Plant nutrition studies on some yellow and red earth soils in northern Cape York Peninsula. 2. Phosphorus: plant response and soil retention

Abstract

The response of a Stylosanthes guyanensislBrachiaria decumbens pasture to phosphorus on a yellow earth soil in northern Cape York Peninsula was studied over three years. Establishment rates of 0 to 130 kg ha-1 P were used followed by various combinations of 0 or 20 kg ha-1 P in the next two years. With comparisons made at the same cumulative P rate the dry matter and nitrogen yields were not affected by timing of application but P yield was increased in the third year when P was freshly applied. The dry matter yield response was modified by the botanical composition of the pasture. In the first year the pasture was 90-95 per cent legume and 110 kg ha-1 P was required to give 90 per cent of the presumed maximum yield whereas in the third year when the legume content was lower, (increasing from 10 to 40 per cent with P rate) this requirement had been reduced to about 90 kg ha-1 P. The third year P yield data were used to show that the value of applied P declined by about 70 per cent each year. After three years all the applied P was recovered in the 0-60 cm zone and the distribution was not affected by timing of application. In the 0-10 cm zone the acid extractable P increased from 0 with no P applied to 40 p.p.m. with 150 kg ha-1 P applied.