Mulching on family maize farms in the tropics: A systematic review

Family farms, predominantly reliant on family labour, produce approximately three-quarters of the World's food. Maize (Zea mays) is the world's most produced cereal. Yet in much of the tropics, actual maize yields are far below those attainable with best-bet practices. While any advantage of adding mulch might depend on soil fertility level, mulch quality, amount of rainfall, irrigation, and other factors, no ranking of their importance has been found. Our objectives were to disentangle these influences to assess how mulch affects yields on different fertility soils under different precipitation regimes. We conducted a systematic review in Web of Science, obtaining 50 papers on experiments from the tropics. Fewer trials have been conducted in Asia and Pacific (n = 10) than in Africa (n = 20) or Latin America and the Caribbean (n = 20). Twenty mulches had been tested of which Leucaena leucocephala had been used in 25% of trials. Mulch was more commonly applied after (n = 15) than before (n = 18) sowing or at sowing (n = 14); three trials did not mention application timing. Mulch increased grain yield and biomass. The positive effect of mulch was greater when combined with mineral fertilizer, implying a synergistic rather than a substitutional effect and demonstrating its applicability, even for farmers able to afford inputs. Mulch increased both maize grain yield and total biomass so is recommended as a sustainable practice in general, but particularly on low fertility soils in lower rainfall areas. Future work should model mass loss and nutrient release of different mulch types under different agroecological conditions.