Biomass Accumulation and Forage Nutritive Value as Influenced by Grazing Frequency of Tropical Grass

Early evaluation of germplasm by grazing animals can facilitate more rapid and efficient selection of forages best adapted to grazing conditions. Mob-grazing allows the study of forage response to severe defoliation on a limited land area. Four grazing frequencies (GF) were tested on eight grass entries in a split-plot experiment. Whole plots consisted of GF (2, 4, 5, and 7 wk) and subplots were grass entries. Whole plots were arranged in three randomized complete blocks. Grass entries consisted of stargrass, Cynodon nlemfuensis Vanderyst var. nlemfuensis cv. Florona; Urochloa brizantha (Hochst. ex A. Rich.) R.D. Webster cv. Insurgente; Urochloa sp. cv. Abundance; U. dictyoneura (Fig. & De Not.) Veldkamp; U. humidicola (Rendle) Morrone and Zuloaga cv. Chetumal; Andropogon gayanus Kunth cv. Llanero and Tun Tun; and Paspalum notatum Flügge cv. Pensacola. Annual fertilization was 170-15-57 kg ha⁻¹ N-P-K plus 1.7 kg ha⁻¹ Cu, Zn, Mn, and Fe (sulfate form) and 0.17 kg ha' B and 3.4 kg ha⁻¹ S in a single application, with N split in June, August, and October. Crude protein (CP) and in vitro organic matter digestion (IVOMD) was determined for the July/August, October, and November periods. Dry biomass (DB) yield was pooled over all harvests and reported as total seasonal yield. Highest DB yield was produced by Florona, Insurgente, and Abundance at all GF. Average yield increased (4.5-11.0 Mg ha⁻¹) and nutritional value decreased (29% for CP and 13% for IVOMD) as GFwas delayed from 2 to 7 wk (avg. of July/August and November sampling periods). Florona stargrass generally had highest CP concentration, while Urochloaentries were generally highest in IVOMD. All Urochloa and Andropagan entries evaluated winter killed, following 1 yr of grazing due to an extreme low temperature of -7.3°C. These data indicated that the Urochloa spp. tested produced high DB yields with good nutritive value, however cold tolerance was insufficient for use in central Florida.