Establishment and Persistence of Legumes in Switchgrass (Panicum virgatum) Biomass and Forage/Biomass Production Systems.

Switchgrass is being used as a biofuel feedstock for ethanol production on marginal land, as well as crop land. Legumes may be interseeded into switchgrass to improve available N in the soil, reduce fertilizer costs, and enhance switchgrass yield and forage quality. The objective of this research is to develop legume management strategies for switchgrass production systems that are economically and ecologically sustainable for biomass and forage production. A total of seven cool and warm-season legumes were examined for four years at the research and education centers East Tennessee (Knoxville), Plateau (Crossville) and Milan. The cool-season legumes were alfalfa, Medicago sativa cv “Evermore”; red clover, Trifolium pretense cv “Cinnamon Plus”; crimson clover, Trifolium incarnatum; common vetch, Vicia sativa; and hairy vetch, Vicia villosa. The warm-season legumes included in the study were Illinois bundle flower, Desmanthus illinoensis; and partridge pea, Chamaechrista fasciculata. The legumes were interseeded into established switchgrass (cv. ‘Alamo’) and monitored for establishment, self-reseeding, and N contribution as determined by increases in yield. Nitrogen fixation rates of common and hairy vetch were determined. Nitrogen fixation rates of common vetch were similar to hairy vetch. Preliminary results indicate that alfalfa and Illinois bundle flower are not feasible for establishment in lowland types of switchgrass. Hairy and common vetch, crimson and red clover, and partridge pea look promising for establishment and self-reseeding in established stands of switchgrass.