Soil Chemistry Aspects of Predicting Future Phosphorus Requirements in Sub‐Saharan Africa

Phosphorus (P) is a finite resource and critical to plant growth and therefore food security. Regional‐ and continental‐scale studies propose how much P would be required to feed the world by 2050. These indicate that Sub‐Saharan Africa soils have the highest soil P deficit globally. However, the spatial heterogeneity of the P deficit caused by heterogeneous soil chemistry in the continental scale has never been addressed. We provide a combination of a broadly adopted P‐sorption model that is integrated into a highly influential, large‐scale soil phosphorus cycling model. As a result, we show significant differences between the model outputs in both the soil‐P concentrations and total P required to produce future crops for the same predicted scenarios. These results indicate the importance of soil chemistry for soil‐nutrient modeling and highlight that previous influential studies may have overestimated P required. This is particularly the case in Somalia where conventional modeling predicts twice as much P required to 2050 as our new proposed model. Plain Language Summary Improving food security in Sub‐Saharan Africa over the coming decades requires a dramatic increase in agricultural yields. Global yield increase has been driven by, among other factors, the widespread use of fertilizers including phosphorus. The use of fertilizers in Sub‐Saharan Africa is often prohibitively expensive, and thus, the most efficient use of phosphorus should be targeted. Soil chemistry largely controls phosphorus efficiency in agriculture; for example, iron and aluminum, which exist naturally in soil, reduce the availability of phosphate to plants. Yet soil chemistry has not been included in several influential large‐scale modeling studies, which estimate phosphorus requirements in Sub‐Saharan Africa to 2050. In this study we show that predictions of phosphorus requirement to feed the population of Sub‐Saharan Africa to 2050 can significantly change if soil chemistry is included (e.g., Somalia with up to 50% difference). Our findings are a new step toward making predictive decision‐making tool for phosphorus fertilizer management in Sub‐Saharan Africa considering the variability of soil chemistry. Key Points Soil geochemical theory is implemented into a widely used phosphorus (P) model, which predicts P required based on food demand To estimate the P requirements in Sub‐Saharan Africa, the soil heterogeneity, especially in Vertisol soils, should be included in analysis This