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Chernozem – rich black soil in Russia

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Chernozem – rich black soil in Russia.

“Chernozem – rich black soil in Russia is the fundamental, incomparable wealth of Russia …” (Mr. V.V. Dokuchaev. Russian chernozem, 1898) “Russia is the owner of a unique natural wealth – chernozem. It is not by chance that chernozem is considered the “king of the soil.” The soil science created by our great compatriot Vasily Vasilyevich Dokuchaev originates from chernozem.

Chernozem - rich black soil in Russia. Map.

Chernozem – rich black soil in Russia. Map.

Chernozem in soil science played the same prominent role as the frog in the history of physiology, calcite in crystallography, benzene in organic chemistry … ”(Mr. V. Vernadsky, 1904). Natural chernozem rocks are represented by loose loess-like sediments and loess, however chernozems are also found on derivatives of dense rocks. As a rule, parent rocks have silty granulometric composition, contain carbonates, their fine fractions consist of mixed-layer mica-smectite formations. Increased porosity and microaggregation of rocks, their good water permeability and high absorption capacity contribute to the formation of chernozem. Chernozems are common both on elevated erosion plains and on low-lying accumulative plains (including terraces), as well as in the foothills and intermountain depressions.

The climate of the distribution of chernozems as a whole is characterized by balanced humidification (Moisturizing Coefficient = 1–0.5) with a summer maximum of precipitation and a relatively even distribution of them in the rest of the time, a warm summer with a profile drying out and its winter freezing. The alternation of these cycles is necessary for the formation of a kind of “chernozem – rich black soil in Russia” humus. Steppe forb-grass vegetation is traditionally considered an important factor of black-earth formation due to the large mass of roots, high ash content and easy degradability of meadow and steppe plants, high biodiversity of cenoses, and, consequently, the cyclical vegetation and depth of root systems. These features of phytocenoses, in combination with a moderately warm and periodically humid soil climate, provide a high biological activity of microbiocenoses, as well as meso- and macrofauna.

Chernozems occupy about 8% of the country’s area, they are most diverse in the European part of Russia, where geographical models of their distribution were created. Chernozems – rich black soil in Russia form a series of subzonal subtypes: forest-steppe — podzolized, leached, and typical; steppe – ordinary and southern. The series is complemented by facial subtypes: in the south of Russia – by the Azov-Pre-Caucasus, and in Siberia – by cryogenic-mycelian and mealy-carbonate. Genetic horizons: The accumulative-humus (dark-humus) horizon is the “calling card” of chernozem, it is almost the same in all subtypes and types of chernozem. It is characterized by a beautiful macrostructure (a, b) and microstructure (c). Water-resistant aggregates, largely created by earthworms and root systems, form a granular structure and “root beads”. Characterized by high porosity (up to 50%) and low density of addition (~ 1 / cm3). The dark color is determined by the high content of humus (5–8%) and its calcium-humate composition (Cgc / Cfc> 2). The horizon is saturated with bases, its reaction is close to neutral. Horizon thickness – 40 – 120 cm.

Accumulative-carbonate horizon in its formation is associated with humus (its saturation with roots and biological activity), hydrothermal profile regimes and carbonate of the rock. The accumulation of carbonates is determined by the seasonal dynamics of CO2 and the migration of soil solutions, and the forms of carbonate neoplasms serve as criteria for the separation of chernozems. Thus, migration forms of carbonates — tubules, pseudomyceliums (g) — are characteristic of chernozems of a relatively humid and warm climate, unlike segregations — white-eyed (e), which are formed in a more continental and arid climate.

Chernozem - rich black soil in Russia

Changing the level of chernozem – rich black soil in Russia from 1888 to 1980

Chernozem – rich black soil in Russia on the Russian plain within the forest-steppe are found in combinations (according to the mesorelief) with gray forest soils. Steppe chernozems form vast homogeneous ranges; on the Volga Upland, chernozems on dense sedimentary rocks contribute to the soil cover; in the Volga among chernozems saline and alkaline soils are common. In the western and central regions, moderately powerful and powerful, low- and medium-humus species and subspecies of chernozem dominate, to the east the humus content in the humus horizon increases and the thickness of the humus profile decreases. The maximum power of the humus profile with a low content of humus is characteristic of the chernozem of Ciscaucasia. The provincial laws regarding the humus profile can also be traced in the zonal series of Siberian chernozems, the most complete of which is represented on the West Siberian Plain. East of the areas of chernozem become fragmented – in the foothills and intermountain depressions (with forest-steppe cryogenic-mycelial chernozems); in Transbaikalia, steppe mealy-carbonate chernozems are combined with meadow-chernozem soils in depressions.

Fertile humus horizon with a high content of humus and a capacity of up to 1 m or more is a distinctive feature of Chernozem – rich black soil in Russia. It is not by chance that in the early soil classifications chernozems “fat” and “superpower” were distinguished. The increased reserves of humic substances in chernozems are associated with the peculiarities of the biological circulation characteristic of virgin grass-feather grass and fescue-feather grass steppes. The main background in them is made up of cereals with developed root systems, so root litter, rich in nitrogen and ash elements, makes up 40–60% of the total input of organic residues into the soil. Their decomposition in optimal hydrothermal conditions at neutral or slightly alkaline pH values ​​contributes to the formation of humus with a predominance of complex humic acids, firmly fixed in the soil. During the period of studies of Russian chernozems by V. Dokuchaev, the founder of Russian soil science, the humus content in the soils of the forest-steppe and steppe zones of then-Russia was from 3–6% to 10–13%, which was reflected on the map of “isogumus bands” (humus content). The map of V. V. Dokuchaev illustrates the level of humus content in the black soil of European Russia at the end of the 19th century; it increased from west to east, reflecting both the provincial features of black soil formation and the longer agricultural use of black soil in the western regions of the country.

The high fertility of chernozem – rich black soil in Russia determines their value in the arable fund of Russia, where they constitute more than half. Large reserves of humus and the main plant nutrients (nitrogen, phosphorus, potassium), favorable water-physical properties led to the active development of chernozem from the XVII – XVIII centuries. In the XX century, small areas of virgin steppes remained only in the protected areas; almost the entire black-earth zone of the country was plowed up. The natural profile of chernozems used in agriculture varies less than that observed in other soils, which is due to the high thickness of the humus horizon and the preservation of grassy type of vegetation. However, in the chernozems under the agrocenosis, the nature of the biological circulation of substances is changing due to the removal of the phytomass of agricultural crops, the application of fertilizers; the microclimate and all soil regimes are transformed; for ordinary and southern chernozems, the negative impact of irrigation is added to anthropogenic influences. Agrogenic degradation of chernozems has been the subject of many studies which have proved that its trigger mechanism is the reduction of the humus content and the change in its qualitative (fractional) composition. Soil dehumification is a consequence of the accelerated mineralization of organic matter and its entry into arable soil in a significantly smaller volume, as well as direct loss of humus during water and wind erosion. Even V. V. Dokuchaev in his work “Our steppes before and now” noted the unfavorable tendencies of humus loss by chernozem soils. The use of intensive technologies in agriculture in the second half of the 20th century caused the dehumification of almost all chernozems. The map compiled by G. Ya. Chesnyak (1986) “in the wake of Dokuchaev” (that is, according to the results of determining the humus content in the same places as in the expedition of V. V. Dokuchaev) shows the spatial trends of humus losses in the Russian plains for 100 years that have passed since the publication of the book by V. V. Dokuchaev “Russian Black Earth”. Especially large losses of humus are noted for the Volga and Pre-Ural regions, which is associated with the initial lower power of humus profiles of these chernozems and the wide development of erosion processes here, caused by a combination of natural factors and relatively low farming culture.

In addition to dehumification, a general tendency during plowing is the deterioration of the soil structure due to the loss of humus, changes in its composition and multiple passes across the field of heavy agricultural machinery. The transformation of the granular or lumpy-granular structure of the upper horizons, with their high porosity and water permeability, into a clumpy-silt is accompanied by the transfer of a part of the subsurface flow to surface and leads to the development of plane (stream) erosion. In addition, arable soil is not covered with vegetation in all seasons of the year, which changes their hydrothermal regime; due to deeper and more prolonged freezing, surface runoff of melt waters increases. The development of erosion has greatly increased as a result of the reduction of areas of watershed forests and unlimited plowing of the slopes, especially on the Central Russian and Volga elevations with their dissected relief and in places with a thin cover of loose sediments. With a high potential fertility of chernozem factors limiting the production of high yields may be the instability of moisture supply of crops (especially in the southern regions and in the Volga region). Large areas of southern and ordinary chernozems are used with regular irrigation. As a rule, when irrigating with moderate norms, secondary salinization of chernozem does not threaten, but such negative effects as salinization, alkalization and deterioration of physical properties are observed: the formation of surface peel and compaction. Concern over the fate of the Russian Chernozem makes domestic soil scientists pay more attention to studying various aspects of the functioning of these soils. The world recognition of the role of chernozem manifested itself in the fact that 2005 was declared the Year of Chernozem – the soil opening a new international public-scientific action “The Soil of the Year”. The alarming situation with the current state and the use of chernozems inevitably raises the question of including a number of chernozem – rich black soil in Russia in the Red Book of Russian soils.

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