Comparative study on thermal properties of intact andrepacked soil samples

Soil thermal properties are essential for studying energy transport in the Soil-Plant- Atmosphere-Continuum. Many laboratory studies have been conducted to investigate the influences of water content, texture, temperature and bulk density on soil thermal properties using repacked soil columns. There are few reports about soil structure effects on thermal properties of intact soil samples. The objective of this study is to examine the influences of soil structure on thermal properties at different water content ranges by comparing thermal properties of intact and repacked soil samples for sandy loam soil and loam soil. Intact soil samples were collected from field and volumetric heat capacity, thermal conductivity, and thermal diffusivity were measured with the heat pulse technique. Subsequently the intact samples were air-dried, crushed, sieved through a 2 mm screen, and repacked into the same cores with identical water content and bulk density. Thermal properties of the repacked samples were then measured following the same procedure. Finally soil water content and bulk density were determined using the gravimetric method. Similar heat capacity values were obtained for repacked and intact soils. For the repacked samples, thermal conductivity of the sandy loam and loam was 9.7% and 9.8%, lower than that of their intact counterparts at intermediate water contents (0.07-0.24 m3/m3 for sandy loam, 0.15-0.31 m3/m3 for loam). Soil thermal diffusivity was increased by the formation of soil structure at intermediate water contents. At the water content near saturation, the intact and repacked samples had similar thermal diffusivity values. In summary, soil structure formation does not significantly affect heat capacity, but increases thermal conductivity and thermal diffusivity, especially at intermediate water contents.