Nitrogen Fertilization and Supplementation Effects on Performance of Beef Heifers Grazing Limpograss

Seasonally low N concentrations in ‘Floralta’ limpograss [ Hemarthria altissima (Poir.) Stapf & C.E. Hubb.] limit intake and weight gain of growing animals. 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 series) or ultic (Pomona series) Haplaquods. During 1992 and 1993, a factorial arrangement 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 plus rumen undegradable protein [CUUP]) were studied in two replications of a completely randomized design. Supplementation with CU increased average daily 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 to 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 pastures received 50 kg N ha −1 , suggesting that low CP was limiting ADG. These data indicate that N deficiencies of cattle grazing limpograss can be overcome by increasing rate of pasture N fertilization or by providing N supplements.