Effects of Biochar and Straw Regulation on Snowmelt Infiltration in Seasonal Frozen Soil Regions of Northeast China

In the seasonal frozen soil region of Northeast China, freeze–thaw processes destabilize soil structure and elevate the risk of spring flooding. While biochar and straw are recognized for their ability to enhance soil structure, their regulatory effects on the characteristics of frozen front migration and snowmelt infiltration in this region have not been thoroughly investigated. This study conducted indoor simulation experiments in 2024, establishing three different initial moisture contents (W1: 20%, W2: 15%, W3: 10%) and four distinct regulation measures (CK: blank control, B: 1.0% biochar, J: 0.5% straw, BJ: 1.0% biochar and 0.5% straw) to investigate the influence of various regulation modes on snowmelt water infiltration in freeze–thaw soils. The experimental results indicate that the application of biochar and straw significantly enhances soil aggregate stability, with the BJ treatment increasing small pores by 58.25–60.17% and micropores by 26.69–77.71%. The application of biochar and straw can increase both the migration depth of the soil freezing front and its average migration velocity. An appropriate amount of biochar and straw can enhance the cumulative soil infiltration amount and infiltration rate. Additionally, biochar and straw enhance the relationship between the cumulative soil infiltration amount and the migration characteristics of the freezing front.