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CORNELL
TROPSOILS PROGRAM
REVIEW
Cornell University
New York State College of Agriculture
and Life Sciences
Ithaca, New York 14853
September, 1987
TROPSOILS
TABLE OF CONTENTS
Pane
Introduction
Original Program Proposal . . . . .. 1
Modified Program Development. . . . . 2
The Research Setting. . . ... . ... 3
Previous Results. . . . . ... .. 4
Research Needs. . . . . ... .. 7
The CPAC Cornell Collaborative Research Program. ....... 9
Active Research Projects and Progress Reports . .. 10
Project Number 101 . . . . . 11
Project Number 102 .- .//. . . 19
Project Number 103 . . . 33
Project Number 104 . . . .... .39
Project Number 105 --/ .. 44
Project Number 106 .--....4 .7 '/.. 53
Project Number 107 . . . . ... 66
Project Number 108 . . . .... .70
Research Projects 1987-1992 . . . .... .76
Project Number 101 . . . . ... 77
Project Number 103 . . . . 81
Project Number 104 . . . .... .85
Project Number 107 . . . . ... .90
Project Number 108 . . . . ... 95
Project Number 109 ....... ... ..... 100
Project Number 110 L o--- IL) l y- 102
Project Number 111 .- C -. ..o. .. .S. 107
Project Number 112. .-) ......... 112
Future Directions. . .. . . .... ... 116
Cornell University Faculty and Staff Involved in TropSoils
Program . . . ... . . .118
Cornell University Graduate Students Involved in TropSoils
Program . . . ....... . 119
Directors of CPAC During Active Program. . . .. 120
Expenditures, 1981-1986, First 5-Year Grant. . . ... 121
Expenditures, January 1 to June 30, 1987, -Second Grant .... 122
The overall TROPSOILS program goal is to develop stable food production
systems on an agronomically, economically, and ecologically sound basis in
the developing countries of the tropics. The Cornell component was
originally planned to take the lead role in the acid savannas with the
host site, at CPAC, in Brazil and a support role in the humid tropics at
the site at Yurimaguas, Peru with NCSU as the lead institution.
Original Program Proposal
The work in the acid savannas under the original proposal as outlined
in the Final Program proposal to USAID of 14 October 1980 had the
following thrusts:
1. Increase the efficiency of fertilizers in acid, infertile Oxisols
through:
a. Decreasing costs of lime and fertilizer applications in crops and
pastures through the implementation of different management
strategies.
b. Increase the efficiency of utilization of the most expensive
input, phosphorus, through the joint use of cheaper sources of P,
varieties tolerant to low levels of available P, and increased
efficacy of mycorrhizal associations.
c. Characterize the dynamics of soil fertility parameters as a
function of time, farming systems and timing of corrective
fertilizer application.
d. Increase knowledge on micronutrient fertilizer responses, basic
micronutrient relationships and critical soil-test levels.
e. Develop practices to maintain an adequate balance of Ca, K and
Mg, and study S-Mg interaction in legumes.
f. Develop crop rotation systems that optimize input use and
control erosion.
g. Determine the economic feasibility of fertilizer and lime use in
the Cerrado.
h. Characterize soils in relation to their productivity limitations.
2. Increase rooting depth of crops and pastures in order to decrease
drought stress through soil management practices such as:
a. Increase the amount and availability of calcium in the subsoil;
b. Identify physical or chemical limitations that prevent deep
root development in Cerrado soils; and
The overall TROPSOILS program goal is to develop stable food production
systems on an agronomically, economically, and ecologically sound basis in
the developing countries of the tropics. The Cornell component was
originally planned to take the lead role in the acid savannas with the
host site, at CPAC, in Brazil and a support role in the humid tropics at
the site at Yurimaguas, Peru with NCSU as the lead institution.
Original Program Proposal
The work in the acid savannas under the original proposal as outlined
in the Final Program proposal to USAID of 14 October 1980 had the
following thrusts:
1. Increase the efficiency of fertilizers in acid, infertile Oxisols
through:
a. Decreasing costs of lime and fertilizer applications in crops and
pastures through the implementation of different management
strategies.
b. Increase the efficiency of utilization of the most expensive
input, phosphorus, through the joint use of cheaper sources of P,
varieties tolerant to low levels of available P, and increased
efficacy of mycorrhizal associations.
c. Characterize the dynamics of soil fertility parameters as a
function of time, farming systems and timing of corrective
fertilizer application.
d. Increase knowledge on micronutrient fertilizer responses, basic
micronutrient relationships and critical soil-test levels.
e. Develop practices to maintain an adequate balance of Ca, K and
Mg, and study S-Mg interaction in legumes.
f. Develop crop rotation systems that optimize input use and
control erosion.
g. Determine the economic feasibility of fertilizer and lime use in
the Cerrado.
h. Characterize soils in relation to their productivity limitations.
2. Increase rooting depth of crops and pastures in order to decrease
drought stress through soil management practices such as:
a. Increase the amount and availability of calcium in the subsoil;
b. Identify physical or chemical limitations that prevent deep
root development in Cerrado soils; and
c. Select varieties of the main crop and pasture species for deeper
root development.
When the original grant was signed, the budget allocation to initiate
the CRSP was much reduced compared to the original request and the acid
savanna component along with the steeplands component were eliminated.
Cornell was left with the support program in the humid tropics along with
a reduced budget. This grant document was effective 25 September 1981.
Modified Program Development
In a program review meeting on 22 October 1981 held by AID/S&T/AGR the
issue of inclusion of research on the acid savannas which had been raised
by the AID Administrator was discussed. Results of the discussions were
relayed to NCSU management Entity and were a main agenda item of the TC at
a meeting in Raleigh, N.C. 28-29 October 1981. By unanimous vote, Cornell
was authorized to initiate collaborative research in the acid savannas
with CPAC/EMBRAPA. The budget available, however, was that which had been
allocated for the previous support role. This decision was relayed to
AID/W on 2 November 1981 and the host institution in Brazil was notified
of this decision on 11 December 1981.
Subsequently, however, AID/W requested further information justifying a
shift in the Cornell program from the support role in the humid tropics to
a lead role in the acid savannas. This information was provided by the
management entity and an amended agreement was finally signed in September
1982 permitting Cornell to assume primary responsibility for a program on
the acid savannas.
Meanwhile Drs. McCants, Lathwell, and Bouldin traveled to Brazil in
April 1982 and met with the CPAC Director and his staff to develop plans
for the collaborative research program. Developing a Memorandum of
Understanding among EMBRAPA, Cornell University, and the Management Entity
was begun in June 1982 and a signed memorandum was executed in June 1983.
The scope of the research to be undertaken under the terms of the
agreement included the following:
A. To increase the efficiency of fertilizer use in acid infertile Oxisols
through:
1. improved legume, fertilizer and soil nitrogen management in
cropping systems;
2. increased utilization of fertilizer phosphorus by management of
crops to make effective use of both currently applied phosphorus
and residual fertilizer phosphorus, and
3. increased knowledge of micronutrient fertilizer responses and
basic soil-micronutrient relationships.
B. To develop improved methods of soil acidity management of Oxisols
by:
1. increased understanding of Al and Mn chemistry as they influence
crop yields and the lime requirement of these soils,
2. developing liming practices to maintain adequate balance of Ca,
Mg and K in soils and plants, and
3. increasing the rooting depth of crop plants to reduce drought
stress by enhancing Ca movement into the subsoil and by
identifying and removing other physical and chemical limitations
to root growth.
C. To develop methods of characterizing soils so that results may be
applied to other acid infertile soils of the tropics.
The position of senior scientist (Senior Research Associate) was
advertised in summer of 1982. The position was offered to Dr. Eric Stoner
and he accepted our offer 21 September 1982 to begin on 1 January 1983.
He along with our first graduate research assistant, Walter Bowen, were
posted to CPAC 1 July 1983.
The Research Setting
The acid savanna regions of the tropics are dominated by the soil
orders Ultisols and Oxisols. These regions are the largest land areas in
the world that are either not farmed or only partially utilized. At least
500 million hectares of acid savannas are found worldwide with major
portions in South America. There are nearly 200 million hectares in
Brazil alone. In addition, large areas occur in Africa and Southeast
Asia. These areas are characterized by a wet-dry cycle with sufficient
precipitation for at least one crop per year. Many of the acid savannas
are rapidly being developed without a sound soil management base resulting
in low productivity and widespread erosion.
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The soils of these areas are deep, well drained, highly permeable, and
have favorable physical conditions so that their potential for food crop
production is high. The principal factor limiting their productivity is
their low fertility. With increasing availability of high-yielding
varieties of food crops the potential of these areas is higher than ever
before. Thus, the low natural fertility of these soils is an even more
crucial limitation than previously. To achieve this potential, however,
it is necessary to determine the most effective and economic amounts and
methods of application of liming materials, nitrogen, phosphorus,
potassium, and micronutrients in relation to cropping systems and
management practices. A ? / / ,/ -
Previous Results / _
Previous research carried out by Cornell from 1969 through 1978 on the
Ultisols and Oxisols of the humid tropics and the acid savannas regions
has identified a number of important management considerations. Some are
new ideas; others are verification and extension of existing knowledge.
The following is a summary of our state of knoMledged at the initiation of
the present project based on the analysis of our previous research:
1. The experimental results demonstrate that-the highly weathered, well
drained acid soils of the tropics as represented in the experimental
sites have a very high production potential. For example, on Oxisols
and Ultisols in Puerto Rico, yields of corn grain with adequate
nitrogen, phosphorus and lime have averaged 4.5 mt grain/ha (average of
14 location years of data); Planaltina, Brazil 6.2 mt grain/ha (4
location years); and in Ghana, 4.5 mt grain/ha (1 location year of
data). Unless lime or phosphorus is added to many of these soils
yields are essentially zero.
2. The potential of these soils cannot be achieved by single practices. A
combination of practices is essential.
3. The native capacity of many of these soils to supply nitrogen is
greater than is generally appreciated and good crop production can be
obtained with moderate applications of properly applied fertilizer
nitrogen during the initial years of cropping. Fertilizer nitrogen
must be supplied and managed in relation to the growth of the crop.
Split applications are most effective for a crop like maize. Timing is
critical and it is greatly affected by rainfall patterns as
demonstrated by the work in Puerto Rico and Brazil. Varietal
differences are important and in preliminary results from Ghana
improved varieties have a much higher yield potential with moderate
applications of fertilizer nitrogen than do local, unimproved
varieties.
4. The problem of supplying sufficient phosphorus to meet crop needs at
reasonable cost requires special consideration for most of the Oxisols
and Ultisols. On the Oxisols of the Central Plateau of Brazil,
phosphorus is extremely deficient on soils which have not been under
cultivation, and they require substantial applications of phosphate
fertilizer in the first years of cultivation for good maize production.
A combination of a large, initial broadcast application of soluble
phosphate as a capital investment, followed by smaller annual
applications of banded phosphate, may be the best practice. Prelim-
inary results on Ultisols of Ghana indicate that only modest quantities
of phosphate fertilizer may be required to meet the phosphorus
requirements for good crop production. Interestingly, method of
application may not be important on these particular soils. The lack
of response to phosphate on similar soils in Puerto Rico which have had
a long history of phosphate fertilization is consistent with the
experimental data collected in Brazil; heavy applications of phosphate
have high residual effects. Crops other than maize appear to require
smaller amounts of applied phosphate for good production.
5. Aluminum and/or manganese toxicity, especially in the subsoil, poses a
problem on extensive areas of Ultisols and Oxisols. It restricts the
root system of many food crops and thus affects the capacity of the
plants to absorb nutrients and water. Incorporation of modest amounts
of lime to depths of 20 to 60 cm helps, but is not the answer for many
situations where such placement is not feasible because of cost.
Recent evidence from the liming experiments in Brazil indicates that
calcium may move into the subsoil more readily than previously
believed. In addition, development of aluminum and/or manganese
tolerant varieties offers promise. Screening procedures to select
maize varieties tolerant to aluminum have been developed at Cornell.
Research during past years in screening about 200 inbred and hybrid
varieties of maize has demonstrated a wide range of tolerance to
aluminum toxicity. The studies have shown that it is feasible to
Develop aluminum tolerant varieties which should produce well with
little or no need for lime. This has important implications for
J i K__ _____- --------- ____ _-- ----- ---^^
farmers in regions where lime is not readily available or is too
costly.
6. Water is likely to be a limiting factor in extensive areas of the humid
tropics even during the rainy season particularly where subsoil acidity
restricts root growth. One or two weeks without rain can nullify the
beneficial effects of all of the inputs described above. For extensive
areas in the Central Plateau of Brazil, it is estimated that average
yields of maize during the rainy season may only be about half of what
is possible if supplementary irrigation were provided or if lime is
Incorporated to 30 cm or more. Experience in Ghana likewise has shown
that uncertainties in rainfall especially in the beginning of the rainy
season may have serious consequences in crop establishment and early
growth. Timing of planting and minimizing of runoff by good
conservation practices where supplementary irrigation is not possible
also should help to insure good crop production.
7. In the absence of toxic levels of aluminum and/or manganese, liming may
be necessary in order to provide sufficient calcium and magnesium for
adequate plant nutrition. This appears to be especially true of some
of the soils of Ghana where toxic levels of aluminum and/or manganese
are not present but the amount of exchangeable calcium and magnesium is
extremely low. The amounts of lime needed for such purposes are
usually small by conventional standards; the pH need not be raised much
above 5 to achieve the necessary soil-plant relations for optimum
productivity.
8. In the Central Plateau of Brazil, sufficient water is available at a
reasonable cost to irrigate 1% to 3% of the land during the dry season
and provide supplemental irrigation during the rainy season. Thus,
U,2c / Al JLZ,4 )
-7-
intensive, year-round crop production on small acreage appears
feasible. Perhaps irrigation coupled with inputs of soil amendments
and intensive management would provide very attractive investments.
Probably enough data is now available to make fairly good predictions
about the economic feasibility of this under a variety of economic
conditions.
Research Needs
Our analysis of our previous research, likewise had suggested future
research needs if reliable soil management systems for sustained
production were to be achieved. These are as follows:
1. Lon-term field trials are essential for soil fertility research in a
specific ecological environment before any valid recommendations for
improved soil management practices can be made to farmers. The
uncontrolled variables from year to year, such as the weather and
insect and disease problems, make it necessary to have field
experiments continue for a number of years. Also, to measure residual
effects of certain treatments such as phosphate and lime, long-term
~ trials are required. These experiments need to be replicated at
several sites on carefully characterized soils and climates which are
representative of extensive areas. The economic potential of the
management systems evolved can only be determined after these variables
have been evaluated. In addition to long-term experiments at the
research station, supplementary trial need to be conducted with the
same crop or cropping sequence on similar soils in a number of other
locations in the region in order to be able to evaluate the effects of
site variability, previous land use history, micro-climate differences,
and other variables which may affect the interpretation of the data.
Although this approach is more costly and consequently little used in
developing counties for this and other reasons, it would provide a
sounder basis for making recommendations to the farmers. To reduce
costs, relatively simple experiments could be used instead of the more
.sophisticated, complex ones.
2. Long-term sustained food crop production is possible on many of these
soils. As an example, one of the sites used in Puerto Rico (Catalina
soil series) had been in continuous food crop production for many
decades previous to our establishing an experimental plot on the site.
In the first crop year, yields of maize averaged 6000 kg/ha with no
response to fertilizer nitrogen. Subsequent yields on this site with
good treatment were as high or higher than the initial year. Other
sites appear to have the potential to sustain long-term food production
also. In certain situations, however, caution must be exercised. In
Brazil, on some of the Oxisols, it appears possible, with continued
tillage, a plow-pan or hard-pan could develop. The consequences of
such a pan formation could be disastrous. On the other hand, continued
research may develop procedures to obviate such a development. In
Ghana our limited experience indicates that the particular nature of
those soils we have worked on (Ultisols, in this instance) makes them
particularly vulnerable to erosion. Likely, management practices to
control erosion and, at the same time, permit sustained food crop
production can be developed. At the present time, however, such
management systems are not in place.
3. Most of the soil fertility research to date has focused on a
monoculture and though some research has been done to improve
production under mixed cropping, intercropping or multiple cropping
systems, much more emphasis should be given to this work. These
systems are probably more common than monoculture in many developing
countries and greater attention needs to be given to methods for
improving the soil fertility and management practices in these cropping
systems. Recent studies have shown mixed cropping or intercropping
sometimes can produce more than a single crop on the same area of land.
More comparative studies of this sort are needed and techniques will
have to be developed to measure responses to applied nutrients in a
mixed cropping system. For this kind of work long-term experiments are
indispensable.
4. Because of economic and political constraints, soil fertility research
in the tropics directed toward increased crop production with minimum
use of applied nutrients and other inputs will be required in the
future. It is especially relevant to the problems faced by small
-9-
farmers and a low input research strategy would have great significance
throughout the tropics.
5. The use of legumes as a nitrogen source in these cropping systems is of
particular importance. It may be possible by proper selection of
legumes and appropriate management practices to supply much of the
nitrogen requirements of subsequent food crops. The use of edible
legumes, which supply food as well as nitrogen containing residues,
needs to be investigated. Legume green manure crops have the potential
to supply large quantities of nitrogen for subsequent crops. The
possibilities to enhance the nitrogen supply to food crops through
legumes are great.
The CPAC Cornell Collaborative Research Program
Based on what had already been learned from our previous research
effort at CPAC and the ongoing program at the center, and given the
limited funding available to Cornell for the acid savanna program, careful
consideration was given to research topics to be pursued. Within the
framework of the agreements with the Management Entity and EMBRAPA, three
major research topics were selected for the collaborative research
program; 1) nitrogen management in acid savanna soil; 2 quantitative
description of water and chemical budgets in acid savanna soils; and 3)
soil constraints to management of acid savanna soils.
The goals of the nitrogen management work are to find effective ways to
manage crop residues, biologically fixed nitrogen, and fertilizer nitrogen
for sustained crop production and maintenance of soil fertility. With
increased cost of energy and thus, increased cost of fertilizer nitrogen
the thrust is to improve the utilization of biologically fixed nitrogen.
We wish to learn how much nitrogen can be fixed, how much can be utilized
by the succeeding crop, and how to incorporate legume green manures and
crop residues into viable cropping systems. Projects to investigate these
problems are now under way.
The second major topic, the description of water and chemical budgets,
has as its goals the development of a quantitative understanding of water
-10-
and the fate of soil amendments in the acid savanna soils. Experiments
are being carried out to achieve these goals with the objectives of
developing predictive models for use in describing nitrogen and other ion
movement and distribution in the Cerrado soils. Models relating water use
to crop yield will be constructed to be useful in extending experimental
results to other locations.
The third research topic on soil constraints to management of acid
savanna soils has as its goals the identification of chemical and physical
factors of significance to use and management, to understand the genesis
of these properties, and to inventory these properties for use in
management of the acid savannah soils. One project to determine the
relationships between soil color patterns and natural drainage
characteristics, and to develop means of identifying those Oxisols with
restricted drainage has been completed. Further work to evaluate the role
of iron in soil genesis is under way. A project to investigate the effect
of soil compaction and erosion on limitations to crop production is
ongoing.
All of these research topics and associated research projects have been
developed in collaboration with Brazilian counterpart scientists -at the
CPAC. The projects supplement and complement their ongoing research
program on the acid savanna soils. In addition these projects contribute
to the research program of the Agronomy Department at Cornell.
Active Research Projects and Progress Reports
The research projects under each research topic are described in detail
in "TropSoils Program Plan 1984-1989." Revised projects are given in
"Projects and Budgets for the Soil Management CRSP, 1986-1987." These
statements, along with the most recent progress report (1986), follow.
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TROPSOILS
PROJECT STATEMENT
Project Number: 101
Title: Nitrogen Availability from Legume Crop Residues and
Green Manures to the Succeeding Non-Legume Crops
Objectives:
1. To develop procedures for estimating potential for
legume crop residues and green manures to supply ni-
trogen to succeeding non-legume crops.
2. To estimate the effects of climate and management on
the ability of such organic materials to supply ni-
trogen to succeeding nonlegume crops.
3. To investigateisome of the effects of incorporating
roots vs. tops in the use of organic sources of
nitrogen.
Applicability:
Nitrogen management is the most difficult of the nutrients.
The inorganic nitrogen not utilized during the current crop-
ping season is usually lost or incorporated into the soil
biomass. Fertilizer nitrogen is not only expensive, but time
of application is critical. Legumes and green manures have
the potential to overcome both of these disadvantages provi-
ded (1) the legume growth and nitrogen fixation can fit into
the cropping system, (2) the time and quantity of nitrogen
released from the organic residue is sufficient to meet the
needs of the growing crop.
A quantitative evaluation of the nitrogen mineralization
from organic residues permits -the soil incorporation of the
residues and crop development to be timed to make maximum use
of the available N. This evaluation could then be incorpor-
ated into the N model.
The information can be used also for predicting the behav-
ior of organic residues in other parts of the world. Incor-
porating this information along with crop yield data and
climatic information, cropping systems can be developed that
maximize the use of organic N sources for crop production.
Personnel/Institution:" W. S. Reid, Cornell University
R. J. Carsky, Cornell University
W. T. Bowen, Cornell University
Research Site: CPAC, Brasilia, Brazil
Date: Original: October, 1984
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TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period: 1986 Work Plan Period: 1987
Project Leader/lnstitution: Dr. W. Shaw Reid/Cornell University
Principal Collaborators/Institution:
Robert J. Carsky/CPAC, Planaltina, Brazil
Walter T. Bowen/CPAC, Planaltina, Brazil
Allert Suhet/CPAC, Planaltina, Brazil
Research Site(s):
CPAC, Planaltina, Brazil
Cornell University, Ithaca, NY
Project Title:
Project No. 101.
Nitrogen Availability from Legume Crop Residues and Green Manures
to the Succeeding Non-Legume Crops
Project Objectives:
1) To develop procedures for estimating potential for legume crop residues
and green manures to supply nitrogen to succeeding non-legume crops.
2) To estimate the effects of climate and management on the ability of
such organic materials to supply nitrogen to succeeding non-legume
crops.
3) To investigate some of the effects of incorporating roots vs. tops in
the use of organic sources of nitrogen.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Project leader) (Date) (Program Coordinator) (Date)
White: Management Entity Yellow: Program Coordinator Pink: Project Leader
-13-
Project No. 101.
Nitrogen Availability from Legume Crop Residues and Green Manures
to the Succeeding Non-Legume Crops
Dr. W. Shaw Reid/Cornell University
Robert J. Carsky/CPAC, Planaltina, Brazil
Walter T. Bowen/CPAC, Planaltina, Brazil
Allert Suhet/CPAC, Planaltina, Brazil
Introduction
The management of nitrogen for near maximum efficiency remains the most
difficult of all the plant nutrients. Green manures can provide the nitrogen
required by succeeding crops such as maize. For maximum efficiency, the N
mineralization rate from the green manure must approximate that of crop
uptake. There are many legume crops that can be used to supply N, thus a
method is needed to provide an estimate of the N mineralization rate and crop
response to the nitrogen without the necessity of field evaluation of each
legume. The fallow plot technique examined by Bowen is one successful
method. A second method, the buried bag technique has promise for evaluation
of the differences in the total mineralization rates of green manures.
Progress and Achievements
Bowen completed the analyses of the mucuna and soybean mineralization
experiments conducted 1984-85. The conclusions were as follows:
1) Inorganic N in the fallow soil was proportional to N uptake by maize,
provided leaching did not occur. N release from freshly incorporated
mucuna was expressed as Y 25 + 0.81X (r 0.91) for the dry season and Y
- 43 + 0.85X (r 0.97) for wet season; where Y = kg/ha of N mineralized,
-14-
X days after planting maize. About 60% of the N had mineralized from
mucuna after 179 days during the dry season experiment and after 80 days
during the wet season experiment.
2) The uptake of N by maize was proportional to the inorganic N accumulated
in the fallow soil as shown in Figure 1. ( > 'A K L, &) /)
3) The nitrogen accounted for either as aboveground N and residual soil N was
approximately 80% of the inorganic N accumulated in the fallow soil as
shown in Figure 2.
4) The mucuna and soybean residue had very different mineralization rates
(0.32 vs. 0.21 kg/ha/day for mucuna vs. soybean residue during the dry
season experiment) yet inorganic N in the fallow soil adequately predicted
N uptake.
5) The measurement of N mineralization in the fallow soil can be used to
evaluate the ability of various green manures to supply N to the
succeeding maize crop, but leaching, other N not accounted for, will make
the construction of nitrogen budgets difficult.
Carksy buried thin polyethylene bags containing soil and soil mixed with
various legumes from the experimental area at approximately field capacity
within the maize experiment reported by Bouldin et al. (Project 102A). The
relationship between the N in the bags after 3 months and the N uptake by
maize is shown in Figure 3. This method for measuring the relative N
mineralization from green manures looks promising and will receive further
evaluation.
-15-
Work Planned for Next Year
Bowen and Reid will prepare one or more manuscripts for publication.
Research on the buried bag technique will continue along with the evaluation
of a number of legumes for their ability to supply N to succeeding maize
crops.
Publications
Bowen, W. T. 1987. Estimating the nitrogen contribution of legumes to
succeeding maize on an Oxisol in Brazil. Ph.D. Thesis, Cornell
University, January.
200
0 Dry season experiment
-C 0 Wet season experinent
o A Intercroppind experiment
S 150- O
N
z
z
a 100
z
o
0
rr
>
O 50 Y 26 +0.44 X
m (0.060)
r- 0.92
0 I i
0 100 200 300 400
INORGANIC N ACCUMULATED IN FALLOW SOIL (kg/ ha)
Figure 1. Relationship between aboveground nitrogen in maize at harvest and inorganic
nitrogen accumulated in fallow soil at either 83 (dry season experiment), 78
(wet season experiment), or 72 (intercropping experiment) days after planting
maize.
500
400
300 1
200 -
u-L Y =3+0.81 X
O O o(0.054)
Ar 0.98"
100
0 I I
100
200
300
400
-500
600
INORGANIC N ACCUMULATED IN FALLOW SOIL (kg/ha)
Relationship between aboveground nitrogen in maize plus residual soil inorganic
nitrogen (0-120 cm) and inorganic nitrogen accumulated in fallow soil at harvest
(dry season experiment), or either 78 (wet season experiment) or 72 (intercropping
experiment) days after planting maize.
] Dry season experiment
0 Wet season experiment
A Intercropping experiment
Figure 2.
N Uptake in Jorge dry season corn
210-
190-
170-
Maize .150-
N
Uptake'
kg/ha)130-
110-
90-
70-
5in
TREATMENT LEGEND
-feijao de
porco
+ +
0*
0 0
+ mucuna
preta
x crotalaria
juncea
o zornia
latifolia
X SOIL ALONE
I I 1
SI I Al I i I I I I
'I- I I r 1 -
i0 20 30 40 50 60
70 80 90 100 110 20 130 140 150
Initial
N in 0-15 cm layer plus N liberated during 3 months (kg/ha)
Figure 3. Relationship between inorganic N in buried bag after 3 months.plus initial soil
inorganic N and then uptake by maize.
I
0
u
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TROPSOILS
PROJECT STATEMENT
Project Number: 102
Title: Evaluation of Mineralization Potential of Legume
Residues Through Laboratory Incubation Studies
Objectives:
1. To develop and calibrate a laboratory incubation pro-
cedure which will assess the nitrogen mineralization
potential of the soil.
2. To evaluate legume residues as sources of nitrogen i ekg
using incubation/cropping experiments. I
3. To eval te an incubation procedure as a soil test for
nitrogen in field experiments.
Applicability:
These laboratory incubation and screening studies are an
integral component of the overall nitrogen management and re-
search effort. A soil test for nitrogen availability that
would predict reliably the nitrogen supply from soil organic
matter and green manure crops could be used widely for many
soil and climatic conditions. It would reduce the amount of
costlyfield experimental work required to predict fertilizer
nitrogen requirements of cropping systems. If this effort is
successful then the results from laboratory and field experi-
ments already underway could be used directly to translate
results to farmers.
Personnel/Institution: D. R. Bouldin, Cornell University
Allert Rose Suhet, CPAC, EMBRAPA
Jorge Quintana, Cornell University
Research Site: CPAC, Brasilia, Brazil
Date: Original: October, 1984
-20-
TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period: 4/86-4/87 Work P
Project Leader/Institution: Dr. David R. Bouldin/C
Principal Collaborators/Institution:
Jorge Quintana/Cornell University
Allert Suhet/CPAC, Planaltina, Brazil
Research Site(s):
lan Period: 4/87
ornell University
CPAC, Planaltina, Brazil
Project Title:
Project No. 102A.
Evaluation of Mineralization Potential of Legume Residues Through
Laboratory Incubation Studies
Project Objectives:
1) To develop and calibrate a laboratory incubation procedure which will
assess the nitrogen mineralization potential of the soil.
2) To evaluate legume residues as sources of nitrogen using incubation/
cropping experiments.
3) To evaluate an incubation procedure as a soil test for nitrogen in
field experiments.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Date)
(Program Coordinator)
White: Management Entity Yellow: Program Coordinator
White: Management Entity Yellow: Program Coordinator
-4/88
(Project leader)
(Date)
I
Pink: Project Leader
-21-
Project No. 102A.
Evaluation of Mineralization Potential of Legume Residues Through
Laboratory Incubation Studies
Dr. David R. Bouldin/Cornell University
Jorge Quintana/Cornell University
Allert Suhet/CPAC, Planaltina, Brazil
Objective
The objectives of the project are to develop screening procedures for
legume green manures. The two procedures tested here are incubation of
soil samples in the laboratory and measurements of accumulation of mineral
N in fallow plots. 7 d f0 6j 7 2
Progress and Achievements
Four legume green manures were grown during the wet season and their
value as N sources were evaluated under irrigation during the ensuing wet
season by a) measuring accumulation of inorganic N in bare fallow plots,
b) accumulation of N in soil samples taken from the plots and incubated in
the laboratory, and c) by cropping to maize under irrigation. The four
legumes used were: Mucuna [Mucuna aterrima (Piper and Tracy) Merr.],
Crotolaria (Crotolaria paulina Schrank), Jack beans [Canavalia ensitormis
(L.) DC), and Zornia (Zornia latitolia SM).
At the end of the wet season, the bare fallow plots for measuring
accumulation of mineral N were established as follows. One plot which had
grown green manure was left fallow. On a second plot of green manure, the
tops were removed and placed on a third plot which had been fallow during
the preceding wet season. A fourth plot which had been fallow received
1 -22-
nothing. Thus, there were four plots which allowed us to compare the
roots, tops, and the whole plant as nitrogen sources.
In each block, one plot of green manure was. planted to maize and one of
each of four previously fallow plots were treated with 0, 50, 100, or 200
kg/ha fertilizer N. The results are summarized as follows:
1. The yields of corn grain and N in the aboveground dry matter for the
first crop of corn following the fallow and legumes in shown in Table
1. Table 2 lists the value of the green manures as a substitute for
fertilizer nitrogen. Crotolaria, Jack Bean, and Mucuna all replaced
about 150 kg fertilizer N/ha.
2. The mineral N in the fallow plots, 100 days after incorporation of the
green manures, was well correlated with the yields and nitrogen content
of the aboveground dry matter of the maize grown on the corresponding
cropped plots. The results are shown in Figure 1.
3. The mineral N accumulated in the soil samples during 2 weeks of
incubation in the laboratory were correlated with yield and uptake of
maize. The results are shown in Figure 2.
4. The fraction of the total N in the tops of the different legumes
incorporated into the soil varied from about 50% for the Crotolaria to
about 80% or more for the other green manures.
5. Both laboratory incubations and fallow plot sampling are suitable
procedures for screening legume green manures.
Work Planned for Next Year
The data will be summarized and one or more manuscripts prepared for
publication. )}
-23-
Table 1. Grain yield and aboveground N-uptake of corn, dry season, 1986.
Corn Parameters
Treatment Grain yield N-content in aboveground
(Mg/ha) (Kg/ha)
Fertilizer-N
0 Kg/ha 3.74 69
50 Kg/ha 4.60 96
100 Kg/ha 5.57 123
200 Kg/ha 6.72 172
Legume
Zornia 4.72 116
Crotolaria 5.81 149
Jack beans 6.14 169
Mucuna 6.43 159
Table 2. Value of green manure as a substitute for fertilizer nitrogen.
Nitrogen substitution value, kg/ha
Legume First crop (1986)* Second crop (1987)
Zornia 50 10+
Crotolaria 140 50
Jack bean 160 30
Mucuna 170 45
*Average of results with aboveground dry matter, grain yield, and N
content of aboveground dry matter.
+Aboveground dry matter.
-24-
200
150
100
50
50 100 150
200
N in fallow plots Kg/ha
N content of aboveground dry matter of corn plotted against
amount of N accumulated in the corresponding plots kept under
bare fallow. N accumulation under bare fallow or the average
of 62, 77, 98 days after incorporation to a depth of 60 cm.
Fej -Canavalia; Cro Crotalaria; Muc Mucuna; Zor -
Zornia; CK Check (fallow); 50 Mineral N in fallow plus
50 kg of fertilizer; 100 Mineral N in fallow plus 100 kg
fertilizer N.
N
1
*o
Figure 1.
-25-
FEJ
CRO
CK
'ZOR
200
150
100
50
0
MUC
MUC.,0
25 -50
N mineralized in
75
100
125
1 week, microg N/g soil
N. content of aboveground dry matter of maize plotted against
amount of N mineralized in one week from samples taken at the
time of incorporation of the green manure.
Fej -Canavalia; Cro Crotalaria; Muc Mucuna; Zor -
Zornia; CK None.
0
I I I I I
Iz
EO
LC
cD
.L
03
cZ
E
-"O
Figure 2.
-26-
TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period:
Project Leader/Institution:
1986
Work Plan Period:
1987
Stuart D. Klausner/Cornell University
Principal Collaborators/Institution:
A. Suhet/CPAC, Planaltina, Brazil
D. Lathwell/Cornell University
D. Bouldin/Cornell University
Research Site(s):
CPAC, Planaltina, Brazil
Cornell University, Ithaca, NY
Project Title:Project No. 102B.
Estimating N Mineralization by Laboratory Incubation and the
Effect of Soil Sample Disturbance
Project Objectives:
1) To evaluate the effect of soil sample disturbance on N mineralization
from sampling locations differing in soil management practices.
2) To determine the suitability of a laboratory incubation procedure for
estimating N mineralization from soil organic matter and additions of
green manure for corn production.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Date)
(Program Coordinator)
(Date)
White: Management Entity Yellow: Program Coordinator
(Project leader)
Pink: Project Leader
-27-
Project No. 102B.
Estimating N Mineralization by Laboratory Incubation and the Effect of
Soil Sample Disturbance / /
Stuart D. Klausner/Cornell University
A. Suhet/CPAC, Planaltina, Brazil
D. Lathwell/Cornell University
D. Bouldin/Cornell University
Introduction
Laboratory incubation of soil has been used extensively to characterize
N mineralization rates. To date, the validity of soil incubation as a
predictor of N mineralization in the field is questionable.
Most incubation studies in the past involved traditional sampling
procedures where the physical integrity of the soil was destroyed by
mixing, grinding or sieving. Since a portion of the organic N pool is
thought to be in a physically protected state, soils that have remained
relatively undisturbed should have a larger percentage of protected
organic N than those that are tilled frequently. Therefore, the effect of
the physical disruption of soil on the rate of organic matter
decomposition becomes important. In the same regard, a disturbed soil
sample used for incubation purposes may mineralize at a different and more
variable rate than in situ. The value of a laboratory incubation
procedure for predicting N mineralization may be improved if the physical
structure of the sample is maintained.
-28-
Obj ective
The objective of this study was to: 1) evaluate the effect of soil
sample disturbance on N mineralization from sampling locations differing
in soil management practices, and 2) determine the suitability of a
laboratory incubation procedure for estimating N mineralization from soil
organic matter and additions of green manure for corn production.
Methods
Four dark red latosols were sampled. Treatment designations and land
use are as follows: a) 'native' Cerrado (CE) presumably in its natural
state, b) forage grass (FG) sixth year of andropogon, c) corn check (CK)
- third crop of continuous corn, and d) corn following a legume (CL)-
cropping sequence of corn-mucuna-corn.
Disturbed (traditional mixing and compositing) and 'undisturbed'
(cored) soils were sampled at the end of the dry season to a depth of 15
cm. The samples were processed immediately to avoid air drying by
saturating and equilibrating to 0.25 bar water tension on a pressure
membrane apparatus. After equilibration, the aggregate size in the
disturbed sample was reduced to less than 3 mm. All samples were
aerobically incubated at 350C for either a 2, 4, 8 or 12 week period.
Moisture contents were adjusted during incubation.
A second soil sample was taken from each location to determine the
effect of grinding on N mineralization. Air dried soils were sieved to
obtain aggregates of 1-2 mm, and plant residues removed. A subsample was
completely crushed to less than 0.21 mm. Samples were mixed with sand and
water and incubated at 350C for 2 weeks. Inorganic N was analyzed by
steam distillation.
Results
The rate of N mineralization for each location was best described by
linear regression. A test of homogeneity of regression coefficients
(table 1) showed no significant difference in mineralization rate between
the disturbed and undisturbed sample within the native cerrado, continuous
--- -------
corn and corn following mucuna treatments. The andropogon site showed a'
small but significant increase for the undisturbed sample. An analysis of
combined regression coefficients showed mineralization rates in the order
of: corn following mucuna > continuous corn a native cerrado > andropogon
(table 1). It was postulated that the low mineralization rate in the
andropogon site was due to a wide C:N ratio of the large dense root mass
in the soil sample. Mineralization potential in newly cleared cerrado\
soils could be improved with the addition of lime and fertilizer.
Fallow plots, containing the same residual legume treatments (+ and-
mucuna) as the CK and CL sampling sites, were maintained to allow for soil
profile N analysis without N loss due to crop uptake. The data in table 2
suggests that N mineralization in the first year residual mucuna treatment
was not very different from the non-legume check. The absolute difference
between the two is due to N carryover from the previous dry season in the
mucuna treatment. The correlation between N mineralization in incubated
soil with that in the fallow plots showed no meaningful relationship.
Analysis of plant tissue samples and yield has not been completed as of
this date.
The effect of vigorous soil disturbance (grinding) on net N
mineralization is shown in table 3. Nitrogen production during a 2 week
incubation increased appreciably when the soil was finely ground.
-30-
Summary and Conclusions
The data suggests that as lo as some degree of soil aggregation
exists, soil disturbance has no ff n N mineralization. However, more
vigorous disturbance such as grinding caused a significant increase in
mineralization. A mechanism for physically protecting a portion of soil
organic matter against short term N mineralization probably does exist.
The mechanism appears equally effective within the context of normal soil
sampling and preparation but physical protection becomes ineffective when
soil aggregation is completely destroyed.
Laboratory incubation may be effective for qualifying differences in N
mineralization based on soil management practices, but it does not appear
to be a quantitative measure. The predictability of mineralization in the
field was not improved by using an undisturbed soil sample. Laboratory
incubation of a soil planted to corn over-predicted N mineralization in
fallow plots.
Implications
Preliminarily, it appears that normal soil tillage will not increase
the rate of N mineralization by destroying the physical protection of soil
organic matter unless a significant amount of soil aggregates are
destroyed. This implication needs further investigation by conducting
several well designed field experiments.
Table 1. Regression equations and
-31-
decay es of organic N.
dcy so
Sample Decay rate*,kg N ha-lwk-1
Site preparation Equation+ R2 within site between site
CE disturbed Y- 1.4 + 2.39X 91% 3.2 a 3.5 b
undisturbed Y--4.3 + 2.85X 97% 3.8 a
FG disturbed Y- 4.2 + 0.78X 86% 1.2 a 1.5 b
undisturbed Y- 1.4 + 1.24X 80% 1.9 b
CK disturbed Y- 6.1 + 2.69X 93% 4.5 a 5.3 b
undisturbed Y--1.9 + 3.54X 80% 6.0 a
CL disturbed Y- 0.4 + 4.06X 89% 7.0 a 7.9 c
undisturbed Y--0.9 + 5.10X 88% 8.8 a .
*For 0-15 cm. depth and bulk density in table 1. Decay rates followed by
the same letter are not significantly different at the .05 level.
+Y- net N mineralized in ppm, X- time in weeks.
Table 2.
Inorganic N in the top 120 cm. of fallow plots receiving legume
treatments the previous growing season.
Days after corn emergence
Treatment -32 26 57 81 114
----------------kg N/ha------------------
no mucuna 139 137 129 158 195
mucuna 231 259 249 241 308
.I
-32-
Table 3. The effect of soil disturbance on net N mineralization
during a 2 week incubation at 350C.
Sampling Grinding treatment*
site 1-2 mm < 0.21 mm
------------ ppm N --------------
CE 24 a 59 b
FG 20 a 27 b
CK 29 a 40 b
CL 24 a 51 b
* Means followed by the same letter, between grinding treatments, are not
significant @ 5% level.
-33-
TROPSOILS
PROJECT STATEMENT
Project Number: 103
Title: Soil and Crop Management Systems for Acid Savanna
Soils Using Green Manures and Crop Residues as
Nitrogen Sources
Objectives:
1. To develop planting sequences and cropping systems to
mos--effectively use legume and plant residue to supply
their nitrogen requirements.
2. To evaluate the role of legumes and crop residues in
nitrogen cycling anT soil organic matter maintenance.
3. To determine the effects of legumes and crop residues
on long- term solproductivity.
Applicability:
Long-term studies have shown that the nitrogen requirements
of field crops grown in rotation can be supplied by legumes,
manures, mineral fertilizers, or by some combination of them.
Management of organic nitrogen sources is complicated and may
require special cropping sequences and management. Specific
input-output relationships using organic nitrogen relative to
fertilizer nitrogen need to be developed.
The specific need is to develop sources of organic nitrogen
and cropping sequences' o match the nitrogen requirements of
the cropping system with the nitrogen release by the organic
tri-en source. Various_ eumes will be matched_ o cropping
sequences to find the ost effect roving the
required n ior imum on mic cropproduct We
expect to take some of the most promising results to other
regions as the project develops.
Personnel/Institution: David R. Bouldin, Cornell University
D. J. Lathwell, Cornell University
W. T. Bowen, Cornell University
F. Costa, Cornell University
Research Site: CPAC, Brasilia, Brazil
Date: Original: October, 1984
July, 1986
Revised:
-34-
TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period:
Project Leader/institution:
1986
Work Plan Period:
1987
Dr. Douglas J. Lathwell/Cornell University
Principal Collaborators/Institution:
D. R. Bouldin/Cornell University
W. T. Bowen/CPAC, Planaltina, Brazil
F. Costa/Cornell University
Research Site(s):
CPAC, Planaltina, Brazil
Project Title:
Project No. 103.
Soil and Crop Management Systems for Acid Savanna Soils Using
Green Manures and Crop Residues as Nitrogen Sources
Project Objectives:
1) To develop planting sequences and cropping systems to most effectively
use legume and plant residue to supply their nitrogen requirements.
2) To evaluate the role of legumes and crop residues in nitrogen cycling
and soil organic matter maintenance.
3) To determine the effects of legumes and crop residues on long term soil
productivity.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Aulhor(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Date)
(Program Coordinator)
(Date)
t.-i M E Y
White: Management Entity Yellow: Program Coordinator Pink: Project Leader
(Project leader)
I
-35-
Project No. 103
Soil and Crop Management Systems for Acid Savanna Soils Using Green
Manures and Crop Residues as Nitrogen Sources
D. J. Lathwell/Cornell University
D. R. Bouldin/Cornell University
W. T. Bowen/CPAC, Planaltina, Brazil
F. Costa/Cornell University
Accomplishments
Work on this project may be divided into two parts: 1) that done at
CPAC to clarify methods of using green manure legumes so they may be
fitted into soil and crop management systems, and 2) developing an
extrapolation site where results obtained at CPAC might be tested under
different soil and climatic conditions.
Experiments were carried out at CPAC to test differences among green
manure legumes as N sources, and to evaluate placement of the green manure
legumes on N mineralization and accumulation of inorganic N in fallow
soils.
The first study was done to measure the N accumulation of 4 legume
green manures and to measure the rate of inorganic N accumulation in bare
fallow plots following incorporation of the legumes. The four legumes
evaluated were Canavalia insidformes, Crotolaria paulina, Doliches lablab,
and Mucuna aterrina. Q i A 'o c v. /l2 /
The legumes were grown during the wet season of 1985-86 and were
incorporated or surface-placed on the soil at the beginning of the dry
season of 1986. The plots were maintained in bare fallow during the dry
season. Irrigation water was applied to keep the plots moist, but the
N-
-36-
amount applied was kept small enough in any one irrigation to prevent
leaching beyond about 45 cm. Soil samples were taken periodically and
mineral N accumulation was determined.
The bulk density of the soil samples has not yet been determined so
that a quantative summary of the results is not complete. Preliminary
examination of the results indicate the most mineral N was accumulated
under the Canavalia green manure.
In a second experiment, N volatilization from surface placed green
manures during the course of microbial degradation was investigated. A
greenhouse experiment was conducted in which mineral N accumulation was
measured in fallow pots in the green house when Mucuna leaves were
surface-placed or mixed. The decomposition of the surface-placed material
was determined by periodically collecting the residue from the surface and
analyzing for total N. The results were as follows:
After 49 days there was twice as much mineral N in the pots where
Mucuna was mixed as compared to surface-placed Mucuna. In the mixed
treatment, this was about 45% of the organic N added. The total N in the
surface residues decreased rapidly and, after 49 days, was 60% of the
amount added.
Similar studies were made in a field experiment. The results from the
field experiment are currently being analyzed in detail, but preliminary
examination of the data appears to agree with the results obtained int he
green house.
S These results indicate that green manures should be incorporated in
order to prevent possible volatilization losses from surface applications.
An experiment to screen legumes for dry season survival in acid savanna
soils was begun in February 1987. This project has been started under the
i9W~
-37-
auspices of the TROPSOILS CRSP but most of the support for this project
will come from the Special Research Grants of USDA-AID program on factors
limiting symbiotic nitrogen fixation in LDC's. Two different sites at
CPAC of at least 1 ha each were set aside for conducting the planned
experiments. The two sites differ in soil type -- one is a red yellow
latosol (Acrustox) and the other is a dark red latosol (Haplustox) -- and
water table depth. Both sites were cleared of native Cerrado vegetation
several years ago and have been cropped and fertilized with only tillage
varying as a management factor. In late February and early March, both
sites were moldboard plowed, disked, limed (1 t/ha red yellow site; 2 t/ha
dark red site), and fertilized (200 kg/ha of P205 and 120 kg/ha of K20).
Fifty-two different legumes were sown at each site during the period
March 19-21, 1987. Each legume was sown in plots of 6 x 2.4 m size (4 -
rows with 0.6 m between rows) replicated three times at each site. The
CPAC soil microbiology laboratory provided Rhizobium for inoculating all
legume seed at planting. In addition to the 52 legumes, a limited amount
of seed for 35 lines of Canavalia species obtained from CIAT and 7 lines
of Avena sativa selected for good dry season production in southern Brazil
were planted for observation at one site.
Information gathered from these projects will be useful when cropping
systems are developed for acid savanna soils. Efficient use of nitrogen
in cropping systems developed will be a key to their successful adaption
by farmers. Likewise, only green manure legume systems which use them
effectively and economically have a chance to succeed on the farm.
Secondly, we have devoted considerable effort to develop an
extrapolation site in Africa. While possibilities seem to exist none have
materialized as yet. Meanwhile, Dr. Bowen has been stationed in Brazil on
-38-
a temporary basis to assist the program at CPAC and to investigate the
possibility of doing some work on extrapolation of CPAC results to Manaus
in the Amazon Basin of Brazil.
Work Planned for Next Year
The projects at CPAC will be completed within the year except for the
study on dry season survival. The efforts to establish an extrapolation
site will continue. The outcome of these efforts, however, is still to be
realized.
-39-
TROPSOILS
PROJECT STATEMENT
Project Number: 104
Title: Fertilizer Nitrogen movement in Cerrado Soils
Objectives:
1. Develop a comprehensive description in simulationLmodel
orm or nitrogen movement'-"a-htransformation in cropped
soils of the Cerrado.
2. Use the model as a guide in interpreting and designing
field experiments to increase understanding of nitrogen
fertilizer fate in Cerrado soils.
3. Use the model to develop nitrogen management recommend-
ations for other ac!id savanna regions.
Applicability:
Quantitative description of nitrogen behavior in agricul-
tural systems is a strong component of Cornell's continuing
research program. Nitrogen management in Cerrado soils has
been a primary focus of Cornell/EMBRAPA research efforts
during the first three years of this program. Nitrogen
simulation modeling is currently in progress as a component
of this research. This effort serves to integrate empirical
and theoretical information from the nitrogen program as well
as several other disciplines, including soil physics, micro-
meteorology and crop physiology. Its goal is to use this
information to summarize, test and extend our knowledge of
nitrogen behavior in agricultural systems to other acid
savanna regions.
Personnel/Institution: S. J. Riha, Cornell University
Elias de Freitas, CPAC, EMBRAPA
Imo Buttler, Cornell University
Deanna Osmund, Cornell University
Research Site: CPAC, Brasilia, Brazil
Date: Original: October, 1984
July, 1986
Revised:
-40-
TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period: 1986 Work Plan Period: 1987
Project Leader/Institution: Dr. Susan J. Riha/Cornell University
Principal Collaborators/Institution:
Dr. R. J. Wagenet/Cornell University
Dr. Elias Freitas/CPAC, Planaltina, Brazil
Dr. Allert Suhet/CPAC, Planaltina, Brazil
Research Site(s):
CPAC, Planaltina, Brazil
Cornell University, Ithaca, NY
Project Title:
Project No. 104.
Fertilizer Nitrogen Movement in Cerrado Soils
Project Objectives:
1) Develop a comprehensive description in simulation model form of
nitrogen movement and transformation in cropped soils of the Cerrado.
2) Use the model of (1) as a guide in interpreting previous studies and in
designing further field experiments to increase understanding of
nitrogen fertilizer fate in Cerrado soils.
3 D velop a simplified model of nitrogen fertilizer fate in Cerrado soils
hat will be useful in guiding nitrogen management programs.
progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report 'ven)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Project leader) (Date) (Program Coordinator) (Date)
Ml-W ll -A
White: Management Entity Yellow: Program Coordinator Pink: Project Leader
-41-
Project No. 104.
Fertilizer Nitrogen Movement in Cerrado Soils
Dr. Susan J. Riha/Cornell University
Dr. R. J. Wagenet/Cornell University
Dr. Elias Freitas/CPAC, Planaltina, Brazil
Dr. Allert Suhet/CPAC, Planaltina, Brazil
Progress and Achievements
Objective 1: A general purpose simulation model (GAPS) of water
movement in the soil-plant-atmospher has been developed. The program
contains user friendly input/output routines and allows the user to select
from procedures that simulate various components of the soil-plant-
atmosphere system. In addition, the user can choose from a variety of
procedures representing the same component of the system (such as ETP or
soil-water flow routines). Procedures can be selected on the basis of the
data available to the user, the particular modeling objective, or the
level of complexity desired. Extensive documentation of the simulation
procedures accompanies the software package. The program structure allows
the user to incorporate additional procedures into the program. We are
currently in the process of developing procedures for nitrogen
transformation and nitrogen-soil particle surface reactions.
Objective 2: We have been in the process of compiling both the
necessary input data and results of previous CPAC field experiments to run
and evaluate our current nitrogen simulation model. We have initiated a
field experiment at the CPAC to determine the effects of varying rainfall
on nitrogen transformation and movement in highly weathered Oxisols
planted to corn. This experiment is being conducted during the dry season
-42-
so water input can be controlled and manipulated through the use of a
line-source sprinkler.
Objective 3: A comprehensive literature review of nitrogen
fertilization of maize in tropical regions has been initiated and is near
completion. Additionally, we have decided to use a nitrogen partitioning
model similar to one developed by C. T. DeWit, and linked to a simple
expert system as a guide for nitrogen management programs.
Work Planned for Next Year
Objective 1: We plan to fully incorporate nitrogen transformation and
transport simulation routines into the GAPS model and complete all
documentation associated with these routines.
Objective 2: We plan to complete field experiments initiated in the
1987 dry season to determine the effects of rainfall intensity, nitrogen
application rates, and soil chemical properties on nitrate movement and
plant nitrogen uptake. We will use the results of this experiment to
further test our nitrogen simulation model.
Objective 3: We plan to develop a first-version of a partitioning type
nitrogen management model.
Meetings Attended
Buttler, Imo and Susan Riha. Aug. 13-20, 1986. Hamburg, FDR. A
simulation model of nitrogen transporations and transport in acid
savanna soils: Model development. International Soil Science
Meetings.
-43-
Buttler, I., S. J. Riha and 0. M. Bicakci. Nov. 30-Dec 5, 1986. New
Orleans, USA. User friendly software package to generate simulation
models of the soil-plant-atmosphere system. Annual Mtgs. of ASA.
Publications
Buttler, I. and S. J. Riha. 1987. A general purpose simulation model of
water movement with soil-plant-atmosphere (submitted to Applied
Agricultural Research Journal).
-44-
TROPSOILS
PROJECT STATEMENT
Project Number: 105
Title: Ion Movement in Cerrado Soils: The Effects of Gypsum
Amendment on the Charge Properties of the Soils
Objectives:
1. To estimate the sulfate and calcium retention capacity
of the A and B horizons of a dark red latosol and a
red yellow latosol from Brazil.
2. To tuJ e effect of sulfate absorption on the devel-
opmenof charges in the soil.
Applicability:
As soils are brought into cultivation and various soil
amendments are added to them, their productivity changes and
their chemical characteristics likewise change. This is
especially true of Oxisols where much of their charge charac-
teristics are variable depending on degree of weathering and
soil pH. The character of these changes and their perform-
ance likely influences the long term behavior of these soils.
The present research will supply data about the retention
characteristics and charge properties of these soils as a way
to get an understanding of some of the different variables
necessary for modeling ion movement in Oxisols.
Personnel/Institution: M. McBride, Cornell University
E. Marcano-Martinez, Cornell
University
Research Site: CPAC, Brasillia, Brazil
Date: Original: August, 1985
July, 1986
Revised:
-45-
TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period: 1986 Work Plan Period: 1987
Project Leader/Institution: Dr. Murray B. McBride/Cornell University
Principal Collaborators/Institution:
Eugenio Marcano-Martinez/Cornell University
Research Site(s):
CPAC, Planaltina, Brazil
Cornell University, Ithaca, NY
Project Title:
Project No. 105.
Ion Movement in Cerrado Soils: The Effects of Gypsum Amendment on
the Charge Properties of the Soils
Project Objectives:
1) To estimate the sulfate and calcium retention capacity of the A and B
horizons of a dark red latosol and a red yellow latosol from Brazil.
2) To study the effect of sulfate adsorption on the development of charge
in the soil.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Project leader) (Date) (Program Coordinator) (Date)
ME-l)-HS-A
White: Management Entity Yellow: Program Coordinator Pink: Project Leader
-46-
Project No. 105.
Ion Movement in Cerrado Soils: The Effects of Gypsum Amendment on the
Charge Properties of the Soils
Murray B. McBride/Cornell University
Eugenio Marcano-Martinez/Cornell University
Introduction
The application of gypsum as an amendment to overcome deleterious
effects of soil acidity has been suggested by some authors (Ritchey et
al., 1980; Reeve and Sumner, 1972). The greater mobility of gypsum with
respect to lime makes the former a better source of Ca to promote root
growth in the lower layers of the soil.
The rate of Ca moment is dependent on the relative retention and
reactivity of the accompanying anion and on the charge of the soil
minerals. By studying the adsorption of Ca and S04, and the chemical
processes affecting their retention, we can understand some of the factors
that determine gypsum fate and efficiency in these soils.
Objective
1. To estimate the sulfate and calcium retention capacity of the A and B
horizons of a dark red Acrustox (DRA and DRB) and a red yellow Acrustox
(RYA and RYB).
2. To study the effect of sulfate and calcium adsorption on the
development of charge in the soils.
Procedure
Ca and S04 retention were studied by adsorption isotherms of CaC12 and
-47-
K2S04 in a 0.01N KC1 medium using a soil solution ratio of 1:10, in all
four soils. CaS04 adsorption was also studied in a similar way but only
in both A horizons.
Results
Ca adsorption isotherms followed an almost linear behavior and
conformed to the Freundlich equation. These results are shown in Fig. 1
for the DRA. When Ca was applied together with S04 (gypsum) there was a
significantly higher adsorption of Ca above an equilibrium concentration
of 0.04 mM. Precipitation as CaS04.2H20 cannot explain these results
because the solubility product of this compound was not exceeded.
S04 adsorption isotherms had a Langmuir shape in both cases (K2S04 and
CaS04), but the best fit was given by a Freundlich equation. S04
adsorption was also higher when gypsum was applied than when K2S04 was
used as the adsorbate as shown in Fig. 2 for the DRA.
Ca adsorption was not significantly different between the A and B
horizons within each soil; this is probably due to the higher
concentration of A13+ in the A horizon (see previous progress report).
This strongly adsorbed A13+ would block the negative sites.
S04 was retained more strongly in the B horizons than in the A horizons
and the dark red Acrustox showed a significantly higher retention than the
red yellow. This can be attributed to the higher iron content in the
first soil. The CBD-extractable Fe levels were 7.82 and 6.37% for the DRA
and DRB, respectively, and 4.00 and 3.73% for RYA and RYB, respectively.
Ca adsorption did not affect the pH of the soil nor increase the
retention of C1'. On the other hand, S04 adsorption increased the pH of
the solution almost linearly, this effect being more noticeable in the B
-48-
horizons and when S04 was applied as K2S04. The retention of K+ was also
affected by the adsorption of S04 as shown in Fig. 3 for adsorption of
K2S04. Application of CaS04 also caused an increase in the cation
retention which was less linear than in the previous case. The increase
in cation retention may be due in part to an increase in pH that makes the
soil surface more negative due to the pH-dependent charge of these soils
(see previous progress report); this could have been the case for both B
horizons where the increase in pH might have caused a significant change
in negative charge. In the A horizon, the rise in pH was smaller
(probably because of a buffer effect of organic matter) and was not enough
to cause a significant increase in negative charge. Therefore, the higher
K+ retention is attributed to creation of negative charges upon S04
adsorption by a ligand exchange mechanism as shown in the following
reaction:
0H2 OH2
Fe OH + S04 ---> Fe S + OH'
OH S04
This reaction can also explain the higher pH resulting from S04
adsorption.
The maximum Ca adsorption measured in this experiment represented
between 55 and 88% of the total CEC of the soil at its natural pH; thus,
Ca adsorption could be explained by a cation exchange mechanism. S04
adsorption for both K2S04 and CaS04 treatments was higher than the anion
exchange capacity of the soil measured by Cl" retention, on a equivalent
basis. This implies that S04 adsorbs more preferentially than Cl- in
these soils, probably by the ligand exchange mechanism shown above.
-49-
Conclusions
Sulfate and calcium retention are dependent on the equilibrium
concentration of these ions in solution. While calcium retention was
almost linearly dependent on Ca concentration, sulfate tended to approach
a maximum adsorption which was not reached within the experimental range
of S04 additions. Retention of both ions conformed to the Freundlich
equation. Gypsum application caused a greater Ca and SO4 adsorption,
probably due to ion pair adsorption.
Ca was adsorbed as an exchangeable cation without affecting the pH of
the soil nor the total surface positive charge. Sulfate was adsorbed by a
ligand exchange mechanism that caused displacement of hydroxyls from the
surface, raising the pH of the soil solution. At the same time, S04
caused an increase in the total negative charge.
Implications
Data from this study support the specific adsorption mechanism by which
sulfate is adsorbed in oxides. This mechanism affects the balance of
charge in the soil and can be used as a way to reduce cation leaching.
Application of gypsum increases the retention of both Ca and S04 by the
soil, as well as the total CEC. This can have some practical use because
of the importance of these nutrients.
Work Planned for Next Year
The completion of this project coincides with Eugenio Marcano-Martinez
finishing his M.S. thesis in June, 1987.
-50-
8
7 CaS04
6-
5-
4 -
CaC12
3
2
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
EQUILIBRIUM CONCENTRATION (mM)
Figure 1. Calcium adsorption isotherms in the dark red Acrustox.
-51-
CD CaS04
6
E
E 5-
O 4/
K204
m
0 2
< 1
0- i ,,I I I
0.0 0.5 1.0 1.5 2.0 2.5 3.0
EQUILIBRIUM CONCENTRATION (mM)
Figure 2. Sulfate adsorption isotherms in the dark red Acrustox.
-52-
0 1 2 3 4 5 6 7
S0" ADSORBED (mmol/kg)
Effect of sulfate adsorption on the K+ retention
capacity of the soils.
11
E
E
UJ
CO
o
Qr
Figure 3.
-53-
TROPSOILS
PROJECT STATEMENT
Project Number: 106
Title: Ion Movement in Cerrado Soils: The effects of
Inorganic and Organic Amendments on Sulfur
Availability
Objectives:
1. To determine the effects of adding inorganic and
organic amendments to a Cerrado oxisol in the absence
or presence of plants on:-
a. the adsorption capacity of the soil by depth
b. the movement of sulfur into the subsoil
2. To describe the characteristics and rates of sulfur
mineralization in a Cerrado oxisol in response to
additions of several organic and fertilizer sources.
Applicability:
Examining the effects of inorganic and organic amendments
on sulfur availability for plant growth will provide addi-
tional information for the quantitative model for ion dis-
tribution in Cerrado soils. The additional components that
will be addressed are:
1. The effects of inorganic (i.e. besides gypsum) and or-
ganic amendments
2. The effects of plant growth on sulfur distribution
3. The contribution of sulfate mineralization to sulfate
soil levels and to sulfate distribution
By combining soil chemistry and plant nutrition components
with the soil physics and modeling parameters, a better
understanding of acid savanna soils should result. In addi-
tion, by focusing on sulfur availability with an emphasis on
the effects of organic additions, this project is linked to
Cornell's green manure nitrogen project in Brazil.
Personnel/Institution: J. M. Duxbury, Cornell University
P. P. Motavalli, Cornell University
Research Site: CPAC, Brasilia, Brazil
Date: Original: August, 1985
-54-
TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period:
Project Leader/institution:
1986
Work Plan Period:
1987
Dr. John M. Duxbury/Cornell University
Principal Collaborators/Institution:
P. P. Motavalli/Cornell University
W. Goedert/CPAC, Planaltina, Brazil
Research Site(s):
CPAC, Planaltina, Brazil
Cornell University, Ithaca, NY
Project Title:
Project No. 106.
Ion Movement in Cerrado Soils: The Effects of Inorganic and
Organic Amendments on Sulfur (S) Availability
Project Objectives:
1) To determine the effects of selected inorganic and organic amendments
to Cerrado soils on sulfur adsorption capacity and movement into the
subsoil.
2) To describe the characteristics and rates of sulfur mineralization in
Cerrado soils and its response to additions of fertilizer and organic
amendments.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Date)
(Program Coordinator)
(Date)
Yellow: Program Coordinator Pink: Project Leader
(Project leader)
__
White: Management Entity
-55-
Project No. 106.
Ion Movement in Cerrado Soils: The Effects of Inorganic and Organic
Amendments on Sulfur (S) Availability
Dr. John M. Duxbury/Cornell University
P. P. Motavalli/Cornell University
W. Goedert/CPAC, Planaltina, Brazil
Introduction
Oxisols of the Cerrado are potentially deficient in sulfur, although
the use of ordinary superphosphate and gypsum has largely prevented
deficiencies from occurring to date. Recommended management practices for
these acid savanna soils include large additions of phosphorus and lime,
both of which can affect sulfate adsorption and mobility in the soil
profile. Recent work by Cornell TROPSOILS researchers has shown that
legumes, such as mucuna and crotalaria, grown as green manures, supply
substantial amounts of nitrogen to succeeding crops. The green manures
would also be expected to supply sulfur through mineralization processes
and they could further influence sulfur availability by alteration of soil
chemical properties.
Objectives
The purpose of our study is to evaluate the effects of inorganic (Ca,
P, and S) and organic (green manures) amendments on three components of
sulfur availability, namely adsorption reactions, movement in the soil
profile, and mineralization of organic sulfur.
-56-
Progress and Achievements
A. Laboratory Studies of Sulfur Mineralization and Sulfate Adsorption
An incubation experiment was performed using the A and B horizons of a
dark red latosol and a red-yellow latosol in order to evaluate sulfate
adsorption over time as affected by additions of a green manure (alfalfa)
and an organic anion (Oxalate). The experimental design allowed us to
separate the effects of pH and organic additions on sulfate adsorption,
and to measure sulfur mineralization. Soils were incubated for 0, 8, 15,
29, and 63 days. At each time, mineralization was measured using
distilled water and 200 mg P (KH2PO4)/L extracting solutions, and sulfate
adsorption was evaluated at levels of 0, 120, and 240 mg S04/L in 0.01 M
KC1. One group of alfalfa and oxalate-treated soils had pH adjusted to
the pH level of the control in order to examine pH effects on sulfate
adsorption.
Addition of alfalfa caused soil pH to rise immediately by about 1 pH
unit, whereas oxalate addition depressed pH from 0.5 to 1.0 pH units.
Soil pH continued to rise upon incubation with alfalfa to about pH 7.5 to
8.0, while the pH of oxalate-treated soils gradually rose to that of the
unamended soils (4.4 to 5.3). As shown in Fig. 1, addition of alfalfa
immediately reduced adsorption of S04 relative to the unamended soil and
this effect was maintained even after adjustment of pH to that of the
control soil. The effect of alfalfa on S04 adsorption persisted
throughout the 63-day incubation period. Oxalate addition also tended to
reduce adsorption of S04 but the magnitude of the reduction was initially
sensitive to pH and the effect was transient. The B horizons of both
soils adsorbed more sulfate than the A horizons, perhaps due to higher
native organic matter levels in the A horizons.
-57-
The range of sulfur mineralization after alfalfa was added was between
9.2 and 36.7 pg SO4/g soil/week. The patterns of S mineralization varied
both between the soils and soil horizons (Fig. 2).
B. Sulfate Movement in Long-Term Experiments on Dark-Red Latosols at CPAC
Three year P source experiment: Soil samples were collected to 120 cm
from one repetition of plots which had received various levels of P and S
fertilizers. The soils were extracted with a 200 ppm KH2P04 solution and
sulfate determined by ion chromatography. The results are shown in Fig.
3. Without added P, plant growth was poor, uptake of S was low, and
substantial amounts of sulfate were found in the upper 60 cm. With P
addition and much better plant growth, soil sulfate levels were reduced.
Five year gypsum experiment: Three repetitions of plots which had
received gypsum additions (0, 107, 306, and 427 kg S/ha) in 1979 were
sampled to a depth of 120 cm. All plots except those receiving 306 kg
S/ha had also received 4.7 Mt lime/ha. Extractable sulfate levels were
determined as previously described and are shown in Fig. 4. The higher
rates of gypsum addition resulted in more downward movement of sulfate,
which also appeared to be accentuated by lime addition. A significant
correlation between extractable sulfate and Al was found.
Ten year green manure experiment: Different green manure crops
(mucuna/crotalaria, rice, and natural vegetation) were grown three out of
the 10 years. Crop residue was either removed or incorporated and two
levels of lime (1 or 4 Mt/ha) had been applied the first year of the
experiment. Approximately 500 kg S/ha, contained in simple
superphosphate, had been applied over the ten year period. Levels of
phosphate extractable sulfate in the soil profile are shown in Fig. 4.
-58-
Downward movement of sulfate was generally greater at the higher lime
rate, but there was no effect of incorporation of crop residue on sulfate
movement.
C. Field Evaluation of Green Manures as a Sulfur Source
A field experiment was begun on a dark red latosol at CPAC in November
1986. Treatments consisted of an incomplete factorial design with three
rates of gypsum (0, 60, and 600 kg S/ha), three green manure treatments
(0, 10 Mt/ha Canavalia ensiformis, 10 Mt/ha Panicum maxicum on a dry
weight basis), with and without lime treatment (0 and 3.4 Mt/ha), and with
and without crop treatment. Only unplanted plots had the 0 lime
treatment. Plant material for green manure treatments was harvested from
adjacent areas and passed through a forage chopper before being spread
uniformly over the treated plots. There were three replications of each
treatment. A blanket application of 65 kg N/ha, 200 kg P205/ha, and 150
kg K20/ha was made to the experimental area and all plots were rototilled.
Corn (Zea mays L.) was planted on December 2, 1986 and an additional 165
kg N/ha was split into two applications later in the season.
Soil and plant samples were collected at regular intervals throughout
the growing season. Preliminary results of extractable sulfate in soils
from the bare plots showed that liming appeared to improve sulfur
mineralization, especially in the Panicum treatment, and perhaps also
promoted downward movement of sulfate. The experiment was harvested in
early April 1987 and results will be forthcoming shortly.
-59-
Conclusions
Soil sampling of several long-term experiments at CPAC confirmed that
both lime and phosphate additions to Cerrado Oxisols appear to promote
downward movement of S04 in the soil profile. This could eventually lead
to leaching of S04 from the profile and to S deficiencies when plant
rooting depth is not deep.
The laboratory incubation studies showed that additions of plant
material to Oxisols can be expected to reduce S04 adsorption. Several
mechanisms, including effects on soil pH, surface change, and extractable
Al, may be involved in this process. Sulfur also mineralized readily whei
n
alfalfa was added to these soils.
Work Planned for Next Year /l
The field experiment ith green manures will be continued for the next
two growing seasons Additional Panicum and Canavalia will be applied,
--------------------
but no further gypsum will be added.
Further work on sulfur mineralization will be performed using two
different laboratory incubation procedures. In one procedure, soil
samples will be carried through the entire incubation period with leaching
at prescribed times, whereas soil samples will be discarded after leaching
in the other procedure. Several researchers have found large differences
in S mineralization rates measured by these two procedures. In none of
these reports, however, did the authors consider the possibility that
chemical processes could also be responsible for S04 release. Soil
sterilization and/or effects of equilibration time on S04 release will be
used to differentiate between chemical and biological mechanism of S04
release. The laboratory studies will utilize the dark red latosol from
-60-
the field experiment area and this will be amended with several rates of
Canavalia and panicum plant material. Changes in soil pH and exchangeable
Al during the incubation will also be followed.
Publications
Motavalli, P. P. and J. M. Duxbury. 1987. The effects of additions of
alfalfa and oxalate on sulfur mineralization and sulfate adsorption in
latosols of the Cerrado. Submitted to Revista Brasilera de Cienca do
Solo.
-61-
120
0 DAYS
SO~ ALFALFA pH ADJUSTED
100 OXALATE)
O ALFALFA pH NOT
80 OXALATE )ADJUSTED
60
40
20
-20
63 DAYS
100
80
40 -
20
-20 I I I
LEA LEB LVA LVB
Figure 1. Relative adsorption (untreated control soil- 100%) of
sulfate after incubation of the A and B horizon of a dark
red latosol (LE) and a red-yellow latosol (LV) with alfalfa
(5 g/100 g soil) or oxalace (10 mg/100 g soil). Adsorption
measurements were made without pH adjustments and after
adjustment to that of the unamended soil. Data represents
the mean of values obtained for equilibration with solutions
containing 120 and 240 mg SO4/L.
-62-
200
LEA LEB
157 T 0 ALFALFA
114 CONTROL
114 -
71
28
-15
uU 200 LVA LVB
I-.
L1 157
-J
114
71
28
-15
0 10 20 30 40 50 60 70 10 20 30 40 50 60 70
TIME (days)
Figure 2. Mineralization of sulfur in A and B horizons of dark red (LE)
and red yellow (LV) latosols amended with alfalfa (5 g/100 g
soil).
\
\
-63-
N P S
NPS
kg/ha--
0 000
-*- 72 52 0
--'0- 72 52 64
--A-- 72 0 64
0. *-
160
140
120
100
80
60
40
20
0
60
90
30
DEPTH (cm)
Figure 3. Effect of 3 years of N, P, and S fertilizer treatments in
phosphate extractable sulfate in a red latosol.
SI I
I ON
Y
140
120 S Ca
-\ kg/ha--
100 A- 0 4700
S! \ \ --A- 107 4700
W 80 306 0
/ \ -0- 427 4700
~I -I
S 60 \
40-
20 -.
0 *
0 30 60 90 120
SOIL DEPTH (cm)
Figure 4. Phosphate extractable sulfate from a red latosol 7 years
after amendment with gypsum and lime.
-65-
O 1 Mt Ca/ha crop residue Incorporate
lus P fertilizer.
0 1 Mt CaIha crop rosalue removed,
* 4MtCa/ha MJ P ferter
' 1 M' Cha 1'
V 4 Mt Ca/lh
0 1 M Ca/ha
* 4 Mt Calha
crop resldue Incorporate
pklu P fertilizer
crop residue removed,
plus P fertilizer
30 60 90 120
SOIL DEPTH (cm)
Figure 5. Effect of 7 years of cropping interspersed with 3 years of
green manuring on phosphate extractable sulfate in a red
latosol. Green manure crops were natural vegetation (A),
mucuna/crotalaria (B), and rice (C). A total of 500 kg S/ha
was added in simple superphosphate over the 10 yr period
except for the unfertilized treatment in (A).
-66-
TROPSOILS
PROJECT STATEMENT
Project Number: 107
Title: Crop Water Requirements in Cerrados Soils
Objectives:
1. Determine the components of the water budget in cropped
Cerrados soils.
2. Quantify the effects of management practices upon
water availability and soil-water movement and their
impact upon crop yield, evapotranspiration, and
transient soil water regimes.
3. Develop and test a simplified model relating water use
to crop yield, constructed to be useful in extending
experimental results to other locations.
Applicability:
A knowledge of the influence of evapotranspiration and soil
water management on plant growth is important to agronomic
and economic evaluation of irrigation development and for
comparison of the relative benefits of water used for irri-
gation compared to other water uses. However, this rela-
tionship is quite complex and interrelated to many other
factors of which soil fertility and climate are quite
important. The work proposed here will develop a physically-
based, dynamic model to predict yield of several Cerrados
crops as related to water use. In the process, the
sensitivity of the model to soil, climate and plant input
parameters will be determined, and general guidance produced
for future field studies. The model should be immediately
useful in estimating the potential benefits of irrigation,
will identify differences in yield response on different
soils and in wet or dry years, and will produce simulations
useful in economic analysis of irrigation programs. Addi-
tionally, the model will be amenable to future modification
to reflect the influence of gypsum or nitrogen amendments
upon crop growth.
Personnel/Institution: S. J. Riha, Cornell University
R. J. Wagenet, Cornell University
Elias de Freitas, (CPAC), Planaltina,
Brazil
Areovaldo Luchiari, (CPAC), Cornell
University
Imo Buttler, Cornell University
Research Site: CPAC, Brasilia, Brazil
Date: Original: October. IQ^A
-67-
TROPSOILS
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113.
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period:
Project Leader/Institution:
1986
Work Plan Period:
1987
Dr. Susan J. Riha/Cornell University
Principal Collaborators/Institution:
Dr. R. J. Wagenet/Cornell University
Dr. Elias Freitas/CPAC, Planaltina, Brazil
Research Site(s):
CPAC, Planaltina, Brazil
Cornell University, Ithaca, NY
Project Title:
Project No. 107.
Crop Water Requirements in Cerrado Soils
Project Objectives:
1) Determine the components of the water budget in cropped
2) Quantify the effect of soil tillage practices upon water availability
and sil-water movement and their impact upon crop yield,
evapotranspiration, and transient soil water regimes in a manner useful
to irrigation and crop production programs.
3) Devlp d test a simplified model relating water use to crop yield,
constructed to be useful in extending experimental results to other
locations.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
(Date)
(Program Coordinator)
(Date)
ME4)9-85-A
White: Management Entity Yellow: Program Coordinator
Cerrado soils.
(Project leader)
Pink: Project Leader
-68-
Project No. 107.
Crop Water Requirements in Cerrado Soils
Dr. Susan J. Riha/Cornell University
Dr. R. J. Wagenet/Cornell University
Dr. Elias Freitas/CPAC, Planaltina, Brazil
Progress and Achievements
The progress of this project has been greatly helped by the enrollment
of Ariovaldo Luchiari as a graduate student of Dr. Susan Riha's. Mr.
Luchiari conducted several experiments over a number of years with
irrigated wheat that will allow us to test several models for potential
use in predicting wheat water requirements in the Cerrados. This year Mr.
Luchiari visited with Dr. John Norman at the University of Nebraska to
learn how to use a comprehensive crop canopy model (CUPID) he has
developed.
Work Planned for Next Year
We plan to evaluate 3 models for predicting water requirements of
irrigated wheat in the Cerrados. These models differ in their degree of
complexity and amount of input data they require.
1) The Priestly-Taylor equation for estimating evapotranspiration is the
simplest model we will evaluate. The Priestly-Taylor coefficient will
be determined and its relation to published values from other areas, as
well as its variability and predictability, will be explored.
2) The Penman-Monteith equation will be used to predict transpiration.
The canopy resistance term will be determined and its variability
explored in relation to leaf area, stress, and leaf stomatal
resistance.
-69-
3) CUPID, a model that considers heat, vapor, and momentum transport
within the canopy, will be used to predict transpiration. Its
predictions will be compared to the other, simpler models as well as to
other field measurements.
-70-
TROPSOILS
PROJECT STATEMENT
Project Number: 108
Title: Characterization of Root-Restricting Zones in
Cerrados Soils
Objectives:
1. Diagnose soil and management conditions that result in
tEh~eevelopment 'ufroot-restricting zones in Cerrados
soils subjected to continuous annual cropping.
2. Determine the effects of root-restricting zones on
soll-water dnnamcs in the field and the resulting im-
plications for crop yields and soil erosion.
3. Identify management practices which limit the formation
of root-restricting zones.
Applicability:
Physical characteristics of medium and fine textured Cer-
rados Oxisols have generally been considered excellent for
mechanized agriculture. However, deleterious physical situ-
ations are developing in areas subjected to continuous annual
cropping. Shallow rooting in some well drained Oxisols with
improved profile chemical status, has been attributed to soil
strength, reduced macroporosity, and poor aeration rather
S than aluminum toxicity or low nutrient'status of the subsoil.
As a consequence, investments in lime and fertilizer may
not be utilized to a maximum extent. As a result of tillage
pans, the available subsoil moisture is not accessible. The
occurrence of severe plant moisture stress may be the most
serious consequence of soil compaction for rainfed
agriculture in the Cerrados.
Thesoil conditions in root-restricting zones should be
further characterized so that the actual factors'"limitin'
notified. An attempt should be
made to identify the natural factors or induced mechanical
and chemical processes that result in the formation of root-
restricting zones. This should furnish keys to better
management practices for avoidance and/or correction of the
problem.
Personnel/Institution: Eric R. Stoner, Cornell University
Elias de Freitas, EMBRAPA/CPAC
Victor Snyder, Cornell University
Research Site: CPAC, Brasilia, Brazil
Date: Original: October, 1984
-71-
Management Entity, Box 7113, Raleigh, North Carolina 27695-7113
ANNUAL PROGRESS REPORT AND WORK PLAN
Progress Report Period:
Project Leader/Institution:
1986
Work Plan Period:
1987
Dr. Eric R. Stoner/CPAC, Planaltina, Brazil
Principal Collaborators/Institution:
Dr. Elias Freitas/CPAC, Planaltina, Brazil
Research Site(s):
CPAC, Planaltina, Brazil
Project Title:
Project No. 108.
Characterization of Root-Restricting Zones in Cerrados Soils
Project Objectives:
1) Diagnose soil and management conditions that result in the development
of root-restricting zones in Cerrados soils subjected to continuous
annual cropping.
2) Determine the effects of root-restricting zones on soil-water dynamics
in the field and the resulting implications for crop yields and soil
erosion.
3) Identify management practices which limit the
restricting zones.
Progress and Achievements: (Report on attached form)
Meetings Attended: (Name, date, location, title of report given)
Manuscripts in Preparation or Published: (Author(s), title, journal)
Work Planned for Next Year: (Report on attached form)
Signatures:
formation
(Date)
(Program Coordinator)
White: Management Entity Yellow: Program Coordinator Pink: Project Leader
TROPSOILS
of root-
(Project leader)
(Date)
-- --
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Project No. 108.
Characterization of Root-Restricting Zones in Cerrados Soils
Dr. Eric R. Stoner/CPAC, Planaltina, Brazil
Dr. Elias Freitas/CPAC, Planaltina, Brazil
Introduction
Concern over the effects of excessive traditional disc tillage in
monoculture cropping systems devoid of rotational or fallow periods, has
been growing among farmers and researchers in the Cerrado region.
Researchers at Brazil's National Soybean Research Center have noticed
unexplained decreases in soybean yields in corrected Cerrado soils after
ten years of monocrop production, even with the use of improved varieties.
The occurrence of reduced yields is often accompanied by farmer
observations of superficial root development in soils which have had
adequate fertilizer applications and enough time to ameliorate subsoil
acidity.
The pressure packing action of disc tillage implements is well known to
be capable of greatly increasing the bulk density of frequently-tilled
soils, especially when these soils are tilled at high moisture contents as
is often the practice in tillage management of Cerrado Oxisols. This
greenhouse experiment was conducted as a complement to the study of root
restricting zones in Cerrado soils in an attempt to observe the severity
of root restriction of several important crop plants under controlled soil
density and moisture conditions.
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Objectives
-For Cerrado latosols of varying clay content: a) identify which of the
major crop arietie commonly grown in the Cerrado region are most
susceptible to mechanical impedance of root development; and b) determine
the critical soil bulk density levels beyond which little root penetration
can be expected for these crops.
Procedures
Bulk soil samples of dark red latosols were collected within the
Federal District from surface soils of sandy loam (16% clay content) and
clayey (53% and 70% clay content) texture classes. Fertilizer and lime
were added according to recommendations based on soil test levels. Rigid
10 cm dia by 10 cm height PVC cylinders were prepared as pots with gauze
bottoms to hold the soil in place and interior walls covered with paraffin
to avoid root exploration of side walls. An appropriate amount of soil
placed in the pots was compacted with a hydraulic press to a depth of 5 cm
to attain the desired density levels of 1.0, 1.1, 1.2, 1.3, and 1.4 Mg
m-3. Three to 4 cm of loose soil were placed on top of the compacted
layer for seed placement and to assure uniform seedling development among
the compacted treatments.
Frequently planted crop v ~it s in the Cerrado region were seeded
three to a plot (thinned to two): maize (Zea mays, var. Cargill 111),
soybean (Glycine max, var. Doko), wheat (Triticum aestivum, var. BR12),
and beans (Phaseolus vulgaris, var. Carioquinha). Four replications were
made in a randomized block design.
A system of sub-irrigation consisting of a 2 m by 3 m gravel and sand
bed tension table was de ised to maintain a constant moisture tension near
field capacity throughout the one month growing period.
\Y 71d T^ ^ ^u^ ^i\ ^
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Plant roots were harvested by first washing and dyeing the superficial
roots, followed by washing of the roots in the compacted layers. The
visual contrast of dyed and undyed roots served as the basis for
comparison of root development among treatments.
Results
Roots of all four crop species developed normally in the sandy loam
S\ dark red latosol, even at the greatest bulk density of 1.4 Mg m-3. In the
Sclayey dark red latosol with 53% clay content there was root penetration
at all bulk density levels, although slight root restriction was noted in
all four crop species at the bulk density of 1.4 Mg m3.
In the clayey dark red latosol with 70% clay content there were serious
restrictions to root penetration for all four crop p Critical
^<~^ ^~---------7 ^SS
levels of soil bulk density beyond which little or no root penetration
occurred were as follows:
1.4 Mg m-3 no root development in soybean, wheat, maize, or beans.
1.3 Mg m-3 no root development in wheat, maize, or beans.
1.2 Mg m-3 no root development in maize or beans.
1.1 Mg m'3 no root development in beans.
Conclusions
Of the four crop species tested under the above-mentioned conditions,
it can be concluded that susceptibility to mechanical impedance of root
growth is greatest for beans and decreases in the order: maize, wheat,
and soybean. By far the most problematic soil studied was the 70% clay
content dark red latosol which impeded penetration of bean roots at a bulk
density of 1.1 Mg m3.
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Implications
Severe restriction of root penetration in the 1.1-1.4 Mg m-3 soil bulk
density range for the major crop species grown in the Cerrado region
should be cause for special concern given the disc tillage practices
traditionally used here. It should also be pointed out that these root
growth restrictions occurred under conditions in which.soil water was not
a limiting factor, indicating that similar bulk density levels in the
field situation ay/be)even more critical for root development under low
rainfall situations.
Results from this experiment indicate that the high clay content
Oxisols may be more subject to root-restricting soil compaction than low
clay content Oxisols. The prominence of high clay latosols in the Cerrado
region is demonstrated by data from the Soil Survey of the Federal
District that show that 48% of the soils in this area aremappedas
latosols of a clayey surface texture class. Of these latosols, profile
descriptions show clay contents ranging from 40% (from a profile at CPAC)
to 88% (from a profile at the core of the Guided Settlement Plan farming
area) with an average clay content for the 41 profiles studied of 70%.
Dark red latosol profiles from colluvial sites comprising the main
experimental area at CPAC contain surface clay contents of 40 to 45%, well
below the average clay content in excess of 70% for the more common
plateau level dark red latosols where most of the farming is conducted in
the Federal District.
A consequence of this study will be that sampling studies of root-
restricting zones will be focused on farms in the Federal District where
these high clay soils occur. It would be advisable to plan to have future
on-farm tillage trials located near the cooperative headquarters in the
udi-ed-Settlement Plan of the Federal District where these soils occur.
-76-
Research Projects 1987-1992
The following project statements, along with first year tentative
budgets, have been made for continuation or to be phased into the program
as time and budget considerations permit. Project 102 has been completed
and is being replaced by Project 11. Project 105 has been terminated and
will be replaced by Project 112. Project 111 is new and will complement
the work to be done under Project 103. Project l will be terminated
upon completion of the thesis of the student presently working on it and
funds will be transferred to Project 110.
Projects 101, 103, 104, and 107 will continue as revised.
2
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Program: Management of Acid Savannas of the Tropics
Research Topic: Nitrogen Management in Acid Savanna Soils
Project No.: 101
Title: Nitrogen Availability from Crop Residues and Green
Manures to Succeeding Non-legume Crops.
Objectives: a) To develop and evaluate experimental procedures for
estimating the potential of crop residues and green
manures to supply nitrogen to succeeding non-legume
crops.
b) To evaluate the effects of climate and management
on the ability of the manures and crop residues to
supply nitrogen.
c) To evaluate the effects of green manure legumes on
crop performance other than the N effects.
Project Leader: W. S. Reid, Cornell University
Collaborating Scientists: A. Suhet, CPAC, Planaltina, Brazil, and
D. R. Bouldin, Cornell University
Reasons for the Investigation:
Drs. Bouldin, Reid and Stangel (1980) described the use of the general
equation:
Np NS + NM + NL + KFNF
where
Np is N required in the aboveground dry matter for the
selected yield goal.
NS, NM, NL and NF are the nitrogen supplied by the soil organic
matter, and, manures, legumes, and fertilizer.
KF is the use efficiency of the applied fertilizer.
Within this equation, uptake from the other sources is measured within the
plant, thus an efficiency factor is not used. This equation is the basis
for current recommendations in New York and conceptually is the basis for
recommendations in other areas.
For most upland crops and management systems KF is approximately 0.5
to 0.6. KF can be increased to approximately 0.75 by managing (timing)
the fertilizer applications) very carefully. The efficiencies for
mineralization and uptake of nitrogen from crop residues and manures are
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somewhat lower, usually <0.5 but, theoretically could be much higher. For
these efficiencies to be higher the crop need for N and the supply must be
closely balanced. For this to occur, the N mineralization rate from
manure or crop residue must closely approximate the uptake of the crop.
The efficiency factor for NL must contain a mineralization rate function
and a plant uptake fraction.
Relevance to Other Programs:
Estimations of the mineralization rate function in the laboratory
have been the subject of work by Bowen (1986), Quintana (1987), and
currently Carsky. The correlations between N added as green manure on
crop residues have been well correlated with both yield and N uptake, yet
the efficiencies have remained lower than desired. Our ability to
estimate or predict these efficiency factors have not been sufficiently
high to be translocated to other areas without additional experimental
work.
At times, there appears to be a rotational effect on yields that is
not the result of adding additional nitrogen (Bowen 1987 and others).
When this occurs it makes interpretation of nitrogen uptakes difficult.
More importantly some of these rotational effects may provide the impetus
for adoption of a crop rotation beyond the economics of the legume
nitrogen.
Generalized Procedures:
Currently experiments are being conducted by Carsky and Reid to study
the mineralization potential of several legumes using field experiments
and the buried bag technique. The influence of soil, water and
temperature are also being investigated. Assuming these techniques are
successful, an attempt will be made to quantify the mineralization rates
of other legumes and study some of the factors causing differential N
mineralization using modified bag technique. Field studies will be
maintained to provide the yield correlations. Similarly, treatments will
be inserted in these experiments to examine the rotation effects.
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Objectives:
a) Continue screening legumes for desirable nitrogen fixation and
mineralization rates using combinations of fallow plot,
incubation, and field evaluation experiments.
b) Study factors affecting mineralization rates of manures and crop
residues in an effort to quantify these factors for transfer of
technology to other areas.
c) Examine the rotational effects to determine their effects on N
efficiency as well as crop yields. 2 r 7
Principal Site for Experimentation:
Centro de Pesquisa Agropecuaria dos Cerrados (CPAC), Planaltina,
Brazil will be used for field and some laboratory studies and analyses;
Cornell University, Department of Agronomy may be used for laboratory
studies and analyses.
Duration: October 1, 1987 to September 30, 1992
/L< 4sy
-80-
Project 101
Tentative Budget
October 1, 1987 to September 30, 1988
Object Budget
Salaries 8800
Fringe benefits -0-
Allowances 5000
Fees 500
Equipment -0-
Supplies 2000
Travel: U.S. -0-
International 5000
Communications 300
Printing 1000
Shipping 1000
Other direct costs 4000
Indirect costs 8270
TOTAL 35870
Graduate student assigned: R. Carsky
-81-
Program: Management of Acid Soils of the Tropics
Research Topic: Nitrogen Management in Acid Savanna/Humid Tropic Soils.
Project No.: 103 (Revised)
Title: Soil and Crop Management Systems for Acid Savanna/Humid
Tropic Soils Using Green Manures and Crop Residues as
Nitrogen Sources.
Objectives: a) Develop planting sequences and cropping systems to
most effectively use legumes and plant residues to
supply the nitrogen requirements of non-legume
crops.
b) Evaluate the role of legumes and crop residues in
nitrogen cycling and soil organic matter
maintenance.
c) Determine the effects of legumes and crop residues
on long term soil productivity and recycling of
nutrients in acid savanna/humid tropic soils.
Project Leaders: W. T. Bowen, D. R. Bouldin, D. J. Lathwell, and W. S.
Reid, Cornell University
Collaborating Scientist: A. Suhet, CPAC, Planaltina, Brazil and Manoel S.
Cravo, UEPAE-Manaus, EMBRAPA
Reasons for the Investigation:
The collaborative research program between EMBRAPA, Cornell University,
and North Carolina State University has demonstrated that corn production
is significantly increased by the application of nitrogen to Oxisol soils
in both the acid savannas and humid tropics of Brazil. To evaluate
nitrogen as a constraint to production, Bouldin et al. (1980) developed a
model framework as follows:
Np Ns + Nr + KfNf
where: Np N uptake by the plant
Ns N supplied from soil mineralization
Nr N supplied from organic residues and green manures
Nf N supplied as fertilizer
Kf fraction of fertilizer N taken up by the plant.
The relationship between yield and nitrogen content of the aboveground dry
matter of a crop provides a good estimate of the amount of nitrogen that
must be accumulated by the crop. Each component of this model must be
evaluated and in this work we are interested in developing cropping
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systems to maximize the contribution of Nr to the nitrogen needs of the
non-legume food crop.
Corn response studies in limited areas of the acid savannas and humid
tropics have shown that leguminous green manures and crop residues may
supply all or part of the nitrogen needed for maximum production. Few
farmers, however, avail themselves of this seemingly inexpensive,
inexhaustible source of nitrogen. Important reasons why farmers do not
make better use of biological sources of nitrogen include the ease with
which fertilizer nitrogen can be managed; but, more importantly, is the
lack of knowledge of how to manage organic sources of nitrogen. A recent
survey conducted by the agricultural extension service in one state of
Brazil showed that almost all farmers listed management of leguminous
green manures high on their lists of perceived knowledge needs.
Management of organic nitrogen sources is complicated and may require
special cropping sequences and special management. Until the specific
input-output relationship can be developed, the role of biological
nitrogen relative to fertilizer nitrogen cannot be determined.
Relevance to Other Programs:
Farmers in New York make extensive use of manure and legumes as sources
of nitrogen and, in fact, these sources of nitrogen are far more important
than fertilizer nitrogen on many dairy farms. The research program in New
York has evaluated components of cropping sequences and manure management
already in place. We have evaluated manure, crop residues, and previous
legume crops by assigning a specific value to the amount of mineral
nitrogen which each source is expected to furnish to a succeeding non-
legume crop. The values we assign are based on a fairly extensive set of
field experiments performed over many years. In the acid savanna and
humid tropic regions of the tropics we must develop sources of organic
nitrogen and cropping sequences to match the nitrogen needs of the
cropping system with the nitrogen release by the organic nitrogen source.
We expect to take some of the most promising legumes and cropping
sequences to other regions and ecological zones as the project develops.
Generalized Procedures:
Field experiments ill be carried out to develop practical means of
increasing utilization of green manures and organic residues as sources of
nitrogen in cropping sequences. These will be long term experiments in
which green manures and organic residues will be incorporated at various
stages into the cropping systems and their rate of mineralization will be
measured. In a trial already begun in the acid savannas, a large number
of legumes are being tested for dry season survival in the hope of
identifying legumes that could be grown as green manures between wet
season crops. The potential of these materials to supply nitrogen to the
non-legume crop component will be evaluated and input-output relationships
necessary to develop practical management systems using biologically fixed
nitrogen will be developed. Measurements of crop yields, plant nitrogen
uptake, soil nitrogen, green manure and plant residue nitrogen will be
made. Site characterization will be made.
Principal Site for Experimentation:
Detailed field experiments will initially be conducted at the CPAC,
Planaltina, Brazil and the UEPAE, Manaus, Brazil. The necessary
analytical work will be carried out at these respective centers. As this
work develops, experiments derived from these results should be extended
to sites with other soils and environmental conditions in Latin America
and Africa.
October 1, 1987 to September 30, 1992.
Duration:
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Project 103
Tentative Budget
October 1, 1987 to September 30, 1988
Object Budget
Salaries 36000
Fringe benefits 9000
Allowances 18000
Fees -0-
Equipment 10000
Supplies 5000
Travel: U.S. -0-
International 10000
Communications 500
Printing -0-
Shipping 2000
Other direct costs 4500
Indirect costs 19000
TOTAL 114000
SRA assigned: W. T. Bowen
Graduate student assigned: F. Costa (to 12/31/87)
-85-
Program: Management of Acid Soils of the Tropics
Research Topic: Quantitative Description of Water and Chemical Budgets
in Acid Soils of the Tropics.
Project No.: 104
Title: Nitrogen Transformation and Movement in Acid Soils of
the Tropics.
Objectives: a) Develop a comprehensive description in simulation
model form of nitrogen movement and transformation
in cropped soils of the natively acid soil regions
of the tropics.
b) Use the model of a) as a guide in interpreting
previous studies and in designing further field
experiments to increase understanding of nitrogen
fate in these soil crop systems.
c) Develop a simplified model of nitrogen fate in
these soil crop systems that will be useful in
guiding nitrogen management programs.
Project Leaders: S. J. Riha and R. J. Wagenet, Cornell University
Collaborating Scientist: A. Suhet, CPAC, Planaltina, Brazil
Reasons for the Investigation:
There is a need for nitrogen management strategies based upon
comprehensive understanding of the physical, chemical, and biological
processes that affect nitrogen fate in acid soils of the tropics. A great
many field experiments in temperate regions have addressed this issue, and
a substantial data base has been assembled. It remains to generalize
these studies into a broadly based set of nitrogen management guidelines
useful in acid soils of the tropics. One method of achieving this goal is
to summarize nitrogen transport and transformational processes into a
simulation model of nitrogen fate in cropped systems, and to use the model
in a prospective manner to manage nitrogen fertilizer and crop residue.
Several models useful in such applications have been developed (Frissel
and vanVeen, 1981) and applied to field cases (Tillotson and Wagenet,
1982; Wagenet and Rao, 1982). Nitrogen management programs based upon a
modeling approach have been reported by Burns (1980) and Davidson et al.
(1978), and are being used in the United Kingdom on a continuing basis
(Addiscott, 1984). Although a number of such nitrogen fate models have
been developed, they are principally research, not management, tools that
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have been tested primarily on nitrogen fertilizer studies conducted in
soils of the temperate climates of the Northern hemisphere. The basic
formulation of these models provides a starting point for description of
nitrogen in acid soils of the tropics. This project will use a research-
type model of nitrogen movement and transformation in agricultural soils
to guide in the interpretation and design of field experiments and new
management systems. A coefficient type model (deWit and Wolf, 1984) will
be tested for use as a management guide.
Relevance to Other Programs:
Quantitative description of nitrogen movement, and nitrogen soil
fertility are both strong components of Cornell's continuing research
programs. Nitrogen management in Cerrado soils has been a primary focus
of Cornell/CPAC research efforts during the first several years of this
program, and will continue as a research topic in Cornell's efforts over
the next five years. Nitrogen modeling studies are currently in progress
as a component of the applied soil physics program at Cornell.
Generalized Procedures:
Field experiments are currently being conducted at Planaltina, Brazil,
in which the leaching and transformation of NH4N03 is being measured in
plots planted to corn and subject to various leaching rates. Data
collected from these experiments will be used to test models of water
movement (Buttler and Riha, 1987) and models of nitrogen fertilizer
transport, transformation and plant uptake.
Substantial effort will be explored in developing a nitrogen
mineralization component of the model that describes the residue
incorporation studies conducted in previous and proposed Cornell/CPAC
studies. During the course of this project, a Cornell graduate student
will conduct a field experiment at the CPAC that examines the relationship
between depth of rooting, water uptake and nitrate uptake.
Currently, an axial bibliography of the fate of fertilizer nitrogen in
maize cropping systems in the tropics is being developed. From this
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review, from the knowledge of nitrogen transport and transformations in
the tropics and from research conducted at the CPAC, a relatively simple
model to project the fate of fertilizer nitrogen under a range of soil and
climatic conditions will be developed.
Principal Site for Experimentation:
Centro de Pesquisa Agropecuaria dos Cerrados (CPAC), Planaltina, Brazil
(field studies); Cornell University, Department of Agronomy (laboratory
studies and modeling).
Duration: September 1, 1987 to August 31, 1992
Literature Cited:
Addiscott, T. M. 1984. Computer assessment of the N status during winter
and early spring of soils growing winter wheat. (In press, Agric.
Sci., Cambridge).
Burns, I. G. 1980. A simple model for predicting the effects of leaching
of fertilizer nitrate during the growing season on the nitrogen
fertilizer need of crops. J. Soil Sci. 31:175-185.
Buttler, I. and S. J. Riha. 1987. General purpose simulation model of
water flow in the soil-plant-atmosphere continuum. Applied
Agricultural Research (In press).
Davidson, J. M., D. a. Graetz, P. S. C. Rao, and H. M. Selim. 1978.
Simulation of nitrogen movement, transformation and uptake in plant
root zone. EPA-600/3-78-029.
deWit, C. T. and J. Wolf. 1984. The modelling of the response to
nitrogen. Staff working paper SOW-84-13. 16 pp.
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Frissel, M. J. and J. A. VanVeen. 1981. Simulation of nitrogen behavior
of soil-plant systems: Comparison between different approaches.
Centre for Agricultural Publishing and Documentation (PUDOC),
Wageningen, Netherlands.
Tillotson, W. R. and R. J. Wagenet. 1982. Simulation of fertilizer
nitrogen under cropped conditions. Soil Sci. 133:133-143.
Wagenet, R. J. and B. K. Rao. 1983. Description of nitrogen movement in
the presence of spatially variable soil hydraulic properties. Agric.
Water Mngt. 6:227-242.
-89-
Project 104
Tentative Budget
October 1, 1987 to September 30, 1988
Object Budget
Salaries 8800
Fringe benefits -0-
Allowances 2000
Fees 3050
Equipment -0-
Supplies 2000
Travel: U.S. 500
International 3000
Communications 300
Printing 1000
Shipping 1000
Other direct costs 2000
Indirect costs 11240
TOTAL 34890
Graduate student assigned: I. Buttler
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Program: Management of Acid Soils of the Tropics
Research Topic: Quantitative Description of Water and Chemical Budgets
in Acid Soils of the Tropics.
Project No.: 107
Title: Crop Water Requirements in Acid Savanna Soils.
Objectives: a) Determine the components of the water budget in
cropped Cerrados soils.
b) Quantify the effects of soil tillage practices upon
water availability and soil-water movement and
their impact upon crop yield, evapotranspiration,
and transient soil-water regimes in a manner useful
to irrigation and crop production programs.
c) Develop and test a simplified model relating water
use to crop yield, constructed to be useful in
extending experimental results to other locations.
Project Leaders: S. J. Riha and R. J. Wagenet, Cornell University
Collaborating Scientist: A. Suhet, CPAC, Planaltina, Brazil
Reasons for the Investigation:
A knowledge of the influence of evapotranspiration and soil water
management on plant growth is important to agronomic and economic
evaluation of irrigation development and for comparison of the relative
benefits of water used for irrigation compared to other water uses. In
fact, irrigated agriculture is based on the strong relation between plant
growth and water use evapotranspirationn and drainage). However, this
relationship is quite complex and interrelated to many other factors of
which soil fertility and climate are quite important. A number of non-
soil scientists attempt to describe such relationships in statistical or
regression form without considering many of these physical, chemical, and
biological factors. The rather gross models obtained are thereby quite
site specific and limited in their ability to describe experimentally
unstudied locations. The work proposed here will develop a physically
based, simple model to predict yield of several Cerrados crops as related
to water use. Several such models already exist in the scientific
literature, (e.g., Nimah and Hanks, 1973; Feddes et al., 1974; Lemon et
al., 1973; Ritchie, 1972) that provide substantial guidance for
development of a model useful in Cerrados soils, and from these approaches
-91-
a suitably modified simple model will be developed and tested. In the
process, the sensitivity of the model to soil, climate, and plant input
parameters will be determined, and general guidance produced for future
field studies. The model should be immediately useful in estimating the
potential benefits of increased irrigation, will identify differences in
yield response on different soils and in wet or dry years, and will
produce simulations useful in economic analysis of irrigation programs.
The model developed in this project will need to consider the effect of
soil management (tillage) practices upon the ability of Cerrados soils to
hold and conduct water. Such effects have been noted in very recent
studies by CPAC scientists, and provide initial experimental data useful
in developing first-generation models and guiding field experiments to be
conducted. Additionally, the model will be amenable to future
modification to reflect the influence of gypsum or nitrogen amendments
upon crop growth, a revision that will become possible as other research
projects under this topic are accomplished.
Relevance to Other Programs:
Soil water management and resulting impact on plant growth are primary
considerations in a number of Department of Agronomy research programs.
The project leaders have developed and tested simulation models of
evapotranspiration, plant water uptake, and water movement. Current
research of the project leaders emphasizes the effects of root growth
distribution and functioning on water availability to plants. These
activities have been funded primarily by the USDA. The Cornell project
cooperators are investigating such issues through participation in
Regional Research Project W-155, titled "Soil Water Properties, Spatial
Variability, and Implications in Soil-Water Management", and through
current USDA-funded work on "Crop Response to Water Management in the
Presence of Spatially Variable Soil Hydraulic Properties." Development
and testing of simulation models of water movement and crop growth have
been a research activity of the project cooperators for the last eight
years. Cornell University has historically had a strong interest in crop
yield/water management questions, as evidenced by previous cooperative
Cornell/CPAC efforts, and by present activity in the Department of
Agronomy on SCS-funded research investigating the relationships between
-92-
corn yield, soil erosion, and available soil-water (a project that
includes the project leaders). Additionally, other faculty in the
department are working on crop growth simulation models and measurement of
climatological data related to plant growth.
Generalized Procedures:
Data from previous experiments conducted at the CPAC, Planaltina with
irrigated wheat is currently being used to evaluate several existing
models for estimating crop water requirements. Additionally, a crop
growth and water use model will be developed in conjunction with other
modeling efforts of the Cornell TROPSOILS program, to extrapolate
Planaltina results to other regions of the Cerrados.
n the future a simplified model will be tested under a range of
climatological conditions and soil conditions. Additionally, field
experiments will be established to determine the interactions between soil
fertility .treatments, root depth, and length of time without rain during
the growing season.
Principal Site for Experimentation:
Centro de Pesquisa Agropecuaria dos Cerrados (CPAC), Planaltina, Brazil
(field studies, data reduction); Cornell University, Department of
Agronomy (modeling, data reduction).
Duration: September 1, 1987 to August 31, 1991.
Literature Cited:
Feddes, R. A., E. Bresler, and S. P. Neuman. 1974. Field test of a
modified numerical model for water uptake by root systems. Water
Resources Res. 10:1199-1206.
Hanks, R. J. 1974. Model for predicting plant yield as influenced by
water use. Agron. J. 66:660-665.
-93-
Hanks, R. J., J. Keller, V. P. Rasmussen, and G. D. Wilson. 1976. Line
source sprinkler for continuous variable irrigation-crop production
studies. Soil Sci. Soc. Amer. proc. 40:426-429.
Lemon, E. R., D. W. Stewart, R. W. Shawcroft, and S. E. Jensen. 1973.
Experiments in predicting evapotranspiration by simulation with a soil-
plant-atmosphere model (SPAM). pp. 57-76 IN: Field Soil Water Regime.
R. R. Bruce et al. (eds.). Soil Sci. Soc. Amer. Special publication
No. 5, Madison WI.
Nimah, M. N. and R. J. Hanks. 1973. Model for estimating soil water,
plant and atmospheric interrelations. I. Description and sensitivity.
Soil Sci. Soc. Amer. Proc. 37:522-527.
Ritchie, J. T. 1972. Model for predicting evaporation from a row crop
with incomplete cover. Water Resources Res. 8:1204-1213.
-94-
Project 107
Tentative Budget
October 1, 1987 to September 30, 1988
Object Budget
Supplies 1000
Printing 1000
Other direct costs 2000
Indirect costs 2800
TOTAL
6800
Graduate student assigned:
A. Luchiari
D. Osmond
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Program: Management of Acid Soils of the Tropics
Research Topic: Soil Constraints to Management of Acid Savanna Soils
Project No.: 108
Title: Characterization of Root-Restricting Pans in Cerrado
Soils.
Objectives: a) Diagnose soil conditions associated with root
restricting pans in Cerrado soils subjected to
continuous annual cropping.
b) Identify the natural factors or induced mechanical
and chemical processes that result in formation of
root-restricting pans.
c) Determine which mechanisms are primarily
responsible for limiting root development in Oxisol
tillage pans (critical bulk density exceeded,
inadequate aeration, soil pores too small, high
soil strength, toxicity, etc.)
Project Leader: Eric R. Stoner, Cornell University
Collaborating Scientists: Airton Alonco and Elias de Freitas, CPAC/
EMBRAPA
Reasons for the Investigation:
Physical characteristics of medium and fine textured Cerrado Oxisols
have generally been considered excellent for mechanized agriculture
because of the very stable but weakly coherent micro-aggregate structure.
However, evidence is beginning to mount that deleterious physical
situations are developing in areas subjected to continuous annual
cropping. In some fields in the Sao Gotardo region of Minas Cerais State,
a decade of intensive cultivation has resulted in the formation of an
extremely hard compacted layer 10 to 15 cm deep at the top of the horizon
beneath a very loose or fluffy plough layer, forming conditions very
conductive to erosion under high intensity rainfall. Shallow rooting of
the predominant crop in this region, soybeans, has been attributed to soil
strength, reduced macroporosity, and poor aeration rather than aluminum
toxicity or low nutrient status of the subsoil.
As a consequence of the shallow rooting of annual crops, the relatively
costly investments in lime and fertilizer in Cerrado soils may not be
utilized to maximum extent. Nitrogen which is mineralized in the surface
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soil and applied fertilizer N may be carried quickly out of shallow
rooting zones with excessive amounts of percolated water where root
restricting pans occur. Nitrogen losses can also occur from
denitrification when water perches on compacted layers.
The presence of tillage pans reduces water capture from the frequently
brief, intense storms thus limiting replenishment of subsoil moisture.
Even the available subsoil moisture which should be utilized by plants
during short dry spells (veranicos) is not accessible because of root
restriction in the surface horizon. The occurrence of severe plant
moisture stress during rainless periods may be the most serious
consequence of soil compaction for rainfed agriculture in the Cerrados.
Soil erosion, which has not been held to be a concern in these deep,
gently sloping, highly permeable soils is becoming increasingly evident in
Cerrado soils. It is common to observe areas of total removal of surface
soil down to the characteristic marks of the harrowsole in cultivated
fields. Deep gully formation where runoff water is channeled along
contour ridges or be discharged at field edge is a serious problem on soils
where slope lengths may reach several kilometers. Reduced infiltration
and increased runoff associated with subsoil compaction increase the
severity of erosion under these circumstances.
Several factors are suspected to contribute to the formation of
compacted layers in Cerrado soils. Normal farm traffic with heavy
tractors and harvestors contributes to wheel track packing, while the
traditional practice in the Cerrado region of soil tillage almost
exclusively with heavy disk harrows is almost certainly a major
aggravating factor. Once compacted, Cerrado soils may have no natural
correction mechanisms since both shrink/swell, and freeze/thaw cycles are
absent. The presence of tree roots in cleared Cerrado land has
discouraged any form of deep tillage in the initial years of cultivation.
The lack of crop rotation in what frequently are cash grain operations
with out the presence of cattle raising to justify grass-legume leys is
another critical factor.
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A thorough diagnosis has been helpful for situations in which soil
constraints to deep rooting are evident (Kashirad et al., 1987; Taylor et
al., 1964). The soil conditions in root-restricting pans should be
characterized so that possible chemical or physical barriers to root
growth can be identified. Once the nature of the barrier is determined,
an attempt should be made to identify the natural factors or induced
mechanical and chemical processed that result in the formation of root-
restricting pans. This should furnish keys to management practices for
avoidance of the problem before it starts.
Most importantly, the mechanisms which are primarily responsible for
limiting root development in cultivated Cerrado subsoils should be studied
so that the effects of microporosity, high soil strength, or continued
toxicity can be validated under controlled conditions. A better
understanding of these mechanisms should help orient the development of
management strategies for alleviation of barriers to subsoil utilization.
Relevance to Other Programs:
A major area of emphasis of the TropSoils/Acid Savanna program is that
of enhancement of the use of biologically fixed nitrogen and nitrogen in
organic residues for sustained crop production and maintenance of soil
productivity. Production systems utilizing legume green manure crops,
which may be developed as part of this program, are likely to help
alleviate some of the effects of mechanical impedance for succeeding
crops. An integral part of any system for sustained crop production and
maintenance of soil productivity will likewise need to be the adoption of
management techniques for avoidance of serious soil compaction.
Characterization of the tendency for soil compaction in Cerrado soils
should help identify those management techniques that are most advisable.
Generalized Procedures:
Paired sampling sites of adjacent cultivated and virgin soils will be
chosen in several Cerrado areas where preliminary evidence of tillage pan
formation has been found. Pits for sampling will be dug during the rainy
season and measurements will be made of bulk density, mechanical
impedance, moisture content, organic matter content, particle size
distribution, and Fe, Al, and Si. Mineralogical analysis may be performed
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