Tuesday, 11 July 2006

Classification of Taiga Soils Developed in Lithologically Discontinuous Deposits.

Dmitry Kaverin, Institute of Biology, 28, Kommunisticheskya st., Syktyvkar, Russia

Lithologically-discontinued deposits (sands and loamy sands underlain by moraine loams) are one of the most widespread types of quaternary sediments in the North of Europe. Soils developed in lithologically discontinued sediments, are formed at divide ridges under spruce woods. Traditionally, these soils are included in the group of podzolic soils. This classification decision fits the logic of the ecologic-genetic classification of soils of USSR, according to which the zonal position of a soil is the major criterion. The profile-genetic method in study of soil properties allows revealing a diagnostic sign, on basis of which we can classify soils on lithologically-discontinued deposits at high taxonomic level. This feature is presence a texture horizon BT within the soil profile. The automorphic soils having this horizon following to principles of soil classification of Russia are identified as the type of podzolic soils of department of texture-differentiated soils. As the texture of the upper layer of contrasting deposits becomes coarser, the features of clay illuviation (the development of BT horizon) and eluviation of the upper part of the heavy-textured layer become weaker. The automorphic soils having no texture horizon, related to the type of podzols of the department of Al-Fe-humus soils. At the same time, formation of podzols on contrast deposits with heavy-textured lower layer, approaches them morphologically to podzolic soils. Thus, pedogenetic transformation of the upper layer of heavy-textured deposit is accompanied by the appearance of bleached skeletans along fissures and clayey cutans on ped faces. Pedogenetic structuring of soil material similar to that in typical podzolic soils but less expressed. The greatest genetic similarity between podzolic soils and podzols on lithologically discontinued deposits is observed in development Al-Fe-humus differentation. The complete podzol profile and its microprofile forming in podzolic soils are the results of the same processes and differ in thickness only. Thickness and the degree of development of podzolic and Al-Fe-humus horizons increase as upper layer is coarser and thicker. Accordingly to International Abstract Base Soil classification the soils having both podzolic and clay-illuvial (texture) horizons are referred to Albeluvisols. Podzols having no texture horizon are related to Podsols. Soil formation on loose silicate rocks in upland positions within the taiga of European Russia is represented by two different pedogenetic processes: a) Al–Fehumus differentiation (chemogenic differentiation of sesquioxides and organic matter according to the eluvial–illuvial pattern) and b) textural differentiation of the soil profile owing to the selective destruction of clay in the eluvial horizon and the removal of clay from the eluvial horizon (lessivage). Characteristic features of these two major processes are well seen in the profiles of Al-Fe-humus podzols developing from homogeneous sands and texturally differentiated podzolic soils developing from homogeneous mantle loams. Soils developing in lithologically discontinuous deposits can be considered as a transitional group between texturally differentiated podzolic soils and Al–Fe-humus podzols. Using the profile-genetic method within the limits of new Russian soil classification while studying lithologically heterogeneous soils allows to show influence of lithologically discontinued soil forming deposits on soil structure and properties. And to reveal gradualness and continuity of transition from podzolic soils to Al-Fe-humus podzols.

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