Evaluate the Impact of Porous Media Structure on Soil Thermal Parameters Using X-Ray Computed Tomography

Soil thermal parameters are affected by soil texture, soil moisture, and porous media structure. X-ray computed tomography (X-CT) is used for description of soil porosity. The aim of this study was to observe the changes in porous media structure and soil thermal parameters with changes in soil moisture. Moreover, the effect of soil porous media structure, including connectivity and size of pores, on soil thermal parameters was estimated. Soil thermal diffusivity was measured at three different values of soil moisture, whereas soil thermal conductivity and volumetric heat capacity were calculated. Furthermore, the percentages of open, closed, and total porosities, as well as mesopores content were calculated at the same soil moisture using X-CT software programs. The results show that soil thermal parameters decreased along with decreasing soil moisture. In addition to decreasing soil moisture, soil thermal parameters decreased with increasing percentage of total porosity and the content of mesopores. However, the negative correlation between the soil thermal diffusivity and the content of mesopores is weak (r = –0.24). At the same time, a more significant negative correlation coefficient was found between soil thermal diffusivity and tomographic total porosity (r = –0.64) for silty loamy Albic Glossic Retisols. The influence of total porosity on the values of soil thermal diffusivity and other soil thermal parameters is larger than the pore size distribution (mesopores content). Soil heat transfer proceeds through soil particles (solid phase) and is not directly related to pore size distribution. The variations of soil thermal parameters values were in harmony with a quantitative description of soil porous media with the use of X-CT.