Crop production and soil water management in conservation agriculture, no-till, and conventional tillage systems in Malawi

Smallholder farming in southern and eastern Africa is constrained by low water-use efficiency, frequent dry spells, and drought. Conservation agriculture (CA), defined as minimal soil disturbance, year-round ground cover, and crop rotations, is being promoted as a way to sustainably improve water-use efficiency, reduce soil erosion, and boost crop production. 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 agroecological zones in Malawi. Three-year crop rotations of cassava, cowpea, and maize and cassava, soybean, and 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 impact on infiltration, soil moisture content, sediment runoff, earthworm and termite abundance, and crop production from 2011 to 2014. In Nkhotakota, which had high potential evapotranspiration and low soil water-holding capacity, residue retention was positively correlated with infiltration and no-till and CA increased soil water content (0-60 cm) compared to conventional tillage by an average of 20 mm. In Dowa, which had lower potential evapotranspiration, eliminating tillage and retaining residue did not improve infiltration or soil water content. In 2013/2014, no-till and CA reduced sediment runoff by 1537 kg ha−1 and 1309 kg ha−1 in Nkhotakota and 346 kg ha−1 and 209 kg ha−1 in Dowa, respectively, compared to conventional tillage. Tillage and residue management did not have a significant impact on sweet potato, cassava, bean, soybean, or cowpea production. Crop rotations had the greatest impact on maize yields in 2013/14, with CA and conventional tillage rotations increasing maize yields compared to no-till maize by 2525 kg ha−1 and 2145 kg ha−1 in Dowa and 1364 kg ha−1 and 469 kg ha−1 in Nkhotakota, respectively. However, cumulative protein production was greater in no-till than CA and conventional tillage rotations in Dowa and greater than conventional rotations in Nkhotakota. Rotation crop productivity needs to be improved with better yielding grain legumes and other higher protein crops before widespread adoption of diverse rotations can occur on smallholder farms in eastern and southern Africa.