sufficiently to survive the winter. Cover crop residue can modify the conditions under which weeds germinate Cover crops often reduce density and biomass of annual weeds in or regrow in the spring. Such effects could be due to no-till cropping systems. However, cover crops that over-winter also changes in soil temperature, increase in soil moisture, have the potential to reduce crop yield. Currently, there is an interest in annual medics (Medicago spp.) and other annual legumes that release of allelopathic chemicals, and physical impediwinter-kill for use as cover crops in midwestern grain cropping systems. ments to weed seedlings (Facelli and Pickett, 1991; Teas-A 2-yr study was conducted at East Lansing and the Kellogg Biological dale, 1996; Teasdale and Mohler, 1993). Station, Michigan, to investigate the influence of annual legume cover Many legume species that are used as cover crops in crops on weed populations. Two annual medic species [burr medic (M. no-till corn production are winter annuals or short-lived polymorpha cv. Santiago) and barrel medic (M. truncatula Gaertn. cv. perennials. In northern regions of the USA, over-win-Mogul)], berseem clover (Trifolium alexandrinum L. cv. Bigbee), tering species are normally established in the summer and medium red clover (Trifolium pratense L.) were no-till seeded or fall and accumulate most of their biomass when they as cover crops into winter wheat (Triticum aestivum L.) stubble in

Severe winter‐kill of alfalfa (Medicago sativa L.) in some years prompts the need for emergency forages in northern locations. Three annual medic species—barrel medic (M. truncatula Gaertn. cv. Mogul), burr medic (M. polymorpha L. cv. Santiago), and snail medic [M. scutellata (L.) Mill. cv. Sava]—and berseem clover (Trifolium alexandrinum L. cv. Bigbee) and ‘Nitro’ alfalfa were seeded in early spring at East Lansing and the Kellogg Biological Station (KBS) in Michigan in 1994 and 1995. Forage mass was measured at first harvest 60 d after planting and at second harvest 30 d later. Forage mass of annual medics at first harvest ranged from 0.8 to 3.6 Mg ha−1 across locations and years. Berseem clover produced an average forage mass of 2.2 Mg ha−1 at first harvest, which was similar to alfalfa. Crude protein (CP) concentration of annual medics, berseem, and alfalfa ranged from 111 to 210,178 to 233, and 170 to 218 g kg−1, respectively, at first harvest. Regrowth of annual medics (except Mogul) was less than alfalfa or berseem clover; however, the regrowth of Mogul was decumbent and not suitable as hay. Average forage mass and CP concentration of berseem at second harvest was 1.8 Mg ha−1 and 191 g kg−1, respectively, which was similar to alfalfa. Our results indicate that both annual medics and berseem clover can be used as emergency forages in northern locations; however, annual medics have the potential for only one harvest, whereas berseem can be harvested twice during the growing season.

. 1999. Annual legumes as green manure and forage crops in winter canola (Brassica napus L.) rotations. Can. J. Plant Sci. 79: 19-25. Cropping systems that reduce chemical fertilizer N requirements in winter canola (Brassica napus L.) need further study. Studies were conducted in 1994/1995 and 1995/1996 at two locations in Michigan i) to quantify the N accumulated at plowdown by berseem clover (Trifolium alexandrinum L.), alfalfa (Medicago sativa L.) and three annual medic species (Medicago truncatula Gaertn., M. polymorpha L., and M. scutellata L.) when they were managed as green manure or managed as forage; ii) to compare N response of the winter canola crop following the legumes; and iii) to estimate the N fertilizer replacement value (FRV) of the legumes. The legumes were seeded in early May in both years. Winter canola was planted after legume plowdown 90 d after planting (DAP). Four N rates (0, 50, 100, and 150 kg N ha -1 ) were applied to the winter canola in early spring. Herbage N yield at plowdown was highest (103.9 kg N ha -1 ) in berseem clover managed as green manure and this treatment resulted in the highest winter canola yield in 1995, but treatment differences were not significant in 1996. A supplementary effect of some treatments on winter canola yield was observed in 1995. Fertilizer N had a similar effect on winter canola yield across all treatments, and resulted in a quadratic response in 1995 and a linear response in 1996. Winter canola grain yield following annual legumes managed as green manure or as forage were similar. Winter canola yield following berseem clover was higher than when following annual medics. No FRV of legumes on winter canola was observed.