Change in Soil Temperature Depending on Surface Heat Flow

Abstract

Distribution of temperature waves at soil surface and subsurface layers depends on thermal properties (soil heat capacity, diffiisivity and conductivity etc.) and surface heat flow, as well as basic soil properties. In this study, (i) change in soil surface temperature was examined according to solution of heat conductivity equation and Fourier law in case of constant heat flow on soil surface, and (ii) surface heat flow of soil was described analytically as a function of surface and sublayers temperatures, heat diffiisivity and time. During the experimental period, mean soil temperature at the surface and 10 cm depth varied between 18.5 °C and 33.1 °C. where the mean thermal diffusivity coefficient (a) in this layer was 0.671 · 10 -6 m 2 sec -1 . The mean of specific and volumetric heat capacities of dry soil were 0.188 cal gr -1 °C -1 (or 786.800 J kg -1 °C -1 ) and 0.211 cal cm -3 °C -1 respectively. Soil volumetric moisture content (Wθ), volumetric heat capacity (C <inf>h,t</inf> ) associated with moisture content, thermal conductivity(λ) were 0.311 cm 3 cm -3 , 0.522 cal cm -3 °C -1 (or 2.182 · 106 Jm -3 °C -1 ) and 1.476 wattm -1 °C -1 respectively. The heat flow at the soil surface varied between 25.638 and 239.742 wattm -2 changing from surface to deeper soil layers during 09.00-15.00 hours, whereas during 15.00-17.00 horns heat flow varied between -27.725 and -12.473 wattm -2 changing from lower to upper soil layers. Mean relative errors between measured and predicted soil surface temperature values were 7.10%. Predicting surface temperature changes of soils mathematically, and determination of numerical values of thermal properties is one of the necessary stages for modelling soil temperature, and important for monitoring the effect of soil management on soil temperature in both humid and arid regions with consideration of climate change. © 2019, Centenary University. All rights reserved.