COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

This was entirely due to increased nitrogen levels in the 0–150-millimetre soil layers, except in the cases of grazing vetch and faba bean. Faba bean increased nitrogen levels in both the 0–150-millimetre and the 150–300-millimetre soil layers. Grazing vetch did not significantly increase soil nitrogen levels. The relatively high levels of nitrogen in the treatments with Paraggio bur medic, Kelson snail medic and faba bean corresponded with luxurious vegetative growth of the grapevines.Therefore, these legumes should not be established in wine-grape vineyards over the long term. In table and raisin grapes, elevated soil nitrogen may be accommodated by increasing the harvest load, thereby increasing profits. Increases in soil nitrogen by 2002 could be ascribed to all cover crops being sown annually from 1999 onward. However, levels were still lower than in treatments where cover crops had been sown annually throughout.This was especially noticeable in the case of Paraggio bur medic. Figure 7.8 shows the soil nitrogen levels after harvest. Not shown are the nitrogen levels for the 0–150-millimetre, 150–300-millimetre, and 300–600-millimetre soil levels individually.The trend was for nitrogen levels to decrease from shallower to deeper soil levels. ic ic clover er

25,00

20,00

Henog rye Overberg oats Saia black oats Grazing vetch Faba beans

15,00

10,00

Paraggio bur medic Kelson snail medic Woogenellup clover No cover crop

5,00

Nitrogen in milligram per kilogram soil

0,00

2002 Season 10

1996 Season 4

2002 Season 10

1996 Season 4

Weed control August

Weed control October–November

FIGURE 7.8. Soil nitrogen measured after harvest in the 0–600-millimetre soil layer in cover-crop treatments compared to a control in the Coastal region. Adapted from Fourie et al (2007).

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