Comparison of 32 Cover Crops in an Organic Vineyard on the North Coast of California

Abstract

ABSTRACT In a replicated study conducted from 1990 to 1992, cover crops and a control (resident vegetation) were evaluated in an organic wine-grape vineyard (cv. ‘Chardonnay’), located at a valley floor site in Hopland, Mendocino County, California. The purpose was to assess plant phenology, stature, biomass production, competitiveness with resident vegetation, and second-year stand regeneration or persistence in an unfilled vineyard. Legumes (Fabaceae) evaluated included nine annual and two perennial types of clover (Trifolium spp.), bell bean and three other types of Vicia, two types of coolseason annual medic (Medicago spp.), field pea (Pisum sativum ssp. arvense), a mixture of biennial sweetclovers (Melilotus alba and M. officinalis), broadleaf birdsfoot trefoil (Lotus comiculatus). There were six types of cool-season annual grasses (Poaceae) including three cereal grains. Native Californian perennial grasses included one rhizomatous and five bunch types. The sole representative of Brassicaceae was black mustard (Brassica nigra). Unseeded, resident vegetation plots served as a control. In the first year after seeding, all cover crops except purple needlegrass (Nassella pulchra) established stands. Observations of phenological state suggested particularly advanced seed maturity by early May for the annual grasses barley, rattail fescue, soft chess, and cereal rye, as well as for burr medic and ‘Dalkeith’ subterranean clover. By contrast, ‘Austrian Winter’ field pea, berseem clover, biennial sweetclovers, and perennial legumes had not begun flowering. Other entries were at various stages of flowering. Height was generally greatest for black mustard followed by annual grasses, perennial grasses, vetches, field pea, and was similar for annual clovers and medics. Eighteen cover-crop regimes produced vegetational cover in excess of 90%. Particularly great percentages of vegetational cover were obtained for control (resident vegetation), common vetch (Vicia sativa), annual ryegrass (Lolium multiflorum), oat (Avena sativa), and berseem clover (Trifolium alexandrinum). Particularly small percentages of vegetational cover by cover crops occurred (in increasing order) for creeping red fescue (Festuca rubra cv. ‘Molate’), broadleaf birdsfoot trefoil, and biennial sweetclovers. Particularly great biomass estimates were obtained (in decreasing order) for barley (Hordeum vulgare), oat, black mustard, purple vetch (Vicia beghalensis), rye, ‘Koala’ subterranean clover (Trifolium subterraneum ssp. brachycalycinum) soft chess (Bromus hordeacens), woollypod vetch (Vicia villosa ssp. dasycarpa), and common vetch (Vicia sativa). Especially low biomass production was observed (in increasing order) for creeping red fescue (Festuca rubra), biennial sweetclovers, strawberry clover, meadow barley, and the mix of ladino and strawberry clovers. Biomass for resident vegetation in the control plots was significantly greater than biomass produced by creeping red fescue. In the second May following seeding, cover crop stands were inspected visually and regeneration scored qualitatively and subjectively as none, very poor, poor, fair, good, and very good. Percentage of vegetational cover by crops was also assessed visually. Stands scored as having good or very good regeneration were assessed for biomass as in 1991. The following entries attained good or very good regeneration: soft chess, California brome, annual ryegrass, both forms of blue wildrye, oat, cereal rye, crimson clover, four varieties of subterranean clover, and both the mixture of ladino and strawberry clovers and the sole seeding of strawberry clover. Particularly great biomass values were obtained for crimson clover and for ‘Mt. Barker’ and ‘Trikkala’ subterranean clovers. None of the three vetches attained high percentages of cover in the second year; these are thought to benefit from tillage, which was not used in this study. Biomass readings were, for the most part, lower than in 1991. This may have been due to low soil moisture during autumn as a result of a lack of irrigation and rain.