Determining optimum fertilizer rates for cotton in Northern Ghana

The soils of the major cotton growing zones in Northern Ghana are characterised by low levels of nitrogen (N), phosphorus (P) and sometimes potassium (K). The response of cotton to NPK fertilizer was studied at Nyankpala and Wa in 1991, 1993 and 1994 to determine economic rates for cultivation of the crop. Cotton responded to N, P and K except for K at both locations in 1991 where K was applied alone. The 1993 and 1994 response data at Nyanpkala and Wa were fitted with second order regression functions to generate response curves for the various nutrient elements. The economic optimum for each element was determined from a combination of the first differential of the quadratic functions and the price ratios of cotton and fertilizer materials. At Nyanpkala, the economic optimum across years for N, P and K were 53, 30 and 30 kg ha-1, respectively. The respective values at Wa were 73, 38 and 37 kg ha-1 NPK. Further multilocational on-farm testing is required to establish reliable response curves and economic optimum for each element (au)