K.B. ADDISON1, D.G. CAMERON2 and G.W. BLIGHT3
1Formerly Queensland Department of Primary Industries, Brian Pastures Pasture Research Station, Gayndah, 4625.
2Queensland Department of Primary Industries, P.O. Box 46, Brisbane, 4001.
3Queensland Department of Primary Industries, Rockhampton, 4700.
The effect on pasture and animal production of three rates of nitrogen fertiliser — 22.5, 45 and 90 kg ha-1 nitrogen-applied annually to initially five year old green panic pastures was studied for four years. The pastures were stocked at 2.5 yearling steers ha-1 from early September to the end of February (spring/summer) each year. The residual herbage at the conclusion of each grazing season was either cut for hay and fed back ad libitum next spring, or left standing in the paddock.
Pasture dry matter yields responded linearly to increasing nitrogen rate and there was always more dry matter on the unmown paddocks. Green panic shoot number was not influenced by nitrogen rate, but was increased by mowing for hay. Green panic remained the most important species at the highest nitrogen rate, but at the lower nitrogen rates the native grasses increased in importance.
Due to almost complete utilisation of the dry matter available, hay-making was not possible every year at the lowest nitrogen rates, and only small quantities were eaten when hay was fed back.
Up to December each year, nitrogen application increased faecal nitrogen content but not later in the season; mowing had no effect on faecal nitrogen.
Liveweight gain increased linearly with increasing rates of nitrogen application and, at the low nitrogen rate mown pastures were less productive than unmown. The spring/summer average daily gain across all treatments increased as the trial progressed from 0.571 kg hd-1 in the first year to 0. 705 kg hd-1 in the final year