The thermal conductivity of soil under a given set of conditions is most important as it relates to a soil's microclimate. The early growth and development of a crop may be determined to a large extent by microclimate. The effect of bulk density, moisture content, salt concentration, and organic matter on the thermal conductivity of some sieved and repacked Jordanian soils was investigated through laboratory studies. These laboratory experiments used the single probe method to determine thermal conductivity. The soils used were classified as sand, sandy loam, loam, and clay loam. The two salts used were NaCl and CaCl2, while addition of peat moss was used to increase the organic matter content. For the soils studied, thermal conductivity increased with increasing soil density and moisture content. Thermal conductivity ranged from 0.58 to 1.94 for sand, from 0.19 to 1.12 for sandy loam, from 0.29 to 0.76 for loam, and from 0.36 to 0.69 W/m K for clay loam at densities from 1.23 to 1.59 g cm−3 and water contents from 1.4 to 21.2%. The results also show that an increase in the amount of added salts at given moisture content (volumetric solution contents θ ranged from 0.03–0.12 m3 m−3 for the sand and from 0.09–0.30 m3 m−3 for the clay loam) decreased thermal conductivity. Increasing the percentage of soil organic matter decreased thermal conductivity. Finally, it was found that the sand had higher values of thermal conductivity than the clay loam for the same salt type and concentrations.

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