Comparison of Stylosanthes humilis with S. hamata and S. subsericea in the Queensland dry tropics: effects on pasture composition and cattle liveweight gain

Abstract

Two new accessions of perennial legumes, Stylosanthes hamata cv. Verano and S. subsericea, were compared under grazing with the annual S. humilis (Townsville stylo) at four sites in the dry tropics. One of the new accessions, S. subsericea, was largely eliminated from the comparison because of its susceptibility to anthracnose. Although Townsville stylo was well adapted at two of the sites where average rainfall exceeded 850 mm annually (Lansdown and Wrotham Park), the yield of Verano was significantly more after the establishment year. At these sites the original grasses were replaced by the annuals Diqitaria ciliaris and Brachiaria miliiformis. Where soil fertility was high (Lansdown), these grasses competed vigorously with the legumes; where soil fertility was low (Wrotham Park), the sward remained legume-dominant. The yield of Townsville stylo was low at the two sites where annual rainfall was less than 750 mm annually (Kangaroo Hills and Westwood). Verano produced very high yields at the warmer site (Kangaroo Hills) and became dominant in the third year; in subsequent years there was an increase in the improved grass Urochloa mosambicensis, which responded to the increase in soil fertility. At the cooler site (Westwood) the yield of Verano was poor. Cattle liveweight gains were similar on both the Townsville stylo and Verano pastures at Lansdown, and better on the Verano pasture only in one year at Wrotham Park. At Kangaroo Hills and Westwood, liveweight gains were significantly greater on the Verano pastures. The data suggested that differences in liveweight gain did not occur when the legume yield on both pastures exceeded 600 kg ha-1. This threshold was usually achieved at Lansdown and Wrotham Park, but rarely with Townsville stylo at Kangaroo Hills. Townsville stylo has until recently been the only legume suited to pasture improvement in the dry tropics. The results from this experiment show that the perennial legume Verano can now extend the range of legume-based pasture improvement in the dry tropics of northern Australia.