Grazing Frequency Effects On Bahiagrass Cultivars Fertilized with Low N Levels.

Warm-season grasses require N fertilization to achieve their full production potential; however, increased N fertilizer costs have limited the use of fertilizer by beef cattle producers. The objective of this study was to test the effects of two grazing frequencies (2 and 4 wk) on production and nutritive value of ‘Argentine’, ‘Pensacola’, ‘Tifton 9’, and ‘UF-Riata’ bahiagrass (Paspalum notatum Flugge) cultivars fertilized with 60 kg N ha^-1 in the spring. The study was conducted in Ona, FL from May to October 2010. Treatments were the eight factorial combinations of grazing frequency and cultivar arranged in a randomized complete block design with three replicates. Plots (4 x 7 m) were mob grazed by beef cows (505 ± 30 kg) for approximately 8 h to a 7.5-cm stubble height. An area of 0.93 m^-2 was harvested before each grazing event to determine herbage accumulation (HA) and nutritive value. Light interception was measured using the Sunscan^® (Delta-T Devices, Cambridge, UK). Tiller density was determined at the end of the grazing season. There was cultivar x month interaction (P < 0.001) for HA, height, and light interception. UF-Riata and Tifton 9 had greater HA, height, and light interception than Argentine and Pensacola in May, however, no differences were observed in the remaining months of the experimental period. Crude protein (CP) and in vitro digestible organic matter (IVDOM) concentrations were similar among cultivars. Plots grazed at a 4-wk interval had greater (P < 0.001) HA (1.4 vs. 0.9 Mg ha^-1), light interception (83 vs. 57%), and height (23 vs. 14 cm) but lesser CP (100 vs. 130 g kg^-1) and IVDOM (510 vs. 540 g kg^-1). Plots grazed every 2 wk had lesser tiller density than the 4-wk interval (850 vs. 1100 tillers m^-2). Bahiagrass cultivars receiving low N fertilization levels increase herbage accumulation but decrease nutritive value with longer regrowth periods.