Changes in Zero Point of Charge (ZPC), Phosphate Retention, and Specific Surface Area of Some Variable Charge Soils after Several Chemical Treatments

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Zero point of charge (ZPC), phosphate retention percentage, phosphate absorption coefficient, and specific surface area of variable charge soils subjected to several chemical treatments were determined for the evaluation of the intrinsic properties which would not appear in the untreated state. Three extraction reagents, 1 M KCl, acid-oxalate, and dithionite-citrate-bicarbonate, were used for the treatment of samples from two volcanic ash soils from Japan and two strongly weathered soils from Thailand, and the amounts of Al, Fe, and Si in the extracts were determined. All of these values were closely related with each other, reflecting the characteristics of variable charge components. In particular, the values of ZPC, phosphate absorption coefficient, and specific surface area were considered to be useful parameters to analyze amorphous oxides or hydroxides qualitatively ; their high contents resulted in higher values of ZPC, phosphate absorption coefficient,, and specific surface area. In addition, in soil samples with a low ZPC, it was pointed out that Al dissolution due to strong acidification of the time of the determination of ZPC, and subsequent development of permanent negative charges of crystalline layer silicated may result in ZPC values lower than those operating under field conditions.
社団法人日本土壌肥料学会の論文