Thermal Diffusivity of the Cryomorphic Soils of Steppe Complexes on Limestone

摘要

Thermal diffusivity of the cryomorphic soils formed on limestone in the Orenburg oblast (Russia) has been studied. Soils are identified as cryomorphic basing on the morphological features, such as polygonal microrelief, ground wedges, involutions, accumulations of coarse fraction, and platy structure. The complex soil cover comprises Calcaric Regosols on microhighs, Calcaric Regosols (Ochric) on microslopes, and Rendzic Calcaric Phaeozems in microdepressions. Soils are characterized by high spatial variability of basic physical properties: the soil texture varies from sandy loams to clays and soil bulk density ranges from 1.07 to 1.53 g/cm(3). The objective of present study was to investigate soil thermal diffusivity versus water content dependencies for different soil horizons in the examined complex. Thermal diffusivity was measured using the unsteady-state method in the range from the maximum soil water content after the saturation of samples under pressure to the air-dry state. A relatively low thermal diffusivity (1.53 x 10(-7) to 2.88 x 10(-7) m(2)/s) is typical for humus horizons in a microdepression; the soil horizons on microslope and microhigh have higher thermal diffusivities (1.76 x 10(-7) to 5.06 x 10(-7) m(2)/s). Soil thermal diffusivity positively correlates with soil bulk density, thickness of platy aggregates, and content of limestone fragments (gravel and stones) and negatively correlates with the contents of organic matter and clay.