Differences in water-use efficiency among perennial forages used by the dairy industry under optimum and deficit irrigation

The cost and scarcity of water is placing increasing pressure on Australian dairy farmers to utilise water for forage production as efficiently as possible. This study aimed to identify perennial forage species with greater water-use efficiency (WUE) than the current dominant species, perennial ryegrass ( Lolium perenne L . ). Fifteen perennial forage species were investigated under optimum irrigation and two deficit irrigation treatments, over three years at Camden, NSW, on a brown Dermsol in a warm temperate climate. Under optimal irrigation, there was a nearly twofold difference in mean WUE t (total yield/evapotranspiration) between forages, with kikuyu ( Pennisetum clandestinum Hochst. ex. chiov.) having the highest (27.3 kg ha −1 mm −1 ) and birdsfoot trefoil ( Lotus corniculatus L.) the lowest (14.8 kg ha −1 mm −1 ). Kikuyu was also the most water use efficient forage under the extreme deficit irrigation treatment, although its mean WUE t declined by 15% to 23.2 kg ha −1 mm −1 , while white clover ( Trifolium repens L.) in the same treatment had the largest decline of 44% and the lowest WUE t of only 8.8 kg ha −1 mm −1 . In order to maximise WUE for any forage, it is necessary to maximise yield, as there is a strong positive relationship between yield and WUE t .