Skip to main content

Currently Skimming:

Appendix C: Soil Research for Agricultural Sustainability in the Tropics
Pages 66-90

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 66...
... Bringing new land under production through deforestation of tropical rain forests has severe ecological, environmental, and sociopolitical implications. Some of the potentially arable land Rattan Lal is associate professor of soil physics at the Department of Agronomy, The Ohio State University.
From page 67...
... A principal constraint may be nonavailability of essential inputs at affordable prices, the breakdown of resistance of improved cultivars to pests and pathogens, and the degradation of soil quality. Neglect, misuse, and mismanagement of soil resources are in large part responsible for the low yields, widespread poverty, and severe problems of soil and environmental degradation in tropical and subtropical regions.
From page 68...
... from the maximum per capita land availability of 0.14 ha or less. Technological options for sustainable management of soil and water resources in the twenty-first century must address this basic constraint.
From page 69...
... First, soil resources and population are unevenly distributed. Regions and countries with high demographic pressures are also characterized by low available land reserves, for example, South Asia, China, southeastern Nigeria, Rwanda, Burundi, the East African highlands, Central America, and the Caribbean.
From page 70...
... Bringing new land under production through deforestation of tropical rain forests, as noted, has severe ecological, environmental, and sociopolitical implications. The actual extent of deforestation in the tropics is still the subject of debate, however (Myers, 1981~.
From page 71...
... In addition to burning and deforestation, other agricultural practices that result in higher greenhouse emissions from tropical ecosystems include use of rice paddies (a major source of methane) ; intensive use of marginal lands without inputs, which leads to mining and depletion of soil organic matter; uncontrolled and excessive grazing with high stocking rates; and indiscriminate use of chemical fertilizers.
From page 72...
... Soil Erosion Accelerated erosion is a serious problem in several ecologically sensitive regions: the Himalayan-Tibetan ecosystem, the Andean region, the Caribbean, eastern Africa, and other densely populated regions with severe land shortage. Steeplands, which make up a large percentage of the total land area in these regions, are overexploited and grossly misused.
From page 73...
... soil erosion (United Nations Environment Program, 1983~. Siltation of reservoirs in northern India is about 200 percent more than was anticipated in their design (Table C-5; Dent, 1984~.
From page 74...
... Structural degradation, caused by a decline in soil organic matter and clay content and reduction in biotic activity, leads to crusting, compaction, reduced infiltration rate and low available water-holding capacity, increased soil detachability, and accelerated runoff and soil erosion. High erosion risk is a direct consequence of deterioration of soil structure.
From page 75...
... Soil erosion is also increased by the reduction in biotic activity of soil fauna that occurs with a decrease in soil organic matter content. In addition to decreases in structural stability, reductions in organic matter content have important implications in terms of plant-available water reserves in the soil.
From page 76...
... Fertility Depletion and Leaching Continuous and intensive cropping with low or no off-farm input, necessitated by land hunger and poverty, cause fertility depletion and low yields. Many of the soils cultivated by shifting cultivators and subsistence farmers of the tropics and subtropics are subject to fertility depletion through decline in soil organic matter, reduction in nutrient reserves by crop removal, leaching, and acidification.
From page 77...
... RESEARCHABLE PRIORITIES Improvement in subsistence farming can be realized through increasing production, sustaining the higher level of net output, and preserving the productive potential of natural resources through restorative measures of soil and crop management. The desired high net output must be achieved
From page 78...
... with a minimum of soil degradation, however. The soil quality and its productive capacity must be preserved and improved by preventing soil erosion, promoting high biological activity of soil fauna, improving soil organic matter content, and replacing the nutrients harvested by crops and animals through chemical fertilizers and organic amendments, supported by effective nutrient-recycling mechanisms.
From page 79...
... Highly weathered oxisols/ultisols and alfisols, being inherently low in nutrient reserves, must have a regular and supplemental nutrient supply if they are to be intensively cultivated for increased food production. Intensive land use and high yields on soils of low inherent fertility can only be achieved by raising the nutrient levels through the use of inorganic fertilizers, organic amendments, and nutrient recycling.
From page 80...
... In this regard, it is important to quantify losses by volatilization, leaching, and erosion in relation to conservation tillage, application by split doses, fertilizer placement, and slow-release formulations. Technological options for nutrient recycling must be researched for crop residue management and mulch farming, legume-based rotations, ley farming with different stocking rates and controlled grazing, and agroforestry systems, including alley cropping.
From page 81...
... Residue Management A regular and sizable addition of organic material to soil is essential to maintain favorable organic matter content and to stimulate biotic activity of soil fauna, including earthworms and termites. Structural collapse of soils with predominantly low-activity clays can be avoided by maintaining high organic matter content and by enhancing the activity of soil fauna.
From page 82...
... How long does it take improved soil organic matter content to affect soil structure favorably? Fallow Management When crop residue mulch is inadequate, practical means must be developed to procure mulch through incorporation of an appropriate cover crop or planted fallow in the rotation.
From page 83...
... The technical and social issues related to water delivery, water allocation, and water-use efficiency must also be addressed, however. Each of the alternatives involves a different set of problems and pos
From page 84...
... Widespread and severe problems of accelerated erosion and sedimentation, perpetually devastating floods, land degradation beyond the point of no return, eutrophication of water, and environmental pollution in general are traceable to poor planning and mismanagement of landscape units within watersheds. Scientific criteria for the choice of appropriate land uses, exploitation of water resources for irrigation and domestic purposes, and the development of infrastructure (including access roads)
From page 85...
... Thus, sustainability of soil and water resources must be judged with tangible criteria soil and water conservation, productivity, restoration of degraded soil, reduction in off-farm inputs for the same level of production and profitability, increase in labor productivity, and so forth. Major considerations in terms of research and development priorities are outlined below.
From page 86...
... The emphasis on these surveys is not for soil classification and mapping per se, but for assessing the potential of, and constraints on, natural resources and for developing management options for sustained production without causing degradation of fragile land resources. The data bank established on natural resources can be used to provide site-specific information for choosing technological options through the use of geographic information systems, global positioning systems, and digital elevation models.
From page 87...
... The ecological limits to the application of these no-till techniques can be greatly extended by improving the agronomic practices associated with their implementation. Tillage systems should be geared toward alleviating specific soil-related constraints to crop production soil temperature, soil and water conservation, soil compaction, maintenance of soil structure, and soil organic matter content.
From page 88...
... 1981. World population growth, soil erosion, and food security.
From page 89...
... 1984. Soil erosion from tropical arable lands and its control.
From page 90...
... Annual Report, Manoli Watershed Development Project. Photocopy.


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.