COVER CROPS in South African Vineyards

CHAPTER 10 PRACTICAL GUIDELINES

Olifants River valley Paraggio bur medic should preferably be sown in the last week of March, whereas rye, black oats, pink serradella, and grazing vetch produce the most fibre if sown during the second week of April. Dry-matter production of cover crops sown at different dates is shown inTable 10.4.

TABLE 10.4. Effect of sowing date on dry-matter production of different cover crops in the Olifants River valley as measured at the end of August. Adapted from Fourie et al (2001).

Dry-matter production in tonnes/hectare

Cover crop

Sown 25–31 March Sown 13–18 April

Sown 6–12 May

Rye Black oats Pink serradella Paraggio bur medic Grazing vetch

5.08 4.97 6.09 6.58 5.96

5.92 5.85 6.40 5.25 6.73

4.72 4.07 4.63 5.10 4.49

In this semi-arid region, the cover crops should receive 18 millimetres of water weekly for the first eight weeks after being sown. Thereafter, 18 millimetres of water should be applied every two weeks until grapevine bud- break. Fertilisation In vineyards where the ratio of grape yield to shoot mass is more than five, grass cover crops should receive 28 kilogram of nitrogen per hectare at the two- to four-leaf stages. Where the ratio of grape yield to shoot mass is between four and five, grass cover crops should receive 14 kilogram of nitrogen per hectare at the two- to six-leaf stages. If the ration of grape yield to shoot mass is less than four, no nitrogen should be applied. Control of cover crops In non-irrigated and drip-irrigated vineyards, post-emergence chemical control should be applied from just before grapevine bud-break. Where full-surface micro-sprinkler irrigation and a covered chemical sprayer are available, chemical control in the work-row can be postponed to the first

182