Nitrogen fertilizer responses of pasture grasses in south-eastern Queensland

Abstract

The results are reported of field experiments with nitrogen-fertilized pasture grasses at Samford and D'Aguilar in south-eastern Queensland. The main findings were :- 1. Nitrogen applied as urea or ammonium sulphate increased the annual yield of dry matter under mowing from 1,000- 5,000 lb up to 10,000-20,000 lb an acre, and rates of fertilizer in excess of 400 lb of elemental nitrogen an acre a year were required ,for maximum grass yields during favourable seasons. 2. Ammonium sulphate, applied at rates up to 400 lb N/acre/year, had relatively little effect on the percentage of nitrogen in Rhodes grass (Chloris gayana Kunth.), Paspalum dilatatum Poir., and P. commersonii Lam., cut three times a year. Rates of urea above those required for maximum growth markedly increased the percentage nitrogen content of a Sorghum almum Parodi-blue couch (Digitaria didactyla Willd.) mixture. 3. In an experiment with Rhodes grass, P. dilatatum and P. commersonii, nitrogen recovery rose with increasing rates of ammonium sulphate. At 70 lb N/acre/year the average nitrogen recovery by Rhodes grass was 10 per cent; at 400 lb N/acre/year it was 47 per cent. 4. The residual effects of ammonium sulphate, measured on Rhodes grass during the growing season following two years of fertilization, were very small indeed. 5. Use of nitrogen fertilizers sometimes caused marked changes in the botanical composition of the sward.