Winter survival, biomass accumulation and N mineralization of winter annual and biennial legumes sown at various times of year in Northern Temperate Regions

Weed suppression and green manure effects are two potential benefits of including a legume cover crop in vegetable cropping systems. A requirement for using autumn established cover crops, however, is to find species and cultivars adapted to the local climate and latitude. Knowledge about optimal sowing time is also needed. The objective of this study was to monitor the crop behavior, with special emphasis on winter survival and biomass production, of winter annual and biennial legumes sown at various times of year before the establishment of vegetables in the subsequent year. Low growing species/cultivars, including annual medics (Medicago spp.) and subterranean clover (T. subterraneum L. cv. Denmark), which may be suitable when vegetables transplanted directly into a senesced living mulch, showed poor winter survival and are thus not recommended for our climate. Taller species, including hairy vetch (Vicia villosa Roth.), crimson clover (T. incarnatum L.) and yellow sweetclover [Melilotus officinalis (L.)], which require mowing before the establishing of vegetables, showed much better winter survival and biomass production the subsequent year. The study showed however, that the suitability of these cover crops depends on cultivar, sowing time and climate region. The mineralization study showed that hairy vetch and white clover were rich in N and showed a high N mineralization rate. Mineralization of N from crimson clover and yellow sweetclover was lower. We conclude that hairy vetch, crimson clover and yellow sweetclover, used in the proper way, have potential as cover crops under northern conditions.