(156) Improved Cover Crop Establishment and Growth Is Related to Planting Date in Organic Concord Grape Production

Abstract

Concord grape (Vitis labrusca L.) accounts for a majority of juice grapes produced in Washington State. Because synthetic nutrients are not permissible in USDA organically-certified production systems, legume cover crops are used to supply nitrogen (N) to the crop. In order to supply a sufficient amount of N, the cover crop must successfully establish and produce large quantities of biomass. This study evaluates how the planting date influences emergence and biomass production of hairy vetch (Vicia villosa subsp. villosa L.) and yellow sweet clover [Melilotus officinalis (L.) Lam.] when used as legume green manures. The research was conducted on a commercial vineyard and a research vineyard from 2003–05. Treatments for the study consisted of yellow sweet clover and hairy vetch planted in both the spring and fall. Plots receiving soluble N sources were planted with wheat (Triticum aestivum L.) or rye (Secale cereale L.). Because of the large relative seed sizes of rye, wheat, and hairy vetch compared to yellow sweet clover, these treatments established faster with good stands in 2004. In 2005, clover plots had high emergence and biomass production because of water management modifications. Biomass data from the commercial vineyard in May 2005 indicates that fall-planted vetch produced more biomass than spring-planted vetch. Fall-planted hairy vetch and yellow sweet clover in the research vineyard showed higher biomass production than spring- and fall-planted hairy vetch and yellow sweet clover. When hairy vetch and yellow sweet clover are planted in the fall, they generally have better seedling emergence and biomass production due to the heightened aggressiveness exhibited by competing weed species during late spring and summer.