COVER CROPS in South African Vineyards

CHAPTER 8 EFFECT OF COVER CROPS ON GRAPEVINE NUTRITION AND PERFORMANCE

determined for the vines. Grape juice was analysed, and research wine prepared and evaluated. Nitrogen status of vines Figure 8.1 shows the nitrogen levels measured as nitrates in the leaf petioles of grapevines in the cover-crop treatments where full-surface chemical was applied from the end of August. Figure 8.2 shows nitrogen levels in treatments where full-surface chemical control was started at the end of November, as well as for the dwarf-fescue treatment. Nitrate-nitrogen was never deficient in the cover-crop treatments, other than in the first season of the dwarf-fescue treatment. However, levels tended to decrease from 2000/01 to 2002/03 in many of the treatments, and vines ended up being slightly under-supplied in most treatments as well as in the control. Nitrate-nitrogen levels above 1 000 milligram per kilogram were observed in some years of the grazing-vetch treatment with weed control inAugust, and in the two-yearly rotation of triticale and grazing vetch.These high nitrogen levels did not lead to excessive vegetative growth, but did improve grape yield in the rotation treatment. mix annual rotation

1600

1400

1200

1000

1995/96

1999/2000 2000/01

800

600

2001/02 2002/03

400

Nitrogen in milligram per kilogram

200

0 Triticale Grazing vetch Rye|faba bean Triticale|vetch No cover crop mix annual rotation

FIGURE 8.1. Nitrogen measured as nitrates in the leaf petioles of grapevines in cover- crop treatments compared to a control in the Breede River valley. Full-surface chemical control was applied at the end of August. Box indicates acceptable range. Adapted from Fourie (2011).

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