COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

they reached the two-to-four-leaf stages. Two weeks after grapevine bud- break, 42 kilogram of nitrogen per hectare was applied. Soil nitrogen levels were measured in the work row at grapevine full bloom, in early November, and again after harvest, in March. Figure 7.11 shows the soil nitrogen levels at grapevine full bloom for treatments where cover crops were sown annually, and where full-surface chemical control was applied from just before grapevine bud-break to harvest. Total inorganic nitrogen levels were significantly higher in the pink serradella treatment than in the other treatments in the third season. Nitrogen levels were also higher in the grazing vetch treatment. Based on these results, together with excessive vegetative growth of grapevines, the inorganic nitrogen application was halved from the third season onward in the pink serradella and grazing vetch treatments. Despite this, soil nitrogen levels remained relatively high in these treatments compared to the other cover crops and the control.

10,00

9,00

8,00

7,00

Henog rye Overberg oats Saia black oats

6,00

5,00

Paraggio bur medic Parabinga bur medic

4,00

Pink serradella Grazing vetch No cover crop

3,00

2,00

Nitrogen in milligram per kilogram soil

1,00

0,00

1996 Season 3

1998 Season 5

1999 Season 6

FIGURE 7.11. Soil nitrogen measured at grapevine full bloom in the 0–300-millimetre soil layer in cover-crop treatments compared to a control in the Olifants River valley. Adapted from Fourie et al (2007). Similar patterns were seen when pink serradella and grazing vetch were sown every two years, and chemical weed control started at the end of November, as well as when grazing vetch was sown annually and controlled mechanically.

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