COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

Dry-matter production was compared to cover crops that were resown annually, and where full-surface weed control was applied before grapevine bud-break or after véraison. In these trials, no grasses were able to re-establish. Only legumes were able to re-establish, and their success varied between regions and soils. Even when legumes did self-sow, annual sowing was usually still required to maintain dry-matter production, although at a lower seeding density. Managing cover crops for re-establishment carries the risk of reduced grapevine production. This aspect is discussed in more detail in Effect of Cover Crops on Grapevine Nutrition and Performance in Chapter 8 (p140). The use of different implements for seedbed preparation, seed covering, and planting can also impact the performance of cover crops. Trials in the Coastal region found that cover crops with small seeds, like Paraggio bur medic, and cover crops with medium-sized, round seeds, like grazing vetch, should preferably be established using a rotary harrow. A cultivator, also commonly known as a ghrop, should not be used to cover the seeds of grasses after sowing. The incorporation of plant residues from the soil surface with a rotary harrow (not a rotavator) four to six weeks before sowing improves the dry- matter production of cover crops with small seeds (such as Paraggio bur medic) and with medium-sized, elongated seeds (such as rye). Lastly, trials comparing different fertiliser regimes showed that application of nitrogen, phosphorus, and potassium just after sowing, followed by nitrogen at the 2–4-leaf stage, improved dry-matter production of black oats in sandy soils. Re-establishment of cover crops Coastal region This trial was conducted at the ARC Infruitec-Nietvoorbij research farm in Stellenbosch in the Western Cape over a period of six years. The goal was to assess the effect of different management practices on the ability of cover crops to re-establish. Eight cover crops were evaluated: rye, Overberg oats, black oats, grazing vetch, faba bean, Paraggio bur medic, Kelson snail medic andWoogenellup

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