Craig C. Sheaffer
University of Minnesota, St. Paul, MN 55108
Annual medics (Medicago spp.) have been evaluated for a variety of uses in Midwest cropping systems. They are a good source of quality forage and N. Zhu et al. (1996) reported that some Australian medics produced 5.5 Mg/ha in a single harvest of forage when spring seeded and used as a short-season crop for harvest in fall or summer. Most annual medics had equal or higher crude protein and lower fiber concentrations than alfalfa. Shrestha et al. (1998) also reported that spring-seeded medic yielded 5.0 Mg/ha when harvested twice. Moynihan et al. (1996) evaluated medics as intercrops with spring barley (Hordeum vulgare L.) to provide ground cover and N for subsequent crops. Medics reduced fall weed biomass by 65% and contributed from 66 to 140 kg/ha of N in the fall, but also sometimes reduced barley yields. As an alternative to intercropping with a spring seeded small grain, Fisk et al. (1998, unpublished) no-tilled annual medics into wheat stubble following harvest and reported that accumulated above-ground N production ranged from 44 to 194 kg/ha of which 19 to 62% was from N2 fixation. Zhu et al. (1998) reported that spring seeded medic monocultures fixed from 100 to 200 kg/ha of N when harvested in August.
Medics have also been evaluated as intercrops with corn to suppress weeds, provide ground cover and add N. De Haan et al. (1997) seeded medics concurrently with corn and reduced weed dry weight production by 55% compared to a weedy control, but also reduced corn grain yield by 18%. Squire et al. (1998), showed that the effectiveness of annual medics as intercrops was increased when medics were seeded 28 days after corn planting. They found that the N fertilizer replacement value of annual medics for a subsequent corn crop was 36 kg/ha. Use of annual medics as intercrops with row crops is limited by unpredictable competition, inconsistency in favorable weather, and uncertain financial return.
References
1.De Haan, R.L., C.C. Sheaffer, and D.K. Barnes. 1987. Effect of annual
medic smother plants on weed control and yield in corn. Agron. J. 89:813
821.
2. Moynihan, J.M., S. R. Simmons, and C.C. Sheaffer. 1996. Intercropping
annual medics with conventional height and semidwarf barley grown for grain.
Agron. J. 88:823-828.
3. Shrestha, A., O.B. Hesterman, J.M. Squire, J.W. Fisk, and C.C. Sheaffer.
1998. Annual medics and berseem clover as emergency forages. Agron. J.
90:197-201.
4. Squire, J.M., J.J. Kells, O.B. Hesterman, and C.C. Sheaffer. 1998.
Annual medics for intercropping with corn to provide N and suppress weeds.
Agron. J. (In review)
5. Zhu, Y., C.C. Sheaffer, and D.K. Barnes. 1996. Forage yield and quality
of six annual Medicago species in the North-Central USA. 1996. Agron. J.
88:955-960.
6. Zhu, Y. C.C. Sheaffer, M.P. Russelle, and C. P. Vance. 1998. Dry matter
accumulation and dinitrogen fixation of annual Medicago species. Agron. J.
90:103-108.