Chernozem is a typical steppe soil. They are formed under steppe herbaceous vegetation under conditions of different topography and on different parent rocks (except for quartz sandstones).
The most typical chernozems are developed in flat terrain on loess-like sandy loams, loams and loess.
Chernozem soils have a thick humus horizon of black or black-brown color.
They are characterized by a granular or lumpy structure, a high content of humus confined to the upper and middle parts of the soil profile, accumulation of lime in the lower part, and the absence of easily soluble salts.
Among the chernozems, the following types are distinguished: leached chernozems, typical, podzolized, ordinary and southern chernozems. The chernozem process reaches its maximum development in typical chernozems.
The top layer in these soils is steppe felt. It is 3-5 cm and is developed only on virgin lands.
The next layer is humus, its thickness is 40-60 cm. Its color is black, hence the common name of soils. The structure of the layer is granular, becoming lumpy towards the bottom. This layer is saturated with plant roots.
The bottom layer of typical chernozems is the soil-forming rock. It often contains carbonate formations. They are quite widespread.
Leached ones are distributed along the northern periphery. They differ from typical chernozems in the significantly lower position of the boundary of carbonate rocks. Chernozems of this type are developed in areas with highly dissected topography and developed erosion processes.
Podzolized chernozems are also developed in more northern regions. It is assumed that these chernozems were formed in forest-steppe conditions under forests. They have some properties that make them similar to typical forest gray soils.
Ordinary and southern chernozems are distributed, respectively, to the south of typical ones. They are characterized by a lower thickness of the humus and transition layers.
Chernozem has the highest degree of fertility of all types of soil. It is suitable for growing all kinds of plants. Since chernozem is enriched with minerals and humus, and has a neutral composition (pH 7-7.5), it does not require additional fertilizers.
Chernozem is also used to prepare soil mixtures with peat, sand and compost. Adding black soil to the soil makes it healthier. Gardeners know: this has a lot of obvious advantages for a summer cottage or farm. Chernozem is used for arranging lawns and growing various crops. By adding chernozem, soils are healed and improved, making them more fertile.
There are several main areas of distribution of chernozems in the territory of the former USSR. The specific features of chernozems in each region are determined by bioclimatic conditions.
The first region is Southern European, which includes Moldova, Ukraine and the Ciscaucasia. The chernozem of this area is distinguished by a large thickness of the humus horizon with a fairly low content of humus and easily soluble salts.
The second region occupies most of the European part of Russia. Here the thickness of the humus layer is already less, but it is in this area that the chernozem contains the largest amount of humus.
The third region is located on the territory of Western Siberia and Kazakhstan, and also occupies part of Central Siberia. The chernozems of these areas are characterized by the presence of deep humus streaks formed as a result of deep freezing of the soil. The humus content in the upper parts of the chernozem is quite high, but it quickly decreases with depth.
And the last, fourth region is the Transbaikal steppes. The humus content in these chernozems is low and the thickness of the humus layer is small.
Also, chernozem soils are developed in some countries of Central Europe: Hungary, Romania and Bulgaria. There are also black soils in North America.
INTRODUCTION
Russia contains more than 10% of the world's farmland. According to media reports, our country remains the last large reserve of agricultural land on the planet, at least in the “civilized” world. Therefore, knowledge about our land resources suitable for agriculture has recently become of utmost importance. According to the founder of Russian soil science V.V. Dokuchaev, “our plant-terrestrial soils (of which chernozem is a representative) are not some kind of mechanical, random, lifeless mixtures, but, on the contrary, are independent, definite, natural-historical bodies subject to known laws” (1).
1. CHARACTERISTICS OF CHERNOZEM
Compound
Chernozem is a rather heterogeneous mass: here you can find pieces of quartz, flakes of humus, and sometimes fragments of limestone, feldspar and even granite pebbles.
It is very rich in humus (dark organic matter, one might say, natural manure) and the most important, easily soluble plant nutrients, such as: phosphoric acid, nitrogen, alkalis, etc. Typical chernozem is usually fine-grained, crumbly and always reveals the closest relationship (both in structure , and composition) with the underlying rocks (subsoil), which themselves (loess) in the vast majority of cases are very rich in soluble nutrients and endowed with excellent physical properties.
Structure
Chernozem is a plant-terrestrial soil whose thickness on average is about 60 cm. Under the turf, 5-8 cm thick, there is a dark, homogeneous, loose mass - humus, consisting of grains or grains, sometimes roundish, but more often representing irregular polyhedra. This horizon in unplowed, virgin places is overcrowded with hundreds of thousands of living and dead underground parts of herbaceous plants. The average thickness of the A horizon (accepted designation according to V.V. Dokuchaev) is 30-45 cm. Below, the soil horizon merges completely imperceptibly with the transition horizon, which indeed, in all its features (physical and chemical), represents a gradual transition from the upper (A) horizon to the lower (C) subsoil. The thickness of horizon B is also 30-45 cm. The subsoil - the base (C) in the vast majority of cases consists of loess (light yellow, very loose, carbonate-rich loam), but often it also consists of sandy loam, chalk, limestone, marl, etc. ., and always the subsoil (C) gradually passed into the upper soil horizons (A and B), giving them a strictly defined mineral character. Thus, chernozem in all natural sections, not disturbed (in one way or another) represents a gradual, closest genetic connection with the subsoil, whatever its composition.
Types
The following subtypes of chernozem soils are distinguished:
Podzolized chernozems,
Leached chernozems,
Typical chernozems,
Ordinary chernozems,
Southern chernozems.
Properties
1. Due to its composition, chernozem always has a more or less dark color and is favorable to heat and moisture. Color is a typical external feature: the color of chernozem, whether it contains humus up to 15% or no more than 3-4%, always turns out to be more or less dark,
2. Replenishment of chernozem, that is, the ability to become much more ripe (in the agricultural sense), that is, one whose subarable horizon is approximately the same composition in structure as the arable one.
3. Another typical constant feature is the average thickness of chernozem, which ranges from 60 to 140 cm.
2. AREAS OF DISTRIBUTION
According to V.V. Dokuchaev chernozem is always and everywhere the result of cumulative activity:
a) bedrock (subsoil), on which it currently lies;
b) the climate that surrounds this soil now and surrounded it in the past (latitude and longitude, the nature of precipitation, temperature, winds);
c) wild vegetation that grew there and still grows to this day in places untouched by culture.
The areas of distribution of fertile plains in the world are: the steppes of Europe and Asia, the savannas of Africa, Australia, the prairies of North and Pampas of South America, Venezuela, Brazil.
On the territory of Russia, chernozems are distributed in the regions of the Volga region, the Urals, the North Caucasus, the Lower Don and Western Siberia. The heart of the black earth strip is the Voronezh and Saratov regions. The volume of chernozem soils in the world is 48%, in Russia - 8.6%, which is 1.53 million km 2.
3. APPLICATION
Chernozem soils can withstand long-term cultivation without any fertilizer and, whenever climatic conditions are favorable, they produce excellent yields of rice, grains, sunflowers, beets, fodder, fruits, grapes and other industrial and vegetable crops. The natural fertility of chernozem soils makes it possible to fully satisfy the population's need for food, provides a significant part of the raw materials for light industry, and ensures livestock breeding.
Chernozem is a highly fertile land, dark in color, chernozem is rich in humus, with a pronounced granular-lumpy structure, usually chernozem is formed in forests, loams or clays, in a temperate continental climate.
Chernozem is rightfully considered the best soil for agriculture; chernozem is formed under perennial herbaceous vegetation, in the climatic conditions of the steppe and forest-steppe territorial zones.
On the territory of our country, black soils are found in the central black soil regions, the Volga region, Western Siberia and the North Caucasus; there are many black soil lands in Ukraine, as well as in some European countries, China, South and North America.
Chernozem, as a soil, is rich in humus, formed on loess-like loams or clays, usually in a temperate continental climate, with periodic precipitation, under perennial vegetation, usually herbaceous.
Conditions of soil formation of chernozems
For persistent soil formation of chernozems, the following conditions are necessary: the climate is temperate, or moderately continental, there must be an alternation of moistening and drying, with the dominance of a positive temperature regime. The average annual temperature should not be lower than +3 +7 degrees Celsius, and the annual precipitation amount should be 300-600 mm.
The relief of the chernozems is undulating-flat, in some places cut by depressions, ravines, and river terraces.
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The vegetation on chernozems is perennial herbaceous, meadow-steppe. In appropriate climatic conditions, its decomposition occurs, as a result of which humus compounds are formed, which, accordingly, accumulate in the upper layers of the soil.
Together with humus in chernozem soil, in the form of complex organic and mineral compounds, plant nutrients such as nitrogen, iron, phosphorus and sulfur are formed, etc. site/node/2879
About the properties of black soil
Chernozems in their properties - have fairly good water-air qualities, but chernozem is distinguished by a lumpy or granular structure, a high calcium content in the soil from 70 to 90%, and is characterized by a neutral or almost neutral reaction.
Chernozem on earth is valued for its increased fertility, natural and intense humification, and a fairly high, about 15%, humus content in the upper layers of the soil.
What types of black soil are there?
Chernozems are divided into the following types:
Podzolized chernozem - these chernozems are common in broad-leaved grassy forests;
Leached chernozem - such chernozems are formed under the meadow forb-grass steppes of the forest-steppe zone;
Typical chernozem - the formation of this type of chernozem occurs under forb-grass soil, i.e. meadow-steppe, vegetation in forest-steppe zones, loess-like and cover loams;
Ordinary chernozem - these chernozems can be found in the northern part of the steppe zone, and they are formed under forb vegetation;
Southern chernozems - these chernozems are formed under fescue-feather grass vegetation; they can be found in the southern part of the steppe zone.
Having a large amount of humus in its composition, chernozem is valued as a highly fertile soil that produces a high and stable harvest. It also contains a fairly large amount of other useful substances for fertility, so necessary for plants: nitrogen, sulfur, iron and phosphorus. Chernozem in its structure has a dense lumpy structure, and southern chernozem is considered one of the most fertile, it is even called “fat chernozem”.
Because of their fertility, black soils have always been valued throughout the world. And now, in modern times, black soil is the best type of land for growing vegetables, fruits, berries, trees and shrubs. Although it is worth knowing that for some plants, when planting them in the ground (chernozem), peat, sometimes sand or compost should be mixed in to loosen the earth (soil), because chernozem itself is quite dense, it is not very loose.
Application of chernozem
As we already know, black soil is the best soil for plants. As the name suggests, chernozem is dark-colored land (soil) that is very fertile.
Chernozem is used as vegetable soil and is used when laying out lawns, in gardening and as garden soil, etc. Chernozem is also used when cultivating land with a high clay content, land with poor drainage, to create a favorable air-water regime, and also, if necessary, to create a loose, lumpy soil structure.
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For characteristics of chernozem black or very dark color of the earth is the very first visual sign. Organic matter gives it this color. humus. The intensity of the dark color depends on the amount of humus present in the soil. The layer of chernozem in different places can vary greatly: from 30 cm to 1.5 m.
And the humus in the layer can be from 3% to 15%. And so, the humus content determines the fertility of the soil. Humus is formed from organic plant residues under the influence of moisture, heat, microorganisms, earthworms, and molds. Microorganisms play a particularly important role in processing plant residues.
According to studies, the total weight of all microorganisms in 1 hectare of soil can be several tons. Imagine how many of them are in the soil! And from this it follows that in order for a plot to produce a good harvest, it is necessary to provide a large number of microorganisms, and this is only possible with a sufficient amount of organic residues.
And at the same time, treat the arable layer especially carefully so as not to upset the balance of all living things in it. On chernozems, the subsoil layer is also fertile. But there is not enough air in it, plant roots do not grow there, it is denser and it contains very few microorganisms. As the arable layer decreases, it can be dug in little by little.
The acidity of chernozem soils is neutral or completely alkaline. This is exactly what most garden and garden plants love. Fresh, not depleted black soil produces good yields without the application of any fertilizers.
, podzolized, leached and typical forest-steppe chernozems.Typical black soils. Typical chernozems are soils in which the characteristic properties inherent in chernozem soils are most clearly expressed. They are distributed mainly in the western regions of the forest-steppe zone of the European part of the USSR and only in isolated spots penetrate into the region of the black earth steppe. Small tracts of them are also found on the western slopes of the Altai Mountains, in conditions of somewhat increased moisture.
Typical chernozems are characterized by an intense black color, a clearly defined granular structure of the A horizon, the largest reserve of humus in the humus layer, a gradual transition from one horizon to another, effervescence at the border of the A and B horizons or within the B horizon, and a clearly defined carbonate horizon of significant thickness.
We provide a description of the soil profile of a typical thick chernozem (Poltava region, K.I. Bozhko).
Horizon A - 0-46 cm. Dark gray, humus, up to 20 cm depth - arable cloddy-grainy, from 20 cm- grainy. There are earthworm tunnels.
Horizon B - 46-90 cm. Also dark gray with a fawn tint (in the lower part), grainy-lumpy, at a depth of 52 cm- deposits of coal salts in the form of carbonate “mold”. Effervescence from acid at depth 46 cm.
Horizon C - 90-130 cm. Dirty-fawn carbonate loess, heavily dug up by excavators, grainy and blocky. There are a lot of carbon salts in the form of “mold” and in the form of thin “veins”.
Typical thick chernozems are characterized by very deep penetration of humus, the presence of calcium and magnesium carbonates deposited at a depth of 52-120 cm in the form of carbonate “mold”, and large excavations of the soil layer by excavators.
Their profile does not reveal movement of iron and aluminum hydroxides. As for calcium, its sharp increase with depth is due to the presence of calcium carbonate salts in the carbonate horizon. In this regard, in typical chernozems, differentiation of their genetic horizons by mechanical composition is not found.
The results of agrochemical analyzes are given in table. 50 show the presence of extremely low acidity in typical chernozems (pH varies in the upper horizon from 6.0 to 6.8).
Hydrolytic acidity is weakly expressed and is mostly 0.4-2.8 m-eq by 100 G soil/
In the lower horizons of these soils, the value of exchangeable and hydrolytic acidity decreases even more. The colloidal fraction of typical chernozems is predominantly saturated with Ca ++ and Mg ++ with a ratio of the latter from 10: 1 to 8: 1. The degree of saturation is very high and reaches 94-99%.
Containing a large amount of humus and silt particles and being highly saturated with bases, typical chernozems have a well-defined granular structure, which determines favorable water and air regimes. Podzolized chernozems. Podzolized chernozems develop mainly under deciduous forests of the forest-steppe zone, where, due to a more humid climate, the processes of leaching and podzolization in the soils manifest themselves to a noticeable extent. According to a number of characteristics and properties, podzolized chernozems are very close to dark gray forest-steppe soils.
Podzolized chernozems are characterized by a small reserve of humus in the humus horizon; a non-carbonate layer is located deep in the carbonate horizon between the humus and carbonate horizons. In these soils, carbonates lie at such a depth that their rise to the humus horizon is not always ensured. Therefore, in the lower part of the humus horizon, a calcium deficiency in the soil solution and a slightly acidic reaction may periodically occur.
A slightly acidic environment causes some solubility of humus and promotes the movement of sludge. In the upper part of the humus horizon, under the influence of the turf process, there is an intensive accumulation of ash elements of plant residues and new formation of organomineral colloids with high absorption capacity occurs.
The lower part of the humus horizon is characterized by a periodically weakly acidic reaction, since the supply of bases here is limited both from above and from below. This is where signs of podzolization are found, which are morphologically expressed in the form of “siliceous powder” at the boundary of the humus and transition horizons.
A nutty structure is observed in the illuvial horizon (B). In some cases, chernozems show signs of significant surface podzolization. (removal of sesquioxides and silt fraction).
The morphological structure of podzolized chernozems can be represented by the description of the following section (Bashkir Autonomous Soviet Socialist Republic; D.V. Bogomolov).
Horizon A n - 0-20 cm. Dark gray, almost black, lumpy-dusty.
Horizon A 1 -20-29 cm. Dark gray, almost black; the structure is fine- and medium-grained with well-defined angular edges.
Horizon A 2 - 29-40 cm. Dark gray, with a clear, sharp-edged, medium- to coarse-grained structure; on the edges of the structure there is a small coating of siliceous powder, which appears most clearly when the soil dries out.
Horizon B 1 -40-59 cm. Darkish brown, lumpy-nutty; somewhat compacted, along the edges of the structure there is a weakly expressed siliceous powder.
Horizon B 2 - 60-82 cm. Reddish-brown, lumpy-prismatic, and nutty; compacted
Horizon Sun - 82-96 cm. Brown, with a reddish tint and with the same structure, but somewhat less pronounced; compacted
Horizon C - 96-120 cm. Yellowish-brown, dense deluvial clay; boils slightly from hydrochloric acid.
Weakly podzolized chernozems are morphologically distinguished by the intense dark gray color of the humus horizon, the presence of a well-defined granular structure, and the appearance of signs of podzolization in the lower part of the humus horizon and in the upper part of the illuvial horizon.
The illuvial horizon of weakly podzolized chernozems is noticeably pronounced, significantly compacted and, having a nutty and lumpy-prismatic structure, its structure is close to a similar horizon of dark gray weakly podzolized forest-steppe soils.
The mechanical composition of slightly podzolized chernozems does not change very much along the profile.
A higher content of the silty fraction is observed in the humus-accumulative horizon. Deeper into the soil profile, the amount of silt particles gradually decreases, and then slightly increases in the illuvial horizon. This distribution of the silty fraction along the soil profile indicates the presence of podzolization in them, although weakly expressed.
The content of absorbed bases in these soils is quite high, but depending on the mechanical composition it varies significantly. In soils that are heavier in mechanical composition, the number of exchangeable bases is 48.2-61.54 m-eq for calcium and 4.7-16.0 m-eq for magnesium, in lighter ones - the number of absorbed bases decreases to 43-44 m-eq for calcium and 4.3-5.4 m-eq for magnesium.
Weakly podzolized chernozems have a slightly acidic reaction, while the exchangeable acidity varies within the range of pH = 4.7-6.6.
The degree of base saturation of these soils is very high and usually ranges from 80 to 90%, often reaching 95%. The content of mobile forms of P 2 O 5 in podzolized chernozems is quite low and, according to many analyses, mostly ranges from 1.5 to 7.5 mg by 100 G soil. In this regard, podzolized chernozems in most cases are in great need of phosphorus fertilizers.
Leached chernozems. Leached chernozems are widespread in the forest-steppe, and also partially in the steppes, far from forests, in conditions of increased moisture.
They have larger reserves of humus in the humus layer (Table 49). The thickness of the humus horizon (A + B) in leached chernozems in different parts of the described zone varies greatly. Within the Ukrainian SSR, the humus layer reaches 120 cm and more, in the eastern regions it decreases significantly and, with the exception of some foothill areas, rarely exceeds 70 cm. Carbonates in these soils lie less deeply than in podzolized chernozems. Therefore, in leached chernozems, they periodically rise with soil solutions to the humus horizon.
The depth of carbonate boiling in these soils varies greatly, but most often lies at the level of 90-120 cm from the surface, and in areas of wet forest-steppe - at a depth of 150-200 cm.
As a result of leaching processes, leached chernozems are also characterized by a noticeable compaction of the transition horizon, in which a slightly increased content of colloidal substances and sesquioxides is found. The structure of this horizon is granular or nutty.
Leached chernozems differ from podzolized chernozems by the absence of silica accumulations in the lower part of horizon A.
The absorption complex of leached chernozem, along with absorbed calcium and magnesium, contains a very small amount of absorbed hydrogen.
Depending on the depth of boiling, the degree of expression of the illuvial horizon and the nutty structure associated with it, as well as depending on the greater or lesser content of absorbed hydrogen in the absorbing soil complex, leached chernozems are divided into weakly leached, moderately leached and highly leached. The latter include those leached chernozems in which not only the B horizon, but also the soil-forming rock does not boil.
The morphological structure of leached chernozems can be represented by the following typical profile (Bashkir ASSR, D.V. Bogomolov).
Horizon A n - 0-18 cm. Dark gray, almost black, quite heavily atomized; compaction is noticeable in the lower part of the arable layer.
Horizon A 1 - 18-30 cm. Same color, loose, fine- and medium-grained structure, somewhat rounded in shape, with poorly defined edges.
Horizon A 2 - 30-39 cm. Same color, with a slight brownish tint; the structure somewhat coarsens and becomes predominantly medium-grained.
Horizon AB - 39-50 cm. Dark gray with a clearer brownish tint; somewhat compacted, granular-lumpy.
Horizon B 1 - 50-66 cm. Darkish brown, slightly compacted; the structure is lumpy, elongated, somewhat prism-shaped.
Horizon B 2 - 66-85 cm. Reddish-brown, somewhat denser; the structure is lumpy-prismatic, and under pressure it breaks down into smaller lumpy and granular units.
Horizon Sun - 85-115 cm. Brown, with a reddish tint, compaction decreases somewhat; the structure is less pronounced; in the middle of the horizon there is a slight effervescence from hydrochloric acid and veins of lime appear.
Horizon C - from 115 cm. Yellowish-brown dense deluvial clay.
Characteristic morphological features of leached chernozems are the presence of a compacted illuvial horizon with a cloddy-prismatic structure, a reduced level of boiling and, at the same time, the absence of signs of podzolization.
Differentiation of the soil profile by mechanical composition is manifested in leached chernozems to a much lesser extent than in podzolized chernozems. The silt fraction in leached chernozems gradually increases down the soil profile to the B2 horizon, and then slightly decreases in the BC and C horizons.
Leached chernozems are distinguished by a high absorption capacity and a relatively high content of absorbed Ca ++ and Mg ++ . The ratio between absorbed calcium and magnesium in these soils is quite wide (8:1 and 7:1). Leached chernozems have low metabolic acidity, which usually fluctuates between pH = 5.7-6.1. Their hydrolytic acidity is relatively low, in most cases not exceeding. 3-6 m-eq by 100 G soil.
The amount of absorbed bases is expressed in large quantities and most often fluctuates between 30-40 m-eq by 100 G soil. At the same time, leached chernozems are characterized by a high degree of base saturation, reaching 87-95%. At the same time, the content of assimilable phosphoric acid in these soils is very low.
The amount of P 2 O 5 ranges from 1.5 to 9.0 mg per 100 g of soil and only in isolated cases is expressed in higher numbers. In this regard, leached chernozems need phosphorus fertilizers to the same extent as podzolized chernozems.
A significant part of leached chernozems in terms of humus content belongs to high-humus chernozems. However, in nature, the development of medium-humus and low-humus leached chernozems is often encountered.
Zone of ordinary and southern chernozems of the steppe. Southern chernozems. Southern chernozems are distributed in the southern, driest regions of the chernozem zone. Precipitation in this part of the zone is about 350-400 per year. mm, soils are little wetted.
The vegetation here is less developed and is represented mainly by southern feather grass species with a significant participation of ephemerals. Due to weak soil wetting, the root system of plants penetrates to a shallow depth.
The productivity of the vegetation cover in this subzone is very low, and a small amount of organic matter enters the soil each year. The processes of mineralization of plant residues in drier and warmer climatic conditions proceed more vigorously. Therefore, the humus content in southern chernozems is significantly lower compared to other subtypes of chernozems and usually ranges from 4 to 6% (Table 53).
The thickness of the humus horizon of southern chernozems is small; in western, more humid areas it reaches 60-70 cm, in the eastern regions, in particular in Siberia, rarely exceeds 40 cm.
The color of southern chernozems is dark gray or gray with a brownish tint.
Due to weak wetting, calcium and magnesium carbonates are found within the humus layer, and in the eastern regions sometimes even from the surface. In such cases, soils boil from the surface or in the upper part of the humus horizon.
In this regard, the absorption complex of southern chernozems is saturated mainly with Ca and Mg. Often the composition of absorbed bases also includes absorbed Na in small quantities, which gives these soils signs of weak solonetsity (Table 54).
The absorption capacity of southern chernozems is quite large and often reaches 30-40 m-eq by 100 G soil. The reaction of the aqueous extract is slightly alkaline. Their structure is most often lumpy, somewhat less often granular.
In terms of water-air, thermal and biochemical properties, as well as the content of the most important nutrients, southern chernozems are not inferior to ordinary ones. A peculiar representative of the southern chernozem is the Azov, or Cis-Caucasian chernozem.
The Azov or Cis-Caucasian chernozems, first studied and described by Acad. L.I. Prasolov, lie east of the Sea of Azov, extending all the way to the foothills of the Caucasus. These chernozems are distinguished by a highly developed humus horizon, the thickness of which reaches 1.5-1.8 m or more. The humus content is relatively small - 4-6%. Due to the insignificant amount of humus, these subtypes of chernozem have a brown or dark gray color.
The effervescence of lime carbonate is detected from the very surface of the soil or at a slight depth. They have a well-defined coarse-grained structure. The reaction of the soil solution is slightly alkaline.
Possessing a thick humus horizon, and therefore a high content of organic matter, the Azov or Cis-Caucasian chernozems are highly productive. In this respect, they are almost not inferior to other groups of chernozem soils.
Features of other subtypes of chernozems. Along with the soils described above, the chernozem zone contains meadow-chernozem soils, carbonate chernozems, saline chernozems and solodized chernozems.
Meadow-chernozem soils develop in those places of the chernozem zone where soil formation occurs with the participation of groundwater lying at a depth of 3-5 m. They are found mainly on flat, wide, poorly drained watersheds of the Oka-Don lowland and on the wide above-floodplain left bank terraces of the Dnieper and Volga. Meadow-chernozem soils are very widespread in the West Siberian Lowland.
Developing with the participation of groundwater, meadow-chernozem soils in the lower part of the profile usually show signs of restoration processes in the form of rusty and bluish spots of gleying. They are distinguished by a higher humus content, sometimes reaching 14-18%.
Due to the periodic capillary pull of the soil solution to the surface, in all horizons of meadow-chernozemic soils, easily soluble salts may appear in small quantities, which impart to the soil signs of solonchakity, solonetsity and solominization.
Carbonate chernozems are chernozems that effervesce from the surface and contain a significant amount of carbonates throughout the profile.
There are primary carbonate and secondary carbonate chernozems. %
Primary carbonate chernozems are not widespread and occur in the form of separate spots confined to outcrops of tertiary carbonate clays, limestones, calcareous sandstones, marls and their eluvium.
Thus, primary carbonate chernozems are soils enriched with carbonates due to the highly carbonate soil-forming rock.
Secondary carbonate chernozems develop in conditions of a poorly drained plain, where in the hot season, ascending currents of soil solutions and enrichment of the upper horizons with carbonates are possible.
Primary carbonate chernozems are found in the western regions of Ukraine, on the Volga Upland, in the High Trans-Volga region, secondary carbonate ones - in the lowland Ciscaucasia and in Northern Kazakhstan.
Alkaline chernozems are soils whose absorption complex contains more than 5% of the amount of exchangeable bases of absorbed sodium. They are distinguished by the fragile structure of horizon A, strong compaction, lumpy and blocky nature of horizon B, slightly alkaline reaction, and the ability to float and form a crust.
Solonetz chernozems have less favorable water-air properties and, therefore, somewhat lower productivity. They are usually found in small spots, confined mainly to small micro-relief depressions, or bottoms. They have a significant distribution in the West Siberian Lowland.
Solodized chernozems are formed from solonetsic chernozems as a result of the process of leaching and solodization. According to morphological characteristics, they somewhat resemble leached or podzolized chernozems, having a nutty structure of the transition horizon and revealing silica spots in the lower part of the A horizon.
The absorption complex of these soils contains absorbed sodium and a small amount of absorbed hydrogen. In this regard, the reaction of the soil solution in the surface horizons is slightly acidic, and in the lower ones it is alkaline. They are also characterized by the formation of an illuvial horizon. Solodized chernozems are most often found in Western Siberia.
These are, in basic terms, the essential features that characterize individual soil subtypes of the chernozem soil type.
To what has been said, it should be added that among the chernozem soils, solonchaks, solonetzes and solods are found in separate small spots. These soil formations are especially widespread in the West Siberian Lowland. But since these soils are discussed in more detail below, we will not dwell on them here.
All the subtypes of chernozems discussed above are in turn subdivided according to their mechanical composition into clayey, heavy loamy, loamy, light loamy and sandy loam. The most common of them are loamy and light loamy chernozems. Ordinary black soils. Ordinary chernozems are distributed mainly in the steppe zone, under conditions of slightly reduced moisture. Due to the greater dryness of the climate, vegetation develops here weaker, and in connection with this, consequently, the enrichment of the soil with organic substances occurs in more limited quantities.
Ordinary chernozems contain about 6-8% humus (Table 51).
The total thickness of humus and humus transition horizons in ordinary chernozems is 70-80 cm. At the same time, in the northern part of the subzone adjacent to the southern border of the forest-steppe, the thickness of the humus layer of ordinary chernozems increases to 90 cm, and when moving to the subzone of dry steppes, the humus layer decreases to 60-70 cm.
Ordinary chernozems acquire somewhat greater thickness in pre-gully depressions, as well as in barely noticeable depressions of the plateau. These chernozems are usually more deeply leached from calcium and magnesium carbonates. On the contrary, on the hills, even barely visible to the eye, lie ordinary chernozems with carbonates raised high to the surface. These facts indicate the presence of complexity of the soil cover in the distribution zone of ordinary chernozems.
In ordinary chernozems of the European part of the USSR at a depth of about 3-4 m A horizon of release of easily soluble salts and gypsum (salt horizon) is often observed. In ordinary chernozems of Western Siberia, the salt horizon appears at a depth of about 200 cm.
Ordinary chernozems are somewhat different in morphological characteristics from typical chernozems. They have a less intense color of the humus horizon, usually less thickness, a less distinct granular and more lumpy structure.
The amount of humus in them decreases very gradually with depth along the soil profile, and along with the humus, the color intensity gradually decreases.
In some cases, for example in Western Siberia, the transition horizon of chernozem has a heterogeneous tongue-like, or pocketed, color, caused by humus leaks from the humus horizon into the underlying horizons.
Formation of tongues of humus in Western Siberian chernozems, according to. according to K.P. Gorshenin, is explained by the influence of a cold, sharply continental climate, in which in winter the soil moistened by autumn rains sharply cools, as a result of which cracks form in it. The same cracks can form in summer when the soil dries out too much. Through these cracks, in the warm and humid season, humus penetrates to a considerable depth, forming the indicated tongues.
The predominant component of humus in ordinary chernozems are humic acids. As for fulvic acids, they are of subordinate importance here.
Unlike podzolized and leached chernozems, ordinary chernozems do not contain absorbed hydrogen. Ordinary chernozems are saturated with Ca ++ and Mg ++ and only in some cases do they contain traces of absorbed Na + (Table 52).
Due to such saturation of soil colloids with bases, the pH of the salt extract of ordinary chernozems fluctuates around 7.0; a neutral or close to it reaction in the surface horizon becomes weakly alkaline with depth.
Ordinary chernozems are characterized by high porosity, increased moisture capacity and aeration, and at the same time significant water permeability. The large porosity in these soils ensures rapid and complete absorption of water from atmospheric precipitation, and the high value of field moisture capacity allows a large amount of water to be retained in capillary suspension. Within a 1.5-meter layer of soil, according to N.P. Remezov, about 500 mm water.
The deepest soaking of these soils is observed in the spring; autumn precipitation penetrates to a shallower depth than spring precipitation. In summer, the upper part of the soil profile almost completely retains all precipitation, which is then used by plants for transpiration and synthesis of organic matter.
Zone of dark chestnut and chestnut soils of the dry steppe. Mountain provinces.
Soil formation of chestnut soils
Chestnut soils develop in the subboreal subarid (semiarid) climate, which is characterized by warm, dry summers and cold winters with little snow cover. The temperature in July is 20-25°C, in January from -5 to -25°C. The average annual temperature is 2-10°C. The sum of active temperatures (> 10°C) is 2200-3500°C. The annual precipitation is 200-400 mm, the maximum precipitation occurs in the summer, it often falls in the form of showers. Evaporation exceeds precipitation, the humidification coefficient is 0.25-0.45. Dry winds are frequent. Climatic indicators determine the non-flushing type of water regime, due to which the movement of substances occurs only within the soil profile. The relief of the chestnut soil zone is predominantly flat or slightly undulating, associated with ancient water-accumulative lowlands. Steppe depressions are widespread, in which saline soils, solonetzes, solods, and meadow-chestnut soils are formed, creating a greater complexity of soil cover. The soil-forming rocks are loess-like carbonate loams, saline marine rocks, eluvium-deluvium of various bedrocks - saline and uninhabited, carbonate and non-carbonate. Chestnut soils are formed in the zone of dry steppes, under the canopy of a low-growing sparse complex herbaceous cover. Coverage rate 50-70%; it decreases as the zone's climate becomes drier. Within the Caspian region and Kazakhstan, three subzones of dry steppes are distinguished: fescue-feather grass, wormwood-fescue, fescue-wormwood steppes replace each other from north to south. On saline and alkaline chestnut soils, peculiar associations of wormwood, twig, and chamomile are formed. The soil surface is covered with crusts of lichens and blue-green algae and diatoms. In dry steppes, the biomass of plant communities averages about 200 c/ha, with more than 90% being roots. The annual growth of green mass is about 30 c/ha, the growth of roots is 110 c/ha. Every year, about 600 kg/ha of ash elements and about 150 kg/ha of nitrogen are involved in the biological cycle; return is approximately equal to consumption. Among the elements participating in the cycle, N, Si, and K predominate. In terms of the number of microorganisms, chestnut soils differ little from chernozems, but the total annual biological activity here is weaker due to a longer dry period.
general characteristics
Chestnut soils are soils with an A-Bca-C type profile, formed in the dry steppes of the subboreal zone. The humus horizon A of these soils has a chestnut color, in the first meter of the soil profile there are abundant releases of carbonates, and in the second (in many cases) gypsum. Chestnut soils on the northern border of distribution are close in structure and properties to southern chernozems (dark chestnut soils), and on the southern border - to brown semi-desert soils (light chestnut soils). Their separation from soils of neighboring types is carried out based on a set of bioclimatic indicators. The term “chestnut soils” was introduced by V.V. Dokuchaev in 1883. He identified chestnut soils as a special type in the 1900 classification along with brown semi-desert soils. S. S. Neustruev, A. A. Rode, E. N. Ivanova and others made a great contribution to the study of the geography, genesis, properties, and methods of rational use of these soils. Chestnut soils occupy 262.2 million hectares on the globe, located almost exclusively in the northern hemisphere. In Eurasia they form a strip to the south of the chernozem zone, in North America - to the west of the chernozem zone at higher absolute levels. In the USSR, the area of chestnut soils is 107 million hectares (4.8%).
Starting with V.V. Dokuchaev and N.M. Sibirtsev, the origin of chestnut soils was associated with the aridity of the climate and the xerophilic nature of the vegetation, the active mineralization of plant residues and humus, and the weakening of humus accumulation compared to chernozems. Aridity also determines the weak leaching of the profile from carbonates, gypsum and easily soluble salts. V.A. Kovda expressed a point of view about the paleohydromorphic past of chestnut soils formed on the low plains of the dry steppe. This point of view was confirmed for a number of regions, in particular for chestnut soils of the Caspian lowland (I.V. Ivanov et al., 1980). Thus, it has been established that over the past 9 thousand years, the light chestnut soils of the drainless plain of the Northern Caspian Sea have gone through the stages of meadowness, salinization, desalinization, alkalinization, and steppe in their development. The same processes involved in the formation of chestnut soils as in the formation of chernozems. The most important of them are turf, as well as the process of migration and accumulation of carbonates. In chestnut soil, the turf process is less developed than in chernozems. The zone of chestnut soils is characterized by the development of complexity of the soil cover. Chestnut soils form complexes with solonetzes and meadow-chestnut soils. The reason for the high complexity of the soil cover is the microrelief, which determines differences in the water-salt regime of soils, as well as diversity in the properties of soil-forming rocks, the activity of excavators, spotty vegetation against the backdrop of a dry climate and drainage-free territory. An example of exceptionally high complexity of soil cover in the zone of chestnut soils is the territory of Prikaspiisk