On-farm evaluation of yield and economic benefit of short term maize legume intercropping systems under conservation agriculture in Malawi

Low crop yields due to continuous monocropping and deteriorating soil health in smallholder farmers’ fields of sub-Saharan Africa have led to a quest for sustainable production practices with greater resource use efficiency. The aim of the study was to elucidate the short term effects of conservation agriculture (CA) systems on soil quality, crop productivity and profitability. In Balaka market and Ntonda sections of Manjawira Extension Planning Area (EPA), in Ntcheu district, central Malawi, we compared continuous monocropped maize (Zea mays) under conventional tillage practice (CP) with different CA systems in continuous monocropped maize (CAM) and intercropping with pigeonpea (Cajanus cajan) (CAMP), Mucuna pruriens (CAMM), and Lablab purpureus (L.) (Sweet) (CAML). The study was conducted from 2008 to 2011 in 72 plots in 24 farmers’ fields. In Balaka market section CA plots with maize + legumes produced up to 4.3 Mg ha−1 of vegetative biomass against 3.5 Mg ha−1 for maize alone in CP. In Ntonda section CA plots with maize + legumes produced up to 4.6 Mg ha−1 of vegetative biomass against 2.4 Mg ha−1 for maize alone in CP. In both sections, during the entire study period, CA did not have a negative effect on crop yields. During the drier seasons of 2009/10 and 2010/11, CA had a positive effect on maize grain yield at both sites (average yield of 4.4 and 3.3 Mg ha−1 in CA and CP respectively). However, associating maize with legumes reduced maize yields compared to CAM particularly in drier years of 2009–10 and 2010–11. Farmers spent at most 47 days ha−1 producing maize under CA systems compared to 65 days ha−1 spent under conventional tillage practices. However, total variable costs were higher in CA systems compared to conventional practice (at most US$416 versus US$344 ha−1). CAMP resulted in more than double gross margin compared to CPM (US$705 versus US$344 ha−1). Infiltration estimated as time to pond was highest in CA maize legume intercrops (8.1 s) than CP (6.8 s). Although it was not feasible to directly estimate effects on water balances of these farmer-managed experiments, it can be assumed that the yield differences between CA and CP could be attributed to tillage and crop residue cover since other farm operations were generally the same. Intercropping maize and pigeonpea under CA presents a win-win scenario due to crop yield improvement and attractive economic returns provided future prices of maize and pigeonpea grain remain favourable.

► Principles of conservation agriculture had an overriding effect on maize yield due to better soil water balance.
► Maize legume intercropping increased the quantity of residues produced and retained as surface mulch.
► Maize legume intercropping under CA resulted in more than double gross margin compared to conventional tillage.
► For extensive adoption, considerations on residues management; and markets for legume seed and produce are required.