The technique of numerical analysis of three-dimensional tomographic images of the pore space of soil objects has been used in this paper. It applies methods of integral geometry, topology and morphological analysis. To characterize quantitatively the transformation of the pore space structure, tomographic images of four undisturbed soils were analyzed, i.e., heavy loamy agro-gray soil (Retic Phaeozem), agromineral (Sapric Rheic Mineralic Histosols), and hypnum (brown moss Sapric Rheic Histosols) peat soils in dry and wet conditions. For samples of the subplow horizon in agro-gray soil, a decrease in both Betty numbers was observed on wetting, where the zero number ( b 0 ) stands for the amount of topologically simple closed pores, and the first number ( b 1 ) indicates a decrease in pore connectivity, which varies in a narrower range of pore sizes as compared to b 0 . When a sample of agromineral peat soil is moistened, the Euler–Poincaré characteristic is negative ​in the pore range of 0.1–0.16 mm, which points to the predominating complicated branched structure of the pore space and high pore connectivity. When hypnum moss is saturated, a lot of tunnel pores get narrower (“collapse”), and the connectivity decreases due to the structural specifics of long-stemmed plant residues. The number of pores and connections between them in peat soils is an order of magnitude higher than those in the subplow horizon A of the agro-gray soil. The provided quantitative changes in the considered parameters of tomographic images of the soil pore space confirm the possibility of applying them for estimating the transformation of the pore space in soils.

The temperature regime and the dependence of thermal diffusivity on the volumetric water content in high-ash drained peat soils (Sapric Drainic Histosols (Lignic)) on woody peat underlain by grass, sedge, and woody peat layer in the Yakhroma River valley (Moscow oblast) were studied in terrain and laboratory on undisturbed samples. In the laboratory, the dependences of thermal diffusivity were determined in the course of sample drying by the Kondrat’ev method (a steady-state radial heat flow); whereas the terrain dynamic data on the daily temperature variations were used to solve the inverse problem by the heat wave method. The dependences obtained by laboratory and field methods showed a dome-like shape, the maxima of which were close (at the volumetric water content equal to 57–60%), but the thermal diffusivity obtained from the terrain data was 1.2 times lower at the maximum point. Considering the further use of dependences in predictive mathematical models, approximation of the curves by the method of Chang and Horton made it possible to evaluate the accuracy of the approximation parameters and to compare them. According to the laboratory method, the approximation errors grew reliably with an increase in the measured thermal diffusivity, which points to a systematic error in the laboratory measurement of the latter as dependent on the water content; this effect was not registered in the field method. The systematic errors in laboratory studies must be associated with shrinkage and vapor transfer.

The water retention curve (WRC), density, botanical composition, and ash contents were determined for high-ash lowmoor peat soils (Rheic Sapric Histosols) developing on the floodplain of the Yakhroma River (Moscow oblast) from the herb–hypnum and hypnum peat enriched in carbonates, agromineral peat soils (Rheic Drainic Sapric Histosols (Mineralic)), and peat soils developed from woody peat underlain by herb, sedge, and woody peat layers (Rheic Sapric Histosols (Lignic)). The WRC was determined by capillarimetric method in the range of water pressure from 0 to 80–90 кPa. For the studied peat soils, the WRC represents a close to linear dependence of the water content on the water pressure in semilogarithmic scale. In contrast to mineral soils, a characteristic point of the air-entry pressure is virtually absent on the WRC of peat soils. The WRC of peat largely depended on their density: denser peat samples were characterized by a higher water content at the same water pressure, which attests to the increased water retention capacity. An increase in the degree of decomposition of peat and its ash content also leads to the rise in the water retention capacity, but the effect of these factors is considerably smaller than the effect of peat density.