Features of the mineralogical composition of solod and solod meadow-chestnut soil, the case of soils of the liman depression at Dzhanybek research station of the Institute of Forest Science RAS

Abstract

The structure of the soil cover at the territory of the clayey semidesert of the Northern Caspian Sea is represented by triparted soil complex and peculiar soils like solod. Solods are formed in relief elements that are constant for this territory – mesodepressions, which are referred to limans. Two soil profiles were studied in the bottom of the liman – solod, and on its peripheral part – solodized meadow-chestnut soil. The formation of the solod profile occurs because of periodic moistening with fresh water and systematic flooding during the snowmelt period. The second soil is in the zone of transit of surface water to the liman. The soil profiles have the same type of eluvialilluvial distribution of the clay fraction, while differentiation is more distinct in solod. Mineralogical analysis established the same type of qualitative composition of clay and clastogenic minerals in both soils. Clay minerals are represented by illite, smectite, mixed-layer illite-smectite, accompanied by kaolinite and chlorite. Clastogenic minerals are represented by quartz, mica, K-feldspar, plagioclase, and chlorite. Quartz and feldspars are accumulated in the solodized horizons of the soil profiles; the content of quartz and feldspars decreases in the textural horizons, while the content of mica and chlorite increases. The distribution of the smectite phase in the solod profile reveals a difference in the ratio of illite-smectite packets, structures with a low content of smectite packets predominate in the solod part of the profile, and the proportion with a swelling packet in mixed-layer minerals increases in textural horizons. The solodized meadow-chestnut soil is distinguished by a smaller thickness of the solodized horizon, a higher content of the smectite component, and a calm character of the profile differentiation of clay and clastogenic minerals. In both soils, labile minerals with signs of superdispersion are recorded in the solodized and textural horizons. The superdispersion of labile minerals has different causes. In solod, it is associated with the action of low-mineralized water and the hydrolysis of soil minerals during the wet seasons of the year, as well as with the intense regime of intrasoil weathering in situ, and in the solodized meadow-chestnut soil, with the passage of the stage of solonetz soils. Differences in the smectite component were also revealed: in the solodized horizons of solod, it is represented by individual smectite and the mixed-layer phase of illitesmectite; and in the meadow-chestnut soil – by mixed-layer illite-smectite.