J. STANDLEY

Abstract

Seedlings of Centrosema pubescens cv. Belalto were planted in microplots within larger fertilised plots of guinea grass (Panicum maximum) pasture on a north Queensland krasnozem. With six rates of superphosphate, from 0–320 kg ha^-1 P, there was no increase in guinea grass yield but the phosphorus concentrations were raised by as much as 0.20 % P. Centro yields were increased 10 months after planting but remained below 10 per cent of the total pasture yield. The largest yield increment was to 20 kg ha^-1 P and yields increased up to 160 kg ha^-1 P before, decreasing with 320 kg ha^-1 P. There were only small increases in the phosphorus concentration of centro.
Acid digestible and total phosphorus analyses of the soil indicated that more than 160 kg ha^-1 P was retained at 0–5 cm and that there was no movement of applied phosphorus below 10 cm even with 320 kg ha^-1 P. At least 80 kg ha^-1 P were required for statistically significant increases in acid and bicarbonate extractable phosphorus analyses of surface soil (0–10 cm). Neither soil test detected the response by centro to lower phosphorus inputs.