COVER CROPPING SYSTEMS FOR BRASSICAS IN THE NORTHEASTERN UNITED-STATES .1. COVER CROP AND VEGETABLE YIELDS, NUTRIENTS AND SOIL-CONDITIONS

Vegetable growers in the northeastern United States commonly use cereal rye as a winter cover crop, but rye does not fix nitrogen (N) and ties up N after it is incorporated into the soil. In this study, yield effects on broccoli and cabbage by cover crops of hairy vetch, grown alone or in combination with rye, were compared to rye alone and a no-cover control at four locations in New England. Effects of applied N were evaluated at two sites. Cover crops were grown until flowering and were either soil incorporated or mowed and left on the surface. Brassica seedlings were transplanted into the plots, grown to maturity and assessed for yield, yield components and foliar nutrients. Soil temperature was measured at two sites, and soil moisture and inorganic N at one site. Cover crops of vetch and vetch + rye consistently produced higher broccoli and cabbage yields than rye alone or no cover. Foliar N concentrations indicated that N contribution was a major factor in the yield response, although cover crops sometimes affected concentrations of other nutrients. Rye alone reduced yields, probably through N tie-up. At one location, broccoli yield responded dramatically to applied N (112 kg ha-1 as NH4NO3) regardless of cover crop or management system. No-till cover crop management without herbicides was implemented successfully at two locations by mowing rye and vetch at flowering, and leaving them as a mulch. Cover crop regrowth was negligible at one site, whereas moderate vetch regrowth occurred at the other. No-till severely reduced brassica yields on silt-loam soils at two farms under otherwise conventional management, but did not hurt yields on a sandy loam at a third, organically managed site. At die latter site, soil incorporation of vetch or vetch + rye raised soil nitrate-N levels to 150 kg ha-1, which apparently exceeded crop needs. The mulch also significantly lowered soil temperature and conserved soil moisture. The effects of soil texture, organic matter and biological activity levels on transfer of N from no-till managed cover crops to the following crop should be explored further.