Conservation Tillage Cover Crops and Residue Management

25.3.2.1 Conservation Tillage

Tillage plays a major role in agricultural sustainability through its effects on soil processes, soil properties, and crop growth (Food and Agriculture Organization/World Bank, 1988). It may enhance or curtail these processes depending on initial conditions and type of tillage tools used. Hand hoeing, a common form of minimum tillage practiced by smallholder farmers in Zambia, causes minimum disturbance of the soil, creates a rough soil surface, and provides for surface retention, increased infiltration time, and reduced runoff. Its drawback is in the incomplete inversion of the soil, thus exposing the SOM to other detrimental biotic and abiotic factors.

25.3.2.2 Management of Residual Organic Matter and Soil Organic Matter Sequestration

The culture of proper residue management is not found among smallholder farmers. The common practice is to completely harvest (remove residue from fields), burn residue, or graze off the residue by livestock. This leaves the soil with no external input in the form of organic materials. Burning, as much as it destroys pests and diseases, also destroys residues and SOM, and kills active beneficial microflora and fauna, making the soil inert.

In a maize/bean rotation subjected to various management practices in Kenya, on a Kikuyu Red Clay Loam (Humic Nitisol, Food and Agriculture Organization; Alfisol, U.S. Department of Agriculture), the C content of the soil ranged from 1830 kg C ha-1 for stover application to 7940 kg C ha-1 for stover/fertilizer/manure management practice (Woomer et al., 1998; Swift et al., 1994). Addition of fertilizer, in this case, reduced soil C. The efficiency of C sequestration ranged from 1.4% for stover-fertilizer management to 6.9% for fertilizer management (Woomer et al., 1998).

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