Fertilizer and grain prices constrain food production in sub-Saharan Africa

To increase crop yields in many regions of sub-Saharan Africa, farmers would need to use more fertilizers. However, estimating the local maize yield responses to fertilizers shows that the fertilizer and maize price ratio presents a strong barrier to achieving higher yields in most regions. Crop yields across sub-Saharan Africa are much lower than what is attainable given the environmental conditions and available technologies. Closing this 'ecological yield gap' is considered an important food security and rural welfare goal. It is not clear, however, whether it is economically sensible for farmers to substantially increase crop yields. Here we estimate the local yield response of maize to fertilizer across sub-Saharan Africa with an empirical machine-learning model based on 12,081 trial observations and with a mechanistic model. We show that the average 'economic yield gap'-the difference between current yield and profit-maximizing yield-is about one-quarter of the ecological yield gap. Furthermore, although maize yields could be profitably doubled, the economic incentives to do so may be weak. Our findings suggest that agricultural intensification in sub-Saharan Africa could be supported by complementary agronomic approaches to improve soil fertility, lowering the fertilizer cost, and by spatial targeting of fertilizer recommendations.