Cost-effective viticultural strategies to adapt to a warmer, drier climate

Summary

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

Objectives
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.

Background
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 nine 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.

Research approach
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.

Industry benefit
The project will provide industry 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

Objectives
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
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.

Research approach
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.

Industry benefit
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.