Updating the classification system of Russian soils as a preliminary procedure to the development of its new version is provided by new data, extensive testing of the system in terrain conditions, online and offline discussions, validation in the course of cartographic works, and addressing to the international experience. The first step in updating—analysis of diagnostic horizons as basic elements of the system—comprised scrutinizing the array of horizons, checking their essence, and improving the scheme of their presentation in the system, which is believed to be more convenient and up-to-date. Eleven horizons were moved to a lower category of diagnostic properties. However, it was proposed to enlarge the set of human- modified horizons by introducing the technogenic horizons in addition to the agrogenic horizons, to add a special chernozemic horizon (like chernic horizon in the WRB), and to separate the mesotrophic peat horizon from eutrophic and oligotrophic peat horizons. In the definitions of diagnostic horizons, more strict and formal criteria were formulated along with descriptive characteristics of pedogenesis and the environment. Hence, the volume of definitions of diagnostic horizons increased by approximately three times on the average, while the definitions of diagnostic criteria were preserved intact. Names or symbols were modified for several horizons. As a result, the total number of diagnostic horizons decreased from 51 in the former version-2008 to 47 in the proposed updated version. This paper presents the updated list of horizons and three examples of their revised definitions in the expected updated version. The article provides a proposed general list of diagnostic horizons and 3 examples of new horizon descriptions.

The aim of this analytical review is to systematize information on the quantitative characteristics of variation in the content and stock of organic carbon (C_org) in soils. The review considers the estimates for validity and reproducibility of determined C_org values, as well as the spatial variation and heterogeneity of C_org at different hierarchical levels of the soil cover composition and their changes in time. The most powerful factor of C_org changeability in soils is spatial variation. The absolute standard deviation and coefficient of variation for C_org content and stock in soil shows the trend of an increase with the logarithm of the examined plot area. This trend is observed on the background of a wide range of the values of the indicators of spatial C_org variation in each narrow range of the plot area, which leads to a high uncertainty of the estimates with an increase in the area coverage. Direct dry combustion is considered the preferable method among the methods used to determine C_org content. This method gives valid (i.e., with the least biases) and well reproducible data. The indirect Tyurin and Walkley–Black methods systematically underestimate the C_org content and their reproducibility is comparable to the amplitude of seasonal dynamics and minimum spatial variation indices within an elementary soil area. The estimates for the long-term trend of C_org content require strict adherence to stringent monitoring conditions over the time intervals longer than 15 years. The spatial variation in C_org stock is more pronounced as compared with C_org content, which further increases the requirements to monitoring.

As part of updating the classification system of soils of Russia, analysis and revision were performed for its three diagnostic elements – horizons, properties and materials – as they are in the versions of 2004 and 2008: Classification and Diagnostic System of Russian Soils and Field Guide for Identification of Russian Soils. Our paper on the proposed changes in the composition, definitions, and indexing of diagnostic horizons was published in this journal earlier (vol. 54, no. 8, 2021), and this paper on diagnostic properties is its continuation. Unlike the descriptions of horizons, the scheme for describing diagnostic properties (qualifiers) has been preserved, although some criteria for their identification have been clarified, 20 new qualifiers have been introduced; some definitions and symbols have been improved. New was the approach to diagnostic properties-qualifiers in terms of their taxonomic functions: they were specified for the levels of subtype and genus. The open character of the system allows the expansion of the number of qualifiers if required, as well as the removal of restrictions on their confinement to certain soil types, which was one of the frequent suggestions of users. It is proposed to introduce a special section in the classification system: “Soil-forming rocks and substrates,” to formulate brief definitions of each one there, and to introduce human-affected and artificial materials. As in the case of diagnostic horizons, the proposals are based on extensive materials—field data, publications, discussion with colleagues, and addressing to the international soil classification. An updated list of qualifiers is attached.

The soil cover of the forest-steppe and steppe zones of the East European Plain is characterized by diverse soil combinations revealed during large-scale and detailed soil mapping against the background of a traditional zonal sequence of dominant automorphic soils alternating from the north to the south and clearly displayed on small-scale soil maps. The composition, configuration and functioning of particular soil cover patterns are determined by the soil forming factors acting within a given area. The elementary soil areas (detailed scale) and elementary soil cover patterns maps (large scale) of the Central Russian, Kalach, and Volga Uplands are created by both traditional and digital soil mapping methods. Low-contrasting soil combinations with the background Haplic Chernozems (Loamic or Clayic, Pachic) alternating with zooturbated Haplic Chernozems (Loamic or Clayic, Pachic) on convex elements of the microtopography and Luvic Chernozems (Loamic or Clayic, Pachic) on concave elements of the microtopography prevails under conditions of thick clay loamy parent materials and free drainage. Under conditions of shallow embedding by low-permeable clayey sediments, the soil cover includes Chernozems or Chernic Phaeozems with stagnic features in some part of the soil profile or even Mollic Stagnosols. The presence of shrink-swell clays of different ages leads to the formation of Bathyvertic Chernozems, Vertic Chernozems, Vertic Chernic Phaeozems and/or Pellic Vertisols. The presence of soluble salts in the parent material leads to the development of solonetzic soil complexes consisting of Protosodic or Sodic Chernozems and different types of Solonetzes.

A digital version of the map of salt-affected soils on a scale of 1 : 2.5 M has been used to calculate the areas of these soils in the four federal okrugs (the Southern, Central, Volga, and Northwestern) of European Russia. The total area of soils with soluble salts in the upper meter reaches 23.3 million ha. More than half of them are solonchakous soils (with soluble salts in the layer deeper than 30 cm), and about 25% are saline from the surface. Soils of sulfate and chloride-sulfate salinization predominate (>50% of the area of salt-affected soils). Alkaline soda-saline soils and soils with the participation of soda comprise about 6%. We consider this value to be underestimated and requiring refinement, because soils of solonetzic complexes with neutral salts in the upper horizons may also contain soda in the solonetzic and subsolonetzic horizons, which was not always taken into consideration upon assessing the chemical composition of the salts. Solonetzes proper and solonetzic soils predominate among the salt-affected soils in the European part of Russia. The area of solonetzes is up to 9.4 million ha. The area of solonetzic soils (including solonetzic soils with salts in the layers of 0–100 and/or 100–200 cm) is 15.5 million ha. The highest percentage (32.2%) of salt-affected soils is in the Southern federal okrug.

A review of the systems of symbols used for designating the soil horizons and properties identified in the course of profile descriptions has been made with emphasis put on their genetic meaning, adeq