TropSoils technical report

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TropSoils technical report
Soil Management Collaborative Research Support Program
Place of Publication:
Raleigh N.C
TropSoils Management Entity, North Carolina State University
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Publication Date:
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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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The University of Florida George A. Smathers Libraries respect the intellectual property rights of others and do not claim any copyright interest in this item. This item may be protected by copyright but is made available here under a claim of fair use (17 U.S.C. §107) for non-profit research and educational purposes. Users of this work have responsibility for determining copyright status prior to reusing, publishing or reproducing this item for purposes other than what is allowed by fair use or other copyright exemptions. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder. The Smathers Libraries would like to learn more about this item and invite individuals or organizations to contact Digital Services ( with any additional information they can provide.
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16150153 ( OCLC )
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Related Items

Preceded by:
TropSoils triennial technical report

Full Text

r Edited by
Neil Caudle, TropSoils Editor, Department of Agricultural Communications, North Carolina State University Charles B. McCants, Director, TropSoils Management Entity, North Carolina State University
Published June, 1987
F TropSoils is one of the Collaborative Research Support Programs (CRSPs) created to implement Title XII, "Famine Prevention and Freedom From Hunger" of the Foreign Assistance Act. Primary funding is provided by the U.S. Agency for International Development under grant no. DAN- 1311-G-SS-108 3.
l- Copies of this report may be obtained by writing TropSoils Management Entity, Box 7113, North Carolina State University, Raleigh, N.C. 27695-7113, U.S.A.

Preface. . vii
Collaborators. . viii
Introduction... 1
Low-Input Cropping Systems...5
Central Low-Input Experiment...6
Tillage-Phosphorus Interactions Under Low-Input Cropping Systems... 7 Calcium and Magnesium Movement in Low-Input Cropping Systems...9
Legume-Based Pastures...11
Legume-Based Pastures: Central Experiment...12
Potassium Dynamics in Legume-Based Pastures...15 Pasture Germplasm Evaluation and Agronomy...17
Pasture Reclamation in Steeplands...19
Agroforestry Systems...21
Trees as Soil Improvers in the Tropics?...22
Alley-Cropping on Ultisols...23
Peach Palm as a Soil Management Option on Ultisols...26
Gmelina arborea: Intercropping, Coppicing and Nutritional Requirements...28
Contrasting Effect of Pinus caribaea and Gmelina arborea on Soil Properties...29
Improved Fallows... 31
Forest and Soil Regeneration... 35 Comparative Soil Dynamics...43
Collection and Propagation of Agroforestry Species...43
Living Fences...44
Continuous Cropping Systems...45
Land-Clearing and Post-Clearing Soil Management Practices...46
Tillage With Tractors in Continuously Cropped Ultisols...50
Continuous Cropping: Central Experiment...52
Production Potential of Corn-Peanut Intercrops in the Humid Tropics...54
Phosphorus, Zinc and Copper Fertilization...56
Potassium, Lime and Magnesium Interactions and Corn Yields...59 Weed Population Shifts Under Continuous Cropping Systems...65
Chemical Weed Control in Corn...66
Paddy Rice in Alluvial Soils...69
Intensive Management of Alluvial Soils for Irrigated Rice Production...70

Soil Characterization and Interpretation... 73
FCC Adaptation to Wetland Soils... 74
Volcanic Ash Influence on Transmigration Areas of Sumatra... 77
FCC and Site Characterization in Relation to Caribbean Pine... 77
Alluvial Soils of the Amazon Basin.. .78
Ultisol Dominated Landscapes in Southeastern Peru... 80
Soils of Pichis Valley Extrapolation Sites...82
Soil Survey of the Puerto Maldonado Experiment Station... 84
Soil Management Research Network...85
Brazil: Extrapolation to Clayey Oxisols ...87
Soil Nutrient Dynamics and Fertility Management for Sustained Crop Production on Oxisols in the Brazilian Amazon...88
Phosphorus Management in Humid Tropical Oxisols... 94
Potassium Management in Humid Tropical Oxisols ...97
Guarana Fertilization... 100
Lime Requirements and Downward Movement of Ca and Mg... 102
Planting Dates in Relation to Weather Pattern at Manaus... 107
Micronutrient Fertilization on a Typic Acrorthox at Manaus.. .109
Management of Green-Manure Nitrogen on Oxisols at Manaus.. .11
Conditions Other Than Extractable Nutrient Concentrations in the Soil Test Interpretations
for P and Zn...113
Extrapolation of Soil Management Technologies to the Pichis Valley...115
Low-Input Cropping Systems for the Pichis Valley.. 116
Legume-Based Pastures in the Pichis Valley... 118
Agroforestry in Steeplands of the Pichis Valley...120
Soil Erosion and Reclamation...120
Sitiung: Extrapolation to Transmigration Areas of Indonesia...121
Reclamation of Bulldozed Lands ...122 Liming in Transmigration Areas... 125
Phosphorus Management in Transmigration Areas... 131
Effect of Green Manure Applications on Soil Fertility and Crops... 134
Potassium Management of Upland Crops... 137
Sulfur Fertilization... 139
Contributions to North Carolina and U.S. Agriculture... 139
Publications... 140

Introduction... 143
Site Characterization: Soil Variability.. 145
Soil Variability in Forest Land Mechanically Cleared.. .146
Soil Management and People... 155
Indigenous Knowledge Systems Related to Soil Management... 156
Intrahousehold Decision-Making... 157
Collaborative Research With Farmers on Upland Fields... 158
Time-Allocation Study.. 159
Nutrition/Income Survey...162
Collaborative Research With Farmers on Home Gardens...163
Farmers' Perceptions of Constraints to Agriculture ...164
Minang Tree-Farming Study.. 165
Productivity in Farmers' Fields.. .167
Matching Crop Requirements of Rice, Maize, Soybean and Peanut to Soil Characteristics
with Crop Simulation Models...168
Effects of VA Mycorrhizae on Cowpea Response to P Fertilization and Lime in High
Manganese Soil...171
Modeling Phosphorus-Lime Interactions... 175
Application of Expert Systems to the Transfer of Soil Management Technology.. .177
Pasture Grasses and Legumes for the Humid Tropics... 181
Land Reclamation: Soil Physics and Soil Conservation...183
Management of Organic Material in Indonesian Farming Systems...184
Contributions to Hawaii Agriculture...187
Publications.. .188
Introduction... 189
Nitrogen Management... 191
Nitrogen Availability From Legume Crop Residues and Green Manures to Succeeding
Nonlegume Crops ...192

Evaluation of the Mineralization Potential of Legume Residues Through Laboratory Incubation Studies...194
Fertilizer Nitrogen Movement in Cerrado Soils ...195
Water and Chemical Budgets ...197
The Effects of Gypsum Amendments on Charge Properties in Cerrado Soils...198
Ion Movement in Cerrado Soils: The Effects of Amendments on Sulfur Availability.. .200
Soil Constraints to Management... 203
Soil Morphology and Water Table Relations in Some Oxisols of the Cerrado Region... 204
Characterization of Root Restricting Zones in Cerrado Soils... 206
Contributions to New York Agriculture... 208
Publications... 209
Introduction ...211
Soil Data Base...213
Soil Genesis, Phosphorus and Micronutrients of Selected Vertisols and Associated Alfisols of
Northern Cameroon...214
Clay Dispersibility in Sandy Soils of the Sahel, West Africa...218
Iron Oxide Properties Versus Strength of Ferruginous Crust and Iron-Glaebules in Soils ...221
Soil Crusting: Compaction of Soil Particles Due to Impact of Raindrops and Drying.. .222
Soil Properties Versus Crust Strength of Some Texas and West African Soils.. .223
Soil Geomorphology-Hydrology Relationships of Semi-Arid Tropical Landscapes...225
Calibration of Two-Probe Gamma-Gauge Densitometers... 228
Field Calibration of Neutron Meters Using a Two-Probe Gamma Density Gauge.. .229
A Simple Method to Calculate Distribution of a Scaling Factor From Soil-Water Retention
Curves ...230
Simulation and Measurement of Evaporation From a Bare Soil...232
Causes and Control of Pronounced Plant-Growth Variability.. 233
Water and Energy Balance of Sahelian Soils.. .236
Technology for Rainfed Agriculture.. .239
Influence of Tiller Removal on Growth and Production of Millet...240
Pearl Millet (Pennisetum typhoides) Response to Soil Variability in Sandy Ustaffs... 242
Phosphorus Fertilization and Relationships of Root Distribution and Soil Water
Extraction... 244
Sorghum Water-Use Efficiency and Fertilizer Relationships.. .247

Evaluation of the Sandfighter Under Sahelian Conditions... 249
Potential of Contour-Strip Water Harvesting for Cereal Production...250
Soil Moisture Relations of Sandy Soils of Niger ...251
Technology for Forest Lands...255
Soil and Water Management in Degraded Sahelian Soils...256
Agroclimatic Data Base.. .259
Quantification of Rainfall Characteristics, Patterns and Hydrology of Representative Cropped
Soils of Niger.. .260
Influence of Neem-Tree Windbreaks on Microclimate and the Growth and Yield of Cereals
Between the Rows...263
Contributions to Texas Agriculture.. .266
Publications... 268

TropSoils' goal is to develop and adopt improved soil-management technology that will reduce constraints to plant growth, and to ensure that this technology is agronomically, economically and ecologically sound for developing countries in the tropics. Because it is impractical to do this in every tropical nation or region at once, the program has situated and developed its research projects in a way that makes their results applicable over broad areas having similar soils and environments. These areas, or "agro-ecological zones," are the basic units of TropSoils' organization.
This document reports the progress of TropSoils research in three agro-ecological zones: the humid tropics, the acid savannas and the semiarid tropics. Each participating university has taken a lead role in one of these zones. For more information about any of the projects covered in this report, contact the Management Entity or one of the program coordinators listed below.
Program Coordinators
Pedro A. Sanchez Lloyd Hossner
Soil Science Department Dept. of Soil and Crop Science
Box 7619, N.C. State University Texas A&M University
Raleigh, NC 27650-7619 College Station, TX 77843
Goro Uehara Douglas Lathwell
Dept. of Agronomy&Soil Science Department of Agronomy
University of Hawaii Cornell University
Honolulu, HI 96822 Ithaca, NY 14853

Collaborators, N.C. State University
INIPA (Instituto Nacional de Investigacion y Promocion Agraria-Peru) EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria-Brazil) IVITA (Instituto Veterinario de Investigacion del Tropico y Altura) UEPAE-Manaus (Unidade de Execucao de Pesquisa de Ambito Estadual de Manaus) IICA (Instituto Interamericano de Cooperacion para la Agricultura) PEPP (Proyecto Especial Pichis-Palcazu) CPAC/EMBRAPA (Centro de Pesquisa Agropecuaria dos Cerrados) Universidad Nacional Agraria, La Molina, Peru Center for Soils Research, Indonesia CIAT (Centro Internacional de Agricultura Tropical) University of Hawaii
University of Georgia
Wageningen University, The Netherlands Institute of Development Studies, Finland Reading University, United Kingdom Cornell University
U.S. Agency for International Development
Collaborators, University of Hawaii
Center for Soil Research, Indonesia Institute Pertanian Bogor, Nutrition Department Andalas University, Padang U.S. Agency for International Development North Carolina State University

Collaborators, Cornell University
EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria-Brazil) CPAC/EMBRAPA (Centro de Pesquisa Agropecuaria dos Cerrados) U.S. Agency for International Development North Carolina State University
Collaborators, Texas A&M University
ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) ILCA (International Livestock Center for Africa, Ethiopia) CARE (Cooperatives for American Relief Everywhere) INTSORMIL (USAID Collaborative Research Support Program on Sorghum and Millet) IRAT (Institut de Recherches Agronomiques Tropicals, France) INRAN (Institut National de Recherche Agronomique du Niger, Niger) University of Niamey, Niger
IFDC (International Fertilizer Development Center, U.S.A.) University of Wageningen, The Netherlands FLUP (Forest and Land Use Planning Project, Niger) USAID/NIGER (U.S. Agency for International Development, Niger Mission) USAID/Mali (U.S. Agency for International Development, Mali Mission) OICD (Office of International Cooperation and Development, USDA) SAFGRAD (Semi-Arid Food Grain Research and Development, Burkina Faso) ICARDA (International Center for Agricultural Research in the Dry Areas, Syria) IFRSC (Institute Francais de Recherche Scientifique et Cooperation former ORSTOM-France) SMSS (Soil Management Support Services, USDA/AID) I.R.E. (Institut d'Economie Rural, Mali) AGRHYMET (Centre Regional de Formation et d'Application en Agrometeorologie et Hydrologie
Operationnelle, Naimey, Niger)

Traditional shifting cultivation with slash-and-burn clearing has been singled out as a major contributor to deforestation. This deforestation has raised concern world-wide over the prospect of economic and ecological disaster in the tropics. The pressure for new clearing arrises in part from the nature of tropical-rainforest soils, which are typically acid and infertile. Lacking the capital and technology to overcome these soil constraints, shifting cultivators slash and burn the forest, raise one or two marginal crops in its fertile ash, then move on to clear a new field. Many hectares of cleared land are abandoned after only one or two years of use.
The objective of North Carolina State University's TropSoils program in the humid tropics is to develop and transfer, together with national institutions and other universities, improved soil-management technologies that are agronomically, economically and ecologically sound for productive and sustained farming systems in the humid tropics and acid savannas. The program has been rooted in the premise that a stable, productive agriculture is the best means for conserving tropical forests and improving the living standard of farm families in developing countries. The emphasis in on relieving the pressure for new clearing by increasing and stabilizing the production of lands already cleared.
Rather than advocate a single solution for the humid tropics, the program seeks to provide a series of management options to farmers in the process of transition from shifting cultivation to settled agriculture. These management options cover the principal soils, landscape positions and levels of infrastructure development in the humid tropics, and include low-input cropping, continuous cultivation, agroforestry, legume-based pastures, paddy-rice production, and reclamation of humid tropical steeplands.
The program's primary research site is the Yurimaguas Experiment Station in Yurimaguas, Peru. Research is also conducted in Indonesia (supporting TropSoils work in the Sitiung transmigration settlements); at Manaus, Brazil; in the Cerrado of Brazil; and at Pucallpa and Pichis-Palcazu, in the Selva of Peru. These sites represent a range of environments. Soils and climate at Manaus, for example, are intermediate to Yurimaguas (loamy Ultisols and a weak dry season) and the Cerrado (clayey Oxisols with the strong dry season). Pichis-Palcazu has a perudic soil-moisture regime (3400 mm rainfall, Ultisols and Dystropepts), and Pucallpa a near-ustic regime (1500 mm). Technologies showing promise at one site are tested and adapted at others, and are introduced to other countries through a research network, so as to improve the transfer and application of results.
Some of the work reported here is complete; some is only beginning to produce results. While the research is presented as individual projects, most projects were conceived as parts of broader investigations supported by many collaborating scientists and institutions sharing a common goal: to increase food production while conserving natural resources in developing countries in the tropics.

Low-Input Cropping Systems... 5
Central Low-Input Experiment... 6
Tillage-Phosphorus Interactions Under Low-Input Cropping Systems... 7
Calcium and Magnesium Movement in Low-Input Cropping Systems... 9
Legume-Based Pastures... 11
Legume-Based Pastures: Central Experiment... 12
Potassium Dynamics in Legume-Based Pastures.. .15 Pasture Germplasm Evaluation and Agronomy.. 17
Pasture Reclamation in Steeplands...19
Agroforestry Systems... 21
Trees as Soil Improvers in the Tropics?.. .22
Alley-Cropping on Ultisols... 23
Peach Palm as a Soil Management Option on Ultisols.. .26
Gmelina arborea: Intercropping, Coppicing and Nutritional Requirements... 28
Contrasting Effect of Pinus caribaea and Gmelina arborea on Soil Properties.. .29
Improved Fallows ... 31
Forest and Soil Regeneration... 3 5
Comparative Soil Dynamics...43
Collection and Propagation of Agroforestry Species.. .43
Living Fences.. .44
Continuous Cropping Systems.. .45
C learing and Post-Clearing Soil Management Practices.. .46
Tillage With Tractors in Continuously Cropped Ultisols.. .50
Continuous Cropping: Central Experiment... 52
Production Potential of Corn-Peanut Intercrops in the Humid Tropics... 54
Phosphorus, Zinc and Copper Fertilization... 56
Potassium, Lime and Magnesium Interactions and Corn Yields... 59 Weed Population Shifts Under Continuous Cropping Systems.. .65
Chemical Weed Control in Corn... 66
Paddy Rice in Alluvial Soils.. .69
Intensive Management of Alluvial Soils for Irrigated Rice Production... 70
Soil Characterization and Interpretation... 73
FCC Adaptation to Wetland Soils... 74
Volcanic Ash Influence on Transmigration Areas of Sumatra.. .77
FCC and Site Characterization in Relation to Caribbean Pine... 77
Alluvial Soils of the Amazon Basin... 78
Ultisol Dominated Landscapes in Southeastern Peru.. .80
Soils of Pichis Valley Extrapolation Sites...82
Soil Survey of the Puerto Maldonado Experiment Station.. .84

Soil Management Research Network... 85
Brazil: Extrapolation to Clayey Oxisols.. .87
0 Soil Nutrient Dynamics and Fertility Management for Sustained Crop Production on Oxisols in the Brazilian Amazon...88
Phosphorus Management in Humid Tropical Oxisols.. .94
Potassium Management in Humid Tropical Oxisols.. .97
Guarana Fertilization.. .100
Lime Requirements and Downward Movement of Ca and Mg... 102
Planting Dates in Relation to Weather Pattern at Manaus... 107
Micronutrient Fertilization on a Typic Acrorthox at Manaus... 109
Management of Green-Manure Nitrogen on Oxisols at Manaus... l1
Conditions Other Than Extractable Nutrient Concentrations in the Soil Test Interpretations
for P and Zn... 113
Extrapolation of Soil Management Technologies to the Pichis Valley... 115
Low-Input Cropping Systems for the Pichis Valley...116
Legume-Based Pastures in the Pichis Valley... 118
Agroforestry in Steeplands of the Pichis Valley... 120
Soil Erosion and Reclamation...120
Sitiung: Extrapolation to Transmigration Areas of Indonesia...121
Reclamation of Bulldozed Lands...122 Liming in Transmigration Areas...125
Phosphorus Management in Transmigration Areas... 131
Effect of Green Manure Applications on Soil Fertility and Crops.. .134
Potassium Management of Upland Crops... 137
Sulfur Fertilization... 139
Contributions to North Carolina and U.S. Agriculture... 139
Publications... 141

Because it is unlikely that many farmers in the humid tropics can abruptly switch from traditional shifting cultivation to a fertilizer-based agriculture with continuous cropping, an intermediate system of low-cost, "low-input" technologies might be useful as a transitional agriculture that could produce ample food while reducing the need to clear more forest land. The emphasis of this low-input approach is on adapting plants to the soil, rather than correcting soil constraints to meet the plants' needs.
Previous research and interviews with farmers have led to an experimental low-input system largely based on traditional farming practices, with innovations introduced in stages. The strategy developed at Yurimaguas includes slash-and-burn clearing, aluminum-tolerant cultivars, a rotation of upland rice and cowpeas, zero or minimum tillage, chemical weed control, modest rates of fertilizers, and cropresidue management. As soil fertility and crop yields decline with time, the system would shift to such options as continuous cropping, pastures, tree crops or managed fallows.
The low-input system is considered transitory, but has remained productive considerably longer than expected. In the central experiment, seven continuous crops in three years have yielded a total of 13.8 t/ha of rice and cowpea grain, without application of lime or fertilizers in a soil with pH 4.4 and 68% Al saturation. Studies presented here indicate that soil fertility is not the major constraint in this system, as crop yields remain high with only small amounts of phosphorus and potassium after the second year.
As predicted by farmers during the interviews, weeds are a primary constraint to sustained production. Results are not yet available from a study of weed control in low-input systems, but preliminary observations suggest that, without tillage, weeds will limit the system's useful life to about six crop cycles. Research is planned to develop practical weed-control strategies that will prolong the productivity of the low-input system and increase its appeal as a soil-management option in the humid tropics.

Central Low-Input Experiment variety was sown with a planting stick (tacarpo) at the
wide spacing common to the region; a post-emergence
Jos6 R. Benites, N.C. State University herbicide was used to control broad-leaf weeds. After Marco A. Nurefia, INIPA the first rice harvest, at the time farmers typically abanPedro A. Sanchez, N.C. State University don the field, several practices were introduced:
1. All the rice straw was cut and spread evenly.
A central experiment was established at Yurimaguas, 2. "Africano Desconocido," an acid-tolerant, imPeru, to determine the potential of a low-input, crop- proved rice cultivar, was planted with tacarpo at 30
production system based on a rotation of upland rice x 50 cm spacing.
and cowpeas, and to determine how long the system 3. Rice was followed by an acid-tolerant cowpea might remain productive. A one-hectare plot of a ten- (cultivar Vita 6 or Vita 7), also planted with tacarpo.
year-old secondary forest fallow was cleared by slash 4. After threshing, all the rice straw or cowpea stover
and burn in July, 1982. In August, a study was was spread evenly on the field.
established consisting of upland rice and cowpea with 5. The rotation continued for 34 months, fertiliztwo treatments: one-half hectare fertilized at the rate ing only the rice crops in the fertilization treatment.
of 30 kg N, 22 kg P and 48 kg K/ha per rice crop, 6. Pre-plant application of 2-4 D (1.5 L/ha) and
beginning with the second rice crop, and the other Paraquat (2.5 L/ha) were used for weed control.
half-hectare not fertilized. The traditional upland rice
Crop Yields
Table 1. Productivity of a low input system during the first 34 Yields of both rice and cowpea were high. Table months. 1 shows the yields of seven continuous crops harvested
Planting Grain Yields within three years after the experiment began. A total
Crop and Cultivar Date Not Fertilized Fertilized* of 13.8 t/ha of rice and cowpea grain was produced
during this period without any addition of fertilizer
Month t/ha or lime. These results contrast sharply with those from
Rice, Carolino Sept. 82 2.4 2.4 the continuous-cropping system, in which yields apRice, Africano Feb. 83 3.0 3.1 proached zero without fertilizers within a year. The
Cowpea, Vita 7 Sept. 83 1.1 1.2 use of Al-tolerant cultivars, maximum residue return
Rice, Africano Dec. 83 2.8 3.2 and zero tillage are believed to be responsible for this
Cowpea, Vita 7 May 84 1.2 0.9 difference. The first six rice crops showed no response
Rice, Africano Sept. 84 1.8 2.0 to the fertilizers applied. A sharp yield response to ferRice, Africano Feb. 85 1.5 2.5 tilizer was observed in the seventh crop, indicating a
Total 34 Months 13.8 15.3 fertility decline in the check plots, and modest NPK
* 30 kg N/ha, 22 kg P/ha, 48 kg K/ha to Aficano rice crops. applications became important at the end of the third year.
Table 2. Topsoil (0-15cm) fertility dynamics within the first 34 months of the low input cropping system at
Months after Exchangeable Al Avail.
Clearing Fertilized1 pH Al Ca Mg K ECEC Sat. P OM
c mol/L % mg/kg %
3 No 4.4 1.10 0.30 0.09 0.13 1.62 68 20 2.12
14 No 4.6 1.46 0.92 0.28 0.19 2.85 51 13 2.06
Yes 4.7 1.14 0.97 0.27 0.19 2.58 45 18 2.07
34 No 4.6 1.65 1.00 0.23 0.10 2.99 53 5 1.92
Yes 4.6 1.23 1.16 0.20 0.16 2.76 44 16 1.77
CV%2 6 46 46 41 43 9 37 39 20
LSD.052 0.1 0.25 0.17 0.04 0.03 0.20 7 2 0.15
1 Cumulative amount over 34 months: 120 kg N/ha, 88 kg P/ha as OSP, 192 kg/ha as KCI.
2 Comparisons do not include sampling at three months after clearing.

Soil Properties Tillage-Phosphorus Interactions
Topsoil chemical properties (Table 2) improved dur- Under Low-Input Cropping Systems ing the period three to 14 months after clearing, in
response to the fertilizer value of the ash, which in- Mwenja P. Gichuru, N.C. State University creased the base status. From 14 to 34 months, there Pedro A. Sanchez, N.C. State University
was little change in pH, organic matter and exchangeable bases, and a more favorable Al saturation This experiment was begun in May 1982 to study level was maintained. It is noteworthy that soil organic the management of phosphorus in the low-input cropmatter decreased only slightly, a sharp contrast to the ping system being developed on an Ultisol at 25% decrease observed in similar soils under a Yurimaguas, Peru. Its objectives were to study the efcontinuous-cropping system. Apparently this was due fect of no-till versus rotovation on continuous croppto the residue return and absence of tillage. ing without liming, using acid-tolerant crops, and to
The check plots showed a pattern of declining soil determine efficient rates and sources of phosphorus fertility less drastic than results from continuous- for a rotation of acid-tolerant upland rice (Oryza sativa cultivation experiments. Available P and exchangeable L.) and cowpea (Vigna unguiculata). K decreased below the critical levels (12 ppm for P Relevant soil chemical properties at the initiation and 0.15 cmol/L for K). The small P and K additions of the experiment are shown in Table 1. The main in the fertilized treatment were apparently sufficient plot treatments were tillage methods: 1) no-till, with to offset this decrease. broadcast fertilizers, and 2) rotovation before each crop,
with fertilizers broadcast and incorporated to a depth
Conclusions of about 8-10 cm. Subplot treatments were phosphorus
It seems reasonable to assume that this low-input sources, ordinary superphosphate and Sechura system could be sustained by modest fertilizer applica- phosphate rock. The sub-subplot treatments were 0, tions. The crucial limiting factor is a gradual buildup 25, 50, 100 and 200 kg P205/ha. Crop residues were of grassy weeds, particularly during the rice crops. The left on the surface. effect of fertilizer application on weed growth does
not appear to be important. The studies on weed con- Tillage Effects trol for low-input systems show that much needs to Figure 1 shows the influence of tillage on relative be learned about how to control these weeds yields of five consecutive crops (relative yield is a
economically by herbicides, and, as a consequence, percentage of maximum absolute yield). The first crop avoiding tillage does not help, either. It is possible to produced significantly more grain in rotovated control the weeds with hand labor economically, or treatments compared with no-till plots. The better with herbicides at a prohibitively high cost. Conse- growth in rotovated plots is probably due to improvquently, we have reached a crossroads in this transi- ed soil physical properties and a better distribution of tion technology. For the low-input system to succeed, nutrients from the ash left by slash-and-burn. effective and affordable weed control measures are The second and third crops' grain yields showed no needed to bridge the gap between year two and year differences due to tillage treatments. The advantage five. of rotovation in terms of improved physical properResults are promising for the low-input strategy as ties may have disappeared, probably due to constant a transition from shifting agriculture to a more per- traffic during weeding and harvest. Rotovation followmanent system of management. With relatively sim- ed by human traffic is likely to result in greater soil pie practices farmers can grow seven crops where they compaction and poorer crop performance, compared were able to grow only one. This system cannot be with no-till. considered stable at this time, and is viewed as a tran- In the fourth and fifth crop dramatic yield reducsition technology, tions occured in rotovated treatments compared with
no-till plots. Rotovated treatments produced 80% and
76% relative yields, respectively, in the fourth and fifth
harvests (Figure 1). The reason for this sudden negative
response to tillage is not clear. Bulk density
measurements in the 0 to 7.5 cm depth, taken immediately after harvesting the fifth crop, showed high

Table 1. Relevant soil chemical properties at the initiation of the tillage-phosphorus experiment.
Soil Exchangeable Effective Al Avail P
Depth pH Acid Ca Mg K CEC Sat. (Mod. Olsen)
cm c- mol/L % mg/kg
0-15 4.5 1.9 1.3 0.4 0.15 3.7 53 14
15-30 4.3 3.9 0.5 0.1 0.11 4.6 84 4
30-45 4.3 4.1 0.4 0.1 0.09 4.7 88 3
bulk density values both in rotovated plots (1.46 g/cc) Phosphorus Effects
and in no-till treatments (1.42 g/cc). These high values The grain yields ranged from a low of 1.41 t/ha are believed to be mainly due to human traffic, to a high of 3.26 t/ha among the five crops. However, no significant differences were found between the (3.6) (2.4) (1.4) (2.5) (2.7) phosphorus sources in any of the crops. Thus,
100 6 phosphate rock was comparable to ordinary super_ Nti(95%) phosphate in supplying P.
0 The data in Figure 2 show that, in general, only
E the control produced less than 80% relative yield in
0 the first three consecutive harvests. The first P incre"80 0 ment produced slightly over 80% while higher rates
generally produced over 90% relative yields during Rotovated (91%) the same period. The absence of a strong P response 70 is believed to be due to the initially favorable P status
1 2 3 4 5 in the soil, as shown in Table 1.
Crop R R C R R The fourth crop showed vigorous growth, probably
Figure 1. Relative yields of five consecutive crops as due to N fixed by the cowpea crop, but severe lodginfluenced by tillage. Numbers in parenthesis at the ing occured during the grain-filling stage. All treatments top are maximum yields in tons/ha, and numbers to produced yields over 90% of the maximum yield, but the right are average yields of five crops. R = rice; the grain quality was very poor; it had a high percenC = cowpea. tage of half-filled grain because of the lodging. The
fifth harvest produced yields at least 80% of maximum, with the 100 kg P20,/ha rate producing the max100 o imum yield.
.200 9 1. The effect of tillage appears to follow a trend in
which rotovation is superior to no tillage during the 0 79 first crop, about equal for the second and third crops, so 95 and inferior during the fourth and fifth rice crops. A
80 25 5 combination of initial tillage followed by no-till apo6 pears advantageous, but firmer conclusions require additional data.
70 2. Rock phosphate at the rate of 50 kg P20/ha,
applied to the surface, was sufficient to produce 95% S I I of the maximum yields in the low-input system, bas1 2 3 4 5 ed on crop varieties highly tolerant to aluminum. A
Crop R R C R R total of 12.9 t/ha of rice and cowpea grain was proFigure 2. Relative yields of five consecutive crops as duced by five crops on an Ultisol with pH 4.5 and
influenced by phosphorus application. Numbers in no lime application.
parenthesis are maximum yields in tons/ha, and 3. The data show no significant interaction between
numbers to the right are P rates (kg P = 20 = 5/ha) and tillage and phosphorus.
average relative yields, respectively.

Calcium and Magnesium Movement Exchangeable Ca
In Low-Input Cropping Systems Strip-tillage resulted in higher initial levels of exchangeable Ca in the topsoil because the calcium was Mwenja P. Gichuru, N.C. State University applied to about a third of the soil surface area, but Pedro A. Sanchez, N.C. State University there were no significant tillage effects at other depths, Jos6 R. Benites, N. C. State University and the effect on the topsoil had disappeared at twenty months.
This experiment was initiated in May 1982 to study The pattern of exchangeable Ca distribution appears the effect of small additions of dolomitic limestone or nevertheless to be influenced by tillage treatments. gypsum on the downward movement of Ca and Mg Generally, seven months after application, dolomitic as part of the low-input, crop-production strategy under limestone resulted in significantly higher exchangeable development at Yurimaguas. A second objective was Ca in the topsoil compared with gypsum treatments. to determine the effect of tillage methods on the rates The lower exchangeable Ca in the topsoil of gypsumat which these cations moved into the subsoil. treated plots was due to downward movement, as inMain plot treatments were a combination of tillage dicated by higher exchangeable Ca at lower depths methods and nutrient incorporation: 1) no-till and compared with the check and dolomitic-limestone broadcast fertilizers with no incorporation; 2) strip- treatments. Downward movement of Ca was more tillage, with fertilizers applied in strips 15 cm wide pronounced when gypsum was incorporated than (about one-third the total area) and incorporated with when it was applied to the surface, as indicated by a a hoe to a depth of approximately 8 to 10 cm, and larger bulge at the 15 to 16 cm depth in both strip 3) rotovator tillage with fertilizers broadcast and in- tillage and rotovated treatments compared with nocorporated to rotovator depth (about 8 to 10 cm). till treatments (Figure 1). Subplot treatments were calcium sources (dolomitic The effect of gypsum on downward movement of limestone and gypsum). Sub-subplot treatments were Ca was still measurable 20 months after application. 0, 33, 100, 300 and 600 kg Ca/ha. Treatments with However, the exchangeable Ca bulge at the 15 to 45 gypsum as the Ca source were supplemented with Mg cm layer had slightly shrunk despite a substantial from MgSO4. 7H20 in amounts equivalent to that decrease in exchangeable Ca in the above layers. supplied by dolomitic limestone. The crop rotation Slight increases in exchangeable Ca were found at was rice (Oryza sativa L.), rice, cowpea (Vigna 100 cm, suggesting that some Ca from gypsum had unguiculata), rice, rice, cowpea. moved beyond the sampled depth. The application of
Exchangeable Ca (cmol (p+) L)
0 1 2 0 1 2 3 0 1 2
-- -- ---- --
No Till Strip till Rotovated
60 mo. -mo. 7 ao.
,-10 |
0.0 1 2 0 1 2 3 0 1 2
00 -: Rotovated
F r 1No till b Strip till 20 ma.
60 20 ma. i 20 Ma. kglha Source
i! -600 Gypsum
100 __ l.A 600 Dolomite
Figure 1. Exchangeable Ca as influenced by Ca source and rate under three tillage systems.

Table 1. Exchangeable Mg as influenced by the application of dolomitic limestone and gypsum.
Calcium No-Till Strip-Till Rotovated
Applied Doll Gyp2 Doi Gyp Doi Gyp
kgCa/ha c mol/L
7 Months After Application
0 .21 .28 .27 .26 .22 .20
33 .27 .25 .35 .29 .30 .20
100 .31 .17 .75 .23 .37 .39
300 .67 .23 1.03 .24 .55 .23
600 .56 .12 .98 .16 .90 .18
Rate LSD (.05) .25 NS .45 NS .19 NS
Source LSD (.05) 0.09 0.14 0.08
20 Months After Application
0 .15 .17 .18 .20 .11 .13
33 .17 .15 .19 .21 .14 .10
100 .17 .17 .47 .20 .20 .24
600 .58 .26 .97 .41 .53 .29
Rate LSD (.05) .14 NS .25 .16 .10 .11
Source LSD (0.05) 0.06 0.08 NS
1 Dol dolomitic limestone
2 Gyp =gypsum
300 kg Ca/ha showed a similar trend (data not plemental magnesium was split over the cropping cycles
presented here), but the magnitudes were smaller com- and applied at planting.
pared with the application of 600 kg Ca/ha. An exception was observed in no-till treatments, where the Conclusions
calcium bulge was comparable to that of the 600 kg 1. The applications of 300 or 600 kg Ca/ha as gypCa/ha rate in the rotovated treatment. sum resulted in substantial downward movement of
Ca in less than two years, whereas dolomitic limestone Exchangeable Mg application resulted in little or no change in exStatistical analysis of exchangeable Mg data reveal- changeable Ca below the 0 to 15 cmn depth. However,
ed that treatments had little or no significant effect it was difficult to detect the effect of rates lower than below the 0 to 15 cm layer. This was probably due 300 kg Ca/ha, probably because of variability in the to the initial variability of exchangeable Mg in the soil field, which had recently been cleared by slash and
(coefficients of variation of 42, 87, 108, 55, 67 and burn.
59% at increasing depth intervals, respectively). Ex- 2. Rotovation resulted in greater and more uniform changeable Mg status of the topsoil, however, was im- downward movement of Ca, compared with surface
proved by the application of dolomitic limestone (Table application. i
1). But little or no change in exchangeable Mg occured 3. Gypsum application will result in subsoil enrichin gypsum treatments after seven months, although ment with Ca in a short time.
they had received supplemental Mg in equivalent 4. The data from this experiment suggest that, 20 amounts supplied by dolomitic limestone. The high months after application, some Ca had moved
solubiity of the Mg source may have resulted in rapid downward beyond the sampling depth.
leaching beyond the sampled depth. A similar trend Results of this study indicate that relatively low rates was observed 13 months later, except that the highest of gypsum can promote a significant movement of
rates of gypsum produced some increase in ex- calcium into the subsoil.
changeable Mg. In these high rates of gypsum the sup10

Pastures are good news and bad news for soil management in the tropics. Well-managed, they 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. Many thousands of 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, Peru has been closely integrated with the Tropical Pastures Program of Centro Internacional de Agricultura Tropical (CIAT), and with INIPA's National Selva Program, which is now conducting most of the agronomic studies. Research reported here has for the most part concentrated on the relationships among soil fertility, pasture quality, pasture persistence, grazing, the transfer of N from legumes to grasses, and the recycling of nutrients. Several promising grass-legume pastures have produced stable pastures and animal weight gains many times greater than those on the typical humid-tropical farm. After years of sustained production at Yurimaguas, the best of these associations and management techniques are being tested at extrapolation sites.
Some of these extrapolation studies have been initiated near Pucallpa, Peru, but are not reported because they are still in the establishment phase. Two projects are examining the N contribution of legumes to mixed pastures, and determining the optimum schedule for herbicide application during pasture establishment.
Central in the work reported here is the role of legumes in pasture associations. Legume-based pastures have not been studied extensively in humid tropical environments, and the information about their response to such management variables as fertility, grazing pressures and establishment methods are expected to be of use throughout the humid tropics.

Legume-Based Pastures: liveweight production; 2) to evaluate the compatibiliCentral Experiment ty and the persistence of the different grass-legume mixtures under grazing, and 3) to evaluate changes in soil Rolando Dextre, INIPA properties as a consequence of long-term pasture
Miguel A. Ayarza, N. C. State University production.
Pedro A. Sanchez, N. C. State University Four associations remain unchanged, but during the four years the project has been in progress, Panicum The central experiment with pastures, begun in maximum + Pueruaria phaseoloides was replaced by An1980, has sought to develop a practical management dropogongayanus + Centrosema macrocarpum 5056 in system for improving tropical pastures with stable mix- October 1984. Table 1 shows the species, animal tures of acid-tolerant legumes and grasses. Since its in- management and years of evaluation for each associaitiation, the experiment has evolved in response to new tion.
information gained from companion experiments and
from collaboration with the International Center for Animal Production and Botanical Composition
Tropical Agriculture (CIAT) and its Tropical Pastures Changes in animal production are shown in Figure Network. Work so far has shown that proper manage- 1. During the first year, most associations yielded above ment of some grass-legume associations can greatly im- 600 kg/ha/yr of liveweight gains. However, only C.
prove the stability and productivity of previously pubescens and the Brachiaria-based pastures were able degraded tropical pastures, while conserving the soil- to maintain that level of productivity beyond the first
resource base. year.
The objectives of this experiment are 1) to measure A remarkable performance by Centrosema pubescens
pasture and animal productivity on different associa- 438 has been observed. After the first year, A. gayanus tions, in terms of daily weight gain and annual disappeared from this mixture because of establishment
Table 1. Grazing trial mixtures with starting dates of continuous and alternate grazing. (Planting dates: March
to July, 1980 for first four, February, 1982 for fifth and October, 1984 for sixth mixture.)
Treatments Initiation of Grazing Initiation of Grazing Days
Grass Legume Continuous Grazing Days Alternate Grazing Through Sept. 1985
B. decumbens/D. ovalifolium 350 Nov. 15, 1980 238 Oct. 7, 1981 370
P. maximum/P. phaseoloides 9900 Nov. 20, 1980 238 Oct. 6, 1981 1005
A. gayanus/S. guianensis 134-186 May 15, 1981 57 Oct. 6, 1981 1370
C. pubescens 438 0 Oct. 7, 1981 1370
B. humidicola/D. ovalifolium 350 0 Oct. 10, 1982 1056
A. gayanus/C. macrocarpum 50561 0 May 1985 120
1 Replaced Pm/Pp.
Table 2. Nutrient levels of grass and legume mixture components and tannin content of legumes May, 1983.
Species N P K Ca Mg S Zn Tannin
% ppm %
Centrosema pubescens 438 4.46 0.26 1.30 0.93 0.26 0.18 31 2.5
Desmodium ovalifolium 350 2.69 0.16 0.72 0.83 0.21 0.12 10 21.0
Stylosanthes guianensis 136 3.89 0.22 0.32 1.13 0.32 0.16 37 4.0
Pueraria phaseoloides 9900 3.90 0.22 1.30 0.45 0.32 0.12 25 4.0
Brachiaria decumbens 606 2.38 0.24 1.57 0.42 0.42 0.11 14
Brachiaria humidicola 1.70 0.21 1.66 0.28 0.27 0.10 16
Androgogon gayanus 2.11 0.17 1.05 0.36 0.14 0.11 10

900 90
41 39
800 -5-5278 700 --- 29 4
i 29 1000
6600 -100 .
4 40
i 66
C 300 "60
Years: 1 2 3 4 5 1 2 3 1 2 3 4 1 2 3 4 5 1 2 3
Mixture: B. decumbens B. humidicola Centrosema A. gayanus P. maximum
D. ovalifolium D. ovalifolium pubescens 438 S. guianensis P. phaseoloides
Figure 1. Changes in animal production from grass-legume pastures with time in Yurimaguas. A number at the top of a bar is an average annual percentage of legume in the mixture.
problems. In spite of this, the legume has persisted and maintained high levels of production. This must be related to the high quality of the species (excellent 800 palatability and high nutritional content) in comparison to the other legumes in the experiment (Table 2). 0.006
The change from continuous to alternate grazing has 00
favored the presence of grass in the mixtures of B. .E o a
decumbens + D. ovalifolium and B. bumidicola + D. o ovalifolium (Table 2). This has resulted in sustained 4 400 animal gains based mainly on consumption of the grass, i since the legume is of low palatability (Figure 1). Levels of D. ovalifolium in the mixture with B. decumbens, 200 s guianensis
0 D. ovalitolium
however, decreased sharply in May 1984. This was p,aseooies
related to an unusual intake of legume and a rejec- 0
tion of the grass during a short drought at that time. I
In the mixture of A. gayanus + S. guianensis the an- 0 25 50 75 100
nual animal performance was closely related to the con- Legume in Forage on Offer (%)
tent of legume in the association (r2 = 0.75). The Figure 2. Effect of the content of legume in the forage legume almost disappeared in the same period as in- on offer on animal gains in three grass-legume dicated for D. ovalifolium with b. decumbens. pastures growing in an Ultisol of Yurimaguas. (%
Poor animal gains were observed in P. maximum legume expressed as annual mean value.)

4 1980 6 180 weight/ha (Table 3). The association of B. bumidicola
a 4 1980 6 1084
0 U 1984 + D. ovalifolium performed well but had only two
3 5 years of evaluation.
2 4 Changes in Soil Chemical Properties
o In order to follow the changes in the soil properties
1 as a function of time in these pastures, the treatments
X were sampled in 1980 (before grazing, and six months
I I I I after fertilization for establishment) and in 1983 and
1 2 3 4 5 1 2 3 4 5 1984. Figure 3 shows that some of the properties have
Associations Associations changed in the 0-20 cm depth in several pastures. It
1. Panicum maximum +edes 4. Brachia deum nsm is interesting to observe that exchangeable acidity has
PuerriaphasolodesDesmodium ovalitolium
2. Centrosema sp. 438 5. Brachiaria humidicola + decreased in all associations except P. maximum +
3. Andropogon gayanus + Desmodium ovalifolium
Stylosanthes guianensis P. phaseoloides and that pH has increased to 5.0 in B.
10 l 1980 decumbens + D. ovalifolium. Phosphorus levels have
S1984 increased in all associations, probably due to
l 1980 maintenance applications of phosphorus (25 kg P
E.6 E 1984 ha/yr). Most changes have occurred in the 0-20 cm
c depth.
4 -22
+ Progress in 1985
<1 Several changes have been introduced in the manage2ment of the associations. D. ovalifolium and S. guianensis were replanted in their respective associations in
1 2 3 4 5 1 2 3 4 5 order to investigate the effects of different grazingAssociations Associations management procedures.
Grazing periods were reduced from 42 to 28 days,
Figure 3. Changes in the topsoil chemical properties and stocking rates were increased from 4.4 to 5.5
in five grass-legume associations after four years of
in five grass-legume associations after four years of animals per ha during the rainy season, and maintaingrazing. ed at 4.4 during the dry season, in pastures of B.
decumbens + D. ovalifolium and B. bumidicola + D.
+ P. pbaseoloides after three years of evaluation. This ovalifolium. These changes more efficiently use the high appears to be related to the increasing content of levels of available forage and prevent losses in the qualiPueraria. The negative effect of this legume on animal ty of the grass when the pasture remains ungrazed for
gains is reflected in a negative correlation coefficient longer periods.
of -0.77 (Figure 2). The C. pubescens pasture is being maintained with
Centrosema pubescens 438 as a pure legume and the the same 4.4 animals/ha and 28-day grazing and resting
B. bumidicola + D. ovalifolium mixture were the best periods. Stocking rates for the associations A. gayanus pastures in terms of individual animal gains and kg/ha and S. guianensis and A. gayanus and C. macrocarpum have been adjusted to 3.3 animals/ha and 20 to 28
Table 3. Average annual productivity of five associations under days of grazing. grazing. Stocking rate 4.4 animals/ha. The new management has produced positive results
Years of in B. bumidicola and D. ovalifolium. In seven months
Association Grazing Liveweight Gains of grazing, animal gains passed the annual gains for
the previous two years. Furthermore, individual gains
kg/ha/yr g/an/day are excellent at this time, and if this trend continues B. hdumnidicolD, ovalifolium 2 691 429 for the remaining four months of the year, it will be
B. decumbens D. ovalifolium 4 626 379-Centrosema pubescens 438 3 619 459 possible to reach levels up to 900 kg liveweight per
A. gauanus S. guanensis 4 467 357 year in this pasture. The sward is in excellent shape
a. gauu. guaeis 3 45 2 with a 40% legume intimately mixed with the grass.
P. maxim/P. phaseoloides 3 455 296 The Brachiaria decumbens and D. ovalifolium pasture

Table 4. Preliminary results of animal production levels in five associations under grazing until Sept., 1985, Yurimaguas, Peru.
Stocking Rates Animal Gains Legume
Associations Rainy season Dry Season Kg/live weight/ha gm-head/d %
Brachiaria humidicola + 5.5 4.4 697.6 597.6 40
D. ova/ifolium1
B. decumbens + 5.5 4.4 530.2 470.3 40
D. oval/ifolium1
Centrosema pubescens 4381 4.4 4.4 399.4 419.8 100
A. gayanus + 3.3 3.3 387.2 751.4 20
C. macrocarpum 50662
A. gayanus + Stylosanthes 3.3 3.3 282 641.8 60
1 Grazing from January-September
2 Grazing from May-September
is once again showing the problems observed in 1984. Potassium Dynamics Although the grass appears to be doing well, the In Legume-Based Pastures animals are grazing only the legume and making little
use of the grass. This seems to indicate that this grass Miguel Ayarza, N. C. State University is very sensitive to drought stress normally occurring Pedro A. Sanchez, N. C. State University during the dry season. As a result, digestibility pro- Rolando Dextre, INIPA bably falls to levels preventing its consumption.
Measurements will be conducted to test this statement. Tropical pastures on acid soils are stable and proCentrosema appears likely to maintain the animal pro- ductive only when nutrients are sufficient to sustain ductivity observed in 1984. The other two pastures a vigorous forage crop. Maintaining this fertility rehave only six months of evaluation and it is too early quires a management method that takes into account to make any conclusions. A. gayanus + C. macrocar- the nutrient leaching common in areas of high rainpum 5065 is well established with a 15% legume base. fall, as well as the cycling of nutrients among soil, forage and animals. This study, which was conducted
Conclusions at the Yurimaguas Experiment Station, concentrated
1) To date, Centrosema pubescens 438 as a pure legume on one nutrient, potassium. Its objectives were 1) to and the B. bumidicola + D. ovalifolium mixture have quantify leaching losses of K in pastures under clippprovided the best pastures in terms of individual animal ing and grazing; 2) to monitor the effect of K levels gains and kg/ha weight/ha. on the productivity of the pasture and on the dynamics
2) The association of B. humidicola + D. ovalifolium of K in the soil; 3) to estimate the effect of K return performed well but had only two years of evaluation. by animal excretions, and 4) to compare estimated K
3) Exchangeable acidity has decreased and soil P losses from pastures with losses from crops grown in levels have increased in most of the pastures during the same area. the course of this study. The grazing experiment was a factorial of three an4) Adjustments in stocking rates and grazing periods nual rates of K fertilization (0, 50 and 100 kg K/ha) have improved the quality of grasses and made more by two grazing pressures (11 and 7.8 kg green forage efficient use of available forage in several of the grass- dry matter/100 kg liveweight), with three repetitions. legume associations. Two additional experiments were established on 3 x
4 m plots with K rates of 0, 25, 50, 75, 100, 150,
and 300 kg K/ha/yr. The first, 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

Table 1. Effect of cummulative rainfall on exchangeable K status physical properties related to K leaching, and to of 0-5 cm layer in bare and clipped plots, estimate the effect of plant growth on K dynamics.
Bare Plots Clipped Plots Four hectares were planted with a mixture of
Bracbiaria bumidicola and Desmodium ovalifolium in Cumulative Rainfall, mm Cumulative Rainfall, mm December, 1984. Potassium treatments were applied K Rate 25 150 25 150 on May 13, 1985, and grazing began on July 4.
kg/ha Exchangeable K, cmol/L Potassium distribution in the soil with depth was
0 0.07 0.06 0.07 0.07 monitored as a function of precipitation. Changes in
25 0.16 0.09 0.10 0.07 soil and plant K were determined in the small plots
50 0.26 0.12 0.15 0.16 and grazing experiments. Amounts and composition
75 0.28 0.14 0.17 0.18 of plant residues were evaluated under grazing. The
100 0.32 0.18 0.18 0.19 effect of urine on the return of K to the soil is being
100 0.42 0.29 0.25 0.24 studied, comparing plant growth and changes in soil
300 0.78 0.47 0.61 0.48 K in affected vs. unaffected areas under grazing.
LSD .05 0.09 0.28 0.09 0.28
Exchangeable K Dynamics
The Ultisol in the experimental area was characterizExchangeable K (cmol/L) e d as having a sandy loam topsoil texture, Al satura0 0.1 0.2 0.3 0.4 0.8 tion of 74% and K contents of 0.06 cmol/L, far below
0.5 0. the critical range of 0.15 to 0.20. Most of the K ap\plied to the bare soil, however, remained in the top 5 cm, even though 25 mm of rain fell during applica5-20 tion (Figure 1). After an additional 159 mm of rain,
topsoil exchangeable K levels remained constant, except in plots receiving 300 kg K/ha, which lost 0.13 20"40 cmol K/L (Table 1). In the clipping plots, where the
grass-legume mixture was growing rapidly, this decrease at the 300 kg K/ha rate was more pronounced (Table = 40.60 1).
Pasture Response
Results of the first cut of the mixture growing in
60.100 the small plots are presented in Table 2. Total dry
Figure 1. Effect of application of potassium on the matter was not affected by the potassium rates, distribution of exchangeable K in the profile of a san- although the content of the grass in the mixture tenddy loam Ultisol, following 25 mm of rain. ed to increase with K rate. Foliar K in the grass inTable 2. Effect of seven K rates on dry matter yields and uptake of Brachiaria humidicola and D. ovalifoliumb
growing in association in an Ultisol of Yurimaguas, Peru (first cut).
Grass Plant K Content Total Uptake
K Applied Dry Matter Component Grass Legume B.humidicola D.ovalifoium
kg/ha g/m2 % % K kg/ha
0 196.6 a 54 0.96 c 0.74 d 1.32 0.54
25 217.8 a 61 2.21 b 0.91 d 1.83 0.74
50 219.5 a 62 1.51 b 0.90 d 2.29 0.66
75 183.6 a 63 1.62 b 1.31 ab 1.80 0.93
100 201.5 a 51 1.65 b 1.06 bcd 1.72 1.04
150 229.3 a 59 2.19 a 1.24 abc 3.00 1.12
300 268.0 a 71 2.56 a 1.58 a 4.95 1.18
LSD 67.5 14

Table 3. Effect of K applications on dry yields and botanical composition in a pasture of B. humidicola and D. ovalifolium before grazing.
Dry matter K in K in
K Applied Yield Grass Legume Grass Legume
kg/ha t/ha %
0 2.51 53 a 47 a 0.98 1.02
50 3.03 65 b 35 b 1.51 1.29
100 2.95 68 b 32 b 1.72 1.38
creased with potassium applications, and the highest Pasture Germplasm application rate multiplied foliar K 2.6 times the level Evaluation and Agronomy found in grass with no K applied. Compared to the grass, the legume accumulated less foliar K in response Rolando Dextre, INIPA to K fertilization. Miguel Ayarza, N.C. State University
The relation between the potassium content in leaves Jos6 M. Toledo, CIAT and dry matter yield was not consistent in either Mario Calder6n, CIAT
species, suggesting a high luxury consumption by the Jill Lenn6, CIAT grass. Only at 300 kg K/ha was there an increase in Esteban Pizarro, CIAT dry matter of B. humidicola.
The effect of K fertilization on the growth and K Twenty-three species of grasses and legumes have content of leaves before grazing is shown in Table 3. been tested for their adaptation to Yurimaguas condiAs observed in the clipping plots, grass composed a tions according to the methodology suggested by CIAT larger share of the forage mixture when the pasture for regional trials type B. The objectives of these studies was fertilized with K. This was true under grazing, are 1) to introduce new acid-tolerant grass and legume as well. accessions through regional trials and seed production,
and 2) to evaluate tolerance to spittlebug in grasses Animal Behavior and to anthracnose in legumes.
Grazing has shown an expected animal preference Species are harvested at four cutting intervals (three, for the grass, regardless of the potassium level. Little six, nine and 12 weeks). Cover and resistance to pests consumption of the legume was observed, even at the and diseases are also recorded. higher grazing pressure. However, grass recovery after grazing was excellent, especially when potassium was Yields at Cutting Interval present. After 86 days of grazing there was an overall Figure 1 presents the effect of four intervals of cutincrease of 36 kg per animal. Individual gains appear ting on four legumes and three grasses growing on an to be slightly better in the 50 kg K/ha treatment. Ultisol at Yurimaguas. At the 12-week cutting interval, Bracbiaria dictyoneura produced yields similar to Conclusions those of B. decumbens and Andropogon species. GroundThe first stages of this continuing study yield the cover ability and vigorous growth of this species make following initial conclusions: it a promising grass for further evaluation under graz1) Rainfall did not significantly reduce exchangeable ing. Among legumes, the Centrosema macrocarpum K in the topsoil except on plots with the highest rate 5065, 5062, and 5452 appear to have potential for of K fertilization (300 kg K/ha). the Yurimaguas areas. Stable yields during dry and wet
2) Plots receiving K showed an increased percen- periods is an important attribute for their selection. tage of grass in the forage mixture. Centrosema pubescens 5189 produces yields similar to
3) Foliar K levels increased sharply with K fertiliza- those from the 438 ecotype, which is the most suction in grass, but only slightly in the legume. cessful legume at present under Yurimaguas conditions.
New Desmodium accessions have not shown superior yields to the 350 ecotype.
These species seem to require a minimum of six
weeks to recover from cutting.

Maximum Precipitation Minimum Precipitation the most tolerant accessions to this disease. Spittlebug
a. does not appear to be a major problem in any of the
2400 2400 C. macrocarpum 5065 species of Brachiaria under testing. High levels of in* C. pubescens 438 festation can be observed in B. bumidicola pasture under
O D. ovalifolium 350
1800 1800 O Z. lat ifoli a 728 grazing; however, there is no apparent damage.
Animal Preference
1200 1200 -A new criterion was added to the Brachiaria accessions. Animal preference was tested in March, 1984 600 600 (rainy season) for a period of 18 hours using four
animals. The entire area was fenced and the animals
___ I __ I ___were left to graze after spending a night without food.
0 3 6 9 12 0 3 6 9 12 The number of times the animal grazed each accesD 4000 b. sion was recorded every 15 minutes and the total
6000 -A A. gayanus 621 period of time the animals grazed each species are il* B. decumbens
3200 0 B. dictyoneura lustrated in Figure 2. Results indicate a difference in
preference not only among species but also within 4000 2400 species. Brachiaria decumbens 6009, B. hybrid 6298 and
B. bumidicola 629 were among the most preferred 1600 species. It is interesting to observe the low preference
2000 for B. dictyoneura accessions. A new evaluation is pro800 posed for the dry season next year.
I I I II I I to 10
0 3 6 9 12 0 3 6 9 12 E
Figure 1. Effect of four intervals of cutting on four > 6* legumes (a) and three grasses (b) growing in an uJ 4
Ultisol of Yurimaguas. (Mean of two years.) N2
z 2
Seed Production of Promising Forage Species o 0
Four grasses and five legumes, drawn from the most
promising accessions described above, are under evaluation for their potential to produce seed, an important M B. decumbens CM B. emini
attribute of a good forage species. All grasses except 2 S.P. hibrido E3 B. ruziziensis
M B. brizantha L= B. radicums
A. gayanus have to be propagated vegetatively, as they EB B. humidicola
do not produce viable seed under Yurimaguas condi- 40 B. dictyoneura
tions. Between four and five hectares could be planted C
30 -0
with the available material of the Brachiaria accessions. 30
Relatively good yield potential was observed for Cen- 20
trosema accessions 5713 and 5452. E 10
I-" 0Tolerance to Pests and Diseases o ; g o a
Twenty-six accessions of Stylosanthes guranensis have . . .
been studied for tolerance to anthracnose and 26 Figure 2. Animal preference for 26 brachiaria accesecotypes of Brachiaria have been studied for tolerance sions ranked by number of times grazed every 15 to spittlebug. Results after two years of observation minutes in 18-hour period, and by time animal spent
indicate a wide range of tolerance to anthracnose in grazing in 18 hours.
most S. guianensis species. Although the disease is present, it seriously affects only five accessions: 97, 1091, 1017, 1951 and 1893. S. guianensis 136 and 184 are

Pasture Reclamation in Steeplands cm in diameter); 2) minimum tillage (pastures planted
in 50 cm wide, rototilled furrows 2 m apart); and 3)
Rolando Dextre, INIPA total tillage (50 cm wide furrows, with spaces between
Miguel A. Ayarza, N.C. State University furrows gradually cultivated as forage crops grow). The
Pedro A. Sanchez, N.C. State University only fertilizer was Bayovar rock phosphate, applied
at the rate of 50 kg P/ha in the hole or furrow.
There is a substantial area of pasture land in the Although data are not yet available, visual evaluahumid tropics that has very low productivity because tion of the effect of treatments on the replacement of poor soil management, overgrazing or badly adapted of the native species (torourco) can be summarized as forage species. The purpose of this project is to develop follows: The grasses, Bracbiaria bumidicola and B. a simple technique for reclaiming degraded pastures decumbens, which are planted by vegetative propagain Ultisol steeplands. tion, are both well established, but B. bumidicola apA two-factor experiment was installed in a degrad- pears to be better in the zero-tillage treatment. Both ed pasture occupying a 5.18 ha watershed with grasses have almost replaced the torourco between fursideslopes of 20 to 50%. Treatments were establish- rows in the minimum-tillage treatment. ed in an amphitheater fashion, following slope con- The legumes tested, which were planted by seed, initially did not compete as well with the torourco. CenNew-Project Update trosemapubescens 438 is doing better than D. ovalifolium,
This project has not been under way long enough but both require some tillage before planting, in order to yield substantive reports, but should be mentioned to diminish competition for light and nutrients in the because of its importance to the program as a whole, early stages of growth.
Evaluation of biomass production and percent cover
of native grass is planned at four and eight months
tours, with tillage methods as main plots and improv- after planting. The information gathered so far suged species as subplots. The tillage treatments are 1) gests that some tillage is required to establish grass and zero tillage (pastures planted in an array of holes 20 legumes successfully.

Anyone regarding the luxuriant growth of a rainforest might gather that trees are the natural vocation of the humid tropics. Because a variety of commercially valuable species can succeed in this environment, agroforestry, the production of trees alongside crops or pastures, is an important soilmanagement option. In many cases, annual crops may be the wise choice for alluvial sites and soils with a high base status, while trees might be better suited to rolling, upland sites, where they require relatively little maintenance, tolerate acid soils, and afford long-term protection against erosion. Even so, most of the data available on tropical tree production are from areas with fertile soils. Collection and screening of the wide variety of germplasm available for use on acid soils have only begun.
Agroforestry projects at Yurimaguas are focused on tree-soil relationships on well-drained, acid soils. This work has been linked to agroforestry programs supported by INIPA, the International Council for Research in Forestry (ICRAF) and the International Development and Research Center of Canada (IDRC), and the principles being tested are expected to be applicable in the humid tropics world-wide.
The studies presented here have explored three general areas: 1) the selection and production of trees and shrubs valued for fruit and timber production or soil improvement; 2) the integration of trees and annual crops in systems such as alley-cropping; and 3) the role of secondary forest fallows in the improvement of soil properties. Because trees require months or years to become established and productive, these experiments are long-term, and some are in the earliest phases.

Trees as Soil Improvers deciduous, and provided the litter layer is not removIn the Humid Tropics? ed or burned.
6. Closed tree canopies tend to Improve soil strucPedro A. Sanchez, N. C. State University ture and decrease topsoil bulk density, but this effect
varies substantially with tree species.
It is commonly believed that trees are the best op- 7. Closed tree canopies do not increase topsoil
tion for producing food and fiber on a sustained basis organic matter contents. In most cases, soil organic in the humid tropics. Because tree plantations resem- matter is maintained relative to pre-clearing levels.
ble the natural ecosystem more closely than do an- When products such as rubber or oil palm are
nual crops, tree management might be expected to re- harvested, soil organic matter decreases and then
quire fewer inputs. The accumulation of large amounts reaches a new equilibrium level.
of biomass on acid, infertile soils, seemingly due to 8. Some tree species tend to increase topsoil Ca and rapid and efficient nutrient cycling, suggests that Mg by mechanisms not clearly understood. The eftropical forests function in a fundamentally different fect is marked with Gmelina arborea, which appears way than do annual crops and pastures. It is not known to be a calcium accumulator in Nigeria and Brazil. Exif the same conditions exist in production-oriented tree changeable K often decreases to very low levels and crops. The objective of the activity reported here was may trigger deficiencies. Tree species differ in their abili1) to bring together reliable information on the effects ty to alter soil acidity.
of deliberately planted tree crops on soil properties in 9. Leaching losses occur mainly during the treethe humid tropics, and 2) to develop working establishment phase. When well managed tree planhypotheses for agroforestry research. tarins develop a full canopy, leaching losses are as low
Available information on the effect of deliberately as in undisturbed forests. The nutrient-cycling
planted tree crops on soil properties in the humid mechanisms of many perennial tree crops appear to tropics was compiled, examined, and, whenever possi- be very efficient. Sometimes their efficiency is enhanced
ble, compared to alternative systems such as native by fertilization.
forests, annual crops, pastures or fallows. Only data 10. Fertilization and other management practices are sets meeting a set of soil uniformity criteria were us- likely to be needed for second rotations of timber crops, ed in the analysis. A complete report has been publish- as has been clearly demonstrated with perennial crops.
ed. (See publications list.) Expectations are likely to be erroneous that sustained
tropical forestry is possible in acid soils of the humid
Working Hypotheses tropics without using fertilizers.
The main conclusions or working hypotheses are: 11. Trees, therefore, generally maintain or improve
1. Tree crops make the soils initially more vulnerable soil properties in the humid tropics after they have
to runoff and erosion than annual crops or pastures established a closed canopy. Maintenance can be inbecause of their lower rate of canopy development dur- itiated early with a leguminous cover. The main ading the establishment phase. vantages of trees over annual crops or pastures seem
2. The degree of changes in soil properties during to be related to the longer period of time during which
the tree establishment phase depends largely on land- they exert their influence on soil properties.
clearing methods.
3. Protection of the soil surface with well-managed
leguminous covers during the tree-establishment phase can largely prevent deterioration of physical and
chemical properties.
4. When trees close their canopy, they begin to exert four major positive effects on soil properties: (a) soil-surface protection with a double layer (canopy and litter); (b) opening soil pores via root expansion and decomposition; (c) capture of nutrients and storage in biomass, and (d recycling nutrients back to the soil.
5. Closed tree canopies provide virtually complete
protection against erosion unless the trees are

Alley-Cropping on Ultisols equivalent-area basis, only to the 1 m wide tree rows.
In March, 1985, some of the trees showed signs of Lawrence T. Szott, N. C. State University K deficiency. Therefore, 100 kg K/ha was applied on Charles B. Davey, N. C. State Universtiy an equivalent-area basis to the 1 m wide tree rows in Cheryl A. Palm, N. C. State University the lime + P treatment in both experiments. The alley crops receiving K were Cajanus, Inga, and Erytbrina. In areas with increasing demographic pressure, tradi- Food crops were grown between the tree rows, tional forms of shifting cultivation must be supplanted without direct fertilization and at a constant spacing by production systems that yield more food on the within and between rows. The checks were two adavailable land. One technique, shown to be promis- ditional treatments of crops grown without trees ing in Alfisols of West Africa, is the combination of "sole" crops, with and without fertilization. Soil rows of leguminous trees with annual crops grown bet- chemical properties were monitored after each crop ween them. Prunings from the trees form a mulch that harvest. may aid in weed control and provide nitrogen and Trees were pruned before each planting or soon other nutrients, cycled from deep in the soil, to the thereafter, and during crop growth as needed. Pruncrops. The use of such organic additions may prolong ing biomass was measured and subsamples taken to the productivity of the acid, infertile soils found in measure dry matter and nutrients. Prunings from the much of the humid tropics. plot were divided into six equal parts; each part was
This study was conducted at the Yurimaguas Ex- spread over one spacing interval. Therefore, the periment Station. Its objectives were: 1) to assess the amount of prunings per area varied with each spacsuitability of various leguminous trees or shrubs in an ing. alley-cropping system, an assessment based on survival, Weed biomass was measured approximately two biomass production, ability to withstand repeated prun- weeks before every crop harvest. Crop yield was inings, and litter-decomposition characteristics; 2) to itially recorded by row position and fertility level. determine the appropriate spacing between tree rows, Subsequently, yield data were obtained by spacing inas it affects crop yield; 3) to study changes in soil terval, row position and fertility treatment. chemical properties and how they are affected by the Crop Rows Trees
amount of prunings added, and 4) to measure the ef- Crop R Trees
fects of pruning additions on crop yields and yield stability. A I I IFI I I
Six leguminous species were chosen: Inga edulis, 20 m I I 4.0m I
Erytbrina sp., Cajanus cajan, and Cedrelinga catenaefor- I-FK mis were obtained locally while Leucaena leucocephala I IIIIIII I
and L. diversifolia were obtained from the Nitrogen I I I IEl I I I
Fixing Tree Association (NFTA) in Hawaii. Cedrelinga I I I I [
was replaced in late January, 1985 by Desmodium I 2.BIl I I I4I I I I
gyroides, direct-seeded. I
Most species were raised from seed in the nursery F-F-]
and after four to six months were transplanted (Oc- I I I I I I I I I I
tober 1984) to a field that had been slashed, burned I. 'I
and planted with rice. C D
An experiment was established with variable alley I DI
spacings, using a randomized, complete-block design M3.5 I
and four replications. Three rows of trees were planted 1 I
in 9.5 x 23 m plots; the middle tree row was periodical- I I
ly staggered to provide six different intervals between I [
adjacent tree rows. These intervals accommodate two L to seven rows of annual crops (Figure 1). All the trees 75 cm 50cm in each plot received one of three fertility treatments: 1) none, 2) two tons lime/ha or 3) two tons lime + Figure 1. Plot design, variable spacing plots of alleyPhae whsih er a e ton, ton ae + cropping experiment. Capital letters identify spacing 100 kg P/ha, which were applied once, on an treatment.

The first rice crop was harvested in February 1984. and rice). Erythrina had been pruned once and one
Most of it was severely infected with rice blast caused rice crop was harvested.
by Pyricularia oryzae and was left in the field.
Pruning of Cajanus began in March 1984; of Inga Pruning Yields
in August 1984; and of Erytbrina in April 1985. Cedrel- Cumulative pruning yields of the alley-crop species, inga was eliminated in January 1985 and replaced with averaged over fertility treatment and replications, are Desmodium gyroides. By April 1985, biomass produc- shown in Figure 2. Yields, based on 3160 m of treetion and growth of the two Leucaena species were poor. row length per hectare, are 8.3 tons of dry matter per At this time, the average tree height per plot was hectare for Inga and 3.1 t/ha for Cajanus. Erytbrina estimated, all plants were pruned 1 m above the soil, has been pruned only once, producing slightly higher pruning yields were measured, and the prunings were biomass than Inga and Cajanus at six months of age.
placed around the trees. There was no response to lime additions, but the
L. leucocephala yielded 576, 667, and 859 kg of dry lime + P treatment, in comparison with the no-input
prunings per hectare for the no-input, lime, and lime treatment, yielded approximately 8% more prunings + P treatments, respectively; L. diversifolia prunings in Inga and 6% for Cajanus. Erytbrina appears to resaveraged 481, 384, and 438 kg/ha for the same pond to P. The lime Ca + P treatment yielded 625 treatments. While in some cases vertical growth was kg or 38% more prunings than either the no-input good, reaching over three meters, the majority of the or the lime treatment. In addition, there appears to plants appeared spindly, without much foliage. The be a positive response to increases in the clay content
Leucaenas have subsequently been eliminated from the of the topsoil in all alley-crop species.
experiment. The rate of biomass production by Inga appears fairly
By mid-August 1985, Cajanus had been pruned four constant over time and averages 8.7 t/ha/yr after the
times; four crops (corn, cowpea, rice, and rice) were first pruning. In contrast, Cajanus production averages harvested from these plots. Inga had been pruned four 1.8 t/ha/yr and appears to decline with time. Much times also; three crops were harvested (cowpea, rice, of this decrease is due to plant senescence. By January 1985, only about 65% of the original Cajanus plants S9 were still alive, indicating the need for continual
- 0 Inga replacement. Because of different establishment pracS o Cajanus tices, some species were ready for a first pruning before
SV Erythrina others.
. 7 The decomposition characteristics of the prunings
differ by species. Erythrina prunings decompose rapidly; 6 few last longer than one month. A significant proportion of the Inga prunings, on the other hand, can still 5 be observed after three months. The decomposition
o rate of Cajanus prunings is intermediate to those of
4 Erythrina and Inga.
3 Weed Control and Biomass
- Weeds were controlled by herbicide use prior to
2_ planting and hand weeding during the crop, as needced. Herbicide application before planting was the onS1 ly form of weed control used in the corn and cowpea
- _crops. Weeds in the first rice crop following cowpea 0 were controlled with preplant herbicides and two hand1I I I I I weedings; in the subsequent rice crop, all treatments
0 4 8 12 16 20 received preplant herbicides and one hand-weeding.
Months After Transplanting In addition, the Cajanus and control plots required a
second hand-weeding.
Figure 2. Cumulative pruning dry matter yields of Due to the weed-control regimens used, and the difalley crops during the first 18 months after transplan- ferent lengths of time plots have been in cultivation,
ting. Alley length: 3160 m/ha.

the most appropriate comparisons of weed-biomass for all treatments with the exception of the fertilized data are within alley-crop species. check. There are only minor differences between the
A comparison of weed biomass by spacing subplot unfertilized check, Cajanus, and Inga treatments. The for the most recent sampling (7/85) shows surprisingly Inga plots have slightly higher levels of Ca + Mg and little relation between subplot and weed biomass (Table K, but they have also been used for one less crop than 1). It might be expected that weed levels would be Cajanus. Both Inga and Cajanus have slightly higher lowest at the closest spacing due to shading and a levels of soil organic matter than the unfertilized check. greater mulch concentration, especially in the case of In an attempt to further define whether mulch adInga, which has a long-lasting mulch. The data, ditions affect soil chemical properties, the soil was however, do not appear to support this hypothesis. sampled in March 1985 by spacing sub-plot (six comThere is a suggestion that weed biomass decreases posited samples per plot) for the Cajanus and Inga with closeness to the tree rows and that the reduc- treatments. Data for the closest and farthest spacings tion is likely due to shading. The effect appears to be for each species are shown in Table 2. For Inga, the less pronounced in the Cajanus than in the Inga closest spacings, which have received 1.75 times more treatments, presumably due to less biomass and less pruning dry matter than the widest spacings, have shade production in the former, slightly higher levels of exchangeable Ca, Mg, and K.
For each alley-cropping species, there appear to be The closest spacing for Cajanus, on the other hand, significant differences in weed biomass among replica- has virtually the same soil nutrient levels as the widest tions, but the pattern over time is variable and dif- spacing. The topsoil base status under Inga is higher ficult to explain, than under Cajanus, and it appears that, at least in the
In general, weed biomass is usually higher in the case of Inga, there is some slight improvement in soil untilled, unfertilized control plots than in the alley- properties. cropping treatments. It is also interesting to note that
fertilization was related to decreased weed biomass in Crop Yields all sole-crop checks. Crop yields have been adversely affected by insects,
disease and weather. Consequently, yields are low, bear
As might be expected, the effectiveness of weed con- Table 1. Weed biomass as affected by alley crop species and trol by the prunings is less pronounced in Cajanus than by spacing sub-plot, July 1985. Inga due to the reduced quantity of Cajanus mulch Aley crop species
produced. One should note that similar levels of weed Tree biomass were measured for the Inga and Cajanus spacing Cajanus Inga Erythrina
treatments (7/1985), despite an additional hand m g/m2
weeding in the Cajanus plots requiring approximately 2.0 40+34 35+39 87+43
60 man-hours of labor. 2.5 20+26 42+32 65+55
Soil Chemical Properties 3.0 37+ 24 47+30 48+21
In general, topsoil chemical properties degrade with 3.5 43 + 42 40 + 26 58 + 23
4.0 39 +27 51 +33 57 +34
time after burning. Exchangeable cations and available 32 5 27 89+61
4.5 32 +15 36 +27 89 +61
P decrease while acidity and exchangeable Al increase,
Table 2. Effect of alley crop species and mulch application rate on topsoil chemical properties 18 months after planting tree crops (3/85).
Alley crop Alley Mulch Exchangeable Al Avail.
species spacing added pH Al Ca Mg K ECEC Sat. P
m t/ha/18 mos. cmol/L % ppm
Cajanus 4.5 2.6 4.5 1.6 0.64 0.16 0.07 2.47 65 8
2.0 4.5 4.5 1.4 0.65 0.16 0.07 2.28 61 9
Inga 4.5 6.9 4.6 1.6 0.85 0.18 0.10 2.73 59 7
2.0 11.8 4.6 1.5 1.03 0.23 0.13 2.89 52 8

little relation to treatments, and are probably not in- Peach Palm as a Soil Management
terpretable. In general, row position appears to have Option on Ultisols
an effect on yield, but it is uncertain whether these
differences are significant. The data suggest that, with Jorge Perez, INIPA
rice and cowpea, yields increase with distance from Charles B. Davey, N. C. State University
the tree rows. It may be too early in the cropping se- Robert E. McCollum, N. C. State University
quence to identify meaningful patterns. Furthermore, Beto Pashanasi, INIPA
since soil texture seems to affect yields, covariance Jos6 R. Benites, N. C. State University
techniques may be necessary to pick out trends in yield.
The production of peach palm, Guilielma gasipaes,
Conclusions has several advantages as a management option for the
1. Of the six original leguminous trees or shrubs Amazon Basin. It is indigenous and adapted to acid
assayed in an alley-cropping system, Leucaena soils, does not require yearly tillage, has been known leucocepbala, L. diversifalia, and Cedrelinga catenaeformis to remain productive for 20 years, and has potential have been eliminated due to poor survival and low as a source of fruit, heart of palm and lumber for parbiomass production. Cajanus cajan is also unsuitable quet. Results from peach palm experiments establishdue to increased plant senescence and decreased pro- ed at Yurimagaus in 1980 indicate that the crop can ductivity at about one year of age. produce fruit at the rate of 15 ton/ha/yr, beginning
2. Both Inga edulis and Erytbrina appear to have good with the fifth year. At present prices (U. S. $0.17/kg
survival and coppicing ability. Inga biomass produc- fruit), gross proceeds from a peach palm plantation protion is high (8.3 t dry matter/ha/yr, based on 3160 ducing 15 ton/ha/yr would be about S2600/ha/yr.
m of tree-row length per hectare); Erytbrina produc- Although prices would vary with production and tion must be assessed for a longer period. Cajanus, In- market conditions, the economic potential of peach ga and Erytbrina production appears to respond to P palm appears to compare favorably with paddy rice fertilization. production on alluvial soils, the most economically at3. Inga prunings resist decomposition, Erytbrina tractive option in Yurimaguas so far. Because of this
prunings are readily decomposed, and Cajanus prun- potential, several projects related to peach palm proings are intermediate in their rate of decomposition. duction have been conducted at the Yurimaguas Ex4. Weather, insects and disease severely reduced crop periment Station.
yields and made them for the most part uninterpretable. Collection and Propagation
5. A correct comparison of weed levels can only be The objectives of this work were 1) to collect and
made among spacings within a given alley-crop species maintain a permanent collection of spineless-trunk and in this study. There appears to be little relation bet- spiny-trunk peach palm germplasm from Amazonia ween weed biomass and spacing/mulching. nations in order to improve certain characteristics for
6. Soil chemical properties decline with time and higher agronomic value, and 2) to establish a
are similar in all alley-crop treatments and in the unfer- phenological calendar for each accession.
tilized check. Soil chemical properties have improved Yurimaguas is a center of origin for spineless-trunk in the fertilized check. Comparisons of the highest and peach palm. Over 120 spineless accessions have been lowest pruning-addition levels show increases in ex- collected in the area, varying considerably in fruit changeable cations at the highest mulching rates for characteristics. In addition, 80 spiney-trunk accessions Inga and no difference between rates for Cajanus. in an international collection from Brazil, Colombia
New work in this project will investigate the effect and Ecuador have been planted in an area sufficiently
of mulching, nutrient transfers between prunings and distant from the spineless collection to prevent
crops, the effects of different types of prunings, and cross-pollination.
competition between the trees and crops. Peach palm accessions have been planted in two
agroforestry sequences. The spineless collection had
an upland rice-cowpea rotation, while the spiny one
was interplanted with cassava, which yielded 10-30
ton/ha. After the cassava harvest, a ground cover of
Desmodium ovalifolium, was established.

The range in nutritional composition of fruits col- Table 1. Nutritional composition of peach palm fruits collected lected around Yurimaguas is shown in Table 1. It has around Yurimaguas. Fresh-weight basis. higher mean protein content than sweet potatoes with Parameter Mean Range
comparable values. The range indicates the possibility of selecting fruits with very high protein or fat Carbohydrate (%) 33 23.4 42.6
contents. Water (0/0) 56 52 72
Protein ( ) 4.7 3.0 12.8
Nutritional Requirements of Peach Palm Fats (0/o) 6.1 0.7 20.0
A fertilization experiment was established in peach Ash (O/0) 0.9 0.51 1.11
palms transplanted in August, 1982 in order to deter- Fiber (O/0) 1.0 0.56 1.82
mine optimum levels of N, P, K, and Mg and the Energy (cal/1 00gr) 194 126 281
response to lime and Zn in peach palm production. Ca (mg/1 00gr) 45 27 86
Trees were set at a 3 x 3 m spacing on an Ultisol with P (mg/100gr) 102 41 166
topsoil of pH 4.4, 0.1 cmol/L of Ca + Mg, 90% Al Fe (mg/100fr) 2.8 0.7 8.0
saturation and 3.5 ppm available P. The main response Thiamin (mg/100gr) 0.03 0.007 0.042
has been to N. This response was linear during the Riboflavin (mg/100gr) 0.063 0.006 0.216
second year but developed a clear optimum rate of Niacin (mg/1 00gr) 0.455 0.150 2.08
100 kg N/ha by the third year (Table 2). Trees without N showed strong chlorosis. No response to P, Mg or Table 2. Effect of applied N on the growth in height lime has been detected. Potassium responses became of peach palm. evident the second year with a clear peak at 50 kg Applied N (kg/ha)
K/ha/yr (Table 3). There was also a clear response 0 50 100 200
to 2 kg Zn/ha the third year.
Tree age (years) Tree height (m)
Cover Crops in Plantations One 0.6 1.0 1.2 1.2
This project's objective was to observe the effect of Two 1.8 2.3 3.1 4.1
different leguminous ground covers on peach palm Three 2.6 5.5 7.1 7.4
development and production. Peach palms were planted in October, 1980 at 5 x 5 m spacing in a 0.7 ha plot. Four legume covers were planted in February, Table 3. Effect of applied K on the growth in height 1982, in strips without replications. The legumes were: of peach palm. Pueraria phaseoloides (kudzu), Desmodium heterophyllum, K Applied kg/ha
D. ovalidolium and Centrosema hybrid 438. Two of the 0 50 100 200
legumes D. heterophyllum and Centrosema had disappeared, apparently because of drought and shade, Tree age (years) Tree height (m) despite the fact that sunlight passed through the peach One 0.8 1.0 1.0 0.8
palm canopy. The other two legumes were well Two 2.2 3.4 3.4 3.2
adapted, and began invading adjacent areas. Each pro- Three 5.8 7.0 6.8 4.6
duced dry matter of about 800 kg/ha/yr.
Legume ground covers showed no significant differences in their effect on tree growth. After 28 months, peach palm trunk diameter breast height (DBH) ranged from 17.4 to 18.5 cm, and height ranged from 5.0 to 6.1 m.
Three-year topsoil samples show sharp increases in
acidity and base depletion. No fertilizers or lime have been added to this field to date.

Gmelina arborea: Intercropping, Coppic- nual crops were raised in its understory. Tree growth
ing and Nutritional Requirements was retarded by cassava and the legume species, and
stunted by the grasses. The effect of the Brachiaria was
Jorge Perez, INIPA so severe that it may be allelopathic.
Charles B. Davey, N. C. State University
Robert E. McCollum, N. C. State University Soil Properties
This experiment was installed in an area which was
Gmelina arborea is a promising, fast-growing limed to pH 5.5. With time, soil acidity increased and
timber species for the humid tropics. The first stand available P declined. Reports from other regions sugin Yurimaguas was planted in April 1981, and several gest that Gmelina is a topsoil-calcium accumulator.
experiments were conducted in order to evaluate Although soil tests do not provide evidence of this hapGmelina's potential in agroforestry, including systems pening up to this time, analysis of leaves reveals a very of intercropping. The objectives of the experiments high Ca content, about triple that of pasture grasses
reported here were 1) to observe the effects of ground and leguminous plants grown at Yurimaguas.
covers on growth and coppicing behavior of Gmelina
arborea, and 2) to determine this tree's response to ap- Coppicing Behavior
plications of N, P, K, Mg, lime and Zn. When the trees were five years old, they were cut
and allowed to coppice. A cutting height variable was
Effects of Understories introduced but did not show any influence on the
Gmelina planted at a 3 x 3 m spacing grew quickly growth of sprouts. The remarkable aspect is the rate
and reached a height of over 7 m with a 10 cm of regrowth-3 m in 60 days. An upland rice crop diameter at breast height (DBH) in three and a half planted in the area grew so poorly that no yield was years (Table 1). Gmelina did not grow significantly less produced. Apparently the stump regrowth was too
when pineapple, plantain, or a rotation of three an- competitive for water and perhaps nutrients.
Table 1. Effects of understories on the growth of Nutritional Requirements
Gme/ina arborea 3.5 years after planting. The Gmelina fertilization experiment was planted
Diameter in November, 1982 on an Ultisol at pH 4.3 and 75%
at Breast Tree Al saturation in the top 15 cm. Trees were spaced at
Understory Height Height 3 x 3 m. During the first year, trees attained an average
cm m height of 4 m and a DBH of 3.6 cm. Eighteen months
None 10.0 7.4 later, average height reached 9.7 m (a growth rate of
Pineapple 11.8 7.3 32 cm per month) and DBH reached 11.2 cm. By the
Corn-rice-soybeans 11.3 6.8 third year, the canopy had closed, impeding the growth
Plantain 9.1 7.0 of weeds. Damage by leaf-cutting ants continues, but
Cassava 8.5 5.3 is not critical. Gmelina arborea is susceptible to dry
Pueraria phaseoloides 9.7 5.9 periods greater than 60 days. Such droughts cause a
Desmodium ovalifolium 8.9 5.7 general chlorosis and strong defoliation.
Desmodium heterophyllum 7.8 5.6 No significant responses to N, P, K, Mg, Zn and
Brachiaria decumbens 7.9 5.8 lime have been observed. Variability in growth is
Brachiaria humidicola 6.7 5.3 primarily related to areas that are poorly drained.

Contrasting Effect of Pinus caribaea and exchangeable Ca in the top 1 m of this soil, while Pinus
Gmelina arborea on Soil Properties caribaea decreased these parameters as well as available
P, exchangeable K, Mg and total N (Figure 1). A synPedro A. Sanchez, N. C. State University thesis of the changes in total nutrient stocks during Charles E. Russell, Institute of Ecology, the course of plantation establishment and growth is
University of Georgia presented in Figure 2. Total nutrient stock is defined
as the sum of all the nutrients in the plant biomass Reliable data are scarce on soil-fertility dynamics (aboveground, litter, detritus, roots) plus total N, under fast-growing timber species in the humid tropics. available P (by the Mehlich I method), and exThis project was conducted to complement thesis changeable K, Ca, and Mg in the top meter of the research by Charles E. Russell of the University of soil. This estimate, therefore, ignores the total P, Ca, Georgia, who sought additional soils data to quantify Mg, and K contents of the soil. the influence of Gmelina arborea and Pinus caribaea Total plant biomass decreased to about 40 to 60% plantations on soil properties of Typic Paleudults at that of the virgin rainforest at the end of the first rotaJari Florestal Agropecuiria in the state of ParA, Brazil. tion of Gmelina or Pinus. Most of the losses are quanThe discussion that follows draws on his thesis and titatively accounted for by the newly planted trees and laboratory analysis conducted at N.C. State University. the dry matter extracted by harvest.
Gmelina arborea significantly increased soil pH and
pH (soil surface) 8 Total N (tons/ha/ll00 cm)
5 Gmelina 6
Pine Pine
I I I I l I
Exch. Ca (tonslha/100 cm) Exch. Mg (tons/ha/100 cm)
0.8 ,ea0.4
0.4 0.2
Pine Ce
0 0
0.2 Exch. K (tonslhall00 cm) 100 Avail. P (kglhal100 cm)
Gmelina Gme ina
0.1 60
0 20
0.5 8.5 9.5 0.5 8.5 9.5
Years after Clearing Virgin Rainforest Figure 1. Effects of Pinus caribaea and Gmelina arborea plantings on surface soil pH and nutrient content of the top 1 m of a sandy Ultisol in Jari, Brazil.

N 120- P ecosystem, therefore, lost 40% of its total N, and then
10./ha kg/ha reached a new equilibrium.
100- 100.. i .
-H I A remarkable conservation of P is shown in Figure 80 -- H- 80- H I 2. Nutrient stocks ranged from 76 to 116% of the
60- 60 rainforest values. The decrease in P at the second rotation is largely accounted for by the P removed in the 40 40 first rotation harvest. These values reflect only the frac20 20 u, tion of total P extracted by the Mehlich procedure.
2 0 O 20 T
c 9L- CC C E Calculations from total elemental analysis of soils of
0 the Amazon by Marbut and Manifold in 1926 indicate
1.06 120 1.42 an average total P content of the top meter on the
100 t/h 100- -L92 order of 60 times the total P stock indicated in Figure
80 180 H H I Significant losses of K occur when rainforests are
60 60 i converted into tree plantations. Potassium stocks after
H clearing decreased to about 32 % those of the native
40 -- 40 forest. Most of the losses are accounted for by the
20- 20 removal of harvested trees and the rapid leaching losses
0. C a. 0 recorded during this period. After clearing, there were
Biomass Dry Matter slight increases to about 40% of the rainforest value.
Mg 541 The overall stocks and losses of exchangeable K
709 541
100 kgha 100. ha presented in Figure 2 (1.06 t/ha), however, are small
H considering the total K content of these soils, estimated
H 8 at 73 t/ha of K (Marbut and Manifold, 1926). It is
60- 60 H not surprising that research on perennial crops such
40- 40 __ as rubber and oil palm on Ultisols shows rapid depleH' otion of K and the need to fertilize the trees with this 20- = 20 L ci element.
0 L 0 & & II The calcium nutrient stock decreased to about 56%
of the rainforest value upon planting the first Pinus Figure 2. Changes in nutrient stock in fast-growing rotation. The losses were again accounted for by tree plantations on a sandy Ultisol in Jar, Brazil. harvest and slight leaching. This level remained relativeAmount equivalent to 100 indicated in t/ha. H
harvest loss; L = leaching loss; RF = rainforest; ly stable with Pinus but increased to above pre-clearing P-0.5 and P-9.5 = Pinus caribaea plantations of 0.5 levels with Gmelina (Figure 2). The second rotation and 9.5 years old, respectively; G-8.5 = Gmelina ar- started at a lower level, but much of the loss was related borea plantation of 8.5 years old; PHI = 1.5 year Pinus to the amount removed by Gmelina harvest. Losses caribaea second rotation after harvesting eight-year were slight compared to the total Ca in the top meter,
Gmelina. about 13.6 t/ha.
The magnesium nutrient stocks decrease with age
Nutrient Stocks of Pinus plantations, but mature Gmelina plantations
The plantations, of all ages, contained approximately maintained a steady level of about 75% of the level
60% of the total N stock of the rainforest. Most of in the rainforest. The 25% loss appears to be related the decrease in N occured at clearing. Because none to the harvest of the rainforest. The overall losses are of the plantation trees were legumes and no legume small relative to the total Mg content of these soils,
cover crops were used, no N buildup occurred. The about 14.4 t/ha of Mg at the 100 cm depth.

Improved Fallows is worthwhile to consider biomass accumulation, since
Lawrence T. Szott, N. C. State University nutrient immobilization is a function of both the quanCharles B. Davey, N. C. State University tity of biomass and its nutrient concentration. ConCheryl A. Palm, N. C. State University sideration of the planted-fallow biomass only shows
Pedro A. Sanchez, N. C. State University that there is little difference among treatments after
16 months. On average, living aboveground biomass Much of the land available to shifting cultivators approaches 7.5 t/ha; kudzu accumulation is about 2.5 remains idle each year, due to the long fallow periods t/ha lower, and that of Desmodium 2 t/ha greater required for secondary forests to restore the produc- (Figure 1). There are, however, differences in the rate tivity of abandoned agricultural fields. The purpose of biomass accumulation. Stylosanthes and Cajanus proof this project, which was conducted at the Yurimaguas duction, for example, is concentrated in the first eight Experiment Station, was to determine whether pro- months; that of Centrosema and Desmodium appear ductivity in such fields might be regenerated more linear with time; and a large part of the Inga and kudzu rapidly with the use of selected, high-biomass, nitrogen- accumulation occurs between eight and 16 months. fixing fallow species, and to measure the effects of these Measurements of total living aboveground biomass species on soil physical and chemical properties, weed (planted fallow plus other vegetation), on the other supression, and, subsequently, crop yield. hand, show treatment-related differences (Figure 2).
A one-hectare, 15-to-20-year-old secondary forest At 16 months, Desmodium has outperformed the on a loamy topsoil and clay loam subsoil was cut, bum- natural purina, wile the Inga and Cajanus treatments ed, and planted with upland rice using traditional are about equal to it. The biomass of the "spreading" methods in August 1983. The rice was harvested in type fallows (kudzu, Centrosema, and Stylosantbes) is January 1984, and the following treatments were in- much lower. The difference between the two groups stalled in 100 m2 plots, with four replications, in a is due to the presence of non-planted fallow vegetarandomized complete block design: Natural purma tion, primarily trees, bushes, and lianas. This vegeta(secondary vegetation); Cajanus cajan; Inga edulis; tion is naturally excluded from the "spreading" fallows, Stylosantbes guianensis 136; Centrosema macrocarpum; but has readily invaded the tree or bush fallows. It Desmodium ovalifolium 350; Puerariaphaseoloides (kud- is noteworthy that at 16 months after establisment, zu); high-input cropping check (fertilization and mechanization); low-input cropping check (without fer- 10 A Desmodium
tilization or mechanization). Stylosanthes
Changes in soil and vegetation properties during the > Ina
A Centrosema
first 16 months after fallow establishment are reported. 8 Kudzu The experiment will be continued for at least 32 ad- CU 0 Pigeonpea
ditional months, after which the plots will be prepared "
for low-input crop rotations. Crop harvest data will (n be used to assess fallow performance. u 6
Discussion .Fallows may restore the productivity of abandoned 3 4 agricultural land by one or more of the following: 1) .2 enrichment of the topsoil-vegetation system by retain- LL ing nutrients added in rainfall, dust, or mineral weather- Im ing, or by direct contributions from N2 fixation or the S 2 recycling of nutrients from the subsoil; 2) improve- ment in soil physical properties; 3) control of weeds.
Aboveground Living Biomass 0 1
The importance of possibility (1) can be ascertain- 0 4 8 12 16
ed through the construction of a nutrient budget for Months After Establishment
the topsoil-vegetation system. While complete soil and Figure 1. Living aboveground biomass of planted plant-tissue nutrient analyses are presently lacking, it fallows.

weed (grass and broad-leaf herbaceous plants) popula- fallows are similar to it. In general, the "spreading"
tions are low in all treatments and are lower in the type fallows have much less root biomass. Kudzu root planted fallows than in the natural fallows. biomass, for example, is only about 40% that of the natural purma. The large root biomass observed in the Root Biomass Stylosanthes treatment is due to the presence of a large
The pattern of root-biomass accumulation at 16 root ( >10 mm in diameter) remaining from the
months parallels that of aboveground biomass (Table previous forest. If this root is discounted, root biomass 1). No planted fallow has a greater root biomass than for Stylosanthes is similar to that of the other
the natural purma, although the Inga and Cajanus "spreading" fallows.
The quantity and distribution of fine roots, most active in water and nutrient uptake, should also taken 20.0 Desmodium into account. Moreover, their presence in significant
o ca/anus quantity in the subsoil may indicate nutrient "pump0 Inga ma r
* Sty losanthes 1mg, one means by which the topsoil-vegetation system
A centrosema may be enriched.
4 Kudzu
1 Check In general, fine root (< 3 mm in diameter) biomass
15.0 comprises around 85% of the total root biomass,
although this proportion is only 65% in the natural purma. Again, fine root biomass patterns parallel aboveground biomass--treatments with great LSD .05 at aboveground biomass also have greater fine-root
- 16 months biomass. The majority of fine roots are found in the
10.10 upper 15 cm of the soil for all species (Figure 3). Signifi0 cant quantities (- 700 kg/ha) of fine roots, however,
-m *are also found in the subsoil in the Inga, Cajanus, and
natural purma treatments. The Centrosema and Desmodium treatments contain about 500 kg of fine 5.0 roots per hectare, and the Stylosanthes and kudzu
fallows approximately half that much. Hence, the possibility for recycling nutrients from great soil depths 2.5 appears limited for the Stylosanthes and kudzu fallows.
*significantly different from the check
0 I I I Vegetation Structure
0 4 8 12 16 The speed of leaf-canopy development has a number
Fallow Age (months) of important consequences. The development of the
photosynthetic machinery affects vegetative growth .re 2. Total living aboveground biomass ac- rates and concomitantly water and nutrient uptake,
Amulation in fallow treatments. while canopy formation reduces rainfall impact and
Table 1.Total Root Biomass, by Treatment and Depth.
Treatments kg/na
Depth Centro Stylo Inga Cajanus Kudzu Desmo Check
0-5 1074ab 585 b 748 b 1268ab 949ab 998ab 2014a
5-15 576 b 1776a 1019ab 478 b 262 b 621 b 891ab
15-30 256 768 499 457 134 399 297 ns
30-50 234 383 543 515 110 170 563 ns
Treatments significantly different (0.05) from the check at given soil depths are shown by different letters.

Fine Root Biomass (kg/ha) 24 hours after fairly heavy rainfalls. Depending as it
does on the amount and intensity of rainfall and the
100 200 400 600 800 1000 initial moisture status of the soil, a comparison of field
0,] capacity over time may not have the validity of com5 parisons among treatments at a given time. For all
] fallows, field capacity at 16 months is greater than or
g equal to that measured at field abandonment.
"15 However, there are few treatment-related differences
in the values at a given time. At 16 months, field
capacity for Desmodium and Inga is lower, and higher
0a for Centrosema, than that of the purma. Few differences
among treatments are observed in infiltration rates
5 30 measured at 16 months. Differences, if present, may
be obscured by variability in the data. All planted
fallows, with the exception of Stylosantbes, have inQ filtration rates that equal or exceed that of the natural
N 2 purma.
50 Soil Chemical Properties
Figure 3. Fine root (less than or equal to 3 mm diam.) Soil chemical data for the first eight months after with soil depth. Treatments differing significantly establishment indicate a reduction with time in ex(.05) in fine root biomass, at given soil depths, are changeable Ca + Mg and available P levels in the topshown. The average biomass is shown when there soil. Topsoil K, on the other hand, increases during are no significant differences when comparisons are the first four months, probably due to K release from made across treatments. the decomposition of 2 t/ha of rice straw. It soon
declines to levels similar to those measured at fallow
the potential for erosion, as well as moderating the establishment. The reduction in topsoil nutrients can soil microclimate. Indicators of foliage development probably be attributed to plant uptake and immobilizaare the leaf-area index (LAI) and the percentage of tion in the biomass. The lack of significant differences ground cover, among treatments in soil chemical properties can proIn general, LAI correlates well with increasing bably be attributed to all treatments having similar biomass, although Centrosema and the natural purma biomass at eight months, and the relatively short time have lower LAIs at 16 than at eight months, and ranges span during which measurements were recorded. between four and eight at 16 months. It is also notable There seems to be a direct relationship between topthat all fallows develop a fairly high LAI (LAI = 5-6) soil organic matter and available P contents. Both and an almost complete ground cover within four to parameters increase after burning, drop precipitously eight months after establishment for all fallows. during the first eight months of fallow, and increase afterwards.
Soil Physical Properties
Soil physical properties are affected by vegetation Table 2. Representative values for topsoil bulk density, field growth and development and associated changes in the capacity (0-15 cm) and infiltration rate at various times followphysical environment. Changes in soil physical pro- ing fallow establishment. perties are shown in Table 2. Bulk density, while in- Months After Establishment
creasing in the first eight months after field abandon- 0 8 18
ment, appears to decrease to pre-cultivation levels by
16 months. Generally, the treatments with a high fine- Bulk Density (g/cm3) root biomass (purma, Cajanus, Inga) have lower bulk 0 7.5cm 1.16 1.19 1.11
densities than those with little fine-root production 7.5-15 cm 1.32 1.33 1.24
(kudzu). These differences are not statistically signifi- Field Capacity (% H20) 26 28 29
cant, however. Infiltration Rate
Field capacity (see Table 2) was measured in the field at 3 hrs (cm/hr) 19

Weed Control A Desmodium
As noted previously, all planted fallows are successful o cajanus
at controlling grasses and broad-leaf weeds (Figure 4). 7.0 0 Inca
The best and quickest weed control is afforded by the 0 St}tosanthes
"spreading" type of fallow. In effect, these fallows 6.0 # Kudzu
screen out almost all other types of vegetation. The El Check
bush- and tree-type fallows, while allowing a somewhat /
greater invasion of weeds, also permit the establishment of other bushes and trees, resulting in greater
total biomass in those treatments. This may be advan- 4.0
tageous in that more biomass may result in greater
nutrient immobilization. Moreover, a mixture of C 3.0
vegetation types may exploit the soil more complete- E
ly. Furthermore, as observed in the fine-root biomass 2
data, treatments with significant quantities of tree, bush 2.0
and liana biomass not only tend to have more fine
roots, but also the roots are encountered at greater 1.0
soil depths, thus raising the possibility of the recycl- "
ing of nutrients from the subsoil.
Comparisons With Continuous Cultivation 0 4 8 12 16
Grain yields for the mechanically incorporated fer- Fallow Age (months)
tilizer treatment are about double those from the unfertilized plots 10 t/ha vs. 6.3 t/ha (Table 3). *significantly (.05)different from check treatment
However, it is significant that the latter treatment con- Figure 4. Changes in weed biomass with time in
tinues to yield reasonable quantities of grain two years fallow treatments.
after clearing. Similar phenomena have been observed elsewhere at the Yurimaguas Experiment Station continuous-cultivation treatments. This is expected in and suggest that factors other than the decline in soil the fertilized treatment due to periodic nutrient addifertility weed control, for example are critical tions. In the unfertilized, continuously cultivated treatto a farmer's decision to abandon his land. ment, the level of nutrient removal via harvest, which
In comparison with the fallows, soil chemical pro- may be likened to long-term nutrient immobilization
perties are more favorable to crop production in the in the fallows, is likely to be much less. For example, only the nutrients contained in 6.3 t grain/ha have Table 3. Grain yield from continuously cultivated plots included been removed from the cultivated plots vs. the nutrients in the managed fallow experiment, contained in 8 to 17 t biomass/ha in the fallows.
Date Furthermore, decomposition of soil organic matter and
Crop Harvested Treatment Grain Yield crop residues releases nutrients to the soil. With time,
__ t/ha__ of course, soil nutrient levels in the cultivated, unferRice 01-14-84 None 2.82 + .38 tilized treatment should approach or decrease below
Corn 06-04-84 Fertilized 0.93 + .32 that of the fallows due to continued nutrient removal
Unfertilized 0.44 + .11 during harvests, a reduction in the quantity of nutrients
Cowpea 08-29-84 Fertilized 0.86 + 0.21 recycled as plant production declines, and leaching
Unfertilized 0.48 + 0.14 losses.
Rice 12-30-84 Fertilized 2.3 + 1.0
Unfertilized 1.0 + 0.4
Rice 05-14-85 Fertilized 1.91 + 0.45 Conclusions
Unfertilized 0.82 + 0.19 Comparisons of the rates at which natural and imCowpea 07-30-85 Fertilized 1.26 + 0.58 proved fallows restore productivity can be based on
Unfertilized 0.76 + 0.36 soil physical properties, the quantity of nutrient stocks
Total Grain Production Fertilized 10.08 in both soil and biomass, the weed population, and
Unfertilized 6.32 crop yields after the fallow. Considering these factors,

the following conclusions can be drawn: Forest and Soil Regeneration
1. Physical properties improve with time under all
fallows, and there are few treatment-related differences Lawrence T. Szott, N.C. State University in infiltration rate, field capacity or topsoil bulk den- Charles B. Davey, N.C. State University sity. Field capacity and topsoil bulk density improve Jorge Perez, INIPA with time, the bulk-density values at 16 months ap- Cheryl A. Palm, N.C. State University
proaching those following clearing.
2. Available nutrient levels in the topsoil decrease The period of vegetative regrowth following the with time in all treatments, except continuous cultiva- abandonment of agricultural fields has often been tion, probably due to immobilization in the biomass. credited with the restoration of site productivity. SurBiomass nutrient stocks are determined by the quan- prisingly, there have been few studies of soil and vegetatity of biomass present and the concentrations of tion dynamics in shifting cultivation fallows, even nutrients in the tissues. though such studies are necessary for an understan3. After 16 months of growth, total biomass ac- ding of how the most common agricultural produccumulation is highest in the bush or tree fallows (ap- tion system in the humid tropics functions, and may proximately 14 t/ha) and lowest in the spreading types point the way to potential improvements in the system. (approximately 7-10 t/ha). The natural purma biomass Therefore, two complementary projects, addressing difis 14.1 t/ha. High biomass in the bush or tree fallows ferent aspects of old field secondary succession, were is due primarily to the invasion of trees, since the undertaken. One compared secondary successional sites planted-fallow biomass is similar in the majority of of different ages but similar soils (Udults), in order to treatments at 16 months, about 7 t/ha. These dif- determine how soil properties and vegetation strucferences in total biomass are accentuated with time. ture and composition change over fairly long periods
4. Planted fallow biomass accumulation was greatest of time. The other project is a long-term study, at a in Desmodium (9.7 t/ha) and least in Cajanus (5.1 t/ha). single site, of the effects of different levels of soil ferThe difference between total and planted fallow tility on secondary succession in an abandoned biomass is due to the presence of other vegetation, agricultural field. primarily trees. The two studies are complementary in the sense that
5. Foliage development and the establishment of an they address different aspects of old field secondary almost complete ground cover occur within four to succession: how soil properties and vegetation change eight months in all treatments. over fairly long periods of time, and how soil fertility
6. Weed control is better than the natural purma affects these processes. They physically complement except for Cajanus cajan in all planted fallows. Con- each other in that the non-fertilized control plots in trol is quickest and most effective with the "spreading" the fertility study have been used to provide data points fallow types. in the study of different-aged purmas.
7. Based on biomass production, fine-root production and distribution, weed control, and changes in Soil and Vegetation Dynamics soil properties, Desmodium may serve as a good short- In Shifting-Cultivation Purmas term (16-month) fallow. Desmodium, Centrosema, or Three purmas within approximately 1 km of one Stylosantbes may be suitable for fallows of eight months, another were identified. According to their owners, all were previously farmed in the traditional manner
and had suffered little disturbance since abandonment.
The purmas were approximately three, seven and 11
years old. A fourth purina, nearby, used for the undisturbed check plots of the fertility study, was included
to provide data for purmas of age zero (field abandonment) to 17 months. Soil texture in all the purmas
appeared similar, and are classified as sandy loams. Further analysis revealed that the zero-year purma had
a lower clay content, with a classification of loamy

The older purmas were sampled during a two-month period. Soil properties measured included infiltration Trees rate, bulk density, field capacity, pore-size distribution,
60 organic-matter percentage, pH, exchangeable Al, and
nutrient contents (exchangeable Ca + Mg, K, and 40 available P). Biomass estimates of above-ground vegetation, litter, and roots to a 50-cm depth were also ob20 -tained. Subsamples of each vegetation component were taken for nutrient analysis and included tissue samples 5 of all trees greater than 2.5 cm DBH (diameter 1.4
m above the ground), by species. Heights and diameters of all trees greater than 2.5 cm DBH were also measured.
u) Changes in Biomass
E Changes in living above-ground biomass are shown
.2 in Figure 1. Biomass accumulation shows a typical
2 Lianas growth curve with a decline after seven years. The
average rate of biomass accumulation, 6 t/ha/yr, is a bit low for humid tropical forests, which average around 10 t/ha/yr. The seven-year-old purma, however, accumulated biomass at a rate of 8.3 t/ha/yr. Herbaceous In general, grasses dominate during the first year of Weeds
succession and decrease thereafter, presumably due to shading by trees and other vegetation. The biomass Grasses of lianas appears to increase in the early years of succession, maintaining itself at around 2 t/ha thereafter. Tree biomass, while low during the first year, increases
rapidly thereafter and composes the majority of the total biomass after three years. Recruitment of trees Purma Age (years) into the population, as represented by the understory
(trees < 2.5 cm DBH) biomass, remains fairly conFigure 1. Changes in aboveground biomass with time stnwihim(aot15/a)
by vgetaion ype.stant with time (about 1.5 t/ha). by vegetation type. Root biomass, down to a 50-cm depth, is shown
in Figure 2. Discounting roots having diameters greater than 10 mm, root biomass appears to increase with time. The large quantity of roots and the number of
Table 1. Changes in purma vegetation structure with time after large roots found at abandonment likely represent remadandoment. nants of the previous forest. It is generally cited that
root biomass is usually about 20% that of the aboveTime After Dominant Area ground living biomass. Clearly that is not the case here,
as root biomass declines from 39% at 17 months of Abndn n H + nde8 + .7 58+17 age, to 21%, 10% and 9% at three, seven and 11 years
0 1.35 + .28 1.4 + .7 58 + 17 of age, respectively. Root turnover, which may be rapid
4 mo. 2.28 + .29 3.6 + 1.1 93 + 12 and hence contribute greatly to production estimates,
8 mo. 3.56 + .47 6.3 + 1.5 98 + 5 was not measured.
17 mo. 4.04 + .51 4.8 + 1.3 98 + 5 The standing-crop biomass of fine roots-those most
3 years 5.99 + 1.52 not measured important in the uptake of water and nutrients-is also
7 years 12.89 + 1.39 not measured shown in Figure 2. In general, fine root biomass in11 years 14.68 + 2.24 not measured creases with time. This pattern is maintained to a soil
depth of 30 cm; at greater depths, all purmas, regardless

of age, have similar fine root biomass. In general, fine kglha
root biomass declines with depth. The majority of the 0 300 600 900 1200 1500 1800 2100 fine roots are in the upper 15 cm of the soil, while 0 1 1 1 Aki I I I t
very few are found at depths greater than 30 cm.
Changes in Vegetation Structure 5
Rapid changes in vegetation structure occur during the first 17 months (Table 1). Foliage development, as measured by the leaf-area index (LAI) and percentage of ground cover, occurs quickly. Within eight 15 months there is almost complete ground cover and a fairly high LAI. The decrease in LAI between eight E and 17 months is probably due to the senescence of ,. 0
grasses, herbs, and many of the dominant, short-lived 0. 0 3 yr
trees. At the same time, early vertical growth of trees 7 yr
z 11 yr
is extremely rapid (5.33 m/yr at eight months), even- 30 tually decreasing to an average growth rate of 1.33 n m/yr at 11 years.
These changes have a number of important conse- Purma Root Biomass (kglha) to 50 cm soil depth
quences. The development of a multi-layered canopy Age (yr) All Roots Fine Roots (< 3mm diameter
will tend to moderate soil temperature and humidity 0 5,070 1,058
1.4 3,350 2,922
and buffer any changes in these environmental 3 3,400 2,474
tedcmoiin7 10,310 2,858
variables. Microbial activities and the decomposition 7 5,790 3,706
of organic matter may also be affected. The development of a high photosynthetic potential also allows 50 A rapid growth to occur and, with it, a high demand for water and nutrients. Nutrients arriving at the roots, Figure 2. Distribution of fine-root biomass in purmas via water uptake and diffusion along concentration gra- of different age. dients, and their uptake in the biomass, are a conservation mechanism by which losses in leaching, runoff, sent in the three-year-old purina, however, are also or erosion can be reduced. found in the seven- or 11-year purmas, indicating a
very rapid species turnover or nonhomogenous plant Diversity population distributions. The only genera in common
The diversity of the purmas, i.e., the number of to the three-, seven-, and 11-year-old purmas were genera of trees greater than 2.5 cm DBH present, ap- Cecropia (cetico), Inga (shimbillo) and Pollalestra pears to decrease with time. The three-, seven- and (yanavara), and these accounted for 60%, 62.5% and 11-year-old purmas contained 60, 56, and 51 genera 3 9.2% of the individuals in the three-, seven-, and per sampling unit, respectively. Very few genera pre- 11-year-old purmas, respectively. Apparently, although
Table 2. Effects of purma age on topsoil field capacity, infiltration rates and bulk density (g/cm3 using Uhland cores).
Field Capacity Infiltration Rate Soil Depth (cm)
Purma Age 0-15cm at 3 hrs. 0-7.5 7.5-15
% cm/hr g/cm3
0 14.0 + 2.2 1.36 + .07 1.53 + .03
17 ma. 14.9 + 1.91 53.9 + 8.41
3 yrs 16.0 + 0.8 22.2 + 13.4 1.28 + /10 1.48 + .11
7 yrs 19.1 + 2.7 29.9 + 5.8 1.18 + .05 1.35 + .10
11 yrs 16.0 + 1.3 24.8 + 21.9 1.21 + .13 1.42 + .13
1 Measured at 15 months.

the number of genera present may decrease with time, Soil Chemical Properties
dominance also decreases. In general, topsoil acidity, as measured by pH value,
and exchangeable Al, both increase with time (Table
Soil Physical Properties 3). There is a suggestion that exchangeable nutrient
Bulk density was measured using two different cation levels in the topsoil decrease. A fairly large
methods, Uhland cores and the excavation of a known decrease in cation levels appears in the first year after volume of soil. Results obtained using Uhland cores abandonment. This is followed by a period (six to seven suggest that topsoil bulk density decreases with time, years) of little change in the exchangeable cation conthe greatest change occurring in the first year or two. tent of the topsoil before a subsequent decrease is The bulk density in the seven-year old purina is a bit observed in the 11-year old purma. A similar pattern low and may be due to the lower sand content in this is observed at the 15-30 cm soil depth, while little soil. The excavation method shows similar results. Bulk change with time occurs at depths greater than 3 0 cm.
density at the 0-7.5 and 7.5-15 cm soil depths generally A number of factors make the interpretation of this decreases with time, presumably due to organic-matter pattern rather difficult. It is unclear, for example, additions and root growth. At greater depths, however, whether the changes observed in the purmas of difsoil bulk density is higher and does not appear to ferent ages are, in fact, due only to the growth of the change significantly with time. vegetation and passage of time, or whether there are
Topsoil field capacity, measured in the field approx- significant differences in such things as site history and
imately 24 hours after a heavy rainfall, appears to in- clay mineralogy. Additionally, there is a fair amount crease slightly with time (Table 2). Once again, the of variability in the data, especially in the results for higher value for the seven-year-old purma may be due the seven-year old purma, which obscures trends and
to the lower sand content and, hence, macropores in makes interpretation difficult.
this soil. Infiltration rate was measured in the field using The decline in topsoil nutrients during the first year a double-ring infiltrometer. There are probably no can probably be attributed to nutrient immobilization significant differences in infiltration rates for the three-, in living biomass (6.3 t/ha above ground) and leaching seven- or 11-year-old purmas (see Table 2). The rate losses. After this decline, topsoil nutrients appear to measured at 17 months is significantly higher and is change little for six years, while living above-ground probably due to the high sand and low clay content biomass increases nine-fold during the same period.
of this soil. It is likely that the nutrients sustaining this growth are
Table 3. Changes in soil chemical properties with time after abandonment.
Soil Months After Abandonment Years After Abandonment
Parameter Depth 0 4 10 3 7 11
pH 0-15 5.1 + .2 5.0 + .3 4.8 + .1 4.8 + .2 4.6 + .1 4.5 + .2
15-30 4.4 + .1 4.5 + .1 4.6 + .04 4.7 + .1 4.4 + .1 4.5 + .2
30-45 4.4 + .1 4.6 + .04 4.8 + .1 4.5 + .1 4.8 + .1
Exch Al 0-15 0.2 + .3 0.9 + .3 0.8 + .4 0.6 + .1 1.8 + .4 1.1 + .3
(cmol Ll) 15-30 1.3 + .4 1.6 + .4 2.0 + .8 1.6 + .4 3.4 + .6 2.2 + .7
30-45 1.7+3 2.5 + .4 2.3 + .4 3.3 + .6 2.8 + .6
Exch Ca* 0-15 1.3 + .9 0.8 + .3 1.0 + .2 1.0 + .2 1.2 + 15 0.5 + .2
(cmol Li) 15-30 0.5 + .1 0.4 + .1 0.5 + .1 0.5 + .1 0.5 + .1 0.4 + .1
30-45 0.3 + .1 0.4 + .1 0.3 + .1 0.4 + .1 0.3 + .1
Exch K 0-15 .10 + .07 .07 + .03 .09 + .02 0.9 + .02 .11 + 01 .08 + .01
(cmol Li) 15-30 .08 + .05 .07 + .03 .08 + .03 .06 + .01 .07 + .02 .06 + .02
30-45 .06 + .03 .075 + .02 .06 + .01 .07 + .02 .05 + .01
Avail P 0-15 14 + 4 8 + 2 7 + 1 5 +1 5 + 1 4 + 1
(ppm) 15-30 7 + 2 4 +2 4 + 1 3 + 0 2 + 1 2 + 1
30-45 4 + 1 3 + 1 3 + 1 2 + 1 2 + 1
* Values for exch Ca for 0 and 4 months are exch. Ca + Mg.

Table 4. Changes in soil organic matter with time.
Soil Depth Months After Abandonment'
(cm) 0 2 9 12
______________________% organic matter _____________0-5 2.11 + 1.00 1.25 1.34 + .37 1.69 + .50
5-15 1.50 .46 0.96 0.95 + .17 1.20 + .11
15-30 1.26 + .18
Soil Depth Months After Abandonment
(cm) 0 36 84 132
0-15 2.07 + .40 1.05 + .13 1.67 + .19 1.21 + .20
15-30 1.26 + .18 0.63 +.06 0.84 + .32 0.85 + .23
30-45 0.44 +.24 0.83 + .17 0.50 .17
45-100 0.23 + .09 0.65 + .11 0.29 + .10
1 0-12 month data were measured at the same site; 3-, 7-, and 11lyear-old data are from different sites.
provided by atmospheric inputs and the decomposi- should be attributed to a growth phase common to tion of organic matter in and on the soil, and this stage of succession, or to differences in sites. Data retranslocation within the vegetation itself. A build- show that the site of the seven-year-old purina was up in soil organic matter, presumably due to litter fall, less sandy and somewhat more fertile than the others. between three and seven years is observed (Table 4). 5. A number of questions remain. The effect and Changes in the biomass of the forest floor have been importance of changes in soil physical properties on measured, but the data are not available at this time. vegetation growth remain largely unknown, as does
In any case, further analysis, including the contribu- the effect of soil fertility on biomass production and tion of atmospheric inputs and the construction of a vegetation composition. The relative importance of nutrient budget, is needed. atmospheric inputs, N fixation, soil organic matter,
and litter as sources of nutrients for developing vegetaConclusions tion is likely to vary according to soil type, and these
1. Secondary succession is in general very dynamic. factors also need further evaluation. It Is important Pioneer vegetation quickly establishes its photosyn- to conduct long-term studies at permanent sites, in thetic material and a soil cover. Photosynthesis and order to avoid the problems created when site and time transpiration set up soil-water and nutrient gradients are confounded. that enable rapid biomass accumulation and nutrient
immobilization in the biomass. Effect of Soil Fertility
2. Rapid vegetation growth affects soil properties On Shifting Cultivation Fallows
through root growth and turnover, organic matter ad- The purpose of this study was to answer some of ditions, vegetation-mediated changes in soil the questions regarding the effect of soil fertility on
microclimate, and the canopy's ability to reduce the secondary succession in abandoned agricultural fields. impact of rainfall on the topsoil, all probably con- Specifically, the study was designed to quantify the tributing to the decrease in bulk density and improv- size of potential or actual nutrient pools in an abaning the retention of soil moisture. It is interesting to doned agricultural field, and to investigate the effects note that where root biomass is similar, bulk density of soil chemical properties on secondary succession by is also similar. And, while differences in sand content manipulating soil fertility. may influence the increase in field capacity over time, A 0.5 ha abandoned field that had been cropped this increase during the first fifteen months agrees well with a rice-corn mixture was sampled on 24 plots of with increases in soil organic matter over the same 64 m < 2. Analyses included total soil nutrients to period. a 1 mn depth; exchangeable Al, Ca + Mg, K; available
3. Nutrients become impoverished in the topsoil over P contents in the upper 100 cm; and soil organic time, largely as a consequence of nutrient uptake and matter. immobilization by vegetation. Biomass measurements and subsamples for nutrient
4. It is unclear whether the higher biomass accumula- analysis were obtained for litter, crop residue, and living tion and productivity of the seven-year-old purina vegetation. The leaf-area index (LAI), average heights

of the five dominant individuals per plot, and percen- ing K or Mg entrapped in the interlayers. These tage of cover were also measured. nutrients are, for the most part, probably unavailable.
Three rainfall collectors were installed, as well as It has been reported that, after kaolinite, vermiculite
six zero-tension leachate collectors. The lysimeters were is the next most common soil mineral in the
placed in zones of textural change, usually between Yurimaguas soils.
15 and 20 cm depth. In general, the total quantity of nutrients in the soil
Soil physical properties-texture, bulk density, field appears sufficient to support more than one crop
capacity, and pore size distribution-were also sampled. harvest. However, the slow release of minerals into
After the initial sampling, four fertility treatments plant available forms and the possibility of Ca defiwere established: 1) undisturbed controls, 2) litter ciencies or Ca/Mg imbalances would probably removal, 3) litter additions (the equivalent of 3.25 t negatively affect crop productivity. Moreover, available of rice straw and 17.4 t of wood per hectare) and 4) nutrient levels in the topsoil, while not high, generalfertilization with 100 kg P/ha, 100 kg N/ha, 100 kg ly appear sufficient, although K availability may be K/ha and and 50 kg Mg/ha. a limiting factor. The existence of large total nutrient
Soil and vegetation dynamics were studied by means pools deep in the soil profile, on the other hand, raises
of periodic measurements. These included: topsoil the possibility of nutrient "pumping" by deep-rooted
organic matter approximately every two months; ex- plants.
changeable Al, Ca + Mg, K; available P; pH at four, Preliminary analyses of atmospheric inputs suggest ten and 1 7 months after abandonment; topsoil bulk that inputs may be sizeable for K, Na, and Ca, but density at zero, ten and 1 7 months after abandonment; may be within the range reported in the literature. An field capacity at 0 and 15 months; infiltration rate at unexplained anomaly is the rainfall pH value of 6.9.
17 months; and pore size distribution at zero, ten and Rainfall should have a pH of around 5.5. A higher 17 months. The heights of the five dominant in- pH value may indicate contamination. In any case,
dividuals per plot, LAI, % cover, and biomass (weight atmospheric inputs fall far short of supplying the and nutrient concentration by vegetation type, i.e., nutrients needed for continual crop production. Adgrasses, lianas, herbs, and trees) were measured at zero, ditions over a ten-year period, however, may be suffour, ten and 17 months. Root biomass down to a ficient to support one or two crop harvests, assuming
50 cm soil depth was measured at one and 1 7 months, total nutrient conservation and similar atmospheric inRainfall and leachate samples were collected within put levels for all years.
two days after a rain, the quantity collected was The importance of large and small litter pools premeasured, and a subsample was taken for chemical sent at abandonment cannot be assessed at this time analysis. due to the absence of nutrient analyses of litter. Considering that litter biomass ranges between approxNutrient Pools imately three and 11 t/ha, litter decomposition may
Soil total nutrient analyses are shown in Table 5. supply large quantities of nutrients to vegetation
The increase in nutrients observed in the 15-60 cm regrowth.
horizon is due to an increased clay content. The In comparison to nutrient additions, leaching losses
relatively large amounts of total K and Mg reported appear relatively small. Losses were greatest for K, as may be due to the presence of vermiculite-like minerals might be expected based on its chemical characteristics.
having imperfect substitution or Al oxide minerals hay- In general, leaching losses varied by treatment. Losses were greater in those treatments with larger quantities
Table 5. Total soil nutrient stocks present at field abandoment of available nutrients. (mean of three replications).
Depth (cm) Kjeldahl Ca Mg P K Vegetation Dynamics
In general, a great deal of with in-treatment variability
kg/ha is observed in the measurements of living above-ground
0-15 857 292 361 173 669 biomass (Table 6). In many cases, coefficients of varia15-60 2410 67 1264 613 3507 tion are 100% or more. Such variation is due to the
60-100 1431 25 1041 505 2393 1clumpy" nature of vegetation distribution and the
quadrat sampling techniques used. Such variability
obscures trends and makes interpretation difficult.

Table 6. Changes in living aboveground biomass following field adandonment (kg/ha).
Broad-leafed Trees, Trees, Crop
Treatment* Grass Weeds Lianas <2.5cm dbh >2.5cm dbh Remnants
1 Month After Abandonment
1. 28 43 214 108 0 2590
2. 28 35 447 821 0 2113
3. 204 34 249 234 0 2617
4. 210 203 99 272 0 2030
4 Months After Abandonment
1. 928 165 445 763 0 144
2. 520 361 421 531 0 511
3. 1029 477 894 825 0 147
4. 1006 449 1555 3243 0 72
10 Months After Abandonment
1. 3372 628 741 1539 0 0
2. 2085 89 382 720 625 0
3. 2190 54 241 1300 1475 0
4. 2394 549 315 1211 9150 0
17 Months After Abandonment
1. 2467 14 1481 1745 1841 0
2. 2775 177 287 2934 5562 0
3. 1072 72 616 872 5037 0
4. 456 346 638 2217 7038 0
Key to Treatments: 1) Natural secondary succession control; 2) residue removed; 3) residue added; 4) fertilized.
A number of patterns in biomass accumulation are 14 apparent, regardless of fertility treatment (Table 6 and Figure 3). Above-ground living biomass decreases during the first four months after abandonment as crop 12 plants remaining after harvest senesce. The crop plants Treatment are quickly replaced by grasses and trees which are -Cal codominant for a while. The grasses eventually E decrease in biomass as tree biomass continues to in- Cn 0 4 crease both absolutely and in relative importance. Her- E baceous weeds and lianas, although present, are of .2 much lesser importance. Their biomass generally peaks .~8 between four and eight months and decline thereafter. M
There appear to be very few treatment-related differences in biomass accumulation. Up to ten months > 6
after abandonment, total above-ground living biomass is similar in the undisturbed check and the residue 0) treatments. Biomass levels, considered by vegetation S~ type, are also similar across these treatments. During this period, however, greater biomass levels were recorded in the chemically fertilized treatment, primari- 2 ly due to a greater tree biomass. These differences may0 4 8 12 6
not be significant due to variability in the data. Moth Afe Abandnmen
Biomass measurements at 1 7 months show little dif- Mnh fe bnomn
ference between the check and residue-addition Figure 3. Changes in living above-ground biomass treatments, while the residue-removal and chemical- with time.

2.4 -ly fertilized treatments have similar levels of biomass, averaging 2-3 t/ha more than the check. The data sug2.2 -gest that tree growth responds quickly to chemical fertilizer additions. There is little difference among treatments in topsoil or subsoil chemical properties at 2.0 -Treamentten months, with the exception of higher P levels in 0 1 the chemically fertilized treatment. This suggests that
0 2 the nutrients which were added were lost either in surF 1. 3 face runoff or erosion, converted to an unavailable
1.- form, or immobilized in litter and biomass. The latter possibility, at least, can be investigated via nutrient1.6 budget calculations.
g Soil Organic Matter
o 1.4 -Topsoil (0-5 cm) organic matter declined in the first cn six months after the field was abandoned, but increased
from six to 12 months (Figure 4). There was no ap1.2 -parent effect of the different treatment. Similar but less marked changes were also observed in the 5-15 cm layer.
1. The recovery of vegetation in an abandoned 0.8 -agricultural field appears to respond to the application
0 2 4 6 8 10 12 ofl100kgN,l100kgK,l100kgP, and 50kgMgper
Monts Afer Aandomenthectare. This response is mainly apparent in increasMonts Afer Aandomented tree growth. Despite differences in tree growth, Figure 4. Changes in soil organic matter with time there was little effect of treatment on soil physical or (0-15 cm). chemical properties. This suggests the amounts of
nutrients added or removed in vegetation residue is small relative to soil pools and that nutrients added via the application of fertilizers may only be available to the vegetation for a short period of time before they are taken up, leached, or converted to chemical forms unavailable to plants.
2. Further work is needed on the quantity and rate of release of nutrients from soil pools as well as inputs to and losses from these pools.

New-Project Update
This project has not been under way long enough to yield substantive reports, but should be mentioned because of its importance to the program as a whole.
Comparative Soil Dynamics Collection and Propagation
Julio C. Alegre, N. C. State University Of Agroforestry Species
Pedro A. Sanchez, N. C. State University Angel Salazar, INIPA
Luis Arevalo, N. C. State University Jorge Perez, INIPA
Jorge Perez, INIPA Cheryl A. Palm, N.C. State University
Manuel Villavicencio, INIPA Alwyn Gentry, Missouri Botanical Garden
Kenneth MacDicken, University of Hawaii
This project, established on a tract of ten-year-old
secondary forest at the Yurimaguas Experiment Sta- Most tree and shrub species used for agroforestry tion, compares the effects of various crop-management in the humid tropics are successful in high base status systems on changes in the physical, chemical and soils. This project seeks to identify species that can sucbiological properties of an Ultisol upon clearing. The ceed on acid soils. There was progress during 1985 experiment consists of six management options as in several areas: treatments, which are: 1) shifting cultivation, with plots 1) At Yurimaguas, seed of eleven legumes with contracted out to a farmer who planted upland rice potential in agroforestry were collected, identified and intercropped with cassava and plantain; 2) mechaniz- planted at the nursery. ed continuous cropping, with corn and soybean, on 2) Some 200 trees, shrubs and vines, collected a plot cleared with a tractor and straight blade, then around Yurimaguas during a survey by the Flora of logged, burned, disked and fertilized according to soil- Peru Project, are being identified. test recommendations; 3) low-input technology, in 3) A trial to evaluate trees for alley-cropping was which a rotation of two crops of rice followed by established, with eight of twenty tree species planted. cowpea will be carried out until productivity declines; The trees will be studied for survival, growth rate, then it will be placed in managed fallow; 4) combin- regrowth after pruning, biomass production and ed tree and crop production, with rice interplanted nutrient accumulation. with tornillo (Cedrelinga catenaeformis), and Inga edulis 4) In collaboration with the Nitrogen Fixing Tree planted between the Cedrelinga; 5) peach palm Association (Hawaii), a site was prepared for a trial (Gulielma gasipaes), interplanted with the first crop in designed to measure biomass production and N aca sequence of rice, rice and cowpea; and 6) a forest cumulation in species considered strong N-fixers on fallow check, in which the plots were not disturbed, acid soils.
Plots were sampled before and after clearing, and after burning. Soil chemical, physical and biological properties are being monitored intensively.

New-Project Update
Living Fences Llambo pashaco
Jorge Perez, INIPA For this species, 2.5 m stakes were used. Seven days
Jos6 Benites, N.C. State University after planting, 80% of the stakes had sprouts, but the
vigor disappeared quickly and all stakes died.
The objectives of this project are 1) to determine
the most suitable tree species for use in living fences, Huina caspi
and 2) to test the idea that living posts, sprouted from This species grows on upland soils. It is traditionalstakes or poles, could persist on acid soils, reducing ly used as fencing material in the gardens of pueblos the high cost of fence maintenance on farms in the jovenes of Yurimaguas. The same experiment was carhumid tropics. ried out as with mullohuayo, using 0.5 m and 1.0 m
Research was begun at Yurimaguas with three pro- stakes. Results were negative because the macroporosimising species: mullohuayo (Seca floribunda), llambo ty of this species allows a very quick loss of its water pashaco (Eslorabium sp.) and huina caspi (genus and content. Ninety days after planting the survival rate species unknown). was 82%. At 180 days after planting, only 26% of
the living plants were found. The causes of mortality Mullohuayo are not known but sprouts began drying and fell from
Sprouting percentage was determined with 0.5 or the trunks.
1.0 m long mullohuayo stakes as a function of days Further study will test ways to stimulate rooting of storage after cutting. and rapid growth. Native legumes with a high potenOver 80% sprouting was achieved with seven-day- tial for vegetative propagation will also be tested in
old stakes of either size. Similar results were obtained the living fences.
with 2.5 m long stakes.

Continuous cropping is in many ways an attractive system to those in the humid tropics who seek to produce more food on less land, conserving natural forests while developing a more stable agricultural base. Research has shown that the effective use of modern fertilizers and lime can dramatically increase crop yields in the acid, infertile soils of the humid tropics. Before this technology can be applied successfully in developing nations, however, it must first be adapted to local economic, social and environmental conditions.
A stable system of continuous cultivation must overcome several soil-related constraints. The common humid-tropical weather pattern of intense rainstorms followed by dry periods promotes soil erosion and water stress in crops. Most of the available soils are acid and infertile, and are subject to nutrient leaching during heavy rains. Tropical weeds, which have traditionally been controlled by extended allows and very brief periods of cropping, soon dominate food crops if they are allowed to establish themselves in the fields.
The reports that follow describe research aimed at managing each of these primary constraints. Most of the research has been conducted at the Yurimaguas Experiment Station in Peru. Several projects examine various tillage methods and their effect on soil physical and chemical properties. A second group reports experiments in fertilizer management, while a third deals with methods of weed control. The central continuous-cropping experiment incorporates information and methods generated by each of these experiments, so as to develop and refine a comprehensive soil-management program for the continuous cultivation of food crops in the humid tropics.

Land-Clearing and Post-Clearing formance as affected by land-clearing and soilSoil Management Practices management practices of a humid tropical Ultisol.
Julio C. Alegre, N. C. State University Soil Physical Properties
D. Keith Cassel, N. C. State University Clearing methods and burning and tillage treatments Dale E. Bandy, N. C. State University are shown in Table 1, along with bulk-density measurements for two depth intervals, taken 15 days
In the humid tropics, large areas of cleared land have before harvesting the first and last crops. Soils in the
been abandoned because their soils were too com- treatments were 8 to 10% clay, and particle-size pacted, eroded or infertile to support crops. Much of distribution at the 0 to 15 cm depth was not altered this damage has been blamed on the use of bulldozers by land-clearing. Topsoil removal and mixing of topwith straight blades in land-clearing. There has been soil and subsoil are probably more a function of the a need for information on alternatives to straight-blade bulldozer operator than of the clearing method itself.
bulldozing, as well as for soil-management practices Clearing tended to increase the variation in Db that could improve the productivity of cleared land. (Table 2), as indicated by the higher standard deviaThe purpose of this project, which was conducted at tions. Compaction occurred for slash-and-burn clearthe Yurimaguas Experiment Station, was 1) to deter- ing due to foot traffic during slashing and trunk mine the rate of change of selected soil physical pro- removal. The greatest numerical increase in Db ocperties resulting from alternative land-clearing and soil- curred for straight-blade clearing, but it was not management practices, and 2) to evaluate crop per- significantly different from the shear-blade and slashTable 1. Mean bulk density and standard deviation (in parentheses) of Yurimaguas soil at two depths for two
times as a function of land clearing methods, burning and soil tillage treatments.
8 Months After Clearning 23 Months After Clearing
Treatment 0 to 15 cm 15 to 25 cm 0 to 15 cm 15 to 25 cm
Slash/burn 1.17*(0.10)a** 1.37 (0.10) b 1.32 (0.04) c 1.38 (0.04)b
Straight blade/rototill 1.26 (0.16)a 1.44 (0.19)ab 1.42 (0.06)ab 1.56 (0.15)a
Straight blade/chisel/rototill 1.25 (0.09)a 1.49 (0.09)ab 1.46 (0.11)a 1.57 (0.07)a
Shear blade/burn/disk/rototill 1.18 (0.11)a 1.45 (0.15)ab 1.34 (0.11) bc 1.52 (0.11)a Shear blade/rototill 1.28 (0.24)a 1.52 (0.12)a 1.32 (0.12) c 1.58 (0.04)a
Shear blade/disk/rototill 1.31 (0.14)a 1.56 (0.16)a 1.33 (0.11) bc 1.57 (0.06)a
* Each value is the mean of nine measurements in cores of 76 x 76 mm.
Means in a given column with the same letter are not significantly different at the 5% level by the Waller-Duncan
multiple comparison test.
Table 2. Mean bulk density and standard deviaton (in parentheses) of Yurimaguas soil prior to and three months
after land clearing.
Depth (cm)
Time Clearing Method 0 to 15 15 to 25
Before clearing* 1.16 (0.09)b*** 1.39 (0.08)b
Three months
after clearing** slash/burn 1.27 (0.07)a 1.37 (0.10)b
straight blade 1.42 (0.12)a 1.49 (0.12)a
shear blade 1.28 (0.25)a 1.50 (0.15)a
* Each value is the mean of 36 measurements.
** Each value is the mean of 18 measurements.
*** Means in a given column with the same letter are not significantly different at the 5% level with the WallerDuncan comparison test.

and-bum clearing methods. This lack of difference may ween soil water pressures of 13 to 1,500 KPa was be attributed to the high variability produced by the assumed to approximate the soil's capacity for holding mechanical clearing methods. plant-available water before clearing, and was equal
Bulk density in the 15 to 25 cm depth increased to 0.187 m3/m3. The diameter of the largest pore neck for both types of mechanical clearing, but not for slash that retained water at the applied soil water pressures and burn. No differences were found at the upper is also shown in Figure IA. Pores with neck diameters depth before harvesting the first crop, but at the lower > 23 /t m were drained at in situ field capacity. depth greater Db values were observed for some ran- The soil water characteristics at the 0 to 15 cm depth dom treatments compared to slash and burn. After 23 three months after clearing are presented in Figure lB. months, Db of the upper depth for the slash-and-bum Straight-blade clearing increased soil water content for treatments was significantly lower than Db for two soil water pressures < -2 KPa when compared to the other random treatments. At the lower depth, all slash-and-burn and shear-blade treatments. These mechanized land-clearing treatments had greater Db's higher water contents are attributed to destruction of compared to the slash-and-burn treatment. macropores by compaction, which, in turn, increased
the volume of micropores. Soil water characteristics for the 15 to 25 cm depth showed the same trend three Water-Holding and Infiltration months after clearing (Figure 1C). The soil water
The soil water characteristics for the 0 to 15 cm characteristics for the 0 to 15 cm depth for the three depth prior to clearing are shown in Figure IA. The soil-management subtreatments eight months after vertical bar through each point is two standard- clearing are shown in Figure ID. The bedded treatdeviation units long. The amount of water held bet- ment had the greatest total porosity and greatest
A. B.
CE Three Months After Clearing
Prior to Clearing 0 15 cm depth
-0.4 0.4 A Slash and Burn
0_ 6 Straight Blade
.2 A Shear Blade
-0.2 ca0.2
E LSD .05
0 2 0
-1500 -40 -30 -20 -10 0 -40 -30 -20 -10 0
Pressure Head (k Pascal) Pressure Head (k Pascal)
0.19 6.5 7.4 9.8 14.7 29.4
C. Pore Neck Diameter (pM) D.
Three Months After Clearing Eight Months After Clearing
15 25 cm depth 0- 15 cm depth
A Slash and Burn 0.4 E 0.4 0 Flat Planted
Z Straight Blade A Flat Planted/Fertilizer, Lime
A ShearBlade 0 Bedding/Fertilizer, Lime
0.2 0.2
LSD .05I LSD .05
1 0 0u 0 1
-40 -30 -20 -10 0 -40 -30 -20 -10 0
Pressure Head (k Pascal) Pressure Head (k Pascal)
Figure 1. Soil water characteristics of Yurimaguas soil before and several times after clearing.

volume of large pores because less soil disturbance oc- 2 3 months after straight-blade clearing resulted in a curred due to land preparation by hand. low infiltration rate when no other soil-management
The mean infiltration rate before clearing was 420 treatment was used before planting. However, when
mm/hr over a two-hour period (Figure 2A). straight-blade clearing was coupled with chisel plowMechanical clearing with both the straight blade and ing before planting the first crop, cumulative infiltrathe shear blade significantly reduced infiltration rate. tion values were similar to those for the slash-and-burn
Mean infiltration rates during the first two hours of treatment.
infiltration were 304, 14, and 32 mm/hr three months During the 23-month-long period of continuous after clearing for the slash-and-burn, straight-blade and cropping, cumulative infiltration over a two-hour shear-blade methods, respectively. Because infiltration period decreased from 800 to 200 mm for the slashmeasurements were so time-consuming, it was not and-burn treatment (compare Figures 2A and 2B). On
possible to measure cumulative infiltration for all the other hand, cumulative infiltration increased for treatment-subtreatment combinations. However, the straight blade/chisel and the shear blade/disk
measurements were replicated six times for those com- treatment.
binations measured. Cumulative infiltration during a
two-hour period for selected land-clearing sub- Crop Response
treatments 23 months after clearing is shown in Figure Grain yield of rice, the first crop seeded after the 2B. Continuously cropping the Yurimaguas soil for treatments were imposed, was highest for the slashA. and-burn treatment (Table 3). This was expected
because slash and burn supplies nutrients in ash and A Slash and Burn (before clearing) leaves the topsoil in place. The shear blade/burn/disk
800 O Slash and Burn
* Shear Blade 3 mos. after treatment also incorporated nutrients from ash into
6 Straight Blade clearing the soil and produced the second highest yield. Very
little removal of topsoil or mixing of subsoil with topsoil occurred for the shear-blade treatment. The 400 -T bed/fertilization subtreatment had the highest grain
E LSD .051 yelds followed by the flat/fertilization. Soil in the beds
.05 yie
200 maintained good structure, partly because field laborers
never walked on the elevated beds. The highest grain
yield for the second rice crop (the fourth consecutive S 0
crop in the rotation) was for the shear/burn/disk treatment followed by the slash-and-burn and the straight2 tPnblade/chisel treatments (Table 3).
250 0 Slash, Burn, Flat Planted
A Straight Blade, Chisel, Flat Planted In general, rice grain yield was 0.5 to 0.7 Mg/ha E 0 Straight Blade, Flat Planted less for the fourth crop compared to the first crop.
:3 Shear Blade, un lt Planted/ .
200 SnThis was especially true for those plots where no fertilizer was added because most of the nutrients had 150 been removed by the previous crops.
A very poor soybean crop resulted from poor ger100 LSD .05 mination due to dry conditions and low-quality seed.
Yields (Table 4) were low compared to the 2.5 Mg/ha yield obtained from other studies nearby. The highest 50 grain yields occurred for the slash-and-burn, straightblade/chisel, and shear-blade/burn/disk treatments. 0 The response to chiseling land cleared by straight blade
was 0.38 Mg/ha. Based on the general response to 0 20 40 60 80 100 120 chiseling and disking, it appears that soil compaction Time (min) constrained soybean growth and yield.
Figure 2. Cumulative infiltration of Yurimaguas soil Corn height for the third crop was significantly before and after clearing for three land-clearing greater for the slash-and-burn and shearmethods (A), and cumulative infiltration for selected blade/burn/disk treatments (Table 5). For both
land-clearing methods 23 months after clearing (B).

treatments involving burning, some available nutrients altered by clearing or management from their initial still remained and plant height was 0.85 m. Grain condition, and therefore provided a good environment yields for the fifth crop were greatest for the slash- for roots. and-burn and shear-blade/bum/disk treatments (Table 5). There was good response to all treatments receiv- Conclusions ing disk or chisel tillage. Without fertilizer and lime 1. Most of the changes in soil physical properties plants did not survive. Although application of fertilizer occur during the land-clearing process rather than after and lime appeared to compensate for some of the ef- clearing. fect of compaction, corn growth and yield were bet- 2. Degradation of physical properties due to ter on chiseled land. Soil structure in the bedding mechanical land-clearing is sufficient to decrease crop system was favorable to germination and root distribu- yields if no effort is made to improve soil physical contion, and bedding produced higher grain yields. ditions.
For the slash-and-burn treatment, the bed/fertiliza- 3. The least deterioration in soil physical propertion management resulted in the best soil physical con- ties occurred in the slash-and-burn treatment. ditions, less lodging and higher yields. Physical pro- 4. Chiseling and disking after mechanical landperties of the subsoil for this treatment were never clearing tended to offset some of the undesirable efTable 3. Rice grain for the first and fourth consecutive crops as affected by land clearing, tillage and soil management.
Treatment Flat/No Fert. Flat/Fert. Bed/Fert. Mean
First crop
Slash/burn 3.11 3.56 3.98 3.55a **
Straight blade 0.91 2.75 3.38 2.35 cd
Straight blade/Chisel 1.14 2.84 2.85 2.28 cd
Shear blade/burn/disk 2.39 3.06 3.68 3.04 b
Shear blade 1.27 3.02 3.20 2.49 c
shear blade/disk 0.91 2.58 2.74 2.07 d
Fourth Crop
Slash/burn 0.75 3.48 2.82 2.35 b
Straight blade 0.26 1.56 2.00 1.27 d
Straight blade/chisel 0.70 3.04 2.91 2.22 b
Shear blade/burn/disk 1.58 3.44 2.96 2.66a
Shear blade 0.97 2.13 2.28 1.80 c
Shear blade/disk 0.63 1.83 1.96 1.47 d
Table 4. Soybean grain yields for the second crop as affected by land clearing-tillage and soil management.
Grain (Mg/ha)
Treatments Flat/No Fert. Flat/Fert. Bed/Fert. Mean
Slash/burn 0.42 2.32 1.86 1.53ab **
Straight blade 0.10 1.03 1.50 0.88 d
Straight blade/chisel 0.32 1.44 2.03 1.26abc
Straight blade/burn/disk 0.48 2.17 2.05 1.57a
Shear blade 0.18 1.37 1.87 1.14 cd
Shear blade/disk 0.12 2.01 1.56 1.23 bc
** Means in a given column followed by the same small letter and means in rows followed by the same capital letter are not significantly different at the 5% level by the Waller-Duncan multiple comparison test.

Table 5. Corn height for the third crop and corn grain yield for the fifth crop harvest as affected by land clearing tillage and soil management.
Treatment Flat/no Fert. Flat/Fert. Bed/Fert. Mean
Plant height,m
Third crop
Slash/burn 0.85 2.58 2.34 1.92a
Straight blade 0.00 1.48 2.20 1.23 d
Straight blade/chisel 0.28 2.29 2.35 1.64 bc
Shear blade/burn/disk 1.03 2.63 2.23 1.96a
Shear blade 0.45 2.51 2.25 1.74 b
Shear blade/disk 0.31 2.43 2.03 1.59 c
. Grain yield, Mg/ha
Fifth crop
Slash/burn 0.39 2.86 3.30 2.18a
Straight blade 0.00 1.47 1.18 0.88 c
Straight blade/chisel 0.00 1.85 2.87 1.58ab
Straight blade/burn/disk 0.04 2.45 2.82 1.77ab
Shear blade 0.00 1.36 1.76 1.04 c
Shear blade/disk 0.00 0.94 1.95 0.96 c
Means in columns for a given harvest followed by the same small letter and means in rows followed by the same capital letter are not significantly different at the 5% level by the Waller-Duncan multiple comparison test.
fects of land-clearing on soil physical properties. For
example, the infiltration rates for soil cleared by the Tillage With Tractors
mechanized methods were increased by disking and In Continuously Cropped Ultisols
chisel plowing prior to planting the first crop.
5. Declines in soil physical properties under con- Robert E. McCollum, N. C. State University
tinuous cropping were minimized when soil was bedded using a hand hoe. Before January, 1984, the long-term continuous6. Slash-and-burn clearing resulted in higher yields cropping experiment at Yurimaguas had been tilled
for rice, soybean and corn compared to mechanized with a small hand rototiller to a depth of 7 to 10 cm clearing. Of the mechanical land-clearing and tillage since it was first cleared in 1972. While rototilling had methods examined, shear blade/burn/disk produced been considered a possible intermediate step between the highest rice, soybean and corn yields. All crops hand tillage and tractor-drawn implements, it has showed a positive yield response to treatments in which several disadvantages: Tillage with rototillers has soils were chiseled or disked after clearing, resulted in a shallow root system limited to the zone of fertilizer incorporation; small rototillers do not proImplications perly incorporate crop residues; and rototilling is slow.
While all of the land-clearing methods examined The objectives of this project are I) to determine
adversely affect these soils to some extent, traditional whether tillage with tractor-mounted farm equipment slash and burn does the least amount of damage. is possible on humid tropical Ultisols; and 2) to deterMachinery can apparently be used to clear secondary mine whether tillage with tractors is agriculturally and forests for crop production if its use is coupled with ecologically sound in humid tropical environments.
effective soil-management techniques after clearing. Of
the mechanical methods examined, the best alternative Tillage Practices
to slash-and-burn clearing was a combination of fell- An abandoned portion of Chacra I, which is the site ing with a shear blade, then burning the vegetation of the continuous-cropping experiment at Yurimaguas, on-site as traditionally practiced. However, unless was prepared duringJuly-August, 1983 via the followfollowed by disking or chisel-plowing, this method will ing steps: 1) Chop crop residues with rotary mower; tend to produce lower crop yields and less favorable allow to dry; burn; repeat as necessary; 2) disk as soil properties than traditional slash-and-burn clearing, necessary to reduce remaining residues to a manageable

Table 1. Crop yields on Chacra I after initiating tractor-mounted tillage. Months refer to harvest date. Comparisons Rice Corn Corn Corn Corn1
Jan 84 Jan 84 July 84 Jan 85 July 85
Grain yields, th/a, and (number of observations)
General Mean 2.47 (101) 2.96 (42) 3.15 (216) 3.48 (125) 2.90 (36)
Clearing Method
Burned, 1972: 2.56 ( 41) 3.00 ( 8) 3.27( 99) 3.50 ( 64) 2.70 (15)
Bulldozed, 1972: 2.54 ( 43) 2.93 (33) 2.93( 90) 3.70 ( 32) 2.87 (12)
Peripheral Areas2 2.10 ( 17) 3.49 ( 1) 3.42( 27) 3.19 (29) 3.28 ( 9)
Lime + P
None 2.74 ( 16) 2.35 (17) 2.71 ( 56)
Lime + p3 2.42 ( 85) 3.38 (25) 3.30 (160)
Banded P
None 2.54(15)
Banded P 3.19 (27)
1 Low Corn population (29,000 plants/ha)
2 Clearing method unknown
3 2.5 t lime/ha + 100 kg/P/ha
bulk; 3) plow to 20-2 5 cm with a moldboard plow Clearing Method to incorporate plant residues and soil amendments; 4) The site was cleared in 1972 by bulldozing or by disk again; 5) make tractor tracks as row markers; 6) traditional cutting and burning. The data show that construct 75 cm beds; 7) prepare seedbed with any differences between initial clearing methods were rototiller, and 8) plant crop, either by hand or with virtually eliminated by tilling to 20 cm. tractor-mounted Cole planters. Lime and fertilizer applications were consistent with practices developed for Effects of Lime + Phosphorus Chacra I. Weeds were controlled chemically with Lime and phosphorus, broadcast before the first crop, metolachlor. increased corn yields but had not effect on rice. InCorn and upland rice were planted in August, 1983 row banded P resulted in a 26% increase in corn yields and harvested in January, 1984. The same tillage opera- during the first cycle. tions were repeated prior to planting three consecutive corn crops, which were harvested in July, 1984, Observations January, 1985 and July, 1985. Initial observations have been that mechanized tillage
is possible on Ultisols in the Yurimaguas environment. Yields Tillage can be accomplished once a year, during the
Product yields during four biological cycles follow- "dry" season, July-September. Mechanized tillage at ing initiation of tractor-mounted tillage are shown in other times should only be undertaken with strict atTable 1. While there were no treatments in an ex- tention to soil moisture. Continuing work in this area perimental sense, some comparisons based on previous will seek to determine if mechanized tillage is treatment and current management can be made regar- agriculturally and ecologically sound in humid tropical ding clearing method, and the effects of lime and P. environments.

one month after planting, to the foliage of either corn Continuous Cropping: or peanut.
Central Experiment 3. Complete fertilization as follows (in kg/ha/crop):
rice, 100 N; corn, 80 N, 30 P, 100 K; and 30 Mg Robert E. McCollum, N. C. State University to all crops.
Pedro A. Sanchez, N. C. State University 4. Complete fertilization plus 2 kg Mn/ha, applied
Dale E. Bandy, N. C. State University as in treatment 2.
5. Previous crop residues left on soil and
This experiment is a long-term demonstration of a incorporated.
continuous-cropping system for acid soils of the humid 6. Previous crop residues left on soil but not incortropics. The system is based on the judicious use of porated.
fertilizers and the best available soil-management prac- 7. 1.5 times the complete fertilization.
tices. It occupies eight 10 m by 28 m main plots in This report describes results from July, 1981 toJueach of two fields known as Chacra I (site one) and ly, 1985, including the harvests of crops 25 through Chacra III. There were seven fertility-management 31 (Table 1). Prior to January, 1984, all of the plots treatments under each of two rotations, rice-corn- except the check (treatment 1) were rototilled with soybeans and rice-peanut-soybeans, and four replica- a hand tractor to a depth of about 7.5 cm. Tillage with tions each in 4 x 10 m plots. These plots have been tractor-drawn implements to a depth of 20-25 cm was cropped continuously since September of 1972, pro- introduced with crop 29, and was used thereafter in
ducing 31 crops to date in Chacra 1. the corn crops discussed in this report.
From May, 1982 until January, 1984, the seven Continous cropping on Chacra III was discontinued
fertility-management treatments were: in September, 1983. No significant yield differences
1. A check, with no tillage and no fertilizer or lime were noted between Chacras I and III during the last
added. four harvests. Twenty-one crops were harvested from
2. Complete fertilization plus 1 kg Mn/ha, applied Chacra III within a span of 112 months.
Table 1. Crop yields of continuously cultivated plots from January, 1982 to July, 1985.
Crop No., Species and Harvest Date1
25 25 26 27 27 28 28 29 30 31
Treatments2 Corn Peanut Rice Corn Peanut Corn Rice Corn Corn Corn
1/82 8/82 1/83 6/83 6/83 1/84 1/84 7/84 1/85 7/85 Yields,t/ha
1. Check3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
2. Complete + Mn 2.97a 4.63a 3.04 c 1.93b 2.71a 1.21c 1.51b 1.82ab 2.56c 1.85ab
3. Complete 3.28a 4.39a 3.45b 1.62b 2.74a 1.91bc 1.55b 2.76b 3.02bc 1.56b
4. Complete + 2 Mn 2.87a 4.75a 3.68b 1.88b 2-.76a 2.48ab 1.99a 3.05ab 2.94bc 2.06ab
5. Complete + residue 3.21a 4.54a 4.48a 1.68b 2.42a 2.76a 2.00a 3.58ab 3.73a 2.80a
6. Complete + residue 3.20a 3.28b 3.71b 2.04b 2.51a 2.61ab 1.44b 3.91a 3.21ab 2.48ab
7. 1.5 x complete 3.49a 4.54 3.54b 2.66a 2.50a 2.31ab 1.80ab 3.06ab 3.15 1.98ab
Mean 3.17 4.35 3.65 1.97 2.61 2.21 1.72 3.20 3.10 2.12
(No. of obs.) 8 8 16 8 8 4 4 8 8 8
C.V. (%) 19 14 12 28 15 23 14 27 17 39
Crop yields from 1/82 through 6/83 are pooled data from Chacras I and Ill; subsequent harvests are from Chacra
I only.
2 Treatments up to crop #28: uniform fertility and conventional tillage to 20-25 cm to all but treatment 1 for crops
29, 30, 31.
3 Treatment 1 dropped from data array for statistical analysis.

Table 2. Effects of selected treatments on relative yields January, 1982 January, 1984. Crops 25 28 in Chacra I.
Corn Rice Peanut
Treatment (3 crops) (2 crops) (2 crops)
Relative Yield'
3. Complete + residue removed 91 b 94 b 103 a
5. Complete + residue incorporated 104 a 121 a 99 a
6. Compete + residue as mulch 107 a 98 b 86 b
7. 1.5 x complete + residue removed 116 c 99 b 100 a
* Mean yield over all treatments within a cycle = 100.
Crop Performance following observations can be gleaned from crop perYields of crops 25 to 31 from Cbacra I: Check-plot formance, expressed as relative yields in Table 2. yields have been zero for the last ten years. The first Incorporating residues produced significantly higher five harvests include pooled data from the two chacras yields than residue removal in corn and rice, but not because there were no chacra effects. Crop 28 (rice) on peanut (Table 2). Leaving residues as mulch had was affected by pathogen attacks on the grain. Corn a positive effect on corn, neutral on rice, and negative crops 29 and 30 showed nitrogen-deficiency symptoms on peanut. Peanuts are more susceptible to attack from from tasseling to maturity. Crop 3 1's stand was soil disease organisms such as Sclerotium rolfsii, which decreased to 26,700 plants/ha by an intense rainfall causes southern stem rot, when residues remain in the (225 mm in six hours) immediately after planting. The field.
S Tillage to 20 c Extr. P (ppm)
Exch. Acidity Al*. Satn (%)
0Trt. 1: Check 6
+ 0 Trts. 2,3,4: Complete .
0 Trts. 5,6: Complete + Residues Trt
1.0 ~ ~ ~ ~ ~ ~ 5 pHr.7 omlt t.
O~~ 0 Trt. 7,3
0 -0
4 Exch. Ca + Mg 56 pH
2 4 o ._._4.4
123 130 136 142 148 154 160 123 130 136 142 148 154 160
Months After Clearing Months After Clearing
Figure 1. Trends in effective cation exchange capaci- Figure 2. Trends in soil pH, % Al saturation and exty (ECEC), exchangeable acidity and extractable Ca- tractable soil P in soil on continuously cultivated plots plus-Mg of soil on continuously cultivated plots in in Chacra I. The shaded bar at month 148 represents Chacra I. the first tillage with tractor-mounted tools.

The "1.5 x complete" fertilization treatment pro- 3) Most indices showed abrupt declines in soil ferduced significantly higher corn yields than others, sug- tility immediately after the introduction of tillage to gesting the need for N rates greater than 80 kg/ha 20 cm and the mixing of subsoil with topsoil. Testable for this crop. In view of the deficiency symptoms fertility improved by the third crop, however, as lime observed, nitrogen may have been the limiting nutrient, and fertilizers were more thoroughly mixed in the soil.
Rice and peanut did not display this effect (Table 2).
Topsoil Properties After 31 harvests in 12 years, yields of corn, rice
Figures 1 and 2 show relevant topsoil fertility in- and peanut remain high by local standards. With
dices from January, 1982 to January, 1985, during judicious use of lime and fertilizers, it is apparent that the growth of crops 25 to 30. Treatments 2, 3 and acid soils in the humid tropics will produce acceptable 4 were pooled as the "complete" because they were yields of short-cycle food crops under continuous similar with respect to measured soil properties. cultivation. It is also apparent that soil chemical proTreatments 5 and 7 were likewise pooled to summarize perties can be improved while producing high yields.
the effect of residue cycling.
The check treatment had the least desirable soil properties in all fertility categories. Returning crop residue
showed consistent and statistically higher fertility in- Production Potential of Corn-Peanut
dices except for P. Obviously, treatments 5 and 6 have Intercrops in the Humid Tropics
received less fertilizer P than treatments 2, 3 and 4.
The positive effects of residue return on physical pro- Jos6 R. Benites, N.C. State University
perties were apparent each time the land was tilled. Robert E. McCollum, N.C. State University
Lime was applied to these plots at the rate of 2 t/ha Andres Aznaran, INIPA
four years before the results shown in Figures 1 and
2. Soil-acidity indices were stable with less than 20% This experiment was conducted to compare the proAl saturation in treatments other than the check plot. ductive efficiency of a corn-peanut intercrop with This observation indicates a considerable residual ef- monocultures (sole crops) of the intercrop components fect of lime. grown in rotation and with continuous corn. A second objective was to determine the effect of nitrogen
Effects of Tillage to 20-25 cm fertilization on cropping-system efficiency. Corn (Zea
There was an abrupt change in most fertility indices mays L.) and peanut (Aracbis bypogea L.) were grown
when the soil was tilled to 20 cm. Soil pH and available in a "strip-intercrop" arrangement for three biological P dropped while exchangeable acidity, percent Al cycles (trimesters). The strip-intercrop consisted of two saturation and effective cation exchange capacity in- 75 cm rows of corn in an alternating pattern with three creased. Exchangeable Ca + Mg remained stable, 38 cm rows of peanut. This row arrangement permithowever. These changes are a consequence of mixing ted the intercrop to be grown as a corn-peanut rotaa less fertile and heavier-textured, 7-20 cm soil layer tion. Monocultures of the interplanted species, with with the 0-7 cm topsoil. The situation was beginning corn in 75 cm rows and peanut in 38 cm rows, servto stabilize by the third crop under the 20 cm tillage ed as the reference standard (monocultre check) durregime, because the lime and incorporated fertilizers ing each cycle. These monoculture checks were also were then well mixed with a 20 cm plowed layer. grown as a corn-peanut rotation. The third cropping system was continuous corn.
Conclusions Corn in both monoculture and intercrop received
1) Returning crop residues, either by incorporation three levels of N fertilization (0, 100, or 200 kg N/ha),
or as mulch, had a slight positive effect on corn and and the experiment was arranged in a split-plot design rice, but not on peanut. with four replications. Main plots were cropping
2) An apparent response of corn yields to fertilizer system, and subplots were N fertilization. The experiin the "1.5 x complete" treatment, together with ment site was an Ultisol that had been limed and
observed symptoms of N deficiency, suggest that N phosphated before initiating the experiment.
fertilization should be increased for this crop, though All three cropping systems were planted with tractornot for rice. mounted planters on the same date. Within-row
seeding rates were the same for each species in each

Table 1. Yields of corn grain and peanuts as influenced by applied nitrogen and cropping systems. Cropping Species & Crop N Rates (kg/ha)
Systems Trimester duration 0 100 200
days yield, kg/ha
Strip Intercrop:
Corn/Peanuts: Corn (1) 108 779 1751 1602
Peanuts (1) 110 1034 782 795
Corn (2) 109 1806 1980 2297
Peanuts (2) 111 243 175 210
Corn (3) 119 1652 2295 2365
Peanuts (3) 122 357 299 322
Suequential monocultures:
Corn Peanuts -* Corn:
Corn (1) 108 917 2625 3218
Peanuts (2) 111 1086 1086 1086
Corn (3) 119 2595 3450 3185
Peanuts Corn -- Peanuts:
Peanuts (1) 110 2275 2275 2275
Corn (2) 109 3191 3800 3758
Peanuts (3) 122 859 1092 855
Corn Corn -- Corn:
Corn (1) 108 861 2757 3227
Corn (2) 109 2441 3590 3561
Corn (3) 119 2334 3106 3692
Trimester Trimester Trimester
1 2 3
Corn LSD 0.05 Cropping system 452 303 330
LSD 0.05 Nitrogen level 232 257 389
LSD 0.05 Int. CS x N 557 472 640
Peanuts LSD 0.05 Cropping system 544 184 226
LSD 0.05 Nitrogen level 56 36 119
LSD 0.05 Int. CS x N 547 188 260
system. While this methodology provided near- In contrast to corn, the yield of interplanted peanuts equivalent total plant densities for each cropping was severely reduced by overstory corn. When averagsystem, it should be noted that the corn-peanut inter- ed over three cycles, the intercrop produced 31% of crop had only one-half as many corn plants and one- its monoculture check. Peanut plants were severely half as many peanut plants as its companion affected by Cercospora leaf spot during the second cymonocultures. cle, and the detrimental effect of this pathogen seemed more pronounced in the intercrop.
Product Yields
Corn was virtually unaffected by its association with Intercrop Efficiency
peanuts (Table 1); the intercrop produced more than Table 2 shows the effect of N fertilization on area60% of its reference monoculture during each cycle time equivalency ratios (ATER) during each cycle (average relative yield of intercropped corn during three (ATER = LER because intercrop duration equals cycles = 0.64). The N response was positive for all production-cycle duration for each species). When corn cropping systems, and yields were near-maximal at 100 was grown without N fertilization, the corn-peanut kg N/ha. There is some evidence that corn following intercrop used area and time more efficiently than peanuts was less responsive to N than corn following monocultures (ATER > 1.0) during two of the three corn (Figure 1). cycles. When corn was fertilized with 100-plus kg

Table 2. Effects of N fertilization to corn in a corn-peanut inter- N/ha, however, there was no evidence of any intercrop on Area-Time Equivalency Ratio during three biological crop advantage (ATER = < 1.0). Low ATER's durcycles. ing the second biological cycle were due exclusively
kg N/ha Cycle N to extremely low relative yields of interplanted peanuts
to corn 1 2 3 Mean (relative peanut yields = 0.19 for cycle two versus
SAE0.40 for cycles one and three). This observation lends ATER support to the earlier supposition that Cercospora leaf
0 1.34 0.78 1.05 1.06 spot was more severe in the intercrop.
100 0.97 0.67 0.94 0.86
200 0.84 0.81 1.00 0.88 Cropping-System Efficiency
Cycle Mean 1.05 0.75 1.00 0.93 Continuous corn was compared with the two cornlATER relative to sole-crop corn and sole-crop peanuts in the corn- peanut rotations by converting absolute yields to caloric peanut rotation. equivalents and summing over three cycles. Effects of
cropping system and N fertilization on the rate of
Table 3.Effects of N fertilization and cropping systems on rate caloric yield (Mcal/ha/yr) are shown in Table 3. (All of caloric yield and relative croppping-system efficiency. entries in Table 3 are comparable because each entry Cropping N Fertilization (kg N/ha) CS sums over three harvests of the relevant species). ImSystem 0 100 200 Mean plications from the Table 2 data are quite clear: 1)
Without fertilizer nitrogen, the two systems that inCaloric Yield clude peanuts are significantly superior to continuous
____M cal/ha/year
Cont. Corn 16.36 27.44 30.42 24.74 corn in storing energy; but 2) continuous corn with
Corn-Peanut 20.06 25.29 25.12 23.49 adequate N (100-plus kg/ha) gives a higher rate of
Rotation caloric yield than the corn-peanut intercrop or
monocultures of its components grown in rotation.
Corn-Peanut 20.34 23.68 24.71 22.91 If, in fact, caloric yield were the principal basis for deciIntercrop sion making, the only near-equivalent system to wellN Mean 18.92 25.47 26.75 fertilized continuous corn would be continuous peanuts
Relative Efficiency (Continuous Corn = 100) (approximately 25 Mcals/ha/year, not shown).
Corn-Peanut 123 92 83 99
Rotation Implications
Corn-Peanut 124 86 81 97 A two-crop intercrop of corn and peanuts may have
Intercrop merit under low-N regimes in humid tropical enN Mean 124 89 82 vironments. In most such environments, however, the
inherent soil condition is high acidity (high exchangeable aluminum) and low phosphorus. These initial conditions must be corrected with massive doses
Second Crop Cycle Prior Third Crop Cycle of lime and phosphorus before either species can be
crop Por expected to produce the yields reported here.
-- ....- There are some other favorable aspects to the inCon = corn tercrop system described here:
3 1. Three cycles per year are possible because each
.3 1 Peanui species can be grown year-round and because all have
E .05 nearly identical production-cycle durations.
oo I
o 2 2. Most field operations can be done with machines
C) 2-2
or by hand.
3. Since the strip-intercrop system can be managed
- 1as a corn-peanut rotation, there may be some nitrogen
o 54 100 200 0 33 100 200 carryover from the peanuts to the following crop of
N Applied (Kg N/ha) corn.
Figure 1. Apparent N carryover from preceeding
peanut crops to subsequent corn crop.

Phosphorus, Zinc and copper (4 kg Cu/ha). Zinc variables were to have been
Copper Fertilization 0, 2, 4, and 8 kg Zn/ha in 7.5 m by 12 m plots with
eight replications, but an error resulted in a double
Robert E. McCollum, N. C. State University application of P, Cu and Zn on one four-plot group Luis Arevalo, INIPA and a double application of lime on two of them. InAndres Aznaran, INIPA stead of one experiment with eight replications, this
dosage error made it necessary to consider the "zinc
This project evolved after observations on several by banded-P" endeavor as two separate experiments: Yurimaguas sites suggested that band-applied 1) a three-factor experiment (2 lime x 4 zinc x 2 BP) phosphorus induces a micronutrient deficiency in corn. with two replications, and 2) a two-factor experiment The phenomenon was first observed in an experimental (4 zinc x 2 BP) with four replications. field that had been limed and fertilized with N, P, K, At the same time (July-August, 1984), a second conMg, Cu and Zn at recommended rates. The first corn tiguous, eight-plot area that had received lime and crop had been machine-planted in January, 1984 with phosphate a year earlier was selected for a "zinc by TSP in the fertilizer hoppers. Within ten days after copper by banded-P" experiment. Copper was applied corn emergence, virtually the entire planting had at 0 and 4 kg/ha in factorial combination with 0, 2, developed a chlorosis symptomatic of Zn deficiency. 4 and 8 kg Zn/ha. All plots were plowed, disked, beddThe possibility of a micronutrient toxicity was ruled ed, and rototilled. For the first corn crop (September, out because the rate of Zn or Cu applied was only 1984 toJanuary, 1985), the banded-P treatment was 1 kg/ha. achieved by planting four rows without banded P and
In response to these observations, a project was six rows with banded P. This P-banding procedure was designed to meet the following objectives: 1) to deter- reversed for the following crop. mine the effect of banded phosphorus fertilizer on
growth and yield of corn on continuously cropped Crop Yields Ultisols; 2) to explore the hypothesis that band-applied Corn showed statistically significant, positive phosphorus exacerbates zinc deficiency on low-Zn soil, responses to applications of banded P, broadcast Zn and 3) to determine if the nutritional abnormalities and broadcast Cu in terms of grain yields and plant induced by band-applied phosphorus can be populations (Tables 1 and 2), but there was no "Zn
ameliorated by applying zinc or copper to the soil. x banded P" or "Cu x banded P" interaction. Plant
In July-August of 1984, eight plots (two contiguous population was much lower in the second crop because sets of four plots each) that had not received lime or of intense rainfall (226 mm in six hours) immediately phosphate recently were selected for a "banded-P (BP) after planting (Fables 1 and 2), and poor product yields by soil zinc" experiment. All plots received applica- for this cycle are primarily the result of low plant tions of lime (2.5 t/ha), phosphate (100 kg P/ha) and density.
Table 1. Corn grain yields and plant population as affected by boradcast ZN and banded P application in two consecutive crops
Corn Crop Zn Banded P Applied Banded P Applied
(Harvest Date) Applied No Yes Mean (Zn) No Yes Mean (Zn)
Yield, t/ha 1000 Plants/ha
Jan 85 None 2.42 3.08 2.75 36.0 38.2 36.8
Yes* 3.32 3.43 3.38 36.3 37.3 37.1
Mean (BP)** 3.09 3.34 36.2 37.6
July 85 None 1.79 2.01 1.90 20.5 25.5 23.0
Yes 2.28 2.59 2.44 24.3 27.1 25.7
Mean (BP) 2.16 2.45 23.4 26.7
Means of 2, 4 and 8 kg Zn/ha (36 plots) vs. 12 plots for 0 Zn. * Weighted means.

Table 2. Corn grain yields and plant population as affected by broadcast Cu and banded P application in two
consecutive crops.
Corn Crop Cu Banded P Applied Banded P Applied
(Harvest Date) Applied' No Yes Mean (Cu) No Yes Mean (Cu)
kg/ha Yield, t/ha 1000 Plants/ha
Jan 85 0 3.06 3.27 3.17 33.6 35.0 34.3
4 3.72 3.71 3.72 34.8 37.7 36.2
Mean (BP) 3.39 3.49 34.2 36.3
July 85 0 1.80 2.51 2.15 20.1 25.0 22.6
4 2.39 2.52 2.46 23.3 24.6 24.0
Mean (BP) 2.09 2.52 21.5 24.8
1 Extractable Cu levels in the soil were 0.94 and 2.05 ppm Cu for levels 0 and 4 kg Cu/ha.
Banded P Plant Population
Banding P increased corn yields by 8 and 13% in This study underscores the difficulty of assessing
the P-Zn plots (Table 1), and by 3 and 21 % in the treatment effects in crops whose populations are P-Cu plots (Table 2), with an average overall effect variable or inadequate because of such factors as heavy of 11 %. While some of these apparent treatment ef- rainfall, poor seed quality or inconsistencies in sowfects were related to increased plant population, there ing and thinning. A clear-cut estimate of treatment efwas a marked growth response to banded P, which, fects is confounded by the fact that additions of banded unlike similar experiences in North Carolina, was P and micronutrients affect not only the growth and reflected in grain yields. yield of individual plants but also the number of plants
that emerge.
Zinc Response The positive relationship between band-applied P
Corn responded significantly to the first increment and plant population has been apparent in virtually
of Zn (2 kg/ha). Since there was no significant response every banding vs. no-banding comparison to date.
to the second or third increment in applied Zn, all plus- Figure 1 shows the relationship between plant populazinc treatments (2, 4, 8, or 16 Zn/ha) were pooled, tion and yield when the comparison was first made and the data analyzed as a minus-Zn versus plus-Zn (January, 198 3 corn harvested from Chacra I, one of experiment. Data from all relevant plots in the "zinc the original experimental fields at Yurimaguas). Banded
by copper by banded-P" experiment were analyzed
with the Zn-banded P data, and are included in Table 4.4 ABanded P
1. Yield = -524 + 0.0988 x POP;
= 0.25
Zinc plus banded P applications caused a 42% yield 4.0 ON Banded P
increase in the first crop with no effect on plant popula- Yield 525 + 0.080 POP;
tion (Table 1). Zinc alone caused a 2 3 % yield increase. 3.6 R = 0.36
Zinc plus banded P and Zn alone caused a similar yield Average
increase in the second crop, and a 12% increase in .
plant population.
E 2.8
Copper Response 0
Response trends for the "copper by banded-P" data 2.4t
are highly positive. Incorporating 4 kg of Cu/ha in
the top 20 cm of soil caused a 6% population increase 2.0
during each cropping cycle but a 14-17% increase in I I I I
yield (Table 2). 24 28 32 36 40 44 48
Corn Population (x10-3)/ha
Figure 1. Relationship between corn population and grain yield with and without banded-in-row P.

P not only resulted in a higher plant population at Potassium, Lime and Magnesium harvest, but the slope of the yield vs. population curve Interactions and Corn Yields was also steeper. Yield versus population curves have also been generated for other examples, and they show Rob Schnaar, Wageningen University the same trends for more surviving plants with band- Robert E. McCollum, N.C. State University applied P. The slopes of the curves show that each additional 1000 plants up to 50,000 plants/ha pro- A lime-by-potassium study was initiated at duces an additional 60 to 120 kg of grain. These Yurimaguas during July and August, 1984. The obcalculations also show that the corn population is usual- jectives of this study were 1) to construct a potassium ly inadequate. In no instance has there been a signifi- response curve for continuously cropped Ultisols in cant quadratic response to population, and only rare- humid tropical environments; 2) to estimate a critical ly have there been 50,000 plants/ha. soil K level for corn in the soils; 3) to quantify the
recycling of K via crop residues in the soils; and 4) Observations to determine the effect of lime on K responses by food
While it is too early to draw firm conclusions from crops, K utilization by crops, and K retention in the this study, preliminary observations suggest the soils. A between-site magnesium variable was introducfollowing: ed because two liming materials were used. While this
1) Corn yield and plant populations significantly was not part of the original plan, site-related yield difresponded to banded P and broadcast Zn or Cu. ferences provided some useful insights about cation
2) Although there has been no apparent effect of balance and Mg nutrition.
banding P on the response of corn to Zn or Cu in Two experimental sites were selected because the the first two crops (no measureable banded P x soil represents the textural extremes for upland posimicronutrient interaction), yields were low because of tions in the Yurimaguas environment (Table 1). At reduced population density. Since plant population was site #1, the top 45 cm of soil is a clay loam and its also treatment-related, the effects of treatment on pro- texture grades to clay between 45 and 60 cm. Site #2 duct yield are confounded with population effects, has a transitional sandy loam-sandy clay loam sur3) While the observed chlorosis was corrected by face (0-20 cm) with little or no textural change to 60 micronutrients, the initial hypothesis is still unproven. cm.
Each site was cleared of secondary forest with a bulldozer in 1980 and left to regrow without chemical amendments. The sandy site was recleared and made
Table 1. Textural characteristics and effective cation exchange capacity (ECEC) of two Ultisols used for lime-by-potassium studies at Yurimaguas.
Range Site Sand Clay Textural ECEC
cm No. Class
% % meq/lOOcm3
0-201 1 40 31 Clay Loam (Cl) 4.66
2 62 21 Trans. S-SC1 2.69
20-30 1 35 37 Cl 5.20
2 58 25 SC1 3.28
30-45 1 38 36 C1 5.80
2 52 29 SCi 3.63
45-60 1 36 42 C 6.86
2 52 32 SCI 3.89
1 Texture of surface layer determined after mixing to 20cm

tillable in mid- 1983. It was then used for about one respectively) were applied to the once-plowed soil and year to screen germplasm (rice, cowpeas, corn) for incorporated by plowing again with a two-bottom aluminum tolerance with a lime differential of 0 and moldboard plow. After the second plowing, the re2.0 t/ha [lime source = Ca(OH)21 as main plots. The maining half of the various soil amendments [lime lime was incorporated to 20 cm by routine tillage when source = Ca(OH)2] was applied and incorporated by
the site was acquired. routine disking, bedding and rototilling.
The clayey site was renovated by mowing and plow- Potassium treatments (sub-plots) were selected to ining to 20 cm. The soil was sampled in detail. Initial crease the K level in the top 20 cm of soil by 0, 0.05, soil properties were: pH = 4.6;Ac = 3.78; Ca+Mg 0.10, 0.15, or 0.20 meq 100/cm3 (0, 39, 78, 117, = 0.89; Al satn. = 81%; K = 0.07., P = 3ppm. and 156 kgK/ha). The potassium (as KCI) was handA factorial experiment consisting of three rates of lime drilled on the bedded rows and incorporated by routine
and five rates of K was established. Lime levels (whole pre-plant rototilling.
plots) were chosen to neutralize 0, 50% and 100% Corn was machine-planted on each site in late of the exchangeable acidity in the top 20 cm (0, 2, September of 1984 (harvested January, 1985).
and 4 t/ha). One-half of the intended lime dose Nitrogen fertilization (as urea) was 150 kg N/ha with (dolomitic limestone) and one-half of the intended one-third of the total applied pre-plant and the remainblanket doses of P, Zn, and Cu (100, 8, and 4 kg/ha, ing two-thirds at about 40 days after corn emergence.
Total dry matter accumulation at early ear formation
(maximum K accumulation) was estimated by
80 I AI Sat'n. harvesting and processing for analysis six whole plants
I per subplot. The soil was sampled to 60 cm (0-20,
20-30, 30-45, and 45-60) at corn maturity and ana60__lyzed for relevant properties.
I8_ A second corn crop was planted in late March of
40 I-1985 with the same K additions as indicated for cycle
20 one, but excessive rainfall of high intensity resulted
20 I in a low plant population as well as poor weed control, and no meaningful treatment-related yield data
I were obtained. The following summary of treatment
3 effects on soil properties as well as product yield is
for the first biological cycle only.
Soil Properties
1 ExcTwo tons of lime applied to the sandy loam soil in
1 Exch. Acidity 1983 had reduced aluminum saturation from 62 % (pH
o I =4.4) to 38% (pH = 4.7) when the soil was samCi 3 pled about 18 months later (Figure 1). On the clay
- loam soil, aluminum saturation at about six months
after applying 0, 2, or 4 tons of lime was 68% (pH
2 I=4.3), 52% (pH = 4.5) and 34% (pH = 4.8),
respectively. Other pH-related properties followed
1 predictable trends (Figure 1), but there was no
Exch. (Ca + Mg) measurable increase in effective cation exchange capaci0 ty (ECEC) due to liming.
0 1 2 3 4 Extractable soil potassium in the top 20 cm of soil
Tons CaCO, equiv./ha was a linear function of K applied on each site (Figure
A Clay loam. limed Aug., 1984 2), but the steeper response slope for the sandy soil O Sandy loam, limed Aug. 1983 shows that a higher percentage of the K applied was recoverable by the extractant used. These results are
Figure 1. Effect of liming on two Yurimaguas Ultisols typical for soils of differing texture.
on pH-related properties. Both sites sampled in
January, 1985.

Product Yields
Grain yields on the sandy soil were less than 50% K Applied (kg/ha)
of those measured on the clay loam soil (Table 2). 0 39 78 117 156
While there was a positive response to lime on each r I
site, the only measurable response to K was on the 0.24 o
clay loam soil, and grain yields on this soil were near- L Clay loam (Y-103A)
were near-ASandy loam (Y-103B) maximal with 78 kg K/ha. Figure 3 shows the rela- I
tionship between aluminum saturation and corn yield E when data from the two sites were pooled. Since ab- Q solute yields from the two soils differed drastically, 0.16 a "relative yield" was first calculated (Relative yield .
= 100 absolute yield/mean maximum yield at each = 0.12 .............
site), and relative yields were regressed on the percen- w tage of aluminum saturation. The data show that corn < yields are maximal when aluminum saturation is around 30% of the cation exchange capacity. They are therefore in close agreement with results from 0.04 similar studies on Utisols in southeastern U.S. I
Since the clay loam soil was the only site with a 0 0.05 0.10 0.15 0.20
measurable K response, yield data from this experi- K Applied (Meq/1OO cm' in surface 20cm)
ment were used to estimate the "critical" soil K level A Slope M app K) 0.37(t 04),R2 = 0.62
for corn in this environment. Figure 4 shows that yields (Meq. eatr. soilK) 07(- 0.12), R' = 0.60
were near maximal when extractable soil K was 0.12 0 Slope Meq. K applied
meq/100 cm3. Given the fact that these were among Dashed line shows approximate critical level of soil K (see Fig. 4)
the highest corn yields ever recorded for upland posi- Figure 2. Effect of applied potassium on extractable tions at Yurimaguas, the data should provide the most soil K in two Yurimaguas Ultisols after one biological reliable estimate to date of the critical K level; but cycle (six months). similar data from succeeding corn crops and other soils are needed to confirm this estimate.
Table 2. Effects of lime and potassium applications to two Yurimaguas soils on corn yield. Jan. '85 harvest.
Tons of Lime/ha
Soil Kg K/ha 0 2 4 K Mean
kg grain/ha
Clay Loam 0 3724 4525 4968 4406
39 3823 5409 5535 4922
78 3750 5460 6074 5095
117 4197 5587 5619 5134
156 3653 5810 5598 5020
Lime Mean 3830 5358 5559 4916
LSD (0.05); K = 48; Lime = 503; Lime x K = NS.
Sandy Loam 0 968 2653 1810
39 1889 2517 2203
78 1522 2443 1982
117 1672 2761 2216
156 1592 2794 2193
Lime Mean 1529 2634 2081
LSD (0.05); K = NS; Lime = 819; Lime x K = NS.

Potassium Recycling
-- Plateau -------- Quadratic --------------------- Whole-plant samples taken at early ear formation
were used to estimate the amount of K returned to
100 O the soil in corn stover.
. A, A Since K accumulation by corn is maximal at ear forM mation, any K not removed in the grain is returned
E 80 to the soil. Harvested corn grain was not analyzed for
o0 0 AK, but its concentration in mature corn seed is vir_9 60 tually constant at about 0.30%; and this value was
00 used to estimate K removal. "Recycled" K was then
(- estimated as total plant K at ear formation minus K
40 removed in the grain, and a relationship between proZ duct yield and recycled K was shown by least-squares
A Clay loam; V max. 6.07,/ha multiple regression (Figure 5).
20 0 Sandy loam; Y max. = 2.79 t/ha Several features of Figure 5 merit special comment:
I) Data from the two sites could not be pooled because
I the sandy loam produced as much vegetative dry mat10 20 30 40 50 60 70 ter as the clay loam but less than one-half as much
Al. +.+ Saturation (%) grain; 2) recycled K was a linear function of product
Figure 3. Effect of Al saturation in two Yurimaguas yield at each site, but the rate of K recycling was greater Ultisols on corn yield. Quadratic part: Relative yield on the low-yielding sandy loam soil-(recycled K (san= 82.64 = 1.045 (AI+. sat'n)2, R2 = 0.48. Solid dy loam) = 0.022 kg K/kg grain versus 0.016 kg symbols: K = 0. K/kg grain (clay loam))-because a smaller percentage
of silking-stage potassium was stored in grain; 3) recycled K is highly correlated with silking-stage dry matter; and 4) all of the Figure 5 data serve to emphasize
...- Quadratic-Plateau- the point that nutrient cycling via crop residues is a
Ax critical component of fertility maintenance.
Site #1 versus Site #2
6 A With one exception (the exception being soil texAE ture and other properties associated with texture), these
A two experiments were supposed to be conceptually
V identical. Obviously, they were not identical in pracA'A' twice, and it seems worthwhile to speculate on a pro>"A 5 bable cause for the two-fold yield difference between
the two sites. The clues point to a problem in cation
balance (Table 3).
Limed plots on the clay loam soil received a sizeable
Ax dose of magnesium (120 or 240 kg Mg/ha) because
dolomitic limestone (12% Mg) was used. The sandy
4I loam soil, by contrast, was limed with Ca(OH)2 and
0.05 0.10 0.15 0.20 no magnesium was applied. By virtue of using two
Extractable Soil K (meqll00 cm3) different liming materials, widely differing soil chemical
Figure 4. Effect of soil potassium in a heavy-textured environments were created on the two experimental (clay loam) Yurimaguas Ultisol on corn yield (each sites (Table 3-A), and silking-stage cation concentrasymbol is the mean yield of one to eight observations tions, as well as concentration ratios in corn plants at indicated level of soil K). Quadratic part: Yield = (Table 3-B), are a direct reflection of the suite of
2.65 + 49.66K 205.5K2. "Critical" K level = 0.12 nutrient cations in the soil that produced them.
meq/100cm3. While the Table 3 data do not "prove" that the
sandy loam soil was deficient in magnesium, they do

show that limed plots on the clay loam site were well
supplied with this element, and several pieces of ------------.Sandy Loam ...........--- -----------Clay Loam ----------evidence support the view that magnesium nutrition 7
was at least a part of the problem on the sandy soil: 100
1) In the unaltered state, each soil was "nutritionally
low" in Mg(0.18 and 0.12 meq/100 cm3 soil) because N "
Mg saturation of the exchange complex was less than 0 .
5% (5% Mg saturation is considered a "limiting value" / '"
for many crops). 60 ,, 4
2) After liming with dolomite, extractable Mg as :.well as percent Mg saturation in the clay loam soil :40 increased in direct proportion to the amount of Mg 0
applied; two tons of slaked lime on the sandy soil had
no effect on extractable Mg nor Mg saturation. 20
3) Two tons of dolomite on the clay loam lowered
the Ca:Mg ratio in the soil by 22%; two tons of slak- I 3 4 s
ed lime on the sandy loan raised this ratio by 48%. Product Yield (163 kg grainha)
4) On the clay loam soil, whole-plant Mg concentration in silking-stage corn increased in direct propor- Figure 5. Relationship between 1) corn yield and tion to extractable soil Mg. Corn grown on the san- silking-stage dry matter (open symbols), and 2) corn dy loam had less tissue Mg than the unlimed check yield and potassium recycled in corn stover (closed of the clay loam, and it was virtually unaffected by symbols). Corn grown at the same time on differing treatment. soils in the Yurimaguas environment. Data plotted
5) Without lime, the ratio of Ca to Mg in corn tissue over range In product yield for each site. was the same on both sites. This ratio was decreased
by liming the clay loam soil with dolomite; it was in- soil produced nearly 50% more ears per plant (0.94 creased when soil acidity in the sandy soil was neutraliz- vs 0.64), and the harvested ears were more than twice ed with Ca (OH)2. as large (208 vs 98 g/ear). The relatively minor dif6) On the sandy soil, there was a significant positive ference in soil texture is not considered to be the cause effect of K fertilization on the K:Mg ratio in silking- for the large differences in reproductive behavior. The stage corn plants (K/Mg = 2.15 when K = 0., K/Mg Mg-deficiency hypothesis is therefore the more plausi= 4.19 when K = 156 kg/ha); the effect of K treat- ble; it is supported, though indirectly, by the data at ment of the K:Mg ratio was not measurable on the hand. clay loam.
7) There was a highly significant positive response Summary
to K on the clay loam soil (Table 2); there was no In summary, the explanation for the widely differmeasurable response to K on the sandy soil. ing corn yields between the clayey site and the sandy
None of these observations constitutes direct cause- site follows: Initially, the soil on each site was too high and-effect support for the Mg-deficiency hypothesis. in exchangeable aluminum and too low in bases (K, They do show, however, that the suite of cations in Ca, and Mg) to produce corn. When the clay loam the two soils and in the plants differed appreciably was limed with dolomite, the Mg problem was resolvbecause the practices followed were not comparable. ed simultaneously with the acidity and Ca problems, It is also clear that a high-lime, high-Mg clay loam and corn responded to K fertilization as hypothesizsoil produced 5.5 tons of corn per hectare during the ed. Liming the sandy soil with Ca(OH)2 resolved two same period that a high-lime but low-Mg sandy soil of the initial problems (acidity and Ca), but it intenwas producing less than half as much. Furthermore, sifted the inherent Mg deficiency. the yield-component data of Table 3 suggest that the This "imbalance" in nutrient cations was further exsandy-soil problem was associated with pollenation and acerbated by each increment in K fertilization, and corn grain filling. Each site produced comparable amounts could not respond to K because inadequate Mg had of silking-stage vegetative dry matter and would ap- become the principal growth-limiting factor. pear to have similar yield potentials. Yet the clay loam

Table 3. (A) Properties of the soil on two sites used for lime-by-K experiments at Yurimaguas; and (B) some characteristics of corn plants grown on each site under near-equal aerial environments. A. Soil Property Site No. B. Plant Characteristic Site No.
1 2 1 2
1. Textural class (0-20cm) Clay loam Sandy loam 1. Harvested population (plants/ha) 36350 39560 2. ECEC (meq/lOOcm3) 4.66 2.79 2. Total dry matter at silking (Kg/ha) 5884 5528
3. Mg applied (kg/ha)' 3. Product yield (Kg grain/ha) 4916 2081
Lime (t/ha) = 0 0 0 4. Ears per plant 0.94 0.64
Lime (t/ha) = 2 120 0 5. Weight per ear (gm) 208 98
Lime (t/ha) = 4 240 6. [Mg] at silking (%, whole-plant)
4. Extractable Mg (meq/100cm3)2 Lime (t/ha) = 0 0.18 0.14
Lime (t/ha) = 0 0.18 0.12 Lime (t/ha) = 2 0.26 0.17
Lime (t/ha) = 2 0.36 0.13 Lime (t/ha) = 4 0.34
Lime (t/ha) = 4 0.58 7. [cation] at silking (meq/lOOgmO)3
5. Mg saturation (%) Lime (t/ha) = 0 67 62
Lime (t/ha) = 0 3.8 4.3 Lime (t/ha) = 2 86 73
Lime (t/ha) = 2 7.7 4.7 Lime (t/ha) = 4 89
Lime (t/ha) = 4 12.4 8. Ratio: total cations/Mg, at silking4
6. Cal mg Lime (t/ha) = 0 4.75 5.52
Lime (t/ha) = 0 6.82 9.25 Lime (t/ha) = 2 4.14 5.41
Lime (t/ha) = 2 5.31 13.73 Lime (t/ha) = 4 3.36
Lime (t/ha) = 4 4.54 9. Ratio: Ca/Mg, at silking4
Lime (t/ha) = 0 1.10 1.13
Lime (t/ha) = 2 0.97 1.45
Lime (t/ha) = 4 0.83
10. Ratio: K/Mg, at silking4
K (Kg/ha) = 0 2.06 2.15
K (Kg/ha) = 39 1.88 2.51
K (Kg/ha) = 78 2.06 3.47
K (Kg/ha) = 117 2.20 3.52
K (Kg/ha) = 156 2.40 4.19
1 One-half of the limestone applied to site -1 was dolomitic (12% Mg); site -2 was limed with Ca (OH)2.
2 All soil chemical data are based on samples taken at crop maturity.
3 [cation] = summation of Ca, Mg, and K (chem. equivalents).
4 Ratios are as chemical equivalents.

Weed Population Shifts Under Observations
Continuous Cropping Systems Analysis of data from this experiment has not yet
been completed. Therefore, only preliminary concluJane Mt. Pleasant, N. C. State University sions and observations will be given.
Robert E. McCollum, N. C. State University Grassy weeds are by far the most important weed problem in continuously cultivated, short-cycle food In traditional slash-and-burn agriculture, fields are crops (Table 1). Rottboelia exaltata, an annual grass, is abandoned as weeds begin to dominate food crops, potentially the most noxious weed (Figure 1). Rottand a forest fallow is the primary agent in weed con- boelia cannot be controlled in corn except by hand trol. Stable continuous-cropping systems, however, weeding, and controlling it in rice and grain legumes could be expected to require a comprehensive program requires a large herbicide input. In corn and soybeans, of weed management, probably including the use of the continued use of metolachlor alone eliminates all chemical herbicides. The objective of this project was weeds except R. exaltata, which establishes pure stands to test the following hypotheses: among the crops.
1) A given set of weed-control measures, if practiced over time, will cause a change in the spectrum of o--,--opl dry wt. gim2 140
weed species. With intensive chemical control, a few -O1s0
species will become dominant, requiring new control 60 120measures.
2) Effective weed-management programs can be 5- 100, 0
devised for high-input, continuous-cropping systems a) 5 -. in the Amazon Basin. .2 40 80 S. 0
A split-plot experimental design was used in a rice- corn-soybean-rice-corn rotation. Weed-control prac- 30 60
tices in rice were the main plot treatments; methods F" 4L
of weed control in corn and soybeans represented split- 20 plot treatments. In rice, the herbicides used were pro- 10 20
panil and oxadiazon; in corn, metolachlor, and in soybeans, metolachlor, sethoxydim, and bentazon. In the 0 0
second year of the experiment, a no-till treatment was introduced in which paraquat was used to kill existing Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 vegetation. In all crops, hand-weeded and check Figure 1. Trends in the level of infestation by R. extreatments (no weed control) were also included. altata during five production cycles. Yurimaguas, 1983-84.
Table 1. Weight and composition of weed population during five production cycles.
Total dry wt* BLW* Grasses Other Monocots
Cycle/Crop g/m2 % of total
1/Rice (11-83)*** 188 20 52 15
2/Corn (3-84) 46 15 70 15
3/Soybean (9-84) 128 27 69 4
4/Rice (1-85) 266 14 63 23
5/Corn (6-85) 178 6 79 15
Data are an average of four or five weed control treaments per crop, which included hand weeded,
chemcial control and no weed control.
* BLW = Broad leaf weeds
Numbers in parentheses are date of weed sampling. In each case samples were taken near crop

Cyperaceae species are not competitive with either Chemical Weed Control in Corn
crops or grassy species. In addition, they are readily
controlled with most of the herbicides in use at the Jonathan Lopez, INIPA
station. The majority of the cyperaceae found in Jane Mt. Pleasant, N. C. State University
Yurimaguas are annuals, rather than nutlet-forming Robert E. McCollum, N. C. State University
perennials. This probably accounts for their ease of
control. With few exceptions, broad-leaf species are In the selva, chemical weed control in corn may be not important weeds. practical when hand labor is scarce or expensive. There
Crop species have been observed to differ greatly are several herbicides available in Peru for controlling
in their ability to compete against weeds. Lack of weed a broad spectrum of weeds in corn. In Yurimaguas, control in upland rice often means crop failure. Corn, where the primary weed problem is grasses, however, appears to be far more competitive. Yields metolachlor has generally given good control.
may be reduced without weed control, but they are Metolachlor is a preemergence herbicide effective greater than zero. against grasses. It also controls a large number of broadleaf weeds. The objective of this project was to deterPreliminary Conclusions, Implications mine whether other herbicides such as atrazine, used
Even though data are still being analyzed, direct alone or in combination with metolachlor, might imobservations over the course of this experiment strongly prove weed control, or expand the spectrum of species
suggest the following: Weeds can be controlled in in- controlled, and thereby improve corn yields.
tensively managed, short-cycle food crops in this en- Atrazine was selected for the experiment because vironment, but the cost is likely to be high. With the it has been used extensively in temperate regions. Approducts and rates used in this experiment, the average plied together, atrazine and metolachlor control a much price of chemical control is approximately $ 100/ha. broader spectrum of weeds than does either alone. In This is not economical control within the present some treatments, metolachlor was also combined with
price/profit structure in Yurimaguas. other herbicides effective against broad-leaf weeds.
Observations during this study also suggest that Corn was grown for two cycles using eight weedupland rice should be removed from the high-input control treatments in a randomized complete block cropping system, unless yields can be significantly in- design: Hand weeding; no control; atrazine pre (2.25 creased to offset the high cost of weed control. Crops kg/ha); metolachlor pre (2.25 kg/ha); metolachlor pre more competitive against weeds, such as corn and grain + bifenox pre (2.25 + 1.25 kg/ha); metolachlor pre legumes, offer a broader range of weed-control options, + atrazine pre (1.75 + 1.55 kg/ha); metolachlor pre and may therefore be more practical than rice in the followed by 2, 4-D post (2.25 + .30 kg/ha), and high-input system. metolachlor pre followed by bentazon post (2.25 +
This experiment will be continued for at least two 1.0 kg/ha).
more cropping cycles, with corn replacing rice in the Weeds were counted by species in each plot seven rotation. weeks after planting. Prior to corn harvest,
aboveground dry-matter weights of weed species were
recorded. Corn yields on all plots were very low, ranging from 1754 to 2349 kg/ha, due to poor germination and irregular stands. As a result, there were no
significant differences in yield among treatments.
Weed Counts
Weed counts taken early in the season indicated large
differences among treatments. Check plots (those with
no weed control) had 874 weeds/m2, while treatments
with chemical control or hand weeding ranged from
16 to 109 weeds/m2. Grass species were the dominant weeds in all plots, accounting for 47-87% of the
total weed population (Table 1). Three grass species,
Axonopus compressus, Digitaria sanguinalis, and

Table 1. Effect of weed control treatment on number of weeds and composition of weed population in corn seven weeks after planting.
Treatment Total Weeds All Grasses All BLW+ All Cyperac. Commelina
No. Plants/m2 0% of total weeds
1. Hand weed 109 47 41 6 5
2. No control-check 874 53 34 10 2
3. Atrazine 88 84 1 11 3
4. Metolachlor 56 61 14 23 2
5. Metolachlor + bifenox 31 52 3 33 16
6. Metolachlor + bifenox 16 56 0 44 0
7. Metolachlor + 2, 4-D 42 67 0 31 2
8. Metolachlor + bentazon 46 87 7 4 2
+ BLW = broad leaf weeds
Level of significant main
effects ** ** ** ns ns
Species within grasses
A.compressus ns
D.sanguinalis **
P.paniculatumrn **
Paspalumpaniculatum, represented 75-96% of the grass no weed control had significantly more weeds than weeds in all treatments. other treatments. There was no difference between
Cyperaceae species and commelina species were not hand-weeded plots and those receiving chemical conpresent in significant numbers in any treatments, while trol. Metolachlor alone was equal to or better than broad-leaf weeds were found in large numbers in on- all other treatments in controlling both the total ly two treatments, hand-weeded and check. In both number of weeds and also the different components cases Lindernia bumilis comprised more than 85% of of the weed population. No additional control of any the broad-leaf population. This low-growing weed is weed group was obtained by the use of bifenox, uncompetitive with cultivated plants and is of little atrazine, bentazon, or 2, 4-D with metolachlor. In adimportance. dition, the data showed that atrazine alone did not
Planned comparisons were used to determine which control D. sanguinalis. When atrazine alone was comof the treatments were responsible for the significant pared with metolachlor alone or metolachlor plus differences identified by the F test. Single degree-of- atrazine, plots with atrazine alone had a significantly freedom comparisons for relevant treatments are shown greater number of D. sanguinalis. in Table 2. For all categories of weeds listed, plots with
Table 2. Tests of significance for differences in weed counts for planned treatment comparisons.
Level of Significance
All All All P. D.
Contrast Weeds Grasses BLW Paniculatum Sanguin.
1. Handweed vs. all chemical trts. ns ns ns ns ns
2. No control vs. all others ** ** *
3. Metolachlor vs. atrazine ns ns ns ns
4. Metolachlor vs. (metol. + atrazine) ns ns ns ns ns
5. Atrazine vs. (metol. + atrazine) ns ns ns ns **
6. Metolachlor vs. (metol. + bifenox) ns ns ns ns ns
7. Metolachlor vs. (metol. + 2,4-D) ns ns ns ns ns
8. Metolachlor vs. (metol + bentazon) ns ns ns ns ns
ns = Not significant; ** = Highly significant

Weed Weights Before Harvest components of the weed population. It is unlikely that
In all treatments, the poor stand of corn provided there would be any benefit in using additional herlittle or no competition to emerging weeds, which at- bicides in combination with metolachlor to control
tained heavy growth by late season. Total dry weights them.
ranged from 147 to 366 g/ml. Grasses were the dominant species, comprising 83 to 98% of the total weed Implications
weight. Two species, A. compressus and D. sanguinalis, D. sanguinalis is an important species in most fields comprised 65-98% of the grass population. Broad-leaf at the station. Research in temperate regions has shown weeds, cyperaceae species and commelina species were that atrazine has little effect on this grass. Confirming unimportant components of the weed population. this information under Yurimaguas conditions enables
Since A. compressus was the only weed affected by the development of more effective weed-control
treatment, single degree-of-freedom contrasts were measures for corn. A. compressus, a perennial grass, has made in order to determine which treatments were not been an important weed species in short-season relevant to its control. Plots with metolachlor alone food crops in Yurimaguas. An additional cycle of this had much higher weights of this species than plots with experiment is required to determine A. compressus' atrazine alone or atrazine plus metolachlor. All resistance to metolachlor and its importance as a weed
chemical-control treatments also had a much higher in corn.
weight of A. compressus than did hand-weeded plots. Weeds are a critical factor in continuous cropping The data indicated that atrazine controls A. compressus systems. They are as important in limiting yields as while metolachlor does not. soil fertility while their management is considerably
more difficult. Two years of research has shown that
Conclusions the weed populations will change in response to
Despite the lack of corn-yield response to weed- chemical control practices. Species resistant to hercontrol treatments, two conclusions can be drawn from bicides dominate with time, and their control becomes the first cycle of this experiment: increasingly difficult and expensive. At present,
1. Use of metolachlor plus atrazine increased the chemical weed control represents an enormous
spectrum of weeds controlled compared to either her- economic input; it averaged $ 100/ha for upland crops bicide alone. Atrazine alone did not control D. in Yurimaguas. Hand weeding is often much cheaper,
sanguinalis early in season, while metolachlor alone but in many cases labor is simply not available. Confailed to control A. compressus later in the season. tinued research effort will be required to develop weed
2. Broad-leaf weeds and non-grass monocots such management practices that are agronomically effective
as cyperacea sp. and commelina sp. are not important as well as economically viable.

Technology tested at Yurimaguas for sustained irrigated rice production in fertile alluvial soils of the Amazon has been validated and is now being transferred to producers through Peruvian extension programs. Peru recently became self-sufficient in rice, due in part to the expansion of flooded-rice agriculture into the Amazon. Several general principles of Amazon flooded-rice production have been established, including the following:
1) Land can be cleared by slash and burn or by bulldozing, as the usually detrimental effects of soil compaction by bulldozers do not seriously affect paddy rice. Care must be given not to displace topsoil during the land-leveling operation.
2) Supplemental irrigation every two weeks increases yields by about 50% as compared to yields from crops dependent entirely on rainfall. The source of water may be gravity canals or pumping from rivers.
3) Transplanting provides higher yields than broadcasting seeds for the first two crops due to insufficient leveling. Broadcasting pregerminated seeds is highly advantageous after the paddies are adequately leveled.
4) Fertilization will be minimal. No significant responses to N or P fertilization have been observed during eight consecutive crops grown in a four-year period. N deficiencies are expected to appear with continous use.
5) A combination of herbicides provides satisfactory weed control.
6) Two crops a year with recommended short-statured varieties can produce annual yields of 12 to 15 ton/ha or 5.2 to 6.6 t/ha/crop. Considering that one hectare of acid soils must be cleared every year to produce one ton of upland rice, every hectare under irrigated rice production might save from 12 to 15 hectares of tropical forests annually from deforestation.
Research and extension activities are now the responsibility of INIPA's National Rice Program. The work reported here is conducted to further test and refine this technology for long-term floodedrice production.

Intensive Management of Alluvial Soils with a Cyclone-type seeder. One man can seed 1.5
For Irrigated Rice Production to 2.0 ha per day by hand, but the same person can
plant 5.0 ha in one day with the Cyclone seeder .
Luis Arevalo, N. C. State University In the second experiment, three types of herbicides
Robert E. McCollum, N. C. State University were tested with direct-seeded rice. Ten days after Jos6 R. Benites, N. C. State University seeding, the thiobencarb and oxadiazon treatments proAlfredo Rachumi, INIPA duced harmful effects. The check plots gave 100% gerCesar Tepe, INIPA mination, but all the other herbicide treatments gave
Kristinaa Hormia, Institute of Development only 30 to 50%. The effects on yields are shown in Studies, Finland Table 2. Using 2-4 D amine alone at a rate of 2.0 L/ha
resulted in a 20% higher yield than the check plot and Research on this important management option has performed better than the other herbicides. The low
progressed to the point of widespread technology yields obtained in this experiment are probably due transfer, contributing to a 40% increase in rice pro- to herbicide toxicity and an attact of molluscs Arion, duction on fertile, alluvial soils of the Amazon Basin the two together affecting initial plant growth severely.
of Peru. The objectives of this project, which was conducted at the Yurimaguas Experiment Station, were Nitrogen and Phosphorus Fertilization
1) to determine the best methods of planting to achieve After eight consecutive rice crops, there have been maxiumum yields in paddy rice; 2) to determine the no significant responses to either fertilizer N at rates best fertilizer sources, schedules and rates; 3) to deter- up to 200 kg/ha or to P at rates up to 100 kg mine optimal irrigation frequency, and 4) to determine P205/ha. In the N experiment, mean grain yields the effect of water-level fluctuation on the survival of were in the range of 6 to 7 t/ha for all treatments.
paddy-rice seedlings. In the P experiment, mean grain yields were also
around 6 t/ha regardless of P rate or P source.
Transplanting vs. Direct Seeding
A project was initiated in August, 1981 with the Supplementary Irrigation
objective of determining the best planting methods in The paddy-rice production system developed by the paddies newly developed on an Eutric Haplaquept project includes supplemental irrigation. Table 3 shows (clayey, mixed, isohyperthermic), on a high terrace near that the best yields were obtained with supplemental the Shanusi river at Yurimaguas. The results shown irrigation once every two weeks, as compared with in Table 1 indicate that annual mean production was rainfall dependency. Table 4 shows the effect of difonly slightly less with direct seeding than with ferent water depths on crop yields through three transplanting. Two new experiments were initiated in harvests. The data indicate that highest yields were 1985 to develop seeding methods and weed-control obtained when water depth was maintained between practices for direct-seeded rice. The first found that 10 and 20 cm. At higher and lower levels, yields tend
there was no significant difference in yields between to decrease.
crops broadcast-seeded by hand and those broadcast
Table 1. Performance of floooded IR4-2 rice in different land preparation systems in an Eutric Haplaquept
at a "restinga" in Yurimaguas, during the first 26 months after clearing.
Land Planting First Second Third Fourth Fifth Mean per annual
preparation system crop crop crop crop crop crop production1
Grain Yields, ton/ha
Puddled: Transplanted 7.9 5.2 7.1 6.0 6.8 6.6 15.2
Broadcast/direct-seeded2 3.2 4.9 6.4 4.8 6.7 5.2 12.0
Dry: Transplanted 8.3 6.7 6.2 5.6 6.3 6.6 15.3
Broadcast/direct-seeded2 6.3 5.6 4.9 4.6 6.0 5.5 12.6
Assuming 2.3 crops per year
2 Hand-weeded

Conclusions Implications
1) Direct-seeded paddy rice produced mean annual Recommended varieties of paddy rice can produce yields only slightly lower than those from transplanted yields in the range of 12 to 15 ton/ha/yr on alluvial rice. Direct seeding eliminates pre-plant soil puddling Amazon soils without fertilization for the first three and thereby reduces labor costs. years. Direct seeding with a Cyclone-type broadcaster,
2) Broadcast-seeding rice with a cyclone-type seeder coupled with judicious herbicide use, can save substanwas as effective as broadcasting by hand, and required tially on labor, an important factor because skilled less than half the manpower. laborers are scarce in this area. Despite the heavy rain3) Of the three herbicides tested for use in broadcast- fall in the Amazon, supplemental irrigation from rivers seeded rice, 2-4 D amine used alone gave the best or ponds every two weeks improves rice production results. 50%. These results are being tested in farmers' fields
4) Best rice yields were obtained with supplemen- in the Tupac Amaru settlement near Yurimaguas. tal irrigation once every two weeks, which maintained the water level between 10 and 20 cm. Table 3. Effect of the irrigation frequency on the rice yield for
cultivar IR4-2.
Table 2. Effects of week-control methods on directseedd 1R-2 pddy ice.Supplemental
seeded IR4-2 paddy rice. Irrigation Number of Harvests
Herbicide Rate, L/ha Rice Grain Yield, t/ha Frequency 1st 2nd 3rd Mean
Thiobencarb 7.0 + 3.0 4.64 L/ha
2-4 D amine Once/2weeks 5.78 6.74 6.00 6.17
Rainfall only 4.08 5/13 3.99 4.40
Thiobencarb 8.0 + 2.0 4.56
2-4 4 D amine
Table 4. Grain yield as affected by different water levels. Rice
Oxadiazon 2.0 + 3.0 4.51 variety IR4-2.
2-4 D amine Number of Harvests
Oxadiazon 4.0 + 2.0 4.32 Water Levels 1st 2nd 3rd Average
2-4 D amine cm L/ha
0 5.48 3.80 5.13 4.80
2-4 D amine 2.0 4.79 10 6.77 5.03 5.44 5.75
20 6.45 5.18 6.18 5.94
Check 3.90 30 5.66 4.92 4.48 5.02

Knowledge of the properties and distribution of soils in the humid tropics serves as the basis for soil management. Proper selection of sites for extrapolation work requires good soil characterization and classification by Soil Taxonomy, as well as interpretations practical in agronomic terms. The Fertility Capability Classification (FCC) system is being adopted in many areas of the world as a basis for research planning and technology transfer because it helps identify the soil characteristics that affect crop production. Coupled with Soil Taxonomy, the FCC system is an effective tool in the development of soil-management technologies adapted to specific sites and conditions.
An example of the widespread applicability of this approach is an FCC map of Africa, being developed by the Food and Agriculture Organization of the United Nations (FAO). By providing planners with an inventory of Africa's soils characterized by their productive potential, the FAO's map will assist in long-range agricultural research and development. N.C. State University collaborators on this project are developing software for personal computers that will allow soil maps to be digitized, so that users might have at their fingertips maps with any soil grouping desired. The work described here concentrates on two general areas. The first is the adaptation and refinement of the FCC system for various tropical ecosystems and crops. The second is the study of soils in several humid tropical regions on the agricultural frontier, where soil characterization lays the groundwork for future research and development.

FCC Adaptation to Wetland Soils The FCC interpretations of aquic soils were tested
by workshop participants from the International NetPedro A. Sanchez, N. C. State University work on Soil Fertility and Fertilizer Evaluation for Rice
Stanley W. Buol, N. C. State University (INSFFER) and Soil Management Support Service
(SMSS), during a five-day field trip in Central Luzon,
The Fertility Capability Classification system (FCC) Phillipines, where 16 profiles were examined. Inforhas been tested on many sites around the world in mation from these profiles was related to the condiorder to adapt it to various soils and conditions. In tion of rice plants growing on adjacent plots established each case, the primary aim has been to identify soil for INSFFER fertilizer trials. The FCC system was constraints to crop production and to guide decisions successful in predicting Zn deficiency by the presence about how to relieve or offset these constraints. At of either the b (calcareous) or the g' (prolonged the request of the International Rice Research Institute flooding) modifiers. Two other characteristics, ease of (IRRI) and Soil Management Support Services (SMSS), puddling and difficulties in regenerating the puddled the FCC system was applied to soils with aquic soil- structure for rotation with upland crops, were also moisture regimes in order to relate soil classification readily identified by FCC classes. The possibility of with soil-productivity parameters that are important low N fertilizer efficiency indicated by the v (vertic) for flooded-rice production. and b (calcareous) modifiers was confirmed by the
Interpretations for FCC soil types and substrata types results of the INSFERR trails. Table 3 shows the Soil
for wetland soils are shown in Table 1, and for con- Taxonomy and FCC designation of the pits studied
dition modifiers in Table 2. The FCC system iden- and the fertility problems encountered.
tified specific soil characteristics directly related to most
of the physiological disorders of rice, except for iodine Conclusions
and boron toxicity. Iron toxicity caused by Fe-rich in- The workshop's soil-fertility group recommended
terfiow from adjacent uplands requires an FCC the following in relation to FCC:
classification of such upland soils. One additional con- 1. The FCC system should be tested and applied dition modifier was necessary to include in the FCC: to wetland rice soils as a means for grouping together
a g' modifier for constantly flooded soils. soils with similar constraints.
Table 1. Interpretations of FCC type and substrata types for rice cultivation in aquic soil moisture regimes.
High in infiltration, low water-holding capacity, more difficult to do thorough puddling; traffic pans infrequent; relatively easy to regenerate structure for rotation with other crops. Level of management (nutrients and water) required for
high rice yields is higher than in L or C soils.
Medium infiltration, medium water-holding capacity, usually easy to puddle (except Lx), and medium difficulty in regenerating structure. Traffic pans important in these soils except for Lx. L soils are generally more productive
for rice than S soils and less than C soils, provided condition modifiers are similar.
Low infiltration rates, high water-holding capacity (except Ci), easy to puddle and difficult to regenerate previous structure (except Ci); traffic pans not common. Generally higher productivity for rice than L or S soils provided condition modifiers are similar.
Deep organic or peat soils, with little to no potential for rice production.
CC, CL or OS
Shallow organic soils with a mineral layer of less than 50 cm depth. Potential for rice production
Somewhat better water-holding capacity and thus better suitability for rice production than S soils.

Table 2. Interpretations of FCC condition modifiers for rice cultivation in aquic soil moisture regimes.
When only one modifier is included in the FCC unit, the following limitations or management requirements apply to the soil. Interpretations may differ when two or more modifiers are present simultaneously or when textural types are different.
Defines wetland soils. Preferred moisture regime for rice cultivation.
Prolonged submergence causes Zn and perhaps Cu deficiency.
Topsoil moisture limited during dry season unless irrigated. Generally only one rainfed rice crop can be grown a year. Irrigated rice during the dry season has higher yield potential and responds to higher N rates.
Low inherent fertility because of low reserves of weatherable minerals. Management levels higher than in soils without this modifier. Potential K deficiency depending on base contents of irrigation water.
Low ECEC reflects less gradual N release, more exacting N management. Identifies degraded paddy soils with SLa or L-Ca and low organic matter contents. If so, potential H2S toxicity can occur if (NH42S04 is used as N source. Potential Fe toxicity if adjacent uplands have Fe-rich soils.
Aluminum toxicity will occur in aerobic layers. Soil test for identifying P deficiency recommended.
Potential P deficiency under continuous rice cropping. Otherwise optimum aerobic pH for flooded rice production. If combined with SLe or I-Ce, potential Si deficiency.
High pH may induce Fe deficiency when aerobic, and Zn deficiency when water-logged. High N volatilization loss potential from broadcast N applications. NH4+ fixation by 2:1 clays possible. Mollusk shells indicative of Zn deficiency.
High P fixation by Fe; P deficiency likely; Fe toxicity potential; soils difficult to puddle and will regenerate original structure rapidly. Inter-flow from Ci uplands may cause Fe toxicity to e soils with lower topographic position.
Volcanic materials indicate high inherent fertility with no potential Si deficiency; N and P deficiencies common and soil may fix large quantities of P; soils difficult to puddle and will regenerate original structure rapidly.
Soils will shrink and crack when dry, causing excessive percolation losses afterwards. Easy to puddle but difficult to regenerate structure. P deficiency suspect and should be determined by soil tests. Soil fixes applied NH4' and releases it later to the rice crop a positive attribute. Cracks may not close after reflooding due to ripening-water percolation and additional N losses.
Defines saline soils. Drainage needed but must consider conductivity of irrigation water.
Defines alkali soils. Reclaiming with drainage and gypsum applications may be needed.

Acid sulfate soils causing Fe and S toxicity when anaerobic and AI toxicity when aerobic. Depth at which c modifier occurs determines feasibility of rice production. Strong P deficiency likely and Al toxicity when aerobic.
Presence of gravel limits land preparation and water holding capacity.
Skeletal soils with limited potential for rice production.
The higher the % slope, the narrower the paddies will be and the higher the rise between terraces will be.
2. The FCC modifier for acid-sulfate soils (c) needs to characterize in a systematic and quantitative basis further refinement to establish a better limit. An ad- extremely important factors such as: 1) water-table ditional modifier for cation imbalance ratios (r) should depth during dry and wet seasons, 2) frequency, depth, be developed; additional modifiers for high organic speed, and duration of natural flooding, 3) quality of nitrogen in the topsoil (q), and for high available native irrigation, flood or ground water and other relevant topsoil phosphorus (p), should be investigated and in- hydrological parameters. A working group should be corporated into the system if reliable quantitative limits established to develop the HCC. Hydrological concan be identified. straints often override soil constraints in rice produc3. Field trials in rice fertility and soil management tion. The development of this technical system is, should have the soil classified according to Soil Tax- therefore, considered an urgent matter. onomy at the family level. Emphasis should be given In addition, the INSFFER network meeting conto mineralogy characterization, in relation to fixation cluded that Soil Taxonomy is to be used to characterize and release mechanisms. FCC should not be considered network sites and that the FCC system is to be tested an altenative to Soil Taxonomy, but as a technical by all countries participating in the network, which system that facilitates its interpretation for agronomic are: Burma, Bangladesh, China, India, Indonesia, purposes. Malaysia, Nigeria, Nepal, Pakistan, Philippines, Sri
4. A Hydrological Capability Classification (HCC) Lanka, Thailand, and Vietnam. Tests are under way system should be developed along similar lines as FCC in many of these countries.
Table 3. Field testing of FCC system in 14 pedons of Luzon, Philippines, and nutritional deficiencies observed in adjacent INSFERR trials.
Zn P N Mg/K
Taxonomy FCC deff response inefficiency imbalance
Andaqueptic Fluvaquent CLg' X
Vertic Haplaquoll Cg'v X
Vertic Tropaqualf Cgh X
Udorthentic Pellustert Cgdv X X
Aeric Tropaquept Cg
Entic Pellustert Cgdhv X X
Aeric Tropaquert LCgd
Fluvaquentic Haplustoll CLdbg X
Entic Chromustert Cdvbg X
Andic Palehumult Lkax no trial
Typic Haplaquoll Lgdbk X X
Cummulic Haplaquoll LCgdbk X X
Typic Tropaquept Lgd
Aquic Ustifluvent LSdeh

New-Project Update FCC and Site Characterization
Several projects in this series have not been under In Relation to Caribbean Pine way long enough to yield substantive reports, but should be mentioned because of their importance to the pro- Leon H. Liegel, USDA Southern Forestry gram as a whole. Station, Puerto Rico
Stanley W. Buol, N.C. State University
Robert E. Hoag, N.C. State University
Volcanic Ash Influence on Pedro A. Sanchez, N.C. State University
Transmigration Areas of Sumatra The purpose of this project was to evaluate the FerHardjosubroto Subagjo, Center for Soil tility Capability Classification system (FCC) in relaResearch tion to an important commercial tree crop, Caribbean
Stanley W. Buol, N.C. State University pine, and to determine if the system needs modificaJohn R. Thompson, University of Hawaii tion for use with perennial tree crops. To date samples
Michael K. Wade, N.C. State University have been taken at 46 sites in Venezuela, 44 in Jamaica,
Mohammed Sudjadi, Center for Soil and 29 under Caribbean pine (Pinus caribaea, var.
Research honurensis). These samples were analyzed for particleI. Putu Gedjer, Center for Soil Research size distribution, pH value, extractable Al, Ca, Mg, Agus B. Siswanto, Center for Soil Research K, and P. Brief profile notes were made at each site.
Using these data, each site was classified by FCC The objective of this project is to determine the criteria.
amount, thickness and effect on phosphate chemistry A preliminary summary of the data reveals that the of amorphous material in the major soil and geographic majority of the Venezuela sites were coarse to medium areas around the Sitiung-Bangko transmigration set- in texture, types S, L, or SL, and had high Al concentlements, on the island of Sumatra. The western part trations (a), low CEC (e), an ustic soil moisture regime of Sumatra belongs to the Bukit Barisan mountain (d), and low potential to supply potassium (k). The range, where faulting and folding have been accom- Jamaican sites were medium to fine in texture, types panied by volcanism. Along the foot of these moun- L or C, with many having no obvious chemical contains lies a vast, undulating and rolling plain. straints. Some did have acidity constraints (h), and a
Two transects extending from the lowland to few had Al constraints (a). A low potential to supply volcanoes were studied, along with sites intermediate K was also present at several sites. Soils studied in Puerto them in the transmigration areas. Profiles were to Rico were also medium and fine in texture, types described and soils were sampled to a depth of 2 m L and C, with no subtype texture modifier. These at each site. The tentative classification of these soils generally contained more Al, and were universally low is generally Paleudults or Haplorthox at the lower in their potential to supply K. Further work on this altitudes (40-160 in), Topudults at the middle altitudes project will compile soils data, comparing tree growth (300-350 in), and Dystrandepts or Hydrandepts on and FCC grouping for each site. the lower slopes of the volcanoes (1200-1350 in). As this project continues, soils will be further characterized and analyzed at the Center for Soil Research and at N.C. State University.

Alluvial Soils of the Amazon Basin volcanic rock strata, the tributaries dissect limestonebearing marine deposits along the eastern flank of the
Robert E. Hoag, N.C. State University mountains. This group of nine sampling sites has pH Stanley W. Buol, N.C. State University values throughout their profiles of 5.0 to 6.5, and tend Jorge Perez, INIPA to be near a value of 6.0 in the upper horizons.
Mineralogy of the sand fraction is mixed, and montAlluvial soils are usually considered to be of high morillonite dominates the clay fraction. Characterizanative fertility. The purpose of this work was to test tion data for the sampling site along the Cashiboya such a hypothesis, which would be useful in ex- are representative of this group, although textures may
trapolating soil-management options for alluvial soils be loamy rather than clayey.
in the humid tropics. To do so, the investigators sampl- The third group of soils includes those sampled along ed soils from three different types of deposits in the rivers that originate among pre-weathered, within-basin Amazon Basin of Peru, determined their physical, sediments of Peru. Chemical properties of soils sampled chemical and mineralogical properties, and developed along two rivers that originate from within-basin a means of predicting the occurrence of the contrasting sediments and northern portions of the Andes in soil properties on flood-plain landscapes in the region. Ecuador are also included with this group. These soils
The 20 sampling sites, placed into three groups, were are strongly acid, with pH values ranging from 4.0
selected on the basis of the geologic formation from to 5.0. The clay fractions of these soils are dominated which the tributaries originate. Representative data are by either montmorillonite or kaolinite, with both given in Table 1. Sampling sites in Group One were minerals being present in abundance. Aluminum along rivers that originate within the Eastern Peruvian saturation is high and may exceed 85% of the exchange
Cordillera. As predicted, these soils have relatively high complex.
pH values throughout their profiles, ranging from 6.5 The soil profiles were classified according to soil taxto 8.5. (Complete data for each of the profiles sampl- onomy and results are presented in Table 2. Classificaed are in Mr. Hoag's thesis). tion according to the Fertility Capability ClassificaSampling sites in Group Two were along rivers that tion system (FCC) was based upon data obtained from
originate in the foothills of the Peruvian Andes, where samples submitted to the N.C. State University Soil
carbonaceous and non-carbonaceous sandstones Testing Laboratory.
predominate in the headwaters. These soils have
chemical properties similar to those sampled along cer- Conclusions
tain rivers that originate in the Ecuadorian Cordillera. Physical, chemical and mineralogical data support Although upper elevations of the Ecuadorian Andes the premise that information describing the geologic are composed predominantly of acid igneous and formations from which tributaries in the Amazon Basin
Table 1. Summary of topsoil fertility and FCC classification of Peru originate may be useful in predicting soil prorepresentative of sampling sites in three groups of soils in the perties on floodplains. Soils along rivers with headAmazon Basin of Peru. (Chemical values are for top 20 cm) waters in the Eastern Peruvian Cordillera are generally of high base status and pH values. Montmorillonite
Location dominates the clay fraction of these soils. There may
Group 1 Group 2 Group 3 be some question as to the availability of P and
Soil Property Rio Mayo Rio Cashiboya Rio Yavari micronutrients due to complexing at the high pH levels. Soils developing in sediments eroded from the
FCC Classification Cgvb Cg Cga calcareous sedimentary deposits of the Andean foothills
Ph 7.5 5.6 4.0 in both Peru and Ecuador tend to be slightly acid with
Al Saturation 0 0 78
Ca, meq/100 g 39.7 29.7 1.8 no serious chemical or mineralogical problems. In the
Mg, meq/100 g 9.7 7.0 0.5 Eastern portion of the Peruvian Basin, the floodplain
2, 0eq/100 g .0 0.69 0.36 soils tend to be strongly acid with very high levels of
K, nmeqf900 g3 aluminum saturation. Repeated sequences of weatherMn, ppm 90 130 35
Cu, ppm 6.2 4.9 2.3 ing, erosion and deposition over a long period of time
Zn, ppm 4.5 3.2 have apparently contributed to the leaching of solu, ppm 145 2 6 ble bases and dominance of Al on the exchange
P, ppm 145 29 6 complex.

Table 2. Taxonomic classification of representative profiles of alluvial soils of the Upper Amazon. Location Classification
Rio Aguaytia -Typic Tropofluvent, clayey over loamy, mixed (nonacid) isohyperthermic.
Rio Blanco -Aeric Tropaquept, fine, montomorillonitic (acid), isohyperthermic.
Rio Cashiboya -Aeric Tropic Fluvaquent, very-fine, montmorillonitic (acid), isohyperthermic.
Rio Cumbaza -Typic Tropofluvent, coarse-loamy, siliceous (nonacid), isohyperthermic.
Rio Cushabatay -Aeric Tropic Fluvaquent, coarse-loamy, mixed (nonacid), isohyperthermic.
Rio Mayo -Aquic Hapludoll, very-fine, montomorillonitic (calcareous), isohyperthermic.
Rio Mazan -Aeric Tropic Fluvaquent, fine, kaolinitic (acid), isohyperthermic.
Rio Nanay -Aeric Tropic Fluvaquent, fine-loamy, siliceous (acid), isohyperthermic.
Rio Napo -Typic Tropofluvent, coarse-silty over clayey, mixed (nonacid), isohyperthermic.
Rio Nucuray -Typic Eutropept, fine-silty, mixed, isohyperthermic.
Rio Paranapura -Typic Tropofluvent, coarse-loamy mixed (nonacid), isohyperthermic.
Rio Pastaza -Typic Fluvaquent, coarse-loamy, mixed (nonacid)
Rio Putumayo -Aeric Tropaquept, very-fine, kaolinitic (acid), isohyperthermic.
Rio Samiria -Typic Tropofluvent, fine-silty, mixed (nonacid), isohyperthermic.
Rio Tamshiyacu -Typic Fluvaquent, fine, montmorillonitic (acid), isohyperthermic.
Rio Tapiche (upper) -Aquic Fluvaquent, fine montmorillonitic (acid), isohyperthermic.
Rio Tapiche (lower) -Aquic Eutropept, fine-silty, mixed, isohyperthermic.
Rio Tigre -Aeric Tropic Fluvaquent, fine-loamy, mixed (acid), isohyperthermic.
Rio Utoquinea -Aeric Tropic Fluvaquent, fine-silty, mixed (acid), isohyperthermic.
Rio Yavari -Typic Tropaquept, very-fine, montmorillonitic, (acid), isohyperthermic.
Soils of the humid tropics are diverse not only on may be extrapolated. The study may serve to idenuplands and mountains, but also on floodplains. The tify regions that may require additional research if notion that all alluvial soils within the Amazon Basin agriculture is to expand in them. As an example, it of Peru are homogeneous is clearly mistaken. As may be necessary to use lime or Al-tolerant genotypes chemical and physical properties diverge from one loca- in the very acid alluvial soils in Eastern Peru. Data tion to another, so must management recommenda- from this study may also prove to be useful in selections. Results of this study may help to identify the ting drainage systems for more intensive soil-genesis geographical boundaries within which research data or fertility investigations.

Ultisol Dominated Landscapes the other occupies the lower areas associated with
In Southeastern Peru stream drains.
Surface 1 covers the level and nearly level uplands.
Laurie J. Newman, N.C. State University It is the oldest and most stable surface of the three.
Stanley W. Buol, N.C. State University Surface 2 consists of the side slopes and dissected porRafael Chumbimune, INIPA-CIPA XVII, tions of the uplands. Within this group are landscape
Madre de Dios positions with greater than 3% slope. Surface 3, on
the recent flood plains, occupies the smallest portion
An area of southeastern Peru was selected for a study of the study area. This surface is the youngest and may
whose objectives where 1) to characterize the physical, be subject to rapid changes in morphology with the
chemical and mineralogical properties of the soils of movement of the nearby channel.
the region, and 2) to determine the relationship of soil The soils have textures ranging from loamy fine sand properties to landscape position. The research site, 450 to clay. All of the upland soils in the sandy area have ha near Puerto Maldonado, Madre de Dios, is con- an increase in clay content and a decrease in sand considered representative of the soils, climatic conditions, tent with depth. In the flood plain of the third order landscapes and vegetation in the region. Results from stream, organic soils are dominant. On the uplands this project may assist in the extrapolation of research of the sandy area, clayey soil families are located beside to areas within the region where knowledge of the soils with coarse loamy control sections. These abrupt soil resource is scarce. changes in texture laterally across the landscape are
The topography of the region is characterized by characteristic of areas where soils have developed in
level uplands, dissected side slopes and recent flood alluvial parent materials.
plains. Lower base levels caused drainage entrenchment Soil pH values for the upland soils are generally and formation of the associated convex and planar side higher at depth in the profile than at the soil surface.
slopes. The flood-plain soils are forming in Holocene, Values determined in water range from 3.4 to 4.9 local alluvium and organic parent materials. (Table 1). The soils in the recent flood plain of the
Ultisols with ustic soil moisture regimes are the second-order streams have pH values ranging from 1.9
predominant soils of the uplands. These Ultisols can to 5.6. The pH values of the upland soils of the region be characterized as having pH values ranging from 3.9 may be a result of soil formation in acid parent to 4.9, aluminum saturation values greater than 70% materials, or of formation in higher pH materials where
of the effective CEC in the argillic horizons, and sur- bases have been leached out over time.
face horizon cation exchange capacities of 1 to 6 cmol Soil reaction data from the flood plains of the Madre (+)/kg. Textures of the Ustults vary from clayey to de Dios and Tambopata Rivers indicate that recent course-loamy, as a function of the texture of the in- alluvium is neutral to slightly acid reaction, having pH itial materials and position on the landscape. There values ranging from 5.2 to 6.9. Because the presentare few weatherable minerals in the sand size fractions day rivers have a similar source as the sediments in of these soils. The dominant clay mineral is kaolinite. which the upland soils are formed, it is assumed that Some muscovite mica, vermiculite and hydroxy-Al- the soils of the upland have developed in sediments interlayered vermiculite are present. Paleusults, located with neutral reaction and that post depositional in positions where water tables fluctuate within the removal of bases is responsible for the increase in soil
profile, have features associated with oxidizing and acidity.
reducing conditions such as mottling, plinthite and in- Extremely low pH values of 1.9 to 2.1 have been durated iron. measured in the epipedon and subsurface horizon of
The poorly drained soils formed in recent alluvium a buried soil in the second-order stream drain (Table
are Placaquods and Troposaprists. The texture of these 1). pH values of less than three are rare in saturated soils is dependent on the depositional environment of soils, but have been recorded in sulphitic soils, a result the alluvial materials. The sand fraction is primarily of oxidation after soil drainage. Pyrite (FeS) may be quartz. Magnetite, pyrite and kyanite are present in present in these horizons and may be assumed to be trace quantities. The soils are strongly acid to medium controlling the very acid soil reaction. The organic soils acid and vary in base status. associated with the Rio Chonta have pH values similar
Three geomorphic surfaces have been defined within in range to those on the upland.
the area. Two of these are located on the upland, and The amount of exchangeable aluminum of the

Table 1. Physical and chemical properties of selected profiles in Puerto Maldonado, Peru.
Depth Clay Sand Org.C pH Al Ca Mg K ECEC ECEC Al sat.
(cm) --- % --- H20 --- c mol(+)kg --- cmol(+)kg clay %
Soils of the Level Upland (Surface 1):
Carretera; Typic Paleustult; clayey, kaolinitic, isohyperthermic
0-9 27 26 1.6 3.9 4.1 0.1 0.2 0.2 5 19 81
9-25 30 22 0.7 3.9 4.2 0.1 0.1 0.1 5 17 82
25-52 39 19 0.6 4.2 5.3 0.1 0.1 0.2 7 17 79
52-70 44 18 0.5 4.4 6.4 0.1 0.1 0.1 7 16 90
70-118 48 17 0.5 4.5 6.8 0.0 0.1 0.1 8 16 89
118-155 47 16 0.7 4.6 6.7 0.0 0.2 0.1 8 17 86
155-200 46 21 0.3 4.6 6.3 0.0 0.2 0.1 8 16 86
Estacion; Typic Paleustult; coarse-loamy, siliceous, isohyperthermic
0-9 3 81 0.4 4.3 0.3 0.4 0.4 0.1 2 53 18
9-24 2 70 3.9 1.0 0.1 0.2 0.1 2 73 60
24-53 5 69 3.9 1.7 0.1 0.1 0.1 2 43 73
53-82 15 62 4.1 1.4 0.2 0.2 0.1 2 14 68
82-110 16 68 0.3 4.1 1.4 0.0 0.0 0.1 2 12 74
110-153 18 66 4.1 1.4 0.0 0.0 0.1 2 10 79
153-200 19 64 4.1 1.7 0.0 0.0 0.1 2 10 84
upland soils in the study area range from 0.1 to 7.5 Soils of the recent flood plain have cation saturacmol(+)/kg. The maximum occurs in the lower B tion values for calcium, magnesium, and potassium in horizon of the Palma Real profile, a somewhat poor- mineral soils ranging from 0.06 to 0.89, 0.26 to 4.49, ly drained soil with clayey textures throughout the and 0.02 to 0.06, respectively and values for calcium, solum. The minimum occurs in the surface horizon magnesium, sodium and potassium in organic horizons of the Amable profile, a sandy textured epipedon on ranging from 2.37 to 4.71, 8.95 to 18.10, 0.10 to a 12% slope. In the upland soils, exchangeable 0.33 to 0.17 to 0.68 cmol(+)/kg, respectively. High hydrogen is a significant portion of the acidity, com- concentrations of calcium and magnesium could be prising up to 25 percent in B horizons. In all well drain- a result of the deposition of sediments from more basic ed soils, the total exchangeable acidity is higher in B waters of the Tambopata that flood the Chonta River horizons than in the surface horizons, during the wet season.
All upland soils in undisturbed forests have low con- In the surface and some subsurface horizons of the tents of exchangeable bases throughout. Soils that have coarser-textured soils, effective CEC values range from recently been cut and burned for agricultural use have 23 to 82 cmol( +)/kg. The presence of muscovite mica, concentrations of calcium and magnesium in the sur- vermiculite and hydroxy-Al-interlayered vermiculite face horizons of 0.30 to 0.41 cmol(+)/kg. Basic ca- with cation exchange capacities of 20-40, 100-150, and tion content ranges in most B horizons are 0.01 to 10-40 cmol(+)/kg account for the greater CEC. Soil 0.05 cmol(+)/kg for calcium, 0.0 to 0.22 for horizons that have organic carbon contents greater than magnesium, and 0.2 to 0.15 for potassium. The highest 2% have higher exchange capacities than clayey convalues are found in soils with clayey family particle tent CEC correlations could suggest as a result of the size classes. The location of Estacion profile has been 100-300 cmol(+)/kg CEC associated with organic used in the past for lime rate experiments. This may matter. In these samples, effective CEC values range account for the calcium concentrations of 0.10 from 44 to 275. cmol( +)/kg to 82 cm in the profile. The pH-dependent charge ie., CEC, ECEC, increases

Carretera Estacion
carreter Amable Estacion anisotrapic kyanite and the isotropic magnetite.
Clayey Coarse Loamy Coarse Loamy All of the soils in the study area have developed from
Paleustults Paleustults
Pama e Paleust Palestuts Palestuts unconsolidated sediments. Most have formed in anPalma Rel Pa--3st(0--6s
alaea (0-16) cient alluvium, and some are formed from more reClayey
Plinthaquic cent alluvial deposits. Soil morphology and genesis difPaleustults Carretera fer in these soils as a result of differing textures of the
(0-3%): Clayey original parent materials, their geomorphic position
Paleustults and their relationship with the present day water table. (0o-a/o) The idealized block diagram in Figure 1 presents seven major map units and their position on the landscape.
Laberinto Soils of Pichis Valley Extrapolation Sites
Sandy Astillero Coarse Loamy Laurie J. Newman, N. C. State University
0-Pla2%)aquoda Fine Loamyts Aquic Dennis del Castillo, N. C. State University
(02 ) Paleustultslenstuts
(2-36%) (5-12%) -PEPP
Figure 1. Relationship of soil map units to landscape The purpose of this project was to characterize the positions. soils where the Pichis Extrapolation Project is adapting soil-management technologies developed at
with depth in all mineral soil profiles, reflecting an in- Yurimaguas to a location in the High Selva of Peru.
crease in kaolinite in the clay fraction. This property The extrapolation sites are two neighboring experihas been observed in Ultisols of the southeastern ment stations situated on opposite sides of the Pichis United States. River. Compared to Yurimaguas, this area has lower
X-ray diffraction was used to identify and quantify night temperatures, 50% more rainfall and steeper
the minerals present in the clay fraction of selected slopes. The important landscapes for agriculture are horizons. Diffraction patterns show the predominance alluvial positions and gently rolling to steep uplands.
of kaolinite in all of the horizons analyzed. Muscovite Four pedons were sampled in October 1984 and mica, low-charge vermiculite and hydroxy-aluminum samples were analyzed at the Yurimaguas laboratory.
interlayered vermiculite are present in varying quan- Mineral family was inferred from the sum of cations tities, as are minor amounts of goethite, gibbsite, and and clay content. The results shown in Table 1 intalc. dicate that the alluvial terrace soils are Fluventic
Soils with clayey family particle size classes have ver- Eutropepts, slightly acid, but with otherwise high
miculite as the second most abundant clay mineral, native fertility (Pedon A). Soils on the upland, rolling All other soils in loamy, sandy and organic particle sites at La Esperanza Station are clayey, kaolinitic Typic size classses have muscovite mica as their second most Paleudults (Pedon B). Soils on the high, nearly level abundant clay mineral. The sandy, poorly drained soils terraces at both stations are Typic Palehumults and in the second-order stream drain have the lowest Typic Tropohumults, with high topsoil organic matamount of vermiculite of any of the soils. Gibbsite ter contents (Pedons C and D).
is present in the B horizons of profiles that contain On the basis of the four pedons described and analyzplinthite. The trace contents of talc, which is a stable ed, soils at the extrapolation sites differ only slightly product of metomorphism, have probably been from those at Yurimaguas. The Pichis soils contained
transported from the sedimentary parent material proportionately more clay and organic matter, and source in the Andes. there are probably more 2:1 clays. These
In the clay fraction the sequence: mica- ver- characteristics, taken together, indicate that these soils
miculite (expanded hydrous mica)--hydroxy in- will retain more exchangeable Al. Lime requirements
terlayered vermiculite---kaolinite represents the suc- are expected to be higher, and percolation of bases less cession of the stages of weathering, than those on soils at Yurimaguas. The high base status
All sand fractions examined by petrographic analysis soils on the low terraces at the extrapolation site apwere greater than 95% quartz. Muscovite mica was pear comparable to soils on the low terrace at
present in small amounts as were the heavy minerals, Yurimaguas.

Table 1. Characteristics of four soil profiles on the Pichis Valley, Peru.
Exchangeable Al Organic
Horizon Texture pH Al Ca Mg K ECEC sat. matter
cm (H20) cmol(+)/L % %
El Vivero, low terrace, Fluvaquentic Eutropept, clayey, mixed, isohyperthermic. FCC:LCh.
Ap 0-9 silt loam 5.4 0.3 9.00 2.08 0.24 11.62 3 3.4
Btl 9-24 silty clay 5.5 0.5 9.45 1.83 0.14 11.92 4 1.3
Bw 254 silty clay 5.1 5.4 4.53 1.50 0.10 10.53 51 0.7
Ab 54-89 loam 5.3 3.7 3.77 1.24 0.09 8.80 42 0.3
Bwgl 89-130 5.4 1.8 6.75 2.48 0.15 11.18 16 0.3
Bwgl 130-151 silty clay 5.7 1.0 7.44 3,41 0.16 12.01 8 0.2
Cg 151-180 clay 6.0 0.4 8.59 3.79 0.16 12.94 3 0.4
Esperanza Experiment Station, upland area secondary forest. 11% slopes. Typic Paleudult, clayey, mixed, isohyperthermic. FCC:LCak.
A 0-6 loam 3.8 5.3 0.20 0.20 0.16 5.86 90 5.2
Btl 6-33 clay loam 4.2 5.8 0.20 0.17 0.05 6.22 93 1.4
Bt2 33-65 clay loam 4.3 6.7 0.24 0.14 0.06 7.14 94 1.0
Bt3 65-114 clay 4.5 8.4 0.23 0,10 0.03 8.76 96 0.3
Bt4 114-150 fine sandy 4.7 9.3 0.20 0.09 0.05 9.44 99 0.3
BC 150-180 fine sandy 4.7 6.9 0.20 0.09 0.05 7.24 95 0.3
El Vivero, high terrace, 3% slope on gently undulating topograph.Typic Palehumult, claey, mixed, isohyperthermic. FCC:LCa.
Ap 0-2 silt loam 4.2 5.9 1.74 1.02 0.22 8.88 66 6.2
Apb 2-13 clay loam 4.3 6.9 0.40 0.36 0.16 7.82 88 1.7
A 13-36 clayloam 4.4 7.3 0.27 0.24 0.12 7.93 92 1.3
Bt 36-84 clay loam 4.4 8.8 0.27 0.23 0.08 9.38 94 1.2
Btg 84-123 clay 4.3 9.1 0.47 0.16 0.07 9.80 93 0.5
BC 123-165 clay 4.7 10.1 0.43 0.14 0.06 10.73 94 0.4
Cg 165-180 clay 4.8 15.3 0.20 0.14 0.06 15.70 97 0.2
Esperanza Experiment Station, virgin forest. 0-2% slopes. Typic tropo humult, mixed, isohyperthermic. FCC: LCak. A 0-8 clay loam 3.7 7.9 0.23 0.18 0.12 8.4,3 94 4.2
AB 8-19 clay loam 4.1 5.6 0.27 0.18 0.10 6.15 91 2.3
Btl 19-46 clay loam 4.6 4.4 0.53 0.17 0.08 5.18 85 1.13
BT2 46-79 clay 4.5 7.0 0.23 0.10 0.03 7.36 95 0.8
Bt3 79-96 clay 4.5 6.1 0.20 0.10. 0.03 6.43 95 0.9
Bt3 96-120 clay 4.6 5.6 0.20 0.10 0.03 5.93 94 0.7
Btg 120-142 si. clay 4.7 5.2 0.20 0.10 0.03 5.53 94 0.2
Bxl 142-162 loam 4.7 5.1 0.23 0.09 0.03 5.45 94 0.2
Bx2 162-180 loam 4.8 4.8 0.23 0.09 0.03 5.15 93 0.4
Bx2 180-200 loam 4.8 4.8 0.13 0.09 0.04 5.06 95

Soil Survey of the Puerto Maldonado mend management options for similar soils in the
Experiment Station region. The station is in the Acre alluvial basin of
southeastern Peru. The upland soils have ustic soil Laurie J. Newman, N. C. State University moisture regimes, and the natural vegetation is seasonal
Stanley W. Buol, N. C. State University semi-evergreen forest.
Rafael Chumbimune, INIPA, CIPA XVII, Table 1 presents the soils classified by Soil TaxPuerto Maldonado onomy and Fertility Capability Classification (FCC).
The complete Soil Survey of the Puerto Maldonado ExThe purpose of this study was to obtain an perimentStation (Newman, L.J. 1985)is available from
understanding of soils, including their genesis and mor- the Tropical Soils Research Program, Box 7619, N.
phology, at the Puerto Maldonado Experiment Sta- C. State University, Raleigh, NC 27695-7619, USA.
tion, so that local agriculturalists will be able to recomTable 1. Classification of the soils of the Puerto Maldonado Station, Peru Soil Taxonomy
Name Sub Group Family FCC
Soils of the Level Upland
Carretera Typic1 Paleustult clayey, kaolinitic, isohyperthermic LCadk
Estacion Typici Paleustult coarse-loamy,siliceous, SLadek
Palma Real Plinthaquic Paleustult clayey, kaolinitic, isohyperthermic Cadgk
Soil of the Upland Sideslopes
Astillero TypicI Paleustult fine-loamy, siliceous, Ladek
Amable Typici Paleustult coarse-loamy, siliceous, Ladek
Mashco Aquic Palestult coarse-loamy, siliceous, SLadegk
Soils of the Recent Floodplain
Laberinto Aeric1 Placaquod sandy, siliceous, isohyperthermic Sdeghk
Chonta Typic Troposaprist dysic, isohyperthermic Ok
1 Sub group not presently defined in Soil Taxonomy (Soil Management Support Systems, 1985).

In the humid tropics, the limited resources and qualified professionals of national institutions often prevent programs from pursuing improved soil-management practices beyond the primary research sites. Linking programs and institutions into a network, however, can pool talent and resources, accelerating the flow of information among scientists and specialists, and the transfer of soil-management technology to producers.
Work led by TropSoils, REDINNA and IBSRAM scientists has launched the development of a soil-management research network for the humid tropics. The network's objectives are 1) to develop the capability of collaborating country personnel to conduct, interpret, and report user-oriented, soilmanagement research, and 2) to validate and extrapolate available soil-management technologies to other countries beyond the TropSoils primary research sites.
Work during 1985 was geared at promoting the establishment of such a network at three levels: nationally in Peru in cooperation with INIPA; regionally in Tropical America in cooperation with REDINNA and AID's Latin America and Caribbean Bureau; and tropics-wide in cooperation with IBSRAM. An underlying assumption has been the need to link with other insitutions, because of the limited time and resources available for research validation in TropSoils and the fact that actual technology transfer is the mandate of other projects or institutions. TropSoils' role in networking is viewed as catalytic, educational and as a major source of new management technology for the humid tropics. Agencies with a clear mandate for technology transfer such as national insitutions like INIPA, and network institutions like REDINNA and IBSRAM, are viewed as the means to conduct the networks. The U.S. Agency for International Development (USAID) participates in the network, and the project has engaged the cooperation of several USAID bureaus, as well as USAID missions in the humid tropics around the world.
Although countries with significant areas in the humid tropics differ widely in their stage of soilmanagement technology development, they all share one common limitation: lack of up-to-date knowhow on management of humid tropical soils by scientists and extension agents stationed in the humid tropics. They may have excellent backing from top scientists, most of whom are in the nation's capital. Although they may exert considerable positive influence on program direction, it is the people in the field who determine the success of technology transfer. The vast majority of them are the B.S. level (ingeniero agr6nomo or similar title) who received university training based on now oboslete concepts of tropical soil management (lime to pH 7, for example). This project intends to focus on such individuals as the real validators and transformers of technology.

Catalyzing Events
In order to promote network development, TropSoils personnel in 1985 helped conduct a series of workshops, courses and meetings, organized jointly with several agencies and institutions. Highlights included:
0 IBSRAM's Inaugural Workshop to Launch the Acid Tropical Soils Management Network, in Yurimaguas, Manaus and Brasilia, April 24-May 3. There were 67 participants, representing 13 national institutions, seven donor agencies and a number of international centers and universities. The sponsoring institutions were INIPA, EMBRAPA, ACIAR-Australia, ORSTRM-France, Soil Management Support Services (SMSS), USAID and N.C. State University. Acting on expressed country interests, participants determined that the Acid Tropical Soils Management Network will concentrate its technology-validation activities on 1) pedology and fertility interactions, 2) soil acidity, 3) phosphorus fertilization, 4) management of the soil surface, 5) rehabilitation of degraded, acid tropical lands, and 6) soil dynamics. A TropSoils scientist participates in the follow-up acitivities as a member of the network's coordinating committee. Initial emphasis will be given to humid tropical Africa.
Also supported was IBSRAM's sister Inaugural Workshop on Land Clearing and Development, held in Jakarta in August, 1985, which was attended by a scientist who summarized TropSoils research experience on land clearing and reclamation in both Peru and Indonesia. The TropSoils scientist is a member of that network's coordinating committee.
* Agroforestry Research Course for the Humid Tropics, in Yurimaguas, June 3-22. This course was co-sponsored by INIPA and ICRAF with IDRC-Canada. There were 27 participants from Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela. Follow-up acitivities include research validation in soil management for agroforestry systems throughout the Amazon.
* National Selva Program Planning Workshop, in Yurimaguas, October 24-3 1. Ninety Peruvian research and extension workers of INIPA's National Selva Program met and determined priorities for technology transfer throught the Selva. Other participants came from Peruvian universities, from IIAP and from the USAID-sponsored Selva Special Projects. A TropSoils senior scientist was assigned the task of coordinating technical aspects of the Selva Program. The 22 soil scientists present developed and recommended 11 specific activities for technology validation and transfer.
New Collaboration
Plans are to expand the network by capitalizing on collaborative research and training activities already planned or conducted by NCSU and TropSoils in some 33 countries around the world, and by maintaining contact with the several hundred students and professionals who have received training or degrees while participating in NCSU and TropSoils projects. Interest is especially strong in Asia, where the INSFERR Network has begun widespread testing of the Fertility Classification System (FCC). Countries with collaborative, network relationships with N.C. State University TropSoils are:
Latin America (13): Bolivia, Brazil, Colombia, Costa Rica, Dominican Republic, Ecuador,
Jamaica, Mexico, Panama, Peru, Puerto Rico, Trinidad, Venezuela.
Africa (8): Burundi, Cameroon, Congo, Ivory Coast, Madagascar, Nigeria, Zambia, Zimbabwe.
Asisa (11): Burma, China, India, Indonesia, Malaysia, Nepal, Pakistan, Phillipines, Sri Lanka,
Taiwan, Thailand.

Research conducted at Manaus, Brazil has offered the opportunity to select promising soil-management technologies from the primary research site at Yurimaguas, Peru, and test them in an ecosystem with different soils and climate. The ecosystem which includes Manaus occupies approximately 57 percent of the Amazon Basin. It is near-ustic, and the predominant vegetation is semi-evergreen, seasonal, primary forest, whereas vegetation at Yurimaguas is typically secondary forest. The soils at Manaus are Oxisols, found in 45 percent of the Amazon Basin, mostly in near-ustic and ustic soil-moisture regimes. They are clayey, very fine, kaolinitic Typic Acrorthox on flat plateaus, in contrast to the fine loamy, siliceous Typic Paleudults of Yurimaguas. Phosphorus sorption capacity for the clayey Oxisol at Manaus is intermediate between the high levels for the Cerrado Oxisols and the low levels found in Yurimaguas Ultisols.
Research has been conducted to discover how these differences in soils and climate affect the adaptation of soil-management technologies to the ecosystem found at Manaus. The first experiment examined the response of crops under continuous cultivation to a range of nutrients. It was designed to establish the times at which the application of each nutrient was required in order to sustain longterm production. As this central experiment indicated the need for more detailed information related to individual nutrients, satellite experiments were established. The work reported here is a cooperative project conducted at the UEPAE/Manaus Station (Unidade de Execucao de Pesquisa de Ambito Estadual de Manaus), conducted jointly with EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria).
This section also includes a report on work conducted in the Cerrado region, in collaboration with the Centro de Pesquisa Agropecuaria dos Cerrados (CPAC/EMBRAPA).

Soil Nutrient Dynamics and Fertility Phosphorus
Management for Sustained Ash analysis indicated that approximately 10 kg/ha
Crop Production on Oxisols of P were added to the soil by the burn. Crop yields
In the Brazilian Amazon for the absolute check treatment (Figure 2) suggested
that yields, in the absence of fertilizer inputs, would Thomas Jot Smyth, N. C. State University be negligible after the first crop. Despite the initial inManoel Cravo, EMBRAPA
Joaquim B. Bastos, EMBRAPA
LLSD .03
The objectives of this project were 1) to establish 3
the patterns of soil-nutrient depletion as a function of 0
time after clearing for a Central Brazilian Amazon Ox- 2
isol under continuous cultivation; 2) to determine the 0 2
fertilizer inputs required for sustaining continous crop M production on these Oxisols; and 3) to determine how
a soil-fertility management system for the Manaus Oxisols would differ from one for the Yurimaguas Ultisols. 1
During the four years in which this study has been pH
conducted, eight crops have been harvested in the se- 5.0 60 >
quence described in Table 1. Table 2 shows selected
fertilizer treatments during continuous cultivation. Cj
Other treatments included a check (no fertilization), 40 C
and a treatment with residue incorporation. A judicious "."
monitoring of soil and plant nutrient levels for every A.0 20
crop determined when each treatment was establish- Al Sat.
ed. Treatments for copper and lime were initiated in 0
the second soybean crop, for sulfur in the second corn 2
crop, for boron and zinc in the third corn crop, and Q1
for manganese in the third cowpea crop. \
Topsoil nutrient-depletion patterns for this Oxisol A 1
are shown in Figure l and Table 3 for the absolute Ei .5
check treatment, which has not received any fertilizer .
or lime. Soil nutrient levels initially increased as a result
of ash additions from burning the primary forest. The P "0
liming effect of the ash reduced Al saturation values 0.)
from 73% to 18% during the first crop.10 6
Table 1. Sequence of crops, varieties and time after 80 p
burning for the cultivation of each crop. E 4
Crop Variety Planting to Harvest Time 6 "
'e 0 "o.0
Months After Burning .05 2
Rice JAC 47 3.0 7.4 20
Soybeans Tropical 8.9- 12.6 0 K
Soybeans Tropical 18.5 22.3 0
Cowpeas Manaus 22.9 25.2 0 10 20 30 40 60
Corn BR 5102 27.6 31.3 Months After Burning
Cowpeas VITA 3 32.7 34.9 Figure 1. Soil dynamics for carbon, total N, acidity,
Corn BR 5102 37.2 41.8 exchangeable Al, Ca, Mg, K and Mehlich I P during
Soybeans Tropical 42.3 46.2 the initial 44 months after clearing the primary forest
on a Manaus Oxisol.

crease in Mehlich 1 extractable soil P (Figure 1), rice Potassium yields were doubled by the broadcast application of Topsoil K levels had declined from 107 to 56 ppm 22 kg P/ha (Figure 2). Although all succeeding crops before planting the second crop (Figure 1). Treatments showed a significant response to P fertilization, the evaluating three rates of K were, therefore, initiated optimum P rate was related to the timing of fresh P with this crop. Yield responses to K and the incorapplications and crop P requirements. Relationships poration of residues from the previous crop are'shown between crop yield and soil-test P suggested optimal in Figure 3. The crop-residue treatment was J'fcluded Mehlich 1 P levels in the range of 5- 10 ppm for corn, to evaluate the effects of returning residues when these 8-10 ppm for cowpeas and 10-15 ppm for soybeans. are harvested for threshing the grain. Yield for this Cumulative yields for the total applications of 88, 176, treatment was low on the initial soy ,ean cropsince and 264 kg P/ha were 11.3, 13.5, and 16.7 t/ha, P was only applied prior to planting the th~rd crop respectively, in the study (Table 2). Yields for the crop-reside treatTable 2. Fertilization history for selected treatments in the nutrient-dynamics study.
P, P2 P3 N1 N2 N3 K1 K2 K3
Crop Fert.
N 60 60 60 30 60 90
P 22 44 66 44 44 44
N 20 20 20 0 0 0 20 20 20
P 22 44 66 44 44 44 88 88 88
K 50 50 50 50 50 50 25 50 100
Mo .02 .02 .02 .02 .02 .02 .02 .02 .02
N 54 54 54 27 54 80 54 54 54
P 0 0 0 0 0 0 22 22 22
K 50 50 50 50 50 50 25 50 100
Cu 1 1 1 1 1 1 1 1 1
(no fertilizer applications in these treatments) Cowpeas
K 0 0 0 0 0 0 25 50 100
N 80 80 80 40 80 120 80 80 80
P 22 44 66 22 22 22 22 22 22
K 50 50 50 50 50 50 0 0 0
Lime (t/ha) 2 2 2 2 2 2 2 2 2
K 0 0 0 0 0 0 25 50 100
N 80 80 80 40 80 120 80 80 80
K 50 50 50 50 50 50 25 50 100
P 22 44 66 44 44 44 44 44 44
K 50 50 50 50 50 50 25 50 100
K 50 50 50 50 50 50 25 50 100
* Crop failed in 43-day drought. Corn was cut and the stover incorporated.

4 Applied P (kg/ha) ment, relative to the K treatments, declined progressiveED1Check ly following the first corn crop and were primarily
Z 22 related to a continual decline in soil K (Table 4) and
3 [44 increasing levels of soil acidity.
Yield response to fertilizer K has not exceeded 50 kg K/ha for any crop. Foliar K levels with this treat2 ment approached the recommended values in most
crops (Table 4). Topsoil K data suggested that residual S .effects from fertilizer K were low (Table 4). This was
STable 3. Mehlich 1 extractable soil micronutrient .......levels on the absolute check treatment as a function
0 '' of time after burning.
Rice Soyb. Soyb. Cowp. Corn Cowp. Corn Soyb.
Time After Melich 1 Extractable
Figure 2. Grain yields for eight consecutive crops on Burning Cu Mn Zn
the absolute check and P treatments.
months ppm
Applied K (kg/ha) 0 0.1 2 1.0
rI Residues 2.6 1.8 10 0.9
3- E2"2 25
3 Eo25 6.3 1.5 4 0.5
0 ~ o 8.7 2.2 6 1.2
. 11.8 0.8 6 1.0
2 18.6 1.8 5 1.0
2 LSD .05 19.7 2.0 6 1.0
" 24.3 1.5 6 2.5
1 29.8 1.0 2 0.8
1-34.1 1.1 3 1.0
39.2 3
0 44.0 2
Soyb. Soyb. Cowp. Corn Cowp. Corn Soyb.
Figure 3. Effects of K fertilization and crop residue LSD .05 0.6 2 0.5
incorporation on yields of seven crops.
Table 4. Effects of K fertilization and crop-residue incorporation on soil K and foliar K levels at flowering
stage during seven consecutive crops.
Applied Crop Sequence
K Soyb. Soyb. Cowp. Corn Cowp. Corn Soyb.
kg/ha soil K, ppm
25 61 20 29 16 30 18 23
50 91 26 48 19 50 25 48
100 78 30 68 19 97 64 110
Crop Residues 124 32 52 24 50 21 25
LSD .05 19 9 12 ns 15 11 15
leaf K, %
25 1.26 1.40 0.90 1.23 1.25 1.14 1.44
50 1.85 1.70 1.16 1.68 1.56 1.50 1.63
100 1.99 1.86 1.12 1.80 1.95 1.64 1.81
CropResidues 1.64 1.92 1.09 1.93 1.44 1.29 1.45
LSD.05 0.35 0.21 0.26 0.31 0.36 0.17 0.19