Estimation of Soil Freezing Curve Based on Water Retention Curve Measured with a Vapor Sorption Analyzer.

A soil freezing curve (SFC) represents the relationship between temperature and liquid water amount in frozen soil. Obtaining accurate SFC is fundamentally important to predict water, heat and solutes transport in frozen soil. SFC is often derived from water retention curve of unfrozen soil (SWC) through the Clausius-Clapeyron equation by assuming that ice-liquid interface in freezing soil is similar to the air-water interface in drying soil. The temperature change from -1 to -10 ºC corresponds to the change in matric potential from -1.2 to -12 MPa. Such low water potential can be measured reliably, for instance, by a chilled-mirror dew potentiometer. However, homogeneity and reproductively of water condition of soil sample becomes increasingly inaccurate as soil dries, so that it is still difficult to estimate accurate and continuous SFC from SWC. Recently, a vapor sorption analyzer (VSA), which measures water potential with the chilled-mirror technique while gravimetrically tracking the sample weight during wetting and drying processes, becomes available for quick measurement of low potential range of SWC and its hysteresis. .Thus, we measured SWCs of sand, silt and Andisol by using VSA and compared to the SFCs obtained by NMR and TDR measurement. Then, SFC estimated from the SWC was applied to numerical calculation to investigate its sensitivity and effect of hysteresis on water flow during soil freezing.