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

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