COVER CROPS in South African Vineyards

CHAPTER 7 EFFECT OF COVER CROPS ON SOIL CARBON AND MINERALS

Where chemical control was started in August, soil nitrogen levels were higher in the fourth season in the faba-bean treatment, largely due to significantly higher nitrogen levels in the 150–300-millimetre soil levels. Where chemical control was started later, the highest soil nitrogen levels in the fourth season were measured in the Kelson snail-medic treatment.There appeared to be a tendency toward higher soil nitrogen levels when cover crops were controlled later. Together, these results suggest that the timing of cover-crop control affects the levels of nitrogen at grapevine full bloom and harvest. Control in mid- October results in more nitrogen being available after grapevine harvest. Control just before grapevine bud-break results in more nitrogen being available during grapevine full bloom. Similar, but more pronounced, results were found on sandy soils in the Olifants River valley.This indicated that producers could manipulate nitrogen availability through cover-crop management during the grapevine-growing season. Other minerals Soil samples were analysed for phosphates, potassium, and exchangeable cations during grapevine full bloom and after harvest in 1997, 1999, and 2003. No significant differences in the concentrations of phosphates and potassium were found between treatments. Significant differences were found in the levels of exchangeable cations, but no significant trends were observed. Soil phosphate levels were also measured over four years in trials conducted at Blaauwklippen. Phosphates were initially applied at 30 kilogram per hectare, but this resulted in soil phosphate levels exceeding the grapevine requirement of 25 milligram per kilogram, as can be seen in Figure 7.9. The high phosphate levels seen in 2011 motivated a reduction in application, to 15 kilogram per hectare, in 2012. No phosphate was applied in 2013.These results suggest that phosphates should be applied at 15 kilogram per hectare every second year in these soils. Reference list Fourie JC, Agenbag GA and Louw PJE. 2007. Cover crop management in a Chardonnay/99 Richter vineyard in the Coastal region, SouthAfrica. 3. Effect of different cover crops and cover crop management practices on organic

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