Abstract
Seasonally freeze-thaw (FT) processes affect soil salinisation in cold and arid regions. Therefore, understanding the mechanisms behind soil salinisation during winter and spring is crucial for management strategies effectively alleviating this. This study aimed to explore the soil FT characteristics and their influences on soil water and salt migrations to clarify the underlying mechanism of the springtime soil salinisation in the western Songnen Plain, China. The spatiotemporal distributions of soil water and salt, frozen depths and soil temperatures were examined at depths of 0–200 cm in three typical landscapes (farmland, Leymus chinensis (Trin.) Tzvel (LT) grassland and alkali-spot (AS) land) from October 2015 to June 2016. Results indicated that the strongest freezing process occurred in AS land, which was characterised by the deepest frost depth (165 cm) and highest freezing rate (3.58 cm/d), followed by LT grassland, and then farmland. The freeze-induced upward redistribution and enrichment of soil water and salt caused the rise and expansion of the soil salification layer, which was the main source of explosive accumulations of surface salt in springtime. Therefore, the FT processes contributed to the surface soil salinisation and alkalisation. Landscapes also affected soil water and salt migrations during FT processes, with the trend being AS land > LT grassland > farmland.
Highlights
Soil freeze–thaw (FT) cycles is a constantly repeating process of material exchange and energy transfer that occurs in the surface soil and extends downward into the deeper soil layers[1,2]
There are disparities in the literatures regarding the impact of FT cycles on soil salinisation in the study area, which are the subject of active debate and require further study
On 17 March, 2016, the maximum frozen depth occurred in the Leymus chinensis (Trin.) Tzvel (LT) grassland, whereas this maximum occurred in the farmland and AS land at a slightly later date (27 March, 2016)
Summary
Soil freeze–thaw (FT) cycles is a constantly repeating process of material exchange and energy transfer that occurs in the surface soil and extends downward into the deeper soil layers[1,2]. Wang et al (2009)[14] reviewed the causes of soil alkalisation in the Songnen Plain and emphasised that winter freezing led to latent salt accumulations that induced further soil salinisation during the subsequent spring This was consistent with the findings of Zhang and Wang (2001)[12], who demonstrated that soil salinisation occurred as a strong response to freeze–thaw, yet which has been ignored by some s tudies[8]. This study aims to (1) determine the characteristics of soil FT processes as influenced by different landscapes, (2) explore the influences of FT processes on water-salt migration in saline-sodic soil and (3) elucidate the underlying mechanism of soil salinisation-alkalisation during the spring in the western Songnen Plain, China
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