COVER CROPS in South African Vineyards

two-yearly rotation fescue

COVER CROPS IN SOUTH AFRICAN VINEYARDS

1800

1600

1400

1200

1995/96 1999/2000

1000

800

2000/01 2001/02 2002/03

600

400

Nitrogen in milligram per kilogram

200

0

Triticale Grazing vetch Triticale|vetch Perennial dwarf fescue

No cover crop

two-yearly rotation

FIGURE 8.2. 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 November, except in the dwarf fescue treatment. Box indicates acceptable range. Adapted from Fourie (2011).

Dwarf fescue was re-established during 1998. Reduced competition between the shallow-rooted young fescue and the grapevines is thought to be the reason for improved nitrate-nitrogen levels in the grapevines from 1999 to 2001. However, in 2002/2003, grapevines in this treatment suffered a serious deficiency. This is further evidence that perennial fescue competes with grapevines, even on relatively fertile soils.

PERENNIAL FESCUE COMPETES WITH GRAPEVINES, EVEN ON RELATIVELY FERTILE SOILS.

Figure 8.3 shows the nitrogen concentrations in the grape juice of vines in the different cover-crop treatments where full-surface chemical control was applied from the end of August, and Figure 8.4 shows the nitrogen concentrations in treatments where full-surface chemical control was applied from the end of November, as well as the perennial dwarf fescue treatment. Nitrogen concentration in grape juice tended to mirror the trends seen in nitrate-nitrogen in the leaf petioles.

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