Study On The Thermodynamics Mechanism Of Saline Alkali Soil Solution Transference In Songnen Plain

Songnen plain locates in the of high altitude or middle altitude of Northern Hemishpheres. The soil is frozen from the end of October or the beginning of November yearly, which will not thawed totally until the end of June or the beginning of July. The causes for the development of alklization contains the strongly evaporation from the drought of climate, the frozen and thawing effect counts a lot as well. Nevertheless. the influence of latter was neglected frequently before. In the past decades some researchers cast light on the transference of soil water and under the condition of frozen and thawing region, however the research preoccupy in the feature illustration. The works about the mechanism of the transference in songnen plain remains rare . In this paper, I analyzed the feature of transference of soil water and salt element in the alklization of songnen plain. Some ion transference process illustrations and the corresponding thermal mechanisms are proposed . As the forthcoming of Spring, the temperature ascend distinguished. The frozen soil cast in the thawing process from the upper soil layer. Due to the unosmatic of frozen soil ,the part of thawed soil water stay on the frozen soil layer and formed over-saturation soil water, which contribute the main cause of accumulation of soil salt ion in Spring. The precipitation amount in the whole Spring is only 49 mm which merely occupy the 11.5 percent of annual precipitation. On the other hand, the potential evaporation rate exceeds the actual rainfall. The effect of strongly evaporation simulate the transference of the accumulation of soil salt in the frozen layer to the surface of soil. When Summer is coming, the rainfall peak ensues, the total precipitation from June to August hold the high percentage of 71.2. The frequent of rainfall and the following of draught bring about the soil salt ion fluctuation. In Fall the total precipitation descend obviously, in comparison to Summer. The potential underground water is abstracted by evaporation through pore of soil gradually, then the attribute of potential underground water will indicate the degree of alklization. Apart the accumulation period in Spring and Fall, the effect of the frozen and thawing contributes a lot to the soil ion transference. The reason for the effect of the frozen and thawing lies in the grad of temperature between the frozen soil layer and the warm soil layer, which cause the soil water potential grad. The underground water and salt ion are abstracted through the pore by the soil water potential grad and temperature grad to the surface of soil. Besides, part of soil water remain unfrozen ,which still can transport freely ,even under fierce frozen condition. The unfrozen water keep the source water transference in Winter. Vast salt ion is accumulated in the surface in frozen season. From the angle of thermodynamics, the cause of the transference of soil water and salt ion in the system of alklization soil consist in the unbalance condition of soil water potential. Such unbalance is caused by physical and chemical effect. For the unfrozen soil apart, the force of movement of soil water and salt ion consist of both the gravitational grad and chemical potential grad. As far as the frozen soil is concerned, the chemical of unfrozen is a function of the temperature and the amount of unfrozen water. In conclusion, the temperature plays a significant role for the phase change of soil water and constraint role the soil water potential.