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.