Smallholder conservation farming in the tropics and sub-tropics: a guide to the development and dissemination of mulching with crop residues and cover crops

Mulching offers great agro-ecological potential: it typically conserves the soil, improves the soil ecology, stabilizes and enhances crop yield and provides various environmental services. However, mulching is not a simple single component technology that can be easily transferred. It is a complex basket of interrelated practices-including (i) necessary practices so as to ensure the production and retention of sufficient mulch and (ii) complementary practices in order to be able to grow a crop and/or maintain yield levels. This typically implies several adaptations to the entire farm production system. Whether mulching actually is a viable component for smallholder conservation farming in developing countries depends on a number of factors, including bio-physical, technological, farm level and institutional factors. The combination of these factors determine the feasibility of and the economic returns to mulching practices-and thereby farmer acceptance. The development and dissemination of mulching for smallholders in (sub)tropical developing countries highlights a number of promising experiences-particularly in (sub)humid areas. Crop residue mulching can offer significant savings implied by reduced tillage and the potential to alleviate binding constraints for crop growth and/or farm productivity (e.g. water conservation; timeliness of land preparation and crop establishment). Its economic potential to a large extent depends on the opportunity costs of retaining the mulch and the opportunity cost of complementary changes (e.g. need for mulch adapted seeding equipment; alternative weed, pest and disease management practices). Cover crop mulching offers opportunities for smallholders by addressing soil fertility and weed management constraints. However, the potential of cover crop mulching seems to be restrained to the (sub)humid zones and instances where the opportunity cost of using land to grow cover crops is limited. Significant opportunities exist in agricultural systems with limited external input use and/or periodic fallowing. The pure investment nature of cover crop mulching remains problematic. Mulching only tends to be viable when property rights over residual crop biomass are observed and tenure is secure. It typically implies a transition phase before becoming fully socio-economically viable-in terms of farmer learning, investments, local adaptation and fine-tuning and institutional change. Further success in the development and dissemination of mulching for smallholders requires targeting areas with specific economic opportunities for mulching and an integrated approach with a practical orientation, farmer participation, community involvement, flexibility and a long-term perspective.