Soil Science in the Tropics-the Next 75 Years

This paper does not describe the future course of soil science in the tropics. Rather, it is concerned with some soil-related issues that tropical countries will have to face, and resolve, in the short and medium term. The topics chosen for discussion here are deforestation, the resultant degradation of the soil resource, and soil management for continuous crop production, with particular reference to the humid tropics. Tropical forests are being lost at a rate of at least 10 million hectares per annum, most of which occurs through conversion to agriculture. The removal of a vegetative cover, depletion of soil nutrients and organic matter, and accelerated erosion have led to drastic declines in soil productivity. The tropical uplands, into which future expansion of the cultivated area should largely occur, are particularly vulnerable to erosion once their forest cover has been removed. In releasing about a quarter of the global CO2 emission to the atmosphere, the large-scale clearing of tropical forests also contributes significantly to the “greenhouse effect”. Another consequence of forest destruction, especially of tropical rainforests, is the loss of biological diversity. Soil-management for sustainable land use is discussed in the context of various cultivation systems. Shifting cultivation is a stable but extensive system of land use, providing for the subsistence of only a few people per unit area of forested land. Because of rising populations and expectations, this traditional farming system is being increasingly supplanted by more permanent and intensive methods of cultivation. Nevertheless, by leaving the litter and undergrowth intact during land clearing operations and practicing appropriate post-clearing soil management, continuous cropping could be sustained in lowland areas with relatively deep soils. In the uplands, however, where the soils are often shallow and easily erodible, agro-forestry appears to be a better alternative in terms of soil conservation. The development and implementation of sustainable farming systems in order to arrest, if not reverse, soil degradation must rest on the willing cooperation of the people involved. Soil conservation programs should not only be acceptable to, but also be compatible with the socio-economic aspirations and conditions of the local community.