Adsorption-desorption of zinc in mollisols and their relationship with uptake of fertilizer-applied zinc by rice
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Zinc (Zn) adsorption in mollisols conformed to the linear form of Freundlich equation. The log K values were positively correlated with silt, clay, and carbonate contents and soil pH, but negatively correlated with sand content. Sequential desorption of adsorbed Zn in 0.05M Ca(NO3)(2), 0.1M Mg(NO3)(2), 0.005M DTPA, and 0.1M HCl revealed that weakly and specifically bound fractions of added Zn, which could easily equilibrate with soil solution, were low and decreased with silt and carbonate contents and soil pH. Weakly bound fraction increased with sand content. Strongly bound and complexed fraction of applied Zn was the maximum and increased with clay, soil organic carbon and carbonate contents and specific surface area, but decreased with sand content. The mineral bound fraction of applied Zn was intermediate and increased with silt, clay and carbonate contents, and soil pH and specific surface area. Zinc uptake due to added Zn fertilizer by rice crop (Y) negatively correlated with log K, but positively related to Zn content in the equilibrium soil extract and Zn desorbed in 0.05M Ca(NO3)(2). Both log K and Vn values together explained 59.5% of the total variation in Y, while Zn content in the equilibrium soil extract, Zn desorbed in 0.05M Ca(NO3)(2), 0.005M DTPA and 0.1M HCl collectively accounted 79.6% of the total variation in Y.
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