Cover crop management in a Sauvignon blanc/Ramsey vineyard in the semiarid Olifants River Valley, South Africa. 1. Effect of management practices on selected grass and broadleaf species

Abstract

A 10-year trial was conducted on a sandy soil in a Sauvignon blanc/Ramsey vineyard in Lutzville, situated in the semiarid Olifants River Valley of the Western Cape. Twenty-three treatments were applied. Eight cover crop species that received the same amount of fertilizer were controlled chemically at the end of August or at the end of November. Two treatments were also applied in which Avena sativa cv. Saia (Saia oats) and Vicia dasycarpa [V. villosa] (grazing vetch) were controlled mechanically during bud break. In addition to these 18 treatments, two fertilizer application rates were applied to Saia oats and grazing vetch. A mechanically cultivated control in which no cover crop was sown was included in the trial. Secale cereale cv. Henog and Ornithopus sativus cv. Emena produced, on average, the highest amount of dry matter at the end of August (3.29 and 3.06 t/ha, respectively) after receiving on average 278 mm of water, of which 172 mm was supplied by means of a microsprinkler irrigation system. The average dry matter produced by Medicago truncatula cv. Paraggio and Saia oats at the end of August was not significantly lower than that of the first-mentioned two species. Under conditions of this experiment, it seemed that P and K at a concentration of 10 and 78 mg/kg, respectively, in the top 300 mm soil layer supplied the needs of grazing vetch. Saia oats performed poorly unless 30 kg P, 30 kg K and 42 kg N were applied during establishment and the early growing phase. All the species, except M. truncatula cv. Parabinga, produced additional fibre from September to the end of November following a dry winter (rain and irrigation totalling 201 mm), while none produced additional fibre if the water supply was luxurious up to the end of August (rain and irrigation totalling 364 mm). The cover crops did not produce enough seeds to reestablish successfully over a period of five years. It will, however, be possible to reduce the seeding density of grazing vetch (40% after two seasons) and the two M. truncatula varieties (20% after five seasons) if the species were left to ripen their seeds.