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Research needs

In view of the ever-increasing demand on limited and fragile resources, the question most often asked is whether soil productivity in TRF ecosystems can be sustained with intensive and continuous farming. The available research data indicate that most tropical soils can be intensively cultivated and produce high and sustained yields by adopting BMPs based on an ecological approach to agriculture. In this connection, land-clearing techniques play an important role. The effects of improper land-clearing methods are observed even 8-10 years after the land has been cleared, and especially when the overall soil fertility has drastically declined. Adopting a land-use system that may produce, say, 60-80 per cent of maximum returns and that avoids causing environmental degradation is a better choice than land-use systems that bring high short-term returns but severely degrade the resource base.

An optimum resource utilization should be based on scientific data obtained through well-designed and adequately equipped long-term experiments. To start meeting this objective, additional research information is needed on evaluating the following:

land capability and the development of criteria for the choice of rational land use and for appropriate methods of removing vegetation,

the economic and environmental consequences of different land-use systems,

methods of restoring forest vegetation and soil quality degraded by land misuse,

ecologically compatible methods of Imperata control,

adaptability of those methods of soil and crop management that enhance production from existing land, thereby reducing the need to clear new land.

Considering the limited resources available and the urgent need to use forest resources efficiently, it is important that priorities are defined and research goals are sharply focused. A coordinated effort is needed to achieve these objectives.

Table 9.19 Land restorative techniques

Soil degradative process Strategies Land restorative techniques
Soil compaction Enhance soil structure Grow planted fallows and deep rooted perennials
  Improve aggregation Use mulch farming techniques
  Enhance activity of soil fauna, e.g. earthworms Avoid excessive vehicular traffic
    Use subsoiling discriminatingly and judiciously
Soil erosion Divert run-on Isolate the area
  Prevent runoff Construct diversion channels
  Minimize raindrop impact Establish permanent ground cover
  Enhance soil structure Use fertilizets and manures
    Establish vegetative hedges on the contour
    Establish micro-catchments and water-spreading devices to enhance water infiltration
Nutrient depletion Stop fertility mining practices Take land out of production and establish planted fallows
  Use balanced fertilizer Augment nutrient capital by the addition of chemical and organic fertilizers
  Develop nutrient recycling mechanisms Establish native trees and deep rooted shrubs to facilitate nutrient recycling

References

Aina, P. O. 1979. Soil changes resulting from longterm management practices. Soil Science Society of America Journal 43: 173-177.

FAO (Food and Agriculture Organization of the United Nations). 1981. Forest Resources of Tropical Africa, Asia and Americas. Rome: FAO.

---- 1982. Tropical Forest Resources. FAO Forestry Paper no. 30. Rome: FAO.
---- 1991. Production Year Book. Rome: FAO.

Ghuman, B. S. and R. Lal. 1991. Land clearing and use in the humid Nigerian tropics. II. Soil chemical properties. Soil Science Society of America Journal 55: 184 188.

---- 1992. Effects of soil wetness at the time of land clearing on physical properties and crop response on an Ultisol in southern Nigeria. Soil & Tillage Research 22: 1 11.

Greenland, D. J. and P. H. Nye. 1959. Increase in the carbon and nitrogen contents of tropical soils under natural fallows. Journal of Soil Science 9: 284 299.

Houghton, R. A. 1990. The global effects of tropical deforestation. Environment Science Technology 24: 414 422.

Juo, A. S. R. and R. Lal. 1977. The effect of fallow and continuous cultivation on the chemical and physical properties of an Alfisol in the tropics. Plant Soil 47: 567 584.

Lal, R. 1976. No-tillage effects on soil properties under different crops in western Nigeria. Proceedings Soil Science Society of America 40: 762 768.

---- 1987. Tropical Ecology and Physical Edaphology. Chichester: Wiley.
---- 1991. Agricultural activities and carbon emission from soils of the tropics. Washington D.C.: US Environmental Protection Agency, mimeo.

Lal, R., D. DeYleeschauwer, and R. M. Nganje. 1980. Changes in properties of newly cleared Alfisol as affected by mulching. Soil Science Society of America Journal 44:827 833.

Myers, N. 1989. Deforestation Rates in Tropical Forests and Their Climatic Imp/ications. London: Friends of the Earth.

---- 1991. Tropical forests: Present status and future outlook. In: N. Myers (ed.), Tropical Forests and Climate. Boston: Kluwer Academic Publishers, pp. 3-32.

NRC (National Research Council). 1982. Ecological Aspects of Development in the Humid Tropics. Washington D.C.: National Academy of Sciences.

---- 1993. Sustainable Agriculture and the Environment in the Humid Tropics. Washington D.C.: National Research Council.

Nye, P. H. and D. J. Greenland. 1960. The Soil Under Shifting Cultivation. Technical Comm. 51. Harpenden, England: Commonwealth Bureau of Soils.

Richards, J. F. 1991. Land transformation. In: B. L. Turner, W. C. Clark, R. W. Kates, J. F. Richards, J. T. Mathews, and W. B. Meyer (eds.), The Earth as Transformed by Human Action: Global and Regional Changes in Biosphere over the Past300 Years. New York: Cambridge University Press, pp. 163 178.

Salati, E., T. E. Lovejoy, and P. B. Vose. 1983. Precipitation and water recycling in tropical forests. Environmentalists 3: 67-72.

Williams, M. 1991. Forests. In: B. L. Turner, W. C. Clark, R. W. Kates, J. F. Richards, J. T. Mathews, and W. B. Meyer (eds.), The Earth as Transformed by H uman Action: Global and Regional Changes in Biosphere over the Past 300 Years. New York: Cambridge University Press, pp. 179-201.

WRI (World Resources Institute). 1988 89. Forests and rangelands. In: An Assessment of the Resource Base That Supports Global Economy. Washington D.C.: WRI, pp. 285 295.

---- 1990 91. Forests and rangelands. In: A Guide to the Clobal Environment. Washington D.C.: WRI, pp. 101-120.

---- 1992 93. Towards Sustainable Development. Washington D.C.: WRI.


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