Abstract: The characteristics of the zero point of charge (ZPC) of volcanic ash soil profiles in Changbaishan and Wu-dalianchi was studied and discussed by means of potentiometric titration curves.The results showed that the two volcanic ash soils had not only a little variable charg, but also a little permanent charge.The clay fractions of the volcanic ash soils carried both variable and permanent charges.The ZPC of eeach layer in both soil profiles all lied in the acid side of titration curve, and increased with increasing soil depth.However, the ZPC displacements (σ_i) decreased with increasing soil depth.The ZPC of surface layer in both soil profiles was lower than that of the volcanic ash soils in foreign countries, but obviously higher than that of Loess soil in the Northwest and of black soil in the Northeast China.The variation of ZPC and Si was affected not only by the deposition of long-rang tropospheric eolian dust from the Asian continent, but also by the accumulation of soil organic matter.Their combined effect was the main reason to the decrease of ZPC and σ_i the increase of σ_i in Changbaishan and Wudalianchi volcanic ash soils.

Key words: Changhaishan, Wudalianchi, Volcanic ash soil, Zero point of charge, Long-rang tropospheric eolian dust