Response of soil phosphorus content, growth and yield of wheat to long-term phosphorus fertilization in a conventional cropping system

The effect of annual banding of superphosphate (0-45 kg P ha(-1)) on soil phosphorus (P) content, growth, and yield of wheat was investigated from 1982 to 1998 in a major rainfed wheat production area of South Africa. Conventional tillage practices in a wheat monoculture cropping system were followed under summer rainfall conditions. The responses of wheat growth to fertilizer P application were evident during early and late tillering growth stages, with decreased responses towards maturity. Although average yields varied between cropping seasons (0.881 to 3.261 t ha(-1)) due to climatic conditions, significant exponential response patterns between yield and fertilizer P applications existed. Optimum yields were achieved with P applications of 10 to 15 kg P ha(-1). The recovery of fertilizer P in the grain decreased with increasing P applications. Results of soil P analyses and calculated P balance indicated a more rapid increase in soil P content with application of fertilizer P at levels above 20 kg P ha(-1), with gradual increases occurring at lower levels.