Does the combined application of organic and mineral nutrient sources influence maize productivity? A meta-analysis

In Sub-Saharan Africa, soil quality declines as population pressures and low yields push the intensity of agricultural production upward. This meta-analysis offers a valuable insight on which external-input sources will have the most impact on Sub-Saharan African maize yields, nitrogen use efficiency, and soil organic carbon (SOC). Fifty-seven studies comprising 104 experimental sites in twelve countries (Benin, Burkina Faso, Cote d'Ivoire, Ethiopia, Ghana, Kenya, Malawi, Nigeria, Tanzania, Togo, Zambia, and Zimbabwe) were grouped according to the application of Organic Resources (OR), nitrogen fertilizers, and OR and N fertilizers. OR quality was further divided into four classes of decreasing qualities. Maize yields increased with increasing OR quality, both with and without N fertilizer application. Greater yield responses were seen with OR and N fertilizer application, however there is no evidence to suggest this was due to improved N use efficiency, as N use efficiency after combined applications was lower compared to N fertilizer application alone. SOC increase was observed in OR and OR and N fertilizer application, but not in N fertilizer application alone. These results suggest that nutrient storage increases with application of higher quality ORs and low levels of N may be added in conjunction with OR to achieve higher yield responses, but not to increase N use efficiency.