Effect of Annual Medic Smother Plants on Weed Control and Yield in Corn
- Robert L. De Haan ,
- Craig C. Sheaffer and
- Donald K. Barnes
Using spring-seeded smother plants for weed control could reduce the environmental impact of corn (Zea mays L.) production. Research was conducted to determine whether currently available medic (Medicago spp.) cultivars are adapted for use as smother plants in corn. In field experiments in 1992 at Becker and Rosemount, MN, Medicago scutellata (L.) Mill. cv. Sava and Kelson were interseeded with corn at 0, 85, 260, or 775 seeds m−2. In 1993, Sava and Kelson, along with M. polymorpha L. cv. Santiago and M. lupulina L. cv. George, were interseeded with corn at 260 seeds m−2 and N fertilizer was applied at 0, 84 (56 at Rosemount), or 168 kg−1. Land equivalent ratios for corn and medic intercrops grown in 1992 were not > 1, indicating that corn and medics competed strongly for resources. Medics seeded with corn at a rate high enough to consistently suppress weeds (260 seeds m−2) reduced weed dry weight 14 wk after corn emergence by 69% at Becket and by 41% at Rosemount compared with monoculture corn. The same seeding rate reduced corn grain yield in weed-free plots by 21% at Becket and 15% at Rosemount compared with monoculture yields. In 1993, medic smother plants reduced weed dry weight more when grown in the 0 kg ha−1 N plots than in the 168 kg ha−1 N plots. Corn yield losses, however, were less severe in the 168 kg ha−1 N treatments than with 0 N. Annual medics managed as smother plants in corn effectively reduced weed biomass; however, additional research is needed to identify medic genotypes and smother plant management systems that reduce corn yields less than those we evaluated, and that provide more consistent weed suppression across environments..
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