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 distu rbance was done by mechanically destroying soil aggregates, and the st ructured soil was obtained by subjecting the disturbed soil to several irrigation and drying cycles. In all soils, five harmonics of a Fouri er-series representation accounted for greater-than-or-equal-to 99% of the variance of daily soil surface temperatures, and two to three har monics 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 th e harmonic method, was higher in the structured soil than in the distu rbed soil. The same was true for the apparent thermal conductivity, si nce the volumetric heat capacities of both the disturbed and structure d soil were similar. The differences in the apparent thermal diffusivi ty and conductivity were attributed to increased heat conduction and w ater vapour transport in the structured soil.