On the measurement of soil water by the thermal conductivity
Shyunji Yamaguchi · Journal of Agricultural Meteorology · 1950
The thermal conductivity of the soil changes by difference of the soil water. So, as a method of measuring soil water without sampling, author made an apparatus as follow and instlled it in the soil. The apparatus consists of cylindrical source of heat and two-points of measuring temperature in a certain distance from it. In the constant flow of the thermal current, calory and difference of the temperature between the two points in the soil was measured, and then the thermal conductivity was calculated.There was logarithmic relation between the thermal conductivity of the soil and the soil water. Namely the rising tendency of the thermal conductivity by the soil water was weak at the moist area and strong at the dry area. So the measurement was undertaken easier in droughter condition of the soil, but difficult in the moist soil without raise the degree of precision of the temperature measurement. The error was caused mainlly by the difference of the appearent specific gravity of the soil, especially in droughter condition.