COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

Long-term trials in the Coastal region, Breede River valley, and Olifants River valley showed that cover crops are effective at raising the carbon content of different soil types. For example, rye, black oats, pink serradella, and grazing vetch significantly increased organic carbon in the 0–300-millimetre layer of a sandy soil, whereas organic carbon declined over the long term where no cover crop was grown.

LONG-TERM TRIALS IN THE COASTAL REGION, BREEDE RIVER VALLEY, AND OLIFANTS RIVER VALLEY SHOWED THAT COVER CROPS ARE EFFECTIVE AT RAISING THE CARBON CONTENT OF DIFFERENT SOIL TYPES.

In addition to the direct benefits of soil carbon to grapevines, soil carbon also helps to store carbon that would otherwise be present as carbon dioxide in the atmosphere. By increasing the levels of soil carbon, growers can reduce greenhouse-gas levels and global warming. Cover crops were also associated with elevated soil nitrogen levels in these trials.Although significant differences in the concentration of phosphates and exchangeable cations occurred in some seasons, no trends were observed. The effect of cover crops on potassium levels varied by region, with excessive potassium seen in the Breede River valley when perennial dwarf fescue was grown. The existing guideline for phosphate fertilisation of cover crops, within the fertilisation guidelines for grapevines, is an annual application of 30 kilogram per hectare. However, research showed that this should be adapted to applications of 30 kilogram per hectare initially, followed by 15 kilogram per hectare every two years, to prevent phosphates from accumulating in the 0–150-millimetre soil level, eventually exceeding the norms for grapevines. The effect of soil type is more important than the region when it comes to soil carbon and minerals. Therefore, readers should consult the section which most closely matches their soil type, even if this is in a different region to their own. Breede River valley Trials in the Breede River valley were conducted at the ARC Infruitec-Niet- voorbij research farm near Robertson in theWestern Cape.

125