The 2022 Coonawarra Rootstock Trial Field Day has demonstrated there is still much to learn about the impact of soil physical attributes on the performance of different grapevine rootstocks.

Soil and viticulture expert David Hansen from Hansen Consulting Group, led discussion on the relationships between rootstocks and soil while examining root growth and canopy growth of the Cabernet Sauvignon vines at the trial site, located in Wynns Coonawarra Estate’s Alexander Vineyard in Coonawarra.

Soil pits were dug for each of the eight rootstocks – Ramsey, Börner, 140 Ruggeri, 1103 Paulsen, 110 Richter, Merbein 5512, Merbein 5489 and Merbein 6262 as well as own-rooted vines.

Rootstocks’ yield and vigour was compared to the measured soil total available water.

“Effective rooting depth, root volume and root density, are the key parameters we can quantify to comparatively assess how the root systems of different rootstocks are making use of their available soil volume to extract soil moisture, and that directly impacts relative vine vigour,” David said.

“We measure what we want above the ground – vine balance, shoot length, yield, fruit quality – but we have an abstract view of what’s happening underground with root growth and soil health. We don’t measure much.”

To better understand soils when planting vines or when looking to solve vine performance issues, David recommends digging numerous soil pits to understand the soil variability across a vineyard and visualising root growth as an indicator of soil structural issues.

In terms of the performance of the eight rootstocks in the trial, higher yields and shoot length tend to be associated with greater soil total available water and higher root volume and density scores.

“In addition, those rootstocks which were able to make the most of their limited soil volume with higher root length densities tended to have higher average shoot lengths and yields,” David said.

The rootstocks which had higher rooting density, root volume and total available water factors, as well as higher shoot lengths and yield were 140 Ruggeri, 1103 Paulsen, 110 Richter rootstocks. Two Merbein rootstocks, M5489 and M5512, also had higher root and total available water factors, shoot length and yield.

At the lower end of root and total available water factors and subsequently yield were Own Roots, Börner and M6262.

For detailed analysis of the rootstocks and available reports and presentations, click here.

Rootstock expert Nick Dry from Foundation Viticulture shared insights about rootstock choice and site. “Rootstock performance is site specific. It’s not until a rootstock is planted on your site that you’ll really understand how the rootstock will perform,” Nick said.

“I recommend planting about three panels of five different rootstocks in your vineyard and see what works for you and delivers what you want to achieve before planting in larger volumes.”

As a guide, Nick said it’s important to understand the history of the rootstock we commonly use in Australia.

“The rootstocks we use in Australia have basically come from three parent species – Vitis rupestris, Vitis berlandieri and Vitis riparia,” Nick said.

“Thinking about these parent species and where they evolved can be very helpful in understanding how the rootstocks will perform in a vineyard in Australia, as site and soil type impact rootstock performance so much.

V. rupestris prefers deep, gravelly, rocky soils next to intermittent streams, so it can deal with periods of dryness but does need some moisture in the system to replenish it.

V. berlandieri comes from south-west Texas in limestone soils where it’s hot and dry. Rootstocks bred from this parent offer some drought tolerance.

“And V. riparia prefers moist soils associated with riverbanks, so rootstocks that come from this parent need water.”

Looking at the parentage of some of the rootstocks used in Australia:

  • 140 Ruggeri, 1103 Paulsen and 110 Richter parentage is V. berlandieri x V. rupestris
  • Schwarzmann, 3309C and 101-14 parentage is V. riparia x V. rupestris

David Hansen also spoke about ways to improve root access to water in limited soils.

“We observed limitations to grapevine root growth, of surface crusting – not allowing grapevine roots to utilise the surface 5 to 10 cm of soil, ‘hard’ soil horizons at 300 to 400 mm depth preventing deeper root growth and wheel traffic compaction,” David said.

“If a greater total available water is desired there are some options available. Surface covers such as a permanent sward, compost or mulch would enable more top soil to be utilised by grapevine roots.

“And for grapevine roots to develop deeper into the mid-row, deep ripping would be required at the Coonawarra Rootstock Trial site. Management options to maintain the improved grapevine root volume would also need to be considered, such as compost at depth and trafficking alternate rows.”