Evaluation of management options for increasing the productivity of tropical savanna pastures. 2. Legume species

Abstract

The effect of legume species, used for augmentation of native perennial grasses, upon forage production and quality and animal production was studied over 4 vears in the semi-arid troPics of northwestern Australia. The legumes were Stylosanthes humilis cv. Paterson (Townsville stylo), S. hamata cv. Verano (Caribbean stylo) and a mixture of perennial species S. scabra cvv. Fitzroy and Seca and S. viscosa (perennial stylo). They were compared at 2 levels of fertility, unfertilised (UF) and with small inputs of superphosphate (F); and at stocking rates of 0.45,0.6 and 0.75 steers/ha for UF and 0.6, 0.8 and 1.0 steers/ha for F. By 1980 only half of the 3 x 12 treatments persisted, 3 Townsville stylo, 9 Caribbean stylo and 6 perennial stylo. Without fertiliser the perennial stylos had the highest wet season yields of 1-2 t/ha which constituted 4040% of pasture yield, compared with 2-20% for the other legumes. Caribbean stylo yields were highest with fertiliser, yielding 2-4 t/ha and 50-90% of the pasture at the end of the wet season, compared with 60-70% for perennial stylo and 5-30% for Townsville stylo. Anthracnose devastated Townsville stylo, and also reduced the productivity of Fitzroy. The perennial stylos had the highest concentrations of nitrogen (N), phosphorus (P), and sulfur (S) during the dry season while Caribbean stylo and its associated grasses had the lowest P and S concentrations during the wet season. When annual liveweight gains for each legume were compared at the same stocking rate-fertiliser level, differences were less than 15 kg, but there were considerable differences in the patterns of growth within the year; these differences were related to the seasonal availability and relative palatability of grass and legume. The overall mediocre animal growth of 30-110 kg/steer.year was attributed to the inadequate supply of nutrients for most of the year, with the possible exception of N.