COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

Organic carbon The trial site had medium-textured soils with approximately 18% clay. Soil organic carbon at the start of the trial, in 1993, averaged 0.51%, and was not significantly different in the different treatment plots. Cover crops were sown annually in autumn. Full-surface chemical control was applied from just before grapevine bud-break to harvest in the treatments and the control. Figure 7.6 shows soil organic carbon in 1993, 1998 and 2003. In general, levels after five years, although increased, were not significantly different to those at the start. After ten years, organic carbon had increased in all the plots, especially in the rye treatment. For all cover crops except grazing vetch and Overberg oats, there was sufficient soil organic carbon that no fertiliser would be required for wine grapes. In table- and raisin-grape vineyards this increase in soil fertility could increase the yields and therefore profits. The increase in soil organic carbon in the control without a cover crop is ascribed to the dominance of annual grasses in the second five years of the trial.

1,40

1,20

Henog rye Overberg oats Saia black oats Grazing vetch Faba beans

1,00

0,80

0,60

Paraggio bur medic Kelson snail medic Woogenellup clover No cover crop

0,40

Percentage soil organic carbon

0,20

0,00

1993

1998 Year

2003

FIGURE 7.6. Soil organic carbon measured in the 0–300-millimetre soil layer in cover-crop treatments compared to a control in the Coastal region. Adapted from Fourie et al (2007).

90 These results demonstrate that annual cover crops can increase organic carbon in the 0–300-millimetre soil layer of a sandy loam soil.

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