Quantification of the Parameters of Zones and Facies of Chestnut Soils in Russia on the Basis of the Climatic-Soil-Textural Index

This study is an attempt to quantify parameters taken into account in separation of the dry steppe soil zone. A detailed analysis of the maps of zoning, vegetation, land use, and soils has made it possible to suggest quantitative criteria of the dry steppe soil zone in Russia and to gain a better correlation between the calculated boundaries of this zone and the maps of vegetation, land use, and soils. Except for the East European Plain, boundaries of the dry steppe zone with chestnut soils do not coincide on different maps of zoning. Climatic parameters—the sum of active temperatures, the humidity factor, and the continentality coefficient—are the main factors specifying the spatial pattern of soil zones and facies on the maps of zoning. Soil characteristics—texture and water-physical properties—play a subdominant role. It is argued that data on the texture, water-physical properties, and solonetzic properties of soils should be taken into account in separation of the dry steppe zone as the factors controlling the depth of soil moistening and the reserves of productive moisture. Together with the accumulated sum of active temperatures, they specify the development of dry steppe vegetation and, hence, the boundaries of the dry steppe soil zone. A new indicator—the sum of monthly excesses of precipitation over evapotranspiration—should be calculated with due correction for the soil texture, solonetzic properties, and the content of carbonates. In combination with the accumulated sum of active temperatures, this indicator makes it possible to perform a detailed zoning of the area of chestnut soils on a quantitative basis and to separate cryoarid areas (cold semideserts) and semideserts with chestnut soils. Soil zones and facies determined with the use of this indicator are in good agreement with geobotanical maps and maps of land use.