Agronomic comparison of six bermudagrasses from southern United States with five tropical grasses in central Puerto Rico

The dry matter yield (DMY), in vitro organic matter digestibility (IVOMD) a nd crude protein (CP) content of eleven grasses were studied during the yea rs 1992 to 1994 under mob grazing conditions. Offered and consumed dry fora ge do not differ significantly (P<0.05) among the highest yielding accessio ns Cynodon nlenfuensis PRPI 2341, Cynodon plectostachium PRPI 11487, and Cy nodon dactylon cv. Tifton 85. However, the commercial Cynodon nlenfuensis P RPI 2341 was consistently the highest yielding accession both years. Among the other grasses, Digitaria eriantha showed the lowest levels of refused d ry forage, thus presenting the best forage acceptability by grazing animals . Digitaria eriantha also showed the highest levels of IVOMD in both the sh ort and the long day seasons. It is concluded that none of the evaluated Cy nodon dactylon accessions from southern United Sates, nor the digitaria and brachiaria species adapted better than the commercial accession Cynodon nl enfuensis PRPI 2341. Warm-season perennial grasses are grown extensively in the southeastern United States. Among the grasses, one of the most widely grown is from the species Cynodon dactylon, commonly named bermudagrass (Ei chhorn, 1984). The choice of a bermudagrass cultivar for establishment of p astures is an important decision for cattlemen seeking high weighs gains of stocker steers throughout the wan grazing season of the southern United St ates (Greene et al., 1989). Selection of improved bermudagrass hybrids has dramatically increased forage yield over that of common bermudagrass. Impro ved forage quality has also resulted in improved performance of grazing ani mals fed harvested hybrid bermudagrass forage (Gates et al., 1989). Reports on average daily weight gains (ADG) of yearling steers grazing different b ermudagrass hybrids varied between 0.68 to 0.79 kg animal(-1) day(-1) durin g the summer season of southern Louisiana (Faw et al., 1986). Hill et al. ( 1993) in Tifton, GA, found yearling ADG of 0.67 and 0.65 kg animal(-1) day (-1) for the recant bermudagrass releases Tifton 85 and Tifton 78, respecti vely. Forage quality dry matter yield and grazing performance support the h ypothesis that Tifton 85 will likely become an important hay and grazing fo rage for the southern United States. In Fuel-to Rico, Cynodon nlenfuensis P RPI 2341 (stargrass) is at present the grass cultivar most frequently grown on dairy farms (Ramos-Santana and Randel, 1996). Yearly ADG of 0.59 kg ani mal(-1) day(-1) has been reported for young steers grazing stargrass in the humid tropical zone of Puerto Rico (Vicente-Chandler et al., 1983). At Ona , FL, lower ADG of 0.54 kg has also been obtained with stargrass (Mislevy, 1989). The objective of this paper is to compare the agronomic performance (dry matter yield and quality) of six of the most outstanding bermudagrass hybrids from the southern United States, with five tropical grasses from th e cynodon, brachiaria, and digitaria genera under the tropical conditions o f central Puerto Rico.