Krasnozems and zheltozems of humid subtropical forests. Brunizems. Soil types

The sum of active air temperatures varies from 4000 to 8000 °C, the growing season is from 200 to 365 days. Thermal resources allow two full crops per year to be grown. The energy supplied to the land surface is the main, but not the only factor in soil formation. Equally important is the degree of atmospheric moisture in the area. Different combinations of solar energy and precipitation determine the distribution of soil types over the earth's surface. Within the same thermal belt, zonal soils are represented by several types in accordance with the moisture content of the territory and the nature of the vegetation. The change of landscapes and soils in the subtropics is mainly due to moisture, which decreases with distance from the ocean coasts.

The agricultural development of the subtropical zone is 17%. The soils of arid and humid regions are most plowed up - brown soils, red soils and yellow soils, black merged and floodplain soils. In semi-desert and desert areas, the main agricultural areas are confined to gray soils and floodplain soils. In the valleys of the Nile, Tigris, Indus, the most ancient centers of agricultural culture arose. The subtropical belt has a wide range of agricultural plants: wheat, cotton, grapes, citrus, fruit, nut and other crops.

Subtropical rainforest areas are areas that receive between 1000 and 2500 mm of precipitation per year. The most significant in terms of area are the North American and East Asian regions. The soil cover is dominated by zheltozems and red soils. In the southern hemisphere, the area of ​​\u200b\u200bhumid subtropics is much smaller; two regions are distinguished - South American and Australian. The soil cover of the South American region is dominated by red soils under coniferous and coniferous-deciduous forests and reddish-black soils - rubrozems under tall-grass subtropical prairies. In rubrozems, weak ferrallitization is combined with intense humus accumulation; the water regime is flushing and carbonates are absent in the profile. Reddish-black soils are also found in the North American subtropical region, in its western less humid part, on the border with dry subtropics. The Australian humid-forest region is characterized by mountainous relief and the predominance of zheltozems and yellow-brown soils. The hydromorphic soils of the humid-forest subtropical regions are yellow earth-gley, meadow, marsh, and alluvial.

The largest massifs of these soils are confined to the eastern oceanic sectors of the continents. In Eurasia, krasnozems and zheltozems are common in the south of Korea and Japan, in Central and Southeast China. In North America, they occupy the southern Appalachians and adjacent plains, as well as the most well-drained areas on the Florida peninsula. In the southern hemisphere, yellow earths and red earths are common in the mountain belt of Eastern Australia, in the northeast of Tasmania, on the North Island of New Zealand and on the extreme southeast coast of Africa. In the subtropical zone of the western sectors of the continents, krasnozems and zheltozems occur locally, in special orographic conditions and in a fairly humid climate; in southern Bulgaria, Yugoslavia, on the Black Sea coast of the Caucasus in Adzharia and Abkhazia, on the Lankaran lowland.

There is a lot of precipitation (1000-3000 mm), mild winters, moderately hot summers. Biomass of forests consisting of oak, beech, hornbeam, maple, chestnut, vines, wild grapes, ferns - more than 400 t/ha, litter - 21 t/ha, up to 0.7 t/ha of ash elements.

These films, like color, are inherited by krasnozems from soil-forming rocks.

Intense weathering leads to the decomposition of almost all primary minerals with the formation of mainly kaolinite and halloysite. Two soil-forming processes dominate: humus-accumulative and eluvial (podzolic type).

Under a layer of weakly decomposed forest litter lies a humus (up to 12% humus) horizon 10-15 cm, gray-brown with a reddish tint and a lumpy structure. Next is Mt. B brownish red, dense, with clay streaks, 50-60 cm thick. Horizon C is red with whitish spots and ferromanganese nodules.

These soils are low in calcium, magnesium, potassium and sodium leached from weathering products and high in iron. The reaction of the environment is acidic throughout the profile, humus - up to 8%. Fulvic acids predominate over humic acids. The removal of elements down the profile is partially compensated by a significant fall and the influx of ash elements during its decomposition. Physical properties are favorable due to high water permeability and moisture capacity with a well-defined water-resistant structure.

Zheltozems are formed on argillaceous shales and clays with poor water permeability; therefore, processes of surface gleying and the formation of ferruginous oxide nodules take place. Usually found in the foothills and lower parts of the slopes of low mountains. Lessivage is often observed. The profile has good differentiation according to the Ao-A1-A2-B-C type. In horizon B and below, yellow coloration and high clay content dominate. The absorption capacity is relatively low for such conditions - 5-10 and up to 20 cmol / kg, although calcium predominates. Very high acidity throughout the profile, significant accumulation of ferruginous nodules in the lower part of the profile. The content of humus, predominantly fulvate, is from 5-6% in A1 with a sharp drop down. Physical properties due to the smaller amount of sesquioxides are worse than in krasnozems.

The soils of the humid subtropics are poor in nitrogen and ash elements; to increase their fertility, the use of organic and mineral fertilizers, especially phosphate fertilizers, is very important. After deforestation, erosion develops vigorously, therefore, anti-erosion measures are extremely important. Krasnozems and zheltozems are the most valuable soils for tea, tobacco, essential oil and citrus crops. A lot is applied for citrus fruits - up to 350 kg/ha of a.i. phosphate fertilizers, up to 250 kg/ha a.i. nitrogen, up to

150 kg/ha of potash fertilizers, lime. On tea plantations, an acidic reaction is optimal.

Brown soils. Brunizems

Subtropical arid xerophyte-forest and shrub-steppe areas are common on all continents. Almost all of them have a complex relief: mountain ranges, plateaus, plateaus and intermountain depressions alternate. Horizontal soil zones are mostly not expressed, and mountain zoning dominates. The soil cover is dominated by brown, red-brown and gray-brown soils.

Brown and red-brown soils are widespread in the dry subtropics of the Mediterranean in Southern Europe and Northwest Africa, Mexico, California, Central Chile, South Africa, South and Southeast Australia. Small areas of brown soils are found in the subtropical mountainous regions of East Asia, in the Western Tien Shan and Pamir-Alai, in the Kopetdag, Crimea and in the dry subtropics of Transcaucasia.

They are formed mainly on siallitic-carbonate weathering crusts, with brown soils occurring under low-growing sparse xerophytic forests, and gray-brown soils under shrub subtropical steppes. They are characterized by a non-flushing water regime under conditions of a variable-humid Mediterranean type of climate, which is characterized by dry, hot summers and humid, warm winters with very short snow cover or without it at all. With a significant amount of precipitation - 600-700 mm, a wet winter season with a temperature of +10 to -3 ° C and a dry summer season are clearly distinguished. Soils are usually non-freezing, formed under dry forests of oak, laurel, maritime pine, juniper tree, shiblyak, maquis, that is, high-ash vegetation. These soils experience the influence of sharply different hydrothermal regimes during the year.

During the winter humid and relatively warm period, there is an intensive weathering of primary and formation of secondary clay minerals of hydromicaceous-montmorillonite-illite composition. Mobile weathering products during the wet winter period are washed out of upper parts soil thickness to a greater or lesser (depending on the amount of precipitation) depth. Usually, easily soluble salts (chlorides, sulfates) are completely removed from the soil profile, while less soluble calcium carbonates are deposited at a depth of 30-50 cm or more and form a carbonate illuvial horizon. There are processes of humification and, to a large extent, mineralization plant residues in a neutral or slightly alkaline environment, rich in bases.

During a hot and rainless summer, the weathering processes slow down significantly, especially in the upper, driest horizon. At a certain depth, where the soil is less dry, these processes continue during the summer, so the most clayey is not the uppermost soil horizon, but the horizon at a depth of 30-80 cm.

The drying of the soil surface causes the pulling of film moisture and dissolved substances from deeper layers. When moisture evaporates, dissolved substances and, in particular, calcium carbonates crystallize, filling the capillary gaps in the soil column above the carbonate nodule horizon. Neoplasms of calcium carbonates have the form of the thinnest white mold or pseudomycelium. During the winter rainy period, when the soil is washed with water saturated with carbon dioxide, the carbonate mold dissolves again and is pushed back into the deeper parts of the profile.

During dry and hot summers, the processes of mineralization of dry matter slow down, which contributes to the polymerization and preservation of humic substances in soils, so the humus content in brown soils is usually 4-7, less often up to 10%, and in gray-brown soils it is 2.5- 4% with a significant predominance of the group of humic acids (Cr / Cf -1.5-2.0). The iron oxides released during weathering are dehydrated during the dry period. This gives the soil a reddish-brown hue, especially bright in the horizon of maximum claying.

There are no thick glacial rocks of the boreal belt, or accumulations of loess and loess-like rocks of the subboreal zone. Pleistocene rocks of small thickness are the main soil-forming rocks. Limestones are frequent, where the A 1 soil layer directly overlies the limestone layer. There are eroded and redeposited red-colored weathering crusts of igneous and metamorphic rocks. Dust materials enter through the atmosphere. The rocks are usually heavily karst, fissured, which contributes to good drainage and exacerbates aridity. Groundwater lies far away and does not affect the processes of soil formation.

At the beginning of the Pleistocene, vigorous erosion of red-colored weathering products took place, finely elutriated accumulations of which were deposited on the surface of limestones. These deposits are called "terra rossa" (red earth). They are especially common on the Adriatic coast. Balkan Peninsula. Similarly, later accumulations of brown clays, called terra fusca, arose.

The humus horizon of brown soils is brown in color, has a lumpy structure, and is 20–30 cm thick. Deeper is a compacted horizon, often carbonate B. C, often rocky, lies even lower. In particular, on the southern coast of the Crimea, soils 20-30 cm thick occur in Mesozoic shales, often involved in the soil due to plantation. A typical soil profile looks like: A 1 -Bm-Bca-C.

Brown soils are characterized by a slow decrease in humus down the profile, a slightly acidic and neutral (often alkaline in the lower horizons) reaction of the medium, and a high cation exchange capacity (25–40 cmol/kg) with a predominance of calcium and magnesium. There is no profile differentiation by chemical composition. They are distinguished by high biological activity, especially in spring and autumn, up to 40 million / g of soil microorganisms. The hydrothermal regime promotes deep weathering of primary minerals. Water-physical properties are relatively favorable.

In brown soils, the total content of nitrogen and phosphorus is high, but mobile forms of phosphorus are not enough in them. In the legend to the soil map of the world, brown soils are assigned to the group of cambisols. In general, the soils of the arid subtropics are highly fertile and widely used for agriculture (wheat, corn), vineyards, citrus and other orchards, and olive plantations. The destruction of natural vegetation provoked severe soil erosion - many granaries of the times of the Roman Empire (Syria, Algeria) became deserted steppes. In Spain, Portugal, Greece, up to 90% of brown soils are affected by erosion. Many areas are in need of irrigation.

The wider use of these soils is hindered by dry summer period, during which many crops require irrigation, mountainous terrain, where farming is often impossible, and horticulture and viticulture cause severe soil erosion. Gray-brown soils in flat terrain are used in agriculture and horticulture. In areas where the winter period is frost-free, they usually grow two crops a year: in winter, without irrigation, cereals (for example, wheat), and in summer, with irrigation, more heat-loving crops (rice, cotton, tobacco, melons). Often gray-brown soils are used for orchards and vineyards.

Brunizems are high-humus chernozem-like soils, leached in the upper part of the profile, with a Bt textural horizon and signs of gleying in the lower part, with a groundwater level of 1.5-5 m. These are prairie and pampas soils. They are formed in a moderately cold subtropical climate with 600-1000 mm of precipitation, average January temperatures from -8 to +4 °С, July - 20-26 °С. More than 75% of precipitation falls in the summer in the form of showers. Moisture coefficient is more than 1. There is a periodically flushing water regime that maintains a relatively high level of groundwater in the watersheds. In South America, rubrezems are distinguished, which differ from brunizems in a reddish color, but are very close to them in morphology and soil properties.

Brunizems are formed in a flat or slightly hilly relief on loess and carbonate moraine loams and clays. Natural vegetation - perennial high (up to 1.5 m) cereals with a deep root system. Above-ground phytomass 5-6 t/ha, underground - 18 t/ha. In terms of properties, brunizems are close to chernozems, but are more leached, often acidic on top, and do not have salt horizons. Among the exchange cations, calcium always predominates, but the proportion of hydrogen can also be quite large. In the northeast of the United States, humus has up to 10%, and in the southwest of the range - 3%.

Brunizems are characterized by intense clay formation due to the weathering of primary minerals; montmorillonite and illite predominate. The age is usually 16-18 thousand years, that is, it is significantly older than the chernozems. The soil-forming process is characterized by humus accumulation, removal of easily soluble compounds and silt; the introduction of elements with a capillary border of soil and groundwater. Brunizems - the most fertile soils USA. Almost all of them are plowed up, used for crops of corn and soybeans (“Corn Belt”). With long-term operation, they lose humus, structure, porosity, and are subject to erosion.

Chernozem soils are located south of the zone of gray forest soils. They stretch in the form of a continuous but uneven strip, starting from the border with Romania to Altai. To the east of Altai, the chernozem zone has an insular character. Chernozems are distributed here along intermountain basins and depressions. The main massifs of chernozems are common in the forest-steppe and steppe zones of Russia - the central regions, the North Caucasus, the Volga region, and Western Siberia.

NATURAL CONDITIONS OF SOIL FORMATION

Climate. It is heterogeneous, especially in the steppe zone. When moving from west to east, the amount of heat gradually decreases, dryness and continentality of the climate increase. The average annual temperature ranges from 10 °C in the west to -2 °C in the east (Transbaikalia). The sum of temperatures > 10 °C is 2400-3200 °C in the west in the forest-steppe part of the zone, 1400-1600 °C in the east, and 2500-3500 and 1500-2300 °C in the steppe part, respectively. The duration of the period with a temperature > 10 °C is 150-180 days in the western regions of the forest-steppe, 90-120 days in the eastern regions, and 140-180 and 97-140 days in the steppe zone, respectively.

The annual amount of atmospheric precipitation in the west and in Ciscaucasia is 500-600 mm, while moving to the east it decreases: in the Volga region to 300-400 mm, in Western Siberia and Transbaikalia to 300-350 mm. Most of the annual precipitation falls in the summer (40-60%), which is unevenly distributed over time and often has a shower character. Winter precipitation is low, especially in Siberia; they form a thin, unstable snow cover, which contributes to deep and severe freezing of the Siberian chernozems.

In the forest-steppe part of the zone, the ratio between the amount of precipitation and evaporation approaches unity; periodically flushing regime dominates here. In the steppe part of the zone, in chernozems, a non-leaching water regime develops; the ratio of precipitation and evaporation is 0.5-0.6. The depth of soil wetting decreases in a southerly direction.

In the western regions of the zone with a longer growing season with snowy and mild winters, a wide range of crops are cultivated. In the east of the zone, severe, long and little snowy winters, which limits the range of agricultural crops, makes it difficult and impossible to overwinter winter crops and the cultivation of perennial legumes, and limits the cultivation of fruit crops.

Relief. The relief of the zone of chernozem soils is flat, slightly wavy or ridged. The territories of the Central Russian, Volga Uplands, General Syrt and the Donetsk Ridge are characterized by the greatest dissection.

In the Asian part, chernozem soils are common in the south of the West Siberian Lowland with a slightly dissected relief. To the east, chernozems are found in the plains and foothills of the Altai, the Minusinsk depression and the Eastern Sayan.

Soil-forming rocks. They are mainly represented by loess and loess-like loams (from light to heavy loams).

Clay soil-forming rocks are found on the territory of the Oka-Don lowland, in Ciscaucasia, the Volga and Trans-Volga regions, in a number of regions of Western Siberia. In some areas, chernozems develop on dense eluvial sedimentary rocks (chalk, flasks, etc.).

Loesses and loess-like loams are very susceptible to water erosion processes, which causes soil erosion on steep slopes and the development of ravines.

A feature of the chemical composition of soil-forming rocks of the chernozem zone is their carbonate content, in some provinces (West Siberian, partially Central Russian) - salinity.

Vegetation. That vegetation, under the influence of which chernozems were formed, is practically not preserved at present. A large area of ​​chernozem soils has been plowed up, the rest is used as pastures and hayfields.

Natural vegetation in the past in the forest-steppe was characterized by the alternation of forest areas with meadow steppes.

Forests are partially preserved along watersheds, gullies and river terraces. In the European part of the zone, forest vegetation is represented mainly by oak, in Western Siberia - by birch pegs.

The herbage of the meadow steppes was represented by mesophilic species, forbs, and legumes: tall-stemmed feather grass, fescue, steppe timothy grass, cocksfoot, meadow sage, meadowsweet, adonis, low sedge, clover, sainfoin, bird-foot, etc. The projective cover reached 90%.

To the south, the meadow steppes were characterized by forb-feather grass and fescue-feather grass associations. In their herbage, xerophytic plants took a relatively greater part, the main background of which in the forb-feather grass steppes was narrow-leaved feather grass, fescue, thin-legged, steppe oats, drooping sage, Volga adonis, bluebells, squat sedge, steppe plantain, euphorbia, mountain clover, etc. In the tip-chak-feather-grass steppes, low-stemmed feathery grass, tyrsa, fescue, wheatgrass, and sedges prevailed. Moisture deficiency contributed to the development of ephemers and ephemeroids in these steppes - mortuk, bulbous bluegrass, tulips, beetroot, wormwood with a degree of projective cover of 40-60%.

To date, natural vegetation has been preserved mainly only on steep slopes, in gullies, stony soils, and protected areas.

GENESIS

Several hypotheses have been put forward about the origin of chernozems. V. V. Dokuchaev believed that chernozems are soils of plant-terrestrial origin, that is, they were formed when parent rocks changed under the influence of climate, steppe vegetation, and other factors. It is known that for the first time this hypothesis about the vegetative-terrestrial origin of chernozem was formulated by M. V. Lomonosov in 1763 in the treatise “On the layers of the earth”.

Academician P. S. Pallas (1799) put forward a marine hypothesis of the origin of chernozem, according to which chernozems were formed from sea silt, decomposition of organic remains of reeds and other vegetation during the retreat of the sea.

The third hypothesis, put forward by E. I. Eikhwald (1850) and N. D. Brisyak (1852), is that chernozems arose from swamps during their gradual drying.

Chernozems, according to some sources, are relatively young soils. Studies using radiocarbon dating have shown that they were formed in the post-glacial period during the last 10-12 thousand years. The average age of humus in the upper soil horizons is at least a thousand years, and the age of deeper horizons is at least 7-8 thousand years (Vinogradov et al., 1969).

Modern ideas about the formation of chernozems confirm the hypothesis of their plant-terrestrial origin. This was reflected in the works of L. M. Prasolov, V. I. Tyurin, V. R. Williams, E. A. Afanasyeva, M. M. Kononova and other scientists.

The most important processes of formation of chernozems are soddy and eluvial. The latter is expressed mainly in the profile migration of calcium bicarbonate, which is formed during the decomposition of plant residues rich in calcium.

These processes develop under the perennial vegetation of grassy steppes in the forest-steppe and steppe zones under conditions of periodically leaching and non-leaching water regimes and form the humus and carbonate profiles of the chernozem.

The annual litter under the vegetation of the meadow steppes of Altai is 10-20 tons of organic matter per 1 ha, of which up to 80% fall to the share of roots. From this mass, from 600 to 1400 kg/ha of nitrogen and ash elements are involved in the biological cycle. This is much more than what comes per hectare from the litter of broad-leaved forests (150-500 kg) or from the litter of dry steppe herbaceous vegetation on chestnut soils (200-250 kg).

The development of the soddy process during the formation of chernozems led to the formation of a powerful humus-accumulative horizon, the accumulation of plant nutrients and the structuring of the profile.

Mineralization of organic remains of herbaceous formations in the Chernozem zone creates conditions close to optimal for humus formation. This is especially evident in spring and early summer, when there is enough moisture in the soil and the most favorable temperature. During the period of summer desiccation, microbiological processes weaken, polycondensation and oxidation reactions intensify, leading to the complication of humic substances. Hummification occurs under conditions of excess calcium salts, saturation of humic substances with calcium, which practically excludes the formation and removal of water-soluble organic compounds.

The chernozem process of soil formation is characterized by the humate type of humus, the complexity of humic acids, their predominant fixation in the form of calcium humates, and the reduced presence of fulvic acids. Under the influence of humic substances, decomposition of soil minerals practically does not occur; their interaction with the mineral part of the soil leads to the formation of stable organo-mineral compounds.

Secondary minerals (montmorillonite, etc.) during the chernozem process are formed both during the weathering of primary minerals and by synthesis from the decay products of litter, but they do not move along the soil profile.

Along with the accumulation of humus during chernozem formation, the most important plant nutrients (N, P, S, Ca, etc.) are fixed in the form of complex organo-mineral compounds, as well as the appearance of granular water-stable aggregates in the humus layer. The latter are formed not only as a result of the adhesive ability of humus substances, but also when the living roots of herbaceous plants act on the soil and the intensive vital activity of soil animals, especially worms.

Thus, the most important features of the genesis of chernozems are the formation of humic substances, mainly humic acids, their interaction with the mineral part of the soil, the formation of organo-mineral compounds, a water-resistant macrostructure, and the removal of easily soluble soil formation products from the upper soil horizons.

The heterogeneity of soil formation factors, changes in climatic conditions, and vegetation determine the features of chernozem formation within the zone.

The most favorable conditions for the chernozem process are formed in the southern part of the forest-steppe zone with the optimal hydrothermal regime, leading to the formation of the maximum biomass. To the north, more humid climate conditions contribute to the removal of bases from the litter, leaching and even podzolization of chernozem soils.

To the south, the amount of precipitation decreases, the moisture deficit in the soil increases, the amount of organic residues entering the soil decreases, and their mineralization increases, which leads to a decrease in the intensity of humus formation and humus accumulation.

In accordance with the characteristics of soil formation factors in the zone of chernozems, the following subzones are distinguished: podzolized and leached chernozems, typical chernozems, ordinary chernozems, and southern chernozems.

The first two subzones belong to the southern forest-steppe, the third and fourth - to the steppe.

Changes in climate and vegetation in the Chernozem zone in the direction from west to east led to facies differences in chernozem soils, manifested in different thicknesses of the humus layer, humus content, forms of carbonate release, leaching depth, features of water and thermal regimes.

The chernozems of the South European facies, Danube and Pre-Caucasian provinces are formed in a milder and more humid climate. They almost do not freeze, quickly thaw, and are deeply washed. The biological cycle proceeds intensively; soil formation covers a thicker layer of soil; a large thickness of the humus horizon is formed with a relatively low content of humus (3-6%). The soil profile is characterized by greater leaching, deep occurrence of gypsum and micellar form of carbonates.

To the east, the continentality of the climate increases, the growing season shortens, and the time and depth of soil freezing increase. The chernozems of the central provinces (Central Russian, Zavolzhskaya) develop in temperate continental conditions and are classified as medium and high humus (6-12%).

The chernozems of the West Siberian and East Siberian facies freeze deeply and slowly thaw; the depth of wetting and the spread of plant root systems are reduced; the period of active decomposition of organic substances is reduced. The thickness of the humus horizon of these chernozems is less than in the central provinces, and the humus in the upper horizon is slightly higher (5.5-14%). The strong cracking of chernozems in cold weather (and the incorporation of Na + into the PPC) determines the linguality of the humus profile. The chernozems of the East Siberian facies are characterized by the smallest thickness of the humus horizon with a humus content of 4 to 9%, which sharply decreases with depth.

As one moves eastward from the central provinces, the amount of precipitation decreases and salt horizons occur at shallower depths. As a result of low soil leaching, there is a complex soil cover.

The noted zonal and facies features of chernozem formation are reflected in the degree of expression of the main features of the chernozem soil type.

Agricultural use of soils significantly changes the natural process of soil formation. First of all, the nature of the biological circulation of substances, the conditions for the formation of water and thermal regimes change.

Most of the generated biomass is annually alienated from arable land for growing crops, and much less organic residues enter the soil. The soil during the cultivation of spring and tilled crops remains without vegetation for a long time, which leads to a decrease in the absorption of winter precipitation by the soil, increased freezing, and deterioration of the water regime.

During the plowing of virgin chernozems, the soil structure is destroyed both under the influence of increased humus mineralization and mechanical treatments. There is a decrease in humus and nitrogen in the arable layer. Thus, the amount of humus in ordinary chernozem has decreased by 27% over 300 years and nitrogen by 28% (Aderikhin, 1964). The average annual loss of humus from the arable layer of typical and leached chernozems is 0.7-0.9 t/ha (Chesnyak, 1983).

In the arable soils of the Central Chernozem zone, compared with virgin and fallow lands, a significant decrease in humus and total nitrogen occurred in the arable layer (Table 43).

43. Changes in the content of humus and total nitrogen in the soils of the Central Chernozem zone (Aderikhin, Shcherbakov)

Especially strongly in arable chernozems there is a decrease in humus and deterioration of other properties under the influence of erosion and deflation. So, on the medium-eroded leached chernozem, the humus content decreased from 5 to 2.4%, on the medium-eroded ordinary chernozem - from 5.7 to 4.6%, nitrogen - from 0.32 to 0.13% and from 0.37 to 0.31% (Lyakhov, 1975).

In the south of Western Siberia (Altai Territory), chernozem soils lost 1.5-2.0% of humus over 18-20 years. Its annual losses amounted to 1.5-2.0 t/ha. A significant proportion of these losses (about 80%) is due to erosion and deflation, and only about 20% is due to the mineralization of humus during the cultivation of agricultural crops.

In order to stabilize and increase the humus content in chernozem soils, it is first of all necessary to stop erosion or deflation by introducing a complex of soil protection measures.

PROFILE STRUCTURE AND CLASSIFICATION

Profile structure. It is characterized by the presence of a dark-colored humus layer of different thickness, which is subdivided into the upper humus-accumulative horizon A, evenly colored, granular-cloddy structure and the lower one - up to humus streaks, uniformly colored, dark gray, with a brownish tint humus horizon AB, nutty-lumpy or granular-lumpy structure. Below, horizon B is distinguished - transitional to a rock, predominantly brown in color, with a gradual or unevenly streaked, tongued, humus content weakening downwards. According to the degree, form of humus content and structure, it can be divided into horizons B 1 B 2; in a number of subtypes, illuvial-carbonate (Bc) horizons are distinguished. The accumulation of carbonates is also observed deeper, in the BC K horizon and in the parent rock (C c); in some southern subtypes, horizons of gypsum accumulation (Cs) are distinguished.

Classification. The chernozem soil type is divided into subtypes according to the structure of the profile, genetic features and properties, each of which has a certain geographical position. In accordance with the subzones from north to south, the following subtypes are distinguished in the zone of chernozems: podzolized, leached, typical, ordinary, southern. Within the subtypes, genera are distinguished. The most common of these are as follows.

Ordinary - isolated in all subtypes; their properties correspond to the main characteristics of the subtype. In the full name of the chernozem, the term of this genus is omitted.

Weakly differentiated - developed on sandy and sandy rocks, typical features of chernozem (color, structure, etc.) are weakly expressed.

Deep-boiling - in the profile there is a gap between the humus and carbonate horizons due to a more pronounced flushing regime due to a lighter granulometric composition or relief conditions. They stand out among typical, ordinary and southern chernozems.

Non-carbonate - developed on rocks poor in calcium; effervescence and release of carbonates are absent. They stand out among typical, leached and podzolized chernozems.

Carbonate - characterized by the presence of carbonates throughout the profile. Among the leached and podzolized chernozems, they do not stand out.

Alkaline - within the humus layer, they have a compacted solonetzic horizon with an exchangeable Na content of more than 5% CEC. They stand out among ordinary and southern chernozems.

Solodified - are characterized by the presence of a whitish powder in the humus layer, darkening of the humus color, differentiation of the profile in terms of the content of silt and sesquioxides, relatively high effervescence and occurrence of easily soluble salts (compared to the usual ones), sometimes the presence of exchangeable sodium. Distributed among typical, ordinary and southern chernozems.

Deep gleyic - developed on two-membered and layered rocks, as well as under conditions of long-term preservation of winter permafrost (Central and Eastern Siberia), with signs of weak gleying in the lower layers of the soil profile.

Merged - developed on silt-clayey rocks, with dense (merged) B horizons, blocky-prismatic structure. They stand out in warm facies forest subtypes. steppe chernozems.

Underdeveloped - have an underdeveloped (incomplete) profile due to their youth or formation on highly skeletal or cartilaginous-rubble rocks.

Solid - characterized by the formation of deep cracks (cold facies).

The genera of chernozems are divided into types according to a number of characteristics (Table 44).

44. Signs of dividing chernozems into types *

In addition, in genera, according to the degree of severity of the accompanying process, chernozems are divided into types of weakly, medium, strongly solonetsous, weakly, medium, strongly saline, etc.

Peculiarities of soil formation in different subtypes of chernozems are reflected in the structure of their soil profile.

Chernozems of the forest-steppe zone are represented by podzolized, leached and typical. The total area occupied by these soils is 60.3 million hectares.

Chernozems podzolized in the humus layer have residual signs of the podzolic process of soil formation in the form of a whitish (silica) powder.

Their structure is expressed by a combination of the following genetic horizons (Fig. 16):

A-A 1 -A 1 B-B 1 -B 2 -B to -C to.

Horizon A dark gray or gray in color, granular-cloddy texture. The lower part of horizon A 1 is clarified with a whitish powder. Horizon A 1 B dark gray or brownish gray, with a grayish tint, lumpy or lumpy-nutty structure, with whitish powder. Horizon B 1 is illuvial, brown, with dark spots or streaks (streaks of humus in the form of tongues and pockets), nutty-prismatic structure, with brown films on the edges of individual parts, denser and heavier granulometric composition than the overlying horizon.

Boiling from HC1 and the release of carbonates in the form of veins, tubules, cranes are most often noted at a depth of 120-150 cm from the surface, and the gap between the humus layer (A + A 1 B) and the carbonate horizon reaches 60-80 cm. The carbonate horizon may be absent in chernozems developed on carbonate-free rocks. In addition to dividing into types according to thickness and humus content, podzolized chernozems are subdivided according to the degree of podzolization into weakly and medium podzolized.

Leached chernozems, in contrast to podzolized chernozems, do not have silica powder in the humus layer. Their morphological structure is expressed by the following horizons (see Fig. 16):

A-AB-B-B K -BC K -C K.

Horizon A is black-gray in color, cloddy, with a granular structure in its subsurface part. Horizon AB dark gray or grey, cloddy. Horizon B brownish in color, with humus streaks, lumpy-nutty or prismatic structure. Illuvial brown horizon B tongued, with streaks, films on the edges of structural units, compacted, slightly enriched in clay particles. Carbonates are found at a depth of 90-110 cm in the form of veins, tubules, cranes. Leached chernozems are characterized by the presence of horizon B leached from carbonates with a thickness of more than 10 cm. The predominant species are medium-humus medium-thick leached chernozems.

Typical chernozems have a deep humus profile: its morphological structure is typical for the chernozem type of soil formation (see Fig. 16):

A-AB-B K -BC K -C K.

Horizon A is intense, black-gray in color, with a well-defined granular water-resistant structure. The AB horizon is characterized by a gradual decrease in the humus color downwards, an enlargement of the structure, which becomes lumpy.

Boiling and release of carbonates in the form of pseudomycelium, tubules, cranes are found in the lower part of the AB horizon or in the upper part of the Bk horizon, usually from a depth of 70-100 cm; there is an abundance of molehills along the entire profile.

The subtype of typical chernozems is dominated by powerful and medium-thick, fat or medium-humus species, common, deep-boiling, carbonate and saline genera.

In the steppe zone common and southern chernozems are common. Together with solonetz complexes, they occupy an area of ​​about 99 million hectares.

Ordinary chernozems have a morphological profile structure close to typical chernozems: A-AB(AB K)-B to -BC K -C. Horizon A is dark gray, with a brownish tinge, with a granular-and-cloddy or lumpy structure. Horizon AB gray (or dark gray), with a clear brown tint, lumpy structure, effervescent in the lower part. The next B to is an illuvial carbonate horizon with a white-eye (CaCO 3), gradually turning into horizon C.

The subtype of ordinary chernozems is dominated by species of medium-humus medium-thick chernozems, ordinary, carbonate, solonetsous and solodized genera.

Southern chernozems are widespread in the southern part of the steppe zone on the border with the zone of chestnut soils of the dry steppe. The structure of the soil profile of southern chernozems is characterized by a combination of horizons:

A - AB K -B k -BC K -C KS .

Horizon A dark gray, with a brownish tint, lumpy; horizon AB K brown-brown, lumpy-prismatic structure; effervescence is usually found in the middle part of the horizon. Horizon B is illuvial-carbonate, with distinct white-eye and compaction.

At a depth of 1.5-2-3 m, southern chernozems contain gypsum in the form of small crystals (C KS). A distinctive morphological feature of the southern chernozems is a shortened humus profile, high effervescence, and the release of carbonates in the form of white-eye.

In the southern chernozems, carbonate, solonetzic, solonchakous are more pronounced than in ordinary chernozems; low-humus medium-thick species predominate.

COMPOSITION AND PROPERTIES

According to the granulometric composition, chernozem soils are diverse, but their medium, heavy loamy and clay varieties predominate.

Along the profile of typical, ordinary and southern chernozems, the silt fraction is distributed evenly. In podzolized and partly leached chernozems (see Fig. 16), as well as in solodized and solonetsous chernozems, there is some increase in silt in the illuvial horizon (B).

Minerals of montmorillonite and hydromicaceous, less often kaolinite groups predominate in the mineralogical composition of the clay fraction of chernozems. Of the other secondary minerals, crystallized iron sesquioxides, quartz, and amorphous substances are widespread. Highly dispersed minerals are evenly distributed along the profile.

The diversity of granulometric and mineralogical compositions is determined by the features of parent rocks and the conditions of weathering of primary minerals.

There are no significant changes in the gross chemical composition of chernozem soils. Typical, ordinary and southern chernozems are distinguished by the greatest constancy of chemical composition. In the profile of these subtypes, the content of Si0 2 and sesquioxides does not change. In podzolized and leached chernozems, there is a slightly increased content of Si0 2 in the humus horizon and the greatest displacement of sesquioxides into the illuvial horizon. The same distribution of SiО 2 and R 2 О 3 was observed in solonetzic and solodized chernozems.

The most important features of the chemical composition of chernozems are also their richness in humus, the illuvial nature of the distribution of carbonates (see Fig. 16) and the leaching of the profile from easily soluble salts.

Humus is characterized by the predominance of humic acids over fulvic acids (C HA: C FA = 1.5 - 2) and their fractions associated with calcium. Humic acids are characterized by a high degree of condensation, and fulvic acids have a more complex composition compared to podzolic soils and the almost complete absence of their free (“active”) forms.

The largest reserves of humus are found in typical and leached chernozems of the East European facies, and the smallest are deep-freezing chernozems of the East Siberian facies.

In accordance with the content of humus, there is the content of nitrogen, as well as exchangeable Ca 2+ and Mg 2+ (Table 45).

The richness of chernozems in humus determines their high absorption capacity, which ranges from 30 to 70 mg eq. The soils are saturated with bases, the reaction of the upper horizons is close to neutral, in the horizons containing free carbonates it is slightly alkaline and alkaline. Only in podzolized and leached chernozems, the degree of saturation is 80-90%, and the hydrolytic acidity is up to 7 mg-eq.

In solonetsous chernozems, there is an increased content (more than 5% of the absorption capacity) of the absorbed sodium ion and a slight increase in the proportion of absorbed magnesium.

Long-term agricultural use of chernozems with a low level of crop cultivation technology leads to a decrease in the content of humus, nitrogen, and cation absorption capacity. The humus content decreases especially strongly during the development of erosion processes.

Chernozems are generally characterized by favorable physical and water physical properties: loose composition of the humus horizon, high moisture capacity and good water permeability.

Leached, typical and ordinary chernozems of heavy granulometric composition have good structure, due to which they have a low density of humus horizons (1 - 1.22 g / cm 3), which increases only in sub-humus horizons (up to 1.3-1 .5 g / cm 3) (Table 46).

Soil density also increases in the illuvial horizons of leached and podzolized chernozems, in the carbonate and solonetsous illuvial horizons of ordinary, southern chernozems.

The good structure of chernozems and their friability determine the high porosity in the humus horizons.

46. ​​Physical and water-physical properties of the chernozems of the Central Russian province (Fraitsesson, Klychnikova)

A favorable ratio of non-capillary and capillary porosity (1:2) provides good air and water permeability and moisture capacity in chernozems.

In soils of medium and heavy granulometric composition, with a decrease in the humus content, the destruction of the water-resistant structure, the density increases, and the water properties of chernozems deteriorate. This is especially noticeable in chernozems subject to water erosion.

THERMAL, WATER AND NUTRITIONAL REGIMES

The thermal properties of chernozem soils are favorable for the growth and development of cultivated plants. Chernozems are characterized by low reflectivity, they heat up quickly and cool slowly; possessing high thermal conductivity, they are able, which is especially important in springtime, to spend the main amount of heat absorbed by the soil on warming deeper horizons.

However, the chernozems of different subzones and facies differ significantly in thermal regime. Thus, the chernozems of the western and southwestern facies practically do not freeze and are characterized as very warm, short-term or periodically freezing. Here you can cultivate medium-late and late, as well as intermediate crops.

The thermal regime of moderately freezing chernozems sharply differs from the long-term freezing chernozems of Siberian facies, in which temperatures from -5 to -15 °C are observed in the 70-110 cm layer throughout the winter. The chernozems of Transbaikalia freeze especially deeply (more than 3 m). Under such conditions, the cultivation of medium-early crops with a shorter growing season is possible.

The chernozem zone is a zone of insufficient moisture. Even in the forest-steppe, the probability of dry and semi-arid years is about 40%.

In the dynamics of moisture in chernozems, G. N. Vysotsky identified two periods: 1 - drying of the soil in summer and in the first half of autumn, when moisture is intensively consumed by plants and evaporates under conditions of ascending currents over descending ones; 2 - wetting, starting in the second half of autumn, interrupted in winter and continuing in spring under the influence of melt water and spring precipitation.

These periods in the water regime of chernozems are typical for all chernozems, but the duration and timing of drying and moistening are different for each subtype. They depend on the amount of precipitation, its distribution over time and temperature.

From podzolized and leached chernozems to southern chernozems, a decrease in the depth of soaking, an increase in desiccation with a lengthening of the period of desiccation are observed. Humidification of chernozem soils to a large extent depends on the topography and granulometric composition. Light loamy and sandy loamy chernozems are soaked to a great depth. On convex relief elements and slopes, moisture consumption increases due to surface runoff and increased evaporation; surface water accumulates in depressions, evaporation is weakened, and conditions are created for deeper wetting of soils. This is especially pronounced in closed depressions, where soil wetting reaches groundwater.

Podzolized, leached, and typical forest-steppe chernozems are characterized by periodically leaching water regime.

The lower horizons of these chernozems, deeper than the maximum wetting layer, always contain a certain amount of available moisture, which can be a moisture reserve for plants in dry years.

In the semi-arid and arid provinces of the steppe zone (Zavolzhskaya, Prealtaiskaya), the water regime of ordinary and southern chernozems is non-leaching. In the lower part of the profile of these soils, a permanent horizon is formed with a moisture content not exceeding the wilting moisture value.

Under grain crops, by the time they are harvested on ordinary and southern chernozems, the root layer undergoes complete physiological drying.

Moisture reserves in chernozem soils are essential in the formation of crop yields. Thus, in the conditions of the Altai Territory (Burlakova, 1984), on leached and ordinary chernozems, 210–270 mm of precipitation is consumed to obtain a spring wheat grain yield of 2.0–2.7 t/ha, with a total moisture consumption of 340–370 mm. In unfavorable years in terms of moisture (150 mm of precipitation during the growing season), in order to obtain approximately 2.0 t/ha of spring wheat grain, it is necessary to create a moisture reserve in the meter soil layer before sowing at least 260 mm, which practically corresponds to the moisture reserve at the lowest moisture capacity. Therefore, all agrotechnical measures should be aimed at the maximum possible restoration of moisture reserves in the entire root layer of the soil by the spring of next year.

All subtypes of chernozems of the East Siberian facies have a periodically leaching water regime. The main source of moisture accumulation here is summer-autumn precipitation.

On arable chernozems, a significant loss of moisture is possible due to the surface runoff of melt water. Snow blowing leads to deeper freezing of soils and their late thawing. The decrease in water permeability of non-thawed soil layers is accompanied by large losses of moisture from surface runoff.

The stocks of nutrients for plants in chernozems are large - they fluctuate depending on the content of humus and the granulometric composition of soils. So, in rich clayey chernozems, nitrogen reserves in the arable layer reach 12-15 t/ha, and in medium-humus medium-loamy chernozems - 8-10 t/ha. With depth, the content and reserves of nitrogen, as well as other nutrients, gradually decrease.

The reserves of phosphorus in chernozems are somewhat less than those of nitrogen, but in comparison with other soils they are very significant. In the arable layer it is 4-6 t/ha; 60-80% of the total phosphorus content is represented by organic forms.

The sulfur reserve is concentrated in the root layer in organic form; in medium-humus medium-thick loamy chernozems it is 3-5 t/ha. In chernozems, large amounts of gross potassium, magnesium, and calcium are concentrated; there is a high content of gross microelements (Cu, Zn, B, Co, etc.)

However, significant reserves of nutrients in the soil do not always guarantee high crop yields. The provision of soils with nutrients depends on the hydrothermal conditions and the applied crop cultivation technologies. Under the same agrotechnical and meteorological conditions, due to different properties, a different nutritional regime is formed, which determines the formation of agricultural crops.

The content of mobile nutrients in soils is dynamic over time, depending on hydrothermal conditions, the cultivated crop, the growing season, the content of organic matter, agricultural practices, and the use of organic and mineral fertilizers. The most favorable nutrient regime for cultivated plants is created in well-cultivated chernozems.

Chernozem soils, as a rule, have a high nitrifying capacity. This applies to fat and medium-humus species that accumulate significant amounts of nitrates, especially on clean fallows. In autumn and spring, nitrates can migrate from the plow horizon. Under conditions of periodically flushing water regime, they can migrate up to 80-100 cm in podzolized, leached, and ordinary chernozems. This process is less pronounced in the southern chernozems. For this reason, winter and early spring crops may lack nitrogen.

Ammonium nitrogen is well absorbed by the soil, but in wet years it can be displaced from the absorbing complex and partially move down the profile. The movement of phosphates along the profile of chernozems is not observed.

SOIL COVER STRUCTURE

The chernozem zone is characterized by coarse contour, less complex and contrasting soil cover.

In the forest-steppe part of the zone, the soil cover structure is dominated by variations consisting of the corresponding subtypes of chernozems of varying degrees of leaching and thickness, with the participation of meadow-chernozem and gray forest soils. There are combinations of typical chernozems with the participation of carbonate and solodized genera.

In the steppe part of the zone, there are variations of chernozems of different thickness and carbonate, as well as combinations of contrasting genera of chernozems (ordinary, carbonate, solonetsous), meadow chernozem soils and solods, in spotted areas - chernozems of different thickness, carbonate content and solonetsity. There are complexes of chernozems with solonetzes.

In areas subject to water erosion, combinations with the participation of the contours of eroded chernozems are distinguished.

In areas of Western Siberia, combinations of chernozems with the participation of solonetz and solonchak-solonetz complexes, meadow-chernozem, meadow and marsh soils are widespread. Transbaikalia is characterized by fine hydromorphic-permafrost combinations consisting of chernozems, permafrost meadow and meadow chernozem soils.

AGRICULTURAL USE

Chernozems account for half of the country's arable land. A wide range of agricultural crops is cultivated here: spring and winter wheat, barley, corn, buckwheat, hemp, flax, sunflower, peas, beans, sugar beets, gourds, garden and many other crops, horticulture is widely developed, and viticulture is widely developed in the south.

Chernozem soils have high potential fertility, but their effective fertility depends on heat and moisture supply, biological activity.

Forest-steppe chernozems are characterized by better moisture supply compared to steppe chernozems. Their productivity is higher. The balance of moisture is especially tense in ordinary and southern chernozems, which leads to a decrease in their effective fertility. The level of effective fertility of steppe chernozems is reduced by the manifestation of dust storms, dry winds and periodic droughts.

Among the most important activities for rational use chernozems include their protection from water erosion and deflation, compliance with the correct crop rotations, saturated with soil-improving crops and allowing you to simultaneously fight weeds and accumulate moisture in the soil.

Measures for the accumulation of moisture in the soil and its rational use in the Chernozem zone are the main ones in increasing the effective fertility of soils. These include: the introduction of clean fallows, early deep plowing, rolling and timely harrowing of the soil, flat-cut tillage with leaving stubble to prevent deflation, tillage across slopes, autumn furrowing and slotting of fields to absorb melt water and reduce the occurrence of water erosion.

In the Chernozem zone, the correct organization of the territory, the arrangement of shelterbelts, and the optimization of the ratio of agricultural land are of great importance. A set of measures aimed at creating a favorable water regime and soil protection was developed by V.V. Dokuchaev and implemented in the Stone Steppe, which still serves as a standard for the rational organization of the territory in the Chernozem zone.

Irrigation is a promising method for increasing the productivity of chernozems. But the irrigation of chernozems must be strictly regulated, accompanied by careful control over changes in the properties of chernozems, since if they are not properly irrigated, they deteriorate. Irrigation is most effective on medium and light varieties of chernozems that are not prone to stratification, in areas with good natural drainage. Irrigation of chernozems should be additional to natural moisture to maintain favorable soil moisture during the growing season.

When irrigating chernozems, it is necessary to take into account their provincial features and water-reclamation properties. Thus, for the chernozems of Western Siberia, seven groups of chernozems have been identified that are unequal in terms of irrigation and reclamation (Panfilov et al., 1988).

The effective fertility of chernozems within each subtype is determined by generic and species characteristics: the degree of alkalinity and carbonate content, the thickness of humus horizons, and the content of humus.

Solotized, solonetsous, carbonate chernozems are characterized by unfavorable agronomic properties that reduce their effective fertility. An increase in the share of solonetzes in complexes with chernozems worsens the soil cover.

In chernozems, there is a significant dependence of crop yields on the thickness of the humus horizon and the content (or reserves) of humus. So, for the chernozems of the Altai Territory, the dependence of the yield of spring wheat on the increase in the thickness of the humus horizon to 50 cm and the humus content in horizon A to 7% increases. A further increase in the thickness of the humus horizon and humus content is not accompanied by an increase in productivity (Burlakova, 1984).

Chernozem soils, despite their high potential fertility and richness in basic nutrients, respond well to fertilization, especially in the forest-steppe, where there are favorable moisture conditions. On ordinary and southern chernozems, the maximum effect of fertilizers is achieved when carrying out moistening measures.

Getting high yields on chernozems is especially facilitated by the introduction of phosphorus and nitrogen fertilizers.

By applying organic fertilizers in chernozem soils, it is necessary to maintain a non-deficient or positive balance of organic matter to prevent a decrease in the humus content, deterioration of water-physical properties and biochemical processes.

Control questions and tasks

1. What is the essence of the chernozem process of soil formation? What are its zonal and facies features? 2. Name the main diagnostic features by subtypes and main genera of chernozems. 3. Give an agronomic description of the subtypes and main genera and types of chernozems. 4. What are the features of the agricultural use of chernozems? 5. What are the main problems of the use and protection of chernozems?

The natural conditions on the territory of our country are diverse. Depending on the climate, vegetation, geological structure The soil cover is also changing. The change of soil types from the northwest to the southeast, i.e., latitudinal zonality, is most clearly expressed. In the mountains, soil types change from the foot to the peaks, i.e., vertical zonality is observed.

The main types of soils. Top left to right: podzolic soil, gray forest soil, black soil, chestnut soil. Bottom left to right: solonetz, solonchak, serozem, krasnozem.

Tundra gley soils are the main soil type in the tundra. The zone of these soils extends north of the Arctic Circle, along the Kola Peninsula, occupies the northern part of the Arkhangelsk region and the Komi Republic, and in Siberia - at the latitude of the Arctic Circle to the Yamal Peninsula, along the coast of the Arctic Ocean and further east to the Kamchatka Peninsula. Tundra gley soils (together with arctic soils) occupy about 6% of the entire territory of Russia.

Tundra soils are thin, acidic (see Soil acidity), poor in nutrients. They contain up to 5% humus, their surface is covered with a layer of peat. The biological activity of these soils is very weak; permafrost occurs at shallow depths. On well-cultivated and fertilized tundra soils, barley, oats, cabbage, and potatoes are grown. The natural vegetation of the tundra is also used for reindeer grazing.

The zone of podzolic, including sod-podzolic, soils is located south of the tundra. It stretches in a wide strip from west to east to the coast Sea of ​​Okhotsk. This type occupies about 30% of the country's territory. Podzolic soils were formed under coniferous and mixed forests under conditions of sufficient moisture. The forest litter (the upper horizon of these soils), which consists of litter (needles, leaves, branches, etc.), is decomposed by microorganisms. In this case, organic acids are formed, which, interacting with the mineral particles of the soil, cause their decay and removal to the lower horizon. This creates an acidic podzolic horizon depleted of nutrients, consisting mainly of barren whitish silica, saturated with iron, aluminum, and magnesium. Below the podzolic horizon, an illuvial horizon is formed, where silty and colloidal soil particles, humus substances and various compounds, mainly iron, washed out from the upper layer accumulate. They give this horizon a reddish-brown color.

The most fertile among podzolic soils are soddy-podzolic soils that form under mixed and deciduous forests. When plant residues decompose, humus is formed. As a result, a humus (humus) horizon is formed at the top, consisting of humus, mineral compounds and undecomposed plant residues. It has a dark color. The more powerful the humus horizon, the higher the fertility of the soddy-podzolic soil. The thickness of the humus horizon in soddy-podzolic soils ranges from a few centimeters to 15–20 cm, and the thickness of the podzolic horizon varies from a few centimeters to 20 cm, sometimes more. The content of humus in the arable layer is 1–6%.

To increase the thickness of the humus horizon and the content of humus in it, soddy-podzolic soils are deeply plowed, organic and mineral fertilizers are added to them, and lime is added. Soddy-podzolic soils - the main arable land in the Non-Chernozem zone of the country, characterized by sufficient moisture. Increasing the fertility of these soils - essential condition creation in the Non-Chernozem region of the region of guaranteed high yields of agricultural crops.

The zone of gray forest soils extends as a narrow discontinuous strip from the Carpathians to Transbaikalia, south of the zone of podzolic soils.

Gray forest soils were formed under broad-leaved forests with a well-developed herbaceous cover. They combine the features of podzolic soils (the upper horizons are depleted in silt and the lower horizons are enriched in it, acid reaction) and steppe chernozems (a well-developed humus horizon).

The humus horizon of these soils is thicker and darker and contains more humus (3–9%) than those of soddy podzolic soils. Gray forest soils are characterized by rather high natural fertility and are widely used in agriculture.

Bog soils are found mainly among podzolic soils, especially in the Non-Chernozem region of Russia, Belarus, Polissya of Ukraine and the Baltic states, where there is a lot of precipitation. These soils are mostly acidic.

Swamp soils cannot be used for growing crops without prior drainage and development. With drainage, proper processing, liming and the introduction of phosphorus-potassium and copper-containing mineral fertilizers, marsh soils turn into highly fertile lands with a high content of humus and nitrogen. Peat is also widely used for fuel, for the preparation of organic fertilizers, for animal bedding.

The zone of chernozems extends in a wide strip from the southwestern borders of the country to the foothills of Altai. It includes the steppes and forest-steppes of Ukraine, the Central Black Earth regions of Russia, the North Caucasus, the Volga region, and Western Siberia. Chernozems are the "golden fund" of our country's land resources, the most fertile soils. The formation of these soils is primarily associated with steppe vegetation and parent rocks, which contain a lot of carbonates. During the formation of chernozems, the accumulation of humic substances and mineral elements of plant nutrition occurs. Humus contributes to the creation of a water-resistant, finely cloddy soil structure. Water-soluble salts are leached and accumulate in the lower horizons of the soil profile.

Chernozems are highly fertile: they are quite air and water permeable, absorb moisture well and retain it, contain many nutrients, and have a neutral or slightly acidic reaction.

Chernozems with a humus horizon up to 65–90 cm thick are typical of the Middle Volga, Trans-Urals, Western Siberia, Northern Kazakhstan, and some other regions. The southern chernozems have a humus horizon thickness of 30–65 cm and a less pronounced structure.

Chernozem soils are almost completely plowed up. In order to maintain their fertility and increase the yield of agricultural crops, it is necessary to apply mineral and organic fertilizers, apply soil protection measures, and follow scientifically based agricultural practices.

Chestnut soils are located south of chernozem soils, on a large territory of the zone of dry semi-desert steppes (in the south of Ukraine and Moldova, in the North Caucasus, in Kazakhstan). Vegetation in arid regions is sparse, organic matter quickly decomposes with the formation of mineral compounds, so there is little humus in chestnut soils (1.5–5%). The humus horizon of these soils is from 15 to 50 cm. In the zone of chestnut soils, droughts and strong winds are frequent, causing the danger of wind erosion, so the fight against drought and wind erosion of soils is the basis of agriculture in this zone. To increase the fertility of chestnut soils, it is necessary to apply fertilizers, especially phosphorus ones. Many agricultural crops are cultivated on chestnut soils, mainly under irrigation.

Salt licks, solonchaks, solods, takyrs and takyr soils are common in the desert zone (Central Asia, southern Kazakhstan). They form a group of saline soils. Agriculture on them is possible mainly after the removal of excess salts from the root layer during irrigation.

Serozems are widespread in the foothill regions of Central Asia and occupy 1.5% of the country's territory. They formed under subtropical semi-desert vegetation, on rocks that consist of sediments (loesses) of rivers, and contain many nutrients. In a dry, hot climate, the organic matter of these soils is rapidly mineralized. Serozems are poor in humus (0.5–4.5%), but their fertility is quite high, since the parent rock is rich in nutrients. When irrigated, many southern crops are grown on them, primarily cotton, grapes, pomegranates, and melons.

Krasnozems - typical soils of humid subtropics Black Sea coast Caucasus and part of the coast of the Caspian Sea in Azerbaijan. Krasnozems were formed under the influence of a weak podzol-forming process, and therefore they are slightly acidic. The red color of these soils is due to the fact that they contain a lot of aluminum and iron compounds. Humus horizon - 15–20 cm, contains 5–8% humus. Krasnozems are fairly fertile soils.

The soils of the mountains differ from the plains in their low thickness and a significant content of rubble. However, some types of mountain soils are almost never found on the plain. Of these, the most common are mountain-meadow and mountain-meadow-steppe soils, which are used mainly as pastures.