Tropical Grasslands (1985) Volume 19, 73–81

THE EFFECTS OF FIVE NITROGEN RATES ON THE YIELD AND NITROGEN USAGE IN SETARIA ALONE, DESMODIUM ALONE AND SETARIA/DESMODIUM MIXED SWARD OVER THREE YEARS

P.C. WHITEMAN O. ROYO, E.A.A. DRADU and P. ROE

Department of Agriculture, University of Queensland, St. Lucia, Queensland, 4067, Australia.

Abstract

A factorial trial with 4 replications applied 5 rates of nitrogen (0, 75, 150, 300 and 600 kg N ha-1) to Setaria anceps cv. Nandi alone, Desmodium intortum cv. Greenleaf alone, and to a mixed sward of both species at Mt. Cotton Research Station in south-east Queensland. The dry matter yield in the setaria plots gave a maximum of 17.9 t ha-1 with 600 kg N ha-1 in year 1. In the setaria/desmodium, yields were always higher than setaria alone, with 19.2 t ha-1 at 600 kg N ha-1 in year 1. Nitrogen rate had little effect on yield in the desmodium alone swards. Total yields of nitrogen of 43 kg N ha-1 were similar in the zero N rate in all years in setaria alone. Nitrogen yield in desmodium alone changed little with increasing N rates. In the setaria/desmodium, mean nitrogen fixation over 3 years in the zero N rate was 150 kg N ha-1 yr while desmodium alone fixed 228 kg N ha-1 yr-1.

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