COVER CROPS in South African Vineyards

CHAPTER 4 COVER-CROP ESTABLISHMENT

subterranean clover. Dry-matter production of plants that were resown annually was compared to that of plants that were allowed to seed themselves. Where plants were resown annually, full-surface chemical weed control was applied from the first week of September, before grapevine bud-break, to the end of March.Where plants were allowed to complete their life cycles and produce seed, full-surface chemical control was only started at the end of November. The results of the trial are summarised in Figure 4.1. Overberg oats and black oats re-established in 1995, but dry-matter production was only 22% and 13%, respectively, of that obtained from the same grasses sown annually. In 1997, none of the grasses re-established.

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1995 Sown annually 1995 Self-sown 1997 Sown annually 1997 Self-sown 1999 Sown annually 1999 Self-sown

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0,00 Rye Overberg oats Black oats Grazing vetch Faba bean Paraggio Kelson Woogenellup bur medic snail subterranean medic clover Dry matter production in tonnes per hectare FIGURE 4.1. Dry-matter production of cover crops sown annually compared to re- establishment from self-sown seed in the Coastal region. Adapted from Fourie et al (2006). Paraggio bur medic was the only legume that showed the potential to re- establish in 1995. However, it did not re-establish in 1997 or 1999. The ability of both faba bean and Kelson snail medic to re-establish improved over the three seasons, but dry-matter production of neither legume ever reached a third of that of the annually sown treatments. Self- sown grazing vetch likewise performed poorly. Against expectation, Woogenellup subterranean clover could not re- establish itself successfully. This was attributed to the soil surface being too hard for this plant to penetrate and to submerge its seedpods in the soil.

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