Chernozems of the southern forest-steppe and steppe zone. Soils, land and forest resources of Russia

The Arctic zone is characterized by the harsh climatic conditions of the Arctic climate zone, short cold summers and long winters with very low air temperatures. The average monthly temperature in January is 16…32° C; July below +8° C. This is a permafrost zone, the soil thaws to a depth of 1530 cm. There is little precipitation from 40 to 400 mm per year, however, due to low temperatures, precipitation exceeds evaporation, so the plant communities of the Arctic tundra (mainly mosses and lichens with the addition of some flowering plants) are in conditions of balanced and sometimes even excessive moisture. The phytomass of the Arctic tundra ranges from 30 to 70 c/ha, of polar deserts - 12 c/ha.

The most common type of automorphic soils in the Arctic are arctic-tundra soils. The thickness of the soil profile of these soils is determined by the depth of seasonal thawing of the soil-ground layer, which rarely exceeds 30 cm. The differentiation of the soil profile due to cryogenic processes is weakly expressed. In soils formed under the most favorable conditions, only the plant-peaty horizon (A 0) is well defined and the thin humus horizon (A 1) is much worse ( cm. SOIL MORPHOLOGY).

In arctic-tundra soils, due to excess atmospheric moisture and the high permafrost surface, high humidity is maintained throughout the short season of positive temperatures. Such soils have a weak acidic or neutral reaction (pH 5.5 to 6.6) and contain 2.5-3% humus. In relatively quickly drying areas with a large number of flowering plants, soils with a neutral reaction and a high humus content (46%) are formed.

The landscapes of Arctic deserts are characterized by salt accumulation. Salt efflorescence is common on the soil surface, and in summer small brackish lakes can form as a result of salt migration.

The tundra zone belongs predominantly to the subarctic climate zone. The climatic conditions of the tundra are characterized by a negative average annual temperature: from 2 to 12° C. The average temperature in July does not rise above +10° C, and the average temperature in January drops to 30° C. The duration of the frost-free period is about three months. Summer time is characterized by high relative air humidity (8090%) and continuous sunlight. Annual precipitation is low (from 150 to 450 mm), but due to low temperatures it exceeds evaporation.

Somewhere on the islands, and somewhere everywhere there is permafrost, the soil thaws to a depth of 0.2-1.6 m. The location of dense frozen soil close to the surface and excess atmospheric moisture causes waterlogging of the soil in the frost-free period and, as a consequence, its waterlogging. The proximity of frozen soils greatly cools the soil layer, which hinders the development of the soil-forming process.

Tundra vegetation is dominated by shrubs, shrubs, herbaceous plants, mosses and lichens. There are no tree forms in the tundra. Soil microflora is quite diverse (bacteria, fungi, actinomycetes). There are more bacteria in tundra soils than in arctic soils - from 300 to 3800 thousand per 1 g of soil.

The soil-forming rocks are dominated by various types of glacial deposits.

Tundra-gley soils are common above the surface of permafrost; they are formed under conditions of difficult drainage of soil-groundwater and oxygen deficiency. They, like other types of tundra soils, are characterized by the accumulation of weakly decomposed plant residues, due to which a well-defined peaty horizon (At), consisting mainly of organic matter, is located in the upper part of the profile. Below the peaty horizon there is a thin (1.52 cm) humus horizon (A 1) of brown-brown color. The humus content in this horizon is about 13%, the reaction is close to neutral. Under the humus horizon lies a gley soil horizon of a specific bluish color. gray, which is formed as a result of restoration processes under conditions of water saturation of the soil mass. The gley horizon continues to the upper surface of the permafrost. Sometimes, between the humus and gley horizons, a thin spotted horizon with alternating gray and rusty spots appears. The thickness of the soil profile corresponds to the depth of seasonal soil thawing.

Agriculture is possible in some areas of the tundra. Vegetables are grown around large industrial centers: potatoes, cabbage, onions, and many other crops in greenhouses.

Now, in connection with the active development of the mineral wealth of the North, the problem of protecting the nature of the tundra, and, first of all, its soil cover, has arisen. The upper peaty horizon of tundra soils is easily disturbed and takes decades to restore. Traces of transport, drilling and construction machines cover the surface of the tundra, contributing to the development of erosion processes. Violation of the soil cover causes irreparable damage to the entire unique nature of the tundra. Strict control of economic activity in the tundra is a difficult but extremely necessary task.

Taiga forests are located in the temperate climate zone. The climatic conditions of the vast territory of the taiga belt are different, but, in general, the climate is characterized by fairly large seasonal temperature fluctuations, moderately cold or cold winters (with an average January temperature of 10 ... 30 ° C), relatively cool summers (with an average monthly temperature close to +14…+16° C) and the predominance of the amount of precipitation over evaporation. In the coldest areas of the taiga zone (east of the Yenisei in Eurasia, northern Canada and Alaska in North America) there is permafrost, but the soil thaws in summer to a depth of 50 to 250 cm, so permafrost does not interfere with the growth of trees with a shallow root system. These climatic conditions determine the leaching type of water regime in areas not constrained by permafrost. In areas with permafrost, the leaching regime is disrupted.

The predominant type of vegetation in the zone is coniferous forests, sometimes with an admixture of deciduous trees. In the very south of the taiga zone, pure deciduous forests are widespread in some places. About 20% of the total area of ​​the taiga zone is occupied by swamp vegetation; the areas under meadows are small. The biomass of coniferous forests is significant (1000-3000 c/ha), but litter makes up only a few percent of the biomass (30-70 c/ha).

A significant part of the forests of Europe and North America has been destroyed, so the soils formed under the influence of forest vegetation have been in treeless, human-altered landscapes for a long time.

The taiga zone is heterogeneous: forest landscapes of different regions differ significantly in soil formation conditions.

In the absence of permafrost, different types of podzolic soils are formed on highly permeable sandy and sandy loam soil-forming rocks. The structure of the profile of these soils:

A 0 forest litter, consisting of pine needle litter, remains of trees, shrubs and mosses at various stages of decomposition. Below this horizon gradually turns into a loose mass of coarse humus, at the very bottom partially mixed with detrital minerals. The thickness of this horizon is from 24 to 68 cm. The reaction of the forest litter is strongly acidic (pH = 3.54.0). Lower down the profile the reaction becomes less acidic (pH increases to 5.56.0).

A 2 eluvial horizon (washout horizon), from which all more or less mobile compounds are carried into the lower horizons. In these soils this horizon is called podzolic . Sandy, easily crumbling, due to leaching of a pale gray, almost white color. Despite its small thickness (from 24 cm in the north and center to 1015 cm in the south of the taiga zone), this horizon stands out sharply in the soil profile due to its color.

B bright brown, coffee or rusty-brown illuvial horizon, in which inwashing predominates, i.e. precipitation of compounds of those chemical elements and small particles that were washed out from the upper part of the soil layer (mainly from the podzolic horizon). With depth in this horizon, the rusty-brown tint decreases and gradually turns into soil-forming rock. Thickness 3050 cm.

C soil-forming rock, represented by gray sand, crushed stone and boulders.

The profile thickness of these soils gradually increases from north to south. The soils of the southern taiga have the same structure as the soils of the northern and middle taiga, but the thickness of all horizons is greater.

In Eurasia, podzolic soils are common only in part of the taiga zone west of the Yenisei. In North America, podzolic soils are common in the southern part of the taiga zone. The territory east of the Yenisei in Eurasia (Central and Eastern Siberia) and the northern part of the taiga zone in North America (northern Canada and Alaska) are characterized by continuous permafrost, as well as characteristics of the vegetation cover. Acid brown taiga soils (podburs), sometimes called permafrost-taiga ferruginous soils, are formed here.

These soils are characterized by a profile with an upper horizon composed of coarse humus and the absence of a lightened leaching horizon characteristic of podzolic soils. The thickness of the profile is small (60100 cm), it is poorly differentiated. Like podzolic soils, brown taiga soils are formed under conditions of slow biological turnover and a small mass of annual plant litter, which almost completely reaches the surface. As a result of the slow transformation of plant residues and the leaching regime, a peaty dark brown litter is formed on the surface, from the organic matter of which easily soluble humus compounds are washed out. These substances are deposited throughout the soil profile in the form of humus-iron oxide compounds, as a result of which the soil acquires a brown, sometimes ocher-brown color. The humus content decreases gradually down the profile (under the litter there is 810% humus; at a depth of 50 cm about 5%, at a depth of 1 m 23%).

Agricultural use of soils in the taiga zone is associated with great difficulties. In the Eastern European and Western Siberian taiga, arable lands occupy 0.12% of the total area. The development of agriculture is hampered by unfavorable climatic conditions, severe soil logging, widespread swampiness of the territory, and permafrost east of the Yenisei. Agriculture is developing more actively in the southern regions of the Eastern European taiga and in the meadow-steppe regions of Yakutia.

Effective use of taiga soils requires large doses of mineral and organic fertilizers, neutralization of high soil acidity, and, in some places, removal of boulders.

In medical-geographical terms, the taiga forest zone is unfavorable, since as a result of intensive leaching of the soil, many chemical elements are lost, including those necessary for the normal development of humans and animals, therefore, in this zone, conditions are created for a partial deficiency of a number of chemical elements (iodine, copper , calcium, etc.)

Climate mixed forests characterized by warmer and longer summers (average July temperature from 16 to 24 ° C) and warmer winters (average January temperature from 0 to 16 ° C) compared to the taiga forest zone. Annual precipitation from 500 to 1000 mm. The amount of precipitation everywhere exceeds evaporation, which causes a well-defined flushing water mode. Vegetation mixed forests of coniferous (spruce, fir, pine), small-leaved (birch, aspen, alder, etc.) and broad-leaved (oak, maple, etc.) species. A characteristic feature of mixed forests is a more or less developed grass cover. The biomass of mixed forests is greater than in the taiga and amounts to 20003000 c/ha. The mass of litter also exceeds the biomass of taiga forests, but due to more intense microbiological activity, the processes of destruction of dead organic matter proceed more vigorously, therefore in mixed forests the litter has less thickness than in the taiga and is more decomposed.

The mixed forest zone has a rather variegated soil cover. The most characteristic type of automorphic soils of mixed forests of the East European Plain are soddy-podzolic soils – southern variety of podzolic soils. Soils are formed only on loamy soil-forming rocks. Soddy-podzolic soils have the same soil profile structure as podzolic soils. They differ from podzolic ones by the smaller thickness of the forest litter (25 cm), the greater thickness of all horizons and a more clearly defined humus horizon A1, lying under the forest litter. The appearance of the humus horizon in soddy-podzolic soils also differs from the horizon in podzolic soils; in the upper part it contains numerous grass roots, which often form a well-defined turf. Color gray in various shades, loose build. The thickness of the humus horizon is from 5 to 20 cm, the humus content is 24%.

In the upper part of the profile, these soils are characterized by an acidic reaction (pH = 4), with depth the reaction gradually becomes less acidic.

The use of mixed forest soils in agriculture is higher than that of taiga forest soils. In the southern regions of the European part of Russia, 30-45% of the area is plowed; to the north, the share of plowed lands is much less. Farming is difficult due to the acidic reaction of these soils, their strong leaching, and in places they are swampy and filled with rocks. To neutralize excess acidity, the soil is limed. To obtain high yields, large doses of organic and mineral fertilizers are needed.

Landscapes of broad-leaved forests, favorable for humans, have been exposed to human influence for a long time, so they are greatly modified: forest vegetation is either completely destroyed (in most of Western Europe and the USA) or replaced by secondary vegetation.

Among the soils formed in these landscapes, two types are distinguished:

1. Gray forest soils formed in inland areas (central regions of Eurasia and North America). In Eurasia, these soils stretch in islands from the western borders of Belarus to Transbaikalia. Gray forest soils are formed under continental climatic conditions. In Eurasia, the severity of the climate increases from west to east, average January temperatures vary from 6° C in the west of the zone to 28° C in the east, the duration of the frost-free period is from 250 to 180 days. Summer conditions are relatively the same - the average July temperature ranges from 19 to 20 ° C. Annual precipitation varies from 500-600 mm in the west to 300 mm in the east. The soils are soaked by precipitation to great depths, but since the groundwater in this zone lies deep, the leaching water regime is not typical here; only in the most humidified areas does the soil layer become completely wetted down to the groundwater.

The vegetation under which gray forest soils formed is represented mainly by broad-leaved forests with rich grass cover. To the west of the Dnieper there are hornbeam-oak forests, between the Dnieper and the Urals there are linden-oak forests, to the east of the Urals, within the West Siberian Lowland, birch and aspen forests predominate, and larch appears even further east.

The mass of litter from these forests significantly exceeds the mass of litter from taiga forests and amounts to 70-90 c/ha. The litter is rich in ash elements, especially calcium.

The soil-forming materials are predominantly cover loess-like loams.

Favorable climatic conditions determine the development of soil fauna and microbial populations. As a result of their activity, a more energetic transformation of plant residues occurs than in soddy-podzolic soils. This causes a more powerful humus horizon. However, part of the litter is still not destroyed, but accumulates in the forest litter, the thickness of which is less than the thickness of the litter in soddy-podzolic soils.

Structure of the gray forest soil profile ( cm. SOIL MORPHOLOGY):

A 0 forest litter from tree and grass litter, usually of small thickness (12 cm);

A 1 humus horizon of gray or dark gray color, fine- or medium-clumpy structure, containing a large number of grass roots. In the lower part of the horizon there is often a coating of siliceous powder. The thickness of this horizon is 20 × 30 cm.

A 2 washout horizon, gray in color, with an unclear leaf-plate structure and a thickness of about 20 cm. Small ferromanganese nodules are found in it.

In , the inwash horizon is brownish-brown in color, with a clearly defined nutty structure. Structural units and pore surfaces are covered with dark brown films, and small ferromanganese nodules are found. The thickness of this horizon is 80 100 cm.

C soil-forming rock (cover loess-like loam of a yellowish-brown color with a well-defined prismatic structure, often containing carbonate formations).

The type of gray forest soils is divided into three subtypes: light gray, gray and dark gray, the names of which are associated with the intensity of the color of the humus horizon. With the darkening of the humus horizon, the thickness of the humus horizon slightly increases and the severity of leaching of these soils decreases. The eluvial horizon A 2 is present only in light gray and gray forest soils; dark gray soils do not have it, although the lower part of the humus horizon A 1 has a whitish tint. The formation of subtypes of gray forest soils is determined by bioclimatic conditions, therefore light gray forest soils gravitate to the northern regions of the strip of gray soils, gray ones to the middle ones, and dark gray ones to the southern ones.

Gray forest soils are much more fertile than soddy-podzolic soils; they are favorable for growing grain, fodder, horticultural and some industrial crops. The main disadvantage is greatly reduced fertility as a result of centuries of use and significant destruction as a result of erosion.

2. Brown forest soils formed in areas with a mild and humid oceanic climate, in Eurasia these are Western Europe, the Carpathians, Mountain Crimea, warm and humid regions of the Caucasus and the Primorsky Territory of Russia, in North America the Atlantic part of the continent.

The annual precipitation is significant (600650 mm), but most of it falls in the summer, so the flushing regime operates for short periods of time. At the same time, mild climatic conditions and significant atmospheric moisture activate the processes of transformation of organic matter. A significant mass of litter is processed and mixed by numerous invertebrates, contributing to the formation of a humus horizon. When humic substances are destroyed, clay particles begin to slowly move into the leaching horizon.

The profile of brown forest soils is characterized by a poorly differentiated and thin, not very dark humus horizon.

Profile structure:

And 1 the humus horizon is gray-brown in color, the humus shade gradually decreases at the bottom, the structure is lumpy. Thickness 2025 cm.

B washout horizon. At the top it is a bright brown-brown, clayey, at the bottom the brown tint will decrease, and the color approaches the color of the parent rock. Horizon thickness 5060 cm.

C soil-forming rock (fawn-colored loess-like loam, sometimes with carbonate formations).

With a large amount of applied fertilizers and rational agricultural technology, these soils produce very high yields of various agricultural crops, in particular, the highest yields of grain crops are obtained on these soils. In the southern regions of Germany and France, brown soils are used mainly for vineyards.

In Eurasia, chernozems extend in a continuous strip across the East European Plain, Southern Urals and Western Siberia to Altai, east of Altai they form separate massifs. The easternmost massif is located in Transbaikalia.

In North America there are also zones of forest-steppe and steppe, to the west of the zones of mixed and deciduous forests. Submeridional strike from the north they border on the taiga zone (about 53° N) and in the south they reach the coast of the Gulf of Mexico (24° N), however, the strip of chernozem soils is located only in the inland region and does not reach the sea coast comes out.

In Eurasia, the climatic conditions of the chernozem distribution zone are characterized by increasing continentality from west to east. In the Western regions, winter is warm and mild (average January temperature 2...4° C), and in the eastern regions it is harsh and with little snow (average January temperature 25...28 ° C). From west to east, the number of frost-free days decreases (from 300 in the west to 110 in the east) and the annual amount of precipitation (from 500600 in the west to 250350 in the east). During the warm period, differences in climate are smoothed out. In the west of the zone, the average July temperature is +19...+24° C, in the east +17...+20° C.

In North America, the severity of the climate in the zone of chernozem soils increases from north to south: the average January temperature varies from 0 ° C in the south to 16 ° C in the north, summer temperatures are the same: the average July temperature is +16 +24 ° C. The annual precipitation also does not change - from 250 to 500 mm per year.

For the entire area of ​​distribution of chernozem soils, evaporation is equal to the annual amount of precipitation or less. Most of the precipitation falls in the summer, often in the form of showers, this contributes to the fact that a significant part of the precipitation is not absorbed into the soil, but is removed in the form of surface runoff, therefore, chernozems are characterized by a non-percolative water regime. The exception is forest-steppe areas, where the soils are periodically washed.

The soil-forming rocks of the chernozem territory are represented mainly by loess-like deposits (loess is a fine-grained sedimentary rock of light yellow or fawn color).

Chernozems were formed under herbaceous vegetation, which was dominated by perennial grasses, but now most of the chernozem steppes have been plowed and the natural vegetation has been destroyed.

Biomass in natural steppe communities reaches 100300 c/ha, of which half dies annually; as a result, much more organic matter enters the soil in the chernozem zone than in the temperate forest zone, although forest biomass is more than 10 times higher than the biomass of steppes . There are significantly more microorganisms in steppe soils than in forest soils (34 billion per 1 g, and for some areas even more). The intensive activity of microorganisms aimed at processing plant litter ceases only during periods of winter freezing and summer drying of the soil. A significant amount of annually supplied plant residues ensures the accumulation of large amounts of humus in chernozem soils. The humus content in chernozems ranges from 34 to 1416%, and sometimes more. Distinctive feature Chernozems is the humus content in the entire soil profile, and down the profile it decreases very gradually. The reaction of the soil solution in the upper part of the profile in these soils is neutral; in the lower part of the profile, starting from the illuvial horizon (B), the reaction becomes slightly alkaline.

The most characteristic feature of these soils, which determined their name, is a powerful, well-developed humus horizon of intense black color.

Profile structure of typical chernozems:

A 0 steppe felt. This horizon, 13 cm thick, consists of the remains of herbaceous vegetation and is found only on virgin lands.

A 1 humus horizon. Its color when wet is intensely black, its thickness is 40 × 60 cm. The horizon is saturated with plant roots.

In , the transition horizon has a blackish-brown uneven color, gradually turning into the color of the soil-forming rock. Humus streaks come here from the humus horizon. The lower part of the horizon contains a significant amount of calcium carbonate. The thickness of this horizon is 40 60 cm.

C soil-forming rock (loess-like deposits).

In Eurasia, to the south of typical chernozems, common , and even further south there are southern chernozems. To the south, the annual amount of precipitation, the total biomass and, accordingly, the mass of annual plant litter decrease. This causes a decrease in the thickness of the humus horizon (in ordinary chernozems its thickness is about 40 cm, in southern ones it is 25 cm). The properties of chernozem soils also change as the climate becomes more continental, i.e. from west to east (in Eurasia).

Chernozems are famous for their fertility; their areas of distribution are the main production base for many grains, primarily wheat, as well as a number of valuable industrial crops (sugar beets, sunflowers, corn). The yield on chernozems depends mainly on the water content in a form accessible to the plant. In our country, the black soil regions were characterized by crop failures caused by droughts.

The second no less important problem of chernozems is soil destruction caused by erosion. On chernozem soils used for agriculture, special anti-erosion measures are required.

The medical and geographical characteristics of chernozems are favorable. Chernozems are the standard for the optimal ratio of chemical elements necessary for humans. Endemic diseases associated with a deficiency of chemical elements are not characteristic of the areas where these soils are distributed.

In arid and extracontinental conditions of dry steppes and semi-deserts, chestnut and brown desert-steppe soils are formed, respectively.

In Eurasia, chestnut soils occupy a small area in Romania and are more widespread in the arid central regions of Spain. They stretch in a narrow strip along the coast of the Black and Azov Seas. To the east (in the Lower Volga region, Western Caspian region) the area of ​​these soils increases. Chestnut soils are very widespread in Kazakhstan, from where a continuous strip of these soils goes to Mongolia, and then to Eastern China, occupying most of the territory of Mongolia and the central provinces of China. In Central and Eastern Siberia, chestnut soils are found only in islands. The easternmost region of distribution of chestnut soils is the steppe of South-Eastern Transbaikalia.

The distribution of brown desert-steppe soils is more limited; these are predominantly semi-desert regions of Kazakhstan.

In North America, chestnut and brown soils are located in the central part of the continent, bordering the chernozem zone to the east and the Rocky Mountains to the west. In the south, the distribution area of ​​these soils is limited to the Mexican Plateau.

The climate of the dry and desert steppes is sharply continental; continentality intensifies as one moves from west to east (in Eurasia). The average annual temperature varies from 59°C in the west to 34°C in the east. Annual precipitation decreases from north to south (in Eurasia) from 300350 to 200 mm. Precipitation is distributed evenly throughout the year. Evaporation (a conditional value characterizing the maximum possible evaporation in a given area with an unlimited supply of water) significantly exceeds the amount of precipitation, so a non-flush water regime prevails here (soils are soaked to a depth of 10 to 180 cm). Strong winds further dry out the soil and promote erosion.

The vegetation of this area is dominated by steppe grasses and wormwood, the content of which increases from north to south. The biomass of dry steppe vegetation is about 100 c/ha, with the bulk of it (80% or more) coming from underground plant organs. The annual litter is 40 c/ha.

The soil-forming rocks are loess-like loams overlying rocks of different composition, age and origin.

Profile structure of chestnut and brown soils:

A humus horizon. In chestnut soils it is grayish-chestnut in color, saturated with plant roots, has a lumpy structure and has a thickness of 1525 cm. In brown soils it is brown in color, a lumpy fragile structure, about 1015 cm in thickness. The humus content in this horizon is from 2 to 5 % in chestnut soils and about 2% in brown soils.

In , the transitional horizon is brownish-brown in color, compacted, and carbonate formations are found below. Thickness 2030 cm.

C soil-forming rock, represented by loess-like loam of yellowish-brown color in chestnut soils and brownish-fawn in brown ones. Carbonate formations are found in the upper part. Below 50 cm in brown soils and 1 m in chestnut soils, new gypsum formations occur.

The change in the amount of humus down the profile occurs gradually, as in chernozems. The reaction of the soil solution in the upper part of the profile is slightly alkaline (pH = 7.5), lower the reaction becomes more alkaline.

Among chestnut soils, three subtypes are distinguished, replacing each other from north to south:

Dark chestnut , having a humus horizon thickness of about 25 cm or more, chestnut trees with a humus horizon thickness of about 20 cm and light chestnut trees with a humus horizon thickness of about 15 cm.

A characteristic feature of the soil cover of dry steppes is its extreme diversity, this is due to the redistribution of heat and especially moisture, and with it water-soluble compounds, across the forms of meso- and microrelief. Lack of moisture causes a very sensitive response of vegetation and soil formation to even slight changes in moisture. Zonal automorphic soils (i.e., chestnut and brown desert-steppe soils) occupy only 70% of the territory, the rest is accounted for by saline hydromorphic soils (solonetzes, solonchaks, etc.).

The difficulty of using dry steppe soils for agriculture is explained by both the low humus content and the unfavorable physical properties of the soils themselves. In agriculture, dark chestnut soils are mainly used in the most humidified areas and which have a fairly high degree of fertility. With proper agricultural technology and the necessary reclamation, these soils can produce sustainable yields. Since the main cause of crop failure is a lack of water, the problem of irrigation becomes especially acute.

In medical-geographical terms, chestnut and especially brown soils are in some places overloaded with easily soluble compounds and have an increased content of some trace chemical elements, primarily fluorine, which can have negative consequences for humans.

The desert climate of Eurasia is characterized by hot summers (average July temperature 2630° C) and cold winters (average January temperature varies from 0 16° C in the north of the zone to 0 +16° C in the south of the zone). The average annual temperature varies from +16°C in the northern part to +20°C in the southern part of the zone. The amount of precipitation is usually no more than 100200 mm per year. The distribution of precipitation across months is uneven: the maximum occurs in winter and spring. Water mode non-washing soils are soaked to a depth of about 50 cm.

The vegetation cover of deserts is mainly hodgepodge and shrubs with ephemeral plants (annual herbaceous plants, the entire development of which takes place in a very short term, usually in early spring). Desert soils contain a lot of algae, especially on takyrs (a type of hydromorphic desert soil). Desert vegetation vigorously grows in the spring with the lush development of ephemerals. During the dry season, life in the desert comes to a standstill. The biomass of semi-shrub deserts is very small - about 43 c/ha. The small mass of annual litter (1020 c/ha) and the vigorous activity of microorganisms contribute to the rapid destruction of organic residues (there is no undecomposed litter on the surface) and a low humus content in gray-brown soils (up to 1%).

Among the soil-forming rocks, loess-like and ancient alluvial deposits, reworked by the wind, predominate.

Gray-brown soils are formed on elevated, flat terrain. A characteristic feature of these soils is the accumulation of carbonates in the upper part of the soil profile, which has the appearance of a surface porous crust.

Profile structure of gray-brown soils:

And the carbonate horizon is a surface crust with characteristic round pores, cracked into polygonal elements. Thickness 36 cm.

And a weakly defined humus horizon of a gray-brown color, weakly held together by roots in the upper part, loose at the bottom, easily blown by the wind. Thickness 1015 cm.

B is a transitional compacted horizon of brown color, prismatic-blocky structure, containing rare and poorly defined carbonate formations. Thickness from 10 to 15 cm.

C soil-forming rock loose loess-like loam, overflowing with small gypsum crystals. At a depth of 1.5 m and below, a peculiar gypsum horizon often lies, represented by clusters of vertically located needle-shaped gypsum crystals. The thickness of the gypsum horizon is from 10 cm to 2 m.

The characteristic hydromorphic soils of deserts are solonchaks , those. soils containing 1% or more readily soluble salts in water in the upper horizon. The bulk of salt marshes are distributed in the desert zone, where they occupy about 10% of the area. In addition to the desert zone, salt marshes are quite widespread in the zone of semi-deserts and steppes; they are formed when groundwater is close to each other and the effluent water regime is present. Salt-containing groundwater reaches the soil surface and evaporates; as a result, salts are deposited in the upper soil horizon, and salinization occurs.

Soil salinization can occur in any zone under sufficiently arid conditions and close proximity to groundwater; this is confirmed by salt marshes in the arid regions of the taiga, tundra and arctic zones.

The vegetation of salt marshes is unique, highly specialized in relation to the conditions of significant salt content in the soil.

The use of desert soils in the national economy is associated with difficulties. Due to the lack of water, farming in desert landscapes is selective; the bulk of the deserts are used for transhumance livestock farming. Cotton and rice are cultivated in irrigated gray soil areas. The oases of Central Asia have been famous for their fruit and vegetable crops for many centuries.

The increased content of some trace chemical elements (fluorine, strontium, boron) in the soils of certain areas can cause endemic diseases, for example, tooth decay as a result of exposure to high concentrations of fluoride.

1. Red soils and yellow soils of humid subtropical forest landscapes

These soils are widespread in subtropical East Asia (China and Japan) and the southeastern United States (Florida and neighboring southern states). They are also found in the Caucasus on the coast of the Black (Adjara) and Caspian (Lankaran) seas.

The climatic conditions of the humid subtropics are characterized by high precipitation (13 thousand mm per year), mild winters and moderately hot summers. Precipitation is distributed unevenly throughout the year: in some areas the bulk of precipitation falls in the summer, in others - in the autumn-winter period. The rinsing water regime predominates.

The composition of forests in the humid subtropics varies depending on the floristic region to which a particular area belongs. The biomass of subtropical forests exceeds 4000 c/ha, the mass of litter is about 210 c/ha.

A characteristic type of soil in the humid subtropics is red soil, which received its name due to its color due to the composition of the soil-forming rocks. The main soil-forming rock on which red soils develop is a layer of redeposited weathering products of a specific brick-red or orange color. This color is due to the presence of tightly bound hydroxides

Soil profile structure:

A 0 weakly decomposed forest litter, consisting of leaf litter and thin branches. Thickness 12 cm.

A 1 humus horizon is gray-brown in color with a reddish tint, with a large number of roots, a lumpy structure and a thickness of 1015 cm. The humus content in this horizon is up to 8%. Down the profile, the humus content quickly decreases.

In , the transition horizon is brownish-red in color, the red tint intensifies downward. Dense, lumpy structure, streaks of clay are visible along the passages of dead roots. Thickness 5060 cm.

C The soil-forming rock is red with whitish spots, there are clay pellets, and there are small ferromanganese nodules. Films and streaks of clay are noticeable in the upper part.

Red soils are characterized by an acidic reaction of the entire soil profile (pH = 4.74.9).

Yellow soils are formed on clayey shales and clays with poor water permeability, as a result of which gleying processes develop in the surface part of the profile of these soils, which cause the formation of oxide-iron nodules in the soils.

The soils of humid subtropical forests are poor in nitrogen and some ash elements. To increase fertility, organic and mineral fertilizers are needed, primarily phosphates. The development of soils in the humid subtropics is complicated by severe erosion that develops after deforestation, so the agricultural use of these soils requires anti-erosion measures.

2. Brown soils of landscapes of dry subtropical forests and shrubs

Soils called brown, formed under dry forests and shrubs, are widespread in southern Europe and northwest Africa (Mediterranean region), southern Africa, the Middle East, and several areas of Central Asia. Such soils are found in warm and relatively dry regions of the Caucasus, on the southern coast of Crimea, and in the Tien Shan mountains. In North America, soils of this type are common in Mexico; under dry eucalyptus forests they are known in Australia.

The climate of these landscapes is characterized by positive average annual temperatures. Winters are warm (temperatures above 0° C) and humid, summers are hot and dry. The annual amount of precipitation is significant about 600700 mm, but its distribution throughout the year is uneven most of the precipitation falls from November to March, and in the hot summer months there is little precipitation. As a result, soil formation occurs under conditions of two alternating periods: wet and warm, dry and hot.

Brown soils formed under dry forests of various species composition. In the Mediterranean, for example, these are forests of evergreen oak, laurel, seaside pine, tree-like juniper, as well as dry shrubs such as shiblyak and maquis, hawthorn, dwarf tree, downy oak, etc.

Profile structure of brown soils:

A 1 is a humus horizon of brown or dark brown color, lumpy structure, with a thickness of 20-30 cm. The humus content in this horizon is 2.0-2.4%. Down the profile its content gradually decreases.

In , the compacted transition horizon is bright brown, sometimes with a reddish tint. This horizon often contains new carbonate formations; in relatively humid areas they are located at a depth of 11.5 m; in arid areas they can already be found in the humus horizon.

C soil-forming rock.

The soil reaction in the upper part of the profile is close to neutral (pH = 6.3), in the lower part it becomes slightly alkaline.

The soils of subtropical dry forests and shrubs are highly fertile and have been used for a long time for agriculture, including viticulture, olive and fruit trees. Deforestation to expand the area of ​​cultivated land, combined with mountainous terrain, contributed to soil erosion. Thus, in many Mediterranean countries, the soil cover was destroyed and many areas that once served as granaries of the Roman Empire are now covered with desert steppes (Syria, Algeria, etc.).

3. Gray soils of dry subtropics

In arid landscapes of semi-deserts of the subtropical zone, gray soils are formed , they are widely represented in the foothills of the Central Asian ranges. They are distributed in northern Africa, in the continental part of the south of North and South America.

The climatic conditions of the gray soil zone are characterized by warm winters (the average monthly temperature in January is about 2°C) and hot summers (the average monthly temperature in July is 2728°C). Annual precipitation ranges from 300 mm in the low foothills to 600 mm in the foothills above 500 m above sea level. During the year, precipitation is distributed very unevenly throughout the year; most of it falls in winter and spring; very little falls in summer.

The vegetation of gray soils is defined as subtropical steppes or low-grass semi-savannas. The vegetation cover is dominated by grasses, with giant umbellifers being typical. During the period of spring moisture, ephemerals and ephemeroids - bluegrass, tulips, poppies, etc. - grow vigorously.

The soil-forming rocks are predominantly loess.

Serozem profile structure:

And the humus horizon is light gray in color, noticeably turfed, with an unclear lumpy structure, 15-20 cm thick. The amount of humus in this horizon is about 1.5-3%, down the profile the humus content decreases gradually.

A/B intermediate horizon between humus and transition horizons. More friable than humus, thickness 10 15 cm.

In , the transition horizon is brownish-fawn in color, weakly compacted, and contains new carbonate formations. At a depth of 6090 cm, new formations of gypsum begin. It gradually transitions to the soil-forming rock. Thickness is about 80 cm.

С soil-forming rock

The entire profile of sierozems bears traces of intense activity of diggers - worms, insects, lizards.

Gray soils of semi-deserts of the subtropical zone border on gray-brown soils of deserts of the temperate zone and are connected with them by gradual transitions. However, typical gray soils differ from gray-brown soils in the absence of a surface porous crust, a lower content of carbonates in the upper part of the profile, a significantly higher content of humus and a lower location of gypsum formations.

Gray soils contain a sufficient amount of chemical elements necessary for plant nutrition, with the exception of nitrogen. The main difficulty in their agricultural use is related to the lack of water, so irrigation is important for the development of these soils. Thus, rice and cotton are cultivated on irrigated gray soils in Central Asia. Agriculture without special irrigation is possible mainly in elevated areas of the foothills.

Tropical soils occupy more than 1/4 of the world's land surface. The conditions of soil formation in the tropics and high latitude countries are sharply different. The most noticeable distinctive features of tropical landscapes are climate, flora and fauna, but the differences are not limited to these. Most of the tropical territory (South America, Africa, the Hindustan Peninsula, Australia) represents the remains of the oldest land (Gondwana), on which weathering processes took place over a long period of time, starting from the Lower Paleozoic, and in some places even from the Precambrian. Therefore, some important properties of modern tropical soils are inherited from ancient weathering products, and individual processes of modern soil formation are complexly related to the processes of ancient stages of hypergenesis (weathering).

Traces of the most ancient stage of hypergenesis, the formations of which are widespread in many areas of ancient land, are represented by a thick weathering crust with a differentiated profile. These ancient crusts of tropical territory, as a rule, do not serve as soil-forming rocks; they are usually buried under more recent formations. In areas of deep faults that dissected sections of ancient land in the Cenozoic and were accompanied by powerful volcanic eruptions, these crusts are covered by thick covers of lavas. However, over an immeasurably larger area, the surface of ancient weathering crusts is covered with peculiar red mantle deposits. These red-colored deposits, cloak-like covering a vast area of ​​tropical land, represent a completely special supergene formation that arose under different conditions and at a significantly later time than the ancient weathering crusts underlying them.

The red deposits have a sandy-loamy composition, their thickness varies from several decimeters to 10 m or more. These deposits were formed under fairly humid conditions that favored high geochemical activity of iron. These deposits contain iron oxide, which is what gives the deposits their red color.

These red-colored deposits are the most typical soil-forming rocks of the tropics, which is why many tropical soils have a red or similar color, as reflected in their names. These colors are inherited from soils, the formation of which can occur in various modern bioclimatic conditions. Along with red-colored sediments, gray lacustrine loams, light yellow sandy loam alluvial deposits, brown volcanic ashes, etc. can act as soil-forming rocks; therefore, soils formed under the same bioclimatic conditions are not always the same color.

The most important feature of the tropical zone is stable high air temperature, so the nature of atmospheric humidification is of particular importance. Since evaporation in the tropics is high, the annual amount of precipitation does not give an idea of ​​​​the degree of atmospheric moisture. Even with a significant annual precipitation in tropical soils, throughout the year there is an alternation between a dry period (with a precipitation amount of less than 60 mm per month) and a wet period (with a precipitation amount of more than 100 mm per month). In accordance with soil moisture, there is a change in non-leaching and leaching regimes.

1. Soils of landscapes of rain (constantly wet) tropical forests

Permanently humid tropical forests are distributed over a large area in South America, Africa, Madagascar, Southeast Asia, Indonesia, the Philippines, New Guinea and Australia. Under these forests, soils are formed for which different time Various names have been proposed red-yellow lateritic, ferrallite and etc.

The climate of these forests is hot and humid, average monthly temperatures are more than 20° C. The annual precipitation is 1800–2000 mm, although in some places it reaches 5000–8000 mm. The duration of the dry period does not exceed 1

The abundance of heat and moisture determines the largest biomass among the world's biocenoses - about 5000 c/ha and the mass of annual litter - 250 c/ha. There is almost no forest litter, since almost all litter is destroyed throughout the year due to the intensive activity of soil animals and microorganisms. Most of the elements released as a result of the decomposition of litter are immediately captured by the complex root system of the rain forest and are again drawn into the biological cycle.

As a result of these processes, there is almost no humus accumulation in these soils. The humus horizon of rain forest soil is gray, very thin (57 cm) and contains only a few percent of humus. It is replaced by a transitional horizon A/B (1020 cm), during which the humus tint completely disappears.

The peculiarity of these biocenoses is that almost the entire mass of chemical elements necessary for plant nutrition is contained in the plants themselves and only because of this is not washed out by heavy precipitation. When a tropical rainforest is cut down, precipitation very quickly erodes the top thin fertile soil layer and barren lands remain under the cleared forest.

2. Soils of tropical landscapes with seasonal atmospheric moisture

Within the tropical landmass, the largest area is occupied not by permanently wet forests, but by diverse landscapes, where atmospheric moisture is uneven throughout the year and temperature conditions vary slightly (average monthly temperatures are close to 20°C).

With a dry period lasting from 3 to 6 months a year and an annual precipitation amount of 900 to 1500 mm, landscapes of seasonally wet light tropical forests and tall grass savannas develop.

Light tropical forests are characterized by a free arrangement of trees, an abundance of light and, as a result, a lush cover of cereal grasses. Tall grass savannas are various combinations herbaceous vegetation with islands of forest or individual trees. The soils that form under these landscapes are called red or ferrallitic soils of seasonally wet tropical forests and tall grass savannas

The structure of the profile of these soils:

At the top there is a humus horizon (A), more or less sodded in the upper part, 1015 cm thick, dark gray in color. Below is a transition horizon (B), during which the gray tint gradually disappears and the red color of the soil-forming rock intensifies. The thickness of this horizon is 30

These soils are widely used in tropical agriculture. The main problem with their use is the easy destruction of soils due to erosion.

With a dry period lasting from 7 to 10 months a year and an annual precipitation of 400-600 mm, xerophytic biocenoses develop, which are a combination of dry trees and shrubs and low grasses. The soils that form under these landscapes are called red-brown dry savanna soils.

The structure of these soils:

Under the humus horizon A, about 10 cm thick, of a slightly gray tint, there is a transition horizon B, 25 cm thick.

These soils are widespread in the central and western regions of Australia and in some areas of tropical Africa. They are of little use for agriculture and are used mainly for pastures.

With an annual precipitation of less than 300 mm, soils of arid tropical (semi-desert and desert) landscapes are formed , having common features with gray-brown soils and gray soils. They have a thin and poorly differentiated carbonate profile. Since the soil-forming rocks in many areas are red-colored products of [Neogene] weathering, these soils have a reddish color.

The soil-forming material on such islands is snow-white coral sands and reef limestones. The vegetation consists of shrub thickets and coconut palm forests with intermittent cover of low grasses. The most common here are atoll humus-carbonate sandy soils with a thin humus horizon (510 cm), characterized by a humus content of 12% and a pH of about 7.5.

Often important factor soil formation on the islands is avifauna. Colonies of birds deposit huge amounts of droppings, which enrich the soil with organic matter and promote the appearance of special woody vegetation, thickets of tall grasses and ferns. A thick peat-humus horizon with an acidic reaction is formed in the soil profile. Such soils are called atoll melano-humus-carbonate.

Humus-carbonate soils are an important natural resource of numerous island countries of the Pacific and Indian Oceans, being the main plantation for the coconut palm.

One of the distinctive features of the structure of mountain soils is the thinness of genetic horizons and the entire soil profile. The profile thickness of a mountain soil can be 10 or more times less than the profile thickness of a similar flat soil, while maintaining the structure of the profile of the flat soil and its features.

Mountain areas are characterized by vertical zoning (or zonality) soil cover, which refers to the natural replacement of some soils by others as one rises from the foot to the tops of high mountains. This phenomenon is due to the natural change in hydrothermal conditions and vegetation composition with height. The lower belt of mountain soils belongs to the natural zone in which the mountains are located. For example, if a mountain system is located in a desert zone, then gray-brown desert soils will form on its lower belt, but as they rise up the slope, they will alternately be replaced by mountain chestnut, mountain chernozem, mountain forest and mountain meadow soils . However, under the influence of local bioclimatic features, some natural areas may fall out of the vertical zonation structure of the soil cover. An inversion of soil zones can also be observed, when one zone turns out to be higher than it should be by analogy with the horizontal ones.

Natalia Novoselova