Soil health – the bedrock of Thelema success

Gyles Webb left the corporate grind to establish Thelema, a wine cellar now dubbed one of SA’s best. Wouter Kriel discovers that cutting-edge technology and balanced soils keep them in the top 10.
Issue date : 27 June 2008

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Situated on the Helshoogte Pass outside Stellenbosch, Thelema Mountain Vineyards was nominated the second-best cellar in SA in a 2007 reader poll by Wine magazine. This internationally acclaimed cellar is one of Wine editor Christian Eedes’ top 10 favourites. Thelema’s owner and cellar master Webb seems unaffected by the hype. At the age of 28 he left his life as a charted accountant in Durban to study winemaking full-time at the University of Stellenbosch.

In 1983 Gyles bought a derelict plum, apple and pear farm, where today Thelema produces 25 000 cases of premium wine on 50ha of mainly decomposed granite high-potential soil. Cultivars include Sauvignon Blanc, Rhine Riesling, Chardonnay, Cabernet Sauvignon, Shiraz and Merlot.

Irrigation water is stored in a farm dam fed by winter rain draining off the Simonsberg Mountain. Growth precision G yles believes in combining natural balance and cutting-edge technology to produce excellent wines year after year. The vertical shoot positioning (VSP) system, which arranges shoots to grow upwards, is used to balance growth with grape production. Gyles says his perfect VSP vine has a 12cm spur spacing, and two buds left after pruning.

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During spring, two shoots should grow with 17 or 18 leaves each. Two bunches will form on each shoot, and after vertical shoot growth of 1,2m, these bunches will ripen to suit requirements. “In practice, we manage each block according to its potential,” he says. “If growth is too vigorous, the fruit won’t ripen. As a corrective measure, we’ve experimented with the double Guyot pruning system, where instead of pruning the shoots, new leaders are developed each season.” Soil health the natural way n the vineyards, Gyles showed Farmer’s Weekly the friable soil structure and the abundance of living organisms present.

Sample holes were dug, and we were amazed at the depth of root penetration and the amount of hair root development. “That looks like healthy soil and vines to me, so I’m happy,” observed Gyles. He sees soil health as the foundation of quality wine and an intrinsic part of sustainable production. “About six years ago we noticed a decline in our production,” he recalls. “Plant vigour was going down, so we had soil samples analysed. The results showed an alarmingly high count of plant-parasitic nematodes, and very few other living organisms.”

“We were advised to use an extremely costly, intensive chemical programme, which would have set us back R30 000/ha, but nematologist and retired academic Professor Bertus Meyer suggested using ompost to restore soil balance naturally – a cheaper, and far more environmentally friendly solution.” With the help of Barbara Von Wechmar, an expert on composting, Thelema set out to rebuild its soil. “At first we bought compost, which we placed on the bunkies and covered with straw,” explains Gyles.

“Buying these materials was expensive, but we had to start somewhere. In the meantime, Barbara taught us how to make our own compost with material available on the farm. “Cellar waste is notoriously difficult to decompose, but with the correct inoculants, which she supplied, even grape skins can make excellent compost. Thelema can now use all its cellar waste for composting.” Recently Thelema bought a mower with a side chute so that cover crops could be mulched, instead of buying in straw.

Barbara’s technique also doesn’t require the windrows to be continually turned by expensive machines. Today Thelema removes all pruning material from the vineyards, chips it and adds it to the compost mixture. This helps prevent disease, as the heat generated by the compost wind row kills the pathogens in the cuttings. Compost extract is prepared with an aerator and applied through the dripper irrigation, according to Barbara’s prescriptions. “In 2005 the lab recommended we chemically treat 12 vineyard blocks,” says Gyles.

“This number came down to one block in 2007.” Cover crops Viticulturist Conrad Schutte explains Thelema’s cover crop strategy. “We use cover crops for weed control and to suppress vine vigour in some blocks. We use as little herbicide as possible, and our ryegrass has been manageable up to now. Blocks with very vigorous vine growth are planted to a permanent cover crop.

We use fescue (Festuca arundinacea), which the rep claimed is the same grass as on Newlands,” Conrad smiles. Pruning intensity and production is carefully monitored. If a decline is noticed, every alternate row is cleared of fescue and an annual crop such as triticale is established instead. Blocks with medium vigour are planted to triticale, and low-vigour is remedied with purple vetch, a natural nitrogen fixer, mixed with triticale. Irrigation management Irrigation is managed with the help of a pressure bomb and a continuous capacitance soil moisture probe. As Conrad explains, “We used to use a conventional moisture measurement system until two years ago. But it was like taking a photo. It didn’t tell you what was happening in-between measurements. The new probe system takes electronic measurements every 30 minutes, which can then be downloaded onto a computer.”

This allows for far more accurate irrigation management. “For instance, during véraison (when the berries change colour), we don’t want undue moisture pressure on the vine and irrigate accordingly,” says Conrad. “Other stages require the vine to be stressed, so we limit water to achieve the exact amount of stress required. “The better our information, the better we can manage this process.

We also combine data from Aqua Check test strips with pressure bomb samples that measure leaf and stem water potential, because while the soil might be at the correct moisture level, the plant may not be functioning optimally due to root disease or some other factor. “Together with experimental plot data from sample vines, we get a clear picture of our vineyard’s condition.

This also helps us predict the crop size so the cellar can budget for the right number of barrels, and the marketing department can do strategic planning,” concludes Conrad. Contact Thelema Mountain Vineyards on (021) 885 1924, e-mail [email protected] or visit |fw