Abstract
Field experiments were conducted during two winters to examine the influences of the frost soil structure on snowmelt infiltration at an agricultural field of volcanic ash soil in Tokachi, Hokkaido, Japan. Two experimental plots were prepared. Snow on one plot was removed to deepen the soil freezing (treatment plot ; TP). Snow on the other plot was left in its natural condition (control plot ; CP). During the first winter, frost depths were 27cm for CP and 52cm for TP. A concrete-like structure (Concrete frost) was formed throughout the frozen layers. When snow disappeared, surface ponding was observed for Concrete frost, indicating interference of snowmelt infiltration by soil freezing, irrespective of the freezing depth. During the second year, in contrast, soil to a depth of 20cm exhibited a honeycomb-like structure (Honeycomb frost), which included numerous macropores. Snowmelt water infiltrated freely to a frost depth of 22cm through the Honeycomb frost for CP. In contrast, surface ponding appeared for TP after collapse of the honeycomb structure at a shallow depth because of the interference of snowmelt infiltration by the Concrete frost that formed below 20cm depth. Results suggest that the frozen soil surface structure and deeper parts of the frozen soil structure are important to evaluate snowmelt infiltration into the frozen soil under field conditions.
