Clarification of a role of unfrozen water on water movement of freezing and thawing of soils in agricultural area of cold region under climate change.

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Contribution of both the matric potential and osmotic potential on depression of the water potential of frozen volcanic ash soils associated with soil freezing was assessed in Abashiri region of Hokkaido Prefecture, Japan. The effect of the osmotic potential was negligibly small when EC_<1:5> was less than 0.17dSm^<-1>. Using those results, in-situ monitoring of matric potential was conducted, and changes in the matric potential of frozen soil layer were compared with that of unfrozen subsoil. It is revealed that the matric potential of unfrozen subsoil associated with changes in the matric potential of the frozen soil layer. The matric potential of frozen soil layer was considerably smaller than that of unfrozen subsoil.