SummaryThe pH0and ZPC of two Hydiandepts were determined by potentiomettic titiation in NaCl and by ion adsorption measurements from NH4NO3, respectively. The decrease of pH, pH0, and ZPC due to drying was explained by the hydrolysis reaction. Partial drying, high organic matter content, and low Al2O3concentration in the surface soil were responsible for its low pH, pH0and ZPC. The high pH0of subsoils was attributed to the presence of amorphous aluminosilicates and mixed polymeric gels of Fe(III) and A1 with high water content. The significant decrease of nitrate adsorption due to dehydration is discussed in relation to the change in pH, pH0, ZPC, and surface area on drying.