This project determined the impact on vine performance of irrigation strategies to mitigate low rainfall during winter. Rainfall was excluded using shelters between May and August. Despite top-up winter irrigation to a similar level as average winter rain, a reduction in yield was still observed. Applying irrigation to refill the soil profile in spring generally stimulated vine growth, which negatively affected grape and wine composition without restoring yield. Reduced winter rainfall (one third of average) improved grape and wine composition at the cost of a significant drop in yield. Growers are advised to maintain soil moisture using irrigation throughout winter.
In many Australian wine regions, grapevine production relies on soil moisture stored during the winter in addition to supplementary irrigation during the growing season. The combination of winter rainfall decline and restricted water for irrigation (~ 1.5 ML/ha per season) will place increasing strain on these production systems.
This study investigated the effects of winter rainfall exclusion and rainfall replacement options on (i) vine balance, (ii) fruit quality parameters, (iii) wine chemical and sensory characteristics, (iv) root growth and (v) carbohydrate reserves storage. The project commenced in 2013 with the installation of the field trial (shelters and irrigation system); and the results from the 2015/16 to the 2017/18 inclusive are included in this report.
Three seasons of results showed that a reduction in winter rain is associated with major changes in grape production. Despite top-up winter irrigation either using sprinklers or drippers to a similar level as natural winter rain, a reduction in yield was still observed. This is likely to be due to the irregular soil pattern of wetting caused by the irrigation and its influence on root growth and longevity and then vine performance. Unfortunately, root growth and development are very difficult to accurately assess. The irrigation to refill the profile at budburst generally stimulated vine growth across most measured parameters, which negatively affected grape and wine composition without restoring yield. Reduced winter rainfall (in the lowest two deciles) improved grape and wine composition at the cost of a significant drop in yield in the two dryer seasons.
If water is available for irrigation during a dry winter, growers are recommended to maintain soil moisture throughout the season as opposed to waiting until budburst to refill the soil profile. Further research is needed to explore alternative application times and methods which can fully compensate for the yield loss as a result of a reduction in winter rainfall.
This project was completed as a collaboration between the South Australian Research and Development Institute and the Commonwealth Scientific and Industrial Research Organisation. It was supported by Australian grapegrowers and winemakers through their investment body Wine Australia, with matching funds from the Australian Government. The Commonwealth Scientific and Industrial Research Organisation and the South Australian Research and Development Institute are members of the Wine Innovation Cluster in Adelaide.