COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

Grape and wine quality In general, the berry mass and volume, as well as the potassium and phosphate concentrations of grape juice in the dwarf fescue treatment were higher than in the other treatments. No significant differences in wine quality were observed. Root distribution A trial on root distribution was conducted by Brink (2007) on a sandy clay loam soil in the Breede River valley. He examined soil cores to determine the effect of different soil management practices on root distribution. Samples were collected at the end of a long-term cover- crop trial.

Overall root density per grapevine did not differ significantly between treatments. However, the trend was for higher grapevine-root density in the annual cover-crop treatments than in the perennial dwarf fescue treatment, or in the treatment without a cover crop in which mechanical weed control was practiced. Grapevine root densities at different soil levels are shown in Figure 8.8. For all the treatments, the highest root density occurred in the 150-300-millimetre soil layer.

GRAPEVINE- ROOT DENSITY WAS HIGHER IN THE ANNUAL COVER-CROP TREATMENTS THAN IN THE PERENNIAL DWARF FESCUE TREATMENT.

The relatively low root density in the 0–150-millimetre layer of the mechanical weed-control treatment was most likely due to root disturbance, whereas the low density in the dwarf fescue treatment was most likely to root competition. Grapevine root densities in the vine row compared to the work row are shown in Figure 8.9. The greatest difference occurred in the dwarf fescue treatment, where root density was significantly less in the work row. Competition with dwarf fescue in the work row is potentially highly detrimental to grapevines, especially considering that the work row constituted nearly 73% of the vineyard area in this trial. On the other hand, triticale and annually sown grazing vetch promoted root growth in the work row, thus helping the grapevines to use this substantial soil volume more effectively than in the other treatments.

147