Nitrogen supply, rotation and variety are critical predictors of the water use efficiency of wheat in grower's paddocks in Victoria

ictorian grain crops rarely reach their water limited yield potential. Few Australian studies have systematically ranked the relative importance of various genetic, environmental and grower management attributes on this gap under commercial conditions. Wheat crops growing in 136 paddocks in the Victorian Mallee, Wimmera and High Rainfall Zone were monitored from 2013 to 2016 to assess the relative importance of 53 environmental, genetic/cultivar and grower management attributes on water use efficiency (WUE). Growing season rainfall ranged from Decile 1 to 10 and grain yields from 0 to nearly 10 t/ha in the study and WUE averaged 11.5 kg grain/mm/ha. Conditional forest analysis identified grower management as the key determinant of WUE, with N supply, previous crop rotation and variety as the most important factors. The results indicate the need to focus future extension messages and research priorities on N management, rotation and variety selection to maximise WUE.