The production and persistence of grazed irrigated pasture mixtures in south-eastern Queensland

Abstract

Five irrigated pasture mixtures (four containing tropical and temperate species and one containing only temperate species (winter mixture) ) were compared under grazing at three nitrogen levels -nil, 100, and 300 lb N an acre a year as urea-over a four-year period 1960-1963. Pastures were grazed for approximately one week every six weeks with a twelve-week rest period in the winter of 1962 and 1963. Under this management mean annual yields of dry matter increased from 15,700 lb to 25,000 lb an acre over the four-year period. Pasture growth rates varied from over 90 lb DM an acre a day in early summer to 10-40 lb DM an acre a day in winter due to variations in radiation and temperature. Urea increased pasture dry matter yields and also the yields of nitrogen measured in 1961 and 1962. Mean response was 19 lb and 14.5 lb DM/lb N applied at the N100 and N300 rates respectively. Yield of nitrogen was increased by a mean of 79 lb an acre a year by application of urea, but there was no significant difference between rates. Dry matter responses to urea were small in winter and spring and large in summer and autumn. The N300 rate reduced the yield of white clover in the first two years of the pasture, but there was no reduction in the yield of white clover at the N100 rate compared with the N0 treatment. There were no significant differences in yield between the pasture mixtures in the establishment year. In subsequent years mixtures containing summer and winter species outyielded (P<0.001) the winter mixture, particularly in summer and autumn. The pattern of production was similar for all mixtures and there was no significant difference between mixtures in yield of nitrogen. Chloris gayana Kunth CV. Samford and Setaria sphacelata (Schum) Stapf and C. E. Hubbard CV. Nandi. were the most successful summer grasses and Bromus unioloides (Willd.) H.B.K. cv. Priebes, the best winter grass. Three Paspalum species failed to compete with the Setaria and three winter grasses were low yielding after the first year. Trifolium repens L. CV. Ladino was the only successful legume of three winter and three summer legumes sown. It enabled yields of 400 lb N an acre a year to be achieved, increased total soil nitrogen, and made an estimated contribution of 760-810 lb N an acre over the four-year period. It is considered to be the key species for irrigated pastures in south-eastern Queensland.