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It is well-acknowledged that climate change is impacting the grape and wine sector in Australia. Specific challenges due to warming include: (a) compressed harvests, (b) disruption of the balance between sugar, colour and flavour in ripening grapes, leading to high alcohol wines, and (c) potential loss of regional character due to warmer ripening conditions. Wineries lack the harvesting and crushing capacity to deal with a narrowing harvest window, leading to fruit becoming overripe and a reduction in quality. The expansion of processing facilities places more strain on a capital intensive industry. Viticultural practices are needed to deal with these challenges.
The aim of the first part of the project was to test delayed pruning as a tool to counteract warming effects. Delayed pruning seeks to spread maturity, hence decompressing harvest, and shift berry development into cooler conditions, hence preserving the balance between sugar, colour and flavour and regional wine styles. Delayed pruning is environmentally and economically superior to double pruning and chemical treatments.
Two trials were established with Shiraz in the Barossa Valley. First, using the open top chambers constructed in previous industry-funded projects, we increased vineyard temperature and evaluated the interaction between delayed pruning and temperature in SARDI’s experimental vineyard at Nuriootpa. Second, using large scale trials, we explored the feasibility of this practice in a commercial vineyard at Marananga. This trial further tested the carry-over effect of repeated late pruning. Three pruning dates were tested in both trials: winter control (current practice), budburst, and 2-3 leaves.
Delayed pruning was shown to satisfy four criteria. It shifted phenology and delayed grape maturity (by up to two weeks), was neutral or positive for yield, was neutral or positive for wine quality, was neutral for cost and fitted well with standard commercial vineyard practices. It is therefore a feasible practice to counteract the negative effects of global warming on viticulture and winemaking.
Another consequence of a changing climate is the increasing occurrence of extreme heat events. Several successive hot nights, rather than hot days, appears to result in permanent damage to vine canopies and crop (leaf and berry scorch or sunburn). One strategy to reduce the impact of heatwaves is therefore evaporative cooling of vineyards during hot nights. Such use of water is a trade-off with water use efficiency as this water is specifically applied to evaporate, however, if successful, this technique may a have positive cost-benefit ratio.
Three large-scale field experiments were established, two in the SA Riverland and one in Coonawarra, to investigate the effectiveness of under- and over-canopy sprinklers on lowering vineyard temperature during hot nights experienced during a heatwave. Large temperature data sets were generated during several heatwave events during the 2015/16 season, however there was little effect on temperature and humidity within the meso-climate of the bunch zone and vine canopy. At the two Riverland sites there was a 20-30% increase in yield as a result of activating under canopy sprinklers on just six nights between December and harvest in late January/early February. The value of the additional crop far outweighed the cost of the water used for cooling. In addition, there was a significant increase in yeast available nitrogen in must, which resulted in more rapid fermentation. Early indications suggest differences in wine sensory attributes; these will be reported later.
In summary, this work has demonstrated that activating under canopy sprinklers only at night during heatwaves had only a minor impact on temperature within the canopy, however there was a large, yet unexplained, increase in yield and positive impacts on grape must and potentially wine quality.
Abstract
Climate change is already impacting the grape and wine sector in Australia. This project evaluated two vineyard management strategies to adapt to a water–constrained and warmer climate. One of the measurable effects on viticulture is that hotter temperatures are causing earlier and compressed ripening of grapes. This places a strain on harvesting and winery infrastructure and changes berry chemistry and resulting wine quality.
This project showed that delayed pruning is a practical, environmentally sound and economically viable tool to shift grape berry ripening. Experiments at two trial sites, including a commercial vineyard, showed that late pruning can delay grape ripening in Barossa Shiraz by up to two weeks, potentially spreading harvest with no deleterious effects on vine vigour, yield, grape quality or wine quality.
The second part of the project investigated the use of evaporative cooling in vineyards to counteract intense heat events. It appears that temperature effects of sprinklers on grapevine meso-climate are minimal and transient. Nonetheless, results from two Riverland trial sites showed a significant improvement in yield, a positive cost/benefit, reduction in grape sunburn and early indications of improved wine quality in “cooled” vines. Clearly another, unknown plant physiological response occurred.
Objectives
This overall project has two sub-projects: (1) Practical pruning methods to ensure controlled harvest and grape quality; and (2) Irrigation methods to manage the effects of hotter temperatures and heat events
Practical pruning methods to ensure controlled harvest and grape quality
This project has two objectives:
- To evaluate the extent to which late pruning can be used to cancel the effects of warming on vine development and berry composition
- To evaluate the feasibility for which delayed pruning can spread harvest time and improve the balance between sugar, flavour and colour in fruit and wine on commercial scale vineyards.
Irrigation methods to manage the effects of hotter temperatures and heat events
Evaporative cooling through the use of micro–sprinkler irrigation will be evaluated as a mechanism to cool the vine canopy, generating a more favourable meso–climate that will counteract intense heat events.
Background
Practical pruning methods to ensure controlled harvest and grape quality
Climate, specifically warmer temperatures, is thought to be playing a large part in the onset of earlier grape harvest. The preservation of grape integrity and resultant wine quality is paramount. However, not all wineries have the harvesting and crushing capacity to deal with a narrowing harvest window; often resulting in longer fruit–hang time (leading to overripe characters and potential wine quality degradation) and logistical chaos. Expansion of processing facilities places great strain on a capital intensive industry. Therefore, viticultural practices are needed to deal with these challenges.
Sadras et al (2014) has shown that the gap between harvest of Chardonnay and Cabernet Sauvignon at McLaren Vale has been compressed from 21 to 9 days in the last 20 years. Sadras and Moran have also shown that warming disrupts the sugar/anthocyanin balance in Shiraz (AGWA project SAR 0901).
Delayed pruning has the potential to modify phenology and shift ripening into cooler, more favourable conditions, thereby allowing the key grape flavour and aroma compounds to develop. It is hoped that by altering ripening times, congestion of harvest will be lessened and logistically, the vintage process will be more manageable.
Irrigation methods to manage the effects of hotter temperatures and heat events
Over the last decade, there have been noticeably more frequent and intense heat events. In places such as the Riverland, events >30oC have prolonged for up to 16 consecutive days. Such climatic conditions places great strain on a vineyard meso–climate, and high water inputs are often required to reduce heat stress symptoms and sustain fruit quality.
This project will investigate the application of vineyard evaporative cooling to mitigate the impacts of extreme heat events. It is thought the most commonly used irrigation system, drip, may not provide sufficient capacity to offset heat impacts on vine production.
Approach
Practical pruning methods to ensure controlled harvest and grape quality
Two Shiraz vineyard trial sites have been established in the Barossa, South Australia. The project spans three growing seasons including 2013–14, 2014–15 and 2015–16.
In Trial 1, experiments combining two temperature regimes (control, elevated temperature) and pruning dates (mid–winter, budburst, and 2–3 leaves expanded) are being investigated. Artificial heating is being imposed through passive open–top chambers, which were constructed in a previous AGWA project (SAR 0901).
In Trial 2; a six hectare commercial vineyard, pruning will also be conducted in winter, budburst, and 2–3 leaves expanded.
Phenological, physiological and harvest data will be collected and analysed for each trial site for the three growing season. Small-lot wines will also be made and chemical and sensory analysis will be investigated.
Irrigation methods to manage the effects of hotter temperatures and heat events
Under-canopy micro-sprinklers will be installed in three mature commercial vineyards in the South Australian Riverland and Coonawarra regions, and designed so they can operate independently of the primary drip irrigation system.
The micro-sprinklers will be activated during heat events, primarily at night, (grower observations suggest high night time vineyard temperatures accentuate heatwave damage) to create a cool under-vine meso-climate. At each of the three sites, there will be an adjacent vineyard block that will serve as a control (without the under-canopy micro-sprinklers) to assess differences between the treatments.
A series of vertically mounted loggable temperature sensors from below ground to above the height of the canopy will be installed to measure vertical temperature profiles when the micro-sprinklers are in operation. Wind speed and direction and other environment indices will be collected. The timing, duration and frequency of micro-sprinkler operation on vineyard temperature will be examined. These data will be used to develop a heat transfer model to quantify the effectiveness of evaporative cooling under a range of climatic conditions.
Over two growing seasons (2014–15 and 2015–16), data will be collected on canopy and soil temperature, soil moisture, vineyard water use, vine yield parameters (berry and bunch number, pruning weight), micro sprinkler installation and annual operating costs. Immediately prior to harvest, collaborating winemakers will be invited to undertake in-field assessment of grape berry taste characteristics and based on these assessments small to commercial size wine making will be undertaken to enable full sensory profiling of finished wines.
Sector benefits
Practical pruning methods to ensure controlled harvest and grape quality
The project will provide the sector with new knowledge and benefit of modifying pruning techniques that can delay ripening into cooler conditions without compromising fruit and wine quality
Irrigation methods to manage the effects of hotter temperatures and heat events
The project will produce new knowledge on improved and modified irrigation management and scheduling techniques to manage heat events, including development of a model to better predict the optimal use of water during heat waves.
