MORPHOGENETIC BASIS OF THE UNIFIED STATE REGISTER OF SOIL RESOURCES OF RUSSIA

Nomenclature and taxonomic diversity of soils and their horizon-profile diag-nostics/descriptions define morphogenetic soil indicators used in the Unified State Register of Soil Resources of Russia (with Russian abbreviation of EGRPR). Most of these soil indicators are of non-metric origin, i.e., estab-lished conventionally by agreement. Subject area of soil science includes a hierarchy of 5 types of soil objects (pit, profile, horizon, morphological element and sample), 380 indicators, 607 methods and 3019 values of the indicators.


INTRODUCTION
Morphogenetic features of soils develop in the course of soil formation. They reflect the past and current soil processes and phenomena and serve as informational and methodological basis for modern soil science. Studying the morphological features of soil profile allows us to understand relationships between soil-forming factors and processes, to develop soil nomenclature and taxonomic identification, etc.
New soil information recourse was ratified in Russia in 2014 -"Edinyi gosudarstvennyi reestr pochvennykh resursov Rossii" -EGRPR (Unified State Register …, 2014). The EGRPR includes complete and unified digital data set on all soils of Russia, their properties and distribution.
The EGRPR concept comprises a model of spatial organization of soil cover, digital representation of soil data and systematization of soil features at different scales, i.e., soil recourses all over the country and within each of the Federal Subjects of Russia and soil-ecological regions (Stolbovoy and Molchanov, 2015). By a systemic approach the EGRPR interconnects and integrates the above elements into a unified system, with the morphogenetic soil indicators playing a key role in providing consistent database on soils countrywide.

NOMENCLATURE AND TAXONOMIC DIVERSITY OF SOILS
The nomenclature of the EGRPR includes 205 soil units at different taxonomic levels. Soil features that determine soil taxonomic position are reflecting the integrated influence of soil-forming processes and factors. Therefore, the EGRPR represents a unified image of geographic diversity of soil taxa.
A soil unit is an integrated index of soil based on its combined characteristics. In the Russian school of soil science a priority is given to soil genetic features. In the EGRPR a soil unit is an identifier containing a brief description of distinguishing features of that particular soil. These units follow the Russian soil science tradition of hierarchical structure of soil names, beginning with type and continued to subtype, genus and species. The nomenclature and taxonomic diversity within the EGRPR is represented by 57 soil types, 107 soil subtypes, 47 soil genera and 11 soil species.

DIAGNOSTICS OF HORIZONS WITHIN A SOIL PROFILE
In EGRPR, the primary units of soil description and diagnostics are morpho-genetic horizons, with secondary importance being given to their additional features. The main morpho-genetic horizons are formed by leading soil-forming processes. These horizons are labelled by capital letters of the Latin script supplemented by Arabic digits (Table 1). They can be subdivided into sub-horizons by quantitative change in the main diagnostic features, e.g., О11, О12, А21, А22, etc.).
Transitional morpho-genetic horizons with a gradual change from one horizon to the other are labelled by the indices of respective horizons above and below, starting by the index of the horizon, which contributes more of its features to the transition horizon, e.g., А2В1 and А1В1.
Transitional morpho-genetic horizons having combined features of the horizons above and below are labelled by the indices of respective horizons above and below divided with a slash, e.g., А2/В1 and А1/В1.
A buried horizon is marked by square brackets, e.g., [А1]. Organic horizons. By volume, they contain more than 70% of organic matter with different rates of decomposition. Any minerals present are mostly a mechanical admixture. The horizons are usually at the soil surface or, if buried, anywhere within the soil profile. These horizons may form the entire soil profile (in the case of peat soil) О1 Horizons formed mainly of well-preserved or slightly decomposed plant remains, which retain the main features of their initial composition. О2 Horizons formed mainly of moderately decomposed plant residues, partially retaining their initial features (such as portions of plant fabric) О3 Horizons formed by well-decomposed plant residues that have completely lost their initial features Organo-mineral horizons АО The upper organo-mineral horizons containing considerable quantities (30-70% by volume) of organic matter at different stages of decomposition. They usually have a mechanical mixture of organic and mineral material, which, however, could be easily separated А1 The upper mineral horizons, which are usually the most darkcoloured within the soil profile. They contain well-humified organic material, which is formed in situ and closely linked to the mineral phase Mineral horizons А2 Usually underlying horizons O, AO, or A1, but in heterogeneous profiles may occur under any horizon of the overlying profile. They are the most bleached and colorless horizons in the soil profile, and do not have the gleying characteristic of the G horizon В Mineral horizons, underlying horizons AO, A1, or A2 (or O horizon if the above-mentioned are lacking). They are identified by any differences of colour, structure, or texture in comparison with the overlying horizon A and underlining horizons G and C G Mineral gley horizons that reveal uniform or alternating bright blue, blue-grey, green, or rusty colours throughout the dominant part (not less than 70%) of the freshly cut surface G1 Gley horizons with uniform or alternating bright blue and dark blue colours G2 Gley horizons mottled with blue, grey-blue, and rusty tints G3 Gley horizons, that have olive, green, or greyish-green colors Index Definition C Parent material, mostly unchanged by soil formation D Underlying rock, different from the soil parent material, underlies the soil profile, and has no features caused by soil forming processes S Horizons, cemented in both moist and dry conditions, may form an impermeable layer and resist sheet erosion. They are formed by the concentration of various chemical compounds (oxides of iron, silica, carbonates of calcium and magnesium, salts, etc.) Cementing the soil mass K Fragile, porous crusts, not more than 5 cm thick, forming the surface of the profile Frozen, water-resistant and ice-cemented morpho-genetic horizons are labelled by the main horizon index with a special mark in front of it, e.g., ┴ВC.
Morpho-genetic horizons that have negative temperature at the time of description, but aren't water-resistant (with an optional presence of ice) are labelled by the main horizon index with a downward arrow in front of it, e.g., ↓ВС.
Additional features of morpho-genetic horizons (presence of calcium carbonate, salinity, alkalinity, etc.), which result from secondary processes developed over a background soil-forming process, are given a lowercase letter behind the main horizon index, e.g., Bsvisible salt pedofeatures within the B horizon, Bslsolonetzization (alkalization) within the B horizon, Асаcalcium and magnesium carbonate pedofeatures within the A horizon. If the secondary features reach their maximal degree of development, then their lowercase letter is underlined, e.g., Bca, Вm, Bс, etc. If there are several secondary features within the same main horizon, their respective lowercase indices are divided with commas, e.g., В1m,f,g.
Every soil profile has its specific sequence of morpho-genetic horizons from the top to the bottom, which is referred to as a "formula of soil profile structure". The guidelines for correctly presenting such formulas are set in the EGRPR.

MORPHOGENETIC CHARACTERISTICS OF SOILS
The morphogenetic characteristics of soils include their visually perceivable appearances and easily assessable (e.g. by tape measure) parameters. Sometimes they are supplemented by micromorphological features being identified with more precise instruments of visual investigation, e.g., a polarizing microscope.
Definitions of the morphogenetic characteristics of soils used in the EGRPR are presented in Table 2 and definitions of morphogenetic elements of soilsin Table 3. Details describing soils in the system of the Unified State Register of Soil Resources of Russia is available in the Guidelines for soil description (Guidelines …, 2016).

FORMAL MODEL OF PRESENTING THE MORPHOGENETIC CHARACTERISTICS
As shown above, the morphogenetic characteristics of soils registered in the EGRPR are derived from the nomenclature and taxonomic diversity of soils and their profile descriptions. Such approach to choosing the morphogenetic characteristics of soils is based on soil research data. Indeed, the soil cover is a continuous mantle, not subdivided by distinct boundaries into soil taxonomic units. Our concepts of soil variety are always conventional and based on classifications being accepted and study methods being practiced in field and laboratory. A close relationship between the nomenclature and taxonomic diversity of soils and their profile descriptions/diagnostics makes the EGRPR truly unified, with soil morphogenetic indicators proving for integrity and interconnection.
There is a formal mathematical expression of soil morphogenetic description in the EGRPR (Unified State Register…, 2014). There is a logical sequence, where each soil object is described by the associated set of soil indicator values and the whole soil is expressed as a tree of   Morphological assessment of the abundance of large pores/fissures (more than 3 mm wide and more than 1 mm in diameter) Abundance of small pores/fissures Morphological assessment of the abundance of small pores/fissures (less than 3 mm wide and less than 1 mm in diameter) logical formulas. Precise positioning of each set of soil morphogenetic data in the EGRPR digital format gives us a possibility to restore soil descriptions in visually available form without information loss and distortion. The precision of descriptions supplied by their authors is being controlled and supported by complete meta-data on the subject area of soil science, i.e., the Universum 1 of soil cosmos (pedosphere) including an entire range of soil objects with an entire diversity of their properties and features. The subject area is also a sphere of theoretical development of soil science that can be realised only within the area of soil objects, their morphogenetic characteristics and other parameters. CONCLUSIONS 1. The EGRPR is an innovative national soil information resource, being a system for organizing spatially-distributed morphogenetic characteristics and other parameters of soils.
2. The unified morphogenetic characteristics of soils in the EGRPR play a key role in ensuring the unity of soil information base of our country. The set of morphogenetic characteristics is determined by the nomenclature and taxonomic diversity of soils and descriptions/diagnostics of their horizons and profiles. There are 57 types, 107 subtypes, 47 genera and 11 species of soils. The EGRPR as a system represents an integrity of diverse soil taxa (conceptual morphogenetic images of soils) within a geographical continuum of soil morphogenetic properties.
3. In digital format the EGRPR opens a possibility for restoring soil descriptions in visually available form without information loss and distortion. The precision of descriptions supplied by their authors is being controlled and supported by complete meta-data on the subject area of soil science, which includes a hierarchy of 5 types of soil objects (pit, profile, horizon, morphological element and sample), 380 indicators, 607 methods and 3019 values of the indicators.