Abstract:
Pastures at Glenormiston in western Victoria, sown with Phalaris tuberosa cv. Australian (phalaris) or Lolium perenne cv. Victorian (ryegrass) each with Trifolium subterraneum (subterranean clover), were grazed continuously by wethers at six rates of stocking over the range 19.8 to 32.1 sheep ha-1 from October 1966 to March 1971. Pasture growth was measured at three rates of stocking. During a four-year period, the phalaris and ryegrass pastures produced average annual yields of 10.4 and 8.0 t dry matter ha-1 respectively. The growth of phalaris pasture was usually greater in winter when it produced approximately 30 per cent more dry matter than ryegrass pasture. The effect of rate of stocking on pasture growth was rarely significant except in the final six months of the experiment when there was a reduction in growth rate as stocking rate increased. The basal cover of phalaris declined in the two years after a drought in 1967-68 to about 20 per cent irrespective of stocking rate. The basal cover of ryegrass also declined during this period, to a greater extent than phalaris, but in 1969 and 1970 there was some recovery at the lower stocking rates when the ryegrass was able to set seed. The basal cover of subterranean clover was about 20 per cent at 19.8 sheep ha-1 in most years and usually less at the higher stocking rates. The main species that replaced the sown species were Poa annua, Trifolium cernuum, Trifolium glomerata, Arctotheca calendula and Holcus lanatus. The amount of pasture present above a cutting height of 1.5 cm was less than 2 t ha-1 during most of the experiment and decreased as rate of stocking increased. The crude protein concentration of pasture present was always greater than 11 per cent except during the drought in 1967-68, when it fell as low as 5.2 per cent on the ryegrass pastures and to half this level on the phalaris pastures.