Water use in rainfed systems: Physiology of grain yield and its agronomic implications agriculture

Managing climate variability and its effects on water supply to dryland crops has always been a central theme for agriculture in the driest continent on earth. As we write in mid-2019, Australia has already dealt with catastrophic floods in north Queensland, unprecedented droughts and bushfires in Tasmania,and fish kills due to low rainfall and water levels in the Murray Darling river system. In 1987, when Tillage was published, there were many references to water conservation, infiltration and erosion, and an implicit understanding of the importance of efficient water use for agricultural production. Yet there was not one reference to the now classic work of French and Schultz (1984a, b) on water use efficiency,linking wheat yield to seasonal water use and growing season rainfall. French and Schultz’ biophysically strong benchmark, intuitively relates yield and water, and became a hallmark of the next 30 years in Australian agriculture. Whereas more refined benchmarks have been advanced to account for some of the original simplifications (Sadras et al. 2015), the core principle remains: there is an upper limit of yield for a given availability of water, termed water-limited yield potential, and differences between actual and water-limited yield potential reveal yield gaps. The yield gap concept now drives diagnosis and agronomy to address the factors responsible for the failure of crops to achieve water limited yield potential (Hochman et al. 2012, van Ittersum et al. 2013, van Rees et al. 2014, Hochman and Horan 2018).