COVER CROPS in South African Vineyards

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CHAPTER 3 COVER-CROP SELECTION

subterranean clover

6,00

5,00

Faba b ean Paraggio bur medic Kelson snail medic Grazing vetch Woogenellup subterranean clover Weeds

4,00

3,00

2,00

1,00

0,00 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Year Dry matter in tonnes per hectare FIGURE 3.18. Annual dry-matter production of legume cover crops in vineyard trials in the Coastal region. Adapted from Fourie et al (2006). Late sowing during May in the first season led to relatively poor dry-matter production. From the second year onward, earlier sowing in April resulted in improved dry-matter production, indicating that cover crops should be established before the second week of April in this region. The dry-matter production of the grasses, grazing vetch and Kelson snail medic declined slightly from the fifth season onward. The same trend was observed for Paraggio bur medic from the seventh season onward.Although the dry-matter production of Faba bean andWoogenellup subterranean clover varied from year to year, a similar trend was not seen. This suggests that grasses and some legumes should not be sown consecutively for more than four years on sandy loam soils. By comparison, dry-matter production of cover crops on sandy soils in the Olifants River valley did not decline over time. In general, rotation of grasses and legumes every two years is recommend- ed. Long-term consecutive planting of legumes can lead to excessive levels of soil nitrogen. Rotation will also help prevent the build-up of soil-borne diseases that may target a specific cover-crops. Evaluation of cover crops selected to suppress nematodes A third vineyard trial was conducted in the Coastal region, at Blaauwklippen, to evaluate five cover-crops for their ability to suppress nematodes. Four of the five species have biofumigation properties (Kruger et al 2013 and references therein).

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