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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.
Abstract
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.
Objectives
To identify the cumulative effect of winter drying on vine balance and wine quality.
Background
Projections from climate change models indicate a warmer and drier future for most wine growing regions. Although there is less confidence in drying than warming, most climate models suggest a drier winter and spring. In regions where rainfall is greater than irrigation application (e.g. Barossa Valley, Great Western) the latter amount is usually less than 1.5 ML/ha (150 mm irrigation) during the growing season. Any long term decline in rainfall will necessitate increased irrigation from already limited water supplies.
Approach
The project will concentrate on vine activity during dormancy – specifically understanding root physiology and activity and how soil water deficits during dormancy impact overall vine balance and subsequent wine quality. Prior research has not explored these aspects and their correlation to soil water deficit or storage reserves. The experimental design and method incorporates five treatments within an experimental plot at the Nuriootpa Research Station, South Australia. All winter rainfall will be excluded from experimental plots (measurement row and adjacent ‘buffer’ rows) by using rain-out shelters.
Typical and reduced rainfall amounts within the shelters will be simulated using micro sprinklers. Treatment volumes and timing will be determined using winter rainfall deciles, calculated from existing climate information. The rain-out shelters will be removed at budburst and all treatment vines will receive the same level of irrigation during the subsequent growing season.
Sector benefits
This project will assist grape growers to manage vine balance in dry winters in the current climate and prepare for future changes. A series of management strategies will be developed that growers will be able to rapidly implement during years of low winter/spring rainfall based on actual and projected winter rainfall probabilities.
SAR1302 Final Report - Managing the Impacts of Climate Change
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