Effect of Seeding Date on the Performance of Grasses and Broadleaf Species Evaluated for Cover Crop Management in the Breede River Valley Wine Grape Region of South Africa

Abstract

A selection of species suitable for cover crop management in the different wine grape regions is required to enable more producers to apply this environment friendly practice in a sustainable manner as part of an integrated production strategy. The effect of seeding date on the dry matter production (DMP) and weed control efficacy of seven grasses and sixteen N-fixing broadleaf species, as well as varieties of three of these species, was determined. The decomposition rate of the mulches was measured to determine the mulch persistence of the different species. In the cooler climate of Stellenbosch (Coastal region) the Medicago species, subterranean clovers, pink Seradella (Omithopus sativa L. v. Emena) and three Vicia species did not compete effectively with the winter weeds if the weekly precipitation from mid-March to mid-May (autumn) exceeded 18 mm. The two oats varieties, as well as rye (Secale cereale L.) and triticale (Triticale v. Usgen 18), however, produced more than the five tons of dry matter deemed necessary for effective cover crop management if the precipitation exceeded 18 mm per week. The DMP of all the above-mentioned species was consistent between years at the warmer and arid Lutzville (Olifants River Valley) and indicated that these species could be considered for cover crop management in this region as well, if full surface irrigation of 18 mm per week could be applied for the first 10 weeks after sowing, followed by a fortnightly irrigation of 18 mm. Seeding date had a significant effect on DMP in the Stellenbosch region and showed similar trends in Lutzville. The study showed a highly significant correlation (r = 0.85, P < 0.0001) between the decomposition rate of the mulches and the initial amount of dry matter present on the soil surface.