Plant and animal production of an irrigated annual pasture following initial gypsum treatment of a heavy clay soil

Abstract

The response of an irrigated annual pasture to gypsum (calcium sulphate) was assessed in terms of pasture yield and animal production on a heavy clay soil (Riverina clay). Gypsum was either broadcast (4480 lb an acre) before sowing or dissolved (560 lb an acre) in the water at the first irrigation. Both methods of application increased seedling emergence and pasture production. In the first year of grazing at seven sheep per acre the untreated pasture barely survived, whereas the treated pastures were satisfactory. After four years of grazing, spring yields of the untreated pastures equaled gypsum treated pastures, but only when the stocking rate of the controls had been reduced by three sheep per acre for nearly 18 months. The proportion of sown species was still lower than on treated pasture. The large differences in pasture production were reflected in liveweight gains and wool production an acre. In the final phases stocking rates of five sheep per acre on untreated plots and eight sheep per acre on the gypsum treated plots gave the same production per sheep. An estimate of costs and returns from wool alone indicated that an initial gypsum treatment was profitable.