Practical approaches to soil organic matter management for smallholder maize production in Southern Africa
1998
Giller, K.E. | Gilbert, R. | Mugwira, L.M. | Muza, L. | Patel, B.K. | Waddington, S.R.
We review the potential for organic materials to supply nutrients for plant growth and/or to build soil organic matter, and highlight priorities for research. The major problem for utilization of organic manures are the limited quantities available within different cropping systems. Grain legumes often contribute little to soil fertility as much of the N fixed is removed at harvest. Approaches that produce a large amount of N-rich biomass, such as improved legume fallows occupy land which could be used for growing crops and often are not productive on less-fertile soils. Intercropping green manure legumes with maize can give positive benefits without marked reductions in yields of maize when rainfall is not strongly limiting. However, in drought years yields of both maize and the intercropped legumes can be severely reduced due to intercrop competition. Organic amendments decompose rapidly in sandy soils, such that building soil organic matter, or indeed managing nutrient release, are difficult. Greater possibilities exist for both building SOM, and for managing nutrient release by using materials of differing quality, in soils with a greater clay content. Technical research priorities that we recommend are long-term trials on pigeonpea/maize intercropping in Malawi and on manure management in Zimbabwe. Due to the active interest of a number of organizations in implementing zero-tillage or minimum tillage with smallholder farmers, there is an urgent need to understand and test this approach under realistic farmer conditions and measure its interaction with soil fertility.
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