Socio-ecological niches for minimum tillage and crop-residue retention in continuous maize cropping systems in smallholder farms of central Kenya

Soil fertility gradients develop on smallholder farms due to preferential allocation of inputs. A multi-location on-farm trial was conducted in Meru South, Central Kenya whose overall aim was to test minimum tillage and crop-residue retention practices in socio-ecological niches across heterogeneous smallholder farms. We identified three soil fertility classes together with the farmers, namely: good, medium, and poor. In each soil fertility class, two tillage (minimum or regular) and two crop residue (removed or retained) practices were tested for four consecutive seasons. Maize (Zea mays L.) grain yields in the good fields were above 2.5 Mg ha?1 across cropping seasons and cumulated yields were not influenced by tillage or crop residue management. The grain yields in the medium fields ranged between 1.3 and 5.4 Mg ha?1 and were greater with crop residue retention. In the poor fields, grain yield was <3.6 Mg ha?1 and minimum tillage resulted in yield decrease while crop residue addition did not affect yields. Regular tillage and crop residue removal resulted in largest gross benefits in the good fields ($5376 ha?1) while in the medium fields, minimum tillage with residue retention was most profitable ($3214 ha?1). Retention of crop residues will give improved maize performance in the medium fields and the prevailing prices favor minimum tillage and crop residue retention. In the poor fields, the emphasis should be on the rehabilitation of soil physical and chemical attributes because none of the tillage and crop residue practices was profitable

Conservation agriculture in Sub-Saharan Africa

Specific practices of conservation agriculture (CA) in sub-Saharan Africa are diverse and vary according to local farming conditions. However, despite more than two decades of investment in its development and dissemination, adoption of CA is low. Crop responses to CA are highly variable, and not always positive, which is an important hindrance for adoption, especially for resource-poor farmers who need immediate returns with their investments in CA in order to be able to feed their families. In contrast with commercial farms such as in Brazil, reduced costs with CA on smallholder farms in sub-Saharan Africa are not always observed. Another major challenge with the practice of CA is the use of crop residues for mulching since crop residues are a major source of feed for livestock, especially in semiarid regions, where biomass production is limited and livestock plays a crucial role in farming systems. Studies indicate that the three principles of CA, including mulching, are needed to increase crop yields compared with conventional tillage (CT)-based practices. Among the three principles of CA, mulching is certainly the one that is least observed in past and current cropping practices in Africa. CA has a potential to improve the soil water balance and increase soil fertility, and it is undoubtedly a cropping practice that can result in substantial benefits for certain farmers in Africa. The question is when and how it is the best approach for smallholder farmers in sub-Saharan Africa. In general, CA is more likely to be attractive for farmers with a strategy of intensification than for farmers who struggle to produce food for their family. The latter too often face multiple constraints that limit the possibilities to engage in technological innovations. Some farmers may not be interested in new technologies because they earn their income from off-farm activities. Good markets of input supply and sale of extra produce are a prerequisite condition for adoption of CA as they are for any other new agricultural technology that aims at intensification. In sub-Saharan Africa, there is certainly a need to better target CA to potential end users and adapt the CA practices to their local circumstances and specific farming contexts. (Résumé d'auteur