Identifying High Yielding and Water Use Efficient Forages to Feed Dairy Cows in Australia.

Globally water scarcity is becoming an increasingly important issue, particularly in light of climate change predictions, indicating an increase in temperature and decrease in rainfall.  In producing forages, the dairy industry uses some 19% all irrigation water in Australia.  Potential milk production from dairy systems is directly related to the dry matter yield utilized, and nutritive content of the forages grown.  Whilst perennial ryegrass (Lolium perenne) is the dominant forage used, its poor persistence has led dairy farmers to question its suitability, and interest in alternative forage species. In this context, 30 forage species suitable for dairy cows were evaluated in a field cutting experiment over 3 years, to evaluate potential yield, water use efficiency (WUE) and nutritive value. Besides an optimal irrigation treatment, that maximize yield potential, two other deficit irrigation treatments were imposed to investigate how different species responded to reduced irrigation. Under optimal irrigation annual yield ranged from 7 to 31 t DM/ha, with maize (Zea mays) having the highest. The perennial grasses, tall fescue (Festuca arundinacea), prairie grass (Bromus cartharticus) and kikuyu (Pennisetum clandestinum) had the next highest yields of about 25 t DM/ha. A double crop system of wheat grown through the winter (Triticum aestivum) followed by maize over the summer, had the highest yield potential of up to 47 t DM/ha. Under optimal irrigation there was a 3 fold difference between forages in WUE, with maize having the highest up to 45 kg DM/ha.mm. Optimal irrigation was always associated with highest yield and WUE, and when forages were compared over similar growing periods, forages with highest yield potential, generally had the highest WUE. Whilst yield and WUE are important criteria for choosing forages, the choice of forage must be considered on whole farm basis, including emphasis on nutritive value, cost of production and risk.