STUDY ON WATER AND SALT MOVEMENT DURING SOIL FREEZING AND THAWING

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1. As a background and a beginning point of this research, an example of water and salt movement during soil freezing and thawing was introduced from Hetao Irrigation District, Inner Mongolia, China. Regional and field level salt movement, relation between salt accumulation in spring and fall irrigation, soil water supply and leaching effect by the fall irrigation, improvement method of the salinized land were discussed.2. Dielectric constant of frozen cemented soil was measured and the water in it was classified into hydrated and structural bound state. The quantity of those water was estimated. Water potential of the structural bound water was also estimated.3. Thermal conductivity of frozen and unfrozen soil was calculated by analyzing the amplitude of temperature oscillation in relation to depth when sinusoidal temperature oscillation was given to the soil surface. The method was applied to determine the soil temperature change in the field, and thermal conductivity of frozen and u … More nfrozen state was estimated by this method.4. A new method to measure unsaturated hydraulic conductivity of a frozen soil was developed. A frozen soil sample was equilibrated under centrifuge force field and water loss was measured by change of the moisture profile in the sample. The hydraulic conductivity was calculated by the water loss divided by the gradient of centrifuge force and time. The measured hydraulic conductivity ranged from 10^<-9> cm/s to 10^<-8> cm/s.5. Soil was frozen and thawed from the bottom of the soil column, and the soil moisture and salt movement was measured. The result was examined against the initial soil moisture and salt concentration. The higher the initial soil moisture, the water and salt movement increased. Heat flux in the soil was estimated by the thermal conductivity and the measured temperature distribution.6. Soil column was frozen and thawed from the top surface, and water and salt movement was measured under conditions of open or closed surface and high or low initial soil moisture. The frozen depth was influenced little by the initial soil moisture, but greater movement of water and salt toward freezing front was observed at high initial soil moisture. At high soil moisture, salt accumulation was proceeded after thawing under opened surface condition. Less