Alteration of soil thermal properties by structure formation

Temperatures were measured in a disturbed and a structured loess soil to study the influence of aggregation on thermal properties. The disturbance was done by mechanically destroying soil aggregates, and the structured soil was obtained by subjecting the disturbed soil to several irrigation and drying cycles. In all soils, five harmonics of a Fourier-series representation accounted for ≥99% of the variance of daily soil surface temperatures, and two to three harmonics did so below the soil surface. For soil water contents between 0.04 and 0.23 m³ m-³, the apparent thermal diffusivity, computed by the harmonic method, was higher in the structured soil than in the disturbed soil. The same was true for the apparent thermal conductivity, since the volumetric heat capacities of both the disturbed and structured soil were similar. The differences in the apparent thermal diffusivity and conductivity were attributed to increased heat conduction and water vapour transport in the structured soil.