Water-use efficiency of wheat in Tasmania

Emerging developments in Tasmanian grain cropping such as the expansion of low pressure overhead irrigators and increased access to low-cost, plentiful irrigation sources in some areas will have a strong influence on WUE. Conventional estimates of WUE that are based on grain yield per the combined amount of rainfall plus irrigation do not account for stored soil moisture, drainage or runoff events that can be frequent in high rainfall environments. As a result, WUE may be over-estimated. An alternative approach is to estimate WUE as grain yield per the combined amount of surface evaporation, transpiration, drainage and runoff. Direct measurement of these different components to quantify ‘actual’ WUE is difficult and desktop modelling is used instead. This approach can distinguish between ‘attainable’ WUE, which is limited by crop management e.g. nitrogen fertiliser, and ‘potential’ WUE, which is determined by climate and is free of nutrient and biological constraints.