Assessment of the Microstructural Stability of Genetic Horizons of a Typical Podzolic Soil Using Oscillatory Amplitude Sweep Test

Rheological studies of soil samples with the use of oscillatory amplitude sweep test (AST) method on a HAAKE MARS 40 (Thermo Scientific, Germany) modular rheometer are analyzed. Podzolic soil with a microprofile of podzol (Dystric Albic Retisol) developed on mantle loams in the middle taiga zone of the Komi Republic, near the city of Syktyvkar was investigated.The relevance of this work is determined by the need to standardize the methodology for rheological soil studies to obtain reliable data comparable with the results of other research teams. The rheological properties were assayed at the maximum capillary saturation with the use of ground and sieved soil samples compacted to the bulk densities close to native field values and their noncompacted analogues. The use of compacted soil samples reflects the microstructural state of soils in their natural undisturbed state. The upper eluvial horizons (EL[e–hf]–ELf) are the least susceptible to changes in the micromechanical characteristics during the standard soil preparation for analysis. On the contrary, the compacted samples of illuvial (BT) and transitional (BC) horizons exceed the noncompacted analogues in soil strength parameters (G', τL, and τmax) by an order of magnitude and in the parameters of elastic and plastic deformations (LVE–range and Crossover) by two–four times. The horizons with high content of Al–Fe-humus compounds (ELf and BEL) are the exception; standard preparation of samples from these horizons for rheological analysis causes an irreversible loss in the strength of bonds between soil particles. The main factors influencing the rheological behavior of the samples from different genetic horizons of podzolic soil are their particle-size distribution, the content of exchangeable bases, and the content of organic and organomineral Al–Fe-humus compounds. These factors in combination with the bulk density influence the moisture content of the soil samples and, hence, the contact area and the number of contacts between soil particles. This can either decrease or increase the soil microstructure stability in the samples from the same horizon depending on the sample preparation for the experiment.