Mulching is the most important of the three conservation agriculture principles in increasing crop yield in the short term, under sub humid tropical conditions in Zimbabwe

Abstract

Some smallholder farmers in Sub Saharan Africa (SSA) have failed to adopt all the three principles of conservation agriculture (CA) because of various reasons including lack of alternative weed management methods (soil tillage), crop-livestock interactions (crop residue mulch used as livestock feed) and poorly developed markets for other crops (diversified cropping system). Studies have shown that smallholder farmers incorporate one or two CA principles, not all three, at a time in their cropping systems. Our study sought to disaggregate the effects of the three CA principles on crop growth with or without mineral fertilizer in order to determine which principle or combination of principles resulted in highest yield increase in the short to medium term. The research was conducted over four cropping seasons at Hunyani Farm located in Zvimba district in north western Zimbabwe characterized by sub humid tropical conditions and fine sandy loam soils. A split-split-plot design, with tillage as the main plot, mulch as the sub plot, rotation as the sub-sub plot and fertility regime as the treatments was used. Fertility treatments were control (no fertilizer added) and 120 kg N ha−1+ 30 kg P ha-1 +15 kg K ha−1 mineral fertilizer and the experiment was replicated three times. Reduced tillage increased maize grain yield from the third season when compared with mouldboard ploughing. The positive effects of mulching were higher when fertilizer was applied (>90 %) compared with no fertilizer application. Crop rotation (maize-soybean) had no significant effects on grain and aboveground dry matter yield. The benefits of the three CA principles on crop yield followed the order mulch > reduced tillage > crop rotation. The combined effects of the three CA principles on maize grain yield were higher than conventional tillage and any other one or two principles together indicating the importance of integrating the three principles for best results.