EFFECT OF SOIL FERTILITY ON HYBRID GRAIN SORGHUM GROWN UNDER CONDITIONS FAVORING MAXIMUM YIELD

Soil nitrogen and phosphorus supply significantly increased grain yield of irrigated hybrid grain sorghum (Sorghum bicolorL. Moench.) planted at a dense plant population, with a strong nitrogen×phosphorus interaction. Maximum grain yield was obtained with 3.3% leaf nitrogen content at the boot stage (or 100-120 ppm soil nitrates at planting) and 8.1 ppm phosphorus in the soil at planting. Soil potassium ranging from 2.6 to 3.8 ppm did not affect grain yield. Nitrogen×phosphorus interaction was ascribed, at least partly, to increased nitrogen uptake associated with increased phosphorus supply. Farmyard manure and green manure, incorporated earlier in the crop rotation, increased grain yield and interacted significantly with nitrogen supply. Nutrient supply affected grain yield by changing panicle weight and 1000 grain weight. Increased soil fertility (especially nitrogen) decreased stover dry matter weight per plant at heading. Nitrogen supply increased leaf area per plant and leaf area index, at heading. However, deterioration of lower leaves was observed at the highest rate of nitrogen. © 1969 Dr. W. Junk N.V. - Publishers.