Fertilizer Management Effects On Forage And Seed Yield Of Tropical Grasses In The U.S Virgin Islands

Guineagrass (Panicum maximum Jacq.), an important tropical forage in the eastern Caribbean Islands is established from seed. Low seed availability due to seed shattering losses and low germination percentages limits pasture development in the U.S. Virgin Islands. Recent introduction of Atra paspalum cv. Suerte (Paspalum atratum Swallen) exhibited potential as stand-over forage, but more information is needed on dry matter yield (DMY) and seed yield. A field experiment was conducted on a mildly alkaline Fredensborg clay (fine carbonatic, isohyperthermic, Typic Rendols, Mollisols) in 2000 to determine the effect of three N rates (0, 56, and 112 kg ha'1) on DMY and seed yield of guineagrass, Bluegrass, and Suerte. Ammonium sulfate as N source was broadcast applied on cut grass stands (15-cm stubble height) on 15th August 2000 and harvested in November 2000(12 wk). Guineagrass and Suerte differed in DMY (P<0.05). There was also an N linear (P<0.05) effect on DMY for guineagrass, but not for Suerte. Guineagrass DMY averaged 6.5, 8.3, and 9.4 Mg ha"1 for the 0, 56, and 112 kg ha"1 of N, respectively. Suerte averaged 2.56 Mg ha"1. Seed yield of guineagrass compared to Suerte was not different (P>0.05). Seed yield of guineagrass was 242 kg ha"1 and Suerte was 278 kg ha'. There was a trend for seed increase with increasing N rates for guineagrass (P=0.10) and a quadratic response (P<0.05) for Suerte. Results of the study indicate a strong response of guineagrass to N applications. During seed maturity, strong easterly winds may have affected yields of both grasses. Multiple harvests may be needed for these grasses to get a better estimate of seed yield and quality.