Comparative Prediction of Yield Response and Phosphorus Uptake From Soil Using Anion- And Cation-Anion-Exchange Resins

Phosphorus desorbed from 18 South Australian soils by anion-exchange resin (AER-P) and cation-anion-exchange resin (AER-P) at different periods was core-lated with yield response and P uptake by wheat (Triticum aestivum cv. Gabo). The relationship between the quantity of P desorbed by both resin systems and P uptake and grain yield was found to improve significantly as the period of desorption increased up to about 10 h; after that it improved only slightly (up to 21 d). The CAER-P was better correlated with P uptake and grain yield and predicted yield response more closely than AER-P. The quantity of the latter was less than the former at all desorption periods. The two-constant rate equation (Ct = Ktb, where Ct, is CAER-P or AER-P (mg/kg soil), K is the initial desorption rate constant, t is the desorption period (s), and b is the rate coefficient) described P desorption from soils by AER and CAER at different periods (from 10−3 h to 21 d) satisfactorily. The ratio of K (CAER-P)/K (AER-P) was primarily affected by exchangeable calcium and magnesium and clay content of the soil (R2 = 0.91). Thus, the capacity of AER to desorb P compared with CAER was decreased, possibly by the buildup of calcium and magnesium in soil solution and the reduced diffusion of P through soil. The CAER-P may be a better measure of available P than AER-P by its capacity to take up cations as well as P from the soil solution, thus better simulating cations and P uptake by plants.