A SIMPLIFIED RESIN MEMBRANE TECHNIQUE FOR EXTRACTING PHOSPHORUS FROM SOILS

A simplified procedure for determining the amount of phosphate (P) extracted from soils by ion exchange resin membranes is reported. Strips of anion (HCO3- form) and cation (Na+ form) exchange membrane were shaken with suspensions of soil in deionised water for 16-17 hours. After shaking, the strips were thoroughly rinsed in deionised water before the phosphate retained on the anion exchange resin strip was determined by shaking the strip directly with phosphate reagent. Compared to the common use of resin beads in nylon mesh bags, this resin membrane procedure is simpler, more convenient, and because an elution step is omitted, less time consuming. The mixed resin membrane method for soil phosphate extraction was compared to the use of resin bags on four New Zealand soils, contrasting in P sorbing capacity and exchangeable calcium. The soils were preincubated with and without 240 mg P kg-1 soil with three P sources of different solubilities. The resin strips extracted amounts of P which were closely correlated (R2 = 0.972) with that extracted by the resin bags. The amounts of P extracted by the mixed resin procedure were in proportion to the solubility of the P sources in each soil. © 1990 Kluwer Academic Publishers.