Irrigation water productivity of winter-growing annuals is higher than perennial forages in northern Victoria

Abstract

The dairy industry in Victoria, Australia, uses more than half the state’s irrigation water, mainly for growing pasture. Information on the comparative water use of forage systems would be useful for dairy farmers aiming to optimise their forage production under conditions of limited water availability. However, there are few data comparing water use under similar management and weather conditions. This paper reports on an experiment which measured and compared the production, water use, and water productivity (forage removed per unit water input) of a range of 6 border-check irrigated forage systems (3 perennial, 2 annual, and a double-cropped) and 1 spray irrigated, annual forage system, used by the dairy industry in northern Victoria. Forage removal was highest from the perennial pastures, lucerne, double-cropped and Persian clover systems in both 2005 and 2006. Irrigation water inputs in 2005 were comparable with average values reported in the literature and were closely related to the length of the growing season, with around 800–850 mm used for the perennial pastures and 340–440 mm used for the border-check irrigated annual pastures. Irrigation water inputs in 2006 were substantially higher than in 2005, reflecting the drought conditions that prevailed throughout most of Victoria, with 1100–1200 mm used for the perennial species and 450–700 mm used by the border-check irrigated annual pastures. These irrigation water requirements highlight considerable year-to-year variation as low-rainfall years are usually high-evaporation years. Irrigation water productivity (WP) was greater for the annual than for the perennial systems. In 2005, irrigation WP was 30–37 kg DM/ha.mm for the annual pastures compared with 21–27 kg DM/ha.mm for the perennial and double-cropped systems. In the drier year of 2006, irrigation WP was higher for the short-season annuals than for the other forage systems. When rainfall, runoff, and changes in soil water content were included in the calculation of total WP, there were no consistent differences in the total WP of the annual and perennial systems in either year. These findings show that under conditions of limited irrigation water availability, farmers will be able to grow more forage using winter-growing annual systems than perennial systems. However, other factors such as nutritive characteristics, cost of production, and cost of transferring feed also need to be considered when deciding which forages to grow.