Responses of nine tropical grasses to nitrogen fertilizer under rain-grown conditions in south-eastern Queensland. 1. Seasonal dry matter productivity

Abstract

Nine tropical grasses were fertilized with 25, 50 and 100 kg N/ha on ten occasions at two-month intervals. No nitrogen was applied when conditions were too cold and/or dry for pasture growth. Samples (> 10 cm height) were taken at four-week intervals to estimate dry matter yield. Growth patterns of all grasses were similar, with a warm season peak and cool season trough. Nitrogen treatments did not greatly alter the growth pattern, although all species showed a yield response to increasing levels of nitrogen. Cumulative dry matter yields of Chloris gayana cvv. Callide and Katambora, Setaria sphacelata var. sericea cv. Narok, Digitaria decumbens and Panicum maximum cv. Makueni did not differ at N25 (P < 0.05), each producing about 10 t/ha. This significantly exceeded 5 t/ha from Pennisetum clandestinum cv. Whittet and Panicum maximum cv. Gatton. The same high-yielding group produced 15-16 t/ha at N50, while Gatton yielded 11.4 t/ha and Whittet 8.4 t/ha. At N 100, Callide, Katambora and Makueni were the highest yielding grasses (24-26 t/ha), and Whittet the lowest (15 t/ha). Brachiaria decumbens cv. Basilisk and Paspalum plicatulum cv. Bryan died out before the final harvests. Species responsiveness is discussed in terms of increment in dry matter yield per unit of applied nitrogen.