Localized application of manure and fertilizers increases productivity of cereals, resource use efficiency and profitability in sub-Saharan Africa

The combined use of livestock manure and synthetic fertilizers is considered as one of the climate smart and sustainable agricultural practices. However, farmers’ adoption and the benefits and costs of localized application of manure and fertilizers are not well-understood in sub-Saharan Africa (SSA). Therefore, the objectives of this review and meta-analysis were to: (1) provide the evidence for joint adoption of livestock manure and synthetic fertilizers by smallholder farmers; (2) determine farmers’ manure placement practices and the intensity of manure application; and (3) provide a comparative analysis of the productivity of cereals, resource use efficiency and profitability with localized application of manure and synthetic fertilizers in SSA. Review of 32 studies indicated that adoption rates of livestock manure by smallholder farmers is: (1) as high as the adoption rates of synthetic fertilizers; and (2) conditional on the adoption of synthetic fertilizers, improved seeds and soil and water conservation practices. Meta-analyses of data from 106 studies across 19 African countries revealed that mean response ratios of cereals with spot-application (2.16), banding (2.07) or broadcasting (2.39) of manure and fertilizer are not significantly different. On the other hand, rain use efficiency was 43.6 % higher with spot-application than broadcasting of manure and fertilizer. The agronomic use efficiencies of nitrogen and phosphorus were also 15–39 % higher with spot-application than broadcasting. This indicates that localized application of manure and fertilizer can serve as an effective strategy to achieve more efficient utilization of the limited rainfall and applied nutrients by crops. The benefit to cost ratio of spot-application (6.7) was also 81.9 % higher than for broadcasting (3.7). The returns to farmers were estimated at 3.7–4.3 dollars for every dollar invested in manure or manure + fertilizers. It is conclude that spot-application or banding can significantly reduce the quantity of manure needed without compromising crop yields, resource use efficiency or profitability. This review has provided a much needed synthesis of research in ways that advance the understanding of integrating organic and inorganic fertilizers as critical inputs for soil health.