Desorption of Phosphate From Soils Using Anion Exchange Resins

Summary After 100h reaction with Cl‐resin and 300h reaction with HCO 3 ‐resin (approaching equilibrium), the concentration of anions complementary to phosphate was the critical variable affecting the transfer of P from soil to resin. Solution concentrations of H 3 0 + , Ca 2+ and phosphate indicated that desorption of P by OH ‐ , and dissolution of Ca phosphates, controlled P release from soils. P extracted by HCO 3 ‐resin was much greater than by Cl‐resin from an acid soil, due to lower total anion and higher desorbing anion concentrations, but there was little difference between the two resins with a calcareous soil. HCO 3 ‐resin extracted a constant proportion of isotopically‐exchangeable P from different soils whereas Cl‐resin did not. Anion exchange resins provide a convenient means for producing P desorption curves for soils.