Stylosanthes humilis cv. Lawson, S. hamatacv. Verano, S. guianensis cv. Endeavour and Macroptilium atropurpureum cv. Siratro were oversown into native grassland dominated by Arundinaria ciliata and grazed by cattle at 2·5, 3·5, 4·5, 5·5 and 6·5 animal units/ha per half-year during the wet season for 4 years.
Siratro was the most persistent of the legumes but its susceptibility to heavy grazing pressure limited its contribution at the higher stocking rates. At the start of grazing its mean yield was 1420 kg/ha representing 40 % of total pasture yield while at the end of 4 years in the lowest stocking rate treatment it comprised 18% of total yield at 460 kg/ha.
The long-term productivity of the three Stylosanthes species was poor and their percentage contribution to the pastures was either zero or very low by the end of 4 years. Yield of Verano, the most successful of the three, declined from 5000 kg/ha in 1977 to 20 kg/ha in 1980. The main factor contributing to the poor performance of these species was the strongly competitive nature of A. ciliata. Percentage composition, height and yield of this tall, rhizomatous grass increased with time independent of stocking rate, and the illuminance of the Verano canopy was reduced to 0·38–0·65 full sunlight. Cattle showed negative selection for bamboo grass and consumed leaf but not stem; leaf to stem ratio was negatively (and unusually) related to stocking rate.
Stocking rate effects were reduced by the intervening dry season resting periods and the over-riding influence of other factors such as the prevailing climatic conditions, disease occurrence and plant interference.