Verification of freezing point depression method for measuring matric potential of soil water

The matric potential of soil water was determined using the freezing point depression method for a range of soil types. Soil water characteristic curves of these soils were obtained and compared with those obtained by the pressure plate, psychrometer, and vapor pressure methods resulting in excellent agreement between the freezing point depression method and the other methods over the range of -10.0 to -0.1 MPa in matric potential (i.e., temperature range of -8.00 to -0.08°C for freezing point) in all soil types. Over those ranges of matric potentials and temperatures, the effect of temperature-dependence on the freezing point of soils both in terms of specific volume of water and latent heat of water freezing was negligibly small. Freezing point of soils was independent of the bulk density of soils due to the fact that soil water in the range of matric potentials less than -0.1 MPa was affected predominantly by adsorptive forces between water and the soil matrix. The results from this study indicate that the freezing point depression method is a simple and practical technique to determine the soil water content in the vicinity of the wilting point