Abstract
The recent drought across the Murray-Darling basin demonstrated some of the difficulties that Australia’s wine industry will face during future droughts and as a result of climate change. To overcome these threats the industry will need to improve water use efficiency compared with current practice.
Summary
The ‘millennium’ drought demonstrated the impact that reduced irrigation availability can have on the Australian wine industry. When the next such drought will occur is difficult to know, but we can be sure that such a drought will re-occur. Climate change is likely to exacerbate the situation, with predictions of reduced winter rainfall suggesting the water availability in the future will be reduced and the predictions of warmer air temperatures suggesting that the vine will have a greater demand for water. It is clear that Australian viticulture will have to continue to improve water use efficiency compared with current practice.
Improving the scion genetics in this respect requires changing long-established consumer preferences, which is a long-term prospect. However, by utilising more water use efficient rootstocks the industry has an opportunity to improve water use efficiency in the vineyard as part of the normal turnover of plantings. Indeed, through their effect on vine vigour rootstocks have the potential to have a large effect on vine water use, but there is a difference between water use and water use efficiency. This project has attempted to explore the relationship between rootstock conferred vigour, yield and water use, together with their role in drought and salt tolerance.
The field based component of the project utilised seven rootstocks, embedded in a larger, fully replicated, trial at the CSIRO field station in Sunraysia. This trial was over 20 years old and included both high and low vigour rootstocks, all grafted with Shiraz scions. The second component of the project was a series of glasshouse studies that examined the links between rootstock conferred vigour, drought tolerance and salt tolerance.
The field work demonstrated a two-fold range in canopy size between the rootstocks and a four-fold range in pruning weight, but only a 1.7 fold difference between the highest and lowest yields. Actual vine water use (transpiration) was measured using sap flow sensors and was strongly correlated with rootstock conferred vigour, with a greater than three-fold range. Differences in yield were smaller than differences in vigour or transpiration, so water use efficiency, defined as crop produced per unit of water transpired (crop water use index: CWUI), was greater in vines grafted to the lower vigour rootstocks.