M.B. ADJEI, P. MISLEVY and R.L. WEST

University of Florida Agricultural Research and Education Center, Ona, Florida 33865 U.S.A.

Abstract

Yearling steers (240 kg initial liveweight) were rotationally grazed (2 wk grazing, 4 wk rest) at 3 stocking rates (SR) of 7.5 (low), 10 (medium) and 15 (high) head/ha, on 3 stargrasses: 'UF-5' and 'McCaleb' (Cynodon aethioplcus Clayton and Harlan) and 'Ona' Cynodon nlemfuensis Vanderyst var. nlemfuensis); and at the medium SR only on 'Transvala' digitgrass (Digitaria decembens Stent.) and 'Pensacola' bahiagrass (Paspalum notatum Flugge). Grazing commenced in early June 1976 and 1977 and continued for 168 days each year at the University of Florida Agricultural Research and Education Center, Ona, Florida on the sandy siliceous hypermethic family of aeric Haploquods. Total non-structural carbohydrate (TNC) concentration was monitored weekly during summer and autumn in 3 stubble regions; roots/crown (5 cm root + 2.5 cm crown), lower stubble (2.5 cm–10 cm) and upper stubble (> 10 cm).
The region of highest TNC concentration depended mostly on species. The TNC in stargrasses was 5.0, 3.5 and 3.2% of DM for roots/crown, lower, and upper stubble regions, respectively. Bahiagrass roots/crown had 12.2% TNC compared to 3.6% in other regions. Concentration of TNC in Transvala from root to 10 cm stubble averaged 6.2% and the upper stubble averaged 4.7%. The TNC in roots/crown and lower stubble of stargrasses was linearly reduced by increased SR. These data suggest the need for varied grazing management of the tropical grasses in order to maintain a long-term productive stand. Transvala digitgrass should not be grazed below a stubble height of 17 cm to conserve stored TNC whereas bahiagrass could withstand close grazing. Medium to heavy grazing pressure could be imposed on stargrasses during summer but a more lenient pressure may be desirable in the autumn.