Yield, nitrogen uptake and liveweight gains from irrigated grass-legume pasture on a Queensland tropical highland

Abstract

The growth and nitrogen uptake of grazed irrigated mixed pastures based on eleven legumes and Brachiaria mutica (Para grass) was measured over four years. Four of these legumes were also used in two short grazing trials to estimate the fattening potential of irrigated grass-legume pastures. Glycine wightii cv. Tinaroo and Desmodium intortum cv. Greenleaf were the most persistent legumes, had winter growth rates twice that of other legumes, and formed the most stable pastures. Apparent nitrogen fixation was linearly related to legume dry matter yield and became a more efficient process with time. In the final two years each 1000 kg legume DM resulted in an extra 33 kg N in the system. Nitrogen in Macroptilium atropurpureum cv. Siratro pastures was transferred twice as efficiently as in other pastures. G. wightii- B. mutica pastures produced the most rapid liveweight gains of up to 0.61 kg day-1 over a full year, and produced the highest liveweight gain per hectare (860 kg year -1). Increasing stocking rate from 3.4 steers ha-1 to 5.1 steers h-la depressed pasture legume contents and rate of liveweight gain per animal but generally did not increase liveweight gain per hectare.