2013 ASHS Annual Conference

Cover crops release or scavenge nitrogen, and nitrogen availability may influence weed seed decay, weed seed germination, and weed growth. Dry edible beans are poor nitrogen fixers and incorporating a leguminous cover crop may improve nitrogen availability in dry beans. Field experiments were conducted in Michigan at two university research farms and numerous on-farm sites to determine the effect of cover crops on weed populations and yield of organic dry beans. There were four cover crop treatments at the university research farms: medium red clover, oilseed radish, rye, and no cover. The on-farm sites each had one cover crop treatment (clover, oilseed radish, or rye) and one no cover treatment. Weeds were managed uniformly by farmers at each site using various cultivation tools. Weed seeds were placed in mesh bags and buried immediately following incorporation of red clover and rye to determine the influence of cover crop amendments on weed seed decay. Weed density and biomass within the bean rows were sampled using three 0.12 m² quadrats (15 cm wide by 76 cm long) at both the V2 and R1 stages of bean development for all sites. Few differences in weed populations occurred at the on-farm sites.  At the university research farm sites, beans planted following medium red clover had higher weed densities and weed biomass than the other cover crop treatments in some site-years. Available soil nitrogen was greater following a frost-seeded red clover treatment; however, red clover did not increase dry bean yields.