Response by irrigated grain sorghum to broadcast gypsum and phosphorus on a heavy clay soil

Abstract

In two successive field trials at Deniliquin, New South Wales, irrigated grain sorghum was sown at three rates of gypsum (0, 4,480, and 8,960 lb an acre), and four rates of phosphorus application (0, 25, 50, and 100 lb an acre) on Billabong clay, a brown clay commonly found on the Riverine Plain of south-eastern Australia. There was a significant response to broadcast gypsum in terms of seedling emergence, tillering, and panicle production. Furthermore, there was a positive interaction between gypsum and phosphorus response which was clearly demonstrated by the yield of total dry matter and grain in the first year. Although there was a response to phosphorus in the absence of gypsum, the more effective use of phosphorus on the gypsum treatments, particularly at the higher rates of fertilizer application, was attributed to improved soil water storage. In the second year, the residual value of applied gypsum was greater following application at 8,960 lb. an acre than at 4,480 lb an acre during the previous year. Residual phosphorus had little effect in the year following application.