The science is starting to come together on the question of what to do in the undervine region of the vineyard floor, with new research further highlighting the value of cover cropping to enhance soil health.
The key is to pick the right plant species for the vineyard in question and to take a long-term view of what you are trying to achieve.
Triticale mulch, Medic and Mintaro sub/Prima glad clover at a trial site.
Until now, the common practice has been to keep the under-vine region free of weeds and other plants that might take up moisture that could otherwise be going to the vines. Broad-spectrum herbicides make that easy and relatively cheap to do.
It works for growers, the vines seem happy, and no-one has really checked for any negative impacts. But that is changing, according to researcher Chris Penfold, who led the recent project at the University of Adelaide, which was funded by Wine Australia.
‘We are starting to see issues resulting from the long-term removal of plants in the undervine zone,’ he said. ‘Herbicide resistance is the obvious one – growers are having to change herbicide groups more frequently to get the same control as they had before – but there are also problems with water infiltration into the soil. Even up in the sandy soils in the Riverland there are some issues starting to emerge that need to be addressed.
Mr Penfold says the bigger problem is not actually the chemicals themselves; it’s the removal of the vegetation by the use of chemicals.
‘You need vegetation to have root systems, you need root systems to have the soil biology working for you, and you need the soil biology to have the soil structure, to enable infiltration to occur and to enable nutrient release to occur.
‘The soil is meant to be a living entity and when you go removing vegetation you reduce your organic carbon levels in the soil and carbon is what drives the soil biology.’
Planting crops under the vines has always been an alternative, but until recently there were concerns, supported by the results of some vineyard trials on organic systems, that this can lead to significant decreases in yield.
The bigger picture is a little more complex than that, however. For example, recent studies in South Australia have revealed both the importance of undervine vegetation in improving poor quality soils and the negative impact of sustained herbicide use on organic carbon levels.
Armed with all this information, Mr Penfold and colleagues trialled a variety of different crop options over three years on a block of 13-year-old Shiraz vines at the South Australian Research & Development Institute’s Nuriootpa Research centre in the Barossa Valley. The project included the use of next generation sequencing technology to ascertain links between soil and root microbiomes and those in the grapes.
Despite very different growing seasons across the three years, the results were consistent and positive. If the right individual species are selected there is negligible negative impact on yield in good soils and a positive impact on poor soils. At the Nuriootpa site, the use of undervine cropping produced a $5000 per hectare increase in returns in 2016–17, all for the cost of seeding the cover crops at less than $300 per hectare.
Medics and ryegrass emerged as the most valuable crop species in terms of contributing to soil health and vine yield.
Mr Penfold admits to being pleased and relieved. ‘I approached it with a bit of trepidation that we would just have a negative effect on yield, but what other people had suggested and what I hoped would be the case has been vindicated.’
The next phase of research will include a greater emphasis on soil biology, while also measuring the impact of these different management techniques on wine quality. The final report of the just completed project will be released soon.
Wallaby grass under Nebbiolo vines at Clare