1. Animal Output

The results, in terms of live-weight gain, of the first five years, of a large-scale, long-term grazing trial receiving 0, 46, 92, 184 and 368 lb. per acre N are discussed. Two sources of nitrogen were used, calcium ammonium nitrate (20.5 per cent N) and ammonium sulphate (21 per cent N). The sward was a Cockle Park type mixture and the field was direct reseeded in August, 1955. Levels of animal production were measured from each treatment using cattle (750 lb.) and sheep (80 - 90 lb.) maintained on the plots. No material was conserved. Grazing was on a rotational basis and the grazing season extended from early March to mid-November (approximately). Small dressings of N tended to depress production, and dressings up to 368 lb. N gave only 18 per cent increase on average. There was some indication, that the small live-weight increase on the high N treatments could have been due to the low intake of herbage by stock from the ammonium sulphate portion of these plots. The effect of small dressings of N on the sward was to depress clover and increase grass growth, but the increase in grass did not compensate for the reduction in clover. Where the heavy dressings (368 lb.) of N were applied the cattle and sheep preferred the herbage on the calcium ammonium nitrate portion to the ammonium sulphate portion of each plot especially in July and August in the 3rd, 4th and 5th years. Production from the swards depending on clover was reduced in years of low rainfall during the grazing season. Health of stock was excellent except that with 368 lb. N severe scouring occurred in all animals (cattle and sheep) when they were put on the trial at the beginning of each grazing season and again in July and August in the last three years of the trial.