Adsorption strength of zinc for soil humus

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Abstract
Durable soil humus has, as one of its functions, chelation power for di- and trivalent metal ions. One of the authors 0, 2) has reported that the percentage of chelated zinc, which has greater adsorption strength than that of the exchangeable zinc, to the total zinc adsorbed increased with the progress of humification when zinc was added to humic soils, and that the adsorption strength of zinc is closely related to nature of soil humus. Randhawa and Broadbent (3, 4) reported stability constants of zinc-humic acid complexes calculated to be 4.42 at pH 3. 6, 6. 18 at pH 5. 6, and 6. 80 at pH 7.0 by the ion-exchange equilibrium method. Schnitzer and Skinner (5, 7) determined the stability constants of different metal-fulvic acid complexes originating from a podzolic soil by the same method and showes the order of their stability. But in these investigations, only one kind of sample soil has been used, and the relation between the stability constant and nature of soil humus has not been shown. Nair and Mehta (8) showed that there was a significant positive correlation between organic matter and acid-soluble zinc contents in fifty-eight typical soils of western India, but did not refer to the character of soil humus used. Recently Tsutsumi et al (9) determined stability constants of copperhumic acid complexes originating from soils with different degree of humification.