Effects of ridge-furrow topography on soil salinity redistribution under freeze-thaw processes.

Ridge-furrow (RF) cultivation is widely applied in farmlands to improve soil water, heat, and salt conditions and increase crop yields. In cold regions, these farmlands with RF often undergo freeze-thaw processes, while previous studies mainly focused on vertical dynamics of soil water and salt based on the assumption of a flat surface. Based on a well-validated model, this study examined the water and salt dynamics in farmlands with a flat surface and RF topography under freeze-thaw processes. Results show that RF topography promotes the formation of persistent focused downward flow pathways beneath the furrows under freeze-thaw processes. Compared with a flat surface, these focused flow pathways in RF topography markedly change the subsurface flow field and drive faster and deeper downward salt transport. Further quantitative analysis showed that increased ridge height leads to greater downward salt migration, whereas the RF ratio has a negligible influence on salt migration. These findings improve the understanding of topography-controlled water flow and salt transport in seasonally frozen soils and highlight the importance of considering two-dimensional porewater flow when evaluating solute redistribution under freeze-thaw conditions.