| Smallholder farmers in southeastern Africa are constrained by poor rainwater-use efficiency, soil degradation, and limited financial resources. Conservation agriculture (CA), based on the principles of minimal soil disturbance, year-round ground cover, and diverse crop rotations, is being promoted to sustainably improve crop production, food security, and smallholder farm income. Adoption of CA principles in the region has predominately been limited to eliminating tillage and retaining residues, with little adoption of crop rotations. In this study, three cropping systems---continuous no-till maize, CA rotation, and conventional tillage rotation---were established on smallholder farms in the Nkhotakota and Dowa districts, two distinct agro-ecological zones in Malawi. Three-year crop rotations of cassava, cowpea, and maize and cassava, soybean, maize were implemented in CA and conventional tillage, respectively, in Nkhotakota. In Dowa, a 3-year rotation of sweet potato, bean, and maize was implemented in both CA and conventional tillage. Cropping systems were analyzed for their impacts on crop production, soil-water relations, soil quality, and financial returns from 2011 to 2014. No-till maize and CA improved infiltration and the soil water balance compared to conventional tillage in Nkhotakota but did not affect soil-water relations in Dowa. No-till maize and CA increased exchangeable K, Ca, and Mg and reduced soil erosion compared to conventional tillage. In no-till maize, retention of low quality residue resulted in N immobilization. Conservation agriculture improved plant available N and nutrient cycling compared to no-till maize, but less residue cover increased bulk density compared to no-till maize and conventional tillage. Soils in conventional tillage had the most plant available N, which could lead to N leaching and reduced fertilizer-use efficiency. Tillage and residue management did not affect yields of cassava, sweet potato, cowpea, soybean, or bean. Crop rotation, regardless of tillage practice, increased maize yields compared to no-till maize. Net revenue was highest in no-till maize and labor productivity and gross margins were higher in no-till and conventional tillage than in CA rotation. Before widespread adoption of CA can occur, further research is needed to improve alternative crop production under CA management and identify the most appropriate agroecological zones for successful CA. |
