STUDY ON WATER AND SALT MOVEMENT DURING SOIL FREEZING AND THAWING

1. 本文以内蒙古河套灌区土壤冻融过程中的水盐运动为研究背景和出发点。讨论了盐渍化土地的区域和田间盐分运动、春灌和秋灌的盐分积累关系、土壤供水量和秋灌淋滤效果、盐渍化土地的改良方法。测定了冻结胶结土的介电常数，将冻结胶结土中的水分为水合态和结构结合态。这些水的数量是估算出来的。并对结构结合水的水势进行了估计。通过分析土壤表面温度正弦振荡与深度的关系，计算冻土和非冻土的导热系数。将该方法应用于田间土壤温度变化的测定，并对冻土和非冻土状态的导热系数进行了估算。提出了一种测量冻土非饱和导流系数的新方法。在离心力场作用下对冻土试样进行平衡，并通过试样水分剖面的变化来测定水分流失量。通过失水除以离心力和离心力的梯度和时间来计算水导率。测量的水力导率范围为10^<-9> cm/s至10^<-8 >cm /s。从土柱底部开始冻结和解冻土壤，并测量土壤水分和盐的运动。结果与初始土壤水分和盐浓度进行了检验。土壤初始湿度越高，水盐运动越剧烈。通过热导率和测得的温度分布估算土壤中的热通量。采用冻融法对土柱进行顶面冻结和解冻，在地表开放和封闭、初始土壤水分高低两种条件下测量水盐运动。冻结深度受初始土壤湿度的影响较小，但高初始土壤湿度时，水盐向冻结锋移动较大。在高土壤水分条件下，在开放的地表条件下解冻后进行盐积累。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