Australian vineyards could soon look very different at ground level if the results of research by the University of Adelaide have the expected impact.
A four-year study led by agronomist Chris Penfold has highlighted the value and importance of planting cover crops below vines to support the soil and suppress weed growth, rather than – as is the norm – killing the weeds with herbicide and leaving the ground bare.
Barossa cover crop trial site. Photo: Chris Penfold
At four sites in four distinct South Australian regions, annual pasture legume and grass cover crops generated yields and financial gross margins equivalent to or greater than the herbicide controls – with the added bonus of helping to repair soils damaged by too much of the old routine.
In the Barossa, the herbicide control treatment generated a lower gross margin than straw mulch, medic alone or mixed with Safeguard ryegrass, with the latter treatment generating long-run increases in gross margins of $1600 to $1700/ha annually above the $5000/ha of the herbicide control treatment.
Penfold notes that such an increase will not necessarily occur on all soil types across the region, but nevertheless he sees it as an outstanding outcome, ‘providing an option for growers to consider where their soil is likely to be similarly responsive’.
The Eden Valley and Langhorne Creek sites also produced impressive results, but the Riverland raised as many questions as it answered because of its unique conditions.
‘You drive into the Riverland and you don’t see weeds growing up into the canopy because they have very good control mechanisms to stop that happening. When you take that away like we did you do find yourself shocked at just how aggressive weeds can be given the warmth and the water supply and the nutrition being pumped in through the drippers. It’s a perfect storm.
‘What we were tackling there in the Riverland was pretty difficult, but we did learn a lot from it and there’s tremendous scope to pursue that further.’
There’s also an acceptance that this needs to be pursued, as growers see the impact of decades of using herbicides and drip irrigation that puts large amounts of water into the same spots. The soil reacts to the drip irrigation, with the Riverland starting to have issues with poor infiltration even with their light sandy soils.
Penfold’s project, in collaboration with colleagues in Adelaide and Wagga Wagga, has provided the blueprint for how to start ameliorating damaged soil with organic matter.
The key is to get the right plant mix; you can’t just let things go in the under-vine area and hope it will be OK.
You have to make an active decision on adding a species mix that is going to be of benefit to the vines. Get the wrong species and you could have adverse impacts, such as loss of productivity.
Cover crop trial at Nuriootpa. Photo: Chris Penfold
The first step, Penfold says, is to ask a local agronomist for guidance on which pasture species are best suited to local conditions.
He expected there to be interest in the project, given that not a lot of work has been done in this area before, but was surprised and heartened by the extent of it. He has spoken at more than 20 seminars or workshops, and other members of the team have been invited to make presentations.
‘That’s why I do this sort of work, to be honest. It’s just fantastic to have access to the growers, particularly through the AWRI roadshow program. The groups pick the topics they want to hear and this area must be of real interest to have been invited to so many places over the years.’
This year he is starting to see adoption of the practices, with some growers putting their toe in the water with small plot trials, while others are embracing the concept with many hectares being planted.