Front Cover
 Title Page
 Table of Contents
 Join NCSU-Cornell research in the...
 Amazon jungle of Peru
 Central America
 Fertility-capability soil classification...
 Soil characterization
 Economic interpretation
 Communication of results


Tropical soils research program, annual report
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00054173/00001
 Material Information
Title: Tropical soils research program, annual report
Cover title: Agronomic-economic research on tropical soils, annual report
Spine title: Research on tropical soils
Physical Description: 1 v. : ill. ; 28 cm.
Language: English
Creator: North Carolina State University -- Soil Science Dept
Publisher: Soil Science Dept., North Carolina State University.
Place of Publication: Raleigh
Creation Date: 1975
Frequency: annual
Subjects / Keywords: Soils -- Tropics -- Periodicals   ( lcsh )
Soils -- Periodicals -- Latin America   ( lcsh )
Agriculture -- Tropics -- Periodicals   ( lcsh )
Agriculture -- Periodicals -- Latin America   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
serial   ( sobekcm )
Dates or Sequential Designation: 5th, 1975.
 Record Information
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000436827
oclc - 04039139
notis - ACJ6840
lccn - 78643724 //r79
issn - 0161-8857
System ID: UF00054173:00001
 Related Items
Preceded by: Agronomic-economic research on tropical soils, annual report
Succeeded by: Research program on soils of the tropics, annual report for ...

Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Title Page
        Title Page 1
        Title Page 2
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    Table of Contents
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    Join NCSU-Cornell research in the Cerrado center of Brazil
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    Amazon jungle of Peru
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    Central America
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    Fertility-capability soil classification system
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    Soil characterization
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    Economic interpretation
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    Communication of results
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Full Text



Annual Report for 1975

Soil Science Department
North Carolina State University
Raleigh, N.C.

Contract AID/ta-C-1236
with the
U.S. Agency for International Development



Soil Science Department
North Carolina State University
Raleigh, North Carolina 27607

supported by
Contract AID/ta-C-1236
with the
U. S. Agency for International Development

November, 1976


Charles B. McCants, Department Head
Pedro A. Sanchez, Program Coordinator
Bertha I. Monar, Administrative Secretary
Dawn M. Silsbee, Bilingual Secretary
Cathy L. Langley, Research Technician

Cerrado of Brazil
K. Dale Ritchey, Project Leader (Cornell)1
George C. Naderman, Jr., Assistant Professor
Eugene J. Kamprath, Professor
Enrique Gonzalez E., Research Assistant
Russell S. Yost, Research Assistant
Jos6 G. Salinas, Research Assistant
Dale E. Bandy1, Research Assistant
T. Jot Smyth, Research Assistant
Alfredo S. Lopes, Research Assistant
Fred R. Cox, Professor

Amazon Jungle
Pedro A. Sanchez, Project Leader
J. Hugo Villachica, Research Assistant
S. W. Buol, Professor
D. Keith Cassel, Associate Professor
Gordon S. Miner, Assistant Professor
Cesar E. Lopez, Research Assistant
Christopher E. Seubert2, Research Assistant
Edward J. Tyler2, Research Assistant
Michael K. Wade, Research Assistant

Central America
Robert E. McCollum, Project Leader
Donald D. Oelsligle2, Assistant Professor
John J. Nicholaides, Assistant Professor
Clifton K. Hiebsch, Research Assistant
Alvaro Cordero V., Research Assistant
David Anderson, Research Assistant

Extrapolation Studies
Stanley W. Buol, Professor of Soil Genesis
Robert B. Cate, Jr., Associate Professor
Arthur J. Coutu, Professor of Economics
Walter Couto, Research Associate
Robert A. Pope, Research Assistant
Raymond B. Daniels, Professor (USDA)
Richard K. Perrin3, Assoc. Prof. (Economics)
Leonidas Mejia2, Research Assistant
Igo F. Lepsch2, Research Assistant
Jerry M. Bigham, Research Assistant
J. Ram6n Paredes2, Research Assistant
Richard Schargel, Research Assistant
Sahle M. Sertsu, Research Assistant
Michael A. Granger2, Research Associate

lCornell University staff members working on cooperative project.
2Left during the year.
30n leave of absence at CIMMYT.


Highlights of the year ................................ .................. 3
Collaborating institutions and individuals ................. .................. 7
Crop weather ......................................................... 13
Residual effects of lime rates and depth of incorporation ........................ 16
Residual effects of phosphorus applications .................................. 26
Residual effect of lime and phosphorus applications on the loamy
red yellow latosol ................ ................................. 32
Residual effects of zinc applications.................. ..................... 34
Nitrogen fertilization.................................................... 36
Tolerance to aluminum toxicity and low available soil phosphorus ................. 40
Management of water stress periods ....................................... 65
Crop weather ... ......... ............................................ 117
Continuous cropping experiment .......................................... 117
Multiple cropping experiment ................ ........................... 137
Liming monoculture and intercropped systems. ........................... 152
Mulching and green manuring studies ...................................... 166
Phosphorus and sulfur fertilization ................ ......................... 180
Secondary and micronutrient studies ...................................... 183
Varieties and plant population studies with corn................... .......... 192
Adaptation of potatoes to the lowland tropics ............... .............. 194
Nitrogen response by a corn-cassava intercropped system in the Atlantic
Coast of Costa Rica ................................................ 197
Nitrogen fertilization of beans in relay-intercropped corn and beans in
Alajuela, Costa Rica ................................................ 200
Nitrogen management for upland rice in Costa Rica .......................... 201
Accumulation of dry matter and nutrients by cassava .................... ...... 209
Phosphorus fertilization in Guatemala ....................................... 220
Fertilization of forage sorghum in El Salvador ................. ........... 222


Evaluation of the "i" modifier with corn experiments from Brazil ................. 239
System evaluation in Colombia ................ .......................... 240
Improving the "i" modifier............................................... 244
Characteristics of a common toposequence in the Llanos Orientales
of Colombia ...................................................... 253
Soil-landscape relationship in an area of the Occidental Plateau of
Sao Paulo, Brazil ................................................... 270
Characterization and genesis of soils of a climosequence in the Occidental
Coast of Maracaibo Lake, Venezuela ................ ................. 278
Influence of iron oxides on soil color ................. ..................... 280
Ultisols and Oxisols of the savannas and Amazon territory of Venezuela ............ 285
Jenaro Herrera colonization in the Amazon of Peru ........................... 287
Comparison of jungle and savanna soil conditions between South America
and West Africa ................................................... 287
Effects of heating on changes in soil properties in relation to an Ethiopian
management practice ............................................... 296
ECONOMIC INTERPRETATION WORK PLAN ............................... 305
Publications........................................................... 309
Mailing list............................................................. 310
Conferences and symposia................................................ 310
Utilization at the farmer's level ................ .......................... 312



This is the fifth annual report of the Soil
Science Department's Tropical Soils Re-
search Program, supported by the U.S.
Agency for International Development. Con-
tract AID/csd 2806 expired on June 30,
1975 and on that date the program was ex-
tended for an additional three-year period as
Contract AID/ta-C-1236. The overall objec-
tives of the program have been focused more
sharply during the project renewal process
into four major objectives. The first three
consist of developing economically-sound
soil management systems for 1) acid tropical
savannas, 2) tropical rainforests and 3) for
intensive intercropping systems in areas af-
fected by volcanic activity. The field re-
search activities,to achieve each of these ob-
jectives, continue to be based in Brasilia,
Brazil for the savannas, Yurimaguas, Peru for
the jungle areas and Turrialba, Costa Rica
for the intensive cropping systems. The lat-
ter location serves as headquarters for work
throughout Central America.
The fourth objective is to gather addi-
tional information needed for establishing a
sound basis for extrapolating the research re-
sults to other tropical areas around the
world with similar soil management prob-
lems. Three main activities are performed to
achieve this objective. Soil characterization
studies, to determine the soil properties of
little-known tropical areas along with basic
greenhouse and laboratory studies, are de-
signed to understand certain basic concepts
not presently understood.

The second activity is the development of
the Fertility-Capability Soil Classification
System as a practical tool for grouping soils
with similar fertility limitations and thus,
to bridge the gap between the subdisciplines
of soil survey and soil fertility.
A third component of the extrapolation
strategy is an economic interpretation of the
data gathered in a way which evaluates the
profitability of the soil management systems
proposed and at the same time provides phy-
sical coefficients for economic planning
tools such as linear programming and sector
The format of this report now identifies
the staff responsible for each research pro-
ject in order to give more direct credit to the
people involved both from North Carolina
State University and the cooperating institu-

The long-term residual effects of liming
and fertilizer applications on Oxisols of the
Cerrado of Brazil provided additional infor-
mation as most experiments completed their
third year after establishment. Original appli-
cations of 2 to 8 tons/ha incorporated deep
(0-30 cm) were able to maintain from 72 to
97% of the maximum corn yields. Shallow
(0-15 cm) lime incorporations did not per-
form as well. Chemical analysis suggests a
considerable movement of exchangeable cal-
cium and magnesium below the zone of ap-

Phosphorus management continues to be
the most crucial fertility parameter for de-
veloping economically-sound systems. The
long-term residual phosphorus experiment,
now in its fifth consecutive crop, shows that
a broadcast initial application of 80 kg
P205/ha as superphosphate followed by
band applications at the same rate before
each planting produces about 80% of the
yields obtained by a massive initial broadcast
application of 1280 kg P205/ha. The resid-
ual effect of cheaper sources of phosphorus
continued to show the good performance of
high reactivity rock phosphates. With time
the low reactivity Araxd rock phosphate in-
creased its effectiveness dramatically. Ter-
mofosfato, a thermal alteration of Araxa
fused with magnesium silicate, continued to
perform as well as superphosphate.
The residual studies of zinc fertilization
show that an initial rate of 9 kg Zn/ha is suf-
ficient to maintain maximum corn and sor-
ghum yields three years after applications.
A methodology for screening varieties for
joint tolerance to aluminum toxicity and
low available soil phosphorus levels was de-
veloped in the greenhouse and tested suc-
cessfully in the field. Several varieties of
corn, beans, wheat, sorghum and rice were
identified as showing joint tolerance to the
two most adverse factors of Cerrado soils.
When tested in the field, they approached
maximum yields at much lower levels of
lime and phosphorus applications than the
sensitive variety. For example, the tolerant

sorghum variety, Taylor Evans Y-101, pro-
duced 6 tons/ha of grain with only 1 ton/ha
of lime applied three years before, with a
50% Al saturation in the top 30 cms. The
susceptible variety RS-610 produced the
same yield with 4 tons/ha of lime and 20%
Al saturation in the top 30 cms. Many
varieties developed under acid conditions in
southern Brazil exhibit joint tolerance to
aluminum toxicity and low available soil
phosphorus levels in sharp contrast with
CIMMYT's Mexican varieties developed un-
der calcareous soil conditions. These results
have stimulated national breeding programs
of corn and sorghum to include joint toler-
ance as breeding objectives. Coupled with
other management practices identified ear-
lier, such as deep liming, combination of
broadcast + banded phosphorus and cheaper
sources of phosphorus, the identification
and use of tolerant varieties will make eco-
nomically feasible the opening of new acid
savanna areas for intensive crop production.
Crop physiology during water stress per-
iods was better understood through growth
analysis monitoring leaf area index, soil tem-
perature, soil water use, transpiration rates,
stomatal resistance, leaf water potential,
root distribution, yields and nutrient uptake.
These measurements confirm the superiority
of deep liming as a better way to utilize soil
moisture during water stress periods in corn.
Upland rice, however, did not benefit from
deep liming probably because of its greater
tolerance to aluminum levels.

Mulching corn with grass reduced soil
temperature by 2-3 degrees Centigrade in
both seasons while a black plastic mulch in-
creased soil temperatures by that amount.
Both mulches decreased water stress.
Coupled with deep liming, grass mulch dur-
ing the hot rainy season and black plastic
mulch during the dry season increased yields
Amazon Jungle
The continuous cropping experiment suf-
fered a severe yield decline during 1975 even
when levels of fertilization and liming con-
sidered adequate were applied. The causes
for this decline were not related to age after
clearing or to climate. They were identified
as insufficient rates of fertilization and lim-
ing, poor germination and initial stands, soil
compaction and increased insect attacks.
Soil analysis confirmed that the fertiliza-
tion rates applied in 1972 are no longer ade-
quate. Nutrient requirements increased as
the soil approached a new equilibrium level.
Magnesium and potassium deficiencies
occurred and also an imbalance between Ca,
Mg and K. The residual effect of phosphorus
applications was shorter than expected. Poor
germination and initial stands of rice were
corrected by selecting fungus-free seeds and
insect attacks controlled. Soil compaction
problems became evident and were corrected
by mulching and/or herbicide applications to
minimize manual weeding. When fertilizer
applications were increased (to 180-160-150
kg/ha of N, P205 and K20 plus 50 kg MgO/

ha, 24 kg S/ha, 3 kg Zn/ha, 3 kg Cu/ha,
1 kg B/ha and 0.1 kg Mo/ha) pests were con-
trolled and mulches and herbicides used to
diminish soil compaction, the yields in-
creased again. Next year's annual report will
show upland rice yields of over 3 tons/ha,
corn yields of over 4 tons/ha and soybean
yields of over 2 tons/ha. Preliminary eco-
nomic analysis shows that these fertilization
rates are profitable.
Research on multiple cropping combina-
tions showed that five basic crops (corn,
rice, cassava, peanuts and cowpeas) could be
grown on the same land during one year,
producing about 30% more food and net in-
come to the farmers than when the crops
were grown separately.
Although the response to lime is great in
these acid jungle Ultisols, the residual effect
of lime applications is not as long as that ob-
served in the savanna Oxisols. Continuously
humid weather, the use of Ca(OH)2 as the
lime source and the rapid increases in ex-
changeable aluminum a few months after
liming are some of the reasons why. Incor-
porating lime with a hoe, or simply raking it
on the surface gave very favorable responses
and opened practical possibilities in small
farming systems where mechanization is dif-
Mulching or incorporating guinea grass or
kudzu increased crop yields significantly
over four successive crops, and prevented
yield declines in unfertilized fields. Mulching
decreased soil temperatures by about 5 de-

grees Centigrade, prevented compaction,
conserved soil moisture and decreased weed
growth. Green manure applications did all of
the above except for decreasing soil tempera-
tures. When crops were intensively fertilized,
the yield response to these residue applica-
tions diminished.
The responses to sulfur, magnesium, po-
tassium and micronutrients were also identi-
fied and quantified. This led to the formula-
tion of recommended fertilization rates
which increased corn and soybean yields dra-
Field adaptation of Irish potatoes to the
lowland tropics was conducted with germ-
plasm and supervision of the International
Potato Center. The preliminary results show
considerable promise.
Central America
Research on multiple cropping systems
showed that a corn-cassava intercropped sys-
tem in the Atlantic coast of Costa Rica pro-
duced as much yield of both crops per hec-
tare as two hectares of monoculture. In the
ubiquitous corn-beans relay intercropped
system practiced throughout the region, re-
sults showed that nitrogen applications to
the beans after doubling the corn, increased
bean yields significantly and economically.
The efficiency of nitrogen applications to
upland rice in the Pacific coast of Costa
Rica showed an optimum application rate of
110 kg N/ha. A thorough study of dry mat-
ter and nutrient accumulation by cassava
was completed during the year. It provides

basic data for the understanding of this basic
food crop. Phosphorus fertilization studies
in the Altiplano and Pacific coast of Guate-
mala showed that no massive phosphorus ap-
plications are needed to produce adequate
corn and wheat yields. Producing intensively
fertilized forage sorghum during the rainy
season in El Salvador to provide silage for
dry season feeding of livestock was proved
to be economically sound.
Extrapolation Studies
The first formal version of the Fertility-
Capability Soil Classification System was
published. It is presently being used in
Colombia, Venezuela, El Salvador and tested
in other countries, including the United
States. Its applicability to Colombian data
was tested. Problems were found in several
regions related to the use of the parameter
designed to identify high phosphorus fixa-
tion by iron compounds. It was found that
phosphorus fixation could be predicted by
the clay content of Oxisols and Ultisols or
by the product of % clay x % free Fe203.
Soil characterization studies were con-
ducted in areas with very little prior infor-
mation in the interior of South America. A
toposequence study in the Llanos Orientales
of Colombia indicates that all soils are clas-
sified as Oxisols and that they differ only
slightly in their chemical and mineralogical
properties, except for organic carbon which
seems to be closely related with soil mois-
ture regime. A second study in the Occiden-
tal Plateau of Sao Paulo State, Brazil shows

that most soil variation was related to parent
material and geomorphology. In this
region Oxisols, Ultisols and Mollisols occur
in close proximity. A third savanna region in
the west coast of the Maracaibo Lake in
Venezuela, showed that soils varied from
Aridisols to Alfisols and Ultisols, depending
on soil moisture regime. Basic studies also
began on the relevance of yellow and red soil
colors on iron oxide composition and man-
agement implications. Characterization of
Oxisols and Ultisols of the Venezuelan sa-
vannas and Amazon Jungle is also in pro-
gress. At the request of the Ministry of
Food, soils of the Jenaro Herrera coloniza-
tion project in the jungle of Peru were col-
lected for characterization.
A study trip through Nigeria, Ghana and
Upper Volta permitted a comparison of jun-
gle and savanna soil conditions between
these areas of West Africa and South Amer-
ica. The similarities in soil management
problems are very close in both jungle areas
although the West African regions visited
have less soil fertility problems and more soil
physical problems than in the Amazon Jun-
gle. The similarities in vegetation are very
striking between the Cerrado and the Guinea
savannas of Ghana. However, the soils are
totally different and require completely dif-
ferent approaches. A study of the effects of
burning the soil itself rather than the vegeta-
tion was conducted with an Ethiopian soil in
order to gather a basic understanding of the
"guie" system of shifting cultivation prac-
ticed in that country.

The economic interpretation project ter-
minated its initial phase of analyzing already
existing data, finding the most appropriate
models for arriving at fertilizer rate recom-
mendations. A new phase was started in late
1975 consisting of interpreting and analy-
zing data produced by our program in Yuri-
maguas and Brasilia as a basic tool for linear
programming and sector analysis studies.

The research reported is conducted in
cooperation with several national and inter-
national institutions, involving a high degree
of collaboration.
In the Cerrado of Brazil, this project is
conducted jointly with Cornell University
and the Empresa Brasileira de Pesquisa Agro-
pecuaria (EMBRAPA) at the Centro de Pes-
quisa Agropecudria dos Cerrados, located
about 40 km north of Brasilia. The USAID
Mission in Brasilia and the Interamerican In-
stitute of Agricultural Sciences provided
valuable logistical support. EMBRAPA has
assigned Mr. Edson Lobato as project leader,
representing Brazil. Cornell and N. C. State
staff stationed at the Cerrado Center form
an integral part of the Center's research
In the Amazon Jungle of Peru, field re-
search is conducted at the Yurimaguas Ex-
periment Station which is part of the Centro
Regional de Investigaciones Agropecuarias
del Nor-oriente of the Ministerio de Alimen-
taci6n. Supporting laboratory work is con-

ducted at La Molina. The Direcci6n General
de Investigaciones of the Ministry has assigned
Dr. Carlos Valverde as project leader, repre-
senting Peru. Dr. Valverde has been very ef-
fective in expediting administrative matters
with the Peruvian Government. The Interna-
tional Potato Center plays a major role in pro-
viding administrative and logistical support. In
turn, the program grows its potato trials at
Yurimaguas as the lowland tropical station for
adapting potatoes to the region.
In Central America joint projects are con-
ducted with the Centro Agron6mico Tropical
de Investigaci6n y Ensenanza (CATIE) at
Turrialba, Costa Rica; the Ministries of Agri-
culture of Costa Rica and El Salvador and the
Institute de Ciencias y Tecnologia of Guate-
mala. Activities are also linked with the Inter-
national Soil Fertility Evaluation and Im-
provement Program (ISFEIP). Logistical sup-
port is provided by CATIE. Program plans are
coordinated with the ROCAP offices of AID
in the region.
Several extrapolation studies are also colla-
borative in nature. Data for evaluating the
Fertility-Capability Soil Classification System
has been provided by EMBRAPA, the Insti-
tuto Colombiano Agropecuario, Instituto
Geogrdfico Agustfn Codazzi in Colombia. Soil
characterization studies have been conducted
with partial financial support in the form of
scholarships for graduate students from the
USAID Mission to Colombia, the Ministerio
de Obras Publicas of Venezuela, the Fondo de
Amparo a la Pesquisa do Estado de Sao Paulo,

The following individuals from the dif-
ferent cooperating institutions provided sub-
stantial administrative support or are co-
authors of some of the research projects. We
wish to acknowledge and recognize their assis-
tance at this time.
Jose Ireneu Cabral, President of EMBRAPA
Almiro Blumenschein, Director of EMBRAPA
Wenceslau G. Goedert, Associate Director,
Edson Lobato, EMBRAPA Project Coordi-
Gilberto Paez, Head of the Data Processing
Department, EMBRAPA
Wilson V. Soares, former Associate Director,
Cerrado Center
Jose M. Barcellos, former Head of the Brasilia
Experiment Station
William Rodgers, Agriculture and Rural
Development Officer, USA ID-Brasilia
William Gelabert, Acting Director, USAID
Mission to Brazil
John Young, USAID-Brasilia
Matthew Drosdoff, Professor of Tropical
Soils, Cornell University
David R. Bouldin, Professor of Soil Science,
Cornell University
Robert B. Musgrave, Professor of Agronomy,
Cornell University
Elicios Martins, Research Technician,
Cornell-NCSU Project
Clibas Vieira, Professor, Universidade de
Robert Schaffert, Brasilian National Sorghum

Ady Raul da Silva, Brazilian National Wheat
Knut Mikaelson, Centro de Energia Nuclear
na Agriculture
Mariano Segura B., Director General de Inves-
tigaciones Agrarias, Lima
Carlos Valverde S., Project Coordinator for
the Ministry of Food and Director of the
Centro Regional de Investigaciones I-La
Manuel Llaveria, Director del Centro Regional
de Investigaciones Agrarias II I-Tarapoto
Jose del Carmen Muro, Director de Investiga-
ciones, Ministerio de Agricultura, DGIA,
Ruben Mesfa P., Head, Yurimaguas Experi-
ment Station
Carmen Torres, Soils Department, La Molina
Experiment Station
Mario Cano, Soils Department, La Molina
Experiment Station
Humberto Mendoza, Plant Breeder, Inter-
national Potato Center
Richard L. Sawyer, Director General, Interna-
tional Potato Center
Carlos Bohl P., Executive Director, Inter-
national Potato Center
William Hamann, Assistant Executive
Director, International Potato Center
Oscar Gil, Controller, International Potato
Veronica de Franciosi, Assistant to Execu-
tive Officer, International Potato Center
Milton Lau, Food and Agriculture Officer,

Rollo Ehrich, Deputy Food and Agriculture
Officer, USAID-Lima
Manuel Elgueta, Director, CATIE, Turrialba
Eladio Carmona, Director de Investigaciones,
MAG, San Jos6
Alberto Vargas, Subdirector de Investiga-
ciones, MAG, San Jos6
Jorge Soria, Jefe, Departamento de Suelos y
Cultivos Tropicales, CATIE
Arnoldo Romero, Rice Specialist, MAG,
Palmar Norte
Carlos Gonzalez, MAG, Los Diamantes
Antonio M. Pinchinat, Plant Breeder, CATIE,
Rufo BazAn, Soil Scientist, CATIE, Turrialba
Nicolds Mateo, Agronomist, CATIE, Turrialba
Gerardo Ramfrez, Soils Research, MAG,
San Jos6
Rolando Gonzalez, Rice Program, MAG,
Roger Menenses, Agronomist, MAG, Los
Guillermo Iglesias, Soils Section, MAG, San
Rafael Salazar, Soils Section, MAG, San
Armando Alas, Director of Research, CENTA,
Santa Tecla
Jos6 Perez Guerra, Director of Extension,
Centa, Santa Tecla
Jorge Alfaro, Head, Soils Research, CENTA,
Santa Tecla
Francisco Rodriguez, Peace Corps Ag. Coord.,
San Salvador


Jack Morse, Food and Agriculture Officer,
USAID-San Salvador
Julio A. Ringuelet, IICA Representative,
San Salvador
Jos6 Antenor Romero, Livestock Extension,
CENTA, Santa Tecla
Edmidlia GuzmAn de Pefa, Soils Investiga-
tion, CENTA, Santa Tecla
Julia de Men6ndez, Soils Analysis, CENTA,
Santa Tecla
Harry Brokish, Peace Corps, CENTA, Santa
Miguel Fuentes Velarde, Extension, CENTA,
Jos6 Elias Ventura, Extension, CENTA, San
Francisco Gotera
Ralph Kramer, Peace Corps, San Francisco
Gary Larson, Peace Corps, Villa Dolores
Anibal Palencia, Head Plant Nutrition, ICTA
Luis Estrada, Assistant Soil Scientist, ICTA
Julio Brolo, Assistant Soil Scientist, ICTA
Ramiro Ortiz, Assistant Soil Scientist, ICTA
James L. Walker, Regional Director, ISFEIP
Donald R. Feister, Rural Development
Morgan Stickney, Assistant Regional Develop-
ment Officer, ROCAP-USAID
Servio T. Benavides, Instituto GeogrAfico
Agustin Codazzi, Bogota
Luis Alfredo Leon, Instituto Colombiano
Agropecuario, Palmira
James M. Spain, Soil Scientist, CIAT, Palmira

Charles A. Francis, Plant Breeder, CIAT,


Extrapolation experiment in the loamy, Red Yellow Latosol at the Cerrado Center.

This report covers field work conducted
from October 1974 to September 1975, en-
compassing a full agricultural year with the
1974-1975 rainy season and the 1975 dry
season. Research conducted independently
of the seasons is also reported. Unless other-
wise specified all field experiments were con-
ducted on a Dark Red Latosol (Typic Haplu-
stox, fine, kaolinitic, isohyperthermic) loca-
ted on a second erosion surface at the Cen-
tro de Pesquisa Agropecuaria dos Cerrados
(CPAC) near Brasilia. The properties of this
soil were described in the 1973 Annual Re-
port and are typical of acid Oxisols of tropi-
cal savannas.

D. E. Bandy
The monthly rainfall and solar radiation
regime at CPAC is shown in Figure 2.1 in
comparison with the long-term rainfall aver-
age. The monthly rainfall distribution during
the rainy season was unusually uniform but
it included two short-term drought periods
(veranicos). The first one lasted for nine
days at the end of January 1975 but did not
cause serious water stress due to cloudiness
and high humidity. A severe 18-day veranico
did occur from February 27 through March
16, 1975 at the grain formation stage of
many crops. These periods are normal and
play a major role in crop performance.
As data from successive years is gathered
the effects of climatic characteristics on crop
behavior became more apparent. The follow-
ing observations are based on corn, the crop

we have studied more thoroughly. Table 2.1
shows the effect of seasons on tasseling date
and the number of days between 50% tassel-
ing and black spot formation. Corn grain
yields during the dry season averaged 1.31
tons/ha (about 20%) more than during
the rainy season, at near optimum soil fertil-
ity levels and water availability.
Although the mean daily thermal units
are higher during the rainy season, the total
thermal units per crop are superior in the
dry season because of the longer growth du-
ration. Table 2.1 also shows that the mean
daily solar thermal units are higher during
the rainy season but that the total solar
thermal units per crop are higher during the
dry season.
The differences in solar radiation be-
tween rainy and dry seasons are not very
marked as compared with other regions
where solar radiation is substantially higher
during the dry season. A more accurate
study of these differences can be made by
measuring the photosynthetically active ra-
diation (PAR). Figure 2.2 shows average
values expressed in quantum units of light.
The daily average PAR for the rainy season
is approximately 15% more than the dry sea-
son, even with the more cloudy weather.
The additional 7.7 days between flowering
and black spot formation (the grain filling
stage) during the dry season can account for
an additional 1.17 tons/ha of yield assuming
a 4.9 g/day increase in ear dry weight. The
remainder of the difference in yields be-
tween the seasons is probably related to dis-


Table 2.1 Effect of seasons (rainy vs. dry, irrigated) on corn growth stages and yields,
the number of thermal units and the solar thermal units received by corn
crop. Average of six rainy season experiments and four dry season experi-
ments conducted at CPAC from 1972 to 1975.

Rainy Season
Parameter Season (irrigated)

Days to 50% flowering 72.4 99.5
Days from 50% flowering to black spot formation 62.8 70.5
Mean grain yields (tons/ha)/ 6.57 7.88
Total thermal units per crop 5059 6087
Mean daily solar thermal units 18,232 16,337
Total solar thermal units per crop x 106 1.27 1.48

1/ At optimum or near optimum soil fertility and water availability


' 500
- 400


S 200
-- 100

Figure 2.1


Rainfall and solar radiation pattern at the Cerrado
Research Center near Brasilia during the report period.

/ < --Rainy Season
S\ (Jan 14-19,29-30,1975)

0800 1000 1200 1400 1600 1800

Time (hrs)

Figure 2.2

Comparison of rainy and dry season photosynthetic active
radiation measurements on corn.









ease and insect problems and the irregularity
of rainfall. If the assumption that the main
reason for lower yields during the wet sea-
son is a shorter grain filling stage is correct,
then the planting date for rainy season corn
crop should be as near the start of the rainy
season as possible.

J. G. Salinas, E. Gonzalez, E. J. Kamprath,
P. A. Sanchez, W. V. Soares
The long term field experiment where
lime was applied at four different rates and
two depths of incorporation was modified
during the 1974-1975 rainy season to ac-
complish an additional objective: test vari-
etal differences with respect to aluminum
tolerance. The residual effects of lime appli-
cations and the related changes in soil pro-
perties and root development continued to
be measured.
Two grain sorghum hybrids, Taylor
Evans Y-101 and RS-610 were supplied by
plant breeders of the EMBRAPA Corn and
Sorghum Research Center in Skte Lagoas be-
cause differential tolerance to aluminum was
suspected. The original plots were split in
half and sorghum was planted on November
7, 1974 in 60 cm rows at an approximate
population of 250,000 plants/ha. The crop
was harvested on March 11, 1975, after
which a ratoon crop was allowed to grow.
The main crop received broadcast applica-
tions of 150 kg K20/ha as KCI and 50 kg

Mg/ha as MgSO4 and a banded application
of 150 kg P205/ha as triple superphosphate
and 20 kg N/ha as ammonium sulfate. This
was followed by two sidedressed applica-
tions totaling 200 kg N/ha as urea. The ra-
toon crop was not fertilized. No additional
lime has been added to this experiment
since the original application of December
Varietal Differences in Sorghum
The grain yields of the fourth consec-
utive crop are shown in Figure 2.3. Deep
lime incorporation was statistically supe-
rior to shallow incorporation only at the
1 ton/ha rate. There were no differences at
the higher rates as it was observed in the
first and second consecutive crops (1973
and 1974 Annual Reports). The large dif-
ference in this experiment, however, was
the contrasting response between the two
hybrids. Taylor Evans produced dramat-
ically higher yields than RS-610 at the 0,
1 and 2 tons/ha levels of lime. At higher
rates, the differences tended to disappear.
In general, Taylor Evans produced the same
yield with half the rate of lime as RS-610.
Figure 2.4 shows that the differential
response of these hybrids is closely related
to the percent aluminum saturation of the
top 15 cms. Taylor Evans showed a slower
rate of yield reduction with increasing alu-
minum saturation than RS-610. At 40% Al
saturation, for example, Taylor Evans pro-
duced only 27% of the maximum yield at
the same level of aluminum saturation.

Deep Incorporation (0-30cm)

A Taylor Evans Y-IOI
0 RS-610

0 1 2 4 80 1 2 4 8

Lime Applied in

Figure 2.3

1972 (tons/ha)

Differential response of two grain sorghum varieties to rates and
depth of lime incorporation. Brasilia, 1974-1975 rainy season.
Below: Mr. Jose Salinas compares the two sorghum varieties in un-
limed plots. Left: RS-610. Right: Taylor Evans-lOl.

Ilow Incorporation (0-15cm)

The ability of the sorghum plants to
proliferate under high levels of aluminum
saturation was related to the yield differ-
ences. Figure 2.5 shows the relationship be-
tween root lengths and aluminum saturation
in the top 15 cms. Deep liming applications
increased root lengths in both varieties. A
comparison of root lengths in the 15-30 cm
soil depth increment for the two shallow and
deep lime incorporations is shown in Table
2.2 at the rates of 1 and 4 tons/ha. Root
lengths increased in both hybrids with deep
lime incorporation but the effect was most
pronounced in RS-610, the susceptible hy-
These results show the potential for
utilizing aluminum-tolerant cultivars as one
of the management components for acid
Oxisols. A combination of 1 ton/ha of lime
incorporated deeply three years ago and an
aluminum-tolerant hybrid produced a high
grain yield of 6 tons/ha. In contrast, the con-
ventional practice of shallow liming and an
aluminum-sensitive sorghum hybrid required
4 tons/ha to arrive at the same yield of 6
The subsequent ratoon crop performed
very poorly due to considerable bird damage
and poor stand caused by involuntary re-
moval of many plants during the first harvest
as a result of the shallow root system in the
unlimed plots. The results are discarded.
Cumulative Effects of Liming
The cumulative effect of four consecu-
tive crops (3 of corn and 1 of sorghum) is

shown in Figure 2.6. Although there was no
response to depth of liming in the second an
and fourth crop, the overall trend shows a
positive advantage of this practice. Incorpor-
ating lime to 30 cms in effect decreased the
lime rate needed to attain specific yield by
half. As discussed in the previous annual re-
ports, the advantages of deep lime applica-
tions are related to increasing root prolifera-
tion which, in turn, allows for better soil
moisture and nutrient utilization. This favor-
able effect can be expected in other soils
with high aluminum saturation in the sub-
soil. As mentioned in the 1974 Annual Re-
port, no beneficial effects of deep liming can
be expected in soils where the subsoil is not
aluminum-toxic like the Red Yellow Latosol
on the first erosion surface at CPAC. Rou-
tine soil testing for exchangeable aluminum,
calcium and magnesium with depth is recom-
mended as a means for deciding when to in-
corporate lime deeply.
Residual Effects of Liming.
An estimation of the residual effects of
lime applied in 1972 to the first four grain
crops is shown in Figure 2.7, expressed as
percent maximum yield relative to treat-
ment which always gave the highest abso-
lute yield, 8 tons/ha of lime incorporated
to 30 cms. Among the shallow depths of
incorporation, the 1 ton/ha rate has lost
most of its residual effect, producing only
about 26% of the maximum yield during
the fourth crop. In comparison, the 2
tons/ha rate produced 72% of the maximum

Percent Aluminum Sat. (0-15cm)
10 12 33 42 78







Percent Aluminum



Figure 2.4

Effect of aluminum saturation in the top
15 cm on the grain yield of two sorghum
varieties. Brasilia 1974-1975 rainy sea-

Figure 2.5

Varietal differences of sorghum in rela-
tion to root length and percent aluminum
saturation. Brasilia 1974-1975 rainy












yield, the 4 ton/ha rate 83%, and the 8 tons/
ha rates 97%. Consequently, the residual
effect of these rates is still considerable.
The deeply placed treatments, how-
ever, showed a slower rate of decline in their
residual effects. The 1 ton/ha produced
about 47% of the maximum yield, while the
2 and 4 tons/ha rates produced 79 and 86%
respectively. In spite of the lower lime rate
per unit of soil volume, the residual effect of
deeply incorporated lime is superior to that
of the shallow incorporations.
The zig-zag pattern observed in some
treatments with time is typical of data where
relative yields are plotted as a function of
time. The low points are normally associated
with low maximum absolute yields because
other limiting factors prevented a full re-
sponse to the materials added. This was the
case in the third crop which was adversely
affected by extremely wet weather and sub-
sequent pest and disease attacks (1974 An-
nual Report). The overall trend of the experi-
ment suggests that a lime rate of 4 tons/ha
deeply incorporated can provide a good re-
sidual effect with over 80% of the maximum
yield. Deep incorporation of 8 tons/ha re-
mains the best treatment.
Effects on Soil Properties
The changes in soil pH, exchangeable
Al and percent aluminum saturation after
the harvest of the third corn crop (May,
1974), the harvest of the main sorghum crop
(March 1975) and after the harvest of the
sorghum regrowth (July 1975) are shown in

Table 2.3. No major changes in soil pH are
noted. Exchangeable aluminum and percent
aluminum saturation values in the 0-15 cm
layer are increasing with time in all treat-
ments except in 8 tons/ha shallow and deep
treatments. The shallow lime treatments in
the 15-30 layer show a decrease in aluminum
saturation which implies a possible down-
wards movement of calcium and magnesium.
The overall trend in aluminum satura-
tion is shown in Figure 2.8. The decrease in
the residual neutralizing effect of the lime
with time started to be evident after the
third crop was harvested, at about 18
months after application, except for the 8
tons/ha rate in the shallow treatments and
both 4 and 8 tons/ha rate in the deep treat-
ment. The progressive decrease in aluminum
saturation with time in the 15-30 cm layer
of the shallow treatments is also evident in
this figure. Again, a downwards movement
of basic cations is suspected. This important
phenomenon is being studied in greater de-
tail in 1976.
Soil Solution Studies
The soil solution constitutes the most
immediate chemical environment surround-
ing roots. It is in direct physical contact and
hence of utmost importance for nutrient
availability and for toxicity of certain ele-
ments as well. Soil solution studies were
made with soil samples taken from field
plots of each lime treatment during the first
three crops. A displacement procedure was
used to obtain soil solutions. The results

Table 2.2 Varietal differences in sorghum root length as related to rate and depth of
lime incorporation.

applied Depth of Taylor Evans Y-101 RS-610
in 1972 incorporation 0-15cm 15-30cm 0-15cm 15-30cm

tons/ha ---cm- - Root length (cm/100 cm soil) -
0 ------ 31 12 17 9
1 0-15 64 20 39 10
4 0-15 169 25 87 19
1 0-30 72 22 45 17
4 0-30 207 37 106 40

4 Crops 0-30 cm


15 -



0 I 2 4 8

Lime Applied in 1972

Figure 2.6

Cumulative grain yields of four consecutive crops harvested since
the original lime applications. The fourth crop is the average of
the two sorghum varieties. Brasilia, 1972-1975.

Table 2.3 Soil pH, exchangeable aluminum and percent aluminum saturation after the harvest of the third corn crop and
the two sorghum harvests as affected by depth and rate of lime applications in 1972.

Soil pH Exchangeable Al Al Saturation
Depth of Lime Soil May March July May March July May March July
lime incorp. rate Depth 1974 1975 1975 1974 1975 1975 1974 1975 1975

ton/ha -cm-
0 0-15
1 0-15
2 0-15
4 0-15
8 0-15
1 0-15
2 0-15
4 0-15
8 0-15

- 1:1 H20-



meq/100g -



- --cm- --
No lime




- % -


Shallow Placement (0-15cm)
Lime rate
r o8

Deep Placement (0-30 cm)
(4.8) (7.3) (3.6) (7.1)
-- ---" 0 8

F*- '^'^--^4


Crop Sequence

Figure 2.7

Residual effect of lime applications expressed as percent
maximum grain yield relative to the yield of the 8 ton/ha
deep treatment. Numbers in parentheses show the maximum
yields in tons/ha. First three crops corn, fourth sorghum
(RS-610 variety). Brasilia, 1974-1975.








Table 2.4 Cation concentration and pH of the displaced soil solutions of each lime treat-
ment of lime incorporations. Soil sampled after first crop (May 1973).

Depth of Lime Soil Soil Solution
lime incorp. rate depth pH Al Ca Mg K

cm ton/ha cm ppm
No lime 0 0-15 4.3 1.40 22.8 3.3 25.2
15-30 4.2 1.95 13.4 3.6 27.6
Shallow 1 0-15 4.7 0.49 50.8 4.2 20.8
(0-15) 15-30 4.3 1.82 20.0 3.6 22.8
2 0-15 5.7 0.21 112.4 5.0 26.4
15-30 4.5 1.41 30.4 3.6 22.8
4 0-15 6.4 0.06 109.6 5.5 14.0
15-30 4.3 1.29 37.7 4.8 23.6
8 0-15 7.1 0.05 197.6 5.4 12.6
15-30 4.6 1.02 43.8 4.4 22.6
Deep 1 0-15 4.8 0.64 65.8 6.3 26.8
(0-30) 15-30 4.6 0.81 54.0 5.8 22.8
2 0-15 6.3 0.13 114.0 6.2 12.4
15-30 4.7 0.87 61.4 4.7 20.0
4 0-15 6.8 0.03 137.6 6.5 12.4
15-30 5.9 0.20 76.8 4.5 11.0
8 0-15 6.7 0.00 149.0 6.9 12.2
15-30 6.5 0.21 96.0 4.5 15.0

Table 2.5 Effect of levels of aluminum on root length
Soil sampled after first crop (May 1973).

in the 15-30 cms layer of soil.

Lime Al Solution Root
rate satn. Al length

ton/ha % ppm cm/100cm soil
0 79 1.95 147
2 shallow 63 1.41 118
4 shallow 52 1.29 171
4 deep 5 0.20 325
8 deep 5 0.20 346

iAnth Lime 115-30cm Soil Deoth


a 60
c 40




(0-30 cm)

0 I 2 3 4 5 0 I 2 3 4 5

Crop Sequence

Figure 2.8 Residual effects of lime rates and depth of incorporation
on the aluminum saturation after three corn crops and two
sorghum crops. Brasilia, 1972-1975.

I 2 3 4 5 0 I 2 3 4 5


for the samples taken after the first corn har-
vest are presented in Table 2.4.
Aluminum on the exchange site is in
equilibrium with soil solution aluminum. Re-
moval of exchangeable aluminum by neutral-
ization with the various levels of lime de-
creases the level of aluminum in soil solution
and increases the calcium content. Since cal-
citic lime was applied, no increase in magne-
sium was detected. Lime also seems to de-
crease the potassium content to the depth of
lime application.
A consistent relationship was found
between the soluble forms of aluminum,soil
solution and reduction in root growth (Table
2.5). This relationship emphasizes the effect
that high concentrations of aluminum in so-
lution have on the root system of corn.
The shallow application of lime (0-15
cms) did not have an effect on the 15-30
cms soil zone in neutralizing aluminum and
did not increase root growth in the 15-30
cm depth. The deep lime application was ef-
fective in decreasing aluminum in the 15-30
cm depth and in increasing the root length.
There was a concomitant increase in the
level of calcium as lime rates were increased.
From this experiment it is not possible to
separate out the specific effects of aluminum
and calcium root growth. However, it is evi-
dent that aluminum concentrations must be
decreased in order for calcium to have a
beneficial effect on root growth. The field
experiment is being continued by CPAC
scientists to determine how long the residual

effects of lime will last.

R. S. Yost, E. J. Kamprath, E. Lobato,
G. C. Naderman, W. V. Shares
Rates, Placement and Timing of Superphos-
phate Applications.
A fifth consecutive crop of corn was
grown during the 1974-1975 rainy season in
order to continue evaluating the cumulative
or residual effects of ordinary superphos-
phate applications. The experimental design
and methodology has been reported in the
previous annual reports. A decision was
made to stop further banded phosphorus ap-
plications after the fourth crop except for
Treatment number 10 (80 broadcast + 80
banded), the one that had received the least
amount of phosphorus. This permits to com-
pare different treatments at the same levels
of total phosphorus applied. The nitrogen
and potassium applications continued; the
residual effects of the 4 tons/ha of lime and
11 kg Zn/ha were sufficient to produce excel-
lent corn growth.
The yields of the five crops are pre-
sented in Table 2.6. A strong residual effect
is evident in all treatments. The banded
treatments outyielded the broadcast
treatments by about 1 ton/ha at equal rates
of phosphorus applied since 1972. Figure
2.9 shows the trends expressed in relative
yields. The residual effects of the original
broadcast treatments continue to depend on







Broadcast in 1972

S------ 640.
- *2 -. 640






I I I I I 0
I 2 3 4 5

Broadcast + Banded
before each crop
80 Bcst +
A --y 320 Bcst.


40 )-

3 160
o 80


1 2 3 4 5

80 Band. (25)
+ 320 Band.(30)

Successive applications

- No additional P

0 1 2 3 4 5


Corn Crops (1972-1975)

Effects of rate, placement and
phosphate applications to five
yields expressed as percent of
Numbers in parentheses are the
tons/ha. Brasilia, 1972-1975.

residual or ordinary super-
continuous corn crops. Grain
the 1280 broadcast treatments.
cumulative grain yields in



Figure 2.9


the initial phosphorus rate. The 160 kg

P205/ha treatment is only producing about
20% of the maximum yield, the 320 kg

P205/ha about 50% and the 540 kg
P205/ha treatment about 80% of the yield
obtained by the 1280 kg P205/ha broad-
cast rate. The residual effect of four ban-
ded applications was strong during the fifth
crop. Because of the low initial yields dur-
ing the first and second crops, the cumula-
tive yields are similar between the banded
and broadcast treatments at the same levels
of total phosphorus applied (Table 2.6).
The most practical approach appears
to be the combination of an initial broad-
cast application followed by a banded ap-
plication of 80 kg P205/ha before each
crop. When 320 kg P205/ha was broad-
cast initially and was followed by four ban-
ded 80 kg P205/ha applications (Treat-
ment 9) the yields were maintained at
about 80% of the maximum with a total
phosphorus application of 640 kg P205/ha
When the initial broadcast application was
only 80 kg P205/ha and was followed by
five banded applications at the same rate
(Treatment 10) the cumulative yield was
71% of the maximum. These latter two
strategies appear to be most promising
ways of managing superphosphate applica-
tions in this Oxisol with an extremely high
phosphorus fixation capacity.
The changes in available phosphorus
have been monitored after each harvest
using the North Carolina double acid ex-

traction which serves as the basis for fertil-
izer recommendations in the Cerrado. Table
2.7 shows the generally decreasing trend
with time. Comparing this table with the
proceeding figure, it shows that a level of 9
ppm P was needed to produce more than
80% of the maximum yields. If this trend
continues, the residual effect of the 1280
kg P205/ha rates should be expected to
last several more years. This experiment
will be continued by CPAC staff members
in order to fully evaluate the residual ef-
Phosphorus Sources on Pastures
In February 1974 two parallel experi-
ments were planted to evaluate the effects
of cheaper sources of phosphorus in order
to decrease the costs of applications. The
two high solubility rock phosphates, Hiper-
fosfato (North African) and North Carolina
provided similar early growth as ordinary
superphosphate. The low solubility Arax6
rock phosphate produced very little
growth, but when it was thermally altered
as Termofosfato the performance was sim-
ilar to superphosphate. In addition, Termo-
fosfato produced a significant liming effect.
The design and the properties of these ma-
terials were described in the 1974 Annual
Report. The growth of Stylosanthes hu-
milis was very poor and thus, the results are
not presented.
Figure 2.10 shows the results during
the 1974-1975 rainy season for Brachiaria
decumbens. Results of these harvests indi-

Table 2.6 Grain yields of five successive corn crops (Cargill-lll hybrid) as affected by rate, placement,
timing, and residual effects of ordinary superphosphate applications.

Consecutive Corn Yields
Initial Banded Total 1 2 3 4 5 Total
Treatment broadcast applicati*2 applied Rainy Dry Rainy Dry Rainy five Maximum
Number application!/ per crop-' in 5 crops 72-73 73 73-74 74 74-75 crops yields

-------------- kg P205/ha --------------- -------------- tons/ha ---------------- -% --

1 160 0 160 5.23 3.27 0.87 1.78 1.65 12.80 36

2 320 0 320 6.27 5.68 2.20 3.42 3.00 20.57 58

3 640 0 640 6.79 7.48 2.97 6.43 4.82 28.49 80

4 1280 0 1280 7.96 8.53 3.86 9.09 6.25 35.69 100

5 2000 0 2000 2.26 9.54 4.56 9.02 6.60 31.98 90

6 0 80 320 2.42 5.08 3.08 6.03 4.49 21.10 59

7 0 160 640 3.85 6.57 3.41 8.07 5.86 27.76 78

8 0 320 1280 4.79 8.42 4.19 9.03 6.89 33.32 93

9 320 80 640 6.65 7.32 3.33 7.22 5.40 29.92 84

10 80 80 480 4.56 6.00 2.56 6.48 5.79 25.39 71

1/All applied on November 1972 except for Treatment 5
kg P205/ha after the first crop on June 1973.

0.67 0.65 0.88

which received 80 kg

0.79 0.67

P205/ha on November 1972 and 1920

2/All banded applications stopped after the fourth crop, except for Treatment 10 which continued on the fifth crop.

Table 2.7 Soil test values for phosphorus (North Carolina dilute double acid method) after
each corn harvest in the broadcast treatments.

Broadcast 1 2 3 4 5
P applied Rainy Dry Rainy Dry Rainy
in 1972 72-73 73 73-74 74 74-75

kg P205/ha -- Available P (ppm)- - -
160 4.6 3.9 3.6 2.9 3.1
320 8.8 7.4 5.0 4.4 5.1
640 17.7 19.5 10.0 8.0 9.0
1280 68.8 55.8 30.6 25.3 21.9
2000 ---- 103.5 65.6 50.2 42.9



Russell Yost sampling soils in the
residual phosphorus experiment.




12 -

I LS.05


Lime rates
o 0
a 4.5

86 345





I LSD,05

86 345






86 345




N.C. Rock



86 345

P Applied

in February, 1974

(kg P205/ha)

Figure 2.10

Effects of sources and rates of phosphorus and liming on
annual dry matter production of Brachiaria decumbens. Sum
of second and third cuts on December 1974 and March 1975.




cate that the high reactivity rock phosphate
sources (Hiperfosfato and North Carolina)
are continuing to supply phorphorus nearly
as well as the highly soluble ordinary super-
phosphate. The Termofosfato continued to
perform as well as superphosphate.
A comparison of May 1974 yields with
March 1975 yields suggests that the availa-
bility of Araxa rock phosphate increases
with time (Figure 2.11). This effect appears
to be somewhat reduced at the higher level
of lime. Yields of the May 1975 harvest
show less response occurred to soluble phos-
phorus source levels above 345 kg P205/ha
than on earlier harvests. This trend may be
in part due to a more fully developed root
A treatment of 86 kg P205/ha as ordi-
nary superphosphate was surface applied
with no incorporation in November 1974.
The May 1975 yields with this treatment are
very high relative to a similar thoroughly in-
corporated before grass establishment (Fig-
ure 2.11). This suggests surface applications
of phosphate on this grass species can be
quite effective and that some important
feeder roots are near the surface. Future har-
vests will assist in determining how effective
surface applications are relative to incorpo-
rated ones.
Soil pH determined two months after
lime application but before phosphate treat-
ments were added was 4.4, 4.8, and 5.1 with
lime applications of 0, 3, 4.5 tons/ha, respec-
tively. Soil pH, after three additional months

of equilibration, was 4.4, 5.2, and 5.4 with
the respective lime treatments. Lime appli-
cations tended to increase yields when ap-
plied with soluble phosphate but tended
to reduce yields when applied together with
slowly soluble rock phosphate sources. Re-
sults to date suggest citrate solubility of
these sources was more influential on avail-
ability to this grass than pH variations from
4.4 to 5.4.
As measured by grass yields, the Hiper-
fosfato, North Carolina rock phosphates and
the Termofosfato, provided nearly as much
available phosphorus as ordinary superphos-
phate. The low solubility Arax6 rock phos-
phate appears to be increasing in availability
with time and may be economically compet-
itive in the long run.

R. S. Yost, K. D. Ritchey, E. Lobato, G. C.
The first extrapolation experiment was
initiated last year on the loamy Red Yellow
Latosol located on the first erosion surface
at CPAC. This type of Oxisol is very exten-
sive in the Cerrado and at the location where
the experiment was installed it differed signi-
ficantly from the Dark Red Latosol where
all other experiments have been performed
in a higher available water range and in a
lower aluminum saturation in the subsoil.
Soil properties and the first year results ap-





May, 1974





86 345




May, 1974


Lime rates:
o 0
A 4.5

86 345

December, 1974






Al I I I

86 345


December, 1974



12 March, 1975
10 surface



86 345


86 345

P Applied in

February, 1974

(kg P205/ ha)

Figure 2.11

Increased availability of AraxS rock phosphate sources with
time to Brachiaria decumbens.






2 -








peared in the 1974 Annual Report.
The second consecutive rainy season
crop was planted on November 1974. Corn
(Cargill-111) was planted on one half of the
double size plots and grain sorghum (Agro-
ceres-1001) was planted on the other half.
The double sized plots allowed pursuit of
two objectives: 1) The study of residual ef-
fects of the original lime and phosphate ap-
plications with a standard crop and variety
on a second variant of soils of the Cerrado,
and 2) expand the information to include
effects of the fertility treatments to differ-
ent crops such as grain sorghum, soybeans,
etc. Fertilizer treatments and yields of corn
and grain sorghum are shown in Table 2.8.
For comparable phosphorus treatments
there was no significant difference between
deep and shallow lime incorporations for
either crop even though two drought periods
occurred during the growing season. Last
year the deep lime treatments on this soil
gave higher yields of corn though the differ-
ences were not significant. These results dif-
fer from those of the experiments on the
Dark Red Latosol where the deep lime incor-
poration (0-30 cm) has given consistently
higher yields of maize than the shallow lime
incorporation (0-15 cm). One probable ex-
planation is that the percent aluminum satu-
ration in the 15-30 cm layer of the Red Yel-
low Latosol is substantially less than that of
the Dark Red Latosol, 25 versus 53%.
Grain sorghum yields did not respond
significantly to applications of phosphorus

higher than the 400 kg P205/ha broadcast
the previous year. Sorghum was more re-
sponsive to lime applications than was corn
probably because of lower tolerance to ex-
changeable aluminum.
Yields of both crops were high consider-
ing the occurrence of the two drought per-
iods during the cropping season. These
drought periods required supplemental irri-
gation in the experiments later planted on
the Dark Red Latosol. Even though the ex-
periment on the loamy Red Yellow Latosol
was not irrigated, the yield of corn on this
soil was higher than that of the irrigated
Dark Red Latosol, 8.9 tons/ha versus 6.6
tons/ha. This yield difference is probably
due to the fact that the Red Yellow Latosol
contains 30% more available water at field
capacity in the surface 30 cms, and that the
lower percent of exchangeable aluminum in
the Red Yellow Latosol subsoil allows
greater root penetration of aluminum sensi-
tive crops. This experiment points out im-
portant management differences related to
available water capacity and subsoil acidity
among Oxisols with otherwise very similar
properties. The experiment will be planted
again to corn and sorghum for the third con-
secutive rainy season crops in 1976 by CPAC

K. D. Ritchey, F. R. Cox and R. S. Yost
In an effort to evaluate the behavior of

Table 2.8

Residual effects of phosphorus and lime applications on the loamy Red Yellow Latosol on corn
(Cargill-lll) and grain sorghum (Agroceres-1001) yields.

Treatment P applied in 1973 P applied in 1974 Lime applied
Number Band. Bdc. Band. Bdc. in 1973 Corn Yields Sorghum Yields

------------- kg P205/ha ------------- -- tons/ha -- tons/ha* % max. tons/ha* % max.

6 0 2000 0 0 4 deep 8.90 a 100 8.08 a 100

3 100 400 50 0 4 shallow 7.99 b 90 7.82 a 96

7 100 400 100 0 4 shallow 7.69 b 86 8.16 a 100

8 100 400 100 0 4 deep 7.63 b 86 7.36 a 91

2 100 400 50 0 4 deep 7.20 bc 81 7.35 a 91

4 100 400 150 0 4 deep 7.14 bc 80 8.08 a 100

5 0 400 0 0 4 deep 6.67 c 75 7.33 a 91

1 100 400 50 0 no lime 5.85 d 66 3.56 b 44

*Means followed by the same
Multiple Range Test.

letter are not significantly different at the 5 percent level by Duncan's

other crops, the large plots of the residual
zinc experiment were also split in two and
planted to corn and sorghum during the
rainy season of 1974-1975. The corn crop
would permit the evaluation of the residual
effects of zinc sulfate applications of Decem-
ber 1972 with the same hybrid. At the same
time new data was obtained with grain sor-
ghum. The subplots received a broadcast ap-
plication of 150 kg K20/ha as KCI and 160
kg P205/ha as simple superphosphate at
planting. The corn was topdressed with 150
kg N/ha as urea and the sorghum with 271
kg N/ha as urea. Soil samples were taken be-
fore planting and analyzed for zinc using
three different soil test extractants. No addi-
tional zinc, lime, boron or molybdenum has
been applied since 1972. The high lime rate
used raised the soil pH level to 6.6 in 1972.
Figure 2.12 shows the results of the
third consecutive planting. A strong residual
effect of zinc applications was evident. The
optimum level for corn appears to be about
9 kg Zn/ha, which is higher than the level of
3 kg Zn/ha obtained in the previous two
crops (1974 Annual Report). Sorghum pro-
duced a much higher yield than corn with-
out added zinc and approached maximum
yield at the 1 kg Zn/ha rate. Apparently,
sorghum has a lower zinc requirement than
corn, or it is more efficient in extracting
The residual effect on corn is shown in
Figure 2.13 expressed as a percentage of the
maximum yield which was attained by 9 kg

Zn/ha in all consecutive crops. The 3 kg
Zn/ha rate maintained approximately 89%
of the maximum yield in all three crops. The
yields with no zinc applied have been in-
creasing with time. The reasons for this are
not fully understood. Contamination of Zn
from adjacent plots with successive tillage is
also a possibility which is being investigated
during 1976.
An additional treatment without boron
has been included at the 9 kg Zn/ha rate.
This treatment has produced over 90% of
the maximum yield in all crops, which is
probably within the realm of the experi-
mental error. Consequently, no boron defi-
ciencies are suspected in this soil.
Cate-Nelson diagrams shown in Figure
2.14 for all three years indicate that extract-
able soil zinc levels of 1.4 ppm for 0.1 N
HCI, 1.0 ppm for 0.05 N HCI + 0.025 N
H2SO4, and 0.7 ppm for DTPA-TEA appear
to be the critical levels above which there is
enough available soil zinc to eliminate zinc
deficiency on corn on this Dark Red Latosol
limed to pH 6.6.

K. D. Ritchey and G. C. Naderman
For the third continuous corn crop in
the nitrogen experiment grown in the 1974-
1975 rainy season, last year's experimental
design was modified slightly. The sulfur-
coated urea (SCU) treatment was continued
but the material was different from that
used in either the first or second crop. This

"O-0-o--------- -.- ...---.. "o

Corn (Cargill 111)

o Sorghum (RS-610)


Figure 2.12




3 9 26
Zn Applied in 1972 (kg/ha)
Yield responses to residual zinc applications by corn
and sorghum (third consecutive crops). Brasilia 1974-75
rainy season.


. .* 1-- --e I



0 I

Consecutive Corn Crops

Figure 2.13

Residual effects of zinc applications in 1972 to three
consecutive corn crops (Cargill-lll hybrid) growth during
the 1972-1973, 1973-1974 and 1974-1975 rainy seasons in

I kg

< I I

i A










e 1972-73
A 1973-74
o 1974-75


S 11-4 2 3 4 6

0.05N HCI + 0.025N H2SO4


S I l I I

0 I 2 3 4 5






0 0.7 1 15 2 2.5 3

Soil Test Zn

( ppm)

Figure 2.14 Relationship between percent yield of Cargill-lll corn (relative to 9 kg/ha Zn)
and soil zinc removed by three extractants for three years.

m n J w

. 1


Table 2.9

Grain yields (15.5 percent moisture) of the third maize crop of the nitrogen experiment at
Brasilia 1974-1975 rainy season.

Treatment 20 days 30 days 61 days
Number At planting after planting after planting after planting Yield-

--------------------------------- kg N/ha -------------------------------- kg/ha

9 20 100 0 100 7700 a

8 20.2 0 1202/ 0 7438 ab

7 20 60 0 60 7324 ab

5 20 0 120 0 7256 ab

4 20 0 80 0 7015 abc

6 20 40 0 40 6953 abc

1 0 0 80 0 6804 bc

3 20 0 40 0 6336 c

10 1403/ 0 0 0 6254 c

2 0 0 0 0 4201 d

1/Duncan's Multiple Range Test at the 5% level.

2/Lime-coated NH4NO3

3/Sulfur-coated urea 10.1% soluble in 7 days.

material had a slower rate of nitrogen release
than last year's material (10.1% in 7 days)
according to TVA. Maintenance fertilization
consisted of 150 kg K20/ha as KCI broad-
cast and 100 kg P205/ha applied as a band
at seeding. The treatment descriptions and
yields for the third maize crop are given in
Table 2.9.
Grain yields increased from 4.2 tons/
ha with no nitrogen applied to 7.7 tons/ha
with 220 kg N/ha (Figure 2.15). Yields from
the application of 240 kg N/ha approached
the maximum. Increasing the number of
sidedressings from one to two did not in-
crease yields. The application of nitrogen as
ammonium nitrate gave about the same yield
as that applied as urea. The use of 240 kg
N/ha as sulfur-coated urea in a band below
the seed at planting resulted in reduced
stands and lower yields.
During the three years of growing
corn in the nitrogen experiment the coeffi-
cient of variability has gradually decreased
and the yields of the no nitrogen added plots
have increased (Table 2.10). This phenom-
enon has been observed in the Cerrado
farms. Calculations on the soil nitrogen re-
lease after liming and fertilization with other
nutrients appear to account for these differ-

J. G. Salinas and P. A. Sanchez

Aluminum toxicity and phosphorus
deficiency frequently occur together in most
of the Cerrado Oxisols. Previous work con-
ducted in Brasilia has identified both high
levels of exchangeable aluminum and low
available phosphorus as serious limiting fac-
tors of crop production. Up to last year,
phosphorus fertilization and liming to opti-
mum levels along with their residual effects,
have been considered the main strategies to
solving these problems. Tolerance studies on
aluminum toxicity and low available phos-
phorus provide an additional dimension.
This new strategy does not mean the elimi-
nation of phosphorus fertilization and lim-
ing. However, it can decrease phosphorus
fertilizer and lime requirements needed to
obtain adequate yields.
Work during the year included both
greenhouse and field research with the fol-
lowing objectives: 1) To study the varietal
and species differences in tolerating high
levels of aluminum and low levels of avail-
able phosphorus, 2) to identify certain phy-
siological mechanisms responsible for alu-
minum-phosphorus interactions in this dual
tolerance, 3) to determine whether green-
house tests can be used in lieu of field tests
for certain phases of this dual tolerance.
Corn, wheat, beans, sorghum and rice
varieties were tested under greenhouse solu-
tion culture and field conditions. Most of
the varieties were provided by Brazilian in-
stitutions on the basis of possible differences
related to aluminum toxicity and phos-

Y NH4N03
Sulfur-coated urea

Applied in furrow at planting
0 One sidedressing
A Two sided ressings

60 80 100 140 220

Nitrogen Applied (kg/ha)

Figure 2.15

Table 2.10

Corn response to nitrogen applications. Third consecutive
crop. Brasilia 1974-1975 (supplied as urea except where

Effect of successive cropping on corn grain yields (Cargill-lll
hybrid) grown without added N and the coefficients of variabil-
ity of the experiment.

Grain yields of plots Coefficient of
Crop without added nitrogen variability

------- kg/ha -------- -----%-------

1972-1973 3246 16.9
1973-1974 3757 11.2
1974-1975 4201 8.3

phorus deficiency. Varieties were provided
by Dr. Robert Shaffert of the National Corn
and Sorghum Center at S&te Lagoas, Dr. Ady
Raul da Silva of the Cerrado Center, Dr.
Clibas Viera of the Universidade Federale de
Vicosa and Dr. Charles A. Francis and James
M. Spain of CIAT in Colombia. The report
covers the greenhouse studies with corn,
wheat and bean varieties and the field stu-
dies with wheat and bean varieties.
Greenhouse Studies with Corn and Wheat:
A flowing solution culture method was
developed for these studies. The equipment
consists of twelve independent units, each
with a 5 liter-storage tank provided with a
small water pump which is connected
through plastic tubes to five 5-liter pots.
Each pot corresponds to one variety on
which 6 to 20 plants are grown depending
on the species. The flow path is shown in
Figure 2.16. A factorial design was used with
five varieties, two levels of aluminum and
two levels of phosphorus, replicated three
The pH of the nutrient solution was
maintained at 4.5, and the concentration of
Al and P was measured and adjusted to the
original levels every two days. Considering
the large number of pots used in the experi-
ments, the flow culture solution technique
had the advantage of permitting to control
the pH, aluminum and phosphorus levels in
nutrient solution every two days within an
acceptable degree of precision in only

twelve samples.
Corn and wheat seeds were germinated
in trays with sand for 10 or 20 days depen-
ding on the variety. After the seed was de-
tached, seedlings selected for uniformity
were transferred to the flowing solution
culture with a flow rate of about 70 liters/
pot/hour and were grown for seven days in
a complete Hoagland's solution without alu-
minum and with a low phosphorus concen-
tration of 0.05 ppm P. After the harvest of
some of the seedlings, the rest of the plants
were grown for 10 additional days under
two levels of aluminum (0 and 8 ppm Al)
and two levels of phosphorus (0.05 and 0.2
.ppm P). Plant tops and roots were harvested,
dried at 70 degrees Centigrade for a mini-
mum of two days, weighed and ground to
pass a 200 mesh stainless steel screen and
analyzed for aluminum, phosphorus, calcium
and magnesium.
The parameters evaluated were: dry mat-
ter production of roots and tops, root
length, relative growth rates, mean relative
extension rates, and nutrient absorption and
translocation rates for aluminum, phos-
phorus, calcium and magnesium. At the date
of this writing the nutrient analyses are not
Growth Rates (GR), Mean Relative
Growth Rates (RGR), and Mean Relative
Extension Rates (RER) were calculated by
the use of the following formulae: GR=W2-
W-1/t2-t1 (mg/day) and RGR=1n W2-1n
Wl/t2-t1 x 100 (%/day), where W2 and W1











Figure 2.16


Flow path diagram for tolerance experiments in nutrient
culture solution (Brasilia, 1975).


are the top or root weights at time t2 and t1,
respectively. RER=1n L2- in L1/t2-tl x
100 (% day), where L2 and L1 are the root
lengths at time t2 and tl, respectively.
The results are presented in Tables 2.11
and 2.12 and discussed in terms of their tol-
erance to stress factors by comparing indi-
vididual treatment pairs:
Treatment Al P Stress
1 0 0.20 None
2 0 0.05 P
3 8 0.20 Al
4 8 0.05 AI+P
Tolerance to Phosphorus Stress Alone
(Treatment 1 vs. 2)
When the corn and wheat varieties were
subjected to low available phosphorus (0.05
ppm P) in nutrient solution, absolute (GR) a
and relative growth rate (RGR) of roots and
tops, and mean relative extension rates
(RER) of roots decreased in all varieties of
both species. Larger reductions were ob-
served in top growth rates than root growth
rates. These results suggest that the phos-
phorus requirements for roots may be rela-
tively low compared with that for tops. Top
growth rate (GR) was the parameter which
varied the most among varieties. In corn, the
Brazilian varieties or hybrids Tuxpon-5243,
SA-30672, Agroceres-152 and Cargill-111
produced more than 50% of the maximum
top GR under phosphorus stress, while
DeKalb XL45-A (a U. S. hybrid), White Cari-
magua (a Colombian line) and Catete-18267

(a Brazilian line) were most susceptible to
phosphorus stress, attaining less than 33% of
the maximum top growth rate. Among the
wheat varieties the Brazilian ones were as a
group more tolerant to phosphorus stress
than the Mexican varieties. The Brazilian
varieties, with the exception of IAC-5, pro-
duced more than 50% of the maximum top
growth rate, while the Mexican varieties pro-
duced less than 50%. The Brazilian varieties
IAS-20 and BH-1146 were the most tolerant
to phosphorus stress according to top
growth parameters.
Tolerance to Aluminum Stress Alone
(Treatments 3 vs. 1)
In general, most of the corn and wheat
varieties showed a greater reduction in root
growth rates than in top growth rates in re-
sponse to high levels of aluminum in nu-
trient solution. This is the opposite of the
situation when phosphorus was the limiting
factor. These results indicate that the main
effect of aluminum toxicity is the marked
reduction in root growth while the main ef-
fect of phosphorus deficiency is the reduc-
tion in top growth. The reduction in root
growth rates and root length in the presence
of aluminum was the criteria used to eval-
uate aluminum tolerance.
Cargill-111, White Carimagua and
Catete-18267 corn lines were the lease affec-
ted by high aluminum levels as compared to
the control treatment. On the other hand,
Yellow Carimagua, DeKalb KL-45A and
Tuxpon-52453 were the most sensitive. It

0 ppm Al. 8 ppm Al. 0 ppm Al. 8 ppm Al.

Differential effects of aluminum and low phosphorus on root growth of wheat varieties. Left:
BH-1146, a tolerant variety. Right: Sonora-63, a susceptible variety. All roots were grown at the
low phosphorus concentration (0.05 ppm P).

is also of interest to note that Catete-18267
and White Carimagua showed tolerance to
aluminum stress but not to phosphorus
stress. The opposite response was observed
with Tuxpon-52453. These characteristics
should be of interest to plant breeders, sug-
gesting the possibility of crossing to provide
a dual tolerance to both aluminum toxicity
and low available phosphorus.
The varietal differences in wheat essen-
tially followed those observed when phos-
phorus stress was the limiting factor. The
Brazilian varieties BH-1146, IAC-5 and
Toropi were the most aluminum tolerant
varieties, while the Mexican varieties
INIA-66, Paraguai-214, CIANO and
Sonora-63 were the most sensitive. Thus, the
wheat varieties sensitive to aluminum stress
were also sensitive to phosphorus stress, and
those tolerant to one were tolerant to the
A visual characteristic of the sensitive
corn and wheat varieties growth with 8 ppm
Al was that their roots became stubby, thick
and brown. The lateral roots which initiated
during the first 7-day period in nutrient solu-
tion without aluminum did not elongate
when exposed to 8 ppm Al. The leaves
showed the phosphorus deficiency symp-
toms which normally accompany aluminum
toxicity. In corn, the leaves of sensitive lines
were deep purplish-red in color and the sen-
sitive wheat varieties developed a purple
coloration in stems and leaves and after that
a yellowing of leaf tips.

Considering the difficulty of obtaining
seedlings of equal root length for all vari-
eties, due to the inherent genetic differences,
mean relative extension rate (RER) of roots
appears to be a good parameter of evaluating
aluminum tolerance since RER removes ini-
tial root length differences. Moreover, ex-
pressing the rates in relative units (%) as a
function of the maximum rates attained
without phosphorus or aluminum stress pro-
vides a promising test for identifying varietal
According to mean relative extension
rates, the ranking in aluminum tolerance
(from the least to the most tolerant) for the
corn inbred lines was: SA-30672 > Catete-
18267 > White Carimagua > Catete-28150>
Yellow Carimagua > Palha Roxa-15768>
Tuxpon-52453. In the hybrid corn lines the
ranking was: Cargill-111 > Agroceres-259>
DeKalb-XL-45A > Agroceres-152. However,
the hybrid corn lines had smaller differences
in RER's among them than inbred corn
In general, the mean relative extension
rates of roots in all the wheat varieties de-
creased more than 50% when aluminum was
added to the nutrient solution. However,
varietal differences were noted since this
parameter fluctuated between 51% and 83%.
BH-1146, IAS-55 and Toropi showed the
smallest reduction and Sonora-63 and Ama-
zonas had the largest reduction.
Tolerance to Combined Aluminum and
Phosphorus Stress (Treatments 4 vs. 1).

Table 2.11 Effects of phosphorus and/or aluminum stress in culture solution on growth rates (GR) mean
relative growth rates (RER) of corn tops and roots and the mean relative root extension rate
(RER). Expressed as percent of values attained by the treatment without any stress.

Corn Varieties P Stress Al Stress Al and P Stress
or Top Root Top Root Top Root

----------------------------- % of unstressed treatment ------------------------------

DeKalb XL-45A 29 40 44 52 97 57 67 34 42 52 29 39 34 42 34

Catete-18267 33 51 63 78 86 54 71 52 71 53 24 40 35 55 32

White Carimagua 38 47 49 60 58 60 69 51 61 51 33 42 33 43 31

Yellow Carimagua 41 53 57 68 49 37 49 42 53 47 32 44 31 42 43

Agroceres-259 42 58 61 73 75 51 65 49 63 53 18 29 13 22 23

Palha Roxa-15768 45 61 58 73 74 34 49 40 59 38 17 28 15 25 23

Catete-28150 45 62 72 80 93 23 39 62 72 49 15 28 31 42 17

Agroceres-152 52 64 70 79 59 49 61 40 52 43 29 41 28 40 27

Cargill-1ll 54 63 80 86 60 61 70 55 67 58 30 40 24 35 28

SA-30672 63 74 66 79 85 55 68 31 49 56 32 45 14 26 13

Tuxpon-52453 67 77 78 85 80 46 59 48 59 15 35 48 19 27 9

In Treatment 4, phosphorus was low
(0.5 ppm P) and aluminum concentration
high (8 ppm Al). All the growth parameters
evaluated in corn and wheat varieties were
reduced by more than 50% in the presence
of the combined stress when compared to
the control treatment in which neither of
these two elements were limiting. In spite of
this considerable reduction, there was a
range of tolerance within corn and wheat
Within inbred corn lines, the compar-
ison between the inbreds Tuxpon-52453 and
Catete-18267 is of interest. Catete-18267
had a larger reduction in top RGR than in
root RGR and RER compared with Tuxpon-
52453 which showed the opposite response.
Probably this type of response is due to the
different performance of both inbreds under
conditions of critical aluminum and low
available phosphorus in the growth medium.
The inbred SA-30672 seems to present a re-
sponse similar to Tuxpon-52153. Palha
Roxa-15768 and Catete-28150 were the
most sensitive inbreds to both high alu-
minum and low phosphorus conditions.
Within the hybrid corn lines, the exception
was Agroceres-259 which showed the largest
reduction in all the parameters considered in
this dual tolerance evaluation.
The wheat varieties which maintained
the best overall top and root growth rates
and RER of roots in the presence of high
aluminum and low phosphorus in nutrient
solution were BH-1146, IAC-5 and Toropi.

These preliminary results have shown
some varietal differences in important
growth characteristics among corn and
wheat varieties. When nutrient absorption
and translocation rate data (P, Al, Ca and
Mg) are completed in 1976 a much more
complete interpretation will be possible.
Greenhouse Studies with Beans
In the case of beans, due to the con-
siderable number of varieties and unknown
to aluminum, the methodology was modi-
fied for the initial screening. A factorial de-
sign using 10 bean varieties and two levels
of aluminum was replicated three times.
Selected bean seedlings without attached
cotyledons were transferred to the flowing
solution culture and were grown for 15 days
under two levels of aluminum (2 and 8 ppm
Al) and one level of phosphorus (0.05 ppm
P). Consequently, the screening compared
the presence or absence of aluminum stress
both in the presence of phosphorus stress.
Except for this change, the methodology
was the same as used in the corn and wheat
The results are shown in Table 2.13. In
order to remove the effect of inherent
growth characteristics between varieties, the
data for the 8 ppm Al treatment were ex-
pressed as percentage of those for the 2 ppm
Al treatment. These relative yield indexes
were used to calculate the correlation coeffi-
cients of greenhouse and field parameters.
Relative yields of both tops and roots
reflected a wide range in tolerance to alu-

Table 2.12 Effect of phosphorus and/or aluminum stress in culture solution growth rates (GR), growth rates
(RGR) of wheat tops and roots and on mean relative root extension rates (RER). Expressed as
percentage of values attained by the treatment without stress.

P Stress Al Stress Al and P Stress
Top Root Top Root Top Root

---------------------------- % of unstressed treatments








49 55 57 61

42 50 50 55

40 48 45 54

40 46 54 62

43 49 66 71

37 43 40

47 39 47

50 37 45

47 35 41

45 37 44

40 44 33

34 40 21

23 30 42

33 41 31

33 38 17

30 24

34 21

25 26

23 24

15 18 25 30 28







59 66 75 81

53 61 57 60

51 58 67 75

64 71 79 86

48 59 86 89

51 40 48

61 40 48

61 55 62

54 55 62

59 46 57

39 48 36

29 34 48

54 63 45

48 56 43

41 49 31 41 52 40 48 39

18 27

13 36

47 37

49 40

Table 2.13 Response of 18 Phaseolus vulgaris varieties grown in nutrient
solution containing high and low aluminum concentrations and
at a uniformly low level of available phosphorus. Mean of
three replications. Brasilia, 1975 dry season.

Top Yield Root Yield Root Length,
Variety 2ppm 8ppm RTY1/ 2m 8p8pm RRY/ 2ppm 8ppm RRL'

Diacol Nutibara-235


Blue Lake

Manteigao Fosco NI-11




Preto redondao-242

Manteigao preto



Selegao Cuba-1002



Costa Rica-890-37R

Costa Rica-1031




484 176

504 191

477 193

313 155

238 132

329 196

274 179

687 452

625 430

361 264

429 315

316 272

333 262

392 266

397 304

470 399

450 358

354 315


125 52

305 207

306 242

219 129

363 197

150 119

190 148

331 245

263 193

192 172

287 175

101 78

170 106

131 102

208 161

248 206

188 176

217 193

--- cm ---



















1/RTY = Relative Top Yield = (8 ppm A1/2 ppm Al) x 100.

2/RRY = Relative Root Yield = (8 ppm A1/2 ppm Al) x 100.

3/RRL = Relative root Length = (8 ppm A1/2 ppm Al) x 100.

Above: Varietal differences in top growth of beans under high levels of aluminum (8 ppm Al)
and low levels of phosphorus (.05 ppm P). From left to right: Ricopardo-896 (a tolerant
variety), Caraota-260 (a susceptible variety).
Below: Root response to high Al levels in the susceptible bean variety (Diacol Nutibara-235).
Left: 8 ppm Al, right 2 ppm Al.

minum toxicity and phosphorus deficiency
in nutrient solution. For example, relative
top yields ranged from 36% for Diacol Nuti-
bara-235 to 98% for Carioca-1030. Relative
root yields varied from 42% for Diacol Nuti-
bara-235 to 89% for Ricopardo-896 and rela-
tive root length index from 34% for Caraota-
260 to 87% for Carioca-1030. Visual symp-
toms of aluminum injury were noted in the
roots which became thickened, turned
brown, and lateral roots which did not elon-
gate (see photo). This symptom is character-
istic of aluminum toxicity and was observed
to be more severe in aluminum-sensitive
bean varieties such as Caraota-260, Diacol
Nutibara-235, and Manteigao Fosco NI-11
than in aluminum-tolerant bean varieties
such as Carioca-1030, Ricopardo-896, and
Costa Rica-1031.
The relationships for the different para-
meters are shown in Figure 2.17. Correlation
coefficients between the relative top, root
and root length indexes were r = 0.46 for
relative top yields with relative root yields,
r = 0.32 for relative root yields with relative
root length index, and r = 0.64 for relative
top yields with relative root length index.
With the exception of the root yield-root
length index correlation, the other r values
were highly significant at the 1% level. These
results suggest that the best parameters for
evaluating bean tolerance to aluminum toxi-
city and phosphorus deficiency in nutrient
solution are the top yields and the root
length, probably because top yields are af-

fected more severely than root yields when
phosphorus stress occurs and root length is
reduced significantly when aluminum stress
occurs. Consequently, the use of these para-
meters in the screening of bean varieties for
dual tolerance (aluminum toxicity and phos-
phorus deficiency) looks promising.
Field Experiment
The next step in this investigation in-
volved subjecting the varieties to phosphorus
and aluminum stress in the field. A new field
experiment was established during the 1975
dry season where all the material tested in
the greenhouse could be evaluated at three
levels of phosphorus and three levels of alu-
minum saturation. The properties of the
Dark Red Latosol used appear in Table
Figure 2.18 shows the aluminum neu-
tralization and phosphorus retention curves
based on soil-lime incubation and phos-
phorus sorption isotherm studies carried out
on the surface soil. A factorial design with
three lime levels (designed to provide 10%,
35% and 70% aluminum saturation) and
three phosphorus fertilizer levels (to provide
0.008, 0.02 and 0.05 ppm P in the soil solu-
tion) was used, replicated three times. The
lime levels applied were 0.5, 1.5 and 4.0
tons/ha of CaCO3-equivalent. The phos-
phorus rates needed to achieve the desired
levels in the soil solution were 160, 778 and
1374 kg P205/ha as triple superphosphate
broadcast and incorporated into the topsoil.
The lime was applied to the field and incor-

Table 2.14

Chemical characteristics of the Dark Red Latosol site at
CPAC used for the tolerance experiment. Mean of nine

Soil pH Available P Exchangeable
Depth H20 1:1 IN KC1 (NC extractant) A1 Ca + Mg ECEC Al Sat.

-- cm -- ----ppm---- --- meq/100cc --- %
0-20 4.7 3.9 1.9 1.04 0.15 1.19 87.8
20-40 4.6 3.9 1.5 0.90 0.15 1.05 84.8

0.55 1.64 4.37
Dolomitic Lime (tons/ ha)

P in Soil Solution (ppm)

Figure 2.18 Aluminum neutralization and phosphorus retention
the Dark Red Latosol soil (10-20 cm layer).

curves of

porated to 20 cm depth on March 20, 1975.
A detailed sampling of soil was done at one,
six and ten months after incorporation and
standard analyses were made to evaluate the
soil-lime reaction during the dry and wet sea-
During the 1975 dry season the 10
wheat varieties and the 18 bean varieties tes-
ted in the screenhouse were planted in indi-
vidual 6 m rows. Also 26 sorghum lines not
previously tested in the greenhouse were
planted to take advantage of the available
space. The sorghum results will be reported
next year to accompany the greenhouse
data. Corn was planted during the
1976 rainy season and will be reported in
the 1976 Annual Report. The experiment
was planted on May 26, 1975. Beans were
harvested on August 29 and wheat on Sep-
tember 5 and 22, depending on the variety.
A blanket broadcast application of 100 kg
K20/ha as KCI, 10 kg Zn/ha, 10 kg borax/ha
and 0.5 kg Na2MoO4/ha was applied. Nitro-
gen was applied according to the crop:
wheat 80 kg N/ha in two applications and
beans 60 kg N/ha also in two applications.
The performance of the 10 wheat vari-
eties is reported on Table 2.15. All varieties
responded strongly to phosphorus and lime
application but showed marked differences
particularly under both phosphorus and
aluminum stress (0.008 ppm P and 61% Al
saturation), phosphorus stress alone (0.008
ppm P and 24% Al saturation) and under

aluminum stress alone (0.05 ppm P and 61%
Al saturation). Although grain yield data re-
ported on a row basis cannot be directly
interpreted in terms of tons/ha because of
border effects, the maximum yields of each
variety were equivalent to a range from 1.3
to 3.5 tons/ha, which is normal. The range
of yields observed between wheat varieties
was thirty-ninefold under both phosphorus
and aluminum stress, about sevenfold under
aluminum stress alone, fivefold under phos-
phorus stress alone, and about twofold with
no stress. This illustrated the wide varietal
differences in tolerance to the combinations
of high levels of aluminum and low available
phosphorus, the two main adverse soil condi-
tions characteristic of this Dark Red Lato-
Of the ten wheat varieties tested at the
lowest lime-P levels, IAC-5, BH-1146, and
Toropi showed most tolerance. They showed
a better stand and produced significantly
higher grain yields than the other wheat vari-
eties. The most sensitive varieties under both
adverse soil conditions were Sonora-63, Para-
guai-214, and INIA-66 with grain yields less
than 10% of their maximum yields. These
sensitive varieties showed phosphorus defi-
ciency symptoms in stems and leaves during
early growth and after that a yellowing and
necrosis in the leaf tips.
All wheat varieties showed a significant
yield response to phosphorus at all lime
rates. Maximum yields were obtained at the
highest phosphorus rate although at differ-

Table 2.15

Field performance of various wheat varieties at different levels of phosphorus (160, 778 and
1374 kg P205/ha*)and aluminum saturation. Brasilia 1975 dry season (irrigated). Mean of
three repTications.

Lime: 0.5 tons/ha 1.5 tons/ha 4.0 tons/ha
Wheat 67% Al saturation 46% Al saturation 24% Al saturation
varieties 160 778 1374 160 778 1374 160 778 1374

------------------- Grain

yields (g/4m row) -------------------------














78 206






*Equivalent to a soil solution level of 0.008, 0.02 and 0.05 ppm P, respectively.









































ent levels of liming. Maximum yield was ob-
tained with IAC-5 at the lowest lime rate
(0.5 tons/ha), Sonora-63, BH-1146, Para-
guai-214, IAS-55, and IAS-20 at 1.5 tons/
ha, and finally Ciano, Amazonas, INIA-66
and Toropi at the highest lime rate (4 tons/
Varietal differences also were noted
with respect to phosphorus response. While
BH-1146 and IAC-5 produced nearly half of
their maximum yields with the lowest broad-
cast rate (160 kg P205/ha), Sonora-63, Para-
guai-214, and INIA-66 produced only a
tenth of their maximum production at that
rate. Both BH-1146 and IAC-5 were devel-
oped in the periphery of the Cerrado, in
Minas Gerais and Sa'o Paulo, respectively.
From the results it was also possible to
note that the most tolerant wheat varieties
(IAC-5, BH-1146, and Toropi) had smaller
yield increases to the first increment of lime
than the sensitive varieties and showed a
sharp yield decrease at the highest lime rate
(4 tons lime/ha). On the other hand, the
most sensitive varieties such as Sonora-63,
Paraguai-214, and INIA-66 showed a positive
response to all increments of lime. None of
the Brazilian varieties appeared to be sensi-
tive to aluminum stress.
The general trend shows that varieties
bred in Brazil exhibit greater tolerance to
both stress factors than varieties bred in
Mexico. Brazilian varieties were generally se-
lected in acid soil conditions while the Mex-
ican ones were selected under calcareous soil

conditions. Figures 2.19 and 2.20 show this
trend expressed as the mean of the four
Mexican varieties and the five Brazilian vari-
eties. Nevertheless, these appear to be impor-
tant differences between varieties of the
same origin. Among Brazilian varieties, the
two developed closest to the Cerrado, IAC-5
in Campinas, and Bh-1146 in Belo Horizonte
were more tolerant to the stress factors than
those developed in Rio Grande do Sul (IAS-
20 and IAS-55) where the soils, although
acid, are more fertile than in the Cerrado.
Variability is also observed among the Mexi-
can varieties. Figure 2.21 shows an example
of this variability. These results suggest good
possibilities of breeding the tolerance to alu-
minum and phosphorus stress of Brazilian
varieties with the short-statured, lodging re-
sistance properties of the Mexican varieties.
The results of the bean field data are
shown in Table 2.16. All 18 varieties re-
sponded positively to both lime and phos-
phorus applications, although the larger
yield increases (more than 50%) were ob-
served in response to phosphorus than in re-
sponse to liming (less than 30%). In general,
the maximum grain yields of all varieties are
high. If extrapolated on a per hectare basis,
they range from 2.8 to 4.7 tons per hectare;
but these figures include border effects.
Several bean varieties were found tol-
erant to both phosphorus and aluminum
stress. The most tolerant were Carioca-1030,
Ricopardo-896, Costa Rica-1031, Costa Rica-

400 r




0 0.5 1.5

4.0 0.5
Lime Added

160 kg
(3 ppm


4.0 0.5
Ca Co3 equiv. /ha)

1374 kg P205/ha


avail. P)




61 46


61 46 2'
% Al Saturation

61 46 2

Figure 2.19

Differential performance of wheat varieties at various levels of
aluminum as a function of phosphorus under field conditions in
Brasilia. Mean of five Brazilian varieties and four Mexican vari-
eties with three replications each. 1975 dry season.

778 kg P205/ha
(7.4 ppm avail. P)

K Brazlican

,o Mexican


/ Mexican

(16.8 ppm avail. P)


300 F

200 -

.0-- -
00o01 Mexican
s i *

100 l


Lime: 0.5 tons/ ha
(61 % AI Satn.)

IAC-5 (Brazil

/ I AS-5

/ ,A(Brc
/ /



Sonora 63

160 778

Lime: 1.5
(46% Al




1374 160


IAS-55 /





Lime: 4.0 tons/ ha
(24% Al Satn.)

/ IAS-55






P Applied (kg

P205 /ha)


0.05 0.008 0.02
P in Solution



Available P-N.C.

16.0 2.8
Extraction (ppm)

Figure 2.20

Comparison between two Brazilian varieties (TA-C-5 and IAS-55) and two
Mexican varieties (INIA 66 and Sonora 63) to show variability in re-
sponse to aluminum and phosphorus stress under field conditions.
Brasilia 1975 dry season.

/ (I





(ppm )








I I- I




400 Lime: 0.5 ton / ha
(61 % Al Satn.)

q -





100 -

SMexican EO

' .0




Lime: 1.5 tons /ha
(46 % Al Satn.)



eo Mexican




P Applied (kg







P205 /ha)


Lime: 4.5 tons / ha
(24 % Al Satn.)


-/ 0 Mx-- c

o- Mexican







P in Solution

p A




Figure 2.21

P- N.C. Extraction (ppm)

Differential performance of wheat varieties at various levels of phosphorus
as a function of aluminum saturation under field conditions in Brasilia.
Mean of five Brazilian varieties and four Mexican varieties with three
replications each. 1975 dry season.












I I ,dI

Al and P stresses (61% Al sat., 3 ppm avail. P)

Wheat-varietal differences in tolerance to aluminum and phosphorus stress. On the left furrow,
two Mexican varieties (Sonora-63, Ciano); on the right furrow, two Brazilian varieties (IAC-5,

No Al or P stress (24% Al sat., 17 ppm avail. P)

P stress only (24% Al sat., 3 ppm avail. P)

Al stress only (24% Al sat., 17 ppm avail. P)

890-37R and Ricobaio-1014, which reached
yields greater than 50% over the most sensi-
tive varieties at the low phosphorus, high
aluminum stress treatment (0.008 ppm P
and 61% Al saturation). The most sensitive
varieties were Diacol Nutibara-235, Caraota-
260, Blue Lake-141 and Manteiga~o Fosco
NI-11. Table 2.16 shows no relationship be-
tween country of origin or seed coat color
with tolerance to aluminum or phosphorus
Bean yields of the tolerant varieties
were higher than the sensitive varieties at all
phosphorus and lime rates. However, when
these yields were expressed as a percent of
their maximum yields, important varietal
differences were only noted at the two
lowest lime rates (61 and 46% Al saturation)
with the lowest phosphorus rate (160 kg
P205/ha). In response to liming, sensitive
bean varieties showed higher grain yield in-
creases (about 50%) than tolerant varieties
for each increment of lime at the lowest
phosphorus rate. These results show the evi-
dent varietal differences among beans under
both adverse soil conditions and also that
when aluminum is neutralized and available
phorphorus is increased the differences tend
to disappear.
All bean varieties showed a positive
yield increase for each increment of lime ex-
cept at the highest lime-P combination. This
is a different type of response than that of
wheat varieties where essentially the yield
response was only to the first increment of

lime for all phosphorus rates (Figure 2.23).
A comparison of grain yields of the two crop
species on the basis of their relative yields
(% of maximum) shows that wheat had
higher grain production than beans at the
intermediate level of lime and showed no
further yield increases with an additional
lime. This indicates that lime requirements
for beans are higher than those for wheat,
and suggest a lower aluminum tolerance in
beans than in wheat.
With respect to phosphorus response,
the aluminum-tolerant and aluminum-sen-
sitive bean varieties also showed similar tol-
erance or susceptibility to low available
phosphorus. Differences among wheat and
beans also were noted. Figure 2.22 illustrates
the positive response of both crop species as
phosphorus rates increased and also shows
species differences at the lowest broadcast
phosphorus application (160 kg P205/ha).
Wheat showed a higher percentage of maxi-
mum yield than beans at all lime rates. For
example, at the 1.5 and 4 tons lime/ha
levels, wheat produced 50% of its maximum
yield with the lowest phosphorus rate. On
the other hand, beans at the same lime-
phosphorus combination produced only 22
and 34% of their maximum yield, respec-
These preliminary results indicate that
wheat, in addition to tolerating aluminum,
presents a better response to low available
phosphorus than beans. A more detailed
analysis, taking into consideration other pa-

Table 2.16 Bean grain yields at different levels of phosphorus and aluminum saturation in the field.
Mean of three replications. Brasilia, 1975 dry season (irrigated).

Seed 0.5 tons/hal/ 1.5 tons/ha 4.0 tons/ha
coat 61% Al sat. 46% Al sat. 24% Al sat.
Bean varieties Origin* color 160 778 13742/ 160 778 1374 160 778 1374

---------------------- g/4m rows -----------------------

Diacol Nutibara-235 BR Pinto 27 199 278 38 196 271 69 277 286
Caraota-260 VZ Black 49 207 230 70 222 300 134 323 293
Blue Lake-141 US White 34 275 336 69 317 358 89 265 296
Manteigao Fosco NI-11 BR Black 35 225 288 64 278 350 123 238 312
Tocantins-1222 BR Black 55 171 303 79 224 332 106 252 358
897-S-182-N BR Black 77 245 482 101 417 517 163 427 566
Rico-23 BR Black 38 378 479 84 366 469 188 365 475
Preto redondao-242 BR Black 62 289 399 62 327 469 151 353 392
Manteigao preto BR Black 69 170 328 90 277 425 163 310 416
1032-Col-1-63-A BR Brown 55 302 445 110 363 393 137 370 395
Jalo-251 BR Red 52 160 363 72 250 407 151 213 341
Selegao Cuba-1002 CB Black 69 203 404 104 341 462 209 426 453
VI-1010 BR Red 78 251 371 85 338 443 163 417 446
Ricobaio-1014 BR Red 83 279 406 109 381 413 144 422 456
Costa Rica 890-37R CR Red 83 392 457 130 406 515 217 469 503
Costa Rica-1031 CR Black 90 356 381 122 402 493 167 498 496
Ricopardo-896 BR Brown 124 342 464 133 404 501 205 486 563
Carioca-1030 BR Pinto 151 391 432 152 401 489 169 522 530

*BR=Brazil, VZ=Venezuela, U.S.=United States, CR=Costa Rica, CB=Cuba.
i/Lime 2/kg P205/ha








1.5 tons lime
- (46% Al So

/ ha


A C'
~ C

/ ^

I -A

orioca -1030

araota- 260

P Applied





4.0 tons lim/hq
S(24% I / Corioca-
Satn) / 1030

/Caraota 260




( kg P20O/ha)


P in Solution


I 2.8



I 2.8



( ppm )








1.3 2.8



Available P-N.C. Extraction ( ppm)

Figure 2.22

Differential response of two bean varieties (Phaseolus vulgaris) at
different levels of phosphorus and aluminum stress under field con-
ditions. Mean of three replications. Brasilia 1975 dry season

0 160 778 1374


160 778 1374 160 778 1374
P Applied (kg P205/ha)

0.5 tons/ha lime
(61% Al Satn.)
1.5 tons/ha lime
(46% Al Satn.)
4.0 tons/ha lime
(24% Al Satn.)


160 kg P20O/ha
(3 ppm avail. P)
778 kg PAOs/ha
(7 ppm avail. P)
1374 kg P20,/ha
(17ppm avail. P)

Figure 2.23

0.5 1.5 4.0 0.5 1.5 4.0
Lime Applied (tons/ha)

Species differences in tolerance to phosphorus and aluminum
stress between wheat (left) and beans (right) grown at the
same time during the 1975 rainy season in Brasilia. Mean
of 10 wheat varieties and 18 bean varieties and time repli-











rameters, should provide additional informa-
tion useful for selecting crop species and
varieties able to function well in these high
aluminum, phosphorus-deficient Oxisols.
Correlation Between Greenhouse and Field
One of the objectives of these studies
was to determine if varieties and species can
be selected for tolerance to aluminum and
low available phosphorus in greenhouse tests
using nutrient solution culture. The green-
house test was considered an important tool
because it greatly reduced the space and
time needed during the screening process as
compared to field tests.
The correlations between grain yield in
the field and several greenhouse parameters
are shown in Figures 2.24, 2.25 and 2.26 for
varieties under both aluminum and phos-
phorus stress in the field and greenhouse.
Figure 2.24 shows a very close relationship
between wheat yields and mean relative root
extension rates with an r rate of 0.93.**
Figure 2.25 shows the correlation with other
growth parameters which was not as close as
the previous one but ranged in r values from
0.62** to 0.83.
Among bean varieties, Figure 2.26
shows very close correlations between field
grain yields and relative top yields, root
yields and root length under greenhouse con-
These close relationships between
greenhouse and field observations suggest
that preliminary greenhouse screening is ef-

fective in predicting field performance when
high aluminum saturation and low available
phosphorus are the limiting factors in
growth and grain yields. Further evaluations
taking into consideration other important
growth and physiological parameters and
yields of other crops species will provide
additional information for better evaluating
the advantages of using greenhouse tests as a
practical and economical screening method
in tolerance studies.

D. E. Bandy and R. B. Musgrave
Crop physiology studies were con-
tinued during the year with the overall ob-
jective of understanding the relationship be-
tween temporary drought stresses caused by
veranicos and soil fertility management. Two
consecutive experiments continued to evalu-
ate the effect of key soil management prac-
tices on water stress in corn. Two other con-
secutive experiments studied the potential
of mulching as a practice for attenuating
drought stress. A fifth field experiment stu-
dies similar parameters on upland rice.
Soil Management Effects on Water Stress
in Corn
The field experiment initiated during
the 1974 dry season was continued during
the 1974-1975 rainy season and the 1975
dry season. The first crop results were ham-
pered by the slow reaction of lime during
the dry season and the abnormal phosphorus




A Y= -91.30 + 149.54 X
r = 0.93**

I f A I I I





Mean Relative

Root Extension Rate

(% /day)

Figure 2.24

Relationship between mean relative root extension
rates of wheat varieties measured in the greenhouse
and grain yields in the field, both under aluminum
and phosphorus stress. Brasilia 1975 dry season.

200 r

150 F


50 -



: 150



5 50-

r = 0.69*


Y 3.76 + 106.68 X

Y= 3.76 + 106.68 X

r =0.83R*

' LAr




Growth Rate

of Tops (%/day)

Growth Rate of Roots (%/day)

Y= 3.36+ 28.56 X

r 0.62*



- .3541.84A

Y:- 11.35+41.84X

r 0.77 *

' AI A




RGR Tops (%/day)

Figure 2.25


Correlation between growth rate parameters
measured in the greenhouse and wheat grain
both under aluminum and phosphorus stress.

Roots (%/day)

of wheat varieties
yields in the field,
Brasilia 1975 dry

Y= 4.36 + 55.54 X



1 150




A -





Y=-26+ 1.42 X
r=0.80* *

0 20 40 60 80 100
Relative Top Yield (%)




SY=-44+ 1.54X
r' 0.70**

0 20 40 60 80 100
0 20 40 60 80 100


Root Yield (%)

0 20 40 60 80 100
Relative Root Length (%)

Figure 2.26

Relationship between greenhouse and field parameters measuring joint tolerance
to aluminum and phosphorus stress in beans. Brasilia, 1975 dry season.

contents of the superphosphate applied
(1974 Annual Report). These problems were
corrected in the two subsequent experiments
as lime reacted properly and additional triple
superphosphate of known phosphorus com-
position was applied.
The rainy season experiment was
planted in December and was designed to
measure the effects of water stress on plants
as a result of a veranico under five different
soil management treatments as follows: no
lime, 8 tons/ha of lime incorporated into 15
cm depth, 8 tons/ha lime incorporated to 30
cm depth, 640 kg P205/ha broadcast, and
160 kg P205/ha banded. The lime treat-
ments received 400 kg P205/ha of broad-
cast and 100 kg P205/ha banded, and the

P205 treatments received 4 tons/ha lime in-
corporated to 15 cms. A blanket application
of all other required nutrients was given to
all plots.
There were no major changes in plan-
ning and execution of the 1975 dry season
experiment from the previous two experi-
ments. The experiment was planted on June
2, 1975 and was harvested 164 days later.
Two veranicos were simulated by with-
holding irrigation water. The first veranico
(early stress period) occurred during the
rapid stage of vegetative growth, 63 to 80
days after planting. The late stress period
commenced 100 days after planting and
lasted for 10 days. Fifty percent tasseling
was obtained 98 days after planting for the
non-stressed plants and 100-104 days for the

early stressed plants. The results of both
plantings are discussed as follows.
Growth Analysis.
The growth of the unlimed treat-
ment was always inferior to the deep and
shallow lime treatments. There were no
significant growth differences between the
deep and shallow lime treatments during
the early part of vegetative growth with
shallow incorporation at times giving better
growth. From about 50% tasseling on, deep
liming usually showed significant increases
in leaf area, leaf dry weight, and total dry
weight. Figure 2.28 shows this effect for the
rainy season experiment. The better growth
seems to be related to delayed leaf senes-
Phosphorus applied in bands gave bet-
ter seedling vigor than the broadcast appli-
cation because the phosphorus band was
more easily utilized by the young corn root
system. After the seedling stage, the broad-
cast treatments gave significantly superior
growth for the first two crops. The amount
of phosphorus applied in the bands was not
sufficient to maintain optimum plant growth
as Figure 2.28 shows. During the third con-
secutive crop, however, plants in the banded
treatments were able to grow at the same
rate as those in the broadcast treatment be-
cause of the reapplication of phosphorus in
bands for each crop and the diminishing re-
sidual effect of the only broadcast applica-

r --- -1

No Lime

Shallow Lime
Deep Lime

\ \\


I i I I II I

* Broadcast P
0 Banded P











Days After Planting

Figure 2.28

Effects of water stress and fertility treatments on the leaf
area index of corn during the 1974-1975 rainy season. Solid
lines are treatments where no water stress occurred. Dashed
lines are the treatments subject to the veranico. Bars are






I .

-i rII





I F-


S- -- I-


, I



, I

Water stress during the vegetative
growth stage produced significant decreases
in all growth parameters. The plants did not
recover from the effects of the water stress
period during the vegetative stage in the
1975 dry season crop as the measurements
for leaf area (Figure 2.29), leaf dry weight
and plant height, indicate. Other growth
parameters, such as stem dry weight, were
not permanently affected. Fertility treat-
ments usually did not produce differences in
the initial water stress effect, but deep lim-
ing and broadcast-P plants recovered from
some of the stress effects earlier than the
other treatments. Water stress after tasseling
enhanced leaf senescence and reduced leaf
dry weight, stem dry weight, ear dry weight,
and tassel dry weight. Net assimilation rates
(NAR) and relative growth rates (RGR) were
reduced by the early stress period but did
not show a late stress effect. No significant
differences between the five fertility treat-
ments were seen for NAR and RGR.
Soil Temperature
The dry season is not only without
rainfall but it is also the coldest season of
the year with May through August night
temperatures averaging 4 to 5 degrees Centi-
grade lower than the rest of the year. Night
temperatures for 1975 were quite cool in
June and July, averaging 13 and 12 degrees
Centigrade, respectively. The coolest night
was 4 degrees Centigrade. The cool nights re-
sulted in low soil temperatures which were
not conducive to optimum corn growth. Soil

temperatures were found to fluctuate daily
down to a 60 cm depth, as Figure 2.30
shows. The upper soil layer was cooler at
night by 5 degrees Centigrade or more than
deeper soil depths which could cause the up-
ward movement of water due to the asso-
ciated vapor pressure gradient. Soil temper-
atures during the two simulated veranicos
reflect the air temperature differences as the
season progresses. September soil tempera-
tures averaged 6 degrees Centigrade warmer
than August's soil temperatures.
Soil Water Use.
Soil water use was shown to be in-
fluenced by depth of lime incorporation for
all three experiments. Water use during the
early stress period usually did not show a
large deep lime effect. Late stress periods
widened the differences between the nu-
trient treatments with the deep lime treat-
ment always showing the greater soil water
use, especially below the 22.5 cm soil depth.
Deep-limed plants used anywhere from 2 to
18 mm more soil water than the other treat-
ments. Table 2.17 shows that soil water ex-
traction was influenced by lime rates, depth
of lime incorporation and method of phos-
phorus application.
For a proper study of soil-plant water
use it was necessary to get an understanding
of the amount of soil water used by a corn
crop grown under well-watered conditions
and under veranico conditions where the
water contents become very limiting. The
26th of February, 1975 was the last day of a



3.5 No Stress
S-- Early Stress
3.0 ---- Late Stress

1.05 .05 1.05 1.05 i .05

Deep Lime






30 -







34 44 54 64 74 84 94 104 114 124
Days After Planting

Figure 2.29 The effect of plant water
1975 dry season.

deficit on corn leaf area index.




1.05 1.05 1.05 1.05

Figure 2.30 Soil temperature profile of uncropped Dark Red Latosol in Brasilia during the late
dry season and early rainy season of 1975.


Table 2.17.

Comparison of the amount of soil water unused by the corn plant in relation to the deep
liming treatment during the stress periods for three growing seasons.

0-Lime Shallow Lime Deep Lime Broadcast-P Banded-P
Early Late Early Late Early Late Early Late Early Late
Crop Stress Stress Stress Stress Stress Stress Stress Stress Stress Stress

--------------------------------- mm H0 -------------------------------------

1974 Dry 4.4 5.0 4.2 4.1 0 0 5.2 1.5 7.2 8.8

1974-75 Rainy 1/ 5.1 2.1 0 0 2.0 6.2

1975 Dry 8.4 18.6 1.5 6.7 0 0 6.2 5.8 4.0 11.8

Mean 6.4 9.6 2.9 4.3 0 0 5.7 3.1 5.6 8.9

I/ No early stress during

this season.

4-day 96.3 mm rain. Soil water measure-
ments began two days later to determine soil
water use by corn in relation to five fertility
management practices. The results are shown
in Table 2.18.
Over the same 5-day period soil water
lost from a bare soil, with no vegetative
growth (0-45 cm soil profile), to surface eva-
poration and drainage amounted to 3.10
mm. Soil water contents in the same bare
soil area for 12 days of the 18-day veranico
are shown in Figure 2.31. The top 22.5 cm
dried out at the rate of 1.53 mm per day. A
5-day comparison (Table 2.19) was made be-
tween the ET rates from stressed and non-
stressed plants during the veranico to deter-
mine the respective ET rates or amount of
soil water used per day.
Soil water contents were measured in
the early morning and late afternoon to
study the daily water flux and extraction
patterns. In four days under optimum soil
water conditions the corn plants used 47.7%
of the total available water in the 0-45 cm
soil profile. The average soil water tension
after four days was 37.75 centibars. The 30
cm soil depth always showed that soil water
was used during the night. The reason was
probably related to the water extraction pat-
tern for the corn plants as shown in Table
2.20. The extraction pattern was a dynamic
process, changing daily as the soil dries out.
For example, the 0-15 cm soil layer supplied
more than half of the water used during the
first few days but its supplying power dimin-

ishes as the soil dries out. The 45 cm soil
layer supplied very little water at first,
but it was supplying over 20% of the avail-
able water within five days after irrigation.
Plant Water Status.
The various soil management practices
influenced plant water stress with deep
limed plants usually showing less stress in
comparison to the other four treatments.
Deep limed plants became water stressed
later on in the day and returned to less nega-
tive leaf water potentials earlier in the even-
ing. For example, during the 1974-1975 wet
season veranico, shallow limed plants reach
a leaf water potential of -20 bars four days
earlier than deep limed plants (Figure 2.32).
In other stress periods, deep limed plants
never became severely stressed while the
shallow limed plants were near the perma-
nent wilting point. Banded P plants were less
stressed during the first two experiments be-
cause they were much smaller plants. When
the corn plants were equal in size for the
two phosphorus application treatments, the
broadcast P treatment was superior, i.e.,
lower leaf water potential and higher relative
water contents (Figure 2.33).
Stomatal resistance (Rs) and transpira-
tion rate (E) results always showed that deep
lime incorporation delayed and reduced
plant water stress. Diurnal measurements
showed that stomates were closing in the
late morning for shallow limed plants as the
veranico became more severe. The stomates
never closed in the late morning due to plant

Table 2.18.

Average daily evapotranspiration rates over a 5-day period
for corn (Hanway stage 5-6) in relation to five fertility
management practices and LAI. (February 28- March 4, 75).

Treatment ET LAI

mm cm2/cm2

0-Lime 5.12 3.1
Lime-Shallow 6.44 4.2
Lime-Deep 6.16 4.1
Broadcast-P 4.67 3.9
Banded-P 5.07 3.6
Bare Soil 3.10 ---

Table 2.19. Evapotranspiration rates from stressed and non-stressed corn
plants during a veranico.

Date Stressed Non-stressed Bare Soil

-------------------- mm/day -----------------------

August 3 5.66 3.79
September 3 1.12 8.15
October 3 0.95 7.24
November 3 1.95 5.10

Mean 2.41 6.07 1.37

18 20
15 --








Figure 2.31

Soil Water Content (g/100g)
22 24 26 28


/14 ;10l6 5 2
16 12 9
Days After Last Rain

Decreasing soil water content under a bare soil during
14 days without rain. Brasilia 1974-1975 rainy season.

Table 2.20. Soil water extraction pattern for corn, 1-5 days after

Soil Depth (cm)

Date 0-15 15-22.5 22.5-30 30-45

------- ------ % H------------ % H

August 3 44.9 30.7 19.6 4.8

September 3 52.8 20.8 16.0 10.4

October 3 36.2 28.8 21.3 13.7

November 3 6.6 35.4 34.5 23.5

Mean 35.5 28.9 22.9 13.1

Measuring leaf area during water stress periods.

Shallow Lime

6 0
Deep Lime

Figure 2.32

Water Stress

Effect of depth of liming on the leaf water potential for
corn (third leaf from top) taken during a veranico
(February 27-March 17, 1975). Brasilia 1974-1975 rainy

mD -l




Days During


Banded P

Days During Water

Figure 2.33

Effect of phosphorus placement methods on the
leaf water potential of corn during a 17-day
water stress period. February 27-March 17,
1975. Brasilia 1974-1975 rainy season.




water stress in the deep lime treatment (Fig-
ure 2.34). The transpiration rate (E) for
plants in the deep limed plots was shown to
average 68% more than E for shallow limed
plants during the 1974-1975 veranico (Table
Other Effects.
Leaf temperatures generally agreed very
closely with stomatal resistance and trans-
piration results. Plants with the least Rs and
most E had the lowest leaf temperatures.
This occurred in the deep limed plants. Corn
canopy microclimate was usually influenced
by lime depth incorporation. Shallow limed
plant canopies showed lower percent relative
humidities than deep limed plant canopies.
Leaf chlorophyll contents were found to be
degraded with increasing plant water stress
but no nutrient influence was noted. Photo-
synthetic rate measurements were taken on
one experiment only. The results showed
that the deep limed plants averaged 10 mg
CO2 dm-2 hr-1 more than shallow limed
plants during the stress period.
Grain Yield.
At harvest, the deep lime incorporation
plots outyielded shallow limed plots in both
water stressed and non-water stressed treat-
ments. The overall results of the three crops
are shown in Table 2.22. Non-limed treat-
ments yielded less than limed plots. A 10-15
day water stress period during the vegetative
growth stage permanently reduced plant size
but it did not significantly reduce grain
yield. A 10-15 day stress period during the

grain formation stage decreased yields by
100-140 kg/ha/day.
With all other fertilizer treatments being
equal, incorporation of lime 30 cm deep in-
stead of the traditional 15 cm depth pro-
duced 1157 kg/ha more grain for the three
crops under non-water stressed conditions
and produced 2043 kg/ha more grain under
the stressed conditions. On a three crop aver-
age, late stress reduced yields by 19% for
deep limed treatments and 27% for shallow
limed treatments.
Broadcast application of phosphorus
gave less yield reduction in relation to plant
water stress when compared to the banded
application of phosphorus. Both treatments
showed significant reductions in grain yield
when water stress was imposed on the plants
during the grain filling stage.
The effect of the late water stress period
on final grain yield was directly related to
photosynthate production and translocation
to the ear. Stover dry weight decreased dur-
ing the ear filling stage which suggests that
photosynthate stored in the culm during the
vegetative stage was translocated to the ear.
The results also suggest that the late water
stress period (79-90 days after planting)
slowed photosynthate production but in-
creased photosynthate partitioning. Over
30% of the ear dry weight accumulation
occurring during the water stress period
came from photosynthate stored in the
culm, whereas only 2.9% was translocated
in the no water stress period treatment over



40 -Deep Lime 5
20 9

07 8 9 10 II 12 13 14 15 16
Time (hrs.)

Figure 2.34

Effect of the duration of water stress and fertility
variables on the diurnal stomatal resistance of corn
during the first stress period of the 1975 dry season.

Table 2.21. Transpiration rates for maize during the veranico in relation to five fertility

Sampling Days During Water Stress

Treatment 6/3 7/3 8/3 9/3 10/3 11/3 12/3 13/3 Avg.

----------------------- g H2O/cm/sec. --------------------------

0-Lime 1/ 3.1 .93 .80 .42 .60 .38 .57 .76 .95

2/ 3.2 1.13 1.15 .63 .87 .38 .61 .71 1.09

Lime-Shallow 2.1 2.00 1.32 .60 1.44 .52 .55 .74 1.16
3.8 2.60 1.40 .81 1.42 .60 .68 .82 1.52

Lime-Deep 7.8 5.61 8.94 4.02 2.77 2.17 3.03 2.86 4.65
7.0 5.75 12.95 3.17 1.94 2.08 3.21 2.08 4.77

Broadcast-P 2.9 1.42 1.29 .71 .80 .39 .59 .42 1.07
2.4 1.64 .97 .97 1.67 .34 .53 .57 1.14

Banded-P 2.1 1.62 1.14 .49 .58 .55 .84 .52 .98
2.9 3.22 2.71 1.55 .77 .61 1.19 .52 1.68

1/Adaxial side of the leaf.
2/Abaxial side of the leaf.


Table 2.22 Effect of water stress and fertility treatments on corn
grain yields for the soil management experiment averaged
over three cropping seasons. Results are based on a 15.5%
moisture basis.

Treatment No stress Early stress Late stress

----------------- tons/ha ---------------------

0-Lime 4.94 4.45 3.35

Lime Shallow 5.85 5.26 4.15

Lime Deep 6.14 5.12 4.83

Broadcast-P 5.91 5.54 4.78

Banded-P 3.69 3.70 3.30

the same period. In addition, plant water
stress resulted in approximately one gram
per day less of ear dry weight accumulation
when compared to the no water stress treat-
ment. About 50 kg/ha lost each day for 30
days which equals 1500 kg/ha or approxi-
mately the final yield difference between
stressed and non-stressed treatments.
A yield component analysis was con-
ducted to determine what effect the soil
management practices and what effect plant
water stress had on the various yield compo-
nents which influenced final grain yield.
Deep limed plants outyielded shallow limed
plants because they had longer ears, more
kernels/row, more kernels/ear, more grains/
plant, and a better grain:cob ratio. Late
water stress (Hanway, Stage 5) reduced grain
yield by producing fewer rows of kernels/ear
and fewer kernels/ear. For early stress condi-
tions, ear and kernel length/ear were highly
correlated to yield. This seems logical since
the plant stress occurred during the ear
shoot formation stage (Hanway, Stage 2.5).
Root Distribution
Many of the findings shown so far in this
report have been based on the corn plant's
root distribution and ability to extract soil
water in relation to the low pH and high per-
cent Al saturation of the Dark Red Latosol.
To verify the previous results, root measure-
ments were taken when the corn plants had
just started to tassel (Hanway, Stage 4). Two
methods were used. The rubidium-86
method is supposed to only detect the active
portion of the root zone. When this method

was used, the objective was to learn if the
corn roots were entering aluminum saturated
subsoil and still staying active. The second
method was supposed to measure total root
length per volume of soil. When using this
method, the main objective was to measure
the total root distribution in relation to soil
depth as influenced by the five fertility man-
agement treatments.
The percent root distribution as deter-
mined by the rubidium-86 method is shown
in Table 2.23. Both depth and lateral distri-
bution of roots are shown. Deep liming re-
sulted in a fairly uniform rooting distribu-
tion while 0-liming for example, showed a
high concentration of roots in the 0-15 cm
soil layer. The general root pattern was as
expected. Many roots were shallow close to
the row and as lateral distance became
greater, more of the roots were deep. The ef-
fect of phosphorus application on root dis-
tribution was not clearly shown.
The second method, modified Newman
technique, measures root length per 100
cm3 (Table 2.24). No effort was made to
analyze lateral root distribution per se, only
depth of rooting. The results show the bene-
ficial effects of deep liming as well as liming
itself. The banded-P treatment shows more
roots and deeper root penetration than the
broadcast-P treatment. The largest amount
of roots in the 0-15 cm soil layer for the
banded-P treatment could be related to the
high concentration of roots in the band of

Table 2.23.

Percent root distribution for corn as determined by the
rubidium-86 method.

Soil Depth (cm)

Treatment Locationl/ 0-15 15-30 30-45









Mean 9.46 5.48 5.06

1 7.7 1.0 10.6
2 9.1 5.7 8.6
3 2.8 10.4 4.6
4 7.6 2.4 11.4
5 6.6 5.5 6.0

Mean 6.76 5.0 8.24

1 6.2 6.2 2.6
2 7.4 5.8 5.7
3 8.5 5.2 3.5
4 8.8 7.6 9.6
5 5.2 7.4 10.4

Mean 5.72 6.44 6.36

1 15.7 2.8 0.6
2 8.3 7.7 2.2
3 14.2 10.1 5.1
4 4.4 7.5 7.0
5 6.2 4.1 4.0

Mean 9.76 6.44 3.78

1 5.7 11.9 2.5
2 6.0 1.6 7.4
3 9.3 6.6 4.7
4 2.8 13.5 7.2
5 4.3 11.9 4.6




2.5 cm from plant within row. 5 =
17.5 cm from plant within row.
15 cm from plant beside plant between
30 cm from plant beside plant between

45 cm from plant
between row.

beside plant


Table 2.24

Root length (cm/100 cm3) for corn at the start of the
tasseling stage (Hanway, Stage 4) grown during the 1975
dry season.

Soil Depth (cm)
Treatment 0-15 15-30 30-45

0-Lime 68.8 23.1 10.5

Lime-Shallow 99.4 58.4 24.7

Lime-Deep 96.5 76.2 40.4

Broadcast-P 103.0 26.1 4.4

Banded-P 133.6 52.9 10.0

Deep liming improves corn root proliferation. Left: shallow liming (0-15 cm depth).
Right: deep liming (0-30 cm depth). Both received 8 tons/ha of lime.

In conclusion, the rubidium technique is
probably a good method to use to determine
if roots have reached a certain distance from
a specific plant by a certain day. The New-
man technique is a good method to demon-
strate the accumulated total root distribu-
tion of a crop from day of planting to day of
Mulching Experiments
An additional experiment with corn was
initiated to test both soil and crop manage-
ment techniques for conserving soil mois-
ture. The treatments were: 1)Two depths of
lime incorporation (shallow 0-15 cm, and
deep 0-30 cm), 2) dry molasses grass mulch
10 cm thick or no mulch, 3) two corn vari-
eties (Cargill-111 and Agroceres-152), and
4) two types of antitranspirants (Wilt Pruf
and Phenyl Mercuric Acetate), with three
The principle objective is to determine
to what extent the various management
techniques will reduce the negative effect of
a "veranico" on crop growth and produc-
tion. The experiment was conducted on a
previously cropped area which had received
400 kg P205/ha broadcast and 200 kg
P205/ha applied in bands. An additional
134 kg P205/ha was band applied in this ex-
A 15-day veranico occurred 66 days
after planting which coincided with the tas-
seling stage. Water stress measurements were
taken for six days, January 14 through 19,
1975). To learn if the plants were able to

fully recover from the veranico, water stress
measurements were taken for two days (Jan-
uary 29 and 30, 1975) after 47.3 mm of rain
had fallen in the ten-day interim. During the
stress period pan evapotranspiration, max-
imum temperature, and solar radiation were
quite high.
The 1975 experiment is a continuation
of the mulching experiment that was ini-
tiated in the 1974-1975 wet season. Some
modifications were made to verify whether
the grass mulch had a negative effect on corn
growth. A black plastic mulch was installed
along with a continuation of the grass mulch
treatment. The black plastic should increase
soil temperature and at the same time con-
serve soil moisture equal to the grass mulch.
Two lime depth incorporations and two anti-
transpirants were used again. To accommo-
date the plastic mulch treatment, the Agro-
ceres-152 comparison was not continued.
Six plots of Agroceres corn were planted on
shallow limed plots only to allow for a gen-
eral comparison of the two varieties growing
during the dry season.
Methods and procedures for the mea-
surement of plant growth and production
and for the measurements taken during the
plant water stress period were the same as
was explained in the companion experi-
ments. To simulate a veranico, water stress
was imposed on the plants by withholding
irrigation water. The principle objective of
this experiment was the same as in the 1974-
1975 wet season crop management experi-

Overview of corn mulching experiment. Foreground: black plastic mulch.
Background: grass mulch.

ment: to study various soil and plant man-
agement techniques which may reduce the
harmful effects of a veranico. The experi-
ment was planted on September 6, 1975 and
harvested 141 days later. The plastic mulch
was installed eleven days after planting.
Plant Growth
Mulching was shown to influence corn
growth and development in both seasons.
Grass mulch decreased plant growth and
development while black plastic mulch in-
creased plant growth and development in
relation to the non-mulched plots.
During the natural veranico in 1974-
1975 rainy season, leaf area decreased in the
shallow limed plots for both Cargill and
Agroceres. No decrease in leaf area was
noted for either variety in the deep limed
plots. In addition, deep limed plots showed
a slightly superior leaf area index over
shallow liming during the growing season
(Figure 2.35). Cargill's leaf area was larger
than Agroceres but both varieties reacted
equally to mulching and depth of lime in-
corporation in relation to water stress.
The effect of mulching on leaf area index
and tasseling date is shown in Figure 2.36.
The black plastic mulch produced corn tas-
seling from 10 to 15 days earlier than with
the grass mulch.
Soil Temperatures
The grass mulch reduced soil tempera-
tures by 2 to 3 degrees Centigrade in the top
20 cm soil layer in both seasons. The black
plastic mulch, in contrast, increased soil

temperatures substantially. During the 1975
dry season, the 0-45 cm soil layer under the
black plastic was on the average 3 to 4 de-
grees Centigrade warmer than without
mulching (Figure 2.37). Warmer soils were
responsible for increased plant growth in
both seasons. For example, in August 1975
leaf area increased by 54 cm2 plant-1 day-1
for the plastic mulched plants over the non-
mulched plants. This is related to an average
difference in soil temperature of 5.2 degrees
Soil Water
Both mulches reduced surface evapora-
tion of soil water by 4 to 7 mm in the top
20 cm of the soil during the stress periods.
Table 2.25 shows that in the rainy season
crop stress period, deep limed plants used
8.2 mm more water than the shallow limed
plants. In the dry season crop, grass mulched
plants used less soil water during the simu-
lated veranico than the other treatments be-
cause of poorer growth.
Plant Stress
No severe plant water stress was imposed
on the 1975 dry season experiment, thus,
the stress results were not too meaningful.
The natural occurring veranico in the
1975 rainy season, however, was quite se-
vere. During that veranico, plant water stress
was greatly influenced by depth of liming,
mulching, and their combinations. For ex-
ample, the deep lime mulched treatment had
a six day leaf water potential average of
-13.5 bars. Shallow liming without mulch

# Agroceres-Shallow Lime
E o Agroceres-Deep Lime Veranico o
.2 A Cargill- Deep Lime


os / 50% Tassel

0 20 30 40 50 60 70 80 90
Days After Planting

Figure 2.35 Effects of varieties, mulching and depth of liming on leaf area
index of corn plants grown during the 1975 rainy season.