STUDY ON WATER AND SALT MOVEMENT DURING SOIL FREEZING AND THAWING

1.以内蒙古河套灌区中国为研究对象，以内蒙古河套灌区土壤冻融过程中的水盐运动为例，作为研究的背景和出发点。讨论了区域和田间层面的盐分运移、春灌和秋灌盐分积累的关系、秋灌土壤水分供应与淋失效果、盐碱地改良方法。测量了冻结水泥土的介电常数，将水泥土中的水分为水化状态和结构结合状态。估计了这些水的数量。并估算了结构结合水的水势。通过分析正弦温度振荡作用下冻土和未冻土的温度波动幅度与深度的关系，计算了冻土和未冻土的导热系数。将该方法应用于野外土壤温度变化以及冻土和U-…的导热系数的测定。通过该方法可以估计出更多的冻结状态。提出了一种测量冻土非饱和导水率的新方法。在离心力场作用下对冻土样品进行平衡，通过改变样品中的水分分布来测量失水量。用失水率除以离心力和时间的梯度来计算渗透系数。测得的导水率范围为10^~(-9)cm/S~10^~(-8)cm/S.5。从土柱底部冻融土壤，测量土壤水分和盐分运移。对照初始土壤水分和盐分浓度对结果进行了检验。土壤初始含水率越高，水盐运移越大。根据热导率和测量的温度分布估算土壤中的热流密度。土柱从上表面开始冻融，在地表开放或封闭、土壤初始含水率高或低的条件下，测量水盐运动。土壤初始含水率对冻结深度影响不大，但土壤初始含水率较高时，水、盐向冻结锋面移动较大。在高土壤水分条件下，开阔地表条件下解冻后发生盐分积累。较少

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