Maize and sorghum nutrient response functions for Ethiopia

Maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) are important intermediate and low elevation crops in Ethiopia but yields are low. The information for determination of nutrient rate recommendations with site specificity is scarce. On-farm and on-station trials were conducted to determine the yield responses to N and P and to diagnose K-Mg-S-Zn-B deficiencies in central, northern and western Ethiopia. Mathematical functions for grain yield response to applied nutrients were fitted, the economical optimum rates (EOR) were determined, and profit potential for fertilizer use was assessed. Maize and sorghum grain yields were inconsistently affected by N and P application across trials with no response in some cases. The overall mean EOR for N were 47 and 60 kg ha(-1) for maize and 23 and 37 kg ha(-1) for sorghum with high and low cost fertilizer-N, respectively. The overall maize response to P was linear with EOR of P > 30 kg ha(-1) for all fertilizer-P costs. The overall sorghum response to P was too inconsistent to fit a response function and the results indicated an EOR of 0 kg ha(-1) for all fertilizer costs considered. The overall maize and sorghum responses to N were curvilinear to plateau implying that the profit to cost ratio can be improved by applying fertilizer-N at less than EOR giving an opportunity to farmers who are financially-constrained in fertilizer use.