COVER CROPS in South African Vineyards

CHAPTER 7 EFFECT OF COVER CROPS ON SOIL CARBON AND MINERALS

Figure 7.3 shows the soil nitrogen levels at grapevine véraison. In the third season, soil nitrogen levels were higher in most of the annual cover-crop treatments than in the control, and all were higher than in the dwarf-fescue treatment. It is interesting to note the changes in soil nitrogen levels between full bloom and véraison, with the highest levels at véraison in the third season seen in the treatment where grazing vetch was rotated with triticale every two years. However, the treatment with grazing vetch sown every two years still had the highest soil nitrogen levels in the tenth season, and nitrogen levels did not drop between full bloom and véraison in this treatment as it did in the other annual cover-crop treatments. st mber otation ion August Novemb r

30,00

25,00

Triticale weed control August Triticale weed control November Rye|faba bean mix Triticale|vetch two-yearly rotation Triticale|vetch annual rotation Grazing vetch weed control August Grazing vetch weed control November Perennial dwarf fescue No cover crop

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15,00

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Nitrogen in milligram per kilogram soil

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1995/1996 Third season

2002/2003 Tenth season

FIGURE 7.3. Soil nitrogen measured at grapevine véraison in the 0–600-millimetre soil layer in cover-crop treatments compared to a control in the Breede River valley. Adapted from Fourie (2012).

Figure 7.4 shows the soil nitrogen levels after harvest.As seen for full bloom and véraison, soil nitrogen levels in the third season were higher in most of the annual cover-crop treatments than in the control, and all were higher than in the dwarf-fescue treatment. For triticale, nitrogen levels were higher in the treatment where it was sown every second year, than where it was sown annually.

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