‘Keep alert and plan’ is the take home message for grapegrowers from a three-year study that found reduced rain during winter is associated with reduced grape yields.
‘We now know that a reduction in rain from May to August to approximately one third of the historical average rainfall has a major impact on yield of between 20–40 per cent’, said Dr Marcos Bonada, a Senior Viticultural Research Officer with Primary Industries and Regions SA in its research division, the South Australian Research and Development Institute (SARDI).
‘Our advice to growers is to incorporate irrigation during dry winters to maintain soil moisture – even when the vines are still dormant. Don’t wait until the first indications of vine growth in spring to start irrigating.’
To assess the impact that reduced winter rainfall and different methods of soil water replenishment have on grape yield and quality, researchers from SARDI and CSIRO erected a series of rain shelters at the Nuriootpa Research Station over three seasons to test various methods of irrigation to replace winter rainfall.
Rain shelters being installed at the Nuriootpa Research Station
Under the shelters they tried different combinations of sprinklers and dripper irrigation during winter then compared the results with a control site left open to the elements.
The vines that did the best were those in the control group, where there were no covers and the vines were exposed to the long-term average rainfall – followed closely by the vines that were irrigated during winter using micro-sprinklers.
The vines that were irrigated with drippers throughout winter did better than vines that received limited irrigation but did not perform as well as the control.
Surprisingly, irrigation to fill the soil profile at budburst following a dry winter – a common approach used by growers – did not compensate for losses in yield and had a detrimental effect on wine sensory attributes.
‘In fact, refilling the soil profile at the end of winter did not prevent a yield reduction by 10–30 per cent; it increased canopy size and had a detrimental effect on fruit and wine composition’, Dr Bonada said.
Based on these findings, the extended project is now looking at irrigation strategies that restore yield and maintain wine style.
‘As the majority of vineyards in Australia are drip irrigated, the challenge is how to use the existing infrastructure to provide a pattern of soil wetting similar to the rain.’
One method being investigated is multiple laterals in the inter-row space that can wet a larger portion of the vineyard floor. Irrigation timing, such as during the period following budburst, is also being explored.
At the Crush Symposium in September last year, Dr Bonada showed some powerful data from the CSIRO that depicted the drying trend in South-East Australia since the 1960s.
‘Long term weather observations indicate a decline in late autumn and early winter rainfall for South Eastern Australia, where the majority of Australia’s premium vineyards are planted. This will result in the soil profile not being full at the start of spring.’
Dr Bonada said water stored in the soil supported canopy growth and development into summer, and when it was unavailable vines encountered water deficits early in the season. Effective irrigation strategies that maintained yield and wine styles would need to be tailored to account for reductions in rainfall and increasing reliance on supplementary irrigation in drier and warmer years.
‘Growers will need to make full use of soil moisture monitoring systems and seasonal climate outlooks to effectively budget water and fine-tune irrigation’, he said.
The final report is available here.