Characteristic of the micromorphological state of the soils of the flood-lands of the Samara river
Authors: Stryzhak O. V. 
Published: February 2020

The main micromorphological properties of the soils of the riverine valleys, the central and the terrain part of the Samara river have been revealed. The main factors that influence the creation of such a micromorphological organization of these soils are revealed. The basic micromorphological features of the soils of the pririal shaft are: plasma-sand microstructure, humus-argillaceous plasma, which is located in the form of films along grains of minerals; poorly developed porous network, represented mainly by pores-packings; weak aggregation of horizons. The fraction of grains of large size dominates in the skeleton. They are characterized by good roundness. The main reason for such a micromorphological organization of these soils is the immediate proximity to the Samara river. Due to the high water, some horizons can be washed off, or on the contrary, they can be washed by new ones due to the deposition of illuvial material. With the distance from the river and, accordingly, with the decrease in the influence of flood, the biological influence (forest vegetation and the activity of soil organisms) on the micromorphological properties of the soils of the central floodplain increases. This manifests itself in good structuring, developed pore network of upper horizons, presence of organic residues at different stages of decomposition. In the profile, microstructure is inhomogeneous, in the upper horizons it is dusty-plasma, with depth changing to sand-plasma and in the lower horizons – plasma-sandy. Skeletal grains are characterized by traces of transport on their surface (scratches) and good roundness. The plasma is humus-clay, with a share of clay plasma decreases. The clay part of the plasma is characterized by birefringence, orientation and the ability to rebuild. The pore space is most developed in the upper horizons due to burrowing activity of earthworms. With depth, the pore area decreases, often their walls are covered with clay kutans due to illuvial processes. The formation of the profile and the characteristic micromorphological organization of the soils of the central floodplain passed in several stages. The heavier fractions of the illuvial material were deposited on the underlying rocks with the weakening influence of floodplain processes. This can explain the great difference in the content and size of grains of minerals in the upper and lower horizons. Over time, the influence of forest vegetation and the burrowing activity of soil animals create entire coprolite horizons, which leads to an improvement in air and water conditions. The soils of the flood-lands of the Samara River are characterized by the presence of a large amount of plant residues in the upper horizons and a low content of grains of the skeleton. With the depth the plant residues gets less, and the grains of minerals gets more. The profile is characterized by the presence of a large variety of kutans. Specificity of micromorphological organization of soils of the terrain part of the flood-lands of the Samara River is due to the influence of forest vegetation, the close occurrence of groundwater and dynamic oxidation-reduction processes.