Nitrogen fertilizer responses of pasture grasses in south-eastern Queensland
Australian J Exp Agric Animal Husb 3(11): 290-299
Nitrogen applied as urea or ammonium sulfate increased the annual yield of dry matter under mowing from 1000-5000 1b to 10,000-20,000 lb an acre, and rates of fertilizer in excess of 400 lb of elemental N an acre a year were required for maximum grass yields during favorable seasons. Ammonium sulfate, applied at rates up to 400 lb N/acre/year, had relatively little effect on the percentage of N in Rhodes grass (Chloris gayana), Paspalum dilatatum, and P. commersonii, 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) mixture. In an experiment with Rhodes grass, P. dilatatum and P. commersonii, nitrogen recovery rose with increasing rates of ammonium sulfate. At 70 lb N/acre/year the average N recovery by Rhodes grass was 10%; at 400 lb N/acre/year it was 47%. The residual effects of ammonium sulfate, measured on Rhodes grass during the growing season following 2 years of fertilization, were very small indeed. Use of N fertilizers sometimes caused marked changes in the botanical composition of the sward.