Apparent Thermal Conductivity of Rice Stems in Relation to Transpiration Stream

Abstract

The energy balance of stems of rice plants provided a method by which the apparent thermal conductivity of the stem can be evaluated in relation to the rate of water flow in the stem. In this method, the influence of sensible heat transfer between the stem surface and ambient air on the propagation of temperature wave in the stem was taken rigorously into consideration. Water loss evaluated from the theoretical relation was found to agree well with the transpiration loss of water measured directly by weighing potted rice plant. This good agreement indicates that the newly developed method could be applicable to the measurement of the apparent thermal conductivity of the stem and the rate of upward flow of water in the stem due to transpiration. The apparent thermal conductivity of the stem increased with the increment of the rate of upward water flow in the stem, particularly in a range of water flow higher than 0. 003 cm/sec. This implies that the influence of cool flooding water on the thermal regime inrice plants becomes larger in daylight hours than at night. The method was also used to make clear the diurnal course of the rate of water flow in the rice stems under field conditions. © 1979, The Society of Agricultural Meteorology of Japan. All rights reserved.