Conservation agriculture (CA)-the simultaneous application of minimum soil disturbance, crop residue retention, and crop diversification-is a key approach to address declining soil fertility and the adverse effects of climate change in southern Africa. Applying the three defining principles of CA alone, however, is often not enough, and complementary practices and enablers are required to make CA systems more functional for smallholder farmers in the short and longer term. Here, we review 11 complementary practices and enablers grouped under six topical areas to highlight their critical need for functional CA systems, namely: (1) appropriate nutrient management to increase productivity and biomass; (2) improved stress-tolerant varieties to overcome biotic and abiotic stresses; (3) judicious use of crop chemicals to surmount pest, diseases, and weed pressure; (4) enhanced groundcover with alternative organic resources or diversification with green manures and agroforestry; (5) increased efficiency of planting and mechanization to reduce labor, facilitate timely planting, and to provide farm power for seeding; and (6) an enabling political environment and more harmonized and innovative extension approaches to streamline and foster CA promotional efforts. We found that (1) all 11 complementary practices and enablers substantially enhance the functioning of CA systems and some (e.g., appropriate nutrient management) are critically needed to close yield gaps; (2) practices and enablers must be tailored to the local farmer contexts; and (3) CA systems should either be implemented in a sequential approach, or initially at a small scale and grow from there, in order to increase feasibility for smallholder farmers. This review provides a comprehensive overview of practices and enablers that are required to improve the productivity, profitability, and feasibility of CA systems. Addressing these in southern Africa is expected to stimulate the adoption of CA by smallholders, with positive outcomes for soil health and resilience to climate change.

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Research in Latin America has shown numerous benefits of rotations with cover crops under conservation agriculture (CA) to manage N and weeds; however, information from Zimbabwe is limited. The objective of the study was to investigate the benefits of rotating maize (Zea mays L.) with different leguminous and nonleguminous cover crops on maize yield, weed management, and decomposition rates of residues. A study was conducted at University of Zimbabwe (UZ), Domboshawa Training Centre (DTC), and two sites at Henderson Research Station (HRS) with contrasting soil types (clay and sand) from 2008 to 2014. Nine different cover crops were rotated with maize and compared with maize monocropping. During the 2012 to 2013 and 2013 to 2014 cropping seasons, a litter‐bag experiment was set within the experiment at UZ and DTC to investigate residue decomposition rates. Decreases in weed numbers of up to 94% were observed in maize–black sunnhemp (Crotalaria juncea L.) treatment at DTC. At UZ, maize after jack‐bean [Canavalia ensiformis (L.) DC.] (7823 kg ha−1) showed up to 61% more yield than continuous maize (4851 kg ha−1). Maize yields after fodder radish (Raphanus sativus L. var. oleiformis Pers.) were, in most cases, not significantly different from those of uniform maize. Decomposition rates were faster in leguminous residues, with velvet‐bean [Mucuna pruriens (L.) DC. var. utilis (Wall. ex Wight) Baker ex Burck] residues being generally the fastest and therefore not suitable for ground cover. Despite the positive effects of rotations, not a single cover crop was identified that provided all the benefits. There is need to characterize niches for specific cover crops within the farming system to assist farmers in their choices and spatial arrangements of cover crops on their farms.

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Conservation agriculture (CA) and no-till (NT)-based cropping systems could address soil degradation and fertility decline in southern Africa. A multi-location and multi-year experiment was carried out between 2008 and 2014 to assess the effects of different levels of maize residue biomass (0, 2, 4, 6 and 8 t ha−1) and nitrogen (N) fertilizer (0, 30, 90 kg ha−1) on maize performance under no-tillage. In some sites, different (N) fertilizer levels were superimposed to test their effects on maize grain yield and leaf chlorophyll content under different maize residue biomass levels. The different residue levels had no significant effect on maize yield in most growing seasons. Maize residue cover increased grain yield in eight out of 39 site-years across the sites used. However, in some sites, maize yield decreased with increases in residue level in cropping seasons that had average to above average rainfall. At a few sites maize yield increased with increase in residue level. Seasonal rainfall pattern influenced the effect of different residue levels on grain yield at most sites. Nitrogen fertilizer increased maize yield regardless of the residue level applied. This study demonstrates that mulching with maize residues in CA/NT systems results in limited maize yield gains – at least within the first 6 years in different agro-ecological conditions of southern Africa.