Yield and water-use efficiency of contrasting lucerne genotypes grown in a cool temperate environment

In Tasmania, Australia, forage production is maximised by the use of irrigation. However, availability of water for irrigation is often limited, making the water-use efficiency (WUE) of a species/genotype an important consideration when designing forage systems. Field experimentation and an associated modelling study was undertaken to determine the WUE and environmental factors influencing WUE for contrasting lucerne (Medicago sativa) genotypes across six dairying regions within Tasmania. In the field experiment a significant genotype influence on WUE was identified under irrigated conditions and modelling identified a genotype influence on WUE in three out of six regions. WUE was related to the amount of water received (irrigation plus rainfall). The marginal response to the application of irrigation water (MWUE) was greatest for the highly winter-active genotype in the field experiment; however, modelling did not identify a consistent genotype influence on MWUE across regions. MWUE was negatively associated with the amount of deep drainage. The present study identified that lucerne has the potential to improve the WUE of forage systems across six different Tasmanian regions. The linkage of MWUE and deep drainage highlights that deficit irrigation practices could further improve the WUE of this forage crop, particularly in environments prone to deep drainage.