Reaction of labelled 65ZnC12, 65ZnEDTA and 65ZnDTPA with different clay-systems and some alluvial Egyptian soils
1980
Elsokkary, I.H. (Agricultural Univ. of Norway, Aas (Norway). Soil Science Dept.)
The clay fraction separated from an alluvial Egyptian soil and montmorillonite clay mineral were equilibrated with a CaCl(,2) 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 labelled ('65)ZnCl(,2), ('65)ZnEDTAand ('65)ZnDTPA. The effectiveness of these Zn-sources for maintaining soluble Zn(2+) ions in the equilibrium solution was the greatest for ZnDTPA and the lowest for ZnCl(,2). 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 of ('65)ZnEDTA and ('65)ZnDTPA with the seven soils produced higher levels of soluble Zn(,2+) ions in the equilibrium solution rather than ('65)ZnCl(,2) meanwhile ZnDTPA was more effective than ZnEDTA. The calculated Zn(OH)(,2) ion product in the solution of ZnCl(,2)-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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