Physical properties of soils with features of ancient pedogenesis in Barnaul Ob region (Altai territory, Russia)
The study is devoted to identifying the specificity of the physical properties of soils containing a set of modern and Pleistocene horizons in a single profile. Soils located on the key area Volodarka in the left-bank part of the Ob region south of the Alei river mouth, on the territory referred in the literature as Barnaul Ob region are considered as the objects. The soils have features of ancient pedogenesis within the 1.5-2.0 m thickness of the profiles in the form of Pleistocene paleosol horizons located at different depths from the lower border of the modern chernozem. According to the literature, they belong to the Belovsky pedocomplex (corresponding to the stage MIS 17). It consists of three paleosols, which position is clearly traced in the outcropping of deposits of the Ob River. The physical properties of chernozem, formed on thick loess deposits, are considered for comparison. A factual analysis of the obtained data characterizing the particle size distribution, microaggregate composition, bulk density and solid phase density, as well as the parameters of porosity, structure, fineness and aggregation calculated on their basis is given. Comparison of soils with features of ancient pedogenesis and without them showed that the latter have very similar physical parameters to modern horizons formed in the upper part of all studied complex soil profiles: according to their particle size distribution, they can be classified as clay-coarse- silty with the content of clay particles in the absolute majority cases no more than 20-30 %; with a predominance in the micro-aggregate composition of fractions 0.25-0.05 mm and 0.05-0.01 mm, having a high microstructure and very high microaggregation. Paleohorizons differ from modern ones in a heavier particle size distribution, representing a coarse silty-clay light clay, with a lower (not exceeding10-12 %) content of clay particles in the microaggregate composition, which indicates a low potential of paleosols for structuring. In general, paleosol horizons differ from modern ones in higher density, lowerporosity, unsatisfactory microstructure, and very weak microaggregation. Receipt and analysis of thephysical properties of paleosols revealed further evidence of the specificity of soil formation in the territory, where the horizons of modern soils and paleosols are in a single space of the profile.