The continued viability of smallholders in southern Africa is a major challenge for soil and crop scientists. Population pressure on available crop land has made shifting cultivation obsolete, with the result that maize, the dominant smallholder crop, is now planted year round in many areas. The fallows, which traditionally restored soil fertility and reduced the buildup of pests and diseases, are disappearing from the agricultural landscape. Soils are degrading and national increases in maize productivity have been disappointing despite the fact that smallholders have adopted high-yielding germplasm on 33-50 percent of the land under maize. The loss of mineral nutrients from the soils under cultivation generally exceeds nutrient inputs, challenging research and extension organizations to improve productivity without compromising sustainability.
Scientists must now combine the gains available from improved germplasm with complementary improvements in soil fertility management at a price smallholders can afford. Inorganic fertilizers are expensive and impractical for smallholders because blanket applications are recommended even in semi-arid areas. But the profitability of using fertilizer can be increased by developing fertilizer management techniques that are appropriate for smallholders and by ensuring that recommendations for fertilizer use are better targeted to their circumstances.
Fertilizer-use efficiency is often low because of the declining level of organic matter in tropical soils. For this reason, the proportion of locally produced organic materials must be increased to maintain soil organic matter and halt the downward spiral of soil fertility. Improving the efficiency of inorganic fertilizer use in various ways, including the addition of soil micronutrients and small amounts of high-quality organic matter, will consolidate and expand the base of fertilizer users.
In many households, where the cash needed to buy inorganic fertilizer far exceeds total annual income, the best strategy is to emphasize the use of organic nutrient sources, especially legumes, that capitalize on freely available nitrogen in the atmosphere. Legumes are not new to farming systems. Grain legumes, legume intercropping and rotation, green manures, improved fallows, agroforestry, cereal residues, and animal manures can all enhance soil fertility and sustain the soil resource base. However, the potential of legume technologies is rarely realized on farmers' fields because, in broad terms, the larger the fertility benefit expected from legume technology, the larger the initial investment in labor and land must be.
Although combinations of inorganic and organic fertilizers show promise, they do have a cash cost and innovative mechanisms are needed to help farmers access them. One promising approach is to provide start-up cash grants that can be paid into savings schemes from which farmers can obtain loans.
Basic, process-based research provides the foundation for extrapolating from site-specific trials to agronomic recommendations for specific agro-ecological zones and farmer groups. Previous crop husbandry research is often neglected because results are distilled into a few recommendations that ignore important interactions in the system and fail to address the diversity that exists among smallholders. Institutional memory should be maintained and disseminated more widely through computer databases and networks. And the emphasis in both research and extension should move away from rigid and prescriptive approaches to flexible problem-solving formats that lead to conditional recommendations. This would facilitate the evolution of a technology development process driven by smallholders' needs. Failure to develop such a process will result in the further weakening of the natural resource base and a continuing decline in the living standards of rural communities reliant on agriculture in southern Africa.
(CIMMYT Natural Resources Group paper 96-02: John D.T. Kumwenda, Stephen R. Waddington, Sieglinde S. Snapp, Richard B. Bones, and Malcolm J. Jackie: Soil Fertility Management for the Maize Cropping Systems of Smallholders in Southern Africa: A Review)