An increase in the degree of hydromorphism of Chernozems owing to various natural and human-controlled phenomena (rise in the groundwater level, irrigation) leads to changes not only in the labile soil properties and soil regimes (soil temperature and water dynamics, soil aeration, redox potential, etc.) but also in less labile soil characteristics, such as water-physical properties, composition of exchangeable cations, concentration of soluble salts, iron compounds, content and properties of soil humus, etc. In some cases, certain changes are registered in the stable (conservative) soil features, such as the mineralogical composition and the particle-size distribution. The character of these changes depends on the composition and salinity of irrigation water or groundwater, as well as on the initial soil properties and the specificity of parent materials. The changes are seen not only in the soil properties but also in the entire landscape. Under the impact of increasing hydromorphism, certain subsidence of the surface takes place and the areas with waterlogged soils - "mochars" - are formed. Therefore, these changes should be analyzed with respect to the particular forms of micro- and mesorelief. Typical very deep low-humus heavy loamy Chernozems developed from loesslike loams were studied in the Azov-Kuban Plain, Krasnodar region of Russia. The particle-size distribution andl swell-shrink properties were studied in soil catenas within the areas subjected to secondary hydromorphism in different periods (1, 10, and 20 years). The groundwater in the area is fresh (the salt content is about 0.3-0.5 g/l), with the predominance of calcium bicarbonates. At the first stages, the clay fraction content in the subsoil increased at the expense of silt-size fractions, especially, the coarse silt fraction. This is accompanied by the increase in soil swelling capacity. In the soils of mesodepressions with long-term waterlogging, the soil swelling capacity decreases, whereas the soil shrinking capacity increases. The increase in the clay fraction content at the early stages of the process may be due to disintegration of aggregates cemented by iron hydroxides; under standard pyrophosphate pretreatment, these aggregates cannot be destroyed. In turn, the disintegration of these aggregates in the soil is due to the destruction of cementing iron hydroxides under conditions of the lower oxidation-reduction potential and the microbiological reduction of trivalent iron. Some data attest to the activation of weathering of micaceous minerals in the hydromorphic conditions. In this case, the clay accumulation should proceed at the expense of the fine and medium silt fractions. A decrease in the content of the coarse silt fraction may be due to the dissolution of phytoliths that are numerous in the humus horizons of Chernozems. Their content in the coarse silt fraction is considerable. The dissolution of opal bodies of the phytoliths is enhanced by the shift in the reaction of soil solutions toward more alkaline values due to the sulfate-reduction process (in the case when sulfates are present in the soil water). The silica released into the soil solution during the dissolution of the phytoliths enters the composition of the clay fraction and considerably changes its properties with corresponding alteration of the soil swell-shrink capacity.