Food Legume Responses to Applied Nutrients in Sub-Saharan Africa.

Location specific crop nutrient response functions were determined for various crops of 67 recommendation domains across thirteen countries by the project for Optimizing Fertilizer Recommendations in Africa (OFRA). While most of the functions were for non-legumes, there were 76 for soybean, 65 for bean, 58 for groundnut, 53 for cowpea, 14 for faba bean, 6 for pigeon pea, and 3 for green gram. The legume functions are fully based on field research results and included 130 for P, 77 for K, 60 for N, and 8 for Zn. Most of the results were gleaned from past research but 40% of the results were from trials conducted from 2013-15, and >55% of the results were from research conducted within the past 10 years. The response functions were integrated into Excel Solver fertilizer optimization tools (FOT) that use linear programming to determine the fertilizer recommendations that on average would result in the most profit for the farmer’s context. Most smallholder farmers are severely constrained financially in the use of fertilizer and need to get very high returns on their small investment. Therefore the FOT optimizes over numerous response functions considering the farmer’s allocation of land to crops and budget constraint, commodity values, and fertilizer costs in determining farmer specific fertilizer recommendations. In addition to the Excel FOT, paper versions serve for each recommendation domain when no computer is available.