Winter Cover Crop Growth and Weed Suppression on the Central Coast of California1

Abstract

Winter cover crops are increasingly common on organic and conventional vegetable farms on the central coast of California between periods of intensive vegetable production. A 2-yr study was conducted in Salinas, California, to quantify (1) cover crop and weed biomass production during cover cropping, (2) early-season canopy development of cover crops, (3) weed seed production by burning nettle during cover cropping, and (4) weed emergence following cover crop incorporation. The cover crops included oats, a mustard mix, and a legume/oats mix that were planted in October and soil-incorporated in February. Weed and cover crop densities, early-season cover crop canopy development, above-ground weed and cover crop biomass production, seed production by the burning nettle, and postincorporation weed emergence was evaluated. Mustard produced more early-season biomass than oats and the legume/oats mix. There were no differences in above ground biomass production by the cover crops at the end of their growth period. Suppression of weed biomass and seed production of burning nettle was greatest in mustard, and least in oats and the legume/oats mix. The weed suppressive ability of each cover crop was affected by early-season canopy development and was highly correlated with cover crop plant density. Weed emergence following cover crop incorporation was in order of legume/oats mix . oats . mustard in yr 1, but was not different in yr 2. This study provides initial information on cover crop effects on weed management in irrigated and tilled vegetable production systems in the central coast of California. The results suggest that the legume/oats mix could exacerbate weed problems in subsequent vegetable crops. Nomenclature: Burning nettle, Urtica urens L. # 3 URTUR; bell beans, Vicia faba L.; common vetch, Vicia sativa L.; lana vetch, Vicia villosa ssp. dasycarpa Roth; mustards, Brassica juncea (L.) Czern., Brassica hirta Moench; oats, Avena sativa L.; peas, Pisum sativum L. Additional index words: biomass production, canopy development, weed seed production, weed- suppressive ability. Abbreviations: DAI, days after incorporation; DAP, days after planting.