Weed suppression by annual legume cover crops in no-tillage corn

Cover crops often reduce density and biomass of annual weeds in no till cro pping systems. However, cover crops that over-winter also have the potentia l to reduce crop yield. Currently, there is an interest in annual medics (M edicago spp.) and other annual legumes that winter-kill for use as cover cr ops in midwestern grain cropping systems. A 2 yr study was conducted at Eas t Lansing and the Kellogg Biological Station, Michigan, to investigate the influence of annual legume cover crops on weed populations. Two annual medi c species [burr medic (M. polymorpha cv. Santiago) and barrel medic (M. tru ncatula Gaertn.cv. Mogul)], berseem clover (Trifolium alexandrinum L. cv. B igbee), and medium red clover (Trifolium pratense L.) were no-till seeded a s cover crops into winter wheat (Triticum aestivum L.) stubble in a winter wheat/corn (Zea mays L.) rotation system. Density of winter annual weeds we re between 41 and 78% lower following most cover crops when compared with n o cover control in 2 out of 4 site years, while dry weight was between 26 a nd 80% lower in all 4 site years. Impact of cover crops on the density of s ummer annual weeds was infrequent; however, weed dry weights were reduced b y 70% in 1995 following burr medic and barrel medic. Dry weight of perennia l weeds before corn planting were 35 to 75% lower following annual legumes compared with the control, while weed density was not affected. This study indicated a potential for annual legumes to reduce weed density and growth in no till corn grain systems.