THE DETERMINATION OF DESORPTION ISOTHERMS FOR SOIL PHOSPHATE USING LOW VOLUMES OF SOLUTION AND AN ANION EXCHANGE RESIN

Abstract

Summary Phosphate desorption isotherms were determined (a) by shaking 1 g soil with 3 ml 0.01M CaCl 2 solution plus different amounts of an anion exchange resin, and (b) by diluting soil with different volumes of 0.01M CaCl 2 solution. Adsorption isotherms were determined using a soil to solution ratio of 1 g to 3 ml. In soils of intermediate P status adsorption isotherms appeared continuous with desorption by method (a), but not with desorption by method (b), which predicted lower buffer powers than did (a). Method (a) led to increases and (b) to decreases in pH. Additions of dissolved silica had no influence on P desorption by method (b).