COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

Excessive nitrogen in the grape juice could affect fermentation and wine quality.Therefore, two-yearly monitoring of nitrogen concentrations in the grape juice is recommended, especially when pink serradella and grazing vetch are used as cover crops. Vegetative growth and grape yield Shoot mass and grape yield for the grass cover-crop treatments are shown in Figure 8.24, and for the legume treatments in Figure 8.25. In general, shoot mass did not differ significantly between the treatments and the controls in either season.The exception was shoot mass in 2002/2003 for the treatment where pink serradella was sown every two years. Grape yield in 1995/96 was significantly higher than in the control in treatments where grazing vetch and pink serradella were sown annually. In 2002/2003, grape yields were significantly higher than in the control for grazing vetch, pink serradella, and Overberg oats, regardless of whether these cover crops were sown every year or every two years. Grape yield in 2002/2003 was also significantly higher than in the control for the treatments with annually sown Parabinga bur medic and two-yearly sown Paraggio bur medic. Observation of dense canopy formation in the treatments where grazing vetch and pink serradella were sown annually motivated a reduction in

nitrogen fertilisation. Nitrogen application was halved from 1996/97 onward, and omitted from 1998/99 onward. However, high grape yields were still achieved in these treatments, demonstrating the value of these cover crops in reducing the need for nitrogen fertilisation on sandy soils.

CERTAIN LEGUMES CAN REDUCE THE NEED FOR NITROGEN FERTILISATION ON SANDY SOILS.

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