Time of first autumn irrigation and the yield and animal production of a subterranean clover-annual ryegrass pasture

Abstract

In two experiments at Deniliquin, New South Wales, the length of the prewinter growing season of an irrigated pasture was controlled by varying the date of the opening autumn irrigation : Irrigation began in February, March, or April for treatments T1, T2, and T3 respectively. In the first, winter yields of ungrazed pasture (July) fell by approximately 1500 lb DM/acre for each month that the first irrigation was delayed after February. Clover content of the pasture was progressively less as the opening irrigation was delayed. Seed yields were unchanged by length of growing season, but increased markedly with increased phosphate supply. In the second experiment, which was grazed at three stocking rates (5, 7, and 10 sheep/acre), the response to treatments was less than in the first (ungrazed) experiment. Pasture yield (available feed) and liveweight gain were similar on treatments T1 and T2. However, at the 10 sheep/acre rate, T1 plots survived for 14 months longer than T2plots. There was no evidence that a stocking rate of 7 sheep/ acre could not be maintained indefinitely on the treatment T1. Annual production exceeded 68 lb clean wool (90 lb greasy) an acre and the plots were supporting a total liveweight exceeding 1000 lb/acre. The influence of autumn rains on the response to early autumn irrigation and the practical implications of the results are discussed briefly.