Ways to Create Classifications of Soils and Land Resources

Abstract

Abstract—

The possibility of developing algorithms for creating various soil classification systems based on the ideas of soil as a function of the properties of soil horizons (or their morphological elements, morphons), the construction of a soil profile as a given set of horizons (or morphons), and its belonging to a certain group of soil profiles is considered. The fundamental importance of creating a basic classification of soils—the Mendeleev’s soil table—is noted. This classification should be based on a genetic approach and should serve as construction material for any other soil classification. When developing a classification of soil resources, various criteria can be used to identify their groups (classification units): land categories; types of land use; qualitative conditions, ecological state, and administrative belonging of land; subjects of land relations; legal regime of land plots; the degree of contrast in the soil cover; dominant soils and their areas; etc.

APPROACHES TO THE CREATION OF CLASSIFICATIONS OF SOILS AND SOIL RESOURCES

As is well known, classification is “a conventional division of a set of subjects, individuals, objects, phenomena, and processes into groups based on any similar characteristic or several characteristics, regardless of the significance and nature of these characteristics” [16, p. 230]. Moreover, any classification of natural objects not only arranges them into groups (classes) in accordance with certain criteria (developed by the authors of the classification) but also reflects the currently dominant scientific paradigm. Soil classification is a clear and direct confirmation of this thesis.

For a long time, various soil classification systems developed in Russia, starting from the classifications by V.V. Dokuchaev and N.M. Sibirtsev, had a clearly expressed genetic character, since soil was understood as a result (function) of the combined action of various soil-forming factors; later, this was reflected in the well-known formula by the American pedologist H. Jenny [30, p. 16]. Then, this formula was transformed into the SCORPAN model of empirical quantitative description of the relationships between soil and spatially distributed predictors [31].

The Classification and Diagnostics of Soils of the USSR [8], which was the most widely used classification system in Russi, also had a genetic nature. The next soil classification system adopted in 2004 [9], was already largely substantive (based on the characteristics of individual important soil features without special reference to the soil genesis). There is logic in this movement toward substantivity of the new Russian soil classification system; the most important logical argument lies in the convenience of the classification that relies on clearly visible substantive (primarily morphological) features of a given horizon.

Similar trends appeared in world soil science, and have become firmly established by the present time. Thus, the Australian, New Zealand, and many other national soil classifications [29], as well as the World Reference Base for Soil Resources [34], were created based on the American substantive soil classification system [33].

I.A. Sokolov rightly noted that “with the creation of a formalized substantive classification by the Americans, the discussion on the classification problem ceased abroad for a long time… Purely empirical research sharply predominates. Attempts at theoretical generalizations have clearly become fewer…” [21, p. 167].

One of such attempts is the task currently being solved by the International Union of Soil Sciences of creating a novel comprehensive soil classification system—a global (and universal) system that includes a fully populated taxonomic space [29].

Such a comprehensive classification of soils should be a prototype of what is commonly called in Russian soil literature a basic classification of soils, which “will provide material for the construction of classification buildings of any architecture” [21, p. 169].

It should be noted that, given the current digital storage of soil information, any algorithm for generating a soil classification (including the basic one) can be defined. The question is how to properly develop this algorithm.

Representation of soil S in a general form as

1

where a is the properties of the horizon (morphon), b is the construction of the soil profile (the set and order of horizons/ morphons), and c is the belonging of the soil profile to a certain group of profiles, allows us at least to create a set of algorithms for developing new soil classification systems; moreover, it is also possible to determine the main trends in the development of soil science in the field of multi-purpose diagnostics of the state of the soil (as a natural object performing various functions in terrestrial ecosystems; as a means of production and an object of labor in agriculture; as an object of evaluation, including economic assessment; etc.).

Recently, the terms soil resources (SRs), soil-land resources (SLRs), soil and land resources have firmly entered the everyday life of Russian soil science. The Unified State Register of Soil Resources of the Russian Federation [4] was created. Articles, monographs, and textbooks, in which these terms are actively applied, are published [14, 22, 23, 28]. The motto of the VIII Congress of the V.V. Dokuchaev Soil Science Society in 2020 was the resource-oriented phrase “Soils: A Strategic Resource of Russia.” In accordance with [4], “soil resources, by analogy with land resources (GOST (State Standard) 26640-85), can be defined as soils that are used or can be used in sectors of the national economy.” It is also indicated that, currently, land resources in Russia are classified by:

• land categories;

• land use types;

• quality and ecological state;

• administrative-territorial affiliation;

• subjects of land relations and the legal regime [4].

On the one hand, such an interpretation of the concept of soil resources removes the question of the need for their (separate from soils) classification (since soil resources… are soils). On the other hand, it is obvious that the categorical affiliation of land plots/land use types/quality and ecological state of land/administrative-territorial affiliation of land/subject of certain land relations (purchase, sale, lease, etc.)/legal regime of the territory (for example, the legal regime of territories of traditional nature management in places of traditional residence and traditional economic activity of indigenous peoples of the Russian Federation and representatives of other ethnic communities in accordance with Article 7 of the Land Code of the Russian Federation adopted on October 25, 2001 (no. 136-FZ) [6] inevitably leave an imprint on the composition and properties of soils. Thus, if we deal with the legal regime of different land categories/land use types, we should distinguish between specific urban soils (urbanozems), soils of industrial territories (technozems and chemozems (contaminated soils) [1]), and, finally, soils of agricultural lands (agrosoddy-podzolic, agrogray, agrochernozems, etc.) [9]. Thus, we come to formula (2):

2

where SRs denotes soil resources; cat is the land category/land use type; acat is the properties of the horizon (morphon) of soils on lands of a certain category/land use type; bcat is the structure (horizonation) of the soil profile, i.e., the sequence of horizons (or morphons) characteristic of soil resources on land of a certain category; and сcat is the belonging of a given soil profile to a certain group of profiles on land of a certain category/land use type.

In this article, a list of major possible algorithms for creating various classifications of soils and soil resources is considered.

ALGORITHMS FOR CREATING GENETIC SOIL CLASSIFICATIONS

As the development of any genetic classification is based on the assertion that the classified soils have a certain genesis (origin), then formula (2) can be written in the following form:

3

where ag is the properties of the genetic horizon (morphon) (that is, the horizon (morphon), whose formation is specific to a given soil; for example, such properties of the podzolic (eluvial) horizon as whitish color and platy structure); bg is the construction (sequence) of genetically related horizons (for example, E–EB–Bt); and сg is the belonging of this construction of horizons to a group of soil profiles (for example, to the group of podzolic texturally differentiated soils).

Genetic classifications also include situations described by formulas (4) and (5):

4

5

(letter designations in formulas (4) and (5) are the same as in formula (3)).

Formula (4) describes an example of a genetic soil classification system, in which where both the properties of the genetic horizon and the construction of the profile (mutual arrangement, sequence of genetic horizons in the profile) are genetically determined, that is, they are associated with the origin of these soils (or, at least, with our ideas about their origin). Formula (5) captures the situation, where only the properties of the genetic horizon (following the example of the WRB [34] or the 12th edition of the Keys to Soil Taxonomy [32]) are the basis for classification. In essence, such a classification is already partly substantive-genetic, since a significant portion of the characteristics, on the basis of which a soil is assigned to a particular taxon, are not associated with the origin of the soils [9].

ALGORITHMS FOR CREATING SUBSTANTIVE SOIL CLASSIFICATIONS

It is possible to create an essentially infinite number of soil classifications based on the grouping of soils according to various types of their properties (physical, physicochemical, chemical, biological, agrochemical, etc.). In this case, soil systematics and taxonomy should be subordinated to the purposes of the classification.

Production-oriented soil classification systems. The goal of these systems is to classify soils according to characteristics that are important for soil use for a specified utilitarian purpose:

(a) soil use for agricultural production means that soil fertility becomes the main soil characteristic, and soil fertility assessment ends with grouping of the soils according to their suitability for agricultural use; such soil classifications are, as a rule, local (applied to specified territories and a narrow set of purposes);

(b) soil use in those sectors of the economy, where agricultural production is not the main one (classification of soils according to their rheological properties, particle size distribution, etc.).

Environmental (ecological) classifications of soils. Human impact on soils leads to the development of various negative processes that can be subdivided into two groups: pollution and degradation (sometimes, pollution is considered a type of degradation).

Various soil classification systems based on information about soil pollution and soil degradation have been developed. In particular, they include classifications based on 5-point pollution scales and 5-point degradation scales.

In addition to using individual indicators to divide soils into groups, integrated indicators of their ecological state—the loss of ecological quality indicator (LEQI), the total pollution index (TPI), and some others—are often applied.

ALGORITHMS FOR CREATING BASIC SOIL CLASSIFICATIONS

The concept of the basic soil classification system is perceived somewhat differently. Thus, I.A. Sokolov [21] believed that the basic soil classification system pursues two major goals: (1) the creation of cartographic units for soil mapping and (2) the development of agrogroups of soils for their state registration and use for shaping ecologically sound agricultural systems and other economic purposes. This means, that the basic soil classification system should include all fertile substrates and should reflect the genetic independence of soils in Dokuchaev’s sense” [21, p. 172].

A number of specialists propose creating a basic classification based on a classification field [18] or taxonomic space [7], which should be gradually filled with soil taxa (that is, the basic classification is considered a kind of soil “periodic table”). Moreover, any other classification can be suspended into the classification field, as long as its objects contain the indicators adopted in the enumerative classification [18]. In fact, the enumerative classification, which seems to reflect the volume and content of classified objects according to the totality of their properties only formally, can provide a basis for developing and testing concepts about these objects. The creation of such enumerations based on the genesis and fertility of soils; on soil-forming factors; on soil processes and soil regimes; and on various combinations of soil properties can be done quite quickly [18].

The basic classification of soils developed by V.M. Fridland [25, 26] included four soil trunks (synlithogenic organomineral, postlithogenic, peat synorganogenic, peat postorganogenic soils), 28 soil orders, and 53 soil classes (the latter were subdivided into soil types) and was based on genetic principles. However, it did not gain general recognition as insufficiently consistent and coherent in its taxa [15].

In our view, a basic soil classification system should be understood as a division of soils that, on the one hand, relies on indicators that vary little over time (i.e., indicators of soil memory) and, on the other hand, contains information about the origin, material composition, development, and potential uses of soils. A basic soil classification system serves as the basis for creating other classifications (including special purpose-oriented classifications). The genetic classification of soils best fits this definition of a basic classification. However, some experts believe that a basic classification should be the result of ranking soils based primarily on a quantitative assessment of their major properties (e.g., total carbon content/stocks). It seems that soil as a bio-abiotic system performing a colossal number of functions in the biosphere as a whole and in specific ecosystems, continuously evolving (sometimes quite rapidly), and depending on a large number of natural and anthropogenic factors can be classified only on the basis of general knowledge about its genesis, properties, and evolution.

A basic soil classification system is described by formula (6):

6

where ab denotes the major properties of the horizon (or morphon), bb is the horizonation of the soil profile (sequence of horizons/morphons), and cb is the belonging of the soil profile to a certain basic group of profiles. In fact, it remains just a declarative system, which merely reflects our strive for an ideal classification—the periodic table of soils.

INDIVIDUAL AND INTEGRAL INDICATORS OF THE SOIL STATE USED IN SOIL CLASSIFICATION SYSTEMS

Soil diagnostics, which allows us to attribute the soil to a taxon of a certain level (for example, the taxa used in [8] and [9] are: trunk—order—type—subtype—genus—species—variety—rank), is based on a detailed description and detailed accounting of those properties that are called diagnostic. These are the properties related to the categories of a (horizons/morphons), b (sequences of horizons/morphons), and c (type of profile, belonging of a certain group of profiles). Taken together, these properties give us a soil of a particular taxonomic rank. In this case, formula (1) can be rewritten as follows:

7

where ai are diagnostic properties of the horizon (morphon) (i ∈ [1; k]); bj are diagnostic properties of the profile (morphon) (j ∈ [1; l]); and ct are diagnostic characteristic of a group of profiles (t ∈ [1; m]).

In part, such a description of soils corresponds to the mathematical interpretation of the digital model for describing soil data presented in [4]:

8

where S is the soil; V is the value of the soil property indicator; [pID], [hID], [eID], [sID] are the IDs of the soil property indicators of the corresponding type of object (p is the profile, h is the horizon, e is the morphological element, and s is the sample); [p, 0, 0], [p, h, 0], [p, h, e], [p, h, s] are the stored indices of the sets of soil objects:

profile {pID | pID (ObjectTypeID = P)},

horizon {hID | hID (ObjectTypeID = H)},

morphological element {eID|eID (ObjectTypeID = E)},

sample {sID | sID (ObjectTypeID =S)}.

The choice of particular diagnostic properties of horizons, profiles, and groups of profiles determines the kind of soil classification—genetic (profile-genetic), substantive, production-oriented, etc. The name of the soil is created by summing the names of the diagnostic properties of horizons, profiles, and groups of profiles.

STANDARDS, FERTILITY MODELS, CENTROIDS AND CENTRAL IMAGES OF SOILS

The central concept of any soil classification is the standard of the main reference taxon (soil type in Russian soil classification systems, great soil group in the American classification, reference soil group in the WRB system, etc.). Each of these taxons should be characterized by its own uniform way of the input of organic matter and the processes of its decomposition and transformation into humus, the decomposition of the mineral mass and the synthesis of organomineral neoformations, the migration and accumulation of substances, horizonation of the profile, the nature of the genetic horizons, and uniform soil reclamation measures aimed to increase and maintain soil fertility [15]. That is, the place of the reference taxon must be strictly defined in the classification space [18], and this taxon must be understood as either a real soil individual, or a modal individual, which is the result of several approximations (but, as a rule, has no real equivalent in the classified soils) [10]. That is, the question inevitably arises about the reference soil taxon description, i.e., about its morphology, composition, and properties of a real or an ideal (fictitious) soil. Regardless of the reality or fictitiousness of the soil, two fundamentally different approaches are possible: (1) the reference soil represents the most typical (modal) variant and (2) the reference soil is the variant with the best (or optimal) values of the indicators.

Agroecologists address this issue by introducing the concept of a fertility/high-fertility model of agricultural soils—an optimum combination of soil properties, processes, and regimes to obtain the maximum economically feasible yield and the highest efficiency of solar and anthropogenic energy utilization in the agrophytocenosis, while maintaining the environmental safety of the adopted agricultural system and technologies [19]. The fertility model assumes maximum soil tolerance towards degradation under given conditions, as well as reliability and longevity of soil functioning under the existing flows of matter and energy. In this chapter, regional models (standards) of soil fertility are presented in the form of comprehensive passports of high-fertility soil models. Examples of passports for various natural zones are given. Thus, passports of high-fertility models (optimal properties of plow and subplow (subsoil) horizons) have been developed for sandy loamy and silt loamy soddy-podzolic soils, gray forest soils, leached chernozems, and other zonal soil types of the Russian Plain [19]. The different taxonomic levels of the soils, for which these passports were created, are noteworthy.

Another example of a reference soil description obtained using mainly mathematical method (via intersecting the medians of the values of diagnostic properties) is the soil centroid, which is located at a certain (specified by researchers) distance from the neighboring taxa [29]. First, the soil centroid is a virtual, fictitious standard; second, it is also the most typical (modal) version of the reference taxon. The International Union of Soil Sciences is developing a new comprehensive classification of soils sequentially, using centroids from various classification systems (Soil Taxonomy, WRB, New Zealand and Australian soil classification systems, etc.) [29].

Another version of the standard—the central image of a reference taxon—is a representation of the soils of this taxon and the processes occurring in them. The central image reflects the sum of knowledge about a particular soil taxon at a given level of soil science development. For example, a review of specialized literature, as well as a range of mineralogical, micromorphological, and analytical studies, allowed us to develop concepts about the conditions under which the central image of cinnamonic soils forms and the key processes occurring in these soils [11]. In fact, the group of soils forming in the mediterranean (variably humid) subtropical climate extends beyond the cinnamonic soil type. Thus, it was necessary to highlight the most important features of the cinnamonic soils separating them from the other soils. As a result, the following central image of the type of cinnamonic soils was shaped: “Cinnamonic soils are highly biogenic soils that form under conditions of a variably humid subtropical climate (intermediate between semiarid and subhumid with precipitation of 500–800 mm, and the precipitation-to-potential evaporation ratio of about 0.6–0.8), characterized by clear seasonal dynamics, on carbonate rocks containing a reserve of weatherable iron-bearing minerals and clay matter with a large amount of smectitic component. Cinnamonic soils develop under forest (evergreen and deciduous) and shrub vegetation. The influence of the orographic factor of soil formation is manifested through the climatic factor, and also includes lateral input of fresh material by slope processes. Cinnamonic soils are often formed on polynomial (necessarily carbonate) material. The profile of cinnamonic soils has the following horizonation: A(k)—Bt(k)—Bk—BCk—Ck” [11, p. 24].

ALGORITHMS FOR CREATING CLASSIFICATION OF SOIL RESOURCES

Classification of soil resources (SRs) in accordance with land category/land use type. According to [6], seven land categories of are distinguished. Therefore, soil resources can be allocated to each of the existing categories:

(1) SRs of agricultural land;

(2) SRs of the land of settlements;

(3) SRs of the land of industry, energy, transport, communications, radio broadcasting, television, information technology, cosmic activities, defense, and other special purposes;

(4) SRs of the land of specially protected areas;

(5) SRs of the land of forest fund;

(6) SRs of the land of water fund (wetlands);

(7) SRs of the reserved land.

Soil cover of lands belonging to different categories and located within the same natural zone (subzone) may not differ. For example, soil cover of forest land, land of specially protected areas, and reserve land in the southern taiga subzone. This means that the type of land use often has a greater influence on the composition, properties, and morphology of the soils than just the land category. Therefore, it is proposed to distinguish:

(1) SRs of forest land;

(2) SRs of arable land;

(3) SRs of land occupied by perennial plantations (orchards, vineyards, and others);

(4) SRs of land for nature conservation purposes;

(5) SRs of industrial and transport land;

(6) SRs of residential areas.

In this division, SRs of different land uses have their own specificity. Thus, soils under forests are characterized by the presence of forest litter in the soil profile; significant variability of physical, morphological, and chemical properties related to the structure of forest biogeocenoses (soils of near tree trunks elevations, soils under tree crowns, soils of intercrown clearings, etc. [7]).

Soils of arable land have a plow horizon, a plow pan, and some other agrogenic properties.

Soils of specially protected areas are characterized by the minimum influence of industry and human activities, is minimal.

Soils under perennial plantations (orchards, vineyards, etc.) are characterized by deep (40–75 cm and more) plow horizon.

Soils of residential areas include artificially constructed soils (constructozems) and soils without clearly expressed properties of zonality, azonality, or intrazonality, i.e., their natural genetic horizons are replaced by the urbic horizon with a significant number of anthropogenic inclusions, specific chemical properties (close to neutral or neutral reaction, increased content of available phosphorus, etc.).

Soils used by industry and transport are often polluted with various toxicants (heavy metals, PAHs, PCBs, dioxins, etc.) that enter the soil surface mainly from the atmosphere; also, these soils are often mechanically turbated..

Classification of SRs according to the quality and ecological state of soils. Soil productivity (or fertility) is one of its most important production functions [12] and ecosystem services [27]. Therefore, a qualitative assessment of SRs should primarily involve the determination of soil fertility. An assessment of the ecological state of SRs should be based on the contribution of soils to the sustainable functioning of terrestrial ecosystems/biogeocenoses, of which they are a part.

Classification of soils according to their bioproductivity (fertility). Traditionally, soil fertility is assessed through soil quality appraisal. As is well known, soil quality appraisal is a qualitative assessment of soil fertility, productive capacity, and quality [2]. Soil appraisal evaluates soils using quantitative indicators (in points) calculated on the basis of data on the soil properties and average long-term crop yields on these soils.

Quality appraisal of agricultural land is of particular interest; it is necessary for agricultural production. Soil quality appraisal serves as the initial basis for an economic evaluation of land, establishing its standard price, developing land cadaster, preserving the most valuable land for agricultural production, and allocating less productive lands for nonagricultural purposes.

To date, there are three major directions in the assessment of soil quality in Russia and abroad. They have been shaped by the works of many researchers, including V.V. Dokuchaev, N.M. Sibirtsev, S.S. Sobolev, N.F. Tyumentsev, N.G. Shishkina; the methods developed by Storie and by the FAO team are also known. Soil appraisal can be based on (1) inner soil properties, (2) yields of crops grown in these soils, and (3) inner soil properties adjusted for produced yield.

The FAO system of soil appraisal [17] belongs to the third direction [17]. It has been tested in several countries (Nigeria, Brazil) and involves calculating the total current productivity of soils using a formula that takes into account particle size distribution, structure, base saturation, degree of salinity, cation exchange capacity, drainage degree, moisture availability, humus content, the nature of clay materials, and the nature of the material. For each specified diagnostic feature, a special 100-point appraisal scale has been developed. Depending on the influence of a particular feature on the overall soil productivity, it is estimated with a certain number of points. The classification of lands (in our understanding, SRs) includes five classes depending on the current soil productivity:

(I) very high productivity (65–100 points);

(II) high productivity (35–64 points);

(III) moderate productivity (20–34 points);

(IV) low productivity (8–19 points); and

(V) very low productivity (0–7 points).

Classification of SRs according to their ecological state. The ecological state of soils can be generally understood as a set of soil properties complying with the natural and climatic conditions of soil formation and ensuring soil suitability for the sustainable functioning of natural and anthropogenic ecosystems [12]. Moreover, standards for the ecological state of soils—background and maximum permissible concentrations of pollutants, indicators of physical and technological degradation of soils, and other criteria—should be developed for administrative regions with due account for the bioclimatic, lithological, and geomorphic characteristics of the territory, as well as for the land use type (Table 1). Thus, in essence, the ecological state of soils is firmly tied to various characteristics of land resources and, in this regard, is, in fact, can be considered the ecological state of SRs.

Table 1. . Natural and economic factors taken into account when assessing soil quality [12] Subject of the Russian Federation

[See PDF for image]

*SPNAs—specially protected natural areas.

Furthermore, when establishing gradations of indicators of the ecological state of SRs based on the degree of manifestation of individual characteristics, it is necessary to take into account the nonlinear nature of corresponding changes. It is recommended that the ranking of these indicators should be carried out in accordance with existing standards or (in the case of their absence or insufficiency) according to a five-point scale for assessing the state of the environment [12].

The use of individual ranked indicators of the ecological state of SRs allows for the calculation of an integral indicator of the ecological state of SRs for a given area (administrative or natural region) using formula (9):

9

where Ss is the integral value of the ecological state of SRs; Pd is the point value of the dominant indicator of SRs (the dominant indicator is a ranked indicator that determines the maximum level of deterioration of the state of SRs for a given area);

Pad i is the point value of the additional indicator of SRs (additional indicator is a ranked indicator with its rank less than (or equal to) the rank of the dominant indicator in terms of the level of deterioration of the state of SRs for a given area); and

n is the number of additional indicators.

In this case, the point value of the dominant and additional indicators is the middle of the assessment score corresponding to the level of deterioration of SRs established during the assessment: 1st—0.5; 2nd—1.5; 3rd—2.5; 4th—3.5; 5th—4.5.

Soil resource areas corresponding to the first and second levels of deterioration of the environment are generally healthy, and conservation measures can be implemented locally (at landfill sites, industrial sites, waste heaps, etc.). The SRs status of these areas remains within the ecological norms. In the areas with moderate (level 3) degradation, the likelihood of irreversible changes in terrestrial ecosystems is high (although not 100%).

Individual environmental protection measures and their implementation are determined by the factors that have the most significant negative impact on the environment. However, the moderate urgency of these measures allows for a variety of environmental protection measures, among which soil conservation and reclamation (aimed at improving soil fertility) measures play an important role.

Accordingly, one of the possible ways to classify SRs in accordance with their ecological state may be as follows:

(1) Soil resources, the condition of which is within the ecological norm; and

(2) Soil resources, the condition of which is beyond the ecological norm.

Classification of SRs in accordance with their administrative-territorial affiliation as subjects of land relations. The classification of SRs should reflect the various hierarchical levels of the administrative and economic division of Russia—from (1) local (for example, an individual agricultural enterprise, ENT) to (2) municipal (municipal district, MD); (3) federal constituent entity (federal subject, FS); (4) federal district, FD; and (5) the entire Russian Federation, RF.

(1) SRs ENT MD FS FD RF;

(2) SRs MD FS FD RD;

(3) SRs FS FD RF;

(4) SRs FD RF;

(5) SRs PR.

To a large extent, the current Unified State Register of Soil Resources of the Russian Federation [4] includes a detailed description of SRs at the levels of federal subjects, federal districts, and the entire Russia.

A separate issue here is the degree of detail in the description of soils (soil taxa) at each hierarchical level. In [10], unfortunately, multilevel soil taxa are cited when characterizing the regional soil profile [8, 24]. Thus, for Tula oblast, this includes the soil type (gray forest), the soil subtype (light gray, dark gray, podzolized chernozems, leached chernozems), and the soil species (predominantly surface- and shallow-podzolic soddy-podzolic soils).

The above-mentioned classification of SRs according to their administrative-territorial affiliation inevitably overlaps with the classification of SRs as subjects of land relations, since, in accordance with Article 5 [6], participants in land relations include citizens, legal entities, the Russian Federation, constituent entities of the Russian Federation, and municipalities. These participants may be owners and title holders of land plots, land users, landowners, tenants, and holders of easements and public easements.

Classification of SRs as subjects of different legal regimes. As is known, “the legal regime of land plot is determined based on its belonging to a particular category of land and permitted land use in accordance with zoning of the territory, the general principles and procedure for which are established by federal laws and the requirements of special federal laws” (Article 7 [6]). Thus. SRs may have different legal regimes.

The legal regime of land plot is a procedure established by law for state regulation of the use and protection of land, provided by measures to prevent violations and established liability for their commission [5].

The following types of legal regime of land exist:

(1) general (inherent to the entire land resources of the Russian Federation);

(2) special, inherent to certain land categories; and

(3) special, inherent to particular land plots.

The elements of the legal regime of land include:

— determination of the boundaries of land, to which a given regime is applied;

— the procedure for state regulation of land use;

— the presence of subjects of land legal relations, who are obliged to comply with the established rules of the land regime;

— the content of the rights and obligations of subjects of land legal relations participating in the application of the legal regime for particular lands;

— the existence of an efficient legal mechanism to ensure the protection of the legal regime for land use from violations.

The general legal regime applies to all lands, and its element is the requirement for land use for the intended purposes. Thus, agricultural lands are characterized by a legal regime, which stipulates their use directly for agricultural purposes, though a special legal regime can be applied to depleted and degraded agricultural lands. The application of a special regime is necessary to reclaim degraded lands and to prevent their further destruction.

General approaches to defining the concept of SRs and their classification. As is well known, one of the most important methodological foundations of any science is the principle of Occam’s Razor, which briefly states: “One should not multiply things without necessity” [20]. Is not the concept of SRs such a multiplication of things? Can we limit ourselves to the generally accepted terms soil (as a specific natural body, usually of a bio-abiotic nature) and land resources (lands that are used or can be used in particular sectors of the national economy [3])? Probably, the need to introduce such terms as soil resources and/or soil-land resources is due to three main reasons: (1) an indication of the resource nature of soils (soils are the same full-fledged natural resources, as fossil fuels, water, forest, biological, and other resources); (2) the linking of soils to the lands, where they are located (land category, land use type, etc.); (3) the reference to the obligatory spatial component of soils (the concept of soil often narrows the space to a single soil pit or a point on the soil map), which inadvertently brings the proposed resource concepts closer to the concept of soil cover. Indeed, a soil scientist often needs to emphasize that the value of, for example, forest or agricultural lands as sources of some food products is determined by the specific properties of the soils (soil cover) of these lands.

Thus, a situation has arisen in Russian soil science, where soil-related lands/land-use zones will increasingly become the subjects of close study, including their classification. The first task is to correctly define SRs. Several possible definitions are offered below:

(1) soil resources are resources of the soil cover, regardless of the forms of its use (based on the definition given by N.F. Reimers [1]);

(2) soil resources are soils used at present, in the past, and in the future for direct and indirect consumption, for the creation of material wealth, for the reproduction of labor resources, for maintaining the conditions of human existence, and for improving the quality of life.

The advantage of the first definition of SRs is its brevity and comprehensive nature, while the second definition has a direct reference to the concept of total economic value (TEV) and soil ecosystem services [13].

The criteria for classifying natural resources may include not only those listed above (land categories, types of land use, qualitative and ecological status, administrative-territorial affiliation of land, subjects of land relations, and legal regime) but also the degree of contrast of the soil cover, dominant soils (by area), etc. The problem under consideration remains poorly studied; at present, there is no need to identify priority criteria for dividing SRs into some groups. In any case, the solution to systematic and taxonomic problems (including the development of the nomenclature of the taxa of SRs) remains a matter for the future. It is likely that the classification of soil resources should not resemble soil classification systems (any of the existing Russian and foreign versions), so that the concepts of soil and soil resources are separated as far as possible in various sections of theoretical soil science and areas of practical use of the soil cover. Table 2 reflects the groups of SRs discussed in this article as distinguished in dependence on various classification criteria.

Table 2. . Groups of SRs depending on their classification criteria

Criteria for the classification of SRs	SRs group
Land category	1) SRs of agricultural land; 2) SRs of the land of settlements; 3) SRs of the land of industry, energy, transport, communications, radio broadcasting, television, information technology, cosmic activities, defense, security, and other special purposes; 4) SRs of the land of specially protected areas; 5) SRs of the land of forest fund; 6) SRs of the land of water fund (wetlands); 7) SRs of the reserved land
Type of land use	1) SRs of forest land; 2) SRs of arable land; 3) SRs of land under perennial plantations (orchards, vineyards, etc.); 4) SRs of land for nature conservation purposes; 5) SRS of industrial and transport land; 6) SRs of residential areas
Qualitative state of land	I—SRs of very high productivity; II—SRs of high productivity; III—SRs of moderate productivity; IV—SRs of low productivity; V—SRs of very low productivity
Ecological state of land	1) SRs, the state of which is within the environmental norm; 2) SRs, the state of which is beyond the environmental norm
Administrative-territorial affiliation of land	1) SRs ENT MD FS FD RF*; 2) SRs MD FS FD RD; 3) SRs FS FD RF; 4) SRs FD RF; 5) SRs PR
Subject of land relations	1) SRs of citizens; 2) SRs of legal entities; 3) SRs of RF; 4) SRs of the constituent entities of the RF; 5) SRs of municipalities

* The abbreviations are explained in the text.

CONCLUSIONS

The perception of soil as a function of the properties of soil horizon (or its element, morphon), the construction of the soil profile (the sequence of horizons/morphons), and its belonging to a certain group of soil profiles (formula (5)) makes it possible to formulate algorithms for any soil classification. The existing multivariate nature of algorithms for creating various classifications of soils and soil resources, on the one hand, once again proves I.A. Sokolov’s thesis [21] that soil classification is a problem without a definite final solution. On the other hand, the need to develop a basic soil classification system—a periodic table of soils based on the genetic approach and serving as the construction material for any other soil classification—is also beyond doubt. In our view, the approaches to creating such a classification proposed by the international soil community suffer from a certain mechanistic nature, as the centroid position of a reference soil within the classification field is often quite formal, not only failing to provide insight into the genesis of the soils but also obscuring it. The idea of a central image of the reference soils is far more fruitful, as it allows for the identification of diagnostic features of these soils eliminating all unnecessary elements.

The development of soil science and the implementation of its achievements in practical areas of life (environmental management, rationalization of agricultural production, etc.) have led to the appearance of a new term—soil resources—that are understood as resources of the soil cover, regardless of the forms of its use, or as soils used in the present, past, and future for direct and indirect consumption, contributing to the creation of material wealth, reproduction of labor resources, maintenance of living conditions, and improving the quality of life. When developing a classification of soil resources, various criteria for identifying their groups (classification units) can be used—land categories, types of land use, the qualitative and ecological status, and administrative-territorial affiliation of land, subjects of land relations and legal regime of land plots, the degree of soil cover contrast, dominant soils by area, etc.

FUNDING

This study was supported by the Ministry of Science and Higher Education of the Russian Federation, state assignment no. 121042600177-3 “Agrochemical, Ecotoxicological, and Ecological-Economic Assessment of Anthropogenically Transformed Soils of the Northern Moscow Region.”

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

This work does not contain any studies involving human and animal subjects.

CONFLICT OF INTEREST

The author of this work declares that he has no conflicts of interest.

Translated by D. Konyushkov

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