With rain expected this month, the covers are coming off then going on again in the Barossa – but it has nothing to do with cricket or tennis.
Researchers from the South Australian Research and Development Institute (SARDI – a division of Primary Industries and Regions SA) and CSIRO are preparing for the second phase of a project designed to help grape growers best compensate for a lack of rain in winter, a more frequent scenario under climate change.
‘In most of our premium regions the vines rely on the moisture stored in the soil for most of their spring and a good part of their summer growth’, said the project leader, SARDI’s Dr Marcos Bonada.
‘Irrigation is only a supplement to maintain the canopy later in the season in most seasons. If we have a dry winter, we go into spring with quite an empty soil profile and the question is how best to manage this.’
For the past three years, the team has erected a series of rain shelters in autumn that they take down in spring. Under each shelter they have tried different combinations of sprinklers and dripper irrigation during winter then compared the results with a control site left open to the elements. And some clear trends are emerging.
‘Last year confirmed what we had seen for the previous two years’, Dr Bonada said. ‘In the exposed control, where there were no covers, those vines did the best, and the vines irrigated during winter using sprinklers were almost as good’.
‘The ones with the drippers, where we also put the water on all through the winter were OK, but certainly a step back. And the ones that were probably most similar to what a grower would do – we waited until spring and then filled the soil profile up – those vines just grew a great big canopy with either not very many or lighter bunches. So the yield was right down and the fruit wasn’t that great.’
That’s the most important finding to date: instead of just adding water at the end of winter, you need to find a way to assess water needs throughout winter and then meet them. When do you start, how much water do you add, and how do you minimise the risk of overwatering?
SARDI’s winter rainfall shelter frames being moved into position
While it’s perhaps to be expected that sprinklers proved a better substitute for rainfall than drippers, the researchers were surprised that they weren’t actually closer to what rain delivered. Teasing out the reasons will be valuable for those growers who do use sprinklers regularly.
For the majority who use drippers, the question is how to use them most effectively so that they can provide the necessary top up in a dry winter. The next phase of the project will investigate different dripper formats, such as putting them further out into the row or having multiple dripper heads per plant, so they apply water to a larger portion of the soil surface.
Because they are changing the treatment format, the researchers are moving their shelter structures to new rows of vines at SARDI’s research station near Nuriootpa. Hence the current burst of activity.
It’s also a fairly labour-intensive project throughout the year. Bonada and/or his colleagues are at the site most weeks, taking pictures of the roots through clear plastic tubes and monitoring a range of vine, grape and canopy parameters.