Nitrogen fertilization and supplementation effects on performance of beef heifers grazing limpograss

Seasonally low N concentrations in 'Floralta' limpograss [Hemarthria altiss ima (Poir,) Stapf & C.E. Hubb.] limit intake and weight gain of growing ani mals. This research evaluated management alternatives for increasing summer weight gains of beef replacement heifers (Bos spp.) on limpograss pastures in Florida, Soils were sandy, siliceous, hyperthermic, aeric (Smyrna serie s) or ultic (Pomona series) Haplaquods. During 1992 and 1993, a factorial a rrangement of two pasture N fertilization rates (50 and 150 kg ha(-1)) and three diet supplements (NONE, corn [Zea mays L.] plus urea [CU], and CU plu s rumen undegradable protein [CUUP]) were studied in two replications of a completely randomized design, Supplementation with CU increased average dai ly gain (ADG) from 0.06 (NONE) to 0.41 kg on pastures fertilized with 50 kg N ha(-1), but there was no ADG response to CU when N rate was 150 kg ha(-1 ). When no supplement was fed, increasing pasture N fertilization from 50 t o 150 kg ha(-1) increased ADG from 0.06 to 0.36 kg. Grass crude protein (CP ; 73 vs. 56 g kg(-1)) and in vitro organic matter digestion (IVOMD; 542 vs. 509 g kg(-1)) were greater at the higher N rate. Heifer plasma urea N (PUN ) concentration was low (4.2 mg dL(-1)) when no supplement was fed and past ures received 50 kg N ha(-1), suggesting that low CP was limiting ADG. Thes e data indicate that N deficiencies of cattle grazing limpograss can be ove rcome by increasing rate of pasture N fertilization or by providing N suppl ements.