4.3 Implications for degraded farmland wind erosion management
The freeze-thaw cycle is an important factor influencing soil water conditions in agricultural areas and can considerably change the physical properties of the soil (Viklander, 1998). Freeze-thawing cycles increase the possibility of soil erosion by destroying soil bonds (Ala et al., 2016), especially in farmland areas subjected to wind. In terms of practical applications, some studies attempted to use water migration during seasonal freeze-thawing to improve the farmland and woodland water status in spring (Pei et al., 1994). Freeze-thawing can also destroy the structure of soil aggregates, thereby reducing soil strength, decreasing nutrient availability, and reducing soil compaction (Sjursen et al., 2005), thus changing vegetation coverage in the long term and facilitating wind erosion (Yamazaki et al., 2006). Some studies have shown that the freeze-thawing cycle increases soil erodibility (Bryan, 2000; Gao et al., 2018). For example, in a study by Ban et al. (2016), soil erodibility increased after freeze-thawing compared with non-frozen soil. In our study, the surface layer of the soil maintained a water content of 14% prior to freezing.
Soil water expands when frozen, which increases soil porosity and reduces the agglomeration of soil particles. After thawing, the soil generally becomes looser, facilitating wind erosion. Soil freeze–thawing cycles vary with soil types and depths. Seasonal and daily temperature changes caused soil to freeze and thaw repeatedly from upper to deeper layers. Fluctuations in surface soil ST were observed in our study and elsewhere; they can significantly change soil texture (Jamshidi et al., 2015; Gullu et al., 2014). In addition, windy weather in spring also increases the probability of dust events caused by wind erosion (Sun et al., 2019). Along with water migration, soil salt can accumulate and move upward continuously along the channels in the soil (Xue et al., 2017; Hansson and Lundin., 2006), resulting in soil salinization. Especially during freezing, salt migration effects are most significant (Hou et al., 2020), with profound impacts on crop growth. However, soil compaction reduces the occurrence of wind erosion. The C/N cycles and soil wind erosion are strongly interrelated (Quinton et al., 2010). Specifically, soil erodibility increases with freeze-thawing, which further increases the horizontal migration of carbon and nitrogen. The movement of soil particles in the upper layer increases the accumulation of organic carbon, thereby reducing its decomposition. In addition, the increase in surface SWC due to the freeze-thawing will reduce the need for spring irrigation.