Time dependent Zn extraction with diethylenetriaminepentaacetic acid (DTPA) extractant from five soil orders were studied for shaking periods of 1 min to 24 h. Zinc release rate from the studied soils was initially fast followed by a much slower rate trend. Power function was the best model describing Zn release data, followed by Elovich and parabolic diffusion models, respectively. Significant correlation coefficients between Zn extracted at 120 min with those of previous shaking periods such as 1 min suggested that lower shaking periods might be relevant in DTPA soil test for Zn in the studied soils which may lead to quicker Zn extraction methods. Results showed that the rate values of the best fitted models for the studied soils were in the order: Histosols > Mollisols > Vertisols > Inceptisols > Alfisols. The above order well shows the higher potential of Inceptisols and Alfisols for Zn deficiency in comparison with the other soils studied. On the other hand, the organic soils studied are not likely to be Zn deficient. Positive correlations of clay and organic matter (OM) with the rate constants of the best fitted models suggest that clay and OM are most likely the main sites of Zn release in the studied soils.
Key words: Zinc, extraction, soil orders, diethylenetriaminepentaacetic acid (DTPA).
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