Integration of Cool-Season Annual Legumes and Dairy Manure Compost with Switchgrass

Annual cool-season legumes can contribute forage or green manure to warm-season grass pastures or biofuel crops but may interfere with subsequent grass development. Arrowleaf clover (Trifolium vesiculosum Savi cv. Yuchi), common vetch (Vicia sativa L.), and button medic [Medicago orbicularis (L.) Bartal cv. Estes] were oversown on 10-yr-old switchgrass (Panicum virgatum L.) in north-central Texas to evaluate dry matter (DM) yield and nutritive value. Legumes were no-till drilled into a Windthorst fine sandy loam in autumn of 2000 and 2001; plots either received no dairy manure compost or 30 Mg compost ha-1. Forage was harvested when individual legume species reached flowering, when switchgrass regrowth reached boot stage, and at the end of the summer growing season. Switchgrass DM yields (3022-6630 kg ha-1 yr-1) were not reduced by overseeded legumes. Arrowleaf clover had the greatest production among the legume species and yielded more in a monoculture (1762-1923 kg ha-1 yr-1) than with switchgrass (757-814 kg). Cumulative yields increased the second year as a result of legumes, compost, and combinations of the two. Compost increased phosphorus concentrations in both the grass and legumes, but not crude protein or acid detergent fiber concentrations. Cool-season annual legumes may be beneficial in switchgrass forage and biofuel systems, especially in combination with manure compost.