Mineralogical and physico-chemical properties of four Thai soils with Special Reference to specific surface area (SSA) and zero point of charge (ZPC)

Abstract Mineralogical and physico-chemical properties were examined to evaluate the intrinsic properties of soils from four different regions in Thailand. The use of acid oxalate and dithionite-citrate-bicarbonate-extractable Fe and Al and calculated activity ratios enabled to define the site-specific nature of the weathering status. Furthermore, a scattergram of specific surface area (SSA) and zero point of charge (ZPC) enabled to interpret the site specificity. The SSA value was well correlated with σp (residual charge at ZPC) value both among the surface soils and among the subsurface soils. When the organic matter content increased, the σp value increased remarkably whereas the SSA value increased slightly. This phenomenon could be ascribed to the high charge density of organic matter which contributed significantly to the addition of negative charges to soils but not appreciably to the increase of the surface physical capacity to hold cations. Based on a multiple regression analysis, SSA and ZPC cou...