Plant nutrition studies on some yellow and red earth soils in northern Cape York Peninsula. 3. Effects of liming and placement on responses to applied phosphorus

The yellow earth soils in northern Cape York Peninsula are extremely low in both total and extractable P and require large additions of phosphorus for maximum pasture yields. The reasons for this high requirement and the results of various attempts to modify it are reported in this paper. Laboratory studies showed that the soils have a high capacity to sorb P and that exchangeable A1 was high, relative to the other cations. Various liming treatments were therefore tested to see what effect reducing the level of exchangeable Al in the soil had on the shape of the P response curves. In two pot experiments there were moderate responses in dry matter yield of Stylosanthes guianensis, cv. Cook, to low rates of lime (500 kg ha-1 on an area basis). The responses were larger where sodium rather than calcium phosphate was the source of the P. In the field, the response of this legume to liming was quite small and not significant by the second year. Only in one of the pot experiments was there evidence that liming reduced the requirement for P.As expected for a soil with a high sorption capacity, responses to placement of phosphate were found in pots; in the field, however, no worthwhile benefits were obtained from placement