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 (EORN), phosphorus (EORP), and potassium (EORK) 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 EORN 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.
Highlights
Maize is the most important cereal crop in Ghana with an estimated annual production of 750,000 ha (Tetteh et al 2017)
The results indicate that the soil was loamy sand in texture with a low bulk density (1.21 Mg m−3), gravimetric moisture content of 9.18% and Physical properties Sand (%) Silt (%) Clay (%) Texture Bulk density (Mg m−3) Soil moisture content (%) Soil porosity (%)
The economically optimal rate of N (EORN) was 61 kg N ha−1, which is 32% lower than the recommended rate of N required for maize production in the semi-deciduous forest zone of Ghana
Summary
Maize is the most important cereal crop in Ghana with an estimated annual production of 750,000 ha (Tetteh et al 2017). Sanchez (2002) reported that soil fertility depletion in smallholder farmers’ fields was the major biophysical cause for the declining rate of crop production in most sub-Saharan African countries. Intensive agriculture cannot be sustained unless nutrients are applied to the soil to replace the ones removed through crop production (Morris et al 2007). The most common sources of nutrients to crops are mineral and organic fertilizers. Fertilizer use in Ghana is low and the recommended rates for application are usually blanket (Tetteh et al 2017). Climate change has altered the soil biophysical environment and
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