Journal of the Japanese Society of Soil Physics

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Agriculture in Okhotsk-Abashiri region, Hokkaido, Japan has been led by large-scale upland farming systems, and seasonally frozen soil has occurred in this area. Recently, there is a concern that the hydrological environment in this region has been changing due to changes in both rainfall and snowfall patterns associated with climate change. In the current study, continuous monitoring of soil water movement was undertaken in an upland field in this region during the period from July 2011 to June 2012. Particularly, this study focused on clarifying characteristics of the soil water movement caused by soil freezing-thawing and infiltration of snowmelt water. Dielectric water potential sensors were used for measuring soil matric potentials to derive water flux at deeper soil depths. The annual maximum soil frost depth was 0.28 m. The maximum surface soil water content was observed immediately after surface soil melted. The magnitude of downward water flux at a depth of 0.40 m recorded in early April (freezing period) was higher than the magnitude recorded in June (non-freezing period) with large amount of rainfall. Changes in soil water content at deeper layer due to the soil freezing and snowmelt water infiltration were similar to changes of soil water content resulting from drying followed by rainfall infiltration in nonfreezing period. Further, it is revealed that all snowmelt water (116.5 mm) infiltrated into the soil without ponding before the frozen soil layer melted. The results suggest that the soil frost with a depth of 0.28 m observed in the current study was insufficient to impede the infiltration of the snowmelt water associated with high porosity of the soil.

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