Maximizing Net Returns to Financially Constrained Fertilizer Use

Financial constraints commonly limit fertilizer use by smallholder farmers as they strive to maximize net returns on their investments. Fifteen crop–nutrient response functions, including six crops, were derived from the results of 80 trials conducted in Uganda. The net return to nutrient application for typical fertilizer use costs and grain prices in Uganda was greatest for a small amount of N applied to dry bean ( Phaseolus vulgaris L.), followed by N applied to rice ( Oryza spp.), P applied to groundnut ( Arachis hypogaea L.) and soybean [ Glycine max (L.) Merr.], and then N applied to maize ( Zea mays L.) and grain sorghum [ Sorghum bicolor (L.) Moench]. Net returns were less for the remaining nine response functions. The Uganda Fertilizer Optimization Tool was developed for Uganda to maximize net returns to fertilizer use for finance‐limited crop management. It considers the area of each crop to be planted, fertilizer costs, expected grain value, and the money available for investment. The tool optimizes across response functions to provide the crop–nutrient–rate combinations expected to maximize net returns. In an example with 1 ha each of the above six crops and US$170 available for fertilizer use, the optimized net return was US$1918 compared with US$676 and US$804 for US$170 of fertilizer applied to maize and rice, respectively, at rates to maximize net returns per hectare. This approach to fertilizer use of maximizing net returns on investment can gradually enable much increased fertilizer use because of the relatively high returns on investment compared with traditional fertilizer use recommendations.