Nitrogen and Carbon Yield of Annual Warm-Season Legumes.

Annual warm-season legumes provide grazing and browse for livestock and wildlife, soil stabilization, and bioenergy production.  Legumes used for these purposes require no inorganic nitrogen fertilizer input because of their symbiotic relationship with rhizobia.  There is a wide variety of warm-season annual legumes and it is important to understand their adaptation to various environmental and soil environments.  This completely randomized block design experiment evaluated 15 annual warm-season legumes in two environments (Beeville and Stephenville, TX) in two years for their herbage mass, and carbon and nitrogen yields.  Subplots were tests of harvest frequency.  A portion of the plot was harvested at the end of the growing season or every 30 days.  Plots were 6 × 6 m with a 2 m border around plots, the inner 0.25 m² was harvested to 10-cm stubble height and processed to determine herbage mass and for lab analyses.  At both locations, the greatest yielding legumes for both years were Kauffman croatalaria (Crotalaria juncea; 13,000 kg ha^-1) and Tropic Sun croatalaria (13,100 kg ha^-1) harvested at the end of the season.  Nitrogen and carbon concentrations did not differ, so the nitrogen and carbon yields were greatest for these croatalaria species.  Rio Verde and Tecomate lablab (Lablab pupureus), Iron and Clay and Red Ripper cowpeas (Vigna unguiculata) were also well adapted to both locations.  These annual warm-season legumes have potential to provide biomass for livestock and bioenergy in both south and northcentral Texas.