Thermal conductivity of mineral soils relates linearly to air-filled porosity

Soil thermal conductivity (lambda) depends largely on the volume fractions of soil solids, air and water. Previous studies focus mainly on developing saturation or soil water content (0) dependent lambda models. There are reports that lambda is correlated more with airfilled porosity (n(a)) than with 0, and the correlation is less affected by solid fraction and lambda of soil solids. In this study, a simple linear relationship between lambda and n a is developed with both newly measured and published datasets. Independent evaluations showed good agreement between estimated and measured lambda values with root mean square errors less than 0.24 W m(-1) K-1, indicating that the linear lambda-n(a) relationship could be used to approximate A from n a with satisfactory accuracy.