Background Seasonally freeze-thaw cycles significantly influence soil salinization in cold and arid regions. These processes play a critical role in shaping agricultural and ecological environments by altering soil water distribution, heat balance, spring farming practices, and plant germination. Therefore, understanding the mechanisms driving soil salinization during winter and spring is crucial for developing management strategies effectively to alleviate this issue across various landscapes in Songnen Plain of China.
Methods To investigate the mechanisms of salt accumulation in the saline-sodic soils, this study examined five distinct halophytic landscape types from the western Songnen Plain: farmland, Leymus chinensis land (LT), Chloris virgata land (CS), Suaeda glauca land (SG) and alkali-spot land (AS). Soil salinity content, as well as salinization and alkalization indices, were measured at depths ranging from 0 to 200 cm across these landscapes. The relationships between soil salinity, exchangeable sodium percentage (ESP), and environmental factors, including groundwater level, soil temperature, and freezing depth, were analyzed.
Results Freeze-thaw processes induced upward migration and gradual expansion across all five landscapes. During the freezing periods in winter and spring, the freezing rate initially increased and subsequently decreased over time. The freezing rates in SG and AS were 16.80% to 59.11% higher compared to those in FL, LT, and CS. Spring freeze-thaw cycles occurred much more frequently than those in winter cycles. The thawing rate of surface soil was found to be 2.02 to 8.73 times faster than that of deeper soil layers. Furthermore, the thawing rates in FL and LT were 1.05 to 2.07 times higher compared to CS, SG, and AS. These freeze-thaw cycles significantly contributed to surface soil salinization in spring, primarily due to salt accumulation within the frozen layer. The intensity of soil salt migration induced by freeze-thaw processes was influenced by both the landscape type and the initial salt content. Higher salt content led to greater migration intensity, following the order: AS > SG > CS > LT > FL. Furthermore, soil profile salt content and ESP showed an extremely positive correlation with freezing depth (P < 0.01), but a significant negative correlation with soil temperature and shallow groundwater level (P < 0.05).
Conclusions This study elucidates the crucial role of spring freeze-thaw cycles in surface soil salinization, and further demonstrates the close correlation between the degree of soil salinization and land use patterns.
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