Economically Optimal Rate for Nutrient Application to Maize in the Semi-deciduous Forest Zone of Ghana.

Abstract

Low inherent nitrogen (N), phosphorus (P), and potassium (K) contents of smallholder farms limit maize grain yield. Maize grain yield response to N, P, and K mineral fertilizer application and economically optimal rates for nitrogen (EOR^N), phosphorus (EOR^P), and potassium (EOR^K) were evaluated on a Ferric Acrisol within the semi-deciduous forest zone of Ghana. The nutrient rates evaluated were N (0, 30, 60, 90, and 120 kg N ha^-1), P (0, 30, 60, and 90 kg ha^-1 P₂O₅), and K (0, 30, 60 and 90 kg ha^-1 K₂O). The treatments were arranged in a randomized complete block with three replications using an incomplete factorial design. Nutrient responses were determined using asymptotic quadratic-plus plateau functions. The best nitrogen rate for all P and K levels was 60 kg ha^-1, which gave grain yield of 5 t ha^-1 . Nitrogen uptake, N agronomic and N recovery efficiencies peaked at 60 kg N ha^-1 while N partial factor productivity declined with increasing N application rate. Cost to grain price ratios (CP) were 1.29, 1.65, and 1.65 for N, P, and K, respectively. The EOR^N was 61 kg ha^-1, 32% less than the recommended 90 kg N ha^-1 for maize production in the semi-deciduous forest zone of Ghana. Nitrogen application had the lowest CP ratio, making its application economically profitable than P and K. The findings suggest that the application of N at 61 kg N ha^-1 to maize is economically profitable than at higher application rates. However, further studies should be conducted on farmers' fields to validate the results obtained.