In a seasonally frozen soil area, there is frequent energy exchange between soil and environment, which changes the hydrological cycle process, and then has a certain impact on the prediction and management of agricultural soil moisture. To reveal the effects of different modes of regulation on the energy budget of soil in a region with seasonally frozen soil, four treatments, including the regulation of bare land (BL), biochar (CS), and straw (JS), and the combined regulation of biochar and straw (CJS), were used in field experiments. The variations in the soil temperature, liquid water content, and total water content were analyzed, the energy budget of the soil was calculated, the response functions of the soil energy were determined, and the mechanism of soil energy transfer was elucidated. The results showed that, during the freezing period, the JS treatment reduced the amplitudes of the variations in the soil temperature and liquid water content and increased the water content at the soil surface. During the thawing period, the CJS treatment effectively improved the soil hydrothermal conditions. During the freezing period, the heat absorbed by the CS and JS treatments reduced the fluctuation of the soil energy budget. At a soil depth of 10 cm, the spectral entropy of a time series of the soil net energy was 0.837 under BL treatment, and the CS, JS, and CJS treatments decreased by 0.015, 0.059, and 0.045, respectively, compared to the BL treatment. During the thawing period, the CS treatment promoted energy exchange between the soil and the external environment, and the spectral entropy of a time series of the soil net energy was increased; the JS treatment had the opposite effect. The CJS treatment weakened the impact of environmental factors on the soil energy budget during the freezing period, while it enhanced the energy exchange between the soil and the environment during the thawing period. This study can provide important theoretical and technical support for the efficient utilization of soil hydrothermal resources on farmland in cold regions.
Mechanisms of salt rejection at the ice-liquid interface during the freezing of pore fluids in the seasonal frozen soil area
