COVER CROPS in South African Vineyards

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COVER CROPS IN SOUTH AFRICAN VINEYARDS

although both Henog rye and Saia black oats sown annually came very close toward the end of the trial. trol rol

3000

2500

2000

1500

1000

1994/95 1995/96 1997/98 1998/99 2002/03

500

0

Nitrogen in milligram per kilogram

Sown annually

Sown annually

Sown annually

Sown annually

Sown two-yearly

Sown two-yearly

Sown two-yearly

Sown two-yearly

Chemical control

Mechanical control

Paraggio bur medic

Parabinga bur medic

Pink serradella Grazing vetch

No cover crop

FIGURE 8.22. Nitrogen measured as nitrates in the leaf petioles of grapevines in legume cover-crop treatments compared to a control in the Olifants River valley. Box indicates acceptable range. Adapted from Fourie et al (2007).

In the legume cover-crop treatments, grapevine nitrogen levels exceeded 1 000 milligram per kilogram by the third season for pink serradella and grazing vetch sown annually, as well as for grazing vetch controlled mechanically at grapevine bud-break. By the fifth season, grapevine nitrogen levels in all the legume treatments exceeded 1 000 milligram per kilogram, with the exception of Parabinga bur medic sown every two years. Thanks to these increases, nitrogen application during grapevine full bloom could be halved in the legume cover-crop treatments. A reduction in fertilisation did not lead to a nitrogen deficit in the grapevines by the end of the trial. The elevated grapevine nitrogen levels in the pink serradella and grazing vetch treatments indicate that nitrogen fertilisation during full bloom could eventually be omitted in wine grapes under these two treatments. The results suggest that certain cover crops could also enable a decrease in fertiliser application in table and raisin grapes. In addition, the extra available

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