Zinc adsorption isotherms were constructed for five soils from Hawaii which varied in mineralogy and history of phosphate fertilization. Equilibrating conditions were: 25°C, 0.01 M CaCl 2 , soil solution ratio of 1:10, and 6 days. The amount of Zn added ranged from 0 to 600 µg/ml as ZnSO 4 · 7H 2 O. Equilibrium was reached by 72 hours. Unfertilized soils which contained predominantly constant charge colloids absorbed more Zn than soils with variable charge colloids. Phosphorus fertilization increased Zn adsorption by soils that contained colloids predominantly of the variable charge type. The results support the hypothesis that phosphate additions to soils increase Zinc adsorption by increasing the negative charge on iron and aluminum oxide systems. For soils containing constant charge colloids, prior P applications decreased Zn sorption because the fertilizer contained Zn as an accessory element. Zinc sorption conformed to the Freundlich model at concentrations greater than 0.1 ppm Zn in solution.
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Saeed et al. (1979) studied this question.