Combined impacts of freeze–thaw processes on paddy land and dry land in Northeast China

• Freeze–thaw characteristics in the paddy land are different from that in dry land.
• The paddy land has a larger water migration and accumulation than the dry land.
• The initial water condition has significant impacts on soil hydrological pattern.
• An increase of water content after freeze–thaw process may occur in the environment.
• The paddy land can be selected as a pivotal source for the water management.

The quantity of spring snowmelt infiltration and runoff, which affects the hydrology of the freeze zone, depends on the antecedent soil water content (SWC) conditions at the time of the soil's freezing. An understanding of the characteristics of frozen soil is essential for spring sowing in the agricultural freeze zones. The main goal of this study was to evaluate the differences in the freeze–thaw process and the freeze–thaw-induced water redistribution between the paddy and dry lands in a freeze zone. For this purpose, a field study was conducted in the winter of 2011–2012 for two types of farmlands in Northeast China. To illustrate the soil's frost dynamics over time, the measured SWCs at different depths (15, 30, 60, and 90 cm) were transformed into different expressions including the SWC dynamic, the frozen soil's profile, and the freezing and thawing front trace. The freezing characteristics in the paddy land, in contrast to that in the dry land, had a higher freezing point temperature, a larger amount of water movement to the upper layer, and a 2.76 mm larger accumulation of water in the upper layer. However, the increase of SWC (which is equivalent to thawing) was evidently faster than the decrease of SWC (which is equivalent to freezing). The water in the frozen soil's profile was most likely redistributed towards the freezing front before soil temperature (ST) falls below the freezing point. The findings may partially explain the soil's freeze–thaw characteristics for the different stages as well as the combined impact of these characteristics with farmland use types on soil hydrology; the findings may also provide a foundation for forecasting the hydrologic response of the freeze–thaw process and provide guidance for management strategies dealing with seasonally frozen agricultural soils.

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