Effect of freeze-thaw processes on soil water transport of farmland in a semi-arid area

Seasonal freeze-thaw processes affect soil water migration and distribution, especially in semi-arid agricultural areas. These processes play an important role in mitigating harsh environmental conditions and wind erosion. Soil water content (SWC) and soil temperature (ST) were monitored at different depths (0–2 m) and investigated under freeze-thaw conditions from November 2018 to May 2019 in a semi-arid agro-pastoral region of northern China. The initial SWC was the main factor that affected the freeze-thaw process. During the freeze-thaw process, differences in soil thermal conductivity caused the soil to thaw faster than the freezing process, and the upper soil layer (0–60 cm) was significantly affected by temperature changes. Changes in the potential energy of water and pore pressure gradient caused the migration of soil water to the upper layer, which led to a slight decrease in SWC in each layer before ST dropped to the freezing point. The vertical migration distance of soil water exceeded 70 cm, and the SWC above a depth of 100 cm increased significantly, as water was mainly obtained from the soil layer below a depth of 200 cm. Soil compaction was reduced when affected by freeze-thaw processes and the soil particles were more fragmented, leading to wind erosion and dust events. Our results partially explain the occurrence of wind erosion in spring and provide a scientific basis for predicting soil water status and appropriate farmland management strategies.