Abstract
The effect of NPK fertilizers (N at 170 225, 280 and 340kg/ha per year; P at 0 and 100 kg/ha per year; K at 0 and 70kg/ha per year) on the dry matter production and mineral content of elephant grass (Pennisetum purpureum) growing on a colluvial soil in Tobago, West Indies, was examined over three consecutive years. A mean dry matter yield of 35·5 t/ha per year was obtained. The higher rates of only increased yield significantly in the third year whereas P and K caused increases in the second and third years. Over the whole three year period, rates of above the lowest given or addition of P and K did not affect yields significantly. Mean crude protein content was 7·9 per cent and this was not affected by fertilizers. Addition of phosphate fertilizer significantly (P=0·01) increased the percentage of Pin the oven-dry forage but additions of potash had no effect on K concentration. The mean amount of crude protein produced annually was 2895kg/ha and the amounts of N, P and K removed were 463, 96 and 594kg/ha per year respectively. Over the period there was a decline in yield but much wider fluctuations were observed in each year due to changes in rainfall production dropped markedly in the drier months.
