Abstract
A field experiment was conducted to determine the effect of large applications of nitrogen fertilizer on the productivity and protein content of Brachiaria ruziziensis,Chloris gayana, Panicum maximum and Setaria sphacelata. All the grasses responded strongly to nitrogen up to 448 kg/ha with a slight additional response up to 896 kg/ha. Above this level there was a decline in dry matter yield. C. gayana produced significantly more dry matter than S. sphacelata and B. ruziziensis. There was no real difference in yield between C. gayana and P. maximum. Nitrogen increased the dry matter production of the grasses almost threefold. The mean dry matter yields of the grasses ranged from 8·7 to 25·4 t/ ha per annum. The mean crude protein percentage of the grasses more than doubled using high rates of nitrogen. It varied from 7·9 to 16·6 per cent. S. sphacelata had the highest crude protein content but was not significantly higher than P. maximum. C. gayana produced the largest amount of total crude protein, whereas S. sphacelata yielded the lowest amount. The nitrate content in the grasses increased with increasing increments of nitrogen. Concentrations potentially dangerous to livestock were found at the higher nitrogen treatments.
