Growth and yield responses of dryland grain sorghum to nitrogen and phosphorus fertilization in a ferruginous tropical soil (Haplustalf)

Field trials were conducted during the 1980–82 seasons to study the response dryland sorghum to nitrogen and phosphorus fertilization in a ferruginous tropical soil. Treatments tested were factorial combinations of three rates of nitrogen (0, 60 and 120 kg N ha^–1) and four rates of phosphorus (0, 11, 22 and 33 kg P ha^–1). Grain and straw yields and yield components were enhanced by nitrogen fertilization in two out of three years. The optimum N rate for grain yield was 60 kg N ha^–1 while straw yield responded up to 120 kg N ha^–1. The optimum P rate for dryland sorghum was 11 kg P ha^–1. Both N and P enhanced grain weight per head, grain number, test weight and tillering significantly but it was only N which enhanced 1000-grain weight and flag leaf area. Dry matter productin was increased by N fertilization but not by P. There were no significant N × P interactions for any of the parameters studied. Dryland sorghum response to N and P fertilization was influenced by season, time of planting and rainfall distribution.