Maize Yield Response to Nitrogen and Phosphorus Fertilizers Application Rates on Plinthic Acrisol and Gleyic Plinthic Acrisol in Ghana.

Improvement in soil nutrient management requires basic understanding of the soil fertility level and responses to plant essential primary macronutrients. The study aimed at assessing the maize grain yield response to the varying rates of N and P fertilizers application on Gleyic Plinthic Acrisol and Plinthic Acrisol of semi deciduous forest zone of Ghana. Nitrogen and P₂O₅ fertilizers at 0, 30, 60, 90, and 120 kg ha^-1 each, were arranged in RCBD with three replications. The soils were slightly to moderately acid with low levels of organic carbon, total N, available P and exchangeable K contents. Maize showed differential yield response to the individual application of N and P₂O₅ fertilizer treatments. On both soil types, whereas P response was quadratic in function, N response showed no definite trend. Though maize grain yield increased significantly in the range of 0 to 120 kg ha^-1 of applied P fertilizer on both soil types, higher grain yield was obtained on the Gleyic Plinthic Acrisol (R² = 0.63) than the Plinthic Acrisol (R² = 0.92). The efficiency of P utilization in both soil types was significantly higher than N utilization except with N₃₀P₀ treatment on the Gleyic Plinthic Acrisol. Amongst the treatments also, P use efficiency was comparatively higher in Gleyic Plinthic Acrisol than the Plinthic Acrisol. Accordingly, the maximum grain yield was obtained with N₀P₆₀ and N₀P₉₀ treatments on the Plinthic Acrisol and the Gleyic Plinthic Acrisol, respectively. These rates therefore constitute the critical level of P for optimum maize grain yield in these soils. Therefore, application of fertilizer P should not exceed the critical level suitable for the crop-soils system. Also, the non-quadratic response to applied N fertilizer could be an indication that other factors such as P rather than N are limiting maize yield.

Key words: Nitrogen, phosphorus, fertilizer, nutrient response.