Winepress - July 2021

Dirt Poor

Change required to improve vineyard soils

SOPHIE PREECE

COMPACTION UNDER wheel tracks on vineyards is one of the concerns highlighted by a new Marlborough soil quality report, along with reducing levels of soil carbon under vines. “Some vineyards are better than others, there is no doubt about it,” says Marlborough District Council environmental scientist Matt Oliver, who co-authored the technical report, presented to council last month. “But they all have compaction to some degree. They all have degraded soil carbon to some degree.”

The Soil Quality Monitoring Programme has been operating for 20 years, looking at pasture, cropping and viticulture soils, and has begun to clearly identify a declining trend in some soil quality parameters, according to the report.

Matt says compaction is a “fallout of our current practices”, with wheel tracks constantly impacted by mowing, trimming and spray runs. “The compaction is slowly getting deeper and deeper and harder and harder – you are cutting off your supply of nutrients to the vines.” That comes at a cost to business, he adds. “The biggest impact is probably on the bottom line of the producers; on their profits.”

The degraded soil carbon levels mean growers not already doing so need to look at integrated management of the undervine area, he says. “You bite the bullet and do something different, such as undervine mowing or cultivating instead of just spraying.”

The report indicates that vineyard management can yield good remedial results, with three of the four 2020 vineyard wheel samples within the target range, and the observation of “good vineyard management practice in the form of well vegetated wheel tracks” observed during sample collection.

Compaction is also evident in vineyards other than the wheel area, “but seems to be dependent on the length of time a vineyard has been in production and the management regime”, says the report. “Older vineyards tend to have reduced air filled porosity (AFP) in vine, wheel and interrow samples whereas younger vineyards often only show compaction under wheel tracks.” It also notes that compaction may be increased where vineyard soils are stony, due to heavy rollers used to bury stones.

Nurturing soil recovery is not a one size fits all process, and procedures need to consider soil types, vineyard management and the business model, with remediation designed to be “part of a profitable bottom line”, says Matt. It could mean replacing an undervine spray round with mowing, reducing the width of the spray strip, or reducing the number of tractor passes done, and the number done in the wet. Where viable, companies could consider the potential to reduce runs by using multi row machinery, he adds.

Other options available are the addition of compost and other organic matter, or using a side throw mower. “None of this is new stuff,” says Matt. “They are all well proven techniques.” He also notes that if companies are putting in place remedial measures, “they should institute them across their entire vineyard area”.

A third major issue raised by the report is the impact on soils of establishing new vineyards on what was pasture, including through spraying, cultivating, and earthworks around irrigation. “That actually takes out a lot of soil carbon,” says Matt. “Within 18 months the area under vine will have suffered a reduction in soil carbon, and reduced ability to hold water and nutrients in the soil. And there are a whole lot of consequent problems with that.”

He would like to see growers consider the soil more when putting in new developments. “Think about whether you need to do all that cultivation. Could you mulch or just spray the site then rip? If the cultivation is essential, think about how you can put back the soil carbon that you will lose.” Where the ground is to be cleared, growers should consider the addition of compost, or a few years of green crops that are subsequently mulched in or crimp rolled in situ, says Matt. “You don’t need to grow expensive crops - oats are as good as anything.”

Going forward, he would like to see absentee landlords taking note of their soil stats, and for contracting companies to incorporate soil conscious practices in their management regimes, with a checklist looking at soil compaction and undervine soil carbon and spray regimes.

Matt notes that viticulture is a relatively benign land use when it comes to water quality, but less spraying of drains would improve its footprint. “How much money do we spend on spraying out the drains?” he asks. “Those are the sorts of things that have a material impact on water quality.”

Marlborough is in a good place environmentally, “and what we are talking about here is that, irrespective of what land use you indulge in, you have an impact”, he says. “We are trying to become aware of what those impacts are and then address them”.

STEPPING LIGHTER

According to the soil quality report, Marlborough vineyard under-vine areas show soil degradation from reduced carbon levels. The following steps are recommended:

• Reduce use of herbicide; consider integrating herbicide use with minimal undervine cultivation and mowing.

• Allow weeds to grow over winter, use grazing to manage excessive growth.

• Add carbon sources (fish, seaweed, humates) to herbicide applications.

• Apply compost to undervine area. The report says consideration should be given to reduce vehicle trafficking of vineyard rows, and to:

• Use multi-row equipment for as many tasks as possible - e.g, spraying.

• Use lighter equipment for low power tasks such as mowing.

• Ensure tyre pressures are correct. Lower pressures can reduce compaction.

• Ensure wheel tracks are well vegetated and ensure herbicide applications do not kill wheel track vegetation.

• New vineyards are most vulnerable to soil compaction. Keep traffic to a minimum for as long as possible while new swards establish and use light equipment. Find the full report at bit.ly/2020MarlSoilQuality