Annual medics (Medicago spp.) in irrigated corn for fall pasture in Eastern Wyoming.

Craig Alford, James Krall, and Stephen Miller
University of Wyoming, Laramie, WY 82071.

Farmers in the Great Plains have shown an interest in inter-cropping corn Zea mays with annual legumes. Advantages of farming systems which contain an annual legume include reduced soil erosion, improved soil fertility and improved aftermath forage quality. The objective was to first identify the most appropriate pasture legume species and then derive the most appropriate management system (seeding rates or seeding dates) for effective inter cropping in irrigated corn. To accomplish this experiments were conducted in 1996 at three sites (Huntley, WY; Lingle, WY; and Torrington, WY). Two of the sites were under sprinkler irrigation, the other was under furrow irrigation. Plots were 3.05 by 6.10 m with four replications in a RCB, split plot design. Eight legume species were evaluated in corn under both a weed free and weedy situation. In addition, there was a weed and medic free check and a weedy, medic-free check. Corn yields were reduced by the presence of medics in some treatments, others were comparable to the check yields. Medicago lupulina reduced corn yields by 4%, whereas Medicago truncatula reduced corn yields by 17%. Corn yields were reduced approximately 62% by the presence of weeds regardless of medic species. The medics did not significantly suppress weed growth. In 1997 two management systems studies were conducted at Torrington, WY, under sprinkler irrigation. Plots were 3.05 by 6.10 m with four replications. Main plots were medic seeding dates (2 weeks before, at, and 2 weeks after corn planting) and subplots a factorial arrangement of medic species (Medicago lupulina and Medicago sphacrocarpus), medic seeding rate (86, 172 and 344 PLS/m²) and herbicide input level (low - imazethpyr + pendimethalin and high - imazethpyr + pendimethalin + bentazon). Corn silage yields were not influenced by any treatment. There were, however, significant differences between medic species, medic seeding rate, and herbicide input level on grain yield. Corn grown with Medicago lupulina yielded 6% more than Medicago sphacrocarpus. Corn yields were 16% and 13% higher when the medics were seeded with or two weeks after corn than when seeded two weeks before corn. The high herbicide input level increased grain yield 9% compared to the low input level. Corn yields were maintained while providing 2 t/ha of dry matter medic forage to the corn residue pasture resource. Medicago lupulina has been successfully established (92 plants/m²) with corn in large plots for pasture trials this fall.

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