What is the relationship between soil density, soil porosity, moisture content, depth and heat conductivity of soils in field?
The thermal properties of soil are a component of soil physics that has found important uses in engineering, climatology and agriculture. These properties influence how energy is partitioned in the soil profile. While related to soil temperature, it is more accurately associated with the transfer of heat throughout the soil, by radiation, conduction and convection.The main soil thermal properties are:
Volumetric heat capacity, SI Units: J∙m−3 ∙K−1
Thermal conductivity, SI Units: W∙m−1 ∙K−1
Thermal diffusivity, SI Units: m2 ∙s−1
Thermal Properties of Soils as affected by Density and Water Content(Biosystems Engineering (2003) 86 (1), 97–102
doi:10.1016/S1537-5110(03)00112-0)
Abstract :Thermal properties dictate the storage and movement of heat in soils and as such influence the temperature and heat flux in soils as a function of time and depth. The ability to monitor soil heat capacity is an important tool in managing the soil temperature regime to affect seed germination and crop growth. The effect of water content and bulk density on the specific heat, volumetric heat capacity, and thermal diffusivity of some sieved and repacked soils was investigated through laboratory studies. These laboratory experiments used the calorimetric method to determine specific heat of soils. The soils used were classified as sand and clay. For the type of soils studied, specific heat increased with increased moisture content. Also, volumetric heat capacity increased with increased moisture content and soil density. Volumetric heat capacity ranged from 148 to 354MJm3 8C1 for clay and from 109 to 304MJm3 8C1 for sand at moisture contents from 0 to 025
(kg kg1) and densities from 1200 to 1400 kgm3. Specific heat ranged from 117 to 225 kJ kg1 8C1 for clay and from 083 to 167 kJ kg1 8C1 for sand at moisture contents from 002 to 025 (kg kg1) and soil density of 1300 kgm3. The volumetric heat capacity and specific heat of soils observed in this study under varying moisture content and soil density were compared with independent estimates made using derived theoretical relations. The differences between the observed and predicted results were very small. Clay soil generally had higher specific heat and volumetric heat capacity than sandy soil for the same moisture content and soil density. The results also show that thermal diffusivity vary with moisture content and soil texture. Sandy soil exhibited a thermal diffusivity peak at a definite moisture content range. Clay soil, however, did not exhibit a sharptherm al diffusivity peak.PDF enclosed
As such soil moisture properties and soil thermal properties are very closely linked and are often measured and reported together. Temperature variations are most extreme at the surface of the soil and these variations are transferred to sub surface layers but at reduced rates as depth increases. Find below a PDF dealing with changes in thermal properties with depth in response to management practices...
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