TropSoils technical report

Material Information

TropSoils technical report
Soil Management Collaborative Research Support Program
Place of Publication:
Raleigh N.C
TropSoils Management Entity, North Carolina State University
Publication Date:
Physical Description:
v. : ill. ; 28 cm.


Subjects / Keywords:
Soils -- Periodicals -- Tropics ( lcsh )
Soils -- Periodicals -- Latin America ( lcsh )
Soil management -- Periodicals -- Tropics ( lcsh )
Soil science -- Periodicals -- Tropics ( lcsh )
serial ( sobekcm )


Dates or Sequential Designation:
General Note:
"TropSoils is one of the Collaborative Research Support Programs."
General Note:
Latest issue consulted: 1988-1989.
Electronic resources created as part of a prototype UF Institutional Repository and Faculty Papers project by the University of Florida.

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University of Florida
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Resource Identifier:
16150153 ( OCLC )
sn 90040074 ( LCCN )

Related Items

Preceded by:
TropSoils triennial technical report

Full Text


Technical Report for 1986-87

Draft, July 1987

Tropical Soils Research Program
Department of Soil Science
North Carolina State University



Draft, July 1987

Tropical Soils Research Program
Department of Soil Science
North Carolina State University
Raleigh, NC 27695-7619

Supported by
The Soil Management Collaborative Research Support Program
under a grant from the
United States Agency for International Development

Edited by Pedro A. Sanchez and Cynthia L. Garver



Highlights .................................................. 1

Personnel ................................................... 2

2. RESEARCH NETWORK ................................................. 7

Yurimaguas Workshop ...... ................................... 8

Network Development in Latin America: RISTROP ................. 16

Network Development in Africa and Asia ........................ 19

3. LEGUME-BASED PASTURES ............................................ 24

Persistence of Grass-Legume Mixtures under Grazing .......... 27

Evaluation of Animal Preference in Small Plots ................ 42

Nitrogen Contribution of Legumes in Mixed Pastures ............ 44

Potassium Dynamics in Legume-Based Pastures ................... 50

Sulfur Accumulation in Grazed Pastures ........................ 56

Pasture Reclamation in Degraded Steeplands .................... 58

Pasture Reclamation via Herbicides ........................... 63

Legume Shade Tolerance ...................................... 67

Extrapolation in Farmer Fields ............................... 69

4. LOW-INPUT SYSTEMS .............................................. 72

Central Experiment: Transition to Other Technologies .......... 73

Weed Control in Low-Input Cropping Systems .................... 88

5. AGROFORESTRY SYSTEMS ........................................... 96

Multipurpose Tree Selection for Alleycropping ................. 97

Mulch Quality and Nitrogen Cycling ............................ 104

Alleycropping in Ultisols .................................... 112


Alleycropping in Alluvial Soils................................ 114

Inga Rice Interface in Alluvial Soils ....................... 121

Improved Fallows .............................................. 127

Legume Cover Crops for Peach Palm ............................. 129

Mycorrhizae Inoculation in Tropical Palm Nurseries .......... 132

Nutritional Requirements of Peach Palm ........................ 134

Nutritional Requirements of Other Amazonian Fruit Trees ....... 137

Nutritional Requirements of Gmelina arborea ................... 140

6. CONTINUOUS CULTIVATION .......................................... 143

Conservation Tillage under Continuous Cropping ............... 144

Conventional Tillage under Continuous Cropping ................ 156

Central Continuous Cropping Experiment ........................ 160

Nitrogen Carryover in Rotation and Strip Intercropping Systems. 164

Maintenance of Phosphorus Fertility under Continuous Cropping 173

Potassium Buffering in Yurimaguas Ultisols .................... 180

Weed Population Shifts in Continuous Cropping ................. 186

7. COMPARATIVE SOIL DYNAMICS ........................................ 191

Comparative Soil Dynamics under Different Management Options .. 192

Soil Organic Matter Pools as Affected by Management Options ... 206

Root Production and Turnover in Different Management Options .. 210

Root Distribution in Pastures and Alleycropping Options ....... 216

Occurrence of Mycorrhizae in Crops, Pastures, and Tree Species. 219

Effect of Different Management Options in Mycorrhizal Infection 222

Rhizobium Nodulation in Grain Legumes ......................... 227

Soil Macrofauna as Affected by Management Practices .......... 229


NitrogenMineralizationandLeachingasAffectedby Management
Practices .................................................... 233

Nitrogen Mineralization and Soil Moisture Content ............. 241


Utilization of the Fertility Capability ClassificationSystem 244

Alluvial Soils of the Amazon Basin ............................ 252

Volcanic Ash Influence in Transmigration Areas of Sumatra ..... 271


Nutrient Dynamics ............................................. 279

Phosphorus Fertilizer Placement and Profitability ............. 281

Lime and Gypsum Applications .................................. 284

Nitrogen Management ......................................... 290


Comparison of Mehlich-1, Mehlich-3, Bray-1, and Anion Exchange
Resin P Soil Test ........................................... 296

Effects of Soil Texture,Zinc, and pH on Corn Yield and Plant
Zinc Concentration ........................................... 301

-A P-testInterpretation Model forKaoliniticSoilsusing
Mehlich-1 and Clay Content .................................... 307

AP-testInterpretation Model for OxisolsUsingMehlich-3,
Resin ......................................................... 310


RunoffandErosion Process in a Primary Forest Catchmentof the
Humid Tropical Steeplands ..................................... 315

Establishing a Plant Canopy in Eroded Ultisol Steeplands ...... 319

RainfedLow-InputCrop Rotation Patterns inAlluvialSoils
Subject to Seasonal Flooding .................................. 323


Evaluation of Pasture Germplasm under a Perudic Rainfall
Regime ................ ......................................... 329

Recuperation of Degraded Pastures Dominated by Homolepsis
aturensis .............................. ............. .... 334


Response of Upland Crops to Potassium and Lime Applications ... 337

Agroforestry Research Needs ................................... 349

13. PUBLICATIONS ............................... ......... ......... 359


This is the fifteenth continuous year of operations of North Carolina State
University's Tropical Soils Program and the fifth as part of TropSoils, the
Soil Management Collaborative Research Support Program financed mainly by
the U.S. Agency for International Development and collaborating host
institutions: INIPA in Peru, EMBRAPA in Brazil, and AARD in Indonesia. The
year 1986 was simultaneously very difficult but also very rewarding. We
received a 25% budget cut from our donor agency in February 1986, which
resulted in the discontinuation of our field research in Indonesia in August
1986 and in major adjustments in research activities in Peru, Brazil, and on
campus. For the first time in the program's history, we were unable to
offer new graduate assistantships.
But 1986 was also a very rewarding and productive year, partly due to
the momentum of all our projects in full operation and partly by the
implementation of two major initiatives: the soil management research
network, and comparative soil dynamics with emphasis on tropical soil
biology. INIPA's building program at Yurimaguas is almost complete and the
station was officially inaugurated by the Minister of Agriculture. Although
modest by world standards, the Yurimaguas Experiment Station now has
sufficient office, laboratory, and computer facilities to support long-term
experiments and a 30-person training and conference center for on-the-job
training. Three major international workshops were held at Yurimaguas in
1986: a Latin American Agroforestry Workshop in cooperation with ICRAF; the
Third Tropical Soil Biology and Fertility Workshop; and the Latin American
Soil Management Workshop, which trained 31 professionals from the "planting
stick to the computer" in 3 weeks and helped launch the network.
Extrapolation activities were also facilitated in tropical Asia and Africa
through IBSRAM's Acid Tropical Soils Network. These network activities have
paved the way for meaningful technology validation and transfer for 37
countries throughout Latin America, Asia, and Africa.
Work reported herein is carried out in close collaboration with INIPA
in Peru, EMBRAPA in Brazil, AARD in Indonesia, several international
centers, USAID Missions, and our sister TropSoils universities.




Robert H. Miller Depa

Pedro A. Sanchez Prog

Dale E. Bandy Chie:

T. Jot Smyth Assi:

Jos4 R. Benites Proj

Michael K. Wade* Proj

Julio C. Alegre Assi!


Dennis del Castillo Proj

Stanley W. Buol Prof


D. Keith Cassel Prof,

Fred R. Cox Prof<

Charles B. Davey Prof4

Eugene J. Kamprath Prof<

Robert E. McCollum Asso<

Kenneth Reategui Reset

Robert J. Scholes Post


Mary C. Scholes Post

rtment Head

ram Coordinator

f, NCSU Mission to Peru

stant Professor of Tropical Soils

ect Leader, Yurimaguas

ect Leader, Indonesia

stant Professor of Soil Physics,


ect Leader, Pichis Palcazu

essor of Soil Genesis and


essor of Soil Physics

essor of Soil Fertility

essor of Forestry and Soil Science

essor of Soil Fertility

ciate Professor of Soil Fertility

arch Associate, Pichis Palcazu

Doctoral Fellow in Plant Ecology


Doctoral Fellow in Soil

biology (Yurimaguas)

* Resigned during the year.

George C. Naderman, Jr.


Bertha I. Monar

Mariela Gonzalez

Sue Florindez*

Patricia Gowland

Tonya K. Forbes

Olinda Ayre

Rafael Roman

Valeria Medeiros*

Elizabeth Phillips

Amparo Ayarza

Extension Soil Management


Program Administrator

Administrative Assistant, Lima Office

Administrative Assistant, Yurimaguas

Research Technician

Research Technician

Soil Analysis Laboratory, Yurimaguas

Plant Analysis Laboratory, Yurimaguas

Bilingual Secretary

Bilingual Secretary

Translator, Yurimaguas

Graduate Students (with degree candidacy and nationality)

Miguel A. Ara Soil-pastures, Pucallpa (PhD-Peru)

Miguel A. Ayarza Soil-pastures, Yurimaguas (PhD-


Dan W. Gill Soil fertility, Indonesia (PhD-USA)

Ricardo J. Melgar Soil fertility, Manaus (PhD-Argentina)

Ibere D. G. Lins Soil fertility, Brasilia (PhD-Brazil)

Amilcar Ubiera Soil mineralogy, Raleigh (PhD-Dominican


Helmut Elsenbeer Soil physics, Pichis (PhD-Germany)

Jose R. Davelouis Soil fertility, Yurimaguas (PhD-Peru)

* Resigned during the year.

Cheryl A. Palm

Lawrence T. Szott

Erick C. M. Fernandes

Carlos Castilla

Christopher W. Smith

Hadjrosuboto Subagjo

Victor Ngachie

Eleazar Salazar

Eduardo Uribe

Jane Mt. Pleasant

Jonathan Hooper

Marisa R. Fontes

Abdul Karim Makarim**

Mwenja P.

Laurie J.

Robert H.




Soil agroforestry, Yurimaguas (PhD-USA)

Soil agroforestry, Yurimaguas (PhD-USA)

Soil agroforestry, Raleigh (PhD-Kenya)

Soil pastures, Raleigh (PhD-Colombia)

Soil classification, Raleigh (PhD-USA)

Soil classification, Indonesia (PhD-


Soil fertility, Raleigh (MS-Cameroon)

Soil classification, Raleigh (MS-


Soil fertility, Raleigh (PhD-Colombia)

Weed control, Raleigh (PhD-USA)

Soil classification Raleigh (MS-USA)

Soil chemistry, Raleigh (PhD-Brazil)

Soil fertility, Indonesia (PhD-


Soil fertility, Yurimaguas (PhD-Kenya)

Soil classification, Raleigh (MS-USA)

Soil classification, Raleigh (PhD-USA)


Victor Palma*

Lander Pacora

Head of INIPA (and TropSoils Board


Head of INIPA (and TropSoils Board


* Resigned during the year.
** Completed degree in 1986.

Manuel Villavicencio

Angel Salazar

Jorge M. Perez

Pedro 0. Ruiz

Luis A. Arevalo*

Beto Pashanasi

Miguel Bustamante

Rolando Dextre*

Daysi Lara

Marco Galvez

Andres Aznaran

Cesar Tepe

Alfredo Racchumi

Jonathan L6pez

Mercedes Escobar

Wilfredo Guillen

Jorge W. Vela

Luis Zufiga

Jos4 Merino

Hemilce Ivazeta

Marta Gallo

Rodolfo Schaus

Miguel Flores

* Resigned during the

Director, Yurimaguas Station

Agroforestry, Yurimaguas

Agrogorestry, Yurimaguas

Mycorrhiza specialist, Yurimaguas

Soil fertility specialist, Yurimaguas

Soil zoology, Yurimaguas

Training Officer, Yurimaguas

Pastures specialist, Yurimaguas

Pastures specialist, Yurimaguas

Corn-weed control specialist,


Tillage specialist, Yurimaguas

Paddy rice specialist, Yurimaguas

Upland rice specialist, Yurimaguas

Corn and sorghum specialist, Yurimaguas

Economist, Yurimaguas

Grain legumes specialist, Yurimaguas

Pastures specialist, Pucallpa

Soil physicist, Pichis

Head, La Esperanza Station, Pichis


Pastures specialist, Tulumayo, Tingo


Soil specialist, Tulumayo, Tingo Maria

Pastures specialist, Pucallpa

Farming systems specialist, Tulumayo,

Tingo Maria


Jorge Fuigueroa

Juan Lermo

R. Ruiz

G. Cantera

E. Acuia

Farming systems specialist, Tulumayo,

Tingo Maria

Agronomist, Proyecto Especial Pichis

Palcazu, Puerto Bermudez

Pastures specialist, Proyecto Especial

Pichis Palcazu, Puerto Bermudez

Pastures specialist, Proyecto Especial

Pichis Palcazu, Puerto Bermudez

Pastures specialist, Proyecto Especial

Pichis Palcazu, Puerto Bermudez


Erci de Moraes

Manoel S. Cravo

Chief UEPAE de Manaus Station

Soil fertility specialist, Manaus


Mohammed Sudjadi

I. P. G. Widjaya Adhi

Sri Adiningsih

Fahmuddin Agus

M. Heryadi


Putu Wegena

Director, CSR, Bogor

Soil fertility, Country Coordinator,


Head, Soil fertility division, Bogor

Soil physicist, Sitiung

Soil fertility, Sitiung

Soil fertility, Bogor

Soil fertility, Jambi


Tropical soils research has progressed to the point that several
management options for sustainable productivity in agronomic and ecological
terms are ready to be widely tested by national research institutions. The
different options for the humid tropics constitute the model for networking
(see first report). A training workshop, held in Spanish at Yurimaguas
during September 1986, provided on-the-job training for 31 front-line
professionals from the planting stick to the computer. The workshop
participants created RISTROP (Red de Investigaci6n de Suelos Tropicales)
with core experiments on low-input systems, agroforestry, continuous
cropping, legume-based pastures, and paddy rice. This network is now
operating in 11 Latin American countries. Continuing technical backstopping
is being provided to IBSRAM (International Board for Soil Research and
Management) in the establishment of two Acid Tropical Soils Networks in Asia
and Africa. Given the striking similarities in soil constraints between
tropical America and tropical Africa, a similar workshop is being planned in
coordination with IBSRAM to train African soil specialists at Yurimaguas and
establish a viable link between soil management technologies generated in
Latin America and its potential users in Africa.

Yurimaguas Workshop

T. Jot Smyth, N. C. State University, Raleigh
Jose R. Benites, N. C. State University, Yurimaguas, Peru
Dale E. Bandy, N. C. State University, Yurimaguas, Peru
Pedro A. Sanchez, N. C. State University, Raleigh

Tropical soils research has progressed to the point of grouping
promising alternatives into soil management options that account for
differences in physical and socioeconomic conditions within this ecosystem
(Figure 1). Many of the key components for these technologies can now be
transferred to national research institutions, allowing local investigators
to adapt soil management options to their specific conditions. A concerted
validation and extrapolation effort across tropical soil ecosystems in Latin
America would not only encourage interaction among participating
institutions but also identify refinements and modifications that should be
pursued to improve existing management options. Such an effort requires the
identification and training of capable on-site personnel at collaborating
national institutions.
In September 1986, North Carolina State University's TropSoils
conducted a 21-day workshop on tropical soils management at its primary
research site in Yurimaguas, Peru, in cooperation with INIPA, USAID/Lima,
and the Interamerican Institute for Cooperation in Agriculture (IICA).
Purposes of the workshop were to acquaint key Latin American scientists with
the most recent techniques in tropical soil characterization and management
and to identify common interests and establish a soil research network.
Criteria for selection of participants were based on the national research
institutes': (a) interest and capabilities in pursuing soil management
research in tropical ecosystems and (b) designation of workshop candidates,
with at least a B.S. in agronomy or equivalent training, as the personnel
responsible for conducting network investigations resulting from this
workshop. The 31 participants who attended the workshop represented a total
of 23 potential research sites distributed among 15 national institutions in
10 different countries (Table 1). A detailed description of the workshop
and the experiments developed for the research network can be found in a

report to the U.S. Agency for International Development available in English
and Spanish.
Activities were organized around the two workshop objectives and
occurred simultaneously during the 3-week schedule. The sequence of topics
covered during the instructional component included: characterization of
tropical ecosystems; diversity, classification, and taxonomy of tropical
soils; soil physics in relation to land clearing and tillage systems; and
fundamental aspects of soil chemistry, soil fertility, soil testing, and
plant analysis. Emphasis was placed on field activities that gave
participants hands-on experience with the most recent field and laboratory
techniques and computer software used in soil science research. Technology
developed for humid tropical soil management was discussed as five distinct
packages: mechanized high-input continuous crop production, low-input crop
production with acid-tolerant species, agroforestry systems, paddy rice
production on alluvial soils, and legume-based pastures. Approximately one
full day was devoted to field tours of experiments for each management
During their 3 weeks in Yurimaguas, participants installed a low-input
experiment on a secondary forest site. This activity acquainted the group
with the procedures, measurements, and decisions to be made during the
processes of site selection, forest clearing, soil and vegetation
characterization, plot establishment, and planting the initial crop. The

group performed nondestructive forest biomass measurements, burned the
slashed vegetation, collected ash and post-burn soil samples, and analyzed
the ash and soil for nutrient content in the laboratories. Before
departing, participants were able to observe their experiment with an
initial stand of upland rice.
Considerations for network development were initiated by participant
presentations geared to provide opportunities for interaction and
identification of common interests. Each member described the ecosystem,
facilities, research program, and limitations of the experimental site where
they performed studies for their national institutes. Comparative data
among the participants' research sites (Table 2) indicate a broad spectrum
of research thrusts and ecosystems.
Toward the end of the workshop, participants voluntarily chose to
participate in individual working groups on each of the five soil management

options. Each working group was requested to (a) identify soil management
factors that should be investigated in an extrapolation and validation
network, (b) design experiments with clearly defined objectives, and (c)
define experimental methodologies and basic requirements of equipment and
facilities. A brief description of the network studies developed by each
working group follows.

Low-input option
1. Compare the sequence in which nutrient constraints appear in acid
soils, under different ecosystems, under upland rice-cowpea
2. Compare the effects of nutrient additions by ash from burning
different types of standing vegetation in different climatic
3. Establish soil nutrient levels to aid in formulating minimum
fertilizer recommendations for sustained upland rice-cowpea
production in acid soils.
Experimental approach
A total of 13 fertilization treatments, in a randomized complete
block design with four replications, were developed as common to
all network sites. Both udic and ustic moisture regimes exist
among sites, and vegetation varies from primary rainforest to
savanna. Post-clearing management will be constant among all

High-input option
1. Evaluate, under continuous cultivation, crop responses to
increasing rates of K fertilization;
2. Evaluate the effects of crop residues on soil K dynamics;
3. Evaluate crop response to residual fertilizer K;
4. Determine the influence of K rates on K interactions with Ca and
Mg in soils and plants.
Experimental approach
Crop rotations will be corn-soybean or corn-cowpea. Yield

systems. Annual crops will be excluded from the experiment for
steep topography.

Paddy rice option
1. Investigate alluvial soil management systems for paddy rice

2. Evaluate over time changes in soil nutrient availability in
alluvial soils under paddy rice production.
Experimental approach
Paddy rice production has not been practiced in large areas of the
Amazon. Local expertise, therefore, is almost nonexistent.
Farmer acceptance of the system in the lower Amazon Basin is
believed to depend on the demonstration that (a) labor-intensive
dike formation persists after seasonal river flooding, (b)
constant flooding of rice paddies reduces weeding, and (c)
broadcast seeding is a viable alternative to labor-intensive

After reviewing the proposals, participants were asked to identify, on
a priority basis, the top three (if any) experiments they considered most
applicable to their research station activities. Responses suggested
primary interest in the low-input and agroforestry soil management options.
This workshop activity provided valuable feedback information to the
TropSoils program in Latin America, especially because these opinions were
provided by professional field scientists after an intensive review of the
primary research site program.
Participants agreed that a common goal of the network would be the
transferral and validation of improved soil management technologies on acid
humid tropical soils in Latin America. The group requested that North
Carolina State University coordinate information exchange and technical
backstopping among network participants.
The quality of the projects developed by the group suggests that the
workshop was successful in enhancing the soil management research
capabilities of collaborating country personnel. Workshop program
evaluations by the participants highlighted the feasibility of using the

response to K will be evaluated over six K rates, ranging from 0
to 250 kg K/ha. Crop residue effects and interactions with Mg
will be evaluated in four additional treatments. Potassium will
be monitored in both the soil profile and plant tissue.

Improved pastures option
1. Determine the appropriate method for renewing pasture productivity
through legume incorporation;
2. Determine the effects of P fertilization on legume establishment
in pastures;
3. Evaluate the persistence of legume-grass associations as a
function of establishment treatments.
Experimental approach
The experiment will be conducted in degraded pastures and will be
composed of two distinct phases: (a) legume establishment as a
function of tillage and P fertilization and (b) P dynamics and
legume persistence as a function of animal grazing. The initial
phase will be conducted in a network experiment with three P
rates, two tillage methods, and four legume species in a split-
split plot design with three replications.

Agroforestry option
Improve soil fertility and control soil erosion and weed incidence
by improved fallows and tree crops in agroforestry systems.
Experimental approach
The group chose to develop one experiment for improved fallows and
two experiments for tree crops, with a distinction in the latter
for steep and flat topography. The improved fallow study will
compare the effects of a selected tree + groundcover legume short-
term (3-5 years) fallow to a traditional secondary forest fallow
(5-10 years) on the control of weeds, soil erosion, and soil
fertility replenishment for subsequent crop production. The tree
crop experiments will evaluate the productivity, nutrient
distribution, and use of selected perennial crops in multistrata

Yurimaguas Experiment Station research program to provide scientists in the

humid tropics with on-site exposure to knowledge of how to manage soils.

Table 1. Distribution of participants by country, national institutions,
and experiment stations at the Tropical Soil Management Workshop,
Yurimaguas, Aug. 31-Sept. 21, 1986.

National Research Number of
Country institution site participants




Costa Rica

Dominican Republic






Univ. Costa Rica





Porto Velho
Rio Branco


Rio Frfo




Min. Rec. Naturales



La Molina
Univ. Amaz. Peruana



Puerto Maldonado
Tingo Maria




-- - - -- - - - --------------------" "

Table 2. CQparative data aimg potential network research sites.




Costa Rica

Dom. Repub.








Country Instituti





Tirgp Maria






Systa under inVestition Sail
DInant laboratories scientists
sails Pastures TIee corps Food crops available available






Ihiv. Costa




Min. Rec. Nat.


location rainfall

apare 2500-4500

Itabuna 1300

Beln 2200

MMaus 2300

PBrto Vel, 2400

Rio Banco 1800

Ura 20004000

Tnrrialba 2500

Rio Etfo 4000

Santiago 2800

Pichilitnie 2160


EaniL 1000

Calabacito 2500-3300













Note on other institutions:
IUHT SEG/IEI OR conducts soil surveys and land resource evaluations thxogh the entire country.
UNIV. IA MUNA/PERU oducts potato fertilization trials ard M. Sc. this research in agrcncy in the Ieruvian Aaman.
University campus is located in Lima.

1. Plant alyse are performed at the MBAPA stations in Mamus and/or BelMn.
2. Soil and plant analyses are performed at another NIAP station iwthin 200 kn distance.
3. Soil ard plant analyses are performed at laboratories in Tegrcigalpa.
4. Sail and plant analyses are performed at central laboratories in Lina.




native fruits

amerintal &
native fruits









native fruits

cxmercial &
native fruits



















Paddy Rice

Continuous Cropping

Low-Input Cropping



Forest/Farming Mosaic

Regenerating Slopes __
Alluvial Soils Acid Soils Young Soils

Figure 1. Soil management options for sustainable production in the humid tropics used in the
research network.


Network Development in Latin America: RISTROP

T. Jot Smyth, N. C. State University, Raleigh

Participants requested that NCSU provide the central coordination for
the network, which they chose to name RISTROP (Red de Investigaci6n de
Suelos Tropicales). Assistance was requested for research site selection
and characterization, support services for analyses and interpretation of
resulting data, and information exchange between participating national
institutions. Funding was not available to sponsor each participant's
research activities in the network. Participants were therefore
individually responsible for obtaining approval and funding from their
national institutes for their network activities. The limited budget
available for network coordination also led to the stipulation that support
services from NCSU's Tropical Soils Program would only be initiated for a
network participant upon confirmation of the national institute's approval
of network activities.
The network coordination has received positive responses from
participants in 8 of 11 countries, for a total of 27 initiated or planned
experiments, encompassing all management options presented during the
Yurimaguas workshop (Table 1). With the exception of collaborators in
Bolivia, participants have limited their commitments in 1987 to initiating
network experiments, which they identified as first priority during the
Yurimaguas workshop. Participants from IBTA/Bolivia intend to initiate
experiments identified as both first and second priority for their
institutional programs. INIPA stations in Puerto Maldonado, Moyobamba, and
Iquitos plan to incorporate the low-input and agroforestry studies into
experiments on native fruit tree production systems for peach palm, Brazil
nut, and camu-camu. A similar approach is planned for the same network
experiments at EMBRAPA/Manaus in guarana production systems. The Peruvian
government recently established lime management as top research priority for
the Selva region. High-input annual crop experiments at Tingo Maria and
Moyobamba, therefore, will be directed toward comparisons of yield responses
to locally available lime sources.
RISTROP collaborators in Ecuador recommended delaying network

initiatives in their country until funding is available through the recently
established agricultural research foundation. Despite several inquiries, no
response has been received on the network status in the Dominican Republic.
A similar situation in Honduras was transformed into a positive commitment
after discussions with the participant's superiors during recent travel to
Central America. Additional correspondence with Colombian scientists, who
were unable to attend the workshop, may result in implementation of two
studies in that country. Venezuela also was not represented at the
Yurimaguas workshop; however, after reviewing the workshop report,
collaborators from the Universidad Central de Venezuela notified RISTROP
coordination of their intention to participate in three network experiments.
Since the completion of the Yurimaguas workshop, NCSU support
activities for the network have centered on technical visits to
participating institutions during implementation of field experiments. In
addition to assisting participants in adjusting methodologies and field
plans to local conditions, this action has also provided an opportunity to
obtain on-site familiarity with the research programs of the national
institutions. Extensive discussions with participating network scientists
and travel conducted to date have provided the following observations:
The specific needs for technical backstopping by national
institutions and the capacity for NCSU's Tropical Soils Program to
provide this expertise extends beyond the existing scope of the budget
and/or conceptual development of the research network. The type of

required technical support varies among institutions from assistance in
establishing functional soil testing laboratories to the identification
of research priorities through interpretation of existing soils
information. Such limitations often impede participants' abilities to

implement knowledge gained during the Yurimaguas workshop on a broader
institutional scale.
Ongoing national institute research programs, in some of the
visited countries, are often unrelated and nonsupportive to the USAID
Mission agricultural development programs. Quite often network
participants and their superiors have indicated unfamiliarity with
ongoing USAID Mission programs. Synchronization of national institute
and USAID Mission programs would capitalize on the investment made,

thus far, to transfer soil management technology to the network
Although it is not anticipated that soil science expertise in national
institutions will be fully implemented through participation in RISTROP, it
is fitting to consider supportive measures which will ensure that
experiences gained in the network will be maintained and used in future
national research endeavors.

Table 1. Current stage of developments for RISTROP experiments in each
participating country.

Annual crops

Low High Agrofor- Improved Paddy
Country Institution input input estry pastures rice

Guatemala ICTA I
Honduras Min. Recursos Naturales I
Costa Rica Univ. C. Rica/CATIE I
Panama IDIAP A I
Dom. Repub. ISA P
Peru INIPA/Puerto Maldonado A A
INIPA/Tingo Maria A
INIPA/Iquitos A A
INIPA/Moyobamba A A A
INIPA/Yurimaguas I
Bolivia IBTA/Chapare I I I
EMBRAPA/Porto Velho I
Colombia ICA P
Com. Esp. Guaviare P
Venezuela Univ. Central Venezuela I I I

Initiated (I) 6 2 1 2 2
Approved Plan (A) 6 2 4
Potential (P) 3 2

Network Development in Africa and Asia

Pedro A. Sanchez, N. C. State University, Raleigh
T. Jot Smyth, N. C. State University, Raleigh
Stanley W. Buol, N. C. State University, Raleigh

TropSoils and IBSRAM signed a memorandum of understanding in which both
institutions formally agreed to work together toward the development of an
Acid Tropical Soils Network on a worldwide basis. TropSoils input has
concentrated on providing technical leadership through the Network
Coordinating Committees.
The Inaugural Workshop of the Acid Tropical Soils Network was held in
Yurimaguas, Peru, and in Manaus and Brasilia, Brazil, from April 24 to May 3,
1985. It was organized by TropSoils/NCSU and co-sponsored by INIPA and
EMBRAPA with support from various international organizations and donor
agencies. After several days of observing ongoing long-term research in the
humid tropics and acid savannas of South America, representatives from 13
developing countries (Brazil, Cameroon, China, Congo, Ivory Coast,
Madagascar, Malaysia, Mexico, Panama, Peru, Thailand, Venezuela, and Zambia)
decided to form the Acid Tropical Soils Network. The participants identified
a defined target area, six principal research-validation topics, and several
support services.
The Inaugural Workshop Proceedings provide a state-of-the-art review on
management of acid tropical soils and its publication, edited by
TropSoils/NCSU, is expected in early 1987. The proceedings may serve as the
conceptual base of the network.
The first IBSRAM African regional workshop was held in Douala, Cameroon,
on January 21-27, 1986. The five original African countries represented in
the Inaugural Workshop were joined by Rwanda, Burundi, and Nigeria. A total
of 55 individuals from 15 countries participated, under the sponsorship of
the Cameroonian Ministry of Higher Education and Research, with several donor
inputs. The five original countries have all initiated activities without
waiting for additional funds. Sites have been selected for new experiment
stations in Cameroon and Congo, where several of the humid tropical soil
management options seen in Yurimaguas are planned to be implemented. Zambia

began implementing many of the ideas gathered after visiting Yurimaguas,
Manaus, and Brasilia. Proposals for new sites were identified by
representatives for Madagascar, Ivory Coast, Nigeria, Rwanda, and Burundi.
Common methodologies for evaluating edaphic parameters were agreed upon
at the Cameroon Workshop and are shown in Table 1. To assist in project
development, a list of equipment, supplies, and reagents for a fully-
operational laboratory to analyze the agreed-upon edaphic parameters was
prepared by TropSoils/NCSU and submitted to IBSRAM headquarters. A second
African meeting scheduled for April 1987 in Lusaka, Zambia, is expected to
produce concrete experimental designs.
The first IBSRAM Regional Workshop on Soil Management under Humid
Conditions in Asia was held at Khon Kaen and Phitsanulok, Thailand, from
October 13 to 20, 1986, with 82 participants from 17 countries present. It
was co-hosted by Thailand's Ministry of Agriculture and Cooperatives and
IBSRAM, and was funded primarily by the Asian Development Bank (ADB) and the
Australian Council for International Agricultural Research (ACIAR). A total
of eight countries expressed interest in joining the Acid Soils Network.
Included in the list are the three Asian participants at the Inaugural
Workshop--China, Malaysia, and Thailand--and five additional countries--
India, Indonesia, Philippines, Vietnam, and Western Samoa. The common theme
was the limited knowledge base on how to produce food crops on acid upland
soils of tropical Asia.
The participants agreed on two overall types of research activities,
"core" experiment and component research, in addition to site
characterization, a common activity of all networks. The core experiment is
designed to compare current acid upland soil management practices with (1)
low-input systems based on acid-tolerant cultivars, low levels of added P,
and no change in the soil's acidity and (2) an intensive system with liming
to neutralize exchangeable Al and appropriate fertilizer practices for
cropping systems based on corn, soybean, or cotton. Although the specific
cropping system will vary with site, the common thread will be the monitoring
of soil dynamics as proposed at the Inaugural Workshop.
Component research projects focus on (1) liming, (2) screening of acid-
tolerant species and varieties, (3) residual effects of P fertilization, (4)
organic inputs, initially focusing on determining the nutrient contents of
composts, green manures, or animal manures, and (5) Fertility Capability


Participants in the African network have expressed to IBSRAM particular
concern about the need to increase their expertise in acid tropical soil
management techniques among their front-line scientists. Based on the recent
success of a similar activity for RISTROP participants, and on the African
network emphasis on technologies developed in the TropSoils program, IBSRAM
has requested NCSU's assistance with on-the-job training of soil scientists
who will be doing the work in the Acid Soil Management Network. The
experience accumulated in Latin America by the TropSoils program and the
commonality of interests with IBSRAM in transferring such knowledge to
African scientists makes it fitting that assistance be provided toward
network implementation through a workshop/training course at the primary

research site in Yurimaguas, Peru.
Acid tropical soils comprise approximately 1.7 billion ha of land area
in 72 developing countries. Their geographical concentration is primarily in
least-developed Third World regions, many of which are currently undergoing
social unrest and face several food shortages by the next decade. Thirty-
seven of these countries are now involved in RISTROP and IBSRAM and tropical
soils networks (Figure 1). The network support activities offer the
opportunity for concerted worldwide efforts in disseminating existing
information and developing local expertise on management of this fragile
ecosystem in needy countries. Feedback from validation and extrapolation of
existing information would enhance TropSoils' role in the discrimination of
agronomically and economically sound acid soil management technologies
through the identification of refinements and modifications for ongoing

Table 1. Edaphic parameters to be measured in IBSRAM Acid Tropical Soils
Network Experiments, as agreed in the Cameroon Seminar, January,


Parameter 0-10 10-20 20-50 Method


Yes Yes

pH (H20)

pH (KC1)
Exch. Al
Exch. Ca
Exch. Mg

Exch. K
Avail. P
Avail. Zi
Avail. F<
Avail. Ci
Avail. Mi



1:2.5 H20









Al sat.

P sorption

Org. C

pH (NaF)

ZPC (Zero
point of

Yes Yes

Yes Yes

Yes Yes

Yes Yes

Yes Yes

Yes Yes


Bulk density

1/3 bar H20

Yes Yes

Yes Yes

Exch. Exch.
Al + Ca +

Mg +


Exch. Al = ECEC x 100

Fox and Kamprath, Juo and Fox

Walkley Black

If allophane is suspect

If subhorizon approaches
acric properties

At planting time

optional where deficiencies or toxicities suspected.

--------------------------------------- --------------

*Optional. Mn not


Figure 1. Countries involved in acid tropical soils research networks supported by IBSRAM and TropSoils.


Cattle grazing for beef and milk production is one of the major land use
activities of cleared rainforest areas in Latin America. We continue to find
that when they are well managed, legume-based pastures protect the soil,
require relatively few cash inputs, make good use of soils unsuitable for
food crops, and produce milk and meat with grazing animals, which recycle
most of the nutrients they consume. But poorly managed pastures are an
economic and ecological liability. The use of pasture species badly adapted
to tropical soils and environments leads to poor animal nutrition and
therefore low productivity. Several million hectares of rainforest have been
cleared for pastures, only to be abandoned as the pastures became degraded by
overgrazing, soil compaction, and erosion.
Pastures research at Yurimaguas and Pucallpa, Peru, has been closely
integrated with the Tropical Pastures Program of the Centro Internacional de
Agriculture Tropical (CIAT) and with INIPA's National Selva Program, which is
now conducting most of the agronomic studies. Research reported here is
based on an overall long-term strategy shown in Figure 1. All but the last
stage are fully implemented.
Long-term grazing studies show that high animal production levels can be
sustained with three widely differing pastures in acid Ultisols with low
inputs: a mixture of two stoloniferous grass and legume species (Brachiaria
humidicola/Desmodium ovalifolium), a mixture of two erect grass and legume
species (Andropogon gayanus/Stylosanthes guianensis), and one pure legume
pasture of Centrosema pubescens. Other mixtures are failing because of low
quality problems. After 4 to 6 years of continuous grazing, soil physical
properties remain good and chemical properties have improved, because more
than 80% of the P, K, and Ca applied as fertilizer is recycled to the soil.
This year we obtained the first estimate of the N contribution of legumes to
the associated grass under grazing in highly acid soil: the legume
contributed an equivalent of 150 kg N/ha of urea nitrogen. Potassium
dynamics, a Key issue for pasture persistence, continues to be quantified,
and S accumulation in Ultisol subsoils was confirmed.
Perhaps the most exciting accomplishment of this year was the successful
transformation of degraded steepland pastures into highly productive ones by

establishing grass and legume species with minimum tillage and phosphate rock
in slopes ranging from 20 to 80%. In areas where herbicides are available,
the proper combination of tillage and herbicide was determined to eliminate
undesirable species and plant improved ones.





Figure 1. Strategy for developing the pasture soil management option for the humid tropics.


Persistence of Grass-Legume Mixtures under Grazing

Miguel A. Ayarza, N. C. State University, Yurimaguas, Peru
Rolando Dextre, INIPA, Yurimaguas, Peru
Pedro A. Sanchez, N. C. State University, Raleigh

The central experiment for the legume-based pasture soil management
option is now in its sixth year of grazing. Its objectives are (1) to
measure pasture and animal productivity in different associations, in terms
of daily weight gain and annual liveweight production, (2) to evaluate the
compatibility and the persistence of the different grass-legume mixtures
under grazing, and (3) to evaluate changes in soil properties as a
consequence of long-term pasture production.
Four associations remain unchanged, but during the 4 years the
project has been in progress, Panicum maximum + Pueraria phaseoloides was
replaced by Andropogon gayanus + Centrosema macrocarpum 5056 in October 1984.
A sixth association, Brachiaria dyctioneura + Desmodium ovalifolium, was
established at a separate location with grazing initiated in March 1986. The
species previously reported as Centrosema hybrid 438 was reclassified by
plant taxonomists as Centrosema pubescens 438. The main features of the
experiment are shown in Table 1.

Annual Production and Botanical Composition 1985-1986
Annual liveweight gains per hectare (the measure of overall pasture
productivity), individual animal daily gains (an estimate of pasture
quality), legume content, actual grazing periods and stocking rates used are
shown in Table 2 for 1985 and Table 3 for 1986.
Annual liveweight gains were generally better in 1985 than in 1986 due
to a more favorable rainfall pattern in 1985 and a 3-month delay in grazing
initiation in 1986. Stocking rates were adjusted according to forage
availability and divided into two semesters (January to June as the wetter
period, and July to December as the less wet period). Brachiaria
humidicola/D. ovalifolium mixtures produced very high annual liveweight gains
(843 kg/ha), way above the other mixtures. This mixture produced high
available forage throughout the year (Figure 1), which permitted a higher

stocking rate. Liveweight gains decreased in 1986, in spite of legume
content similar to that in 1985.
The B. decumbens/D. ovalifolium mixture performed quite inferiorly,
producing about half the daily animal gains than the previous mixture in
spite of using identical stocking rates (Tables 2 and 3). Although forage
availability was higher with B. decumbens than with B. humidicola (Figure 1),
sharp animal weight losses were observed with the B. decumbens/D. ovalifolium
mixture during the second half of the year. Individual animal gains dropped
drastically from June 1985 and continued dropping until December when the
animals lost more than 300 g/day (Figure 2). The same situation occurred at
the same time in 1986, which was reflected in low individual animal gains.
This problem may be due to photosensitivity, which sometimes occurs with B.
decumbens, or to an unknown nutritional problem during the drier part of the
year. Its solution is likely to require the collaboration of animal
nutrition specialists.
The pure legume pasture C. pubescens 438 maintained good levels of
animal production in both years, in spite of the lower amount of forage on
offer than the mixed pastures (Figure 2), which resulted in no weight losses
during the drier period. Since forage quantity is lower than in the previous
mixtures, the higher quality of C. pubescens 438 over D. ovalifolium (Table
4) is considered responsible for its good performance.
The mixture of erect species A. gayanus with Stylosanthes guianensis
performed remarkably well in 1985 and 1986, particularly in terms of daily
gains, suggesting a higher quality of the legume component (Table 4).
Promising results were obtained in A. gayanus + C. macrocarpum 5065.
Excellent individual animal gains were recorded during 1985 and 1986. Since
this pasture has only been grazed since May 1985, it is not possible to
compare it with the older mixtures, but it certainly shows good promise.
In sharp contrast, the new mixture established in 1985 which began
grazing in March 1986 (B. dyctioneura/D. ovalifolium) performed very poorly
even during the first year (Table 3). This mixture showed an excessively
high content of legume in the forage on offer. This may significantly reduce
animal performance due to the low quality of the legume, in comparison with
the Centrosema species (Table 4). This mixture was eliminated from the trial
in 1986. This is disappointing because this species is being considered an
alternative to the other Brachiarias in the ustic tropics. Apparently this

is not the case in Yurimaguas with a udic soil moisture regime.

Long-term Trends in Persistence and Productivity
A summary of the 6 years of grazing was presented at the American
Society of Agronomy meetings in November 1986. Its summary gives for the
first time a vision of pasture persistence. Only the four most promising
mixtures are included in this analysis. The overall summary (Table 5)
indicates that there are several widely different options, all with very high
animal productivity potential (annual liveweight gains on the order of 500 to
600 kg/ha/yr). Considering that cattle production from unimproved pastures is
of the order of 50-100 kg/ha/yr, each mixture is very attractive. The
quality problem of B. decumbens/D. ovalifolium definitely puts it at a
disadvantage in relation to the other three.
Each of the remaining three represents a different approach: a mixture
of creeper species (B. humidicola/D. ovalifolium), a mixture of erect species
(A. gayanus/S. guianensis), and a pure, high-quality legume pasture (C.
pubescens 438).
The yearly fluctuation in the above parameters gives a feel for pasture
stability. Annual liveweight gains fluctuated considerably, but the greatest
fluctuations were observed in the erect mixture (Figure 3). The legume
content tended to fluctuate less than liveweight gains (Figure 4) and showed
little relationship with annual liveweight gains. Legume content seldom
dropped below 20% of the forage on offer, a level below which is considered
undesirable. Daily liveweight gains (Figure 5) showed less yearly
fluctuations than the previous two parameters. Nevertheless, these yearly
averages include sharp weight losses in the B. decumbens/D. ovalifolium
mixture during the last 2 years. Overall, Figures 3, 4, and 5 suggest a
reasonable degree of stability in the other three mixtures.

Long-term Changes in Soil Properties
Measurements taken in December 1985 indicated a marked decrease in water
infiltration rates in most of the pastures as a result of soil compaction
produced by animals after 5 years of grazing (Table 6). Lowest values were
found in A. gayanus/S. guianensis and A. gayanus/C. macrocarpum. This may be
associated with the erect growth of these species so that they do not cover

the soil as do the other pastures. Statistical analysis, however, showed
that infiltration differences among pastures were not significant, due to the
high variability of the double ring infiltrometer measurement.
The infiltration rate prior to the start of grazing in November 1980 was
12.7 cm/hr with a range of 6.3 to 19.8. Five years later the average
infiltration was 4.1 cm/hr with a range of 1.0 to 10.4 (Table 6). There is
no question, therefore, that 5 years of trampling have decreased infiltration
rates in this sandy loam Ultisol. The magnitude of the decrease has not
produced visible runoff or erosion. This is because rainfall intensity
values average much less than 41 mm/hr (see Continuous Cropping section) and
also because these pasture provide a year-round full plant canopy that
protects the soil from raindrop impact.
Soil Organic Matter
Topsoil (0-20 cm) organic matter and total N for each pasture were
determined in December 1985, and values were compared to those obtained 5
years before the initiation of grazing (Table 7). These data compare the
overall levels of the experiment prior to grazing with the effects of
individual pastures, and not on a plot-per-plot basis. In spite of this
limitation, it appears that organic matter and total N contents either
increased or remained the same during 5 years of grazing. The differences
between pastures cannot be explained in terms of legume content, since both
the highest and lowest levels were observed in mixtures with D. ovalifolium.
The lowest levels were observed with B. humidicola/D. ovalifolium, the most
productive pasture. Topsoil organic matter contents were maintained under
this management option (Table 7).
Soil Fertility Paramenters
Status of soil chemical properties in the 0-20 cm depth is reported in
Table 8. Topsoil pH and P values were higher in 1985 than in 1980 in most of
the pastures. Acidity decreased greatly in topsoils under B. decumbens/D.
ovalifolium. Additional soil characterization at the 0-5 and 5-20 cm depths
on B. humidicola/D. ovalifolium showed that most changes observed in topsoils
were restricted to the 0-5 cm soil surface layer (Figures 6, 7, 8, 9). This
may indicate that nutrient accumulation and cycling occurs mainly at the soil
0-5 m layer.
Nutrient Cycling
The improvements in soil properties in the top 20 cm can probably be

attributed to the original and annual maintenance fertilization schedule
shown in Table 1. It is noteworthy to observe that the annual maintenance
fertilization was not applied in November 1983. The total amounts of P, K,
and Ca added as fertilizers and lime during the 5-year period were compared
by the amount calculated to be removed by animals in terms of annual
liveweight gains. The results, shown in Table 9, indicate that 80% of the P,
98% of the K, and 92% of the Ca added as fertilizer was recycled to the soil
in the B. decumbens/D. ovalifolium mixture. This high level of recycling is
one of the real advantages of grazed grass-legume pastures, where the
nutrients exported on the hoof are very low.

Table 1. Main features of the central, legume-based pastures experiment

Design: Randomized complete block, 2 replications

Plot size: 0.45 ha

Pasture established: Sept. 1979

Stocking rate: 3.3-5.5 an/ha (150-kg Cebu steers)

Grazing management: Continuous from Nov. 1980 to July 1981

Alternate 28-35 day cycles since July 1981


22 kg P/ha as SSP (yearly)

42 kg K/ha as KC1 (yearly)

10 kg Mg/ha as MgS04 (yearly)

500 kg lime/ha (once)

Soil: Typic Paleudult, fine loamy, siliceous, isohyperthermic

Initial topsoil (0-20 cm) properties. Sept. 1979:

Clay: 13% Al sat.: 78%

O.M.: 1.85% ECEC : 3.87 cmol/L

pH : 4.3 Avail P : 2.2 pg/g

Table 2. Animal production, grazing periods, and percentage of legume in five
pastures under alternate grazing in 1985.

Liveweight gains
Stocking rates
Grazing Grazing Rainy Dry Total Indiv. Legume
Pasture years period period period prod. prod. content

----an/ha---- kg/ha/yr g/an/day %

C. pubescens 438 4 Jan. 14- 4.4 4.4 510 342 100
Dec. 19

B. humidicola + 3 Jan. 14-
D.ovalifolium 350 Dec. 19 5.5 4.4 843 482 30

B. decumbens + 5 Jan. 14-
D. ovalifolium 350 Dec. 19 5.5 4.4 469 259 26

A. gayanus + 5 April. 1-
S. guianensis 134-186 Dec. 3 3.3 3.3 363 594 49

A. gayanus + 2 April 23-
C. macrocarpum 5016 Nov. 20 3.3 3.3 502 775 13

Table 3. Animal production, grazing periods, and percentage of legume in five
pastures under alternate grazing in 1986.

Liveweight gains
Stocking rates
Grazing Grazing Rainy Dry Total Indiv. Legume
Pasture years period period period prod. prod. content

---an/ha---- kg/ha/yr g/an/day %

C. pubescens 438 5 Mar. 18- 3.3 3.3 498 636 100
Dec. 4

B. humidicola + 4 Mar. 18-
D. ovalifolium 350 Dec. 22 5.5 4.4 460 336 34

B. decumbens + 6 Mar. 18-
D. ovalifolium 350 Dec. 10 5.5 4.4 223 170 22

A. gayanus + 6 Mar. 18-
S. guianensis 136-184 Dec. 10 3.3 3.3 436 544 34

A. gayanus + 3 Mar. 18-
C. macrocarpum 5056 Dec. 22 3.3 3.3 632 755 33

B. dyctioneura + 1 Mar. 18-
D. ovalifolium 350 Oct. 10 4.4 4.4 131 149 52

Table 4. Nutrient quality of leaf blades (Dec. 1985).
Species protein P Tanninsa
---- ----------------------------------------------------------
-----------------_% ---------------------


D. ovalifolium 12.4 0.22 21.0
C. pubescens 24.8 0.27 2.5
S. guianensis 21.4 0.35 4.0


B. decumbens 11.3 0.22
B. humidicola 10.6 0.22
A. gayanus 10.6 0.27

a. Analyzed in 1983. Vanillin-HCL method.

Table 5. Average annual productivity of legume-based pastures in
grazing experiment at Yurimaguas (1980-86).

the central



Pasture Years of Stocking Total Indiv. Legume
mixture grazing rate prod. prod. content
an/ha kg/ha/yr g/an/day--------------------------------
an/ha kg/ha/yr g/an/day %

B. humidicola/D.ovalifolium
B. decumbens/D. ovalifolium
C. pubescens 438
A. gayanus/S. guianensis



------------------------------------------ ----------------- --

Table 6.

Infiltration values in five pastures under grazing in Yurimaguas for
several years (mean of two replications and four observations per
replication of each pasture).

Years of
Pasture grazing Infiltrationa S.E. x


B. decumbens +
D. ovalifolium 5 4.71 a 1.20

B. humidicola +
D. ovalifolium 3 2.00 a 0.58

C. pubescens 4 10.44 a 2.60

A. gayanus +
C. macrocarpum 1 1.96 a 2.82

A. gayanus +
S. guianensis 5 1.00 a 0.19

LSD0.05 = 10.4

a. Numbers followed by the same letter are not statistically significant at
P = 0.05.

Table 7. Changes in organic matter total nitrogen in the topsoil (0-20 cm) of
five pastures under grazing after 5 years (1980-1985).
Total N

Pasture Organic matter SDa Amountb
--------%-------------- kg/ha

Before grazing (Nov 1980) 1.93+0.4 0.0707+0.016 1837

B. decumbens +
D. ovalifolium 3.35+0.4 0.0895 0.015 2327

B. humidicola +
D. ovalifolium 1.35+0.6 0.0705+0.412 1085

C. pubescens 1.95+0.2 0.0856+0.0025 2225

A. gayanus +
S. guianensis 2.02+0.2 0.0770+0.005 2002

A. gayanus +
C. macrocarpum 2.14+0.2 0.0757+0.009 1969

a. Mean of two composite samples (10 subsamples each). Rest of pasture is
the mean of two replications (10 subsamples each).
b. Value calculated assuming 1.4 g/cc in the 0-20 cm depth. Mean of three
composite samples (10 subsamples each). Mean +standard deviation.

Table 8. Status of soil fertility of the topsoil
after 5 years of grazing in Yurimaguas.

(0-20 cm) of five pastures

Pasture Year pH O.M. Olsen P Ca+Mg K Al sat.

% ppm ----cmol/L---- %

B. decumbens + 1980 4.2 1.9 3.9 1.7 2.7 55
D. ovalifolium 1985 4.6 3.3 8.3 1.0 0.10 0.9 53

B. humidicola + 1980 5.2 1.7 2.2 2.4 1.7 42
D. ovalifolium 1985 5.0 1.3 6.4 1.2 0.12 1.3 49

C. pubescens 1980 4.9 2.2 8.6 2.1 2.5 54
1985 5.0 1.9 6.5 1.8 0.18 2.4 54

A. gayanus + 1980 4.6 2.1 5.8 1.7 2.4 56
S. guianensis 1985 5.3 2.0 7.9 1.6 0.11 1.8 51

A. gayanus + 1980 4.3 1.8 4.3 1.5 2.4 60
C. macrocarpuma 1985 5.1 2.1 1.0 1.1 0.07 2.2 65

a. A. gayanus + Pueraria phaseoloides for the first 3 years.

Table 9. Nutrient balance in B. decumbens/D. ovalifolium during 5 years of

Balance (1980-1985) P K Ca


Added as fertilizers and lime 112 160 505
Removed by animals 22 6 39
Balance 90 154 466
% "recycled" 80 98 92

Jan Mar May Jul

Feb Apr

Jun Aug

Sep Nov
Oct Dec

Grazing periods (1985)

Seasonal changes in available forage on offer of
three pastures in 1985.

o 8. decumbens + 0. ovali folium
a B. humidicolo + 0. ovalifolium
o C. pubescens



Jan Mar May Jul Sep Nov
Feb Apr Jun Fug Oct Dec

Grazing periods (1985)

Seasonal changes in individual liveweight gains
in 1985.


CD 4

- 2


a B. decumbens + 0. oval ifol ium
o B. humidicola + D. ovalifolium
a C. pubescens


Figure 1.





Figure 2.


C 800
c 600
" 400
- 200

Bd/Oo Bh/Oo Cp Rg/Sg

Pasture and grazing year

Figure 3.

Yearly fluctuations in liveweight gains in four
rotationally grazed pastures at Yurimaguas. Bd =
B. decumbens; Do = D. ovalifolium; Bh = B. humidicola;
Cp = C. pubescens; Ag = A. gayanus; Sg =,S. guianensis.




0 -
123456 1234 12345 123456
Bd/Oo Bh/Oo Cp Ag/Sg
Posture and grazing year

Figure 4.

Yearly fluctuation in average legume composition of
the mixture. Bd = B. decumbens; Do = D. ovalifolium;
Bh B. humidicola; Cp = C. pubescens; Ag = A. gayanus;
Sg = S. guianensis.








Pasture and grazing

Yearly fluctuations in daily liveweight
Bd = B. decumbens; Do = D. ovalifolium;
B. humidicola; Cp = C. pubescens; Ag =
Sg = S. guianensis.

Bh =
A. gayanus;

Available P (ppm)
4 6

Available P profile 5 years after grazing a B.
humidicola/D. ovalifolium mixture.

600 F


Figure 5.



Figure 6.


Q- 40-60



Figure 7.



C. 20-

a_ 40-



Figure 8.

Exchangeable Al profile 5 years after grazing a B.
humidicoldD. ovalifolium mixture.

Exchangeable Co + Mg (cmol/L)
0.2 0.4 0.8 0.8 1.0 1,2

Exchangeable Ca and Mg profiles 5 years after grazing
a B.humidicola/D. ovalifolium pasture.

Exchangeab Ie K (cmoI/L)
)2 0.04 0.06 0.08 0.10



C- 40-60


80-100 -

Figure 9. Exchangeable K profile 5 years after grazing a B. humidicola
D. ovalifolium pasture.

Evaluation of Animal Preference in Small Plots

Miguel A. Ayarza, N. C. State University, Yurimaguas, Peru
Rolando Dextre, INIPA, Yurimaguas, Peru

Observation of animal preference at early stages of evaluating new
forage accessions is considered an important tool in selecting desirable
species from both the agronomic and the animal standpoints. Palatability is
crucial in the acid-tolerant tropical legumes we are working with. Factors
dealing with quality and preference can hardly be assessed without animals.

To test whether differences exist in animal preference for 13 legume
accessions at Yurimaguas.

An old regional Trial B, for which agronomic evaluation concluded in
1985, was used in this work. The experiment was fenced in March and animals
were introduced in May 1986. Accessions were arranged in randomized complete
blocks with 3 x 4 m plot size per species. Three animals (180 kg liveweight)
were observed 6 hr/day for 3 days in each replication. Position of the
animals and time spent grazing a particular accession were recorded every 15
Before entering the next replication, animals were kept out of the
experiment on a pure stand of B. humidicola for 3 days in an attempt to
diminish preference effects between replications.

The first evaluation showed average grazing time per species differed
even within a genus. Centrosema macrocarpum 5065 was preferred over the
other Centrosema accessions (Figure 1), and Centrosema macrocarpum 5052 was
hardly consumed at all. Desmodium ovalifolium 366 was preferred over D.
ovalifolium 350.

These results indicate that differences in animal preference for legumes

exist, even within the same genus and species. Although Centrosema species
are known to be palatable, there are important differences in palatability.
The preference for D. ovalifolium 366 is probably associated with its lower
tannin content than D. ovalifolium 350, as has been reported by CIAT. A
simple animal preference test can be included at the earliest stages of
germplasm evaluation to obtain a comparative idea of animal preference with
known species. This procedure could save significant time and effort by
eliminating undesirable accessions before starting a grazing trial.




Centrosema Centrosema Desmodium
macrocarpum pubescens oval i fol ium

Figure 1. Animal preference for 12 legumes at Yurimaguas.


Nitrogen Contribution of Legumes in Mixed Pastures

Miguel A. Ara, N. C. State University, Pucallpa, Peru
Jorge W. Vela, INIPA, Pucallpa, Peru
Pedro A. Sanchez, N. C. State University, Raleigh

Mixed grass-legume pastures are rare in the humid tropics. Most of the
successful mixtures occur in the ustic soil moisture regimes. The success of
some mixed pastures in such areas is often related to the ability of the
legume to provide protein during the strong dry season when grasses cannot.
In the humid tropics, where the grasses remain green throughout the year, the
role of the legume is different. The purpose of this work is to ascertain
the role of legumes under humid tropical conditions. A long-term grazing
experiment was established at the IVITA Principal Tropical Station west of
Pucallpa, Peru, in collaboration with INIPA and IVITA.

1. To estimate the N contribution of two adapted pasture legumes
(Centrosema pubescens and Desmodium ovalifolium) to their respective
mixtures with Brachiaria decumbens in terms of N yield, N availability
to the grazing animals, legume litter accumulation, and N release;
2. To evaluate the effect of different grazing pressures on the mixture B.
decumbens/D. ovalifolium in terms of N availability to grazing animals,
legume litter accumulation, and N release.

A 6-ha degraded pasture was planted to improved pastures to compare the
N-supplying capability of two alternative N sources (legumes vs. different
levels of N-fertilizer) on a grazed Brachiaria decumbens pasture, in terms of
N yield of the standing biomass, N availability to the grazing animals,
legume leaf litter accumulation, and N release. An additional variable, high
grazing pressure, was included in the legume mixture (normal = 4.5 kg
available forage dry matter per 100 kg animal liveweight; high = twice the
pressure). The experimental design was randomized complete blocks with five
treatments and three replications. Grazing was initiated in January 1986.
Replications were utilized as paddocks of a 15-day grazing, 30-day rest

rotation. Brown Swiss and Holstein-Cebu halfbreeds were used. Two
esophagus-fistulated steers were always kept in the same treatment; intact
animals were used as grazers. Animals were weighed before entering each
replication, but only to adjust the grazing pressure.
Slope was used as a blocking criterion. Replication I was located on 0-
5% slope, and replications II and III were located on 75% slopes. Soil was a
Pucallpa series Paleudult. Selected soil properties at the initiation of the
experiment are given in Table 1.
Serious problems in establishing the Centrosema pubescens/Brachiaria
decumbens mixture forced us to discard this treatment.


Forage Availability
Dry matter availability and botanical composition were evaluated using a
double sampling dry weight rank procedure with 100 samples per 0.33-ha
paddock just before grazing began. Dry matter yield and botanical
composition are shown in Table 2 and the corresponding ANOVA for dry matter
available to the treatments is shown in Table 3. No response was obtained
for dry matter availability to the treatments, although a trend of N response
is evident. Legume contents are adequate, but hover at high grazing
pressure, as expected.

Nitrogen Content and Nitrogen Yield
This year we were able to install a micro-Kjeldahl unit on the IVITA
soils laboratory. Results of N content and yield are the first from this
laboratory. Unlike dry matter availability, treatment effects on N content
and N yield of Brachiaria decumbens were well expressed (Table 2). The N
fertilizer effect on N content and N yield was linear with no quadratic
component (Figures 1 and 2). The presence of the legume significantly
increased the N content of the grass by an average of 44% (1.06 vs. 1.53% N).
The effect of grazing pressure of mixed pastures on grass N content was not
On the average, mixtures gave a higher grass N yield than grass alone
with no N fertilizer, equivalent to 151 kg of N (from the regression
equation). This amount is contributed by 28% of the legume component in the

high grazing pressure treatment and 35% in the normal grazing pressure
treatment. These numbers do not include the N content of the legume per se.
Consequently, they provide an early indication that legumes contribute the
equivalent of about 150 kg N/ha/yr to the associated grass during the first
10 months of grazing.

Leaf Litter N Accumulation
Four 0.5 x 0.5 m squares were selected in each legume paddock to cover
the range of legume composition. The squares were fixed with iron stakes,
and the Desmodium ovalifolium leaf litter was collected, dried, and weighed.

Leaf litter dry matter accumulation averaged 14 g/0.5 m2/18 months for the
high grazing pressure treatment and 29 g/0.5m2/18 months for the normal
grazing pressure treatment.
Nitrogen content of the leaf litter averaged 1.60%. Nitrogen
accumulation in litter form during this 18-month period averaged 4.6 kg N/ha
for the high grazing pressure treatment and 10.1 kg N/ha for the normal
grazing pressure treatment. Consequently, the lower the grazing pressure,
the more important will be the N transfer through the litter. This effect
is being measured concurrently with N intake by animals and in excreta to
fully calculate the N contribution of legumes to mixed pastures.

Conclusions to Date
1. There is a strong linear response of Brachiaria decumbens grazed
pastures to N fertilization as high as 300 kg N/ha/yr.
2. Including D. ovalifolium in the mixture contributes about 151 kg N/ha/yr
to the grass, in addition to the legume's N content.
3. Leaf litter N accumulation in mixed pastures decreases with increasing
grazing pasture.

These first year data show the obvious need for some sort of N input in
Brachiaria decumbens pastures established in land that previously had
degraded pastures. Addition of a legume in the mixture apparently makes a
large contribution to meet this need. Continuing to gather data will
demonstrate the effect on animal production and elucidate some of the N
transfer processes involved.

Table 1. Selected soil properties at the initiation of the
experiment. 0-15 cm. December 1985.

Rep Sand Clay pH P Al Ca Mg K O.M. N sat.

----%----- pg/ml ------cmol/L-------- ------%------

I 25.4 25.2 4.6 5.4 2.3 1.83 0.66 0.17 2.33 0.09 48
II 44.3 25.2 4.5 5.7 1.8 1.90 0.66 0.14 2.34 0.10 40
III 51.9 22.2 4.7 4.1 2.1 1.68 0.54 0.11 2.19 0.08 45

Table 2. Forage on offer and botanical composition of B. decumbens pastures
fertilized with N or mixed with D. ovalifolium at two grazing
pressures. Mean of three replications.

N Grazing Forage dry
source pressure mattera Legume Gross N content

kg/ha/yr tDM/ha/cycle % % N kg/ha/cycle

0 Normal 1.34 -1.06 a 140
150 Normal 1.56 1.42 b 222
300 Normal 1.66 1.85 c 308
Legume Normal 1.42 35 1.38 b 218
Legume High 1.38 28 1.58 b 230

a. Mean of seven grazing cycles of 45 days duration each.

Table 3. ANOVA for forage dry matter available.

Degrees of Mean
freedom Squares

Replications 2 46.3047 ns

Treatments 4 140.8177 ns
N linear 1 398.53 ns
N quadratic 1 21.12 ns
Mixtures vs. NQ 1 18.40 ns
HGP vs. LGP 1 5.23 ns


N (kg / ha / year)

Effect of fertilizer N and legume presence
on N content of Brachiaria decumbens pasture
during the first grazing year in Pucallpa,


N (kg/ha /year)

Apparent N contribution of legumes in
relation to N accumulation by fertilized
Brachiaria decumbens pastures in
Pucallpa, Peru.

Y = 1.0483 + 0.0026 x
r = 0.99 **

H U Fertilizer N
0 Legume-normal grazing pressure
0 Legume-high grazing pressure


Figure 1.

Figure 2.

Y = 0.8967 + 0.0028 x
- r 0.99**

M Fertilizer N
0 Legume -normal grazing pressure
o Legume-high grazing pressure

i I

Potassium Dynamics in Legume-Based Pastures

Miguel A. Ayarza, N. C. State University, Yurimaguas, Peru
Pedro A. Sanchez, N. C. State University, Raleigh

Tropical pastures on acid soils are stable and productive only when
nutrients are sufficient to sustain a vigorous forage crop. Maintaining this
fertility requires a management method that takes into account the nutrient
leaching common in areas of high rainfall, as well as the cycling of
nutrients among soil, forage, and animals. This study, which was conducted
at the Yurimaguas Experiment Station, concentrated on one nutrient,
potassium, and one of our most promising mixtures (Brachiaria humidicola/
Desmodium ovalifolium).

1. To quantify leaching losses of K in pastures under clipping and grazing;
2. To monitor the effect of K levels on the productivity of the pasture and
on the dynamics of K in the soil;
3. To estimate the effect of K return by animal excretions;
4. To compare estimated K losses from pastures with losses from crops grown
in the same area.

The grazing experiment was a factorial of three annual rates of K
fertilization (0, 50, and 100 kg K/ha) applied only once by two stocking
rates (3.3 and 6.6 animals/ha), with three replications. Two additional
experiments were established on 3 x 4 m plots with K rates of 0, 25, 50, 75,
and 100 kg K/ha/yr. The first, a clipping experiment in which some plots had
clippings removed while others had clippings returned, provides a comparison
of the effect of grazing on K dynamics. The second was a bare-plot
experiment designed to account for soil chemical and physical properties
related to K leaching and to estimate the effect of plant growth on K
Four hectares were planted with a mixture of Brachiaria humidicola and
Desmodium ovalifolium in December 1984. Potassium treatments were applied on
May 13, 1985, and grazing began on July 4 of that year and terminated 2 years

later. Potassium distribution in the soil with depth was monitored as a
function of precipitation. Changes in soil and plant K were determined in
the small plots and grazing experiments. Amounts and composition of plant
residues were evaluated under grazing. The effect of urine on the return of
K to the soil is being studied, comparing plant growth and changes in soil K
in affected vs. unaffected areas under grazing.

Soil characterization of the area showed very low levels of exchangeable
K in the soil profile (0.05-0.06 cmol/L), except for the 0-5 cm layer, which
averaged 0.16 cmol/L. Soil texture was classified as sandy loam with topsoil
clay contents of 17%.
Application of K treatments produced a significant increase in
exchangeable K in the 0-5 cm of the small plot experiment. Applied K,
however, moved down the profile as a function of precipitation and K rates.
There were significant changes in the 0-5 and 5-20 cm depths after 970 and
1678 mm cumulative rainfall, especially in the 300 kg K rate (Figure 1). The
presence of plants significantly reduced the levels of exchangeable K in the
soil, and this effect increased with the level applied (Figure 2).
Preliminary results about the effect of K rates and plant residues on the
productivity of the association indicated a positive effect of addition of
residues on yields (Table 1). There was also a response to K on the
cumulative yields in both treatments. There were no significant differences
of the effect. The return of plant residues on the soil properties after 1
year is shown in Table 2.
After 255 days of grazing, the effect of K and stocking rates on
aboveground biomass available for grazing are summarized in Table 3. There
was an increase of forage dry matter in response to the treatments; however,
it was not significant, probably due to differences among grazing cycles.
On-site studies of the effect of plant cover on soil moisture were started in
September 1986. In addition, K in the soil solution is being measured in the
small plot experiment.

Conclusions to Date
1. There was a movement of applied K in the soil used in the experiment;
however, the degree of movement depended on the rates applied and on

2. Plants seemed to be able to significantly reduce the amounts of K
susceptible to leaching by absorbing most of the available K in the
3. Plant residues appear to be an important component in the stability of

Table 1. Effect of the return of plant residues on the cumulative yields of
a mixture of B. humidicola + D. ovalifolium (sum of six cuttings).

Applied K No residue return Residue returned Increase

kg/ha -----------t dry matter/ha----------- %

0 9.75 14.87 34
50 11.74 15.34 23
100 13.30 17.93 26
300 15.96 18.05 11

Table 2. Effect of plants and residue return on topsoil (0-5 cm) properties
under a pasture of B. humidicola + D. ovalifolium after 1 year
(mean of three replications).a
Plots P Al Ca Mg K

ppm ------------------cmol/L-----------------

Bare 10.5 b 2.77 a 0.54 a 0.20 a 0.08 a

Planted, no
returned 8.9 a 2.53 a 0.49 a 0.09 b 0.06 a

returned 7.8 a 2.63 a 0.54 a 0.15 a 0.07 a

a. Columns and rows with the same letters are not statistically significant
at P = 0.05.

Table 3. Effect of two stocking rates and three potassium rates on levels
of available forage before grazing (mean of five grazing cycles).
Stocking rate K applied Green dry matter forage Grass
animals/ha kg/ha t/ha/cycle %

3.3 0 3.04 46
50 3.73 51
100 3.85 50

6.6 0 3.26 50
50 4.20 54
100 4.48 58

Exch. K
0 0.04 0.08
i I
















0.12 0.16 0.20 0.25
1 1 a I

50 K (kg/ha)

Cumulative Rainfall

25 mm
0 970 mm

A 1687 mm

100 K (kg/ha)


J 300 K (kg/ha)
100 -

Figure 1. Effect of potassium additions and cumulative
rainfall on distribution of exchangeable K in
bare plots.

. I I I I Il


B I B I m B I

Exch. K
0 0.04 0.08

0.12 0.16 0.20 0.25

50 K (kg/ha)

100 K (kg/ha)

0.30 0.34 0.38 040
I I l I i / I I I I

300 K (kg/ha)

with plants
0 no plants

Effect of plants on the distribution of exchangeable
K in the profile at three potassium rates (mean of
seven sampling dates).









Figure 2.

Sulfur Accumulation in Grazed Pastures

Miguel A. Ayarza, N. C. State University, Yurimaguas, Peru
Pedro A. Sanchez, N. C. State University, Raleigh

Ultisols have increasing clay contents with depth and often accumulate S
in their subsoil because of their higher S sorption capacity. This situation
is well documented in the Southeastern United States and is therefore
expected to occur in Ultisols of Yurimaguas.

Soil samples were taken from a Brachiaria decumbens/ Desmodium
ovalifolium pasture under grazing for 3 years, which had received a total of
116 kg S/ha from yearly additions of ordinary superphosphate and magnesium
sulfate. The topsoil of a degraded and not fertilized nearby pasture was
also sampled to serve as a control. Twenty subsamples per site were
composite and extracted with 0.01M Ca(H2P04)2 for SO0 determination.

Sulfur distribution in the profile of the fertilized pasture is shown in
Table 1. Applied S apparently moved down and accumulated in the subsoil as
expected. Nevertheless, S concentrations in the topsoil of the fertilized
pasture were significantly higher than those in the degraded pasture.
Responses to S applications were observed in a pasture of D. ovalifolium
grown in an Oxisol in Carimagua, Colombia, when extracted SO4 was 12 ppm.
Thus if S assessment of the fertilized pasture were based solely on S status
of the topsoil, a probable response would be predicted. This should not be
the case when the potential contribution from sorbed S in the subsoil is
taken into account. In addition, grass and legume components of this pasture
are Al-tolerant species with extensive root systems in the B horizon.
Use of the weighed profile mean to make better predictions of S
responses in soils has been suggested, and a critical level of 4 ppm of S04
below which S responses must be expected was established by Australian
researchers. Sulfur requirements in Ultisols of the humid tropics should be
established using this approach.

Table 1. Extractable sulfur in an Ultisol under pasture in Yurimaguas.

Site Sampling depth S04a

cm ppm

Not fertilized 0-20 10.30 d

Fertilized 0-20 13.20 c
20-40 26.58 a
40-60 21.42 b
60-100 14.06 c

a. Figures with the same letter are not statistically significant at
P = 0.05.

Pasture Reclamation in Degraded Steeplands

Miguel A. Ayarza, N. C. State University, Yurimaguas, Peru
Rolando Dextre, INIPA, Yurimaguas, Peru

There are several million hectares of degraded, unproductive pastures in
the Amazon, often on steep slopes. The purpose of this project is to develop
a simple technique for reclaiming degraded pastures in Ultisol steeplands,
using different establishment techniques.

A two-factor experiment was installed in a degraded pasture occupying a
5.18-ha watershed with sideslopes of 20 to 50%. Treatments were established
in an amphitheater fashion, following slope contours, with tillage methods as
main plots and improved species as subplots. The tillage treatments are (1)
zero tillage (pastures planted in an array of holes 20 cm in diameter); (2)
minimum tillage (pastures planted in 50-cm wide, rototilled furrows 2 m
apart); and (3) total tillage (50-cm wide furrows, with spaces between
furrows gradually cultivated as pastures grow). The only fertilizer was
Bayovar rock phosphate, applied at the rate of 12 kg P/ha in the hole or
The species included Brachiaria decumbens, Brachiaria humidicola,
Desmodium ovalifolium 350, and Centrosema pubescens 438. The species were
planted in rows 2 m apart from each other. Initial soil chemical and
physical properties are supplied in Table 1. The main degraded pasture
species were of torourco complex. The experiment was initiated in June 1986.
Improved grasses were planted using vegetative propagules and legumes using
several seeds. After 1 month, a standardization cut was done on grasses and
a minimum handweeding on the zero tillage plots.
Performance of species was determined on the basis of percent cover 2
months after planting and the production of biomass 6 months after planting.
Cover was measured using quadrants 4 x 1 m in size. The number of introduced
species was counted and the percent cover estimated. Biomass production was
determined in a 4 x 1 m area in the center of each plot. Two rows and two
strips were included in the sampling area. Results were expressed as fresh
weight of planted species and percentage of the total biomass.


Soil physical properties appeared more limiting than chemical
properties. Penetrometer resistance values indicated that a compacted layer
was present in the 5-10 cm depth, perhaps due to overgrazing (Figure 1).
Relatively high pH and Ca values (Table 1) were associated with the age of
the pasture. The area was burned and cleared 3 years ago to favor the
regrowth of natural grasses.
Fresh biomass production of the four species 5 months after
establishment is shown in Table 2. The two grasses were successfully
established without tillage while the two legumes responded significantly to
minimum or total tillage. The ability of the improved species to take over
the degraded pasture is shown in Figure 2. More than half the area was
covered by the improved species in all cases except where the legumes were
planted without tillage. Total tillage, done progressively in order to avoid
contiguous areas of exposed surfaces, resulted in almost complete cover
within 5 months.
These results suggest that minimum soil disturbance is needed to
establish grasses such as those used in the experiment. The stoloniferous
species are able to rapidly cover new areas and compete strongly with species
already present. On the other hand, legumes require at least minimum
tillage. In general, Centrosema performed better than D. ovalifolium, due to
a faster growth habit and a more aggressive tendency of Centrosema than D.
ovalifolium to cover.
A second phase of the study was initiated in February 1986 to determine
whether the persistence of a species depends upon grazing.
The experimental area was divided into three paddocks, each containing
the four species and the three methods of establishment. Two 150-kg steers
started grazing by replication. Animal management was adjusted to give the
animals the chance to consume all available forage (18 days grazing and 36
days resting). Persistence was monitored by using transects across the plots
for each species x treatment combination before each grazing period. Results
were expressed as percentage of presence of shoots of the species over the
total number of counting every 50 cm along the transect.


After 6 months of grazing, the percentage of grasses increased, whereas
that of legumes decreased (Figure 3). This is probably the result of the
capacity of these Brachiaria species to compete and displace existing
vegetation. Although the legume population is decreasing, an excellent stand
of Centrosema is present.

Promising methods exist to establish improved grasses and legumes in
degraded pastures. The results of this experiment indicate that simple
establishment methods can be successful in compacted Ultisol steeplands but
that some minimum tillage is needed to establish the legumes. Although
minimum tillage was performed by a hand tractor, it is possible to replace it
by using animal power.

Table 1. Initial soil properties of the steepland Ultisol area used for
pasture reclamation in Yurimaguas (mean of seven samples).

Depth pH P Al Ca Mg K Bulk density

ppm ----------cmol/L----------- gm/cc3

0-20 4.7 8.1 3.8 2.88 0.73 0.12 1.37
20-40 4.8 4.4 5.9 2.42 0.64 0.10

Table 2. Effect of three tillage methods on the production of green
forage of two grasses and two legumes after 5 months of

Tillage treatment

Species Zero Minimum Total

---------t fresh wt/ha---------

Brachiaria decumbens 7.70 a 10.6 a 10.3 a
Brachiaria humidicola 6.67 a 10.7 a 12.4 a
Desmodium ovalifolium 0.32 a 1.78 a 4.65 b
Centrosema 438 0.76 a 4.41 b 2.72 b

a. Figures followed by the same letter ard not statistically different
according to Duncan's multiple range test (P = 0.05).


resistance (kg/cm2)
2 3

Figure 1. Soil mechanical resistance measured by a
penetrometer in degraded pasture prior to
treatment initiation (average of 36
observations per depth).



o 0 8. dcu. rsben
K B. hunidicolo
0 Centrosemo 438

SNo tilloge Min. tillogs Total tilloge
Land preparat i on

Figure 2. Effect of tillage method on percentage of
biomass produced by four introduced species
invading a degraded pasture.

invading a degraded pasture.

C. pubescens D. ovoli folium
I. Zero tilloge
2. Minimum tillage
3. Conventional tillage

B. decumbens
1. Zero tillage
2. Minimum tllloge
3. Conventional tlloo

B. humidicolo

Effect of grazing on persistence of two
grasses and two legumes established on a
degraded steepland area in Yurimaguas.

Figure 3.

Pasture Reclamation via Herbicides

Jorge W. Vela, INIPA, Pucallpa, Peru
Miguel A. Ara, N. C. State University, Pucallpa, Peru

Another approach to pasture reclamation is the eradication of the
unsuitable species using herbicides. This approach is important in the
Pucallpa region of the Peruvian Amazon where chemical inputs are more
available than in Yurimaguas.

To obtain the optimum combination of herbicide rate and time of
application after tilling for effective weed control during the
establishment phase of Brachiaria decumbens and Andropogon gayanus.

A trial was carried out from February to July 1986 at the IVITA station
near Pucallpa. Factors under study were three times of herbicide application
and planting after land preparation (after 30, after 45, and after 60 days)
and three glyphosate rates (1, 2, and 4 L/ha) as Round-up. The treatment
structure was a 3 x 3 factorial. The experimental layout consisted of 2 x 6
m plots in a randomized complete block design with six replications.
Variables measured were dry matter yield of Andropogon and Brachiaria at
establishment (120 days of growth); weed reinfestation at 30, 60, 90, and 120
days after tilling; and pasture cover at the same times.
The experiment was laid out on a degraded native pasture. Selected soil
properties at initiation of the experiment are shown in Table 1.

Predominant weeds before land preparation by rototilling and 30 days
after tilling are shown in Table 2. Predominance of weeds changed from before
land preparation: grasses comprised 70% of the weeds before but only 10% 30
days after tilling. Ciperaceae comprised only 1.6% in the early stage but had
the highest percentage (39%) after tilling.
The weed-control treatments had similar results in both Andropogon and
Brachiaria so we will discuss only Brachiaria.

Treatment effects of glyphosate on weed cover 30 days after herbicide
application and crop planting reinfestationn) were highly significant, both
for herbicide rates and times (Table 3) and for their linear and quadratic
interactions. The lowest rate (1 L/ha) applied 30 days after tilling was
able to reduce weed cover by 41%, but the highest reduction was for the
highest rate (4 L/ha) applied 60 days after tilling, which reduced weed cover
by 85%. Higher weed covers for the lowest rate applied at both 30 and 60
days after tilling were the product of a combination of effects--
reinfestation at the "30 days after" treatment and insufficient herbicide at
the "60 days after" treatment. This condition was more or less the same
after 60 and 90 days, after herbicide application and rate. At 90 days,
maximum reinfestation occurred for the "30 days after" treatment (60% weed
cover). After that, the weed cover reflected more the competition with an
already developed Brachiaria than the treatment effect (no significant effect
of treatments).
Effect on the pasture itself is less clear. Thirty days after herbicide
application and crop planting, the percentage of Brachiaria cover did not
reflect any treatment effect but Andropogon showed a highly linear
interaction between rates and times, which is believed to reflect seed
quality and season more than the treatment itself (Table 4). At 60 and 90
days after herbicide application and planting, the Brachiaria cover slightly
reflected weed control efforts, but at 120 days no treatment effect was
observed and cover exceeded 50%. This condition was also observed in the
pasture dry matter yield at establishment, which was not affected by any

No significant differences between the different treatments in dry
matter yield at establishment were present, and it was concluded that the
lowest rate (1 L glyphosate/ha) is as good as 4 L/ha and could be
recommended. With regard to the "times after" treatments, convenience
depends on particular cases, but when low grazing pressure is planned at the
early establishment phase it could be advisable to wait 60 days after tilling
before herbicide application and planting.

Table 1. Selected soil properties at initiation of the experiment, 0-20 cm

Sand Clay pH P Al Ca Mg K O.M. sat.

------%------ Fg/ml --------cmol/L----------- -----%----

43 20 4.7 3.8 2.2 2.07 0.53 0.15 2.73 44

Table 2. Predominant weeds before rototilling and 30 days later.

Approximate coverage

Before 30 days after
Local name Scientific name rototilling rototilling


Torourco Homolepis, Axonopus, 70 10
Paspalum sp.
Pega-Pega Desmodium sp. 8 4
Mimosa Mimosa pudica 6 2
Matapasto Pseudoelephantopus 6 3
Sinchipichana unknown 4 19
Ciperaceae Ciperus sp. 2 39
Guayaba Psidium guayaba 3 0
Broadleaved weeds 0 24

Table 3. Weed cover at 30 days after glyphosate application and Brachiaria
planting. Treatment means of six replications. Highly
significant linear times x rates interaction.

Time of application
Rate of
application 30 days 45 days 60 days

L/ha ------------------%------------------

1 59 63 67
2 43 63 34
4 45 35 15

Table 4. Pasture cover for Brachiaria decumbens and Andropogon gayanus.
Means of six replications. Brachiaria: no significance.
Andropogon: highly significant linear times x rates interaction.

Time of application
Rate of
application 30 days 45 days 60 days

L/ha ------------------%------------------

1 4 3 4
2 4 3 5
4 4 3 4
1 5 2 0.3
2 2 1 0.5
3 2 2 0.3

Legume Shade Tolerance

Jorge W. Vela, INIPA, Pucallpa, Peru
Miguel A. Ara, N. C. State University, Pucallpa, Peru

Acid-tolerant legumes used in the TropSoils pasture management options
may play an important role in agroforestry systems where cattle grazing may
take place under trees. Experience in Southeast Asia indicates a wide
variability of legume response to shade.

To test our most promising legume germplasm under shade of a mature oil
palm plantation to determine their adaptability to this factor.

This experiment was established in November 1985 under an oil palm
plantation managed by CIPA XXIII at km 44 of the Pucallpa-Lima highway.
Three legumes (Desmodium ovalifolium, Pueraria phaseoloides, and Stylosanthes
guianensis) are being evaluated for their dry matter productivity and feed
quality in the presence and absence of oil palm shade. The experimental
design is randomized complete blocks with five replications. Plots are 8 x
16 m, and each plot has two oil palm trees in the same position. A similar
but smaller (3 x 5 plot) experiment was established outside the palm
plantation and will be used as a reference; all the variables will be
analyzed as percentages of full sunlight.

Dry matter production of all three legumes was severely affected by oil
palm shade. Desmodium ovalifolium and P. phaseoloides performed similarly
but yielded only about 22% of the full sunlight value even though they
outperformed S. guianensis, which gave a poor 8% of the reference value.
Crude protein content values for D. ovalifolium and S. guianensis were higher
than full sunlight values, but D. ovalifolium values were highest (Table 1).
Preliminary data suggest that D. ovalifolium is the most shade-tolerant
legume tested. Visual observations show S. guianensis performs quite poorly
and tends to disappear. The stands of both D. ovalifolium and kudzu were

quite acceptable under shade in absolute terms. Since kudzu is a climber,
periodical cutting around trees is required, whereas D. ovalifolium does not
require such cutting.

Table 1. Percentage of dry matter yield and crude protein content
(CPC) of the legumes under shade relative to full
sunlight (means of five replications).a

S. guianensis D. ovalifolium P. phaseoloides

---------------% of full sunlight---------------

Dry matter 7.7 b 23.3 a 21.8 a
Crude protein 113.2 b 128.4 a 84.2 b

a. Means with the same letter in the horizontal rows are not
significant at P = 0.01.

Extrapolation in Farmer Fields

Miguel A. Ayarza, N. C. State University, Yurimaguas, Peru
Rolando Dextre, INIPA, Yurimaguas, Peru

After 6 years of work in the Yurimaguas Station, Brachiaria humidicola,
Centrosema pubescens, Stylosanthes guianensis, and Desmodium ovalifolium have
shown a high potential to increase animal production and good persistence
under grazing. On the basis of the experience gained over the years, it was
decided to test the potential of improved pastures to replace degraded native
pastures, which are common in the area.

A validation trial was set up to demonstrate that degraded pastures can
be put into production by substituting present vegetation or improvement of
present pasture plus incorporation of new species. An agreement was signed
with the Empresa Ganadera Amazonas to conduct a 20-ha validation trial in an
area covered by degraded pastures.
Four pasture renovation options were designed:
1. Introduction of a legume on a degraded pasture of Brachiaria
2. Use of a crop as precursor to establishing improved grass-legume
3. Improvement of native pasture through introduction of a legume;
4. Reclamation of a steepland pasture using improved grasses, legumes,
and trees with minimum tillage.
Work started in December 1985 with soil characterization of the area.
Extremely low native fertility and a predominantly sandy texture existed in
this sandy Ultisol (Table 1).
For option 1, 4 ha of a 10-year-old B. ruzisensis field were disked
slightly to break the soil surface and facilitate planting of C. pubescens
438 and to promote grass regrowth. The legume was broadcast over the area at

a rate of 1 kg/ha. Rock phosphate was applied to supply 25 kg P205 and
dolomitic limestone was applied to supply 50 kg Ca + 10 kg Mg.
Option 2 was installed on a flat area infested by weeds and unpalatable
grass species. Two diskings and two rototiller passes were needed to

completely till 3 ha to eliminate existing vegetation. Cv. Africano
desconocido, an upland rice variety known to be tolerant to Al toxicity, was
planted in strips 12 m wide. The crop received 60 kg N, 40 kg K20, and 50 kg

P205 per ha. Brachiaria humidicola was planted in alternate strips 2 months
After rice harvest, cowpea was planted in rows 50 cm apart and B.
humidicola + D. ovalifolium was planted between rows.
Option 3 was installed on a 2-ha native pasture of torourco (Axonopus
compresus). Strips 4 m wide were opened every 20 m and planted with
Stylosanthes guianensis accessions 136 and 184. Phosphorus was applied at a
rate of 12 kg P/ha using rock phosphate.
Option 4 was installed in a degraded pasture on a 20% slope. The area
was tilled in strips 1 m wide and 4 m apart in contour. Land preparation was
carried out with a 1-1/2 HP manual rototiller. Areas between rows remained
untouched. Brachiaria humidicola and C. pubescens 438 were planted in
alternate strips, and Erythrina popigiana was planted in rows every 12 m
along the contour.

After 8 months, all pasture renovation options were fully established.
In option 1, B. ruzisensis reacted positively to tillage and C. pubescens was
spreading very well over the area. Measurements of botanical composition
indicated 20% of Centrosema in the total biomass, a highly desirable legume
content of a mixed pasture.
In option 2, rice yields were affected by short dry spells during
January and February 1986. In spite of limitations, 1.5 t/ha of rice were
harvested and cowpea yields reached about 800 kg/ha. Both are acceptable
yields for low-input systems. After harvesting the cowpea, B. humidicola was
almost fully established, although it was infested by annual weeds.
In option 3, Stylosanthes established rather quickly, although some
handweeding was required.
Introduced pastures in the steepland covered almost the entire area in
option 4. Both Centrosema and B. humidicola replaced most of the native
species in the nontilled bands. On the other hand, Erythrina did not
establish well. Growth was affected by soil conditions (sandy texture and K
deficiency). Only two of six rows have established.

Costs of renovating degraded pastures are presented in Table 2. Total
investment varied among systems. The most expensive system was the one with
crops (option 2) because of labor and machine costs. Returns from crop
yields were enough to pay for pasture renovation, however, and leave some
extra profit before grazing.

Overall results showed that renovation of degraded pastures can be
accomplished with low monetary inputs in some instances. In other cases
where a complete renovation is required, crops as precursors pay for the
entire cost of pasture re-establishment.
A second phase calls for milk production from cows grazed on the
pastures in every system. This phase will start in 1987 as work supported by
INIPA and the Ganadera Amazonas S.A. and will serve as a thesis for an
undergraduate student from the Universidad Agraria at La Molina.

Table 1. Topsoil chemical property of the soil used for the
extrapolation work in K-17 (Ganadera Amazonas area) (mean
of five samples). December 1985.

pH P Al Ca Mg K ECEC Al sat. Sand Clay

ppm -----------cmol/L-------- ---------------

4.0 3.4 1.1 0.3 0.08 0.05 1.53 72 82 14

Table 2. Cost of renovating a degraded pasture by three methods
of introduction of improved species.

Option 1 Option 2 Option 3

B. ruzisensis + Rice-cowpea- Native pasture
C. pubescens pasture (Stylosanthes)

U.S.$/ha % U.S.$/ha % U.S.$/ha %

Labor 7 11 86 39 20 16
Machinery 9 13 65 29 43 34
Fertilizer 35 53 53 24 6 4
Seed 12 17 16 7 50 40
Other 3 5 11 5 6 5

Total 66 99 231 104 125 99


A low-input cropping system, reported last year as a transition
technology between shifting cultivation and permanent agriculture, collapsed
after seven crops in 3 years due to P and K deficiencies and increasing weed
pressure. This year we report on the nutrient cycling and economic aspects
of this first cropping period, the success of a 1-year kudzu fallow in
overcoming weed constraints, the successful transition to other systems, and
in-depth data on weed build-ups during the first cropping period.
Nutrient cycling from above and below plant residues returned to the
soil more than 80% of the K and Ca accumulated by plants, about half the
biomass produced and half the N and Mg accumulation, but only 37% of the P
accumulated, largely because of grain removal. The system was highly
profitable both with and without fertilizer applications: purchased chemical
inputs accounted for only 8% of the total costs without fertilizer and 16%
with fertilizer. After 1 year of kudzu fallow, the fields were largely
devoid of weeds and showed a higher fertility status. A second low-input
cropping period started with high yields, and the transition to fertilizer-
based continuous cultivation was successful. Weed-control studies indicate
the inability to grow more than five or six low-input crops continuously with
the best combination of herbicides and manual weed control. The main problem
is controlling weeds in upland rice.

Central Experiment: Transition to Other Technologies

Jose R. Benites, N.C. State University, Yurimaguas, Peru
Pedro A. Sanchez, N.C. State University, Raleigh

A low-input cropping system has been developed in Yurimaguas, Peru, to
serve as a transition technology between shifting and continuous cultivation
for acid soils of the humid tropics. Its principal components are (1)
Traditional slash-and-burn clearing of forest fallow, (2) selection of acid-
tolerant cultivars capable of high yields without liming, (3) rotation of
upland rice and cowpea cultivars (no tillage) and removing only the grain,
(4) no fertilizers, lime, or organic inputs are brought in and soil pH
remains at about 4.5, (5) the rotation continues for 3 years, but increasing
weed pressure and decreases in available P and K cause the system to collapse
in agronomic and economic terms. A total of five upland rice and two cowpea
crops were harvested during a 3-year period, as opposed to one rice crop
under traditional cultivation. Crop yields and effects on soil properties
during this first period were presented in the last TropSoils technical
report. This report covers the nutrient cycling effects and economic
analysis of the first cropping period and the transition phase initiated
after the system collapsed at the seventh continuous harvest on June 30,

Nutrient Removal Cycling
Low-input systems should be efficient recycles of nutrients in order to
minimize nutritional inputs that must replace nutrients extracted by crop
The nutrient composition of the acid-tolerant rice (cv. Africano) and
cowpea (Vita 7) plant parts at harvest obtained in neighboring experiments
are presented in Table 1. The calculated amount of nutrient accumulation by
the seven crops is shown in Table 2. Even though only the rice grain and
cowpea pods plus grain were exported from the field, the harvested products
during the 3 year period represented considerable nutrient removal from the
field (Table 2). The amounts of nutrients accumulated by the crops but
returned to the soil as above- or belowground organic inputs was larger than
the amount removed except for P. Crop residues plus root runover returned to

the soil 62% of the dry matter produced, 54% of the N, 59% of the Mg, 87% of
the K, 94% of the Ca, but only 37% of the P accumulated by crops (Table 2).
Root turnover, assuming 100% fine root decomposition, accounted for a
relatively minor proportion of amounts recycled (14% of dry matter, 21% of N,
25% of P, 5% of K, 18% of Ca, and 12% of Mg). The actual amounts returned,
therefore, are equivalent to an annual fertilization rate of 98-7-199-33-13
kg/ha of N-P-K-Ca-Mg. A proportion of the N returned as aboveground residue,
however, may be lost before it enters the soil, via denitrification that may
take place on the mulch-soil surface interface. Biological N fixation by
cowpea, however, may counteract such losses, but neither process was
measured. The P, K, Ca, and Mg inputs, however, are likely to be transferred
entirely to the soil. Phosphorus, therefore, appears to be the critical
nutrient, since about two-thirds of the crop uptake was removed by the
harvested products giving this element the lowest percentage of recycling and
the lowest absolute amounts returned to the soil among the five nutrients

Weed Pressure
In the authors' view, increasing weed control difficulties was the
single most important factor for the instability of this low-input system
during its third year. The initial weed population was mainly broadleaved,
which is typical of shifting cultivation fields in the area. With time, the
weed population gradually shifted to grasses that are more aggressive and not
subject to economically sound control by commercially available herbicides.
Of particular importance was the spread of Rottboelia excelsa, a non-
rhizomatous grass, particularly during rice growth. Cowpea was more
competitive with weeds than upland rice because cowpea covered the soil
surface more thoroughly.
Studies on weed control in low-input systems at Yurimaguas indicate that
the absence of tillage and burning promotes weed build-up (see next report).
Rice straw mulch may decrease weed growth in cowpea, but cowpea residues do
not have the same effect on rice, perhaps because of the fast decomposition
rate visually observed with cowpea residues.

Cost records were kept in this 1-ha experiment. The summary for the

first seven crops in the plots without fertilization is shown in Table 3.
Labor inputs for the first crop include land clearing; thus the subsequent
crops averaged two-thirds of the first crop's labor. Returning and
redistributing crop residues averaged 10 man days/ha, or approximately U.S.
$20/ha per crop. Another major labor input was bird watchers near harvest
time. The next major cost items were interest on crop loans from the Banco
Agrario and government fees for receiving and processing rice at the mills.
Shifting cultivators routinely obtain bank loans, which are used primarily as
an advance on their labor. Interest charges fluctuating from 40 to 101% on
an annual basis in local currency reflect the high inflation rate in Peru,
which averaged 125% annually during the study period. Even in U.S. dollar
terms, the indirect costs averaged about 30% of the total production costs.
In contrast, the cost of purchased chemical inputs (herbicides and
insecticides) and others (seed, bags, thresher rent) comprised 8 and 19% of
the total production costs, respectively.
The low-input system without fertilizer applications was highly
profitable, averaging net returns of U.S. $1144/ha per year, or a 21% return
over total costs (Table 4). The low-input system with fertilizers was also
quite profitable, averaging an annual net return of US$ 1125/ha and a 100%
return over total costs. Fertilizers accounted for 9% of the total cost in
the system, but also resulted in additional labor, interest, thresher use,
and transport costs. The low-input system either with or without fertilizers
is vastly more profitable than traditional shifting cultivation (Table 4).

Transition to Other Systems
This low-input system, therefore, is a transitional technology in both
agronomic and economic terms. After 3 years, the field is devoid of
felled logs and most of the remaining tree stumps are sufficiently decomposed
to be destroyed with a good kick. The land clearing process is thus
complete, providing several options to the farmer. One is to put the land
into a managed fallow and then start a second cropping cycle. A second is to
plow, lime, fertilize, and rotate crops intensively; a third is pastures, and
a fourth is agroforestry.
The experiment described above was modified to address some of these
options after the seventh crop harvest in July 1985. The 1-ha field was
divided into eight 1250 m2 plots, providing four treatments in a randomized

complete block design with two replications. The replicates were located on
the previously fertilized and not fertilized treatments in order to block the
residual effects. Two treatments were designed to test the weed control
factor by continuing the low-input system (cowpea-rice-cowpea), a third was
planted to kudzu fallow, and the fourth was a high-input system.

Continuing the Low-Input System
Prior crop yields suggest that the system collapsed after the seventh
crop. This observation was confirmed by growing three more crops with a
weed-control variable: full weed removal at economically unrealistic levels
vs. the conventional treatment as previously described. The full treatment
consisted of eliminating weeds by a pre-emergence application of 2.25 kg/ha
active ingredient of metolachlor plus 2.5 L/ ha of paraquat, followed by 0.28
kg ha active ingredient of sethoxydim supplemented by handweeding was needed.
The actual cost of this treatment was US $225/ha per crop, a totally
unrealistic level. The conventional treatment was the pre-emergence
application of 1.5 L/ha of 2,4D followed by 2.5 L/ha of paraquat 5 days later
and no handweeding, with a total cost of $25/ha per crop. Both weed control
plots received the same application of NPK fertilizers to rice as stated
previously, in order to eliminate P and K deficiencies.
Grain yields of the eighth, ninth, and tenth consecutive crops under
conventional weed control were low with cowpea, and practically zero with
rice (Table 5). When weeds were totally removed, yields of the ninth (rice)
and tenth cowpeaa) crops reached acceptable levels. Consequently, it seems
reasonable to assume that the collapse of the system is directly related to
weed-control problems.

Kudzu Fallow and a Second Crop Cycle
Traditional shifting cultivation involves a secondary forest fallow
period of 4 to 20 years, supposedly to replenish soil nutrient availability
and control weeds, although the processes involved are not well understood.
Farmer experience around Yurimaguas indicates that a minimum desired age of
fallow is about 12 years, but population pressures effectively reduce this
period to an average of 4 years. Slashing and burning young forest fallows
results in faster grass weed invasion than would occur in older fallows
because the weed seed pool declines with age. Considering the limited

likelihood of long secondary fallow periods in developing humid tropical
areas, the need for an improved fallow is apparent.
Following a farmer's suggestion, we studied the use of tropical kudzu
(Pueraria phaseoloides) as a managed fallow. Unlike its temperate-region
counterpart (Pueraria lobata), tropical kudzu does not produce storage roots
and therefore is easy to eradicate by slash-and-burn. Kudzu fallows were
grown in previously cultivated fields for different durations. In the most
infertile and compacted soils of Yurimaguas, kudzu is slow to establish and
initially shows several classic nutrient deficiency symptoms, but within 3
months a complete canopy is attained, the kudzu leaves become dark green, and
weeds are smothered. Aboveground dry matter and ash biomass accumulation by
kudzu peaks at about 2 years. We observed increases in exchangeable Ca and
Mg and decreases in Al saturation on the topsoil of kudzu fallow plots that
had a lime and fertilizer application history. But no improvements in these
topsoil chemical properties were recorded in the kudzu fallow plots that had
never been limed or fertilized during a previous cropping period.
Consequently, the subsoils must have some nutrients available for recycling
if significant recycling by a managed fallow is to take place in such acid
The same kudzu ecotype was seeded in this low-input experiment, on
August 28, 1985, after harvesting the seventh rice crop, which was heavily
infested with Rottboelia excelsa and other weeds. No fertilizers were added
to the kudzu plots, but one handweeding was used to pull tall Rottboelia
plants. As before, kudzu was slow in establishing, but within 3 months it
had developed a complete ground cover and a surface litter layer. Kudzu was
slashed with machetes on September 13, 1986; after 10 days of dry weather, it

was burned in a total time of 4 minutes for the 1250 m2 plots. Ash sampled 1
day after the burn contained significant accounts of nutrients which were
incorporated to the soil by the first rains (Table 6). A clear residual
effect of the previous NPK fertilization is evident in the ash composition,
particularly in P and K contents.
A crop of Africano rice was planted 3 days after the kudzu burn and
harvested on January 22, 1987. It received the 30-22-40 kg/ha of NPK as did
all previous rice crops. Grain yields were the highest obtained to date at
this site (Table 7). This is partly due to very favorable rainfall
distribution for rice growth as evidenced by similar rice yields obtained in

other experiments at that time, but also due to the absence of significant
weed pressure. The 1-year kudzu fallow, therefore, effectively suppressed
weed growth in a way far superior to the herbicide combinations attempted to
date. The plots are now growing a subsequent crop of upland rice.
Changes in topsoil chemical properties in the kudzu fallow plots are
shown in Table 8 at the end of the first cropping cycle, after 1 year of
kudzu fallow (1 day prior to burning it), and after the first harvest of the
second cropping cycle. The effect of the kudzu fallow on topsoil chemical
properties includes a significant decrease in exchangeable Ca and K,
presumably due to plant uptake with no changes in acidity, Al saturation, or
available P and K (Table 8). Differences in the last four properties are
significant in terms of prior fertilization treatment, which the kudzu fallow
Topsoil chemical properties after the first harvest of the second
cropping cycle show fewer differences due to previous fertilization than at
the end of the first cropping cycle, partly because the entire area was
fertilized with 30-22-48 NPK formula. Nevertheless, there is an overall
trend of increasing available P, K, Ca, and Mg that may be related to the
nutrient content of the ash and prior fertilization during the first cropping
cycle. Topsoil properties at 54 months after burning, representing seven crop
harvests, 1 year of kudzu fallow, and one crop harvest afterwards are about
as good or better than 3 months after burning the original forest (see
previous technical report). Topsoil total organic matter contents have
increased, probably as a result of the kudzu fallow litter inputs (Table 8).
It appears reasonable to speculate that organic-matter contents will decrease
slightly with subsequent cropping as it did during the first cropping cycle.
The second cropping cycle continues in order to determine how long it
will last, except that no fertilizer is being applied and weed control will
only be at the conventional level.

High-Input Crop Production
Another option is for the low-input system to serve as a 3-year
transitional period to intensive, fertilizer-based, continuous cropping
systems for areas that have developed a sufficient road, credit, and market
infrastructure to make this possibility attractive. The fields are certainly
ready for mechanized tillage, provided slopes are suitable, because most of

the felled vegetation has decomposed. One treatment of this field experiment
was tilled to 25 cm with a 50-HP tractor, limed with 3 t/ha of dolomitic
lime, fertilized with 25 kg/ha P as triple superphosphate, 25 kg/ha Mg as
MgS04, 1 kg Zn as ZnSO4, 1 kg Cu as CuSO4, and 1 kg B as borax. Lime and
fertilizers were incorporated with tillage. "Marginal 28," an adapted corn
variety, was planted in ridges at a population of 56,000 plants/ha. This
crop then received 100 kg N/ha as urea and 100 kg/ha of K as KC1 in three
split applications. Weeds remaining after tillage were controlled by 2.25
kg/ha active ingredient of metalochlor. A second crop of corn was then
planted after mechanically incorporating corn stover. It received an
application of 100-25-100 kg/ha NPK and metalochlor, at the same rate. The
corn was followed by soybean (cv. Jupiter), which received an application of
30-25-100 kg NPK/ha. Insecticides were used in corn and soybean as needed to
control mild insect attacks to these crops.
Corn yields were normal for high-input systems for the planting season
(3-4 t/ha), while soybean yields were somewhat lower than normal (2.0 t/ha)
partly because of unusually heavy rains (Table 9). The system appears stable
and of similar productivity to long-term high-input systems grown at
Yurimaguas. A combined total of 8.6 t/ha of high value grain (corn and
soybean) was produced in approximately 15 months. Total productivity of the
entire sequence was 22.4 t/ha of grain in 4 years and 4 months, or 5.2 t/ha
per year. In order to decrease weed infestations, using the kudzu fallow
prior to shifting to high input cropping may be advisable.

Legume-Based Pasture
The low-input system can also serve as a precursor to establishing
improved, acid-tolerant pastures, beginning with the clearing of secondary
forests. Income-generating food crops can be grown and the pasture species
may be planted either vegetatively or by seed under a rice canopy. Several
combinations of persistent, acid-tolerant grasses and legumes produced high
and sustained liveweight grains in Yurimaguas for 6 years, as reported in the
legume-based section. The kudzu fallow itself could be used as a pasture in
rotation with grass-based pastures. Although we have not shifted from low-
input cropping to pastures in an actual experiment, the possibility appears
feasible. Since weed encroachment is a major limiting factor in pasture
establishment, it may be advantageous to limit the number of crops in order

to minimize the weed build-up that occurred during the sixth and seventh
crops. Planting kudzu fallow, burning it after 1 year, and then establishing
the pastures may be a better approach.

The low-input cropping system is a good way of providing cash income and
ground cover during the establishment phase of tree plantations. The
decision, however, has to be made early in order to transplant or seed the
tree crops at adequate spacing shortly after clearing and burning the second
forest. Unless liming is contemplated, the choice of tree crops should be
limited to acid-tolerant ones. Examples of acid-tolerant crops for
industrial purposes are rubber (Hevea brasiliensis), oil palm (Elaeis
guineensis) and guarana (Paulinia cupana); for food production, peach palm
(Gulielma gasipaes); for alleycropping, perhaps Inga edulis. Woody species
known to be sensitive to soil acidity such as Theobroma cacao or Leucaena
leucocephala should be avoided.
The low-input system has been used successfully in nearby experiments
for the establishment of peach palm and multipurpose tree production systems
that include fast-growing (Inga edulis) and slow-growing (Cedrelinga
cataeniformis) species. For peach palm, seedlings are transplanted with the
first rice crop. Within 18 months, the peach palm produces too much shade
for further crop growth; kudzu is then planted as an understory.

The low-input system has several potentially positive environmental
impacts. It provides a low-cost alternative for shifting cultivation in
highly acid soils. In order to produce the grain yields reported for the
first cropping period, a shifting cultivator would need to clear about 14 ha
in 3 years, in comparison to 1 ha in this low-input system. Furthermore, the
use of secondary forest fallows instead of primary forests is emphasized,
although the system should work well starting from primary forest.
Erosion hazards are largely eliminated by the absence of tillage and the
presence of a plant canopy on the soil surface, be it slash-and-burn debris,
crop canopies, crop residue mulch, or a managed fallow. Nutrient recycling
is maximized, but nutrients exported as grain must be replenished by outside
inputs in soils so low in nutrient reserves. Perhaps just as importantly,

the low-input system does not lead the farmer into a corner; it provides a
wide range of options after the first cropping cycle is complete.
There are many unanswered questions about the technology just described.
Although its feasibility during the first cropping cycle followed by a
managed fallow period has been demonstrated, information about the second
cropping cycle is limited to one crop harvest. It cannot be stated at this
point that a modified form of shifting cultivation with a 3:1 crop to managed
fallow ratio is feasible on a long-term basis.
More in-depth knowledge of weed population shifts and fertility dynamics
is needed. Zero tillage poses a major constraint to long-term weed control.
Soil data have been confined to readily determined chemical parameters; soil
physical and biological dynamics are now being intensively studied. Tropical
kudzu is but one of several promising species for managed fallows, and others
are being investigated in terms of above- and belowground biomass
accumulation, nutrient cycling, and weed suppression. A fresh look at the
management of organic inputs and soil organic matter is being researched.
The effect of age of fallow needs to be studied in greater detail. What
are the trade-offs with a longer fallow? Also, can the weed problem be
reduced by having a shorter time period between harvesting and planting?
Time will tell.

Table 1. Nutrient concentrations of rice (cv. Africano desconocido)
and cowpea (cv. Vita 7) grain and straw at harvest, and fine
roots at anthesis, under low-input systems in Yurimaguas.
Mean values of seven rice harvests and three cowpea
harvests for aboveground parts, and two crop harvests each
for roots.

Crop part N P K Ca Mg


Rice Grain 1.40 0.23 0.36 0.03 0.11
Straw 1.01 0.07 2.85 0.28 0.18
Roots 1.19 0.09 0.93 0.21 0.05

Cowpea Grain 3.86 0.35 1.36 0.06 0.21
Straw 1.86 0.13 3.97 0.95 0.23
Pods 0.70 0.06 2.17 0.17 0.22
Roots 1.23 0.12 0.71 0.59 0.19

Table 2. Total dry matter and nutrient accumulation by five rice
and two cowpea crops harvested in 34 months without
fertilization, and amounts returned to the soil.

Plant part matter N P K Ca Mg

t/ha ------------------kg/ha-----------------

Grain + pods 14.2 256 34 87 65 18
Straw 18.1 232 15 565 80 35
Roots 5.2 63 5 32 18 5

Total 37.5 551 54 684 104 58

% returned 62 54 37 87 94 59
to soil

a. Based on mean grain:straw ratios of 0.84 for rice and 0.52 for
cowpea; mean cowpea pod weight of 0.32 t/ha per crop, and fine
root biomass of 0.65 and 0.97 t/ha per crop for rice and cowpea
in the top 30 cm of soil.

Table 3. Labor input, production costs, and revenues incurred in
the low-input system with seven crops without

Crop sequence

1 2 3 4 5 6 7
Input or output Rice Rice Cowpea Rice Cowpea Rice Rice

Labor (man day/ha) 172 79 99 79 99 79 79

Cost (U.S. $/ha):
Labor 380 140 113 134 167 130 95
Herbicides 21 21 25 26 25 24 25
Insecticides 0 11 14 14 13 0 0
Seed 19 17 75 18 51 16 17
Bags 16 18 8 20 7 18 50
Thresher rent 0 34 0 38 0 34 80
Transport to market 12 12 14 14 14 12 14
Loan interest and fees 135 80 86 105 108 111 225

Total cost 583 333 335 369 385 345 506

Grain produced (t/ha) 2.44 2.99 1.10 2.77 1.19 1.84 1.52
Price (U.S. $/t) 321 281 1420 305 1127 265 274

Gross revenue (U.S. $/ha) 783 840 1562 845 1341 488 416

Net return (U.S. $/ha) 200 507 1227 476 956 143 -90

Net return/Cost (%) 34 152 366 129 248 41 -18

Table 4. Cumulative production costs and returns actually incurred with
seven crops in 3 years with and without fertilization and under
shifting cultivation.

Low-input system
Inputs and outputs Not fertilized Fertilized cultivation

U.S. $/ha % U.S. $/ha % U.S. $/ha %


Labor inputs 1159 41 1185 35 380 65

Chemical inputs:
Fertilizers 0 0 292 9 0 0
Herbicides 167 6 167 5 21 4
Insecticides 52 2 52 2 0 0

Other inputs:
Seeds 213 7 213 6 19 3
Bags 137 5 140 4 16 3
Thresher use 186 7 189 6 0 0

Transport to market 92 3 96 3 12 2

Loan interest and fees 850 30 1073 38 135 23

Total costs 2843 100 3351 100 583 100

Gross revenues: 6275 6688 783 -

Net returns: 3432 3377 200 -

% Returns/cost 121 100 30

Table 5. Grain yields of three additional crop harvests in the low-input
system at two levels of weed control.

Weed-control level
Planting Harvest
Crop sequence date date Conventional Full LSDO.05

------------------------------------------------------------t/ ------

8. Cowpea cv. Vita 7 Aug. 19, '85 Oct. 31, '85 0.58 0.58 ns
9. Rice cv. Africanoa Jan. 9, '86 May 9, '86 0.09 1.60 0.19
10. Cowpea cv. Vita 7 July 15, '86 Sept. 25, '86 0.43 0.82 0.26

a. Fertilized with 30-22-48 kg/ha of NPK as previously.

Table 6. Dry matter and nutrient content of 1-year-old kudzu fallow ash 1
day after burning. Mean of 12 observations in the previously not
fertilized treatments and 11 in the previously fertilized
treatment. Date: September 24, 1986, 51 months after clearing.

fertilizer Dry
treatments matter N P K Ca Mg Zn Cu Fe Mn

t/ha ----------------------kg/ha-----------------

Not fertilized 1.45 21 7 42 58 14 0.17 0.08 1.07 0.82
Fertilized 2.29 26 21 103 92 20 0.29 0.12 0.99 1.34

LSDO.05 0.85 ns 9 51 ns ns 0.12 ns ns ns

Table 7. Dates of planting and harvesting kudzu fallow and subsequent crops
and crop yield as affected by a fertilizer differential prior to
planting kudzu.

Grain yield

fertilizer level
Planting Harvest
Crop sequence date date None Yes LSDO.05
---- ------------------------------------------------------------

8. Kudzu fallow Aug. 28, '85 Sep. 13, '86 -- -- --
9. Rice cv. Africano Sep. 26, '86 Jan. 22, '87 3.86 3.98 0.41
10. Rice cv. Africano Feb. 13, '87 in progress

Table 8. Changes in selected topsoil (0-15 cm) chemical properties prior to
and after 1-year fallow, and after harvest of a subsequent crop
in the kudzu fallow plots.
Months Prior Exchangeable
Plot after fertili- pH Al Avail. Organic
status burning zation (H20) -Al Ca Mg K sat. P matter
--------cmol/L------- % mg/dm3 %

End of first 35 No 4.5 1.9 0.98 0.10 0.26 50 4 1.92
cropping cycle Yes 4.5 1.2 0.98 0.16 0.19 46 14 1.77
(seven crops)

After 1 year 52 No 4.5 1.8 0.60 0.09 0.13 68 7
in kuzdu fallow Yes 4.6 1.1 0.57 0.13 0.11 57 14
(before burning)

At first 54 No 4.8 1.6 1.05 0.18 0.23 52 14 2.44
harvest of second Yes 4.5 1.1 0.76 0.20 0.14 49 25 2.71
cropping cycle


0.2 0.3 0.25 0.05 0.05 11 6 ns

4 25 35 32 39 21 48 15

- - - - - - - - - - -

- - - - - -

Table 9. Grain yields of the first three intensively managed
continuous crops after shifting from a low- to high-
input system.

Planting Harvest Grain
Crop sequence date date yield


8. Corn cv. Marginal 28 Sept. 9, '85 Jan. 19, 86 3.86
9. Corn cv. Marginal 28 March 22, '86 July 24, 86 2.90
10. Soybean cv. Jupiter Sept. 11, '86 Dec. 23, 86 1.87

Totals 15 months 8.63

Weed Control in Low-Input Cropping Systems

Jane Mt. Pleasant, N. C. State University, Raleigh
Robert E. McCollum, N. C. State University, Raleigh

Weed control in low-input cropping systems must rely on cultural
practices to increase the crop's ability to compete against weeds and thereby
reduce the amount of herbicide and manual weeding inputs that are needed to
maintain crop yields. Mulching, tillage, timely fertilization, increasing
crop density, and the use of competitive cultivars are all examples of
cultural practices that can aid in controlling weeds.

To identify cultural practices that can form the basis of a weed
management program for a continuously cropped rice-cowpea rotation under
low-input conditions.

The experiment was established after cutting and burning a 5- to 10-
year-old secondary forest at Yurimaguas. Five consecutive crops, identified
as Cycles 1 through 5 (rice-rice-cowpea-rice-cowpea), were planted. The
experimental design was a split-plot, with tillage and residue management as
main plots. There were three main-plot treatments: (1) rototill with
previous crop residues incorporated, (2) rototill with residues mulched and,
(3) no-till with residues mulched. A factorial arrangement of two crop
densities (high and low) and three weed-control practices (handweeding,
herbicide, and no control) comprised the subplot treatments. Oxadiazon and
propanil were the herbicides used on rice, and metolachlor was applied to
Data from Cycles 2 through 5 were combined and analyzed as a single
experiment. Cycle 1 was not included in this combined analysis because there
was no residue management variable in the first crop that succeeded the
forest fallow. The remaining four cycles were consistent in treatment
through the duration of the experiment. Although the emphasis in this report
is on the combined analysis, some data from individual crop cycles are also

Results and Discussion
Crop Species
Rice had more weeds and lower relative yields than cowpea (Figure 1),
and failure to control weeds had a much greater effect on rice than on cowpea
yields (Figure 2). Because cowpea establishes quickly, we hypothesize that
it covers the row and shades out emerging weed seedlings. Rice, in contrast,
is much slower in forming a canopy. With the ground left unshaded, weed
seedlings in rice quickly become competitors.
Weed infestation was also more severe the longer the field was cropped
(Figure 1). Weed levels in Cycle-4 rice were much higher than in Cycle-2
rice. The same pattern was seen in cowpea: weed infestation was higher in
Cycle 5 than in Cycle 3.
Residue Management
Mulching was ineffective as a weed control practice, but relative crop
yields were higher when residue was incorporated (Figure 3). In this
experiment the primary role of residue management appears to be related to
nutrient release rather than weed control. We theorize that rapid
decomposition of residues following incorporation releases nutrients more
quickly for immediate recycling than when they are allowed to decompose on
the surface.
No-till plots had more weeds and lower yields than rototilled plots in
the combined analysis, but the effect of tillage on weed growth changed over
the course of the experiment (Figure 4). In the first cycle, rototilled
plots had many more weeds than no-till plots. By Cycle 5, however, the no-
till treatment had the greater weed infection.
Rototilling in Cycle 1 provided an ideal seedbed for weed seed
germination. With tillage, weed seeds were brought to the surface where they
germinated in a flush. In contrast, weed infestation in Cycle-i no-till
plots was low. Fire destroyed both standing vegetation and surface seeds.
Without soil disturbance to bring buried weed seeds to the surface, weed
infestation in the first crop was minimal.
When the field is cropped continuously, however, lack of tillage through
several cropping cycles brings increased weed problems. Soil disturbance has

a positive effect in a continuous cropping system because existing vegetation
can be completely eliminated between crops. While weeds in no-till plots
were burned back with a pre-plant application of paraquat between crops, they
quickly regrew. Consequently, after five consecutive no-till cropping
cycles, untilled plots had a much larger weed infestation than rototilled
Crop Density
Increasing crop density was an effective weed control measure (Figure
5). In most cycles there were fewer weeds and higher product yields when the
crops were planted at the higher density. But yields, particularly rice,
increased at the higher density even when weed growth was not affected.
Apparently closer-spaced rice was more efficient in intercepting sunlight for
photosynthetic production, and the higher yields were independent of the
effect of crop density on weed growth.
Weed-Control Practice
Failure to control weeds reduced product yields in both rice and cowpea,
but the weed-control method (manual or chemical) had little effect on yield
(Figure 5).

Management and Research Implications
If a viable low-input continuous cropping system is to evolve in the
Peruvian Amazon, it will depend on upland rice as the central cash crop, and
the rice or any associated crop will be planted without tillage. It is now
apparent that we cannot control weeds through repeated cycles of rice-cowpea
rotations without large and unprofitable inputs for weed control. For this
reason, such a cropping system must be considered transitional. It may form
a bridge between shifting cultivation and a more permanent agriculture, but
it is not a stable, long-term alternative to shifting cultivation.
Lack of tillage and the poor competitive ability of upland rice are the
primary causes of the weed-control problem. Weed infestation in rice
increases dramatically with time when a field is cropped continuously without
tillage, even when rice is rotated with cowpea. Because upland rice is such
a poor competitor, grasses invade vigorously and crop yields decline sharply
with successive rice crops.
It is possible to control weeds (either manually or with herbicides) and
maintain yields, but the cost of control is prohibitive for a low-input

system within the present price-profit structure in Peru. With rice yields
of 2 to 3 t/ha and cowpea yields of 1 to 2 t/ha, weed-control costs represent
25 to 40% of the value of the crop.
Based on our present knowledge, a realistic "lifespan" for the low-input
system is probably five or six crop cycles, after which the cropping system
must be interrupted by a fallow period or tillage in order to disrupt and
displace the weed community. Research should now focus on developing
effective and economic weed-control strategies for this transitional low-
input system comprised of no more than six consecutive crop cycles. Our work
suggests several avenues that may be productive.
Weed-control inputs are unnecessary or minimal in the first rice crop
after a forest fallow and in all cycles with cowpea. The majority of weed-
control costs will be concentrated in the second, third, and fourth rice
Increasing the planting density of rice is an effective and cheap form
of weed control. Work is needed to establish optimum planting densities for
rice cultivars in this environment. As demonstrated with cowpea, an
aggressive, fast-growing crop is another form of inexpensive weed control.
Rice cultivars used in the low-input system should be selected for their
competitive abilities. Early canopy formation, to shade out weed seedlings,
is probably a critical characteristic for rice cultivars in this management
We have shown that herbicides can provide excellent weed control in
upland rice. Furthermore, we suggest that this control method may become
economic if herbicide use can be integrated with other control practices so
that the rate and number of applications can be reduced. A practical and
effective weed-management program for a low-input system will combine
cultural practices with chemical and manual methods of control.

"c E--I Rice
\E 7 Cowpea


i 100

0 0

R CP C2 C4 C3 C5

Figure 1. Effect of crop species and number of cropping cycles
on weed infestation in four consecutively-planted
short-season crops. Yurimaguas 1984-1985.
R = rice; CP = cowpea; C2 = Cycle 2; C3 = Cycle 3;
C4 = Cycle 4; C5 = Cycle 5.









H*- Rice
H- Cowpea

No control All control

r-r Cowpea
*-4 Rice
No control All control

Effect of weed control on weed infestation and relative yield in rice and cowpea in four
consecutively-planted short-season crops. Yurimaguas 1984-1985. NO CTRL = no weed control;
ALL CTRL = treated with herbicide or handweeded.

Figure 2.


150 -
0 Mulch
=3 Incorp

100 o

50 k

[-= Mulch
07 Incorp

50 -

Effect of residue management on weed infestation and relative yield in four consecutively-
planted short-season crops. Yurimaguas 1984-1985.

Figure 3.


. 1