Rheological Properties of Taiga Semihydromorphic Soils: Relationship with Physicochemical Properties and Temperature Conditions

The results of rheological studies of semihydromorphic soils of taiga zone in the northeast of the European part of Russia (Komi Republic) on a modular rheometer MCR-302 (Anton Paar, Austria) by an amplitude sweep test (oscillatory method) are considered. Rheological studies of soil samples have been performed with plate-plate measuring systems at maximum capillary water saturation. The strongest interactions between soil particles develop in the horizons with the high content of mobile humus compounds (fulvic acids) and Al-Fe-humus complexes (ELhi,g-ELg-CRM horizons). Increased structural stiffness is due to the binding of soil particles with humus substances and Al-Fe-humus complexes with the development of strong interparticle bonds. Freezing-thawing processes are an important factor of changes in rheological parameters. The impact of seasonal freezing on the rheological behavior is most clearly pronounced in the profile of semihydromorphic svetlozems (Histic Gleyic Stagnosols) in their cryometamorphic (CRM) horizons, where increased stiffness of interparticle bonds is due to condensation compaction of soil particles in the course of the long-term development under temperatures close to 0 degrees & Scy; (zero curtain). With an increase in the soil moistening, disaggregation of the mineral mass takes place, which is seen from a significant increase in the plasticity range. Disaggregated soils are more susceptible to erosion, but a thick moss-peat layer forming in the upper part of the profile of semihydromorphic soils protects them from degradation. In the northward direction, from the texturally differentiated soils of southern taiga to the cryomethamorphic soils of forest-tundra, the stiffness and brittleness of interparticle bonds increase, which is associated with a more active input of fulvic acids, including Al-Fe-humus complexes, as well as with a longer freezing of northern soils. It is shown that rheological parameters can be used as additional indicators in the diagnosis and classification of taiga soils.