Reaction of labelled65ZnCl2,65ZnEDTA and65ZnDTPA with different clay-systems and some alluvial Egyptian soils |
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Authors: | I H Elsokkary |
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Institution: | (1) Soil Sci. Dept., Agricultural University of Norway, NLH Ås, Norway;(2) Present address: Soil and Water Sci., Faculty of Agriculture, Alexandria University, Alexandria, Egypt |
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Abstract: | Summary The clay fraction separated from an alluvial Egyptian soil and montmorillonite clay mineral were equilibrated with CaCl2 or NaCl solution then treated with humic acid isolated from composted clover straw to obtain different clay systems: Ca-clay, Ca-clay-HA, Na-clay, Na-clay-HA, Ca-mont and Ca-mont-HA. These clays as well as seven soil samples were reacted with different amounts of labelled65ZnCl2,65ZnEDTA and65ZnDTPA. The effectiveness of these Zn-sources for maintaining soluble Zn2+ ions in the equilibrium solution was the greatest for ZnDTPA and the lowest for ZnCl2. Ca-clay provided greater Zn sorption capacity than Na-clay, and complexing the clay with humic acid depressed its capacity for Zn sorption. At the pH of the clay-systems (pH=6.5), the possibilities of Zn(OH)2 formation were reduced especially in the presence of Zn-chelates. Reactions of65ZnE DTA and65ZnDTPA with the seven soils produced higher levels of soluble Zn2+ ions in the equilibrium solution rather than65ZnCl2 meanwhile ZnDTPA was more effective than ZnEDTA. The calculated Zn(OH)2 ion product in the solution of ZnCl2-soil systems indicated the precipitation of Zn as Zn(OH)2. However, this was not valid in the Zn-chelates-soil systems. The results also revealed the role of soil carbonate, organic matter and soil texture as soil variables affecting Zn sorption by natural soils. |
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Keywords: | Chelated zinc Clay-systems Equilibrium solution Humic acid Labelled65Zn Solubility products Sorption capacity |
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