LEGUME COVER CROPS AS A NITROGEN-SOURCE FOR CORN IN AN OAT CORN ROTATION

The use of legume cover crops as green manures is a means of reducing the amount of N fertilizer used in corn (Zea mays L.) production, but has not been adequately tested in the upper Midwest. A field study was conducted from 1989 to 1993 near Arlington, WI, to determine the value of legume cover crops in a 2-yr oat (Avena sativa L.)/legume-corn rotation. The objectives of this study were to identify the most productive legume species and planting method to be used with oat, to measure the effect on subsequent corn grain yield, and to evaluate the economic viability of oat/legume-corn rotations. Corn yields following the legumes were compared with those of corn following oat without a legume, using six rates of N fertilizer to estimate the fertilizer replacement value of the legumes. Maximum seeding year N yields (tops and roots) were produced by medium red clover (Trifolium pratense L.) companion seeded with oat, and hairy vetch (Vicia villosa Roth) seeded after oat harvest. Averaged over years, these two cover crop options yielded 118 lb N/acre in the seeding year. Mean corn grain yields (bushels per acre) following these two legumes were 163 for red clover and 167 for hairy vetch. Estimated fertilizer replacement values of these legumes ranged from 65 to 103 lb N/acre. Gross margins (2-yr rotation mean) of these oat/legume-corn rotations were $166/acre using red clover and $153/acre using hairy vetch and were similar to those obtained with an oat-corn and continuous corn rotation where corn was grown with 160 lb fertilizer N. These results indicate a great potential for reducing fertilizer N inputs in corn production by using legume cover crops, without economic penalty for producers who adopt the practice.