Manure utilisation under smallholder farmers in Sub–Saharan Africa. A systematic review and meta-analysis

Abstract Animal manure is utilized to enhance soil fertility and crop productivity in Sub-Saharan Africa smallholder farming, but inappropriate management practices undermine these benefits. The study objective was to conduct a meta-analysis to determine how soil fertility, yield and biomass change under different manure practices (application rate, method, time and type of manure) in the Sub-Saharan Africa region. The meta-analysis used 114 articles published between 2000 and 2022 which examined manure application rate (low, medium, high), time (before, after planting), method (incorporating, broadcasting), and type (poultry, cattle, goat, sheep) on soil fertility (pH, soil organic carbon (SOC), total N (TN), available P (AP), exchangeable K (K)) and crop productivity (yield, biomass) in Sub-Saharan Africa. A combination of keywords was used to retrieve articles from databases accessed through Stellenbosch University Library. The natural logarithm of response ratio was used as a measure of effect size (ES) calculated using the random-effects model. Results shows that manure application significantly (p < 0.001) increased all soil properties, yield, and biomass. Soil pH, SOC, TN, AP, K, yield and biomass had ESs ranging from 0.74 to 0.77, 5.42–5.50, 5.89–6.17, 4.78–5.51, 1.85–2.26, 7.06–7.65 and 4.40–5.62 respectively. The study showed that appropriate application of animal manure can improve soil pH, SOC, TN, AP, K, yield and biomass in smallholder farmers of Sub-Saharan Africa and provided guidelines for manure application. This suggests that soil fertility, yield and biomass can be optimised through high application rate, incorporation method, application before planting, and using poultry manure.