COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

In one treatment, cover crops were sown annually, and chemical control applied from grapevine bud-break. In another, cover crops were sown annually, and mechanically controlled by tilling into the soil at grapevine bud- break. A third treatment had no cover crop. Instead, weeds were allowed to grow naturally, and were mowed during the grapevine-growing season. As illustrated in Figure 8.17, the researchers found significantly greater grape yields in the cover-crop treatments than in a control where natural weed growth was slashed.These results demonstrate the risks of maintaining weeds as a permanent sward in the vineyard.

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Grape yields in tonnes per hectare

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Cover crop Chemical control

Cover crop Mechanical control

No cover crop Weeds mowed

FIGURE 8.17. Grape yields in treatments with cover crops compared to no cover crop in a dryland vineyard in the Coastal region. Adapted from Van Huyssteen and Weber (1980).

Grape and wine quality Average total titratable acidity appeared to be higher in the treatments where cover crops were sown annually than where they were sown two-yearly, but the trend was not statistically significant. However, the observation is consistent with results reported by Conradie (1994), which showed that increased vegetative growth delayed maturity. No trends were observed in the sugar content, pH, or concentrations of potassium, calcium, and magnesium of the grape juice, or in wine quality.

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