Book Description

'Slash and burn agriculture'remains the major food production system in sub-Saharan Africa. However, in a major part of the region, where fallow periods have been shortened below a critical level, the system can no longer sustain crop yield due to decline in soil fertility. In order to allow continuos crop production, principles and practices that mimic natural fallow and enhance soil organic matter build-up need to be integrated into new cropping systems that replace shifting cultivation or 'slash and burn agriculture'. These include (a) returning of organic materials to the soil, (b) ensuring minimum disturbance of soil surface, and (c) use of multipurpose trees and perennials. At the time, inorganic fertilizers are also needed to maintain a positive nutriente balance of the agroecosystem. On the widespread sandy kaolinitic soils in sub-Sahara Africa, numerous published results have shows that without appropiate organic inputs, inorganic fertilizer alone cannot sustain crop yield and maintain soil fertility in the long run because of soil acideification, loss of soil organic matter and compaction. The adoption of management practices that integrate organic, chemical and biological inputs into economically and environmentally sound production systems is an essential step towards sustaining high crop yields and preventing land degradation in the region. In the humid forest region, where root crops and tree crops are ecologically more suitable, agroforestry systems, such as multistory homestead gardens, plantation/crop combinations, and alley cropping, appear to have a high potencial for maintaining soil organic matter at levels adequate for sustaining crop growth. In the subhumid and humid/subhumid transition zones, crop residue mulch, minimum tillage and leguminous cover crops are promising tecnologies for improving nutrient and water use efficiency and sustaining high yields of maize, sorghum and cowpea. In the semiarid regions, however, improvement of millet and sorghum yields is severely limited by the lack of organic inputs. The potencial for increasing and sustaining food crop production in the seminarid zone ultimately depends upon successful integration of crop, fodder and fuelwood production within a farming community.