The growth and development of Townsville lucerne (Stylosanthes humilis) in ungrazed swards at Katherine, N.T

Abstract

At Katherine, N.T., swards of Townsville lucerne (Stylosanthes humilis H.B.K.) were sown in late November and late December, 1964, and sampled every two weeks during the growing season. At each harvest the dry matter, nitrogen, and phosphorus yields of stem, leaf and petiole, inflorescence, unshed pods, shed leaf, and shed pods were determined. Crop growth rates and net assimilation rates (leaf weight basis, ELW), were derived for both plantings and compared with calculated soil water storage. Drought in January and February restricted growth during the vegetative phase, but rapid growth resumed when water stress was relieved by rain in March. Maximum dry matter yield (5400 lb an acre) and mean crop growth rate (42.3 lb an acre a day) for the November sowing were similar to those measured for Townsville lucerne at Katherine and elsewhere. Maximum crop growth rates (250 and 110 lb an acre a day for the November and December sowings respectively) appear to be about the same as those recorded in the field for subterranean clover. The strong influence of water stress on growth was emphasized by the close relationship demonstrated between ELW and calculated soil water storage. Uptake of nitrogen and phosphorus was restricted during water stress and both were redistributed to reproductive parts of the plant during flowering and seeding, nitrogen more readily than phosphorus. Nitrogen and phosphorus contents (1.9-2.0 per cent N and 0.70-0.75 per cent P) were lower than those recorded for other tropical and temperate pasture legumes. The implications of the low phosphorus contents of Townsville lucerne as cattle feed are discussed.