Changes of Thermal Diffusivity Under Extreme High Soil Temperature.

The amount of hot water used for soil sterilization with hot water is depending on the target depth. The step is used by farmers and the increase in soil temperature is necessary to kill soil pests. That amount of hot water is normally decided by the farmers’ experience. We were going to simulate the changes of soil temperature for each amount of hot water to determine the suitable amount for each soil type and volumetric water content in the soil. However, thermal diffusivity which is necessary to doing simulation has temperature dependence. We measured thermal diffusivity for each temperature. We used Andisol and Toyoura sandy soil. We filled up aluminium cylinder with soil by each bulk density and volumetric water content and heat the cylinder in the water bath. We measured changes of soil temperature in soil sample and estimated thermal diffusivity in each temperature. We raised temperature in water bath with step-size of 10^oC from 30 to 90^oC. In this study, we found the thermal diffusivity has the highest value at soil temperature of 60 ^oC. The thermal conductivity has effect on thermal diffusivity. Based on current study,  additional experiment about temperature dependence of thermal conductivity should be carried out.