well below these levels. At bloom the
N concentration in maize leaves was close to 1.35 dag kg ^. These
results suggest a constant N deficiency in the plant throughout the
growing season. Low soil moisture availability during the entire growing
season (Fig. 5-2) may have prevented the plants from absorbing N needed
for grain production. Hanway (1962a) observed that extreme N and K
deficiencies in maize result in premature death of several lower leaves.
This shortens the period over which these leaves carry on
photosynthesis.
This low N concentration observed affected quality as well as
yields. At bloom, leaves and stems contained approximately 8.5 and 2.5
dag kg of protein (dag kg ^ N x 6.25), respectively; well below the
12 dag kg ^ reported by Johnson and Me Clure (1966). However, grain
protein values at harvest (9.4 dag kg ^) compared well with values
reported by Rendig and Broadbent (1979). Jurgens et al. (1978) reported
that water stress caused an increase in percent protein in the grain.
The pattern of N distribution in different components of the plant
did not appear to differ appreciably for the different systems. Nitrogen
was lost from the stems and leaves just prior to bloom. There was little

157
translocation from one plant part to another until after grain formation
began, and then N was translocated from the stem and leaves to the
grain. Translocation of N from the stem preceded that from the leaves.
Both sorghums and the millet followed a similar trend to that
observed in maize. Nitrogen concentration decreased with maturity (Figs.
6-10b, 6-llb, and 6-12b for the M+PS, M+NS, and N+MI systems,
respectively). Leaves and stems from the PS sorghum at bloom contained
approximately 1.4 and 0.48 dag kg ^, similar to the values observed for
maize. At the same stage of growth the NS sorghum leaves and stem
contained approximately 1.5 and 0.9 dag kg Head N concentration in
the NS sorghum decreased constantly to harvest. This may be attributed
to the dilution effect reported by Hanway (1962a). Millet (Fig. 6-12b)
exhibited N concentrations similar to those observed in the NS sorghum.
Lockman (1972a) reported that N concentrations of 1.57 dag kg in the
second leaf of grain sorghum at bloom may be considered deficient.
Phosphorus, K, Ca and Mg Accumulation
There were many similarities between the patterns of P distribution
in different maize plant parts as shown in Figs. 6-13a, 6-14a, and 6-15a
and those shown in Figs. 6-10a, 6-lla, and 6-12a for N. As with N, the
patterns for P did not vary markedly among systems. The amount of P in
the leaves and stems declined sharply between thinning and bloom and was
relatively constant from then until soft-dough, when concentration
increased again. Plank (1979) established the P sufficiency range in
maize ear leaf at bloom between 0.3 and 0.5 dag kg Values observed in
the leaves at bloom was 0.17, 0.20, and 0.18 dag kg ^ for the M+PS,
M+NS, and M+MI systems, respectively, which suggests a deficiency.

158
0.5
0.4
0.3
0.2
O 1
0 0
1 1 1 1 1 i
- (a) o- Stem
o-Leaf
A- Ear
I L
30 60 90 120 150 100
Days After Planting Maize
Days After Planting Maize
Figure 6-13. Effect of the stage of maturity on the P
concentration of 'NB-3' maize (a) and
'Criollo' sorghum (b).

159
130 170 210 250 290
Days After Plontlng Moize
Figure 6-14. Effect of the stage of maturity on the P
concentration of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).

160
0.0
.*
- 0.6
i
en
.*
O)
o 0 4
T3
0.2
0 0
Figure 6-15. Effect of the stage of maturity on the
P concentration of 'NB-3' maize (a) and
'Gahi-3' millet (b).
I
_ (b)
T
r
r
o- Stem
o-Leaf
-
- Head
-
n
1 10
130
150
170 190
Days After Planting Maize

161
Maximum P concentration in the ear occurred at black layer,
decreasing slightly from then until harvest. Translocation of P from the
stem to the ear preceded that from the leaves. Phosphorus concentration
in the leaves was generally higher than that observed in the stem.
Phosphorus concentration in the different plant components of PS
sorghum and NS sorghum decreased with maturity until grain harvest. A
slight increase in leaf P was observed, which in the PS sorghum may be P
remobilized from the head, due to a lack of an appropriate grain sink.
The same increase was observed in the NS sorghum, where no decrease
occurred in the head, suggesting that P uptake was still happening. Leaf
P concentrations observed at bloom for both sorghums fall within the
sufficiency level (0.17 dag kg ^) established by Locke et al. (1964).
Millet exhibited higher P concentration than both sorghums. This is
explained in part by the differences in dry matter accumulation among
these crops. Phosphorus in millet was less diluted due to less growth.
Leaves generally had higher P than the stem. Apparently little P was
translocated to the heads from the stem or leaves.
Potassium accumulation by the M+PS, M+NS, and M+MI systems is shown
in Figs. 6-16, 6-17, and 6-18, respectively. The patterns of
accumulation and distribution observed for K were similar to those of N
and P. K concentration decreased with maturity and did not differ among
maize plants from the different systems at the 0.05 level of
probability. Potassium in the leaves and stem decreased with maturity.
At bloom the K concentration in the leaves was 1.65, 1.75, and 1.85 dag
kg 1 for the M+MI, M+NS, and M+PS, respectively (Figs. 6-18a, 6-17a, and
6-18a); these were within the sufficiency level established by Gallaher
et al. (1975 ). Little K was accumulated in the ear, suggesting that

162
Doys After Planting Maize
Figure 6-16. Effect of the stage of maturity on the
K concentration of 'NB-3' maize (a) and
'Criollo' sorghum (b).

163
Doys Afler Plnnting Mnize
Figure 6-17. Effect of the stage of maturity on the
K concentration of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).

K (dog kg"') K (dog kg
164
Doys After Plonting Moize
Figure 6-18. Effect of the stage of maturity on the
K concentration of 'NB-3' maize (a)
and 'Gahi-3' millet (b).

165
losses from the leaf and stem were shuttled out of the plant. After
grain harvest, an increase in K concentration in the stem preceded the
second period of vegetative growth reported in Chapter 5.
The patterns observed in the sorghums and millet were very similar
to those observed in maize. As maturity progressed, K concentration
decreased in all plant components. However, it is interesting to note a
sharp increase in K concentration in the stem of both sorghums after
grain harvest. Since little K accumulated in the head, these results
suggest that K lost from the leaves was accumulating in the stems (Figs.
6-16b, 6-17b, and 6-18b). At bloom, K concentration in the leaves of
both sorghums was above the 1.7 dag kg ^ sufficiency level established
by Locke et al. (1964).
Maize Ca (Figs. 6-19a, 6-20a, and 6-21a) followed a different
pattern of accumulation and distribution from that observed for N, P,
and K. Calcium concentrations were much lower in the ear than in any
other plant part. Jacques et al. (1975) have reported similar low values
in grain sorghum heads. Calcium concentration in the leaves increased
dramatically with maturity. The need for Ca in Ca-pectate formation of
mature leaf cells may have been responsible for the increased
concentration observed in the leaves (Jacques et al., 1975). Calcium
concentrations in the leaves observed at bloom were within the critical
levels (0.25-0.50) reported by Plank (1979). Calcium in the stem
decreased sharply early in the season and increased slightly towards the
end. Gallaher et al. (1975) reported that plants that accumulate large
quantities of oxalic acid tend to contain large quantities of Ca oxalate
crystals which are insoluble in water, alkalies, and organic acids.

166
Days After Planttng Maize
Figure 6 19. Effect of the stage of maturity on the
Ca concentration of 'NB-3' maize (a)
and 'Criollo' sorghum (b).

167
Days After Planting flalze
Figure 6-20. Effect of the stage of maturity on the
Ca concentration of 'NB-3' maize (a)
and 'Pioneer 895' sorghum (b).

Ca (dag kg ) Co (dag ^g
168
Days After Planting Maize
Figure 6-21. Effect of the stage of maturity on
the Ca concentration of 'NB-3'
maize (a) and 'Gahi3' millet (b).

169
Excessive production of oxalic acid by plants could result in Ca
deficiency, especially when Ca supply is limited.
Both sorghums and the millet presented patterns similar to those
observed in maize. Calcium concentration increased with maturity in the
leaf as it decreased in the stem. Only small amounts of Ca accumulated
in the head. Lockman (1972a) indicated that in dry years the Ca
concentration in the plant will increase.
Magnesium (Figs. 6-22, 6-23, and 6-24) presented a pattern of
accumulation and distribution very similar to that observed for Ca.
Higher concentrations were observed in the leaves of crops than in any
other plant component. Jacques et al. (1975) reported similar results.
However, their data suggest that leaf Mg remains constant through the
growing season, contrary to what was observed in this experiment.
Similar results were observed in millet (Fig. 6-24b).
Ratios among K, Ca, and Mg observed in maize leaves throughout the
growing season are presented in Table 6-1. Gallaher et al. (1975) showed
that when the K:Ca, K:Mg, and K:Ca+Mg ratios exceeded 3.5, 3.6, and 1.8,
respectively, Mg concentration in the leaves is close to the value that
has been found to reduce photosynthesis. Values presented in this
experiment indicate that Mg deficiency and an excess of K in relation to
the other two cations. The K:Ca, K:Mg, and K:Ca+Mg decreased with
maturity as a result of K losses from the plant and the increase in Ca
and Mg concentrations observed (Figs. 6-22, 6-23, and 6-24). This
imbalance observed among these cations may be limiting growth and
yields, as reported by Gallaher et al. (1975).

Mg (dog kg- 1) Mg(dagkg-I)
170
Days After Planting Maize
Days After Planting Maize
Figure 6-22. Effect of the stage of maturity on
the Mg concentration of 'NB-3'
maize (a) and 'Criollo' sorghum (b).

_631 Bap) 614 (. Bap) By
171
40 00 120 160 200
Dnys After Plonting Maize
Figure 6-23. Effect of the stage of maturity on
the Mg concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).

172
40 00 120 160 200
Days After Planting Maize
Days After Planting Maize
Figure 6-24. Effect of the stage of maturity on
the Mg concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).

173
Table 6-1. Ratios among X, Ca, and Mg in maize
leaves as affected by maturity and
cropping system.
System
X: Ca
X:Mg
Ca:Mg
X:Ca+Mg
Thinning
M+PS*
10.7
20.9
2.0
7.1
M+NS
11.9
19.1
1.6
7.3
M+MI
11.1
19.5
1.8
7.1
75 cm Height
M+PS
12.7
19.3
1.5
7.7
N+NS
11.0
18.4
1.7
6.9
M+MI
9.0
17.6
2.0
6.0
Bloom
M+PS
10.9
18.8
1.7
6.9
M+NS
10.4
19.2
1.9
6.8
M+MI
10.7
20.4
1.9
7.0
Soft-Dough
M+PS
9.8
18.3
1.9
6.4
M+NS
13.8
20.4
1.5
8.3
M+MI
6.4
10.0
1.6
3.9
Black Layer
M+PS
6.8
11.7
1.7
4.3
M+NS
10.0
16.9
1.7
6.3
M+MI
5.7
8.0
1.4
3.3
Harvest
M+PS
7.8
13.2
1.7
4.9
M+NS
9.0
16.9
1.9
5.9
M+MI
4.0
6.3
1.6
2.5
30 Days After Harvest
M+PS
8.8
14.7
1.7
5.5
M+NS
6.2
9.6
1.6
3.8
M+MI
7.5
11.7
1.6
4.6
* M = maize,
PS =
photosensitive
sorghum
, NS =
non-photosens itive
sorghum, and
MI = millet.

174
Iron, Cu, Mn and Zn Accumulation and Distribution
Iron (Figs. 6-25, 6-26, and 6-27), Cu (Figs. 6-28, 6-29, and 6-30),
Mn (Figs. 6-31, 6-32, and 6-33), and Zn (Figs. 6-34, 6-35, and 6-36)
concentrations did not differ among maize plants from the different
systems. Similar trends were observed for these nutrients in all crops,
with the exception of Fe. Iron presented a sharp decline at the
beginning of the season but maintained a constant concentration during
most of the growing season until black layer in maize, when it increased
markedly, returning to levels observed early in the season. In general,
Cu, Mn, and Zn concentrations decreased with maturity, and the leaves
contained higher concentrations than the stems.

175
Doys After Planting Maize
Figure 6-25. Effect of the stage of maturity on
the concentration of Fe of 'NB-3'
maize and 'Criollo' sorghum (b).

Fe (mg kg~ ') Fe (mg kg
176
Doys After Planting Maize
Figure 626. Effect of the stage of maturity on
the Fe concentration of 'NB-3' maize
(a) andPioneer 895' sorghum (b).

177
Days Afler Planting Maize
Figure 6-27. Effect of the stage of maturity on
the Fe concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).

Cu (mg leg ) Cu (mg i 178
Figure 6-28. Effect of the stage of maturity on
the Cu concentration of 'NB-3' maize
(a) and 'Criollo' sorghum (b).

Cu (mg kg ) Cu (mg kg~
179
40 80 120 160 200
Dnys After Planting Maize
Days After Planting Moize
Figure 6-29
Effect of the stage of maturity on
the concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).

Cu (mg kg ') Cu ( mg kg-
180
Figure 6-30. Effect of the stage of maturity on
the Cu concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).

Mn (mg kg'1) Mn (mg kg
181
Dogs After Plenting Moize
Figure &-31. Effect of the stage of maturity on
the Mn concentration of 'NB-3' maize
(a) and 'Criollo' sorghum (b).

182
Figure 6-32. Effect of the stage of maturity on
the Mn concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).

Mn (mg kg~ ) Mn (mg kg
183
Figure 6-33. Effect of the stage of maturity on
the Mn concentration of 'NB-31 maize
(a) and 'Gahi-3' millet (b).

184
Doys Afler Planting Molze
Figure 6-34. Effect of the stage of maturity on
the Zn concentration of 'NB-3' maize
(a) and 'Criollo' sorghum (b).

Zn (mg kg* 1) Zn (mg kg
185
Figure 6-35. Effect of the stage of maturity on
the Zn concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).

186
Days After Planting Maize
Figure 6-36. Effect of the stage of maturity on
the Zn concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).

CHAPTER 7
SURVEY OF SULFUR DEFICIENCY IN MAIZE
Introduction
Sulfur deficiency has been recognized as an important factor limiting
cereal production in several parts of the world (Beaton, 1966).
Actually, S-deficient areas are rather widespread throughout the world.
For example, crop deficiencies in S have been reported from countries
in Central and South Africa; India; and North, Central, and South
America (Blair et al., 1980).
The fact that over the past several years crop deficiencies have
been reported with increasing frequency has focused greater attention on
the importance of this nutrient in plant nutrition. As Coleman (1966)
pointed out, S deficiencies are probably ocurring because of 1) the
increased use of S-free fertilizer, 2) the decreased use of S as a
fungicide and insecticide, and 3) increased crop yields, which means
higher requirements of all the essential plant nutrients. Blair et al.
(1980) listed other reasons for the occurrence of S deficiency in
tropical soils: 1) inherent low S content, 2) low availability of
S-containing organic matter, and 3) the consequence of agricultural
practices.
Blair et al. (1980) reported total S values for a range of tropical
soils from 43 to 248 mg kg Rabuffetti and Kamprath (1977) reported
soil-S values from about 6 mg ka in the top 25 cm to 51 mg kg in the
40-55 cm depth of a Goldsboro soil (fine, loamy, siliceous, thermic
187

188
Aquic Paleudult). Mitchell and Gallaher (1979), studying S fertilization
on an Arredondo fine sand (loamy, siliceous, hyperthermic Grossarenic
Paleudult), found that S content increased with soil depth, (2.2 and
16.4 mg kg ^ for the 0-15 and 60-80 cm depths, respectively). Soils of
temperate areas are generally richer in total S. Jordan and Reisenauer
(1957) reported values of 540 and 210 mg kg ^ for a Mollisol and an
Alfisol, respectively.
Coleman (1966) indicated that S is needed in crop production
because plants require it for 1) the synthesis of amino acids (cysteine,
cystine, and methionine) and hence for the elaboration of protein, 2)
the activation of certain proteolytic enzymes such as the papainases, 3)
the synthesis of certain vitamins, (glutathine and coenzyme A), 4) the
formation of the glucoside oils found in cruciferous plants, 5) the
formation of disulfide linkages that have been associated with the
structural characteristics of protoplasm, and 6) in some species the
concentration of sulhydril groups in plant tissue has also been
associated to increased cold resistance.
The problem of human and animal malnutrition due to deficiency and
poor quality of protein has been discussed by several authors (Barrien
and Wood, 1939; Allaway and Thompson, 1966; Coleman, 1966). The four
billion (4 X 10 ) people that inhabit the world require amino acids
containing over 40 Mg of S daily. The ultimate goal of S fertilization
of soils is, therefore, to increase the S-amino acid content of human
diets.
According to Caldwell et al. (1969) little attention has been given
to the effect of S on the availability of other macro and micro
nutrients. It is unfortunate that many workers studying the nutrient

189
composition of plants fail to determine the S content. Tisdale and
Nelson (1964) found that S is required by many plants in about the same
amount as is P. Friedrich and Schrader (1978) and Rabufetti and
Kamprath (1977) found evidence suggesting a NxS fertilizer interaction
for S concentration in the grain.
The critical concentration of S in young maize plants has been
reported to be about 0.20 dag kg ^ (Fox et al., 1964; Stewart and
Porter, 1969; Jones and Eck, 1973; Terman et al., 1973). Mitchell and
Gallaher (1979) in their study of S fertilization of maize seedlings
found that 55-day old maize leaves contained from 0.18 to 0.25 dag kg ^
in the control compared to those plots fertilized with 10 kg CaSO^.2H^0
ha *. At harvest both treatments had 0.11 dag kg ^ S in the grain. Blue
et al. (1981) reported lower values (from .06 to 0.12 dag kg ^) for
35-day old maize herbage.
Dijkshoorn et al. (1960) concluded that the N:S concentration ratio
among species range from 14:1 to 17:1 for legumes. Gaines and Phatak
(1982) found that low S-accumulating crops; maize, soybean (Glycine max
(L. ) Merr.), and cowpea (Vigna Unguiculata (L.) Walp.); had higher and
constant protein N:S ratios than high S-accumulating crops; tomato
Lycopersicon esculentum (L.) Mil 1.), cotton (Gossypium hirsutum L.), and
okra (Abelmoschus esculentum (L.) Moench). This indicates that high
S-accumulating crops have a greater proportion of S-containing proteins
and need a higher S:N ratio than low S-accumulating crops. When S was
sufficient the ratio of protein N to S was 15 to 16 for maize, 20 for
soybean, 15 for cowpea, 12 for tomato, and 8 and 9 for cotton and okra,
respectively.

190
Friedrich and Schrader (1979) found that as plants reach maturity
the ratio of N:S in plant proteins tends to decrease. When leaf material
is used for analyses the amino acid N:S ratio is about 15:1 for a wide
variety of field crops.
Stewart and Porter (1969) observed that mass of maize roots was
greatly affected by applications of S-containing fertilizers. For
example, the mass of maize roots was increased from 2.9 g for the no-S
treatment to 6.7g for the 150-mg kg ^ level. They concluded that in
S-deficient soils the addition of 1 part S for every 15 parts of
fertilizer N will likely prevent S deficiencies.
Mitchell and Blue (1981a, 1981b) reported that millet responded
markedly to S applied to Florida Entisols. Rabufetti and Kamprath (1977)
found little response to S applications at low levels of N applications,
the opposite at higher N rates. Jones and Martin (1964) observed that
the application of S not only increased forage production, with changes
in relative growth rate of various species, but after S fertilization
the chemical composition of the forage was altered as well.
Objectives
Experiment 1
Sixty day-old no-tillage maize (DeKalb 'X L 395 A') was grown in a
65 ha center pivot irrigated field. Plants showed various degrees of
stunting and ranged from dark green healthy plants to very stunted
plants that were light green to yellow. Maize ranged in height from
about 30 to 120 cm. The small stunted plants exhibited intervenial
chlorosis, the degree of which diminished as height increased. The 120
cm plants looked normal and healthy. The hypothesis proposed stated that
the problem was likely associated with soil texture and the solution

191
could be obtained through soil-plant analysis. The objective of this
study was to determine the cause of maize leaf chlorosis and height
variability by analysis of plants and associated soils.
Experiment 2
In maize producing areas of Nicaragua it was apparent that
deficiency symptoms observed in Florida and Georgia were also visible in
these areas. To determine if the symptoms observed in Nicaragua were
also associated with S status in the plant, a study was conducted with
the following objectives: 1) to determine if S deficiency is a
widespread problem in Nicaragua, and if plants with deficiency symptoms
give the same plant analysis results as in Florida and Georgia, and 2)
to evaluate soil tests in relation to leaf analysis in assessing S
deficiency in maize.
Materials and Methods
Field Methods
Experiment 1
Sixty day-old no-tillage maize was grown in a 65 ha field in
Alachua County, Florida. Plants showed various degrees of stunting and
ranged from dark green healthy plants to light green or yellowish
stunted plants. Plant height ranged from approximately 30 cm to 120 cm.
The stunted plants exhibited intervenial chlorosis, the degree of which
diminished as plant height increased. The objective proposed stated that
the problem was likely associated with soil characteristics and the
identification could be obtained through soil-plant analysis.
A completely randomized experimental design was used that included
three replications of five maize treatments. Treatments included 30, 60,

192
75, 90, and 120 cm Call plants. Ten whole plant samples were taken at
random for each replication, as well as the associated youngest mature
leaf and soil samples. Soil samples were taken at several depths within
25 cm from the treatment plants.
Plants and youngest mature leaves were washed in distilled water,
dried at 70C in a forced air oven, and ground in a Wiley mill to pass a
1 mm stainless steel screen. Soils were sampled in 15 cm increments to
45 cm, then later to 90 cm, air dried, ground by mortar and pestle, and
screened in a 2 mm stainless steel screen. Plant and soil samples were
analyzed as described in the section on laboratory procedures of this
chapter.
Experiment 2
Eighteen maize fields in Northern Nicaragua (Esteli and Matagalpa)
that were between 40 and 50 days old were selected as experimental
fields. A second criterion of selection was the occurrence of S-
deficient and sufficient healthy-looking plants (based on the criteria
established in experiment 1). A description of the study area is given
in Table 3-7.
Once inside the experimental field, four deficient and four
sufficient plants were selected. Each pair of plants within a field was
considered to form a replication of a randomized complete block design.
Comparisons among fields were made through a split plot design; sites
were considered as main plots and plant phenotypes as split-plots. The
youngest fully expanded mature leaf was collected for each plant,
described, and measured in length and width. The leaves were weighed,
oven dried, ground in a Wiley mill to pass a 1 ram stainless steel
screen, and stored in air-tight bags for analysis.

193
Four soil samples (from 0 to 30 cm depth) were taken within a 25 cm
circumference around each plant. The samples for each plant were mixed
to form one sample per plant per replication. Samples were air dried,
sieved to pass a 2 mm stainless steel screen, and stored for analysis.
Response variables measured in plants were a) plant height, b) leaf
length, c) leaf width at the widest point, d) dry weight per leaf, e)
leaf concentrations of S, N, P, K, Ca, Mg, Cu, Fe, Mn, Zn. Soil response
variables measured were concentration of the same nutrients measured in
the leaf tissue.
Laboratory Procedures
Soil analysis methods
For both experiments N analysis employed a microKjeldahl procedure
(Bremner, 1960) as modified by Gallaher et al. (1976). A 2.0-g sample
was placed in a 100-ml digestion tube to which 3.2 g of catalyst (90%
anhydrous K^SO^, 10% anhydrous CuSO^), 10 ml concentrated H^SO^ and 2 ml
30% were added. Samples were then digested in an aluminum block
digester (Gallaher et al., 1976) for 2 1/2 hours at 375 C. Upon
cooling, solutions were diluted to 75 ml with deionized water. Nitrogen
concentrations of these prepared solutions were determined using a
Technicon AutoAnalyzer II.
All soil P, K, Ca, Mg, Fe, Cu, Mn, and Zn analyses were conducted
using procedures recommended by University of Florida's Soil Testing
Laboratory. Five grams of air-dried soil were extracted with 0.05 HC1
+ 0.025 H^SO^ at a soil: solution ratio of 1 to 4 (W:V) for 5 minutes
(Mehlich, 1953). Soil P was then analyzed using colorimetry. Potassium
was determined by atomic emission spectrophotometry. Calcium, Mg, Fe,

194
Cu, Mn, and Zn were determined by atomic absorption spectrophotometry.
Soil pH was determined using a 2:1 water:soil ratio.
Soil S was determined by the method described by Bardsley and
Lancaster (1965). Ten grams of soil from a 20-mesh screen were placed in
a 50-ml Erlenmeyer flask and extracted with 39 g of NH^C2H^02 diluted in
one L of 0.025 N_ acetic acid for 30 minutes, 0.25 g of washed activated
charcoal was added and extracted for 3 additional minutes. The soil
suspension was filtered using a sulfate-free Whatman No. 42 filter
paper. Ten ml of the filtrate was pipetted into a 50-ml Erlenmeyer flask
to which 1 ml of acid seed solution (6 _N HC1 + 20 mg kg of S as i^SO^)
was added, swirled and 0.5 g of 83012*2^0 crystal was added. This
solution was left standing for 1 minute, then swirled to dissolve all
the crystals. Soil S concentration was then determined using a
Perkin-Elmer/Coleman 54 spectrophotometer set at 540 nm.
Cation exchange capacity (CEC) was determined by leaching the soil
with 1 M ammonium acetate (NH^OAc) at pH 7.0, followed by leaching with
95% ethyl alcohol to remove excess NH^+ and subsequently with acidified
NaCl to displace NH^+ which was then distilled (into boric acid) and
titrated with HC1 (Chapman, 1965). Soil pH was determined at 1:2 soil
solution ratio in deionized water using a glass electrode.
Plant analysis methods
Nitrogen analysis of plant material employed the microKjeldahl
procedure modified by Gallaher et al. (1976). A 100-mg sample was placed
in 100-ml digestion tubes to which two boiling chips, 3.2 g of catalyst
(90% anhydrous i^SO^, 10% anhydrous CuSO^), 10 ml of concentrated H2S4
and 2 ml of ^02 were added. Samples were then digested in an aluminum

195
block digester (Gallaher et al, 1976) for 2.5 hr. Upon cooling,
solutions were diluted to 75 ml with deionized water. Nitrogen
concentration of these solutions were determined on a Technicon
AutoAnalyzer II.
Phosphorus, K, Ca, Mg, Fe, Cu, Mn, and Zn concentrations were
determined by a mineral analysis procedure in which 1.0 g samples were
placed in 50-ml pyrex beakers and ashed in a muffle furnace at 480C
for a minimum of 4 hours. After cooling each was treated with 2 ml
concentrated HC1 and heated to dryness on a hot plate. An additional 2
ml of concentrated HC1 + water was added to the dry beakers followed by
reheating to boiling and then diluting to 100 ml volume with deionized
water (this gave a solution containing about 0.10 _N HC1). Solutions were
analyzed for P using colorimetry on an AutoAnalyzer. Potassium was
determined by atomic emission spectrophotometry. Calcium, Mg, Fe, Cu,
Mn, and Zn were determined by atomic absorption spectrophotometry.
A sample of 0.3 g _+ 0.05 g of plant tissue was weighed in a clean
boat for total S concentration. The samples were spiked with 0.5 g of
vanadium pentoxide (V^O^). Sulfur concentrations were then determined
using a Leco S Determinator model SC132.
Results and Discussion
Experiment 1
Phenotypic characteristics of treatment plants are presented in
Table 7-1. Plants for the 30, 60, and 75 cm heights were uniformly light
yellow in appearance. Leaf veins were green, but intervenial spaces were
yellow, light yellow, and light yellow, respectively. Plants of the last
two height treatments (90 and 120 cm) had a vigorous appearance and were

Table 7-1.
Phenotypic characteristics
of maize plants
5 .
Plant
Height
Plants
Leaf
Deficiency
symtoms
Veins
Intervenial
Leaf
Mineral
cm
30
Uniformly
Green
Yellow
Chlorosis
in
older
K
Yellow
60
Uniformly
Green
Light Yellow
Chlorosis
in
older
K
Light Yellow
75
Uniformly
Green
Light Yellow
Chlorosis
in
older
N/A
Light Yellow
90
Green
Green
Green
Normal
N/A
120
Dark Green
Green
Green
Normal
N/A
N/A = None was apparent.

197
green and dark green, respectively. No intervenial chlorosis was
observed on the latter treatments. Older leaves of all treatments showed
some degree of chlorosis, but only on the leaves of the 30 and 60 cm
height plants were K-deficiency symptoms observed.
Results of measurements of the first internode of treatment plants
are presented in Table 7-2. Internode diameter increased with plant
height. Plants 30 cm tall had the smallest diameter, while those 90 cm
tall had the largest diameter. The results indicate no difference
(p=0.05) in internode diameter between plants 90 and 120 cm tall. Dry
weight per plant (Table 7-2) followed a trend similar to internode
diameter. As expected, taller plants had accumulated more dry matter
(p=0.05). Plants 120, and 30 cm tall had accumulated 72.3 and 11.5 g of
dry matter per plant, respectively.
Leaf length, width, and dry weight were different (p=0.05) for all
height treatments (Table 7-3). The 120 cm plant height presented the
largest values for all variables. In general, as plant height increased
leaves were longer and wider and had accumulated more dry matter. Leaf
length varied from 49.5 to 96 cm for the 30 and 120 heights,
respectively. Leaf width (at the widest point) varied from 5.33 to 9.53
cm in the 30 and 120 cm heights, respectively. The difference in leaf
weight between the 30 and 120 cm height was 3 g; this is a 100% increase
in leaf weight.
Soil depth to 20% clay varied among treatments (Table 7-4). Twenty
percent clay levels were shallower (15 cm) where 120 cm tall plants were
growing. Roots of the shortest plants would need to penetrate 120 cm or
more to reach cation-rich clays. Cation exchange capacity (CEC) and
extractable bases (EB) increased with depth, except for the 30-cm

198
Table 7-2. Plant characteristics of maize treatments in Florida.
Height First internode
treatment diameter
Dry weight
per plant
cm g
30
1.70 d
11.48 e
60
2.65 c
33.66 d
75
3.06 b
51.78 c
90
3.27a
61.15 b
120
3.18a
72.25a
Values in columns not followed by the same letter are different at
the 0.05 level of probability according to Duncan's new multiple
range test.
Table 7-3. Plant characteristics of maize treatments in Florida.
Height
treatment
Average/leaf
Length Width Weight
30
49.53 e
5.33 e
g
1.845
60
68.58 d
7.87 d
3.166
75
76.20 c
8.64 c
3.778
90
86.36 b
9.14 b
4.014 b
120
96.52a
9.53a
4.885a
Value in columns not followed by the same letter are different at
the 0.05 level of probability according to Duncan's new multiple
range test.

199
Table 7-4.
Selected soil
properties in relation to
maize
plant height
in Florida.
Height
Depth to
CEC
EB
treatment
20% clay
45 cm 90 cm
45 cm
90 cm
1
era-
30
120
2.6 1.9
2.3
1.3
60
90
3.3 4.2
2.2
2.9
75
75
2.2 7.0
1.7
4.5
90
45
5.8 21.6
4.9
18.0
120
15
15.0 70.7
14.5
19.3
CEC = cation exchange capacity, EB = extractable bases.
Table 7-5. Sulfur concentration in maize in relation to
plant height in Florida.
Height
treatment
Tissue
Plant Leaf
cm
dag kg
30
0.090 b
0.090 c
60
0.083 b
0.093 c
75
0.097 b
0.100 c
90
0.090 b
0.117 b
120
0.137 a
0.210 a
Values in columns not followed by the same letter are
different at the 0.05 level of probability according to
Duncan's new multiple range test.

200
treatment. In all cases 120-cm plants were growing in better nutrient
availability conditions than the deficient plant treatments (Table 7-4).
This explains in part differences observed in plant characteristics
(height, leaf length, width and weight) observed among treatments. Roots
of tall plants (120 cm) found higher nutrient concentrations at
shallower depths which caused higher growth rate than those of other
treatments. These findings agree with those reported by Rabuffetti and
Kamprath (1977)and Mitchell and Blue (1981a, 1981b).
Plant and leaf S concentrations (Table 7-5) in relation to plant
height were different among treatments (p=0.05). Whole plant S
concentrations varied from 0.09 to 0.14 dag kg in the 30 and 120-cm
treatments, respectively. Mitchell and Blue (1981a) reported similar
values for maize in different soils in Florida. Leaf S concentration was
generally higher than that of the whole plant. Taller plants (120 cm)
had higher (p=0.05) S concentrations than the other treatments.
According to Plank (1979) S sufficiency range for maize ear-leaf is from
0.15 to 0.50 dag kg This indicates that only those leaves from the
120-cm treatment (0.21 dag kg ^) were within the sufficiency of S level.
Those plants with the highest leaf-S concentration were those with the
highest values for the different phenotypic characteristics and dry
matter accumulation (Tables 7-2 and 7-3, respectively). Therefore, these
results indicate that low S concentration is limiting growth of the
deficient S-plants.
Soil-S concentration in relation to plant height is presented in
Table 7-6. A comparison of S concentration at three soil depths (0-15,
15-30, and 30-45) detected differences (p=0.05) for the 60, 75 and
120-cm treatments. In general, as soil depth increased S concentration

201
Table 7-6. Sulfur concentration in soil in relation to
maize plant height in Florida
Height
treatment
Soil depth
0-15
15-30
30-45
cm
dac kc'1
30
3.17 b
2.83 e
4.00
b
60
2.00 b
3.00 e
4.17
b
75
2.83 b
3.67 b
4.33
b
90
3.00 b
4.33 be
4.50
b
120
4.50a
5.00a
18.67
b
Value in
columns not followed by the same letter
are
different
at the 0.50 level of probability according to
Duncan's
new multiple range test.
Table 7-7.
Nitrogen, P
, and S
concentration
in youngest
mature leaf
of maize in Florida.
Height
Nutrient
treatment
N
P
S
N: S
P: S
dag kg
1
30
4.08
.46
.090
45
5.1
60
3.44
.33
.093
37
3.6
75
3.61
.27
.100
36
2.7
90
2.99
.25
.117
26
2.1
120
2.96
.28
.210
14
1.3

202
increased from 4.5 to 18.7 mg kg in the 0-15 and 30-45 cm depths,
respectively, for 120-cm plants. These findings are in agreement with
data reported by Neller (1959), Bardsley et al. (1964), Kamprath (1977),
and by Mitchell and Gallaher (1979), which indicates that adsorbed
sulfate associated with the argillic horizons of Ultisols is the primary
source of plant available-S in the southeastern United States. In a
comparison of soil-S concentration among height treatments within soil
depths (Table 7-6), soils related to the 120-cm treatment had a higher S
concentration (p=0.05) compared to those related to other treatments.
This finding strengthens the results observed for S concentration in
plant tissue (Table 7-5).
According to Plank (1979) the N, and P sufficiency levels for maize
ear-leaf range from 3.5 to 5 dag kg ^ and 0.3 to 0.5 dag kg ^,
respectively. Nitrogen concentration values reported (Table 7-7) for
treatments 30, 60, 75-cm (4.08, 3.44, and 3.61 dag kg respectively)
are within this sufficiency level. On the other hand, values reported
for the 90 and 120-cm treatments (2.99 and 2.96, respectively) fall
below this range. Nitrogen and P concentration in the leaf tissue
decreased with plant height (Table 7-7), and leaf size (Table 7-2). This
agrees with findings reported by Kumar and Awasthi (1977) and Hanway
(1962a) who attributed this phenomenon to dilution effect. Leaf P
followed a trend similar to that of N; as plant height and leaf size
increased P concentration decreased, and only those levels observed in
the 30 and 60-cm treatments are within the range reported by Plank
(1979). It is noteworthy that both N and P presented an inverse
concentration pattern in relation to S.

203
Dijkshoorn et al. (1960) and Gaines and Phatak (1982) reported that
for maize, the N:S concentration ratio varies from 14 to 17. The N:S
ratio found in the leaves in plants from the 120-cm treatment is
adequate; not so for the other treatments. These high ratios (45, 37,
36, and 26) indicate that S concentration in relation to that of N is
low. Friedrich and Schrader (1978) reported that under S-deficient
conditions the plant's capacity to synthesize protein is affected and N
accumulates in non-protein forms in the plant. Similarly, sulfate will
accumulate in plants when the rate of uptake exceeds the amount required
for protein synthesis. Therefore, this imbalanced observed (N:S)
affected the growth of plants from all treatments, except those from the
120-cm treatment.
The P:S ratio is reported in Table 7-7. Values ranged from as high
as 5.3 to 1.3 for the 30 and 120-cm treatments, respectively. These high
ratios also indicate an inadequate S concentration. Phosphorus-sulfur
interactions have been observed by Kamprath et al. (1956) and Radet
(1966). Caldwell et al. (1969) observed that S applications decreased P
concentration in mature tissue. This could have been due to dilution; as
plants grow plant uptake of S and P concetration in the tissue will be
diluted.
Average extractable K, Ca, and Mg in the top 45 cm of soil in
relation to plant height is reported in Table 7-8. Blue et al. (1981)
reported similar values for two Florida Entisols. According to data
presented by Plank (1979), K is low and Ca high. In general, the trend
observed was that K, Ca, and Mg were higher in the soils related to the
120-cm treatment.

204
Table 7-8.
Extractable
maize plant
cm soil).
nutrients
height in
in soil in relation
Florida (average top
to
45
Height
Nutrient
treatment
ph
P
K Ca
Mg
cm
-1
- mg kg
30
5.9
83
13 290
32
60
5.9
96
16 320
24
75
6.3
366
19 803
28
90
6.4
547
17 1680
45
120
6.7
1395
25 3480
79
r
+ .944
+ .925
+ .925
+ .916
+ .811
R2
.891
.831
.856
.839
.657
P
.044
.029
.0226
.0272
.095
Table 7-9.
Potassium,
leaf.
Ca, and Mg
concentration in maize
Height
Nutrient
Rat io
treatment
K
Ca
Mg
K/Ca+Mg
K/S
- dae kv_1 -
Kal 1.0
30
1.60
.73
.29
.68
17.8
60
1.56
.67
.24
.75
18.8
75
1.80
.61
.16
1.05
18.6
90
1.83
.63
.12
1.13
20.3
120
2.40
.67
.15
1.34
17.5
r
+ .944
+ .912
+ .925
+ .916
+ .811
R2
.891
.831
.856
.839
.657
P
.044
.029
.0226
.0272
.095

205
Leaf K, Ca, Mg concentrations are shown in Table 7-9. Critical
concentration of K in corn ear leaf tissue at silking was found to be
1.75 dag kg ^ (Gallaher et al., 1975). Plank (1979) sets the K
sufficiency range in ear leaf between 1.75 and 2.25 dag kg According
to these critical levels, K is deficient in the leaves from plants in
the 30 and 60 cm treatments and adequate in leaves from the 75, 90, and
120-cm treatments. Calcium concentration appears to be high in
comparison to the sufficiency range (0.25 to 0.50) reported by Plank
(1979). By the same standards, plants from all treatments had adequate
Mg concentrations. In general, the concentration of these nutrients
decreased as plant height increased.
Gallaher et al. (1975) reported that an adequate K:Ca+Mg ratio in
2+ -1
ear leaf is 11.7 to 13.1 mmol(M )kg 38 days after planting and 7.7 to
2+ -i .
8.7 mmol(M kg 86 days after planting. The K:Ca+Mg ratios reported in
Table 7-9 range from 0.68 to 1.34 in the 30 and 120-cm treatments. As
plant height increases the ratio becomes wider. This also implies that
as S concentration in the leaf increases, K concentration is also
increased. These results suggest a K x S interaction in the leaf.
Apparently S deficiency in the leaf accentuates a K deficiency, which in
turn affects growth directly, because the transport of photosynthates
from the leaf must be affected by the K deficiency. This is a possible
explanation for the stunted plants, reduced leaf dry weights, and K
deficiency symptoms observed in Tables 7-2 and 7-1, respectively.
Experiment 2
A representative weekly rainfall distribution for the 1982-1983
growing season in Nicaragua, Central America is depicted in Figure 5-1.
At the beginning of the rainy season intense rains caused a delay in

206
planting, with respect to normal years. These intense rains were
followed by an extremely dry and lengthy "canicula", that in some areas
lasted more than 75 days without significant rainfall. During the
growing season, in the area under study, maize received approximately
500 mm of rain. Available soil moisture (Fig. 5-2) during the growing
season can be considered low for the area (personal observation). With
this caution in mind the results of this study will be presented.
Plants identified as deficient (D-) plants were in all (Table 7-10)
cases less vigorous, yellow to light yellow, and in most cases showed
symptoms of K and S deficiency (orange-yellow leaf tips and intervenial
chlorosis, respectively). Plants grouped as sufficient (SU-) plants
were vigorous, green or dark green, were tall and in most cases showed
no symptoms of K or S deficiency. Plant height (PH), within D-plants
ranged from 186 to 44 cm for sites 9 and 4, respectively (Table 7-10),
and from 224 to 77 cm (sites 17 and 8 respectively) for the S-sufficient
plants. In general, SU-plants were consistently taller than D-plants at
all sites, and in 12 of the 18 sites differences (p=0.05) between SU and
D-plants were observed. These results support those observed in
Experiment 1; that is, plants with no apparent S or K deficiency
symptoms were taller and more vigorous than those with visual symptoms
of deficiency.
The trends observed for leaf dry weight and leaf area index (LAI)
(Table 7-10) were similar to that observed in plant height. Leaves of
D-plants were yellow or pale green with intervenial chlorosis. The older
leaves showed symptoms of K deficiency and in some cases lower leaves
were in the process of decaying. In general, at all sites, leaves from
SU-plants had accumulated more dry matter than those from D-plants; in

Table 7-10. Plant characteristics of maize for 18 sites in Nicaragua.
Site
Plant
Height
Leaf
Dry Weight
Leaf Area
Index
D
SU
D
SU
D
SU
2
- mg kg
in
9
186a
198abcd
14.4
a
17.8abcd
2.2
be
2.4abc
14
156ab
207abc *
10.3
bed
12.2 defg
2.7ab
2.7ab
15
155abc
145 fgh
8.9
edef
18.3abc *
3.0a
2.5ab
10
136 bed
221ab *
13.3
ab
20.2a *
1.8
ede
2.8a
16
133 bede
166 ef
8.4
ede f g
12.5 edefg
2.1
bed
2.5ab
18
133 bede
169 def
8.8
edef
10.8 efg
2.1
bed
2.2abc
17
133 bede
224a *
9.4
ede
15.9abcdef *
1.9
ede
2.5ab
1
123 bede
190 ede *
9.9
bed
17.7abcd *
0.6
g
1.7 be *
7
117 ede
120 h
10.7
bee
10.3 fg
1.2
efg
1.3 c
13
114 de
199abc *
7.0
def g
14.1 bedefg *
1.5
def
2.5ab
3
112 de
191 bede *
11.2
abe
11.6 efg
2.0
cd
2.labe
12
98 de
155 fg *
10.0
bed
14.0 bedefg
1.5
edef
2.labe
11
95 e
208abc *
9.0
edef
19.8ab *
1.1
fg
2.2abc *
2
54 f
123 h *
7.2
defg
16.5abcde *
1.5
edef
2.8ab *
5
49 f
121 h *
5.4
fg
14.0 bedefg *
0.8
fg
2.labe
8
47 f
77 i
5.8
efg
10.8 efg *
1.3
def
2.3abc *
6
46 f
131 gh *
4.9
g
9.3 g
1.0
fg
2.5ab *
4
44 f
117 h *
5.4
fg
13.4 edefg *
0.8
fg
2.5ab *
Value9 in columns not followed by the same letter and rows within subheadings followed by an asterisk are different at the 0.05
level of probability according to Duncan's new multiple range test and F test, respectively.
207

208
10 of the sites differences (p=0.05) were detected among treatments.
Leaf dry weight ranged from a low of 4.9 g in site 6 for the D-plants to
a high of 20.2 g in site 10 for SU-plants. Generally, plants with
heavier leaves had the largest LAI (r=0.53); this implies a larger
photosynthetic capacity for SU-plants. Only a few sites (14, 15, 10, and
2) were nearing the point of maximum LAI. These results are congruent
with those observed in Florida. That is, taller plants have heavier
(r=0.60) and larger leaves (r=0.56).
Soils associated with D-plants were different among sites (p=0.05)
for S, N, and P concentration. Similar results were observed for soils
associated with SU-plants (Table 7-11). Soil test detected differences
for S concentration between soils associated with treatments in sites
14, 3, and 8. Nitrogen differences for treatments were detected at
p=0.05, only at site 8, and no differences between soils for P were
detected. Sulfur and P values are similar to those reported for Central
America. Nitrogen values may be considered high for the area (values
above 3 dag kg ^) Fassbender, (1980). In soils associated with the
D-plants S ranged from 0.115 to 0.303 dag kg in sites 8 and 18,
respectively. In soils associated with SU-plants the S concentration
ranged from 0.155 in site 8 to 0.318 dag kg in site 18. These S
concentrations fall into what may be the low range reported by Blair et
al. (1980). Soil S was positively correlated (r=0.20) with LAI and with
plant height (r=0.32). Soil N was correlated with LAI, plant height, and
LDW (r=0.23, 0.20, and 0.19, respectively).
The intensive rains prior to planting and the cropping system
practiced (maize + sorghum intercropped) may be the cause for this low
concentration of soil-S (Blair et al., 1980). Soil samples were taken

Table 7-11. Soil S, N, and P concentrations at 18 sites in Nicaragua
Site
S
N
P
D
SU
D
SU
D
SU
_1
mg kg
18
0.303a
0.318a
4.4 bede
6.1
ab
16
f
10 c
16
0.263ab
0.305a
5.0 abe
5.0
abed
7
f
12 c
17
0.228
be
0.223
be
5.4ab
6.0
ab
18
ef
5 c
14
0.225
be
0.253
b *
2.5 bede
4.2
abede
2
f
4 c
13
0.218
be
0.215
bed
4.9abc
3.3
abed
59
c
44 c
12
0.213
be
0.213
bed
7.8a
6.5
a
38
de
29 c
1
0.200
cd
0.200
bede
1.9 ede
1.9
ede
111 b
12 lab
11
0.193
ede
0.183
edef
3.8 bede
4.4
abede
21
ef
26 c
15
0.190
ede
0.208
bede
4.1 bede
5.3
abe
4
f
4 c
2
0.185
ede
0.198
ede
1.6 ede
1.3
e
3
f
7 c
10
0.180
ede
0.160
def
4.7abcd
5.2
abe
16
f
7 c
3
0.173
ede
0.210
bede *
1.5 de
0.9
e
3
f
2 c
5
0.153
def
0.170
edef
2.3 bede
2.7
bede
10
f
15 c
4
0.150
def
0.155
ef
1.3 e
5.3
abe
6
f
5 c
7
0.150
def
0.135
f
1.6 ede
1.4
de
52
cd
94 b
6
0.145
def
0.178
edef
2.4 bede
2.1
ede
5
f
16 c
9
0.135
ef
0.168
edef
4.4 bede
1.7
ede
22 b
102 b
8
0.115
f
0.155
ef *
1.9 ede *
5.8
ab *
161a
156a
Values in columns not followed by the same letter and rows within subheadings followed by an asterisk
are different at the 0.05 level of probability according to Duncan's new multiple range test and F test,
respectively.
209

210
from the top 30 cm of soil. The rains probably leached the S from this
top layer and sorghum and maize stover removed from the field
continually mine the soil. In the area of study, burning plant material
is a popular practice. Therefore as pointed out by Bromfield (1974),
this may be a cause for the low S status of these soils. Fritts (1970)
reported that S deficiency occurs in soils derived from volcanic parent
material. In such soils, which are common in the area under study, the
organic matter is closely associated with allophane and mineralization
of the allophane-bound organic matter. Thus, the release of sulfate is
very low.
Plants with the largest leaves (Table 7-10) had larger S
concentration (Table 7-12). Leaves from SU-plants had consistently
higher S content than those from D-plants. Differences between
treatments (p=0.05) were observed in 11 of the 18 sites. Differences
among sites for both the D and SU-plants for S content were detected at
the 0.05 level. Leaf S content values for D-plants observed in sites 8,
6, 4, and 5 (0.007, 0.007, 0.008, and 0.008 g, respectively) were
considerably lower than the values observed at other sites.
Leaf N content was significantly different (p=0.05) among sites for
both D and SU plants. Differences between treatments were observed in
sites 15, 2, 4, and 8. A trend was observed for leaves from SU-plants to
have higher N content than D-plants. Values for N content in the leaves
from SU plants ranged from .102 to 1.09 g in sites 3 and 10,
respectively.
The trend observed for S concentration in the leaf was similar to
that observed for N content (Table 7-12). Only in sites 18 and 13 did
the leaf S concentration in D-plants surpass that reported for

Table
7-12. Leaf
content of
S and N
, concentration
of S
and N, and
the N:S
concentration
ratio.
Sice
S concent
N concent
S Concentration
N Concentration
N: S
D
su
D
su
D
su
D
su
D
SU
-
1
g
18
0.026a
0.034ab
0.40abcd
0.649abcd
0.296ab
0.27abcd
2.08a
2.32a
7.0
8.6
10
0.024ab
0.032abc *
0.63ab
1.090a
0.167
ef
0.17 e
0.74 g
1.06 f
4.4
6.2
14
0.023abc
0.031abcd
0.21 cd
0.492abcd
0.210
edef
0.28abc *
1.68abcd *
2.24ab *
8.0
8.0
16
0.022abc
0.039a *
0.41 abed
0.668abcd
0.265abcd
0.30a
2.03a
2.29ab
7.7
7.6
12
0.021abc
0.031abcd
0.78a
0.992ab
0.170
ef
0.21 de
0.73 g
1.42 def
4.3
6.8
17
0.021abc
0.035ab *
0.49abc
0.971abc
0.225
ede
0.26 bed
1.74abc
2.21 b
7.7
7.6
1
0.020abcd
0.034ab *
0.19 cd
0.345 cd
0.220
ede
0.29 b
1.40 edef
2.07 be
6.4
7.1
3
0.020abcd
0.024abcde
0.17 cd
0.102 d
0.217
edef
0.22 de
1.28 def
1.43 def
5.9
6.5
9
0.019abcd
0.030abcd
0.67ab
0.286 d
0.198
de f
0.23 bede
1.24 def
1.34 ef
5.4
5.8
11
0.017 bed
0.036ab *
0.35 bed
0.932abc
0.146
f
0.18 e*
1.00 fg 1.27 f
6.8
7.1
15
0.016 bed
0.036ab *
0.39abcd
0.951abc *
0.228
ede
0.29 b
1.53 bede*
2.25 b *
6.7
7.8
7
0.016 cd
0.014 e
0.17 cd
0.146 d
0.175
ef
0.21 de
1.17 ef
1.31 ef
6.7
6.2
13
0.015 cd
0.031abcd *
0.39abcd
0.476abcd
0.248
bed
0.22 ede
1.85ab
1.75 ede
7.5
8.0
2
0.013 de
0.033abc *
0.12 cd
0.226 d*
0.213
edef
0.29 b
1.46 bede
2. lOabc
6.9
7.2
5
0.008 e
0.024abcde*
0.12 cd
0.368 bed
0.27 7abc
0.29
1.45 bede*
2lOabc*
5.2
7.2
4
0.008 e
0.021 bede*
0.06 d
0,647abcd*
0.195
def
0.29 b *
1.54 bede
1.83 bed
7.9
6.3
6
0.007 e
0.019 ede
0.13 cd
0.243 d
0.175
ef
0.28ab *
1.20 ef*
1.74 ede*
6.9
6.2
8
0.007 e
0.017 de *
0.10 cd
0.669abcd*
0.319a
0.31a
2.08a
2.23ab
6.5
7.2
Values in columns noc followed by che same letter and rows within subheadings followed by an asterisk are different at the 0.05 level
of probability according to Duncan's new multiple range test and F test, respectively.
211

212
SU-plants, although differences between treatments (p=0.05) were oberved
only at four sites. Leaf S concentration values for SU-plants (except
for sites 10 and 11) were above the critical levels (0.20 dag kg ^)
established by Fox et al. (1964) and fall within the sufficiency range
(0.15 to 0.50 dag kg ^) reported by Plank (1979). On the other hand,
only in a few sites were the leaf concentrations well above the critical
level in the leaves from D-plants.
Leaf S concentration was positively correlated to LAI (r=0.20) and
leaf N concentration (r=0.75). Interestingly, S concentration was
negatively correlated to leaf Ca and Mg concentration (r=-0.23 and
-0.14, respectively) but positively correlated to leaf K concentration
(r=0.30). Other correlation values are given in Tables 7-16 and 7-17.
Leaf N concentration for both treatments are low according to
criteria established by Plank (1979). Differences among sites within
each treatment were significant at p=0.05. Only at sites 14, 15, 5, and
6 were there differences (p=0.05) between treatments (Table 7-12). The
high soil N observed and low N concentration in the leaves suggest that
due to the low amount of available soil moisture, N fertilizer applied
had not been taken up by the plants, causing a N deficiency in the
plant. Further evidence is the low leaf N:S ratio observed (Friedrich
and Schrader, 1978), independent of site and treatment (Table 7-12).
Phosphorus concentration in the leaf and the P:S ratio are
presented in Table 7-13. Diferences among sites within treatments were
observed (p=0.05). Differences between treatments for leaf P
concentration were observed only at sites 11 and 15. According to
sufficiency levels (0.25 to 0.45 dag kg *) reported by Plank (1979),
most of the P concentration levels in the leaves of plants from either

213
Table 7-13. Leaf P concentration and S:P ratio observed in
18 sites in Nicaragua.
SITE
P
P:S
D
SU
D
SU
dag
kg"1
18
0.230abc
0.248abc
0.78
0.92
10
0.114 de
0.121 fg
0.68
0.71
14
0.251a
0.283ab
1.20
1.01
16
0.270a
0.217 bcde
1.02
0.72
12
0.184abcd
0.184 cdefg
1.08
0.88
17
0.198abcd
0.181 cdefg
0.88
0.70
1
0.202abcd
0.296ab
0.92
1.02
3
0.106 de
0.127 fgh
0.49
0.58
9
0.202abcd
0.223 bed
1.02
0.97
11
0.063 e
0.149 defg *
0.43
0.83
15
0.246ab
0.313a *
1.08
1.08
7
0.117 de
0.096 g
0.67
0.46
13
0.263a
0.209 bedef
1.06
0.95
2
0.127 cde
0.150 defg
0.60
0.52
5
0.123 cde
0.210 bedef
0.44
0.72
4
0.140 bcde
0.139 defg
0.72
0.48
6
0.111 de
0.148 defg
0.63
0.53
8
0.206abcd
0.277ab
0.65
0.89
Values in columns not followed by the same letter and rows
within subheadings followed by an asterisk are different at
the 0.05 level of probability according to Duncan's new
multiple range test and F test, respectively.

214
treatment were deficient. Nevertheless, the P:S ratio was within the
appropriate value (Tisdale and Nelson, 1964). Leaf P concentration was
positively correlated to S concentration (r = 0.33), with N
concentration (r = 0.45), and with K concentration (r = 0.74). Other
correlation values are given in Tables 7-16 and 17.
Soil K, Ca, and Mg values observed differed among sites within each
treatment (Table 7-14). No differences were observed between treatments
for any of these elements. Potassium values that fall below 100 dag kg ^
are considered low for the area under study (Fassbender, 1980). Calcium
and Mg values reported are common in these dry tropical areas, and agree
with those reported by Fassbender (1980). Although in most sites
concentrations reported are within the accepted ranges, the ratios
between these nutrients may not be appropriate, especially in the
Ca+Mg:K. As K levels decrease, the ratio becomes wider.
Potassium, Ca, and Mg concentrations in the leaf were different
among sites (p=0.05), as shown in Table 7-15. No differences were
observed between treatments. Potassium concentration appears to be low
for both treatments, Plank (1979) has established the sufficiency range
for K in leaves between 2.0 and 2.5 dag kg Except for leaves from
sites 15 and 8, leaves from all sites and treatments were deficient in
K. In most cases Ca and Mg concentrations were within the sufficiency
ranges established by Plank.
Values for the K:Ca+Mg ratio in the leaves are presented in Table
7-15. These findings suggest an imbalance between these nutrients is
common in the area under study. Gallaher et al. (1975) reported that
when the K:Ca+Mg ratio exceeds 1.8, levels of Mg in the ear leaf are
close to the value at which photosynthesis was reduced. Most of the

Table 7-14. Soil extractable K, Ca, and Mg; and Ca:Mg and Ca+Mg:K ratios from 18 sites in
Nicaragua.
Sice
K
Ca
Mi
Ca : Mg
Ca + Mg
:K
D
su
D
SU
D
SU
D
SU
0
SU
1
283.
262.
3630.b
3450.
539 edef
525 ede
6.7
6.6
14.7
15.2
18
283.
260a
2890 bedef
3310.b
832.
781.
3.5
4.2
13.2
14.5
10
204ab
167 bedefg
2445 def
2125 d
378 f
339 f
6.5
6.3
13.8
14.8
9
198abc
173abcde fg
3280abcd
2755.bed
473 def
424 ef
6.9
6.5
19.0
18.4
13
167 bed
144 edefg
3809a
3460a
610 bede
588 cd
6.2
5.9
26.5
28.0
3
156 bede
186abcdefg
2810 bedef
2940abcd
440 ef
427 ef
6.4
6.9
20.8
18.1
11
156 bede
221.be
2990abcde
2530 bed
474 def
392 ef
6.3
6.5
22.2
13.2
16
147 bedef
242abc
3009abcde
3209ab
404 f
469 def
7.5
6.8
23.2
15.2
12
128 bedef
179abcde fg
2270 ef
30 70ab
474 def
642abc
4.8
4.8
18.7
20.7
7
127 bedef
122 defg
3450.be
3250ab
558 bedef
539 ede
6.2
6.0
31.6
31.1
6
125 bedef
250.b
2360 def
3030abc
733ab
632 be
3.2
4.8
24.7
14.6
5
119 bedef
217abcde
2480 def
2900abcd
711.be
639abc
3.5
4.5
26.3
16.3
17
113 bedefg
173abcdefg
2340 ef
2810.bed
506 def
628 be
4.6
4.5
25.2
19.9
3
95 edef
156 bedefg
2720 bedef
2860abcd
620 bede
644abc
4.4
4.4
35.2
22.5
15
72 def
117 efg
3090abcde
2969abcd
526 def
508 ede
5.9
5.8
51.2
29.7
14
58 ef
89 fg
2870 bedef
2940abcd
641 bed
531 ede
4.5
5.5
60.5
39.0
4
57 ef
80 g
1965 f
2175 cd
507 def
650abcd
3.9
3.3
43.4
35.3
2
51 f
85 fg *
2670 edef
2640abcd
872.
768ab
3.1
3.4
69.5
12.1
Values in columns not followed by Che same
letter and rows
within subheadings followed
by an asterisk
are different
ac the
0.05 level of
probability
according to
Duncan's new multiple range test
and F test,
respectively.
215

Table 7-15. Potassium, Ca, Mg concentrations and the K:Ca+Mg ratio for 60 day old maize leaves
from 18 sites in Nicaragua.
Sice
K
Ca
Mg
K;
:Ca*-Mg
D
SU
D
SU
D
SU
D
SU
dag
kg
15
2.19a
2.34a
0.29abc
0.32abcd
0.19abcd
0.18abcde
4.6
5.0
8
1.96a
2.34a
0.21 be
0.18 d
0.12 cd
0.11 e
5.9
8.1
16
1.62abc
1.39
cd
0.25 be
0.19 d
0.14 bed
0.11 e
4.2
4.6
13
1.60abc
1.22
cd
0.31abc
0.30abcd
0.21abc
0.15 ede
3.1
2.7
9
1.59abc
1.00
cd
0.31 abe
0.46ab
0.13 bed
0.19abcde
3.6
1.5
18
1.59abc
1.38
cd
0.25 be
0.22 cd
0.19abcd
0.22abcd
3.6
3.1
14
1.58abc
1.95ab
0.31abc
0.38abcd
0.24ab
0.23abc
2.9
3.2
1
1.43abc
1.55
be
0.21 be
0.23 cd
0.17abcd
0.15 ede
3.8
4.1
7
1,40abc
0.78
0.27abc
0.29abcd
0.19abcd
0.16 bede
3.5
1.7
4
1.14 be
1.30
cd
0.22 be
0.33abcd
0.20abcd
0.19abcde
2.7
2.5
12
1.13 be
1.10
cd
0.33ab
0.46ab
0.19abcd
0.27a
2.7
1.5
17
1.11 be
1.17
cd
0.22 be
0.40abc
0.14 bed
0.21abcd
3.1
1.9
5
1.06 be
1.31
cd
0.13 c
0.19 d
0.13 bed
0.15 ede
4.1
3.8
6
0.95 c
1.36
cd
0.14 c
0.16 d
0.12 cd
0.13 de
3.7
5.2
10
0.92 c
1.20
cd
0.44a
0.49a
0.26a
0.24ab
1.3
1.6
2
0.92 c
1.58
be
0.18 cd
0.28 bed
0.16abcd
0.24ab
2.7
3.0
3
0.74 c
1.05
cd
0.14 c
0.22 cd
0.09 d
0.15 ede
3.2
2.8
11
0.69 c
0.91
d
0.24 be
0.44ab
0.11 cd
0.17 bede
2.0
1.5
Values in columns not followed by Che same letter and rows within subheadings followed by an asterisk are different at the 0.05
level of probability according to Duncan's new multiple range test and F test, respectively.
216

Table 7-16. Multiple correlation coefficients for plant variables from 18 sites in
Nicaragua.
N
S
Mg
Mn
Ca
K
P
Zn
Cu
Fe
LAI
PH
LDW
N
1.00
S
0.75
1.00
Mg
-0.04
-0.14
1.00
Mn
0.26
0.18
0.43
1.00
Ca
-0.13
-0.23
0.67
0.38
1.00
K
0.34
0.30
0.22
0.53
0.13
1.00
P
0.45
0.33
0.25
0.44
0.17
0.74
1.00
Zn
0.30
0.13
0.52
0.42
0.45
0.39
0.61
1.00
Cu
0.34
0.16
0.30
0.50
0.31
0.64
0.71
0.58
1.00
Fe
-0.01
-0.09
0.30
0.19
0.24
0.19
0.27
0.32
0.33
1.0
LAI
0.26
0.20
0.20
0.23
0.24
0.24
0.22
0.23
0.26
0.10
1.00
PH
0.10
-0.02
0.19
0.07
0.38
0.05
0.22
0.28
0.15
0.06
0.56
1.00
LDW
0.05
0.02
0.18
0.17
0.36
0.00
0.10
0.18
0.05
-0.08
0.49
0.60
1.00
PH = plant height, LDW = leaf dry weight.
217

218
values observed for D-plants and some for SU-plants are well above this
critical ratio. These results suggest that the K:Ca+Mg imbalance may be
a limiting factor to increasing yields in this area.

Table 7-17. Multiple correlation coefficients fo soil variables from 18 sites in
Nicaragua.
S
N
Mg
Mn
Ca
K
P
Zn
Cu
Fe
LAI
PH
LDW
s
1.00
N
0.29
1.00
Mg
0.19
-0.19
1.00
Mn
0.08
0.01
0.21
1.00
Ca
0.18
-0.06
0.26
0.17
1.00
K
0.25
0.07
-0.04
-0.02
0.44
1.00
P
-0.30
-0.08
-0.29
-0.06
0.31
0.31
1.00
Zn
-0.14
1.43
0.39
0.22
-0.21
-0.22
-0.26
1.00
Cu
-0.19
-0.11
0.21
0.05
-0.62
-0.63
-0.47
0.44
1.00
Fe
0.02
-0.10
0.07
0.13
-0.14
0.12
-0.07
0.15
0.13
1.00
LAI
0.20
0.24
-0.05
0.20
-0.09
-0.06
-0.21
-0.10
0.04
-0.17
1.00
PH
0.31
0.20
-0.19
0.11
0.18
0.23
-0.08
-0.30
-0.27
CM
CM

O
1
0.56
1.00
LDW
0.03
0.19
-0.23
0.09
-0.04
0.12
0.01
in

o
1
-0.17
-0.17
0.53
0.63
1.00
PH = Plant height, LDW = Leaf dry weight.
219

CHAPTER 8
SUMMARY AND CONCLUSIONS
During 1982-1983 studies were conducted in Florida and Nicaragua to
provide basic information needed to describe and improve the maize +
sorghum intercropping system. The plan of work included experiments to
a) identify limitations in crop productivity, b) study the relationship
between soil moisture and dry matter accumulation, c) evaluate quality,
dry matter accumulation, energy, and nutrient concentration in the crop
components of the maize + sorghum and maize + millet intercropping
systems, and d) determine if S deficiency is a widespread problem.
Results from the situational analysis showed that maize + sorghum
is the most important food-producing system in Central America.
Environmental stresses, especially drought, are the most important
limitations to crop production. This phenomenon occurs because of the
variability in the rainfall pattern and the "canicula", which in some
areas may last more than 30 days. Drought is accentuated by the existing
physiography, shallow soils, and heavy soil textures. In some areas
nutrient deficiency, particularly N, P, and S, may reduce crop
productivity and can be related to drought. Within the biological
constraints, the wide use of low-yielding cultivars, 'criollos' of both
maize and sorghum, is a limitation that reduces the possibility of
increasing grain crop yields. The primary constraints to the farm system
are the availability of land, labor, and/or capital.

221
Among the most relevant research needs are 1) evaluate the
"guatera" system, 2) evaluate the uses of the maize + sorghum system in
animal and human nutrition, 3) design spatial and chronological
arrangements and rotations that enhance the adaptability of the system
to the environmental conditions, and increase the availability of animal
feed during the dry season, 4) test varieties and/or species to improve
the quantitative and qualitative yield of the system, 5) soil
conservation and management, 6)identify and evaluate exotic forage
species, and 7) evaluate (in vitro and in vivo) the components of the
maize + sorghum system.
Results from the dry matter accumulation study showed that when ear
sink is reduced by water stress during bloom, dry matter will accumulate
in other plant components, particularly in the leaf. The ability of the
non-photosensitive sorghum to accumulate dry matter in the head explains
in part its high grain:stem ratio; conversely, photosensitive sorghums
accumulate more dry matter in the stem than in the head.
Non-photosensitive sorghums compare well to photosensitive sorghums in
dry matter production. Millet, 'Gahi-3' was not adapted to the growing
conditions in Nicaragua and was dramatically affected by water stress.
IVOMD decreased with maturity in the vegetative plant components
but increases in maize ears. Maize leaves had higher IVOMD than the
stems. The photosensitive sorghum maintained higher IVOMD values and for
longer periods of time than non-photosensitive sorghum. 'NB-3',
'Criollo', and 'Gahi-3' presented similar forage quality. Energy
accumulation in the different plant components varied little during the
growing season. Maize and sorghum stover have a potential as livestock
feed.

222
In general, nutrient concentration in plant tissue indicated that
growth was limited by nutrient deficiencies. Most nutrient concentration
declined with maturity, however, if growth was resumed by the plant,
nutrient concentration increased in the growing parts. Nitrogen
concentration and IVOMD were affected similarly by maturity. However, N
concentration in the ear increased with maturity. Very little P was
translocated from the leaf or stem to the head in the sorghums.
Potassium is lost from the plant soon after bloom. Cation imbalance
(K:Ca, K:Mg, and K:Ca+Mg) in plant tissue affected crop yields
adversely.
The S deficiency survey proved that S is a widespread problem in
the maize + sorghum growing areas of Nicaragua and in some areas in
Florida. The S study indicated that healthy plants were positively
correlated to higher cation exchange capacity and extractable bases.
Evidence indicated that stunted plants with intervenial chlorosis were
deficient in S and had a N:S and P:S imbalance. Sulfur deficiency
apparently caused maize leaves to be deficient in K and a K:Ca+Mg
imbalance, even though sufficient K was indicated by whole plant
analysis. Apparently K accumulated in the stems but was excluded from
the leaves as a result of S deficiency.

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BIOGRAPHICAL SKETCH
Francisco Roberto Arias Milla, son of Tina Milla Sosa and Francisco
Arias, was born March 1, 1948, in San Salvador, El Salvador. He
graduated from South San Francisco High School in South San Francisco,
California, in 1966. In 1973 he received the degree of Ingeniero
Agronomo Fitotecnista from the Instituto Tecnolgico y de Estudios
Superiores de Monterrey, Mexico.
In 1974 he became staff member of the Ministerio de Agricultura y
Ganaderia of El Salvador, where he worked for two years before being
admitted to the University of Florida as a graduate student. In 1978 he
was awarded the degree of Master of Science. Upon his return to El
Salvador he was put in charge of the On-Farm Research Project, a
position he held for one year. In May 1980 he joined the staff of the
Centro Agronmico Tropical de Investigacin y Enseanza (CATIE) and was
assigned to Nicaragua as a cropping system specialist.
In 1983 he was awarded an International Fellowship from the W. K.
Kellogg Foundation to pursue a Doctor of Philosophy degree at the
University of Florida. He is an active member in two honorary
fraternities, Gamma Sigma Delta, and Alpha Zeta.
He is married to the former Beneranda Sanchez and they have three
children, Francisco Roberto, Liliana Michelle, and Veronica Cecilia.
238

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Raymond N. Gallaher, Chairman
Professor, Agronomy
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Victor E. Green
Professor, Agronomy
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Clifton L. Taylor
Associate Professor, Agricultural
and Extension Education
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
3?
Maxie 1$. McGhee
Associate Professor, Agr
and Extension Education
icultural

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Mary fi^Collins
Collins
Assi^ant Professor, Soil Science
This dissertation was submitted to the Graduate Faculty of the College
of Agriculture and to the Graduate School and was accepted as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.
August 1985
^ 3as~/
liege of Agrigjilt
Dean,
ture
Dean, Graduate School



Table 7-15. Potassium, Ca, Mg concentrations and the K:Ca+Mg ratio for 60 day old maize leaves
from 18 sites in Nicaragua.
Sice
K
Ca
Mg
K;
:Ca*-Mg
D
SU
D
SU
D
SU
D
SU
dag
kg
15
2.19a
2.34a
0.29abc
0.32abcd
0.19abcd
0.18abcde
4.6
5.0
8
1.96a
2.34a
0.21 be
0.18 d
0.12 cd
0.11 e
5.9
8.1
16
1.62abc
1.39
cd
0.25 be
0.19 d
0.14 bed
0.11 e
4.2
4.6
13
1.60abc
1.22
cd
0.31abc
0.30abcd
0.21abc
0.15 ede
3.1
2.7
9
1.59abc
1.00
cd
0.31 abe
0.46ab
0.13 bed
0.19abcde
3.6
1.5
18
1.59abc
1.38
cd
0.25 be
0.22 cd
0.19abcd
0.22abcd
3.6
3.1
14
1.58abc
1.95ab
0.31abc
0.38abcd
0.24ab
0.23abc
2.9
3.2
1
1.43abc
1.55
be
0.21 be
0.23 cd
0.17abcd
0.15 ede
3.8
4.1
7
1,40abc
0.78
0.27abc
0.29abcd
0.19abcd
0.16 bede
3.5
1.7
4
1.14 be
1.30
cd
0.22 be
0.33abcd
0.20abcd
0.19abcde
2.7
2.5
12
1.13 be
1.10
cd
0.33ab
0.46ab
0.19abcd
0.27a
2.7
1.5
17
1.11 be
1.17
cd
0.22 be
0.40abc
0.14 bed
0.21abcd
3.1
1.9
5
1.06 be
1.31
cd
0.13 c
0.19 d
0.13 bed
0.15 ede
4.1
3.8
6
0.95 c
1.36
cd
0.14 c
0.16 d
0.12 cd
0.13 de
3.7
5.2
10
0.92 c
1.20
cd
0.44a
0.49a
0.26a
0.24ab
1.3
1.6
2
0.92 c
1.58
be
0.18 cd
0.28 bed
0.16abcd
0.24ab
2.7
3.0
3
0.74 c
1.05
cd
0.14 c
0.22 cd
0.09 d
0.15 ede
3.2
2.8
11
0.69 c
0.91
d
0.24 be
0.44ab
0.11 cd
0.17 bede
2.0
1.5
Values in columns not followed by Che same letter and rows within subheadings followed by an asterisk are different at the 0.05
level of probability according to Duncan's new multiple range test and F test, respectively.
216


43
Sul fur
Importance of S
From the time of Liebig S has been known to be one of the elements
required for plant growth, but only recently has this element received
the attention it deserves as a plant nutrient. Despite this early
recognition, the importance of S as a limiting plant nutrient was
largely ignored until recently (Coleman, 1966; Caldwell et al., 1969).
In countries concerned with increasing food production, S is an
element that must not be overlooked. It is required not only for
increased total production, but what is probably far more important, it
is needed for increasing the quality of the protein present in the
foods that are produced (Coleman, 1966).
Allaway and Thompson (1966) indicated that the problem of
malnutrition due to deficiency and poor quality of protein in human
diets has been described by nutritionists and emphasized in the press.
The nutritional quality of a protein depends upon its amino acid
composition. Animals (including humans) must be supplied with the
S-containing amino acid methionine and the S-bearing vitamins biotin and
thiamine.
In areas where protein deficiency in human diets is a critical
problem, animal products are rarely consumed, and plants are the major
source of proteins. In addition, plants are frequently lower in total
protein than are animal products, so that the amounts of food required
to supply 1 g of S-amino acids are higher for plant products than for
animal products. The protein requirements of many areas will need to be
met by direct consumption of plant products. The appropriate ultimate
objective of S fertilization of soils is, therefore, to increase the


167
Days After Planting flalze
Figure 6-20. Effect of the stage of maturity on the
Ca concentration of 'NB-3' maize (a)
and 'Pioneer 895' sorghum (b).


39
Olagunde and Sorensen (1982) reported that in spite of the
substantial decreases in Mg, Ca, and P concentrations in sorghum there
seemed to be no relationship between K/Mg ratio and dry matter yield.
This constant amount of cations in the plants might explain why there
was no substantial change in dry matter yield. The authors suggested
that K, Ca, and Mg carry out plant functions which can be performed by
one cation in the absence of another.
Shukla and Mukhi (1979) noted that applications of Zn to maize
resulted in increased shoot Mg at all levels of K and Na. The
increasing K levels decreased Mg and the decrease was more when Zn or Na
was not applied. The results thus showed that K and Zn had antagonistic
and synergistic relationships, respectively, with Mg. The results also
evidenced antagonism between K and Ca, K and Mg, and synergism between
Mg and Zn.
Gallaher and Jellum (1976) found that leaf concentrations of Zn
and Fe were influenced by planting date for maize hybrids but
interactions between hybrids and planting date were found only for K,
2+ -1
Ca, Mg concentrations and the sum of the mmol(M ) Ca+Mg kg the
2+ -1
mmol(M ) K+Ca+Mg kg and the K:Ca and K:Ca+Mg ratios.
Potassium content in maize tissue and its balance with Ca and Mg
has had widespread interest. Macy (1936) stated that a critical
percentage of each nutrient in each plant species existed, above which
there was luxury consumption and below which there was poverty
adjustment. Critical concentrations of 2 mg K g and 200 mg Mg g \ on
a fresh weight basis were established for optimum photosynthesis in
maize.


158
0.5
0.4
0.3
0.2
O 1
0 0
1 1 1 1 1 i
- (a) o- Stem
o-Leaf
A- Ear
I L
30 60 90 120 150 100
Days After Planting Maize
Days After Planting Maize
Figure 6-13. Effect of the stage of maturity on the P
concentration of 'NB-3' maize (a) and
'Criollo' sorghum (b).


Cu (mg leg ) Cu (mg i 178
Figure 6-28. Effect of the stage of maturity on
the Cu concentration of 'NB-3' maize
(a) and 'Criollo' sorghum (b).


8
Vanderlip and Reeves (1972) have shown that during grain filling
there is a net reduction in stem weight, with grain accumulation occurring
at a greater rate than the rate of total dry matter accumulation.As the
grain approaches physiological maturity the stem again increases in
weight.
Goldsworthy (1970) concluded that a decrease in radiation and a
loss in dry weight from decay and detachment of dead sorghum (Sorghum
bicolor (L. ) Moench) leaves were probably the most important of the
factors that contributed to the decrease in growth rate observed in the
middle of the season. Since net-assimilation rate is also dependent on
leaf area index (LAI), lower leaves were probably making little or no
contribution to dry weight increase at this time. A sharp decline in leaf
area and in net-assimilation rate accounts for the rapid fall in crop
growth rate of the non-photosensitive sorghum after heading, at the end of
September.
Goldsworthy (1970) reported that a large proportion of the increase
in total dry weight of sorghum 'Farafara' (a photosensitive cultivar)
after heading was as dry weight in the stems. During the 3 weeks before
harvest (22-25 weeks after sowing), stems lost weight, and the losses in
weight were similar to the weights gained after head emergence. In
contrast, virtually all of the dry weight increase by 'NK-300' (a
non-photosensitive cultivar) after head emergence was in the heads. In
the first year of his study the weight of stems of the 'NK-3001 reached a
maximum at heading and then remained constant until harvest, whereas in
the second year the stems lost weight before harvest, and it is probable
that, with a smaller supply of assimilate, carbohydrate normally respired


Table 7-16. Multiple correlation coefficients for plant variables from 18 sites in
Nicaragua.
N
S
Mg
Mn
Ca
K
P
Zn
Cu
Fe
LAI
PH
LDW
N
1.00
S
0.75
1.00
Mg
-0.04
-0.14
1.00
Mn
0.26
0.18
0.43
1.00
Ca
-0.13
-0.23
0.67
0.38
1.00
K
0.34
0.30
0.22
0.53
0.13
1.00
P
0.45
0.33
0.25
0.44
0.17
0.74
1.00
Zn
0.30
0.13
0.52
0.42
0.45
0.39
0.61
1.00
Cu
0.34
0.16
0.30
0.50
0.31
0.64
0.71
0.58
1.00
Fe
-0.01
-0.09
0.30
0.19
0.24
0.19
0.27
0.32
0.33
1.0
LAI
0.26
0.20
0.20
0.23
0.24
0.24
0.22
0.23
0.26
0.10
1.00
PH
0.10
-0.02
0.19
0.07
0.38
0.05
0.22
0.28
0.15
0.06
0.56
1.00
LDW
0.05
0.02
0.18
0.17
0.36
0.00
0.10
0.18
0.05
-0.08
0.49
0.60
1.00
PH = plant height, LDW = leaf dry weight.
217


20
dry matter which could be translocated to the grain normally remains in
the stem, also indicate a sink limitation. Conversely, the decrease in
stem weight in the latter part of the grain-filling period, observed by
Daynard et al. (1969), seems to indicate that source may be limiting under
the environmental conditions prevailing in the northern periphery of the
maize-growing area of North America.
McPherson and Boyer (1977) pointed out that another potentially
more serious problem occurs if sink size has been affected by low leaf
water potential. If, for example, crop desiccation occurred during floral
development or pollination, irreversible loss of floral primordia (Moss
and Downey, 1971) or unsuccesful pollination could result. Thus, grain
yield would be limited more by the availability of developing grain than
by the availability of photosynthate (Denmead and Shaw, 1960; Classen and
Shaw, 1970), and prediction of yield based on photosynthesis would be in
error. Such a limitation would be less important where maize is grown for
silage, because shoot dry weight would reflect photosynthesis directly.
Moss (1962) and Allison and Watson (1966) have shown that when the
grain sink is missing, dry matter that would have passed to the grain
accumulates in the stem and husk. The presence of more barren plants
(Goldsworthy et al., 1974) probably explains why more dry weight
accumulated in the stems at Poza Rica than at Tlaltizapan, Mexico. It
would also account for the differences in the values for grain at the two
sites, since barren plants contribute to dry matter but not to grain
yield.
Goldsworthy et al. (1974) reported that dry weight also accumulated
in the stem of fertile plants and that the capacity of the ear to
accommodate the photosynthate produced was a further factor limiting


Ca (dag kg ) Co (dag ^g
168
Days After Planting Maize
Figure 6-21. Effect of the stage of maturity on
the Ca concentration of 'NB-3'
maize (a) and 'Gahi3' millet (b).


65
Figure 3-1. Spatial arrangement of maize (M) + photosensitive
sorghum (PS), maize + non-photosensitive sorghum
(NS), and maize + millet (Ml) intercropping
systems.


CHAPTER 3
MATERIALS AND METHODS
Field Procedures
Fertility Trials
Experiments involving three intercropping systems (Fig. 3-1) and
six fertilizer treatments (Table 3-1) were established at two sites in
Esteli, Nicaragua (Fig. 4-1) during the 1982-1983 growing season. Site 1
(Centro Experimental de Esteli) located 1 km north of the city of Esteli
on the Panamerican Highway at an elevation of 975 m. The average annual
precipitation is 1000 mm distributed in a bimodal pattern (CATIE,
1981a); the largest amounts fall during May, June, August, and September
(CATIE 1980, 1981). This rainfall pattern is the determining factor in
defining the growing season. The average annual temperature is 19C. The
soil may be classified as a Vertisol (CATIE, 1981). The field where the
experiment was established was previously planted to shade tobacco
(Nicotiana tabacum L.) but had been under fallow for the last 7 years.
Site 2 was a production cooperative (Sabana Larga) managed by 15
farmers and located 6 km southwest of the city of Esteli at an elevation
of 930 m. The average annual precipitation and temperature are 1247 mm
and 20.1 C, respectively (CATIE, 1980). The field had been under
continuous maize + beans (Phaseolus spp.) for the last 25 years.
There were 13 treatments with four replications in a randomized
complete block design at each site. The design incorporates all six
63


Passive ua
Energy srti
Recvc*ng
eceoior
360 Kg
o
p-
Figure 4-10. A serai-quantitative description of the maize + sorghum/animal
production system in Central America (Larios et al., 1983).


TO
TINITA, BENERANDA, ROBERTO, LILIANA, AND VERONICA
AND IN MEMORY OF
MICAELA RETANA


Figure 5-2. Percent soil moisture during 1982-1983 growing season in Esteli,
Nicaragua.
X Soil Moisture
n
i
o
*
w.
3
CQ
in
CO
a
w
o
fO OJ JkLnCTi^JCO^O
o oo oooooo
911


139
40 80 120 160 200
Days After Planting Maize
Doys After Planting Maize
Figure 6-1. Effect of the stage of maturity on percent
organic matter of 'NB-3' maize (a) and
'Criollo' sorghum (b).


HYDRIC DEFICIT
Figure 4-6. Interrelationship among size of farms, hydric deficit, and
farming systems in small farms of East and North El Salvador.
(Unpublished data CATIE, El Salvador).
SIZE OF FARM (ho)


117
Table 5-1. Percent soil moisture at three soil
depths in Esteli, Nicaragua.
Weeks after Depths
planting
Maize 0-15 15-30 30-45
3 -3
m ra
1
25.3b*
31.0a
34.6a
2
27.3ab
30.3ab
35.3a
3
23.1b
26,6ab
28.7a
4
23.3c
28.5b
31.8a
5
22.3b
28.5a
30.5a
6
21.7b
29.2a
30.1a
7
22.8b
24.9a
26.2ab
8
39.2a
37.6ab
36.8ab
9
34.0b
36.9a
36.0a
10
34.5
39.0
36.5
11
29.1b
32.lab
40.9a
12
28.2b
32.lab
34.4a
13
25.3b
32.lab
34.4a
14
23.9c
27.5b
33.3a
15
31.9b
32.3a
34.2a
16
26.7b
30.0a
32.9a
17
21.2b
24.3a
26.2a
18
21.7
24.5
25.9
19
19.6b
27.8a
28.5a
20
21.4b
29.6a
31.4a
21
17.3b
26.5a
29.4a
22
18.5b
25.8a
26.5a
23
16.7c
23.5b
28.6a
24
16.7c
25.7b
30.1a
25
14.0c
19.5b
23.7a
26
12.4b
18.7a
20.0a
27
12.4b
15.8a
16.1a
28
11.4
18.0
14.1
29
11.2
14.3
14.7
30
10.4
13.4
14.4
Means within
a week not
followed by
the
same letter
are different
according
to Duncan's
new
multiple
range test at
the 0.05
level of probability.


21
yield. Allison and Watson (1966) have shown that when the grain sink is
removed by preventing pollination the dry matter that would have passed to
the grain accumulates in the stover and that when the source of assimilate
is restricted by removing leaves, stem weight decreases as previously
stored dry matter moves to the grain.
Shih et al. (1981) found that the ratios between dry and fresh
phytomass were computed as 21.4, 35.1 and 35.4% for stalk, leaf, and
panicle, respectively. The ratios for leaves and panicles are similar,
but the ratio for stalks is lower. These ratios can be used to estimate
the dry weight yield based on the known fresh biomass, or vice versa.
Hanway (1962a) found that differences in soil fertility resulted in
different rates of dry matter accumulation but did not markedly influence
the relative proportions of the different parts. He reported crop growth
rates of maize of 250 kg ha ^ day ^ in N-sufficient plots. Hanway and
Russell (1969) found that the leaves, leaf sheaths, stalks, and husks of
maize attained their final mature weights at about stages 4.0, 4.5, 5.0,
and 5.5, respectively. All these plant parts continued to increase in
weight following these stages of development, but this continued increase
in weight was apparently an accumulation of materials which were later
translocated into the developing grain. At stage 6.5 the total
accumulated material in these plant parts was equivalent to about 20% of
the total mature dry weight of the nongrain parts of the plants. The cob
and ear shank attained their maximum dry weight at about stage 6.5 and
showed no later decrease in weight. An average of 42% of the total,
mature dry weights of the plants was grain and 58% was nongrain. However,
the relative proportions of grain and nongrain varied widely among the
different hybrids, years, and plant populations, with the grain varying


K (dog kg"') K (dog kg
164
Doys After Plonting Moize
Figure 6-18. Effect of the stage of maturity on the
K concentration of 'NB-3' maize (a)
and 'Gahi-3' millet (b).


89
1983). This situation is rapidly changing through agrarian reform plans
(personal observation by the author).
Cash flow in and out of the farms is very difficult to quantify,
especially that spent on food and clothing. Farm expenses and farm
activities are closely related to farm size (Fig. 4-4). In crop
production, a low-income farmer on a 7 ha farm may invest up to $200
(US) mainly on fertilizers (70%) and other field supplies and about $45
(US) on animal feeds. Cash flow into the farms comes from activities on
and off the farm, as depicted in Figure 4-4. On small-scale farms most
of the income (approximately 75%) is obtained from the sale of excess
grains (maize and sorghum), dairy products, meat, and draft animals
(CATIE, El Salvador, umpublished data, 1982). In their characterization
studies Arias et al. (1980) and Larios et al. (1983) emphasize the
importance of the animal component in generating income increases as
farm size augments (Fig. 4-5). Cattle are more common on larger farms,
while swine and poultry can be important sources of income among the
smaller farms.
Facilities and equipment
The value of fixed capital (housing, storage, fencing, and animal
shelter) is affected also by farm size; on the average, farmers of these
areas report holdings worth approximately $830 (US) (CATIE, 1980).
Juarez et al. (1979) report that farm equipment is limited to sprayers,
hoes, shovels, and "macanas" or "bordones" (a handweeding instrument
used for planting beans and sorghum into stands of maize). The average
value of this equipment varies from $18 to 40 (US). Very few farmers
own transport facilities other than an oxcart.


135
'NB 3' and 'Criollo' and aim row length from 'Pioneer 895' and
'Gahi-3' every sampling stage (Figs. 5-3, 5-4, 5-5). Sampling began when
the crops were thinned at 21 and 24 days after seeding for the first and
second crops, respectively. At each sampling stage plants were
harvested, separated by components (leaf, stem, flower, head, or ears),
and weighed in the field. Subsamples were weighed and oven dried at
70C for 72 hours (when constant weight was reached), then weighed
again to determine dry matter content. Sub-samples were ground in a
Wiley mill to pass a 1 mm stainless steel screen, and stored in
air-tight bags until analyzed. Soil samples were taken from each plot
before planting and after the last harvest.
Statistical analyses were conducted for the randomized complete
block design. Individual plots were 9.8 by 10 m. Twelve rows of 'NB-3'
maize were planted no-tillage by hand in each plot (52,000 plants ha ^)
on 16 June. The second crops ('Criollo', photosensitive sorghum;
'Pioneer 895', non-photosensitive sorghum; and 'Gahi-3', millet) were
interplanted on 16 September according to the spatial arrangements
depicted in Fig. 3-3. The 'Criollo' was seeded in-between maize rows
(40 cm from the maize hills) in hills spaced 0.80 cm apart and later
thinned 24 days after seeding to six plants per hill to obtain 75,000
plants ha 'Pioneer 895' and 'Gahi-3' were seeded in double rows (20
cm from the maize); 24 days after seeding the rows were thinned to give
120,000 plants ha Maize plants received 30 kg ha ^ of N and P
fertilizer at planting and were sidedressed with 40 kg N ha 25 days
later. Both sorghums and the millet were sidedressed with 30 and 35 kg
ha ^ of P and N, respectively.


28
concentration increased with N fertilization in both crops. Grain sorghum
N concentration was generally equal to or greater than that of maize.
Residue yields of both crops were increased significantly by 90 kg ha *
with no further increase at the higher N rate. Maize grain:stover ratios
increased with increasing N levels. Crude protein of grain sorghum
residues was consistently higher than that of maize while IVDMD values
were consistently lower in grain sorghum. Crude protein increased
significantly in grain sorghum residue with each increasing N level while
little increase occurred in maize.
Martin and Wed in (1974) reported that row-crop residues, although
present in great quantities in the midwestern United States, are often
considered to be of low quality. Consequently, grain sorghum stover on
millions of hectares is not utilized by livestock. Stover often remains
as a leafy, succulent, growing plant following grain harvest and should
be considered as a feed source for ruminants being maintained for
reproductive purposes.
Under Iowa conditions (Perry and Olson, 1975) grain sorghum
continues growth during the interval between grain harvest and killing
frost. This unique characteristic allows the ratoon crop to maintain and
perhaps improve its nutritional composition before utilization for winter
grazing or silage harvest. Burns et al. (1970) postulated that forage
sorghum produces photosynthate after maturation of seeds and until frost
and accumulates a reservoir of water-soluble carbohydrates in the pith of
the stalks.
Perry and Olson (1975) observed that maize dry matter yields
decline as much as 30% within 100 days of harvest. Any decline in crude
protein and digestibility following grain harvest of maize and grain


147
In general, IVOMD values observed in both sorghums compared well
with those observed in maize. Hall et al. (1965) reported similar
findings. However Schmid et al. (1975) concluded that lower cell wall
digestibility observed in low-grain-yielding sorghums (similar to the PS
sorghum in this study) was detrimental to total digestibility. In
high-grain-yielding sorghums the rapid increase in the amount of highly
digestible starch in the grain compensates for the decline in cellulose
digestion. In Chapter 5 it was reported that dry matter accumulation was
greater in the stem than in other plant components in the PS sorghum;
this may account for the higher IVOMD observed in the stem.
In millet, IVOMD was constantly higher in the leaf than in the stem
or head (Fig. 6-6b). Grain set in the head was low; therefore its
digestibility was low in relation to other plant components and to
sorghum heads. However, leaves and stems in millet reached similar
values to those observed in the sorghums and maize. These results are
supported by data presented by Clark et al. (1965), in which there were
no differences in the carrying capacity, milk production, or dry matter
production of millet and a sorghum x sudangrass hybrid.
Metabolizable energy as affected by maturity stage is depicted in
Figs. 6-7, 6-8, and 6-9 for M+PS, M+NS, and M+MI, respectively. No
differences among components were found from maize plants from the
different systems at the 0.05 level of probability. As expected, higher
energy values were observed in the ear and flowers than in the other
components. Flowers at 50% bloom contained 18.5 MJ kg ^dm and declined
to nearly 16.5 MJ kg ^ in all three systems (Figs. 6-7a, 6-8a, and
6-9a). Ears reached a maximum at soft-dough (18, 17 and 17 MJ kg *dm for
the M+PS, M+NS, and M+MI, respectively. Energy in the leaves declined


This research showed that late planting coupled with inadequate
soil moisture resulted in poor growth. Results suggest that grain yield
was more susceptible to water stress than total dry matter yield. The
highest crop growth rate observed (756 kg ha ^day was in maize plants
from the maize + millet system. Striking differences in dry matter
distribution were observed between the photosensitive and non
photosensitive sorghums. At grain harvest, both sorghums had accumu
lated similar amounts of dry matter (14.3 and 14.9 Mg ha \ respective
ly). However, the distribution of the dry matter in the stems, leaves,
and heads of photosensitive sorghum and the non-photosensitive was 46,
37, 17 and 28, 17, and 55%, respectively.
Water stress affected IVOMD and nutrient concentration in all
crops. In the photosensitive sorghum, the stem had higher IVOMD than any
other plant component. In general, nutrient concentration declined with
maturity. However, leaf Ca increased with maturity. An imbalance between
K:Ca, K:Mg, and K:Ca+Mg was observed in maize plants from all systems.
Sulfur deficiency is a widespread problem in some areas of Nic
aragua and Florida. Stunted chlorotic plants observed in both areas were
deficient in S and had a N:S and P:S imbalance. Sulfur deficiency appar
ently caused maize leaves to be deficient in K, resulting in a K:Ca+Mg
imbalance, even though sufficient K was indicated in the whole plant
analysis.
Vll


79
product), making it difficult for scientists to analyze interactions or
competition within the system.
According to Arze et al. (1983), in a research scheme for sorghum
cropping systems it is necessary to analyze the problem in a series of
logical and sequential phases, beginning with broad aspects and ending
with specific matters. This analysis permits the hierarchic
identification of relations between components of the system and the
determination of restrictions to crop production. The identification of
these restrictions is a basic element for the successful design of
research; it will also enhance the possibilities of accomplishing
specific proposed objectives.
In a general way, and considering sequence, the phases designed by
Arze et al. (1983) can be summarized as follows: 1) definition of the
problem, 2) characterization and diagnosis, 3) design of the research,
4) implementation, 5) validation, and 6) diffusion.
Few attempts have been made in the area to describe the maize +
sorghum system. Some of the most recent attempts include those conducted
in different areas of El Salvador by Rodriguez et al. (1977), Guillen et
al. (1978); Alvarado et al. (1978), Alegria et al. (1979); and Arias et
al. (1980). Kass (1980) and Fuentes and Salguero (1983) give a brief
description of the system in Guatemala. In Honduras, Mateo et al. (1981)
described the system in some detail. Hawkins et al. (1983) and Larios et
al. (1983) have provided the only recent descriptions of what may be
considered the typical maize + sorghum cropping system in Central
America.
The objectives of this research were 1) to locate and describe the
maize + sorghum system in Central America, 2) to describe the relations


71
Growth Analysis
To conduct an analysis of the growth of the systems under study in
the fertility trials, treatments 6, 9, and 13 were selected as
representatives of each system. Crop growth rate (CGR) of the 'NB-3' +
'Criollo', 'NB-3' + 'Pioneer 895', and 'NB-3' + 'Gahi-3' systems were
estimated on different phases of growth (Table 3-6). Total above-ground
growth was harvested from six hills of 'NB-3' and 'Criollo' and 1 m row
length from 'Pioneer 895' and 'Gahi-3' every sampling stage. Sampling
began when the crops were thinned, and at 21 and 24 days after seeding
for the first and second crops, respectively. At each sampling stage
plants were harvested, separated by components (leaf, stem, flower,
head, and/or ears) and weighed in the field. Subsamples were weighed and
oven dried at 70C for 72 hours (when constant weight was reached) then
weighed again to determine dry matter content. The change in average
plant dry weight on the n^ (day n + t) day since the previous harvest
(on day t) was divided by n to estimate crop growth rate (CGR) expressed
in kg ha ^day for each day in the period. Sub-samples were ground in a
Wiley mill to pass a 1 mm stainless steel screen, and stored in
air-tight bags until analyzed.
Green leaf area measurements were made at 50% bloom, soft-dough,
and at black-layer stages. All the leaves of the 12 maize plants from
each of the three plots were measured from base to tip and at the point
of maximum width. Leaf area was converted to leaf area indices (LAI) as
described by Dale et al (1980).
Daily precipitation data (Fig. 5-2) were obtained by averaging
readings from four rain gauges placed in the the four replications. Soil
samples from three 15-cm sections to a depth of 45 cm were taken on a


Zn (mg kg* 1) Zn (mg kg
185
Figure 6-35. Effect of the stage of maturity on
the Zn concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).


CHAPTER 7
SURVEY OF SULFUR DEFICIENCY IN MAIZE
Introduction
Sulfur deficiency has been recognized as an important factor limiting
cereal production in several parts of the world (Beaton, 1966).
Actually, S-deficient areas are rather widespread throughout the world.
For example, crop deficiencies in S have been reported from countries
in Central and South Africa; India; and North, Central, and South
America (Blair et al., 1980).
The fact that over the past several years crop deficiencies have
been reported with increasing frequency has focused greater attention on
the importance of this nutrient in plant nutrition. As Coleman (1966)
pointed out, S deficiencies are probably ocurring because of 1) the
increased use of S-free fertilizer, 2) the decreased use of S as a
fungicide and insecticide, and 3) increased crop yields, which means
higher requirements of all the essential plant nutrients. Blair et al.
(1980) listed other reasons for the occurrence of S deficiency in
tropical soils: 1) inherent low S content, 2) low availability of
S-containing organic matter, and 3) the consequence of agricultural
practices.
Blair et al. (1980) reported total S values for a range of tropical
soils from 43 to 248 mg kg Rabuffetti and Kamprath (1977) reported
soil-S values from about 6 mg ka in the top 25 cm to 51 mg kg in the
40-55 cm depth of a Goldsboro soil (fine, loamy, siliceous, thermic
187


231
Juarez, M., C. Deras, and R. Santos. 1979. Diagnostico de sistemas de
produccin agropecuarios del municipio de Tejutla, Depto. de
Chalatenango. El Salvador. CENTA/MAG, El Salvador. 92 pp.
Jung, G. A., and R. I. Reid. 1966. Sudangrass studies on its yield,
management, chemical composition, and nutritive value. West Virginia
Exp. Sta. Bul. 524-T.
Jurgens, S. K., R. R. Johnson, and J. S. Boyer. 1978. Dry matter
production and translocation in maize subjected to drought during grain
fill. Agron. J. 70:678-682.
Kamprath, E. J., J. W. Fritts, and W. L. Nelson. 1957. Sulfur removed
from soils by field crops. Agron. J. 49:289-293.
, W. L. Nelson, and J. W. Fritts. 1956. The effect of pH,
sulfate and phosphate concentrations on the absorption of sulfate and
phosphate by soils. Soil Sci. Soc. Amer. Proc. 20:463-466.
Kang, B. T., and 0. A. Osiname. 1979. Phosphorus response of maize grown
on Alfisols of Southern Nigeria. Agron. J. 71:873-877.
Kass, D. 1980. Algunos sistemas de produccin de cultivos anuales en
Guatemala. In R. Moreno (ed.) Reunion de Consulta sobre localizacin de
sistemas de produccin de cultivos en Centroamerica. CATIE, Turrialba,
Costa Rica. pp. 7-47.
Kumar, V., and K. S. Awasthi. 1977. Efficiency of different manures in
relation to their effect on yield and nutrient uptake by grain sorghum.
Agrochimica 21(3-4):328-334.
Lancaster, D. L., M. B. Jones, J. H. Oh, and J. E. Ruckman. 1971.
Effects of sulfur fertilization of forage species on yield, chemical
composition, and in vitro rumen microbial activity of sheep. Agron. J.
63:621-623.
Larios, J. F., J. F. Arze, and F. R. Arias. 1983. The animal component
in maize-sorghum farming systems in Central America. In J. Fitschu, R.
D. Hart, R. A. Moreno, T. 0. Osushi, M. E. Ruiz, and L. Singh (ed.)
Procs. Workshop Research on crop-animal systems. CATIE/CARDI/WINROCK.
Turrialba, Costa Rica.
, R. Moreno, and W. E. Amaya. 1982. Una
estrategia para mejorar la agricultura en zonas afectadas por sequia. In
J. F. Larios (ed.) Agricultura en zonas afectadas por canicula
interestival en El Salvador. MAG/CATIE. San Andres, El Salvador, pp.
246-267.
Leopold, A. C. and P. E. Kriedemann. 1975. Plant growth and development.
Second Edition, McGraw-Hill Book Co., New York.
Locke, L. F., H. V. Eck, and B. B. Tucker. 1964. Grain sorghum
fertilization in northwestern Oklahoma. Okla. Exp. Sta. Bull. 627.


98
MAIZE GROWTH
SORGHUM GROWTH
. Relation between the sunrise, sunset and duration
of day length with variations in the relative
growth of the maize + sorghum system. (j. Arze,
CATIE, Costa Rica, unpublished data, 1983).
Figure 4-9
GROWTH (relative values)


27
maturity (Johnson et al., 1966). Protein content in the whole plant
declined slowly during ear maturation.
The IVDMD for the stover silage reported by Colenbrander et al.
(1971) ranged from 41 to 50%. Results from this experiment indicated that
a low quality roughage such as maize stover silage can provide an
alternative source of nutrients for growing dairy heifers. Green (1973),
studying the yield and digestibility of bird-resistant grain sorghum,
observed that IVDMD varied from 79.8 to 50.5%. All of the NBR varieties
had higher values. The correlation coefficient calculated to ascertain
the relationship between yield and IVDMD for the 41 varieties was low
(r=+0.52) and not significant, indicating they were not related. Schmid
et al. (1975 ) reported that IVDMD values at the 4-week growth stage
ranged from 71.7 to 84.2% for five brown midrib sorghum mutants compared
to 67.1 to 78.3% for their normal counterparts.
Crop Residues
Plant populations, row-spacings, and soil fertility affect not only
grain yields, but also the yields and quality of residues. Residue yields
from maize are normally greater than from grain sorghum but lower in
crude protein. Crude protein concentration of grain sorghum residues was
consistently higher than that of maize while IVDMD values were
consistently lower in grain sorghum.
Crop residues of grain sorghum and maize have attracted attention
as an alternate economical forage resource for livestock utilization.
There are few data available on agronomic production factors affecting
yield and quality of crop residues (Perry and Olson, 1975).
Perry and Olson (1975), studying the effects of N fertilization on
yield and quality of maize and sorghum residues, observed that grain N


Mn (mg kg~ ) Mn (mg kg
183
Figure 6-33. Effect of the stage of maturity on
the Mn concentration of 'NB-31 maize
(a) and 'Gahi-3' millet (b).


145
100
00
O)
S 60
Q
> 40
(o)
20
o- Stem
o- Leaf
A- Ear
40 80 120 160 200
Days After Planting Maize
Days After Planting Maize
Figure 6-6. Effect of the stage of maturity on the
IVOMD of 'NB-3' maize (a) and 'Gahi-3'
millet (b).


17
partly explained on the basis of greater total water use and it must have
been partly due to an increase in total water use efficiency.
In an irrigation study Sivakumar et al. (1979) found that the
non-irrigated sorghum crop used 213 mm of water to produce 510 kg ha ^ of
dry matter, whereas, the irrigated sorghum used 321 mm of water to produce
930 kg ha ^ of dry matter. Szeicz et al. (1973) observed that average
sorghum crops in Texas use approximately 320 mm of water throughout the
growing season to produce around 0.8 kg dry matter m
Leaf Area Index
Dale et al. (1980) reported that growth and duration of green leaf
area of a crop determine the percentage of incident solar radiation
intercepted by the crop canopy and thereby influence canopy
photosynthesis, evapotranspiration, and final yields. Leaf area index is
defined as the ratio of the area of one side of the green leaves of a
plant to the area of soil surface allocated to the plant.
Shih et al. (1981) reported that LAI is often used as an indicator
of plant growth and for evaluating assimilation and transpiration rates in
plant physiological studies. This growth parameter is also frequently
used in agronomic studies to model yield and to make crop production
decisions. Ashley et al. (1965) found good correlation between LAI and
leaf dry weight of cotton (Gossypium hirsutum L.). Rhoads and Bloodworth
(1964) and Pearce et al. (1965) also found strong correlations between
leaf area and dry matter yield in cotton and orchard grass (Dactylis
glomerata L.).
According to Hanway (1963), the genetic characteristics of the
plant, day length and various environmental conditions prior to stage 1 of
growth, have determined the number of leaves that will develop on maize


142
observed in the stems. As stem percent OM increased in the PS sorghum,
percent OM decreased in the head (Fig. 6-lb). The opposite occurred in
the NS sorghum (Fig. 6-2b); as dag kg 1 OM decreased in the stem dag
kg 1 OM in the head was increasing rapidly. These results support those
reported for dry matter accumulation discussed in Chapter 5 (Figs. 5-3b
and 5-4b).
Both leaves and stems from millet plants (Fig. 6-3b) increased in
dag kg ^ OM. Values observed in millet were generally lower than those
observed for sorghum. This is probably so because of the effect of the
late planting on the growth of millet. The data suggest that millet did
not reach the exponential growth stage.
Values for IVOMD are depicted in Figs. 6-4, 6-5, and 6-6 for the
M+PS, M+NS, and M+MI systems, respectively. In general, leaf, stem, and
flower digestibility decreased with maturity in all crops. While the
digestibility of the ear increased constantly until harvest, sorghum
heads increased to a maximum at soft-dough and thereafter decreased
until harvest. These results are similar to those reported by Cummins
(1970), Johnson et al. (1966), and Schmid et al. (1975).
IVOMD values observed in maize did not differ among components from
maize plants from the three systems at the 0.05 level of probability. In
general IVOMD was higher in the ear than in any other maize plant
component. There was no general trend in IVOMD differences between
leaves and stem, but higher values were observed in the leaves (Figs.
6-4a, 6-5a, and 6-6a). The low IVOMD values (less than 50%) observed
after soft-dough may have been caused by water stress and low available
soil moisture (Figs. 5-1 and 5-2, respectively); however, Cummins (1970)
observed similar IVDMD values. From soft-dough to harvest IVOMD in the


BIOGRAPHICAL SKETCH
Francisco Roberto Arias Milla, son of Tina Milla Sosa and Francisco
Arias, was born March 1, 1948, in San Salvador, El Salvador. He
graduated from South San Francisco High School in South San Francisco,
California, in 1966. In 1973 he received the degree of Ingeniero
Agronomo Fitotecnista from the Instituto Tecnolgico y de Estudios
Superiores de Monterrey, Mexico.
In 1974 he became staff member of the Ministerio de Agricultura y
Ganaderia of El Salvador, where he worked for two years before being
admitted to the University of Florida as a graduate student. In 1978 he
was awarded the degree of Master of Science. Upon his return to El
Salvador he was put in charge of the On-Farm Research Project, a
position he held for one year. In May 1980 he joined the staff of the
Centro Agronmico Tropical de Investigacin y Enseanza (CATIE) and was
assigned to Nicaragua as a cropping system specialist.
In 1983 he was awarded an International Fellowship from the W. K.
Kellogg Foundation to pursue a Doctor of Philosophy degree at the
University of Florida. He is an active member in two honorary
fraternities, Gamma Sigma Delta, and Alpha Zeta.
He is married to the former Beneranda Sanchez and they have three
children, Francisco Roberto, Liliana Michelle, and Veronica Cecilia.
238


233
, and 1981b. The sulfur fertility status of
Florida soils. II. An evaluation of subsoil sulfur on plant nutrition.
Soil and Crop Sci. Soc. of Fla. Proc. 40:77-82.
, and R. N. Gallaher. 1979. Sulfur fertilization of corn
seedlings. Soil and Crop Sci. Soc. of Fla. Proc. 39:40-44.
Moore, J. E., G. 0. Mott, D. G. Dunham, and R. Omer. 1972. Large
capacity in vitro OM digestion procedure. J. Anim. Sci. 35:232.
Moss, D. N. 1962. Photosynthesis and barrenness. Crop Sci. 13:371-76.
Moss, G. I., and L. A. Downey. 1971. Influence of drought stress on
female gametophyte development in corn (Zea mays L.) and subsequent
grain yield. Crop Sci. 11:368-372.
Neller, J. R. 1959. Extractable sulfate-sulfur in soils of Florida in
relation to amount of clay in the profile. Soil Sci. Soc. Am. Proc.
23:346-348.
Nelson, L. B. 1956. The mineral nutrition of corn as related to its
growth and culture. Adv. in Agron. VIII:321-375 Academic Press Inc.
N.Y.
Olagunde, 0. 0., and R. C. Sorensen. 1982. Influence of concentrations
of K and Mg in nutrient solutions on sorghum. Agron. J. 74:41-46.
Olson, R. A. 1957. Absorption of sulfur dioxide from the atmosphere by
cotton plants. Soil Sci. 84:107-111.
Palmer, A. F., G. H. Heichel, and R. B. Musgrave. 1973 Patterns of
translocation, respiratory loss, and redistribution of C in maize
labeled after flowering. Crop Sci. 13:371-376.
Pearce, R. B., R. H. Brown and R. E. Blaser. 1965. Relationship between
leaf area index, light interception and net photosynthesis in orchard
grass. Crop. Sci. 5:553-556.
Pearson, R. W., F. Abruna, and J. V. Chandler. 1962. Effect of lime and
nitrogen applications on downward movement of calcium and magnesium in
humid tropical soils of Puerto Rico. Soil Sci. 93:77-82.
Peaslee, D. E., and D. N. Moss. 1966. Photosynthesis in K and
Mg-deficient leaves. Soil Sci. Soc. of Ameri. Proc. 30:220-223.
, J. L. Ragland, and W. C. Duncan. 1971. Grainfilling
period of corn as influenced by phosphorus, potassium, and the time of
planting. Agron. J. 63:561-563.
Perry, L. J. and R. A. Olson. 1975. Yield and quality of corn and grain
sorghum grain and residues as influenced by N fertilization. Agron. J.
67:816-818.


CHAPTER 6
NUTRIENT CONCENTRATION, IVOMD, AND METABOLIZABLE ENERGY OF
INTERCROPPED MAIZE + SORGHUM AND MAIZE + MILLET SYSTEMS
Introduction
Maize (Zea mays L.) + sorghum (Sorghum bicolor (L.) Moench)
intercropping systems are popular in the semi-arid regions of Central
America (Larios et al., 1983). This practice allows expansion of animal
feeding without additional capital investment by expanding the use of
land, facilities, and residues. In spite of the importance of the maize
+ sorghum system in procuring food and feed for the majority of the
population and animals in these regions there is little research
information upon which to base fertility or management decisions.
Information is needed concerning the accumulation of nutrients and
quality of the different plant components (Arze et al., 1983).
Plant analysis has long been used in various ways for diagnosing
plant nutrient adequacy and estimating fertilizer needs (Pierre et al.,
1977). According to Bates (1970) the diagnosis of nutrient deficiencies
and the prediction of fertilizer requirements from plant analysis are
based on a critical nutrient concentration or nutrient fraction within
the plant below which growth or yield is restricted. Macy (1936)
proposed a basic theory, the central concept of which is that there is a
critical concentration of each nutrient in each species, above which
there is luxury consumption and below which there is poverty adjustment
which is almost proportional to the deficiency until a minimum
131


213
Table 7-13. Leaf P concentration and S:P ratio observed in
18 sites in Nicaragua.
SITE
P
P:S
D
SU
D
SU
dag
kg"1
18
0.230abc
0.248abc
0.78
0.92
10
0.114 de
0.121 fg
0.68
0.71
14
0.251a
0.283ab
1.20
1.01
16
0.270a
0.217 bcde
1.02
0.72
12
0.184abcd
0.184 cdefg
1.08
0.88
17
0.198abcd
0.181 cdefg
0.88
0.70
1
0.202abcd
0.296ab
0.92
1.02
3
0.106 de
0.127 fgh
0.49
0.58
9
0.202abcd
0.223 bed
1.02
0.97
11
0.063 e
0.149 defg *
0.43
0.83
15
0.246ab
0.313a *
1.08
1.08
7
0.117 de
0.096 g
0.67
0.46
13
0.263a
0.209 bedef
1.06
0.95
2
0.127 cde
0.150 defg
0.60
0.52
5
0.123 cde
0.210 bedef
0.44
0.72
4
0.140 bcde
0.139 defg
0.72
0.48
6
0.111 de
0.148 defg
0.63
0.53
8
0.206abcd
0.277ab
0.65
0.89
Values in columns not followed by the same letter and rows
within subheadings followed by an asterisk are different at
the 0.05 level of probability according to Duncan's new
multiple range test and F test, respectively.


44
S-containing amino acid of human diets (Allaway and Thompson, 1966;
Coleman, 1966).
In a review article Coleman (1966) pointed out that S is needed in
crop production because certain plant functions require it for 1) the
synthesis of amino acids, cysteine, cystine, and methionine, and hence
for protein elaboration; 2) the activation of certain proteolytic
enzymes such as the papainases; 3) the synthesis of certain vitamins, of
glutathione, and of coenzyme A; 4) the formation of the glucoside oils
found in onion, garlic, and cruciferous plants; 5) the formation of
certain disulfide linkages that have been associated with the structural
characteristics of protoplasm; and 6) in some species the concentration
of sulfhydril (-SH) groups in plant tissue,which is related to an
increase in cold resistance.
The importance of S in animal nutrition has been summarized by
Allaway and Thompson (1966). They reported that the S-containing amino
acid requirement of chicks has been estimated at 0.8% of the total
ration when the ration is 23% protein. In the case of ruminant animals,
where synthesis of S-containing amino acids from inorganic S by rumen
microflora has been established, the total S content is normally used to
appraise S status of a ration. The optimum S level in lamb diets was
found to be approximately 0.17 dag kg ^ S when methionine was used to
increase the S content of a lowS basal diet. The authors suggested a
N:S ratio of 15:1, or less, as an appropriate guide to the S adequacy of
a ration for dairy cows. A precise evaluation of the optimum N:S ratio
for ruminant animals is probably impossible, because ruminants adjust to
low levels of N and S through recycling processes.


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161
Maximum P concentration in the ear occurred at black layer,
decreasing slightly from then until harvest. Translocation of P from the
stem to the ear preceded that from the leaves. Phosphorus concentration
in the leaves was generally higher than that observed in the stem.
Phosphorus concentration in the different plant components of PS
sorghum and NS sorghum decreased with maturity until grain harvest. A
slight increase in leaf P was observed, which in the PS sorghum may be P
remobilized from the head, due to a lack of an appropriate grain sink.
The same increase was observed in the NS sorghum, where no decrease
occurred in the head, suggesting that P uptake was still happening. Leaf
P concentrations observed at bloom for both sorghums fall within the
sufficiency level (0.17 dag kg ^) established by Locke et al. (1964).
Millet exhibited higher P concentration than both sorghums. This is
explained in part by the differences in dry matter accumulation among
these crops. Phosphorus in millet was less diluted due to less growth.
Leaves generally had higher P than the stem. Apparently little P was
translocated to the heads from the stem or leaves.
Potassium accumulation by the M+PS, M+NS, and M+MI systems is shown
in Figs. 6-16, 6-17, and 6-18, respectively. The patterns of
accumulation and distribution observed for K were similar to those of N
and P. K concentration decreased with maturity and did not differ among
maize plants from the different systems at the 0.05 level of
probability. Potassium in the leaves and stem decreased with maturity.
At bloom the K concentration in the leaves was 1.65, 1.75, and 1.85 dag
kg 1 for the M+MI, M+NS, and M+PS, respectively (Figs. 6-18a, 6-17a, and
6-18a); these were within the sufficiency level established by Gallaher
et al. (1975 ). Little K was accumulated in the ear, suggesting that


Table 5-5. Dry matter distribution as percent of total dry weight of 'Criollo'
sorghum, 'Pioneer 895' sorghum, and 'Gahi-3' millet.
DAP
Criollo
DAP
Pioneer
895
DAP
Gahi-3
Stem Leaf
Head
Stem
Leaf
Head
Stem
Leaf
Head
-days-
dag kg
-days-
dag
kg
1
-days-
- dag kg 1
45
43
57
45
48
52
45
45
36
19
80
45
33
22
52
46
30
24
85
39
20
41
99
58
19
23
69
50
19
31
160
46
37
17
101
28
17
55
190
66
34
136
50
50
DAP = Days after planting


90
Figure 4-4. Percentage of income derived from farm activities
in different farm sizes (unpublished data, CATIE,
El Salvador).


154
Figure 6-11. Effect of the stage of maturity on the N
concentration of 'NB-3' maize (a) and
'Pioneer 895' sorghum (b).


146
leaves dropped from 52% to a low of 38% at harvest but increased later.
Martin and Wedin (1974) reported similar results for sorghum. Stem IVOMD
was high at thinning (approximately 73%)in the M+PS to less than 40% 30
days after grain harvest. Maize flower IVOMD decreased constantly until
reaching a minimum of approximately 20% at 30 days after harvest (Figs.
6-4a, 6-5a, and 6-6a).
Maturity affected IVOMD less dramatically in the PS sorghum (Fig.
6-4b) than that of the NS sorghum (Fig. 6-5b). Stem IVOMD in the PS
sorghum were generally higher than leaf IVOMD (Fig. 6-5b). After grain
harvest, leaf values decreased below 40%, while stem values were
maintained above 50%. Head IVOMD increased to a maximum of 68% at
soft-dough but decreased rapidly to near 40% by grain harvest. Again,
due to the lack of a well developed grain sink, photosynthates that
would have accumulated in the grain were shunted to the stem as reported
by Goldsworthy (1970) and Schmid et al. (1975), who observed that IVOMD
of stalks in tall sorghum hybrids increased with maturity. These results
also agree with the values for 41 sorghum varieties reported by Green
(1973 ).
Fig. 6-5b depicts the effects of maturity on the NS sorghum. IVOMD
in the leaves and stems declined rapidly from thinning to bloom stage
and was relatively stable thereafter. Schmid et al. (1975) reported
IVOMD values for grain sorghum 4 weeks after planting ranged from 67.1
to 78.3%, values which are similar to those found in this research at
thinning. At all sampling stages the leaves were more digestible than
the stem, contrary to what was observed in the PS sorghum. Head IVOMD
reached a maximum value of approximately 65% and then decreased to 57%
by harvest.


86
semi-humid areas an excess of water occurs in September, contributing to
an increase in the availability of residual moisture through December.
The number of months in a year with a moisture deficit in the semi-arid
and semi-humid regions ranges from 7 to 10 and from 5 to 6,
respectively.
Southeastern Guatemala, southern Honduras, northeastern El
Salvador, and northwestern Nicaragua correspond to what have been
described as semi-arid regions (Larios et al., 1983). The agroclimatic
characteristics of these regions are similar to other semi-arid regions
of the world. These are summarized by Larios et al. (1983) as follows:
1. The beginning of the rainy season is uncertain.
2. More than 90% of annual precipitation occurs during the wet
season, which lasts generally from four to seven months.
3. Precipitation during the wet season is often extremely variable,
not only from year to year but also within seasons.
4. Mean daily rainfall intensities are two to four times greater
than in many temperate regions. The short duration intensities
frequently exceed the water intake capacity of the soil.
Mateo et al., (1981) claimed that the areas where maize + sorghum
is found most frequently correspond to what Holdridge classified as 1)
Bh-S(c), humid sub-tropical forest with biotemperature above 24C, 2)
Bs-T, dry tropical forest with biotemperatures below 24C but with
annual average air temperatures above 24C, and 3) Bs-S, dry
subtropical forest. Arias et al. (1980) and Larios et al. (1983) agree
that the cultivation of sorghum is related to biotemperatures or air
average annual temperatures above 24C.


96
Figure 4-8. Spatial arrangements maize/sorghum cropping
systems.
a = Equidistant single rows,
b = single rows sorghum at foot of maize,
c = single rows of maize, sorghum broadcast
(Personal observation).


70
Table 3-5. Statistical analysis model used in the growth analysis. For
treatment 6, 9, and 13.
Source
df
REPLICATIONS
3
(r-1)
TREATMENTS
12
(t-1)
ERRORS
36
(r-1) (t-1)
TOTAL
47
(rt-1)


206
planting, with respect to normal years. These intense rains were
followed by an extremely dry and lengthy "canicula", that in some areas
lasted more than 75 days without significant rainfall. During the
growing season, in the area under study, maize received approximately
500 mm of rain. Available soil moisture (Fig. 5-2) during the growing
season can be considered low for the area (personal observation). With
this caution in mind the results of this study will be presented.
Plants identified as deficient (D-) plants were in all (Table 7-10)
cases less vigorous, yellow to light yellow, and in most cases showed
symptoms of K and S deficiency (orange-yellow leaf tips and intervenial
chlorosis, respectively). Plants grouped as sufficient (SU-) plants
were vigorous, green or dark green, were tall and in most cases showed
no symptoms of K or S deficiency. Plant height (PH), within D-plants
ranged from 186 to 44 cm for sites 9 and 4, respectively (Table 7-10),
and from 224 to 77 cm (sites 17 and 8 respectively) for the S-sufficient
plants. In general, SU-plants were consistently taller than D-plants at
all sites, and in 12 of the 18 sites differences (p=0.05) between SU and
D-plants were observed. These results support those observed in
Experiment 1; that is, plants with no apparent S or K deficiency
symptoms were taller and more vigorous than those with visual symptoms
of deficiency.
The trends observed for leaf dry weight and leaf area index (LAI)
(Table 7-10) were similar to that observed in plant height. Leaves of
D-plants were yellow or pale green with intervenial chlorosis. The older
leaves showed symptoms of K deficiency and in some cases lower leaves
were in the process of decaying. In general, at all sites, leaves from
SU-plants had accumulated more dry matter than those from D-plants; in


Cu (mg kg ') Cu ( mg kg-
180
Figure 6-30. Effect of the stage of maturity on
the Cu concentration of 'NB-3' maize
(a) and 'Gahi-3' millet (b).


60
four forage species but not in alfalfa. Gas production increased for
the grasses and decreased in the legumes with increased S application.
Total plant S and sulfate-S levels were increased with additional S
applied for all species; however, the percent protein decreased in the
grasses and increased in the legumes.
Lancaster et al. (1971) also found that the percentages of fiber
and lignin in the crops they studied were not influenced by S
fertilization, except for the second clipping of sudangrass and the 20
and 40 mg kg ^ levels applied to alfalfa. The critical level of S in
these trials appears to be less than 10 rag kg ^ S applied to the soil.
There were positive correlations between gas production and S
concentration for the grasses but there were negative correlations for
the legumes.
Caldwell et al. (1969) reported that the effect of S on the yield
of alfalfa was striking. Three times as much hay was produced by the
treated plots as by the check plots. The untreated alfalfa contained
from 0.146 to 0.221 dag kg S. Lancaster et al. (1971) reported that
the dry matter production in the grass species they studied was
increased by the addition of S, but for the legumes this increase was
not significant.
Rabuffetti and Kamprath (1977) reported that S had little effect
at low N rates on N accumulation in maize stover. However, they found
that at N rates of 168 and 224 kg ha ^ there was an increase in N
accumulation in stover with S rates of 44 and 66 kg ha 1 on the
Goldsboro soil and 33 and 66 kg ha ^ on the Wagram soil. Total S
accumulation in grain was found to be increased by N application at both
sites .


Mg (dog kg- 1) Mg(dagkg-I)
170
Days After Planting Maize
Days After Planting Maize
Figure 6-22. Effect of the stage of maturity on
the Mg concentration of 'NB-3'
maize (a) and 'Criollo' sorghum (b).


150
Days After Planting Maize
Figure 6-9. Effect of the stage of maturity on the
amount of metabolizable energy of 'NB-31
maize (a) and 'Gahi-3' millet (b).


Table 7-10. Plant characteristics of maize for 18 sites in Nicaragua.
Site
Plant
Height
Leaf
Dry Weight
Leaf Area
Index
D
SU
D
SU
D
SU
2
- mg kg
in
9
186a
198abcd
14.4
a
17.8abcd
2.2
be
2.4abc
14
156ab
207abc *
10.3
bed
12.2 defg
2.7ab
2.7ab
15
155abc
145 fgh
8.9
edef
18.3abc *
3.0a
2.5ab
10
136 bed
221ab *
13.3
ab
20.2a *
1.8
ede
2.8a
16
133 bede
166 ef
8.4
ede f g
12.5 edefg
2.1
bed
2.5ab
18
133 bede
169 def
8.8
edef
10.8 efg
2.1
bed
2.2abc
17
133 bede
224a *
9.4
ede
15.9abcdef *
1.9
ede
2.5ab
1
123 bede
190 ede *
9.9
bed
17.7abcd *
0.6
g
1.7 be *
7
117 ede
120 h
10.7
bee
10.3 fg
1.2
efg
1.3 c
13
114 de
199abc *
7.0
def g
14.1 bedefg *
1.5
def
2.5ab
3
112 de
191 bede *
11.2
abe
11.6 efg
2.0
cd
2.labe
12
98 de
155 fg *
10.0
bed
14.0 bedefg
1.5
edef
2.labe
11
95 e
208abc *
9.0
edef
19.8ab *
1.1
fg
2.2abc *
2
54 f
123 h *
7.2
defg
16.5abcde *
1.5
edef
2.8ab *
5
49 f
121 h *
5.4
fg
14.0 bedefg *
0.8
fg
2.labe
8
47 f
77 i
5.8
efg
10.8 efg *
1.3
def
2.3abc *
6
46 f
131 gh *
4.9
g
9.3 g
1.0
fg
2.5ab *
4
44 f
117 h *
5.4
fg
13.4 edefg *
0.8
fg
2.5ab *
Value9 in columns not followed by the same letter and rows within subheadings followed by an asterisk are different at the 0.05
level of probability according to Duncan's new multiple range test and F test, respectively.
207


29
sorghum appears to be associated with environmental factors. Martin and
Wedin (1974) observed that grain sorghum stover lost 28.3% of its
original dry matter yield by 76 days after grain harvest. The leaves lost
dry matter more rapidly.
Any consideration of grain sorghum stover as a feed for ruminants
is dependent on meeting all or some of the animal's nutrient
requirements. For example, a 500-kg, dry pregnant beef cow consuming 7.6
kg of dry matter requires 5.9% crude protein and 50.0% total digestible
nutrients.
Using percentage IVDMD as roughly equivalent to percent TDN, data
presented by Perry and Olson (1975) indicate that IVDMD in stover before
frost is ample to maintain a pregnant beef cow or other ruminants.
Grazing grain sorghum stover must be reconciled with the high prussic
acid potential in sorghum species.
Energy
Net energy has become widely accepted in recent years for
expressing the value of a ration and the energy requirements for feedlot
cattle (Croka and Wagner, 1975). The energy value of livestock feeds can
be expressed as digestible or metabolizable energy or as the cultural
energy necessary to produce the feed. Livestock feeds are priced
essentially on their digestible energy content, except for high protein
feeds which are fed in supplemental amounts.
Energy reserves may be considered as organic accumulates
synthesized by the plant which are available for plant growth,
development and metabolism (Matches, 1969). Although soluble
carbohydrates are found throughout grass plants, their concentrations are
usually greater in the stubble than in the roots or leaves. Much of the


Table 7-17. Multiple correlation coefficients fo soil variables from 18 sites in
Nicaragua.
S
N
Mg
Mn
Ca
K
P
Zn
Cu
Fe
LAI
PH
LDW
s
1.00
N
0.29
1.00
Mg
0.19
-0.19
1.00
Mn
0.08
0.01
0.21
1.00
Ca
0.18
-0.06
0.26
0.17
1.00
K
0.25
0.07
-0.04
-0.02
0.44
1.00
P
-0.30
-0.08
-0.29
-0.06
0.31
0.31
1.00
Zn
-0.14
1.43
0.39
0.22
-0.21
-0.22
-0.26
1.00
Cu
-0.19
-0.11
0.21
0.05
-0.62
-0.63
-0.47
0.44
1.00
Fe
0.02
-0.10
0.07
0.13
-0.14
0.12
-0.07
0.15
0.13
1.00
LAI
0.20
0.24
-0.05
0.20
-0.09
-0.06
-0.21
-0.10
0.04
-0.17
1.00
PH
0.31
0.20
-0.19
0.11
0.18
0.23
-0.08
-0.30
-0.27
CM
CM

O
1
0.56
1.00
LDW
0.03
0.19
-0.23
0.09
-0.04
0.12
0.01
in

o
1
-0.17
-0.17
0.53
0.63
1.00
PH = Plant height, LDW = Leaf dry weight.
219


Abstract of Dissertation Presented to the Graduate School of the
University of Florida in Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy
PRODUCTION ASPECTS OF MAIZE + SORGHUM INTERCROPPING SYSTEMS IN
CENTRAL AMERICA
By
Francisco Roberto Arias Milla
August 1985
Chairman: Raymond Noel Gallaher
Major Department: Agronomy
Farmers in the semi-arid areas of Central America have developed a
maize (Zea mays) + sorghum (Sorghum bicolor (L.) Moench)-animal mixed
production system in response to resource availability and family food
needs. The objectives of this study were to a) describe the maize + sor
ghum system in its bio-physical and socio-economic environment, b) study
the relationship between soil moisture and dry matter accumulation, c)
describe dry matter, energy, and nutrient accumulation by the system,
and d) determine if S deficiency is a widespread problem in areas where
the system is used.
From a situational analysis it was found that marginal soils, ir
regular rainfall pattern, lack of appropriate technology, and limited
resources are characteristics of farms in the areas where the system is
practiced. During a growing season a farmer on a 7 ha farm may invest up
to $200 (US), mainly on fertilizers (70% of the total cash investment)
and $45 (US) on animal feeds.
vi


IVOMD (dag kg-1) IVOMD (dag kg
143
Days After Planting Maize
Figure 6-4. Effect of the stage of maturity on the
IVOMD of 'NB-3' maize (a) and 'Criollo'
sorghum (b).


105
In the cropping subsystem, the association of maize and sorghum
requires products such as fertilizers, insecticides, herbicides and, in
some cases, seed from outside the farm. Production includes grains used
as food for the family and animals and the residues are sold or fed to
the cattle. Swine and poultry consume the damaged ears or grain that
falls in the field.
The "guatera" cropping system has not been studied in detail. The
farmer spends little time managing this system, especially in planting
and harvesting. Forage (from sorghum and occasionally maize) can be cut
and piled in the field or consumed directly by the animals.
Animals are produced for family consumption and for commercial
purposes, providing pork meat, milk, cheese, eggs, and live animals
(chicken, pigs, and calves). Ccmmon input expenses in animal production
are for salt and fish meal. Little is known about cash flow in this
production system.
Constraints
There are many constraints to crop production, animal, crop/animal,
and to farming systems. One of the main problems in discussing this
subject lies in delimiting the system to be analyzed. In the following
sections some of the most relevant will be discussed.
Crop production constraints
Arias et al. (1980), Guzman (1982), Francis (1983), and Hawkins et
al. (1983 ) agree that environmental stresses, especially drought, are
the most important limitations to crop production. This phenomenon
occurs because of the variability in the rainfall pattern and the
"canicula", which in some areas may last more than 30 days. Drought is
accentuated by the existing physiography, shallow soils, and heavy soil


106
textures. In some areas nutrient deficiency, particularly N, P, and S
(CATIE 1980, 1981a, 1981b, 1982a; Rico 1982; Hawkins et al., 1983), may
reduce crop productivity and can be related to drought.
Within the biological constraints, Arze et al. (1983) and Clara et
al. (1983) identified the wide use of low-yielding cultivars 'criollos'
of both maize and sorghum as a limitation that reduces the possibility
of increasing crop yields. Another disadvantage of these varieties is
that they are highly susceptible to downy mildew (Sclerospora spp. and
Sclerophthora spp.). Although a new disease (first reported in the area
in 1975, personal observation by the author), downy mildew has rapidly
gained importance in some regions of El Salvador, Honduras, and
Nicaragua. All the constraints for crop production activities also
affect animal yield directly.
Animal production constraints
Feed quality and availability are the primary constraints to animal
production (E. DeLa Hoz, CATIE/Honduras, personal communication 1983).
During the dry season maize and sorghum residues and "guateras" are the
only sources of feed, since pasture growth is limited to the rainy
season. The quality of the feed may be considered poor, protein intake
is low, and the low availability of feeds accentuates this constraint.
If feed availability were the main constraint to the animal production
system, then the most important constraint to the maize + sorghum/animal
system would be the same as those listed for crops; if more residues
were available, then more feed would be available.
Farming system constraints
The primary constraints to the farm system are the availability of
land, labor, or capital (Green (1974); Arias et al., 1980; Larios et


33
accepted that critical concentrations vary from species to species
although it has been suggested that this may not be so for all
nutrients.
Nutrient Accumulation
Jacques et al. (1975) suggested that nutrient uptake precede dry
matter production because the nutrients are required for growth and dry
matter accumulation. More than half of the total nutrient uptake occurs
before maximum vegetative dry matter was produced. Nutrient
concentrations varied among sorghum plant parts and changed throughout
growth. Concentrations in most vegetative plant parts were highest
right after emergence, decreased until maximum vegetative dry weight had
been produced, and changed little, if at all, while grain developed.
Lockman (1972b), studying the mineral composition of sorghum,
found that N levels in plant samples were well correlated with yields at
all growth stages and in both years (1968-69). Dry weather during the
first year of his experiment decreased N levels slightly relative to the
normal moisture data from the same plots in the second year. Results
are quite convincing that the critical level for N will not drop below
3.0% even at late stages of growth.
Lockman (1972b) observed that P levels also were well correlated
with grain yields at all stages and in both years. Dry weather caused
higher P levels, which are considered to be simple accumulation effects
with less growth. Data presented by Lockman (1972b) indicated that K
levels were correlated with grain yield in only the seedling and
vegetative samples; K levels in grain sorghum plant samples decreased
almost linearly with age. Dry weather appreciably decreased relative K
levels in seedling samples in one year.


129
leaves, and head respectively. Thirty days after harvest, stems and leaves
represented 66 and 34% of total dry matter, respectively.
Dry matter accumulation by 'Pioneer 895' is depicted in Figure 5-4b.
It differed from that observed in the photosensitive 'Criollo' (Fig.
5-3b). At bloom 4.3 Mg ha ^ (approximately 25% of the total dry matter)
had accumulated. Leaves and stems represented 52 and 48% of the total,
respectively. Heads developed rapidly at the expense of leaf and stem dry
weight. Maximum dry matter accumulation (14.9 Mg ha *) occurred 101 days
after planting (grain harvest); heads, stems, and leaves had accumulated
55, 28, and 17%, respectively.
The most striking difference in the dry matter distribution patterns
between the photosensitive 'Criollo' and the non-photosensitive 'Pioneer
895' sorghum is the amount of accumulation by the head. Both sorghums
produced similar amounts of dry matter (14.3 and 14.9 Mg ha ^ for
'Criollo' and 'Pioneer 895', respectively). However, at harvest
non-photosensitive sorghum distributed 55% of the total dry matter
accumulated to the head, while the photosensitive sorghum had distributed
only 17%. Conversely, 'Criollo' accumulated 46% of the dry matter in the
stem while 'Pioneer 895' only allocated 28% of the total dry matter
accumulated in the stem. Goldsworthy (1970), comparing photosensitive and
non-photosensitive sorghums, reported similar results. His data suggest
that this difference can be explained in terms of the number of spikelets
present at heading. The number and/or potential size of the developing
grain in photosensitive sorghums appear to be too small to accept all the
assimilate produced. After head harvest, 'Pioneer 895' lost dry matter at
a rate of 156 kg ha *day ^(Table 5-3). Most of the loss in both the


51
solution still obtained about 30% of their S from the atmosphere. When
plants were grown in a S-deficient nutrient solution, they obtained up
to 90% of their S from the atmosphere, but the total amount absorbed was
insufficient for normal growth. There is considerable evidence that
sulfurous gases in the atmosphere may be absorbed directly by soil.
However, Blue et al. (1981) reported that S additions to soils through
the atmosphere and rainfall are inadequate for intensive production
systems.
Jones et al. (1979) estimated that an average of 8.4 kg ha ^yr ^
of atmospheric S was absorbed directly by the soil in South Carolina
from 1973 to 1977. No data are available on the amount of S that may be
absorbed directly by the plant foliage as sulfite.
Sulfate is absorbed by plants with more difficulty than other
anions and it has been shown that the uptake proceeds even more slowly
in the presence of more mobile anions such as chloride and nitrate.
Usually S and N are absorbed in the form of sulfate and nitrate from the
soil and subsequently undergo metabolic conversion into organic S and N.
Any quantity above that needed to supply sulfate and nitrate to the
metabolic process is stored up provisionally as inorganic sulfate and
nitrate in the plant (Spencer and Freney, 1980).
Friedrich and Schrader (1978) suggested that N-reductase (NR), the
rate-limiting enzyme in nitrate-N assimilation, serves as a primary
regulatory coupling between nitrate and sulfate assimilation, while
Reuveny and Filner (1977) postulated that ATP-suIfurylase, the initial
enzyme in the pathway of sulfate assimilation, acts in synchrony with NR
to coordinate nitrate and sulfate assimilation in cultured cells.


4
will alleviate this deficiency. A summary of the scheme presented by
Arze et al. (1983) to accomplish this task follows:
1. Identify important cropping systems used in the semi-arid
regions of Central America.
2. Study the performance of the cropping patterns under different
environmental variables.
3. Determine the degree and form of relationship among these
variables.
4. Use the previous information to maintain, arrange or re-design
the system so that it operates optimally with respect to its objectives.
Several authors (Rodriguez et al., 1977, Arias et al., 1980; Mateo
et al., 1981; Guzman, 1982; Fuentes and Salguero, 1983; Hawkins et al.,
1983; Larios et al., 1983) have identified environmental stresses
limiting crop productivity in the semi-arid regions of Central America,
their listings including drought, nutrient deficiencies, particularly N,
P and S (CATIE, 1980, 1982a; Rico, 1982; Hawkins et al., 1983), and
water and wind erosion. These areas are primary sources of cereal
grains, oilseed crops, fruits, vegetables, table legumes, meats, and
dairy products for a large majority of the rural and urban population of
the Isthmus. Basic research projects to overcome environmental stress
limitations have been notably successful in many crops and can provide
data for future significant progress with adaptive research.
Maize + sorghum was selected as the subject of this research
project because of its importance in food production. The maize +
sorghum cropping system is predominant in semi-arid areas of Central
America at elevations below 1,000 m. The system apparently increases
the productivity and reduces risk of loss in areas with marginal


235
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leaves by a dry weight method. Agron. J. 56:520-522.
Richards, F. J. 1969. The quantitative analysis of growth. _In Plant
Physiology, F. C. Stewart (ed.). Academy Press, Inc., New York. Vol. 5A,
pp. 3-76.
Rico, M. A., 1982. Aspectos Edaficos y fisiograficos relacionados con el
problema de sequia. In J. F. Larios (ed.) Agricultura en zonas afectadas
por canicula interestival en El Salvador. MAG/CATIE. San Andres, El
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Rodriguez, R., M. Alvarado, and H. Amaya. 1977. Estudio
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production of sweet sorghum. Agron. J. 73:1027-1032.


Table 7-14. Soil extractable K, Ca, and Mg; and Ca:Mg and Ca+Mg:K ratios from 18 sites in
Nicaragua.
Sice
K
Ca
Mi
Ca : Mg
Ca + Mg
:K
D
su
D
SU
D
SU
D
SU
0
SU
1
283.
262.
3630.b
3450.
539 edef
525 ede
6.7
6.6
14.7
15.2
18
283.
260a
2890 bedef
3310.b
832.
781.
3.5
4.2
13.2
14.5
10
204ab
167 bedefg
2445 def
2125 d
378 f
339 f
6.5
6.3
13.8
14.8
9
198abc
173abcde fg
3280abcd
2755.bed
473 def
424 ef
6.9
6.5
19.0
18.4
13
167 bed
144 edefg
3809a
3460a
610 bede
588 cd
6.2
5.9
26.5
28.0
3
156 bede
186abcdefg
2810 bedef
2940abcd
440 ef
427 ef
6.4
6.9
20.8
18.1
11
156 bede
221.be
2990abcde
2530 bed
474 def
392 ef
6.3
6.5
22.2
13.2
16
147 bedef
242abc
3009abcde
3209ab
404 f
469 def
7.5
6.8
23.2
15.2
12
128 bedef
179abcde fg
2270 ef
30 70ab
474 def
642abc
4.8
4.8
18.7
20.7
7
127 bedef
122 defg
3450.be
3250ab
558 bedef
539 ede
6.2
6.0
31.6
31.1
6
125 bedef
250.b
2360 def
3030abc
733ab
632 be
3.2
4.8
24.7
14.6
5
119 bedef
217abcde
2480 def
2900abcd
711.be
639abc
3.5
4.5
26.3
16.3
17
113 bedefg
173abcdefg
2340 ef
2810.bed
506 def
628 be
4.6
4.5
25.2
19.9
3
95 edef
156 bedefg
2720 bedef
2860abcd
620 bede
644abc
4.4
4.4
35.2
22.5
15
72 def
117 efg
3090abcde
2969abcd
526 def
508 ede
5.9
5.8
51.2
29.7
14
58 ef
89 fg
2870 bedef
2940abcd
641 bed
531 ede
4.5
5.5
60.5
39.0
4
57 ef
80 g
1965 f
2175 cd
507 def
650abcd
3.9
3.3
43.4
35.3
2
51 f
85 fg *
2670 edef
2640abcd
872.
768ab
3.1
3.4
69.5
12.1
Values in columns not followed by Che same
letter and rows
within subheadings followed
by an asterisk
are different
ac the
0.05 level of
probability
according to
Duncan's new multiple range test
and F test,
respectively.
215


_631 Bap) 614 (. Bap) By
171
40 00 120 160 200
Dnys After Plonting Maize
Figure 6-23. Effect of the stage of maturity on
the Mg concentration of 'NB-3' maize
(a) and 'Pioneer 895' sorghum (b).


148
Figure 6-7.
Effect
amount
'NB-3'
of the stage of maturity on the
of metabolizable energy of maize
(a) and 'Criollo' sorghum (b).


202
increased from 4.5 to 18.7 mg kg in the 0-15 and 30-45 cm depths,
respectively, for 120-cm plants. These findings are in agreement with
data reported by Neller (1959), Bardsley et al. (1964), Kamprath (1977),
and by Mitchell and Gallaher (1979), which indicates that adsorbed
sulfate associated with the argillic horizons of Ultisols is the primary
source of plant available-S in the southeastern United States. In a
comparison of soil-S concentration among height treatments within soil
depths (Table 7-6), soils related to the 120-cm treatment had a higher S
concentration (p=0.05) compared to those related to other treatments.
This finding strengthens the results observed for S concentration in
plant tissue (Table 7-5).
According to Plank (1979) the N, and P sufficiency levels for maize
ear-leaf range from 3.5 to 5 dag kg ^ and 0.3 to 0.5 dag kg ^,
respectively. Nitrogen concentration values reported (Table 7-7) for
treatments 30, 60, 75-cm (4.08, 3.44, and 3.61 dag kg respectively)
are within this sufficiency level. On the other hand, values reported
for the 90 and 120-cm treatments (2.99 and 2.96, respectively) fall
below this range. Nitrogen and P concentration in the leaf tissue
decreased with plant height (Table 7-7), and leaf size (Table 7-2). This
agrees with findings reported by Kumar and Awasthi (1977) and Hanway
(1962a) who attributed this phenomenon to dilution effect. Leaf P
followed a trend similar to that of N; as plant height and leaf size
increased P concentration decreased, and only those levels observed in
the 30 and 60-cm treatments are within the range reported by Plank
(1979). It is noteworthy that both N and P presented an inverse
concentration pattern in relation to S.


165
losses from the leaf and stem were shuttled out of the plant. After
grain harvest, an increase in K concentration in the stem preceded the
second period of vegetative growth reported in Chapter 5.
The patterns observed in the sorghums and millet were very similar
to those observed in maize. As maturity progressed, K concentration
decreased in all plant components. However, it is interesting to note a
sharp increase in K concentration in the stem of both sorghums after
grain harvest. Since little K accumulated in the head, these results
suggest that K lost from the leaves was accumulating in the stems (Figs.
6-16b, 6-17b, and 6-18b). At bloom, K concentration in the leaves of
both sorghums was above the 1.7 dag kg ^ sufficiency level established
by Locke et al. (1964).
Maize Ca (Figs. 6-19a, 6-20a, and 6-21a) followed a different
pattern of accumulation and distribution from that observed for N, P,
and K. Calcium concentrations were much lower in the ear than in any
other plant part. Jacques et al. (1975) have reported similar low values
in grain sorghum heads. Calcium concentration in the leaves increased
dramatically with maturity. The need for Ca in Ca-pectate formation of
mature leaf cells may have been responsible for the increased
concentration observed in the leaves (Jacques et al., 1975). Calcium
concentrations in the leaves observed at bloom were within the critical
levels (0.25-0.50) reported by Plank (1979). Calcium in the stem
decreased sharply early in the season and increased slightly towards the
end. Gallaher et al. (1975) reported that plants that accumulate large
quantities of oxalic acid tend to contain large quantities of Ca oxalate
crystals which are insoluble in water, alkalies, and organic acids.


54
Friedrich and Schrader (1978) studied S deprivation and N
metabolism. In maize seedlings, leaf fresh weight was not affected by S
deficiency. However, stem fresh weight was reduced 24% compared to
normal plants. The authors concluded that it may be that S deficiency
was having a greater effect on the young, rapidly elongating culms and
unfurled leaves in the stem fraction than on the older leaf blades.
There are few data, however, that indicate to what degree yield and
quality are related.
According to Allaway and Thompson (1966) the importance to human
and non-ruminant animal nutrition of the S-containing amino acids cannot
be overstated. Many studies of the nutritive value of proteins have
shown that the lack of S-containing amino acids is the factor that
limits the biological value of the protein. The investigators making
this survey further concluded that a large segment of the world's
population is living on a diet that is strongly deficient in methionine.
If the animals are fed a ration low in total S, they will not make the
best utilization of the N in the diet. This means that meat, milk, or
wool production will be reduced.
Under conditions of S deficiency and high N fertilization, protein
synthesis is retarded by a lack of the S-containing amino acids,
cysteine and methionine, and this is reflected by marked accumulation of
unassimilated N in the plants as nitrate-N, amides, and free amino
acids. Such forage when fed to animals represents an unbalanced ration
in which N content may exceed requirement, which in turn can result in
nutritional disorders, especially in ruminants. High nitrate-N in
forage, for example, can cause nitrate poisoning and hypomagnesemia in
grazing dairy cattle. It arises from an inadequate absorption of Mg and


152
increased slightly between bloom and soft-dough stages; it remained
constant thereafter. Head energy content was higher at bloom than at
grain harvest. This last finding does not agree with data presented by
Schmid et al. (1975 ).
The contrasting differences observed between the PS and NS sorghums
may explain in part the preference of the Central American farmers for
the PS sorghums. Besides accumulating higher energy, PS sorghum also
maintained a higher level of energy for a longer period of time after
grain harvest (Figs. 6-7b and 6-8b). This coupled with higher dry matter
accumulation in the stem and leaves by the PS sorghum makes it a first
choice for the semi-arid regions of Central America, where it is the
main source of feed for ruminants during the long dry season.
Energy values observed in millet are presented in Fig. 6-9b. Due to
the short duration of the growth period observed in millet, the
accumulation of carbohydrates did not reach its potential. In general,
lower values were observed in millet than in the sorghums or maize.
Leaves and stems followed similar patterns, increasing to bloom and then
declining. Heads maintained a constant amount of energy during the
growing season.
The distribution of N in the different plant parts of the maize
plants from the M+PS, M+NS, and M+MI systems throughout the season are
presented in Figs. 6-10a, 6-lla, and 6-12a, respectively. No differences
(p=0.05) were observed in N concentration among plant parts during any
stage of growth. Nitrogen concentration was affected by maturity in a
very similar manner as IVOMD. As maturity progressed N concentration
decreased in plant components with the exception of maize ears, in which
N concentration increased until harvested. Kumar and Awasthi (1977) and


RELATIVE GROWTH
95
PERIOD (months)
Figure 4-7. Relation between chronological arrangements and
relative growth of the raaize/sorghum systems with
the rain distribution in El Salvador. (Personal
observation of the author, Mateo et al., 1981;
and Hawkins et al., 1983).


99
Table 4-1. Typical management activities in cropping subsystems.
Activity
Man/
Days
Input
Output
Type
Quantity
Product
Quantity
Weeding
12.0
0 M
?
Burning
7.0
ashes
?
Herb. Applic.
3.0
Paraquat 2.4 1 ha
mulch
?
Planting
3.2
Seed
16*
Fert. Applic.
3.0
N-P
0 to 20-20
Weed (M)
3.6
0 M
1000*
Planting (S)
0.9
Seed
6-12*
Fert. Applic.
0.9
N
20*
Weeding (M)
5.0
0 M
?
Bend-over (M)
4.1
0 M
?
Weeding (S)
Harvesting (M)
ears
?
Shelling (M)
5.0
cobs
331*
grain
1700*
Harvesting (S)
6.0
forage
?
grain
57 0/1900*
(M) = maize, (S) = sorghum, 0 M = organic matter; *kg ha ; ** sorghum
planting date varies from 30 to 90 days after planting the maize.


214
treatment were deficient. Nevertheless, the P:S ratio was within the
appropriate value (Tisdale and Nelson, 1964). Leaf P concentration was
positively correlated to S concentration (r = 0.33), with N
concentration (r = 0.45), and with K concentration (r = 0.74). Other
correlation values are given in Tables 7-16 and 17.
Soil K, Ca, and Mg values observed differed among sites within each
treatment (Table 7-14). No differences were observed between treatments
for any of these elements. Potassium values that fall below 100 dag kg ^
are considered low for the area under study (Fassbender, 1980). Calcium
and Mg values reported are common in these dry tropical areas, and agree
with those reported by Fassbender (1980). Although in most sites
concentrations reported are within the accepted ranges, the ratios
between these nutrients may not be appropriate, especially in the
Ca+Mg:K. As K levels decrease, the ratio becomes wider.
Potassium, Ca, and Mg concentrations in the leaf were different
among sites (p=0.05), as shown in Table 7-15. No differences were
observed between treatments. Potassium concentration appears to be low
for both treatments, Plank (1979) has established the sufficiency range
for K in leaves between 2.0 and 2.5 dag kg Except for leaves from
sites 15 and 8, leaves from all sites and treatments were deficient in
K. In most cases Ca and Mg concentrations were within the sufficiency
ranges established by Plank.
Values for the K:Ca+Mg ratio in the leaves are presented in Table
7-15. These findings suggest an imbalance between these nutrients is
common in the area under study. Gallaher et al. (1975) reported that
when the K:Ca+Mg ratio exceeds 1.8, levels of Mg in the ear leaf are
close to the value at which photosynthesis was reduced. Most of the