THE SUSTAINABILITY OF AGRICULTURAL FOOD COMMODITY PRODUCTION IN THE HUMID TROPICS OF CENTRAL AND WESTERN AFRICA

The African humid-tropical rainforest is converted into agricultural land far more rapidly than Latinamerican or Asian rainforest. In Africa this process is primarily propelled by smallholder subsistence agriculture. The sustainability of the methods conventionally utilized in this process (shifting, slash-and bum, swidden cultivation) ist threatened by the shortening of fallow periods due to increasing rural population pressure. Similarly, continous, monoculture-based field crop production on humid-tropical soils with massive external input use is linked with considerable ecological risks and constraints. Since humid-tropical soils are strongly weathered and therefore present low inherent fertility, low nutrient and water retention capacity, and unbalanced ion load in the exchange complex, and since continously high ambient temperatures, high rainfall amounts and high rainfall intensities accelerate the processes of soil deterioration and soil loss, these soils require maximum biological protection for their sustainable utilization. In analogy to the conditions prevailing within the rainforest which can provide such soil protection, the sustainability of the soil resource in field crop production is intimately linked with its association with tree vegetation. It appears that only genetically diverse, complex, integrated tree-, crop- and animal-based land use with low-external, but normally high internal input use in the sense of integrated agro-sylvo-pastoral systems are in a position to sustainably satisfy the high requirements of the humid-tropical ecology. Experiences gathered in the Central and Western African region with the Alley Farming concept which systematically combines nutrient pumping and soil stabilizing legume shrubs and trees with field crops and small ruminants indicate that the sustainability of smallholder field crop based land use in the humid tropics can be assured under conditions of low external input.