Cotton, wheat and white lupin differ in phosphorus acquisition from sparingly soluble sources

Low responsiveness of cotton to P fertilizer application on soils with low soil-test P values indicates that cotton might take up P from stable P pools. The ability of cotton to acquire P from sparingly soluble P sources was examined by comparing with wheat and white lupin. The plants were grown in washed river sand, with P sources applied at a rate of 40 mg P kg⁻¹, as sparingly soluble AlPO₄, FePO₄, or hydroxyapatite. Cotton was inefficient in accessing P from any of the sparingly soluble P sources. Thus, the low responsiveness of cotton to P fertilizers could be attributed to factors other than efficient P acquisition from the stable P pool in the soil. In contrast to white lupin which accessed little P from the sparingly soluble P sources in this study, wheat showed an outstanding ability in utilizing AlPO₄. When compared with the control, total uptake of P from AlPO₄ by wheat was approximately 9 times higher than cotton and 7 times higher than white lupin, which was possibly related to its high root Al concentration and high root:shoot ratio. The study concludes that the three species differed substantially in P acquisition from the sparingly soluble AlPO₄, with cotton being least efficient and wheat most efficient.