EFFECT OF MOBILE CHELATING AGENTS ON DIFFUSION OF ZINC IN SOILS

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Abstract
The effect of DTPA, EDTA, and fulvic acid (FA) on the self-diffusion of Zn in an alkaline and a calcareous soil was studied. The apparent diffusion coefficient of Zn in soil increased significantly with addition of DTPA, EDTA, FA, and the respective Zn-chelates at the rate of 8 x 10-8 mole/g soil. This increase was attributed to the conversion of the solid phase soil Zn into soluble Zn complexes, thereby increasing the concentration gradient of total diffusible Zn. Evaluation of the contribution of different chelating agents to solution and adsorbed phase diffusion of Zn indicated that chelation of Zn greatly enhanced its adsorbed phase diffusion in addition to that in solution phase. The increase in apparent diffusion coefficient of Zn by the application of different chelating agents and their Zn-chelates synchronized with their relative stability as defined by pH and cation competition in these soils. The results indicate that chelating agents (natural or synthetic) play an important role in overcoming the rate-limiting steps of solution and adsorbed phase diffusion which are mainly responsible for the movement of Zn ion in alkaline and calcareous soils.
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