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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