Abstract
To avoid CO2 degassing and the following pH increase in soil water, pH measurement using the tensionic method was carried out and its performance was discussed. The pH of distilled water stored in a buried-type tensiometer equilibrated with the pH of surrounding soil water more rapid than the concentration of dissolved ions. This was theoretically supported by much greater diffusion coefficient of proton due to its particular diffusion mechanism in solution. The time to reach the equilibrium condition of dissolved ions became longer as the soil was getting drier. The pH of the stored water was lower than that of soil suspension, and higher than that of pure water under the same CO2 concentration. Concentrations of CO2 and dissolved ions suggested that CO2 dissolution and cation exchange reaction affected soil water pH. In conclusion, it is possible to measure the pH of soil water under high CO2 concentrations in soils by applying the tensionic method.
