Abstract 171

Adjei,-MB; Mislevy,-P; West,-RL

Agric. Res. and Education Cent., Univ. Florida, Ona, FL 33865, USA.

Tropical-Grasslands. 1988, 22: 2, 50-56; 30 ref.

Yearling steers (240 kg initial liveweight) were rotationally grazed (2 weeks of grazing, 4 weeks rest) at stocking rates (SR) of 7.5 (low), 10 (medium) and 15 (high) animals/ha, on pastures consisting of Cynodon aethiopicus cv. UF-5 and McCaleb and C. nlemfuensis var. nlemfuensis cv. Ona and at the medium SR only on Digitaria decumbens cv. Transvala and Paspalum notatum cv. Pensacola. Grazing commenced in early June 1976 and 1977 and continued for 168 days each year at Ona, Florida on the sandy siliceous hypermethic family of aeric Haploquods. Total non-structural carbohydrate (TNC) concn was monitored weekly during summer and autumn in 3 stubble regions; roots/crown (5 cm root + 2.5 cm crown), lower stubble (2.5-10 cm) and upper stubble (above 10 cm). The TNC in Cynodon spp. was 5.0, 3.5 and 3.2% of DM for roots/crown, lower and upper stubble regions, resp. P. notatum roots/crown had 12.2% TNC compared with 3.6% in other regions. TNC concn 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 Cynodon spp. was linearly reduced by increased SR. It was suggested that grazing management of the tropical grasses be varied in order to maintain a long-term productive stand. D. decumbens should not be grazed below a stubble height of 17 cm to conserve stored TNC whereas P. notatum could withstand close grazing. Medium to heavy grazing pressure could be imposed on Cynodon spp. during summer but a more lenient pressure could be desirable in autumn.