Почвы степей Нижнеоронгойской котловины (Западное Забайкалье)

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The morphological structure, granulometric composition and basic physical and chemical properties of steppe soils in the model site of the Nizhneorongoy Depression (Republic of Buryatia) were investigated on the basis of data from a series of full-profile transects and excavations on petrophytic and meadow steppes. The diversity of steppe areas of the Nizhneorongoy Basin is represented by three types of soils: lithozem, light-humus saline and non-saline, light-humus accumulativecarbonate solonetzic. Lithozems and light-humus soils are widespread in the foothill part of the Khamar-Daban ridge. They are characterized by good aeration, light granulometric composition (sandy, sandy loam), low content of humus and exchangeable cations, dominance of exchangeable calcium in the composition of cations (60-82 % of the sum) typical for steppe type of soil formation, absence of salinization. Differences between lithozem and light-humus soils are expressed in profile thickness, stoniness. Complex neotectonic structure of the territory determined heterogeneity of geomorphologic structure of the inner field of the depression. In its accumulative part there are numerous rises, on which grass steppes grow. Soils of these positions are represented by light-humus saline and light-humus accumulative-carbonate solonetzic soils. These soils have neutral and slightly alkaline pH reaction, higher indices of humus quantity and absorption capacity in comparison with lithozems. The features of these soils are heavier granulometric composition (loam, clay), high share of exchangeable magnesium in the composition of exchangeable cations, carbonation and weak salinization of the lower part of the profile. Salinization chemistry is chloride-sodium and soda-chloride in terms of anions, sodium and magnesium-sodium in terms of cations. In all studied soils there are no median metamorphic horizons. The main soil-forming processes are light-humus accumulation of organic matter, hydrogenic accumulation of carbonates and salinization processes. The diagnostic value of exchangeable calcium and magnesium ratios has been established, which shows steppe (calcium dominance) or meadow (magnesium dominance) trends of soil formation.