Annual legumes for forage systems in the United States gulf coast region
Forage-livestock systems in the U.S. Gulf Coast are based on perennial C4 grasses. System productivity often is predicated on significant inputs of N fertilizer, but rapidly escalating fertilizer prices raise questions about the sustainability of these systems and provide impetus for legume research. There are few successful forage legumes in the region, suggesting that alternative species merit evaluation. The objective of this study was to determine the productivity and nutritive value in North Florida of adapted legumes whose primary use is not forage. Species tested included soybean [Glycine max (L.) Merr.], cowpea [Vigna unguiculata (L.) Walp.], and pigeonpea [Cajanus cajan (L.) Millsp.]. Legumes were grown in field plots during 3 yr and sampled biweekly until the recommended maturity stage for harvest as forage. At the recommended maturity stages for harvest as forage, soybean, and pigeonpea had greater (P < 0.01) herbage mass than cowpea. Leaf-to-stem ratio decreased with maturity and was greater for cowpea than the other legumes from 10 through 14 weeks after planting (WAP). At the recommended maturity for harvest as forage, pigeonpea, soybean, and cowpea had crude protein (CP) concentrations of 121, 176, and 188 g kg–1, respectively; neutral detergent fiber (NDF) concentrations of 695, 423, and 447 g kg–1, respectively; and in vitro true dry matter (DM) digestibility (IVTD) of 351, 729, and 689 g kg–1, respectively. Of the three legumes studied, soybean and cowpea had the greatest potential to provide forage with the highest nutritive value for livestock in North Florida, but soybean provided greater N yield.