Effect of Different Chloride Salts on the Transport of Water, Heat, and Solutes in Sandy Soil under Freezing Conditions

Owing to the scarcity of land resources, the rational development and utilization of frozen soil resources and solutions to frozen soil disasters have become extremely important. In this study, a time-domain reflectometer was used to monitor the temperature, moisture content, and electrical conductivity (EC) of sandy soil in the laboratory. Simultaneously, a nonlinear model of temperature, concentration, and EC was constructed to convert EC values into a soil solute concentration to quantitatively analyze solute concentrations. Based on this, the influence of different chloride solutes on the transport of water, heat, and solutes in sandy soil under freezing conditions was analyzed. The experiment results demonstrate that: (1) the concentration of solutes in soil water and its temperature are the main factors that affect the EC. The conversion between EC and concentration can quantitatively analyze the solute changes in the soil. (2) Different types of chloride affect the transport of water, heat, and solute in sandy soil. Compared with NaCl and KCl solutes, MgCl2 solute soil column has a shorter freezing stability time, lower stable temperature, higher temperature drop rate, lower unfrozen water content, and larger variation amplitude under freezing conditions. (3) Compared with MgCl2 and CaCl2 solutes, the concentration of NaCl and KCl solution was more affected by cooling, and NaCl and KCl tended to accumulate in the upper layer obviously. In winter and spring at high latitudes, the sodium and potassium content in surface soil will increase due to the redistribution of salt caused by freezing, which will affect the growth of crops.