Forage Yield and Quality of Summer Grain Legumes and Forage Grasses in Cheju Island

Soybean [Glycine max (L.) Merr.), mungbean [Vigna radiata (L.) Wilcz.], cowpea [V. unguiculata (L.) Walp.], adzuki bean [V. angularis (Willd.) Ohwi & Ohashi], maize [Zea mays L.], sorghum [Sorghum bicolor (L.) Moench], sorghum $\times$ sudangrass [So bicolor intraspecific hybrid], and Japanese millet [Echinochloa crusgalli var. frumentacea (Link) W.F. Wight] were grown at two planting dates (18 June and 15 July) at Cheju in 1997 to select the best forage legumes adapted to Cheju Island for grass-legume forage rotation. Averaged across planting dates and cultivars, dry matter (DM), crude protein (CP), and total digestible nutrient (TDN) yields were 5,646, 1,056, and 3,637 kg/ha for soybean, 4,458, 676, and 2,661 kg/ha for mungbean, 3,289, 553, and 2,055 kg/ha for cowpea, 3,931, 674, and 2,489 kg/ha for adzuki bean, 12,695, 969, and 7,642 kg/ha for maize, 17,071, 1,260, and 8,857 kg/ha for sorghum, 16,355, 1,163, and 8,543 kg/ha for sorghum $\times$ sudangrass hybrid, and 8,288, 929, and 4,091 kg/ha for Japanese millet. Soybean was higher in CP, ether extract (EE), and TON content but was lower in nitrogen free extract content compared with the three other legumes. The legumes had much higher CP (13.7 to 21.9%), EE (2.42 to 6.23%), and TDN (58.7 to 69.9%) content but lower in crude fiber (CF) content (17.3 to 25.3%) than did the grasses tested except maize which had relatively lower CF content but higher TDN content. These results suggest that soybean could be the best forage legume for grass-legume forage rotation in the Cheju region.