COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

Nitrogen in the grape juice was measured as total juice nitrogen.These values reflect uptake, but are not directly related to yeast assimilable nitrogen. Legume cover crops allowed a reduction in the amount of nitrogen applied during grapevine full bloom on sandy soils.The additional nitrogen supplied by the legumes can also help to complete the development of the permanent structure of young non-bearing grapevines. On the other hand, a legume should not be used every year on sandy loam soils, as it may lead to excessive vegetative growth. Rotating a legume with a grass yearly or two-yearly improved grapevine performance while preventing luxurious vegetative growth. Long-term use of a legume cover crop may also increase grape-juice nitrogen levels to problematic levels, so grape juice should be monitored in these situations. Permanent cover crops competed with grapevines for nitrogen.Therefore, permanent cover crops should be avoided in vineyards, especially during the first four seasons after establishment, even on the more fertile sandy clay loam soils. In general, the relationship between grapevine performance and cover- crop treatments was heavily influenced by the age of the vineyard and the region. Cover crops enabled increased production with reduced nitrogen inputs if controlled before or during bud-break. However, when annual cover crops were controlled as late as berry set, they competed with grapevines, especially in young vineyards. Growers should therefore base their decisions on the results of trials in the region that most closely matches their conditions. Breede River valley A trial in the Breede River valley was conducted at the ARC Infruitec- Nietvoorbij research farm near Robertson in the Western Cape. Different treatments using triticale, grazing vetch, rye, faba bean, and perennial dwarf fescue were compared to a control without a cover crop. Nitrogen was applied at 14 kilogram per hectare during the first week of March. Grass cover crops also received 14 kilogram per hectare at the two- to-four-leaf stages. The grapevines were in full production from 1996/97 onward. Shoot mass, grape yield, berry mass and volume, and leaf-petiole nitrogen were

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