Soils of semi-deserts and deserts. soil formation conditions. Desert and semi-desert soils how deserts arise

semi-deserts - territories of Eurasia. These are the territories of Kazakhstan, Mongolia and China. In the US and Argentina in the south.

Semi-deserts are characterized high temperatures for the summer months. Rainfall ≈ 100 - 250mm. And the evaporation rate is ≈ 1500mm. This causes the aridity of the climate and the rapid drying of the soil. Biomass 100c/ha. Most of relate to root systems (90%).

Brown semi-desert soils. Possess a weak differentiated profile. A, ABt(lessivage),bca, BSa(gypsum),BCs, C. Lessivage in the arid zone (when dry and hot). Movement of the silt fraction from top to bottom. This lessivage is not modern (it is a residual phenomenon). “Soils are the mirror of the landscape and also its history.” This is the cause of the last glacial glaciation. During the period when there was more precipitation, there was lessivage.

Humus content - 1%. Humus reserves - 60 - 65 t / ha. surface carbonates. Gypsum at a depth of 50 cm. Chlorides are present in the upper part. At a depth of 70 - 80 cm. Absorption capacity ≈ 10 - 15 mg/eq. Ph ≈ 7.5 - 8, hence high-alkaline. Soils are little used in agriculture. lack of N and no fertilizer. Herd-pasture animal husbandry. And the introduction of N pollutes the environment (water) and products. Nitrogen fertilizers (NO3) are converted into NO2 by the body. And NO2 is converted to nitrosamines.

The soil cover is mosaic. The zonal type are brown semi-desert, brown semi-desert solonetsous, solonchaks, solonetzes.

Deserts. They are located in Asia, Mongolia, China, North and South America. Vegetation does not form a continuous cover and is represented by xerophytes (plants adapted to life in arid places - camel thorn, sand acacia). Desert landscapes are characterized by low rainfall< 100 мм (т.к. не ежегодные). К < 1 (К < 0,1). Биомасса 40 ц/га. Основная масса под землёй.

Gray-brown desert - formed on loamy soils. They have a thin soil profile. A(k) - fine earth cemented with salts in a crust (2 - 5 cm), A(E) - up to 10cm, bca, bsacs, C.

These soils are characterized by the content of gypsum and salt on the surface. Low humus content. Humus reserves - 4 kg / ha. Ph ≈ 8 - 8.5. Absorption capacity< 10 мг/экв.

Takyr- soils of flat clay depressions in the deserts of the subtropical zone. The surface hard horizon (pink or pale-gray) is broken up into cracks. Contains 0.2-0.5% humus. Common in Wed. Asia, Kazakhstan, Mongolia, Western Asia, North. America, Australia, etc.

There are not many salt marshes in the deserts.

25. Conditions of soil formation and soils of non-permafrost provinces of the taiga zone.

	East-Eur. province (to the Urals).		Zap.-Sib. province (up to the Yenisei).
northern taiga	Permafrost taiga.
	1) Gley-podzolic soils.		1) Gleepodzolic.
	2) Podzolic illuvial-umus.		2) Illuvial-humic.
	3) Bog-podzolic.		3) Bog-podzolic.
	4) Swamp		4) Swamp
Middle taiga	1) Podzolic on clays.		1) Podzolic.
	2) Podzols on the sands.		2) Podzols.
Southern taiga
		1) Sod-podzolic.		1) Sod-podzolic.
		2) Podburs.		2) Podburs.

The soils of the taiga-forest territories are affected by the presence of outcrops of cabon-sedimentary rocks (marls). Sod-calcareous soils will form on them. In the eastern part of Eurasia - permafrost-taiga fawn. Soil formation is influenced by Precambrian rocks. During the weathering of these rocks, Quaternary deposits of light mechanical composition are formed. Podzols are widespread. Well expressed ao, Aov. The north in the composition of humus is dominated by fulvic acids.

Precipitation. Moisture coefficient > 1. The leaching type of the water regime dominates, it can be frozen stagnant. Permafrost is of great importance for soil formation - it is an aquiclude. When not in large numbers precipitation → stagnation, subpermafrost gleying occurs. Permafrost type of water regime. For the soils of permafrost regions, the absence of clearly defined soil horizons. cryoturbation processes. In the taiga zone, where the leaching type of the water regime is favorable for soil formation, where the non-leaching type is the conditions for the development of gleying.

Soils of the northern taiga.

In the eastern European province and the West Siberian province, on soils of heavy mechanical composition (loamy moraine) under taiga-coniferous forests, the following are formed:

1. gley-podzolic, who have a profile: ao, A1(g), A2(g), B(g), C(g).

In gley-podzolic soils, signs of gleying are expressed in almost all horizons. The content of humus (A1) is about 2-3% and its sharp decrease with depth. Acidity at the level of 4-5% - acidic soils. Absorption capacity at the level of 15-20 mg / eq. Low content of mobile (digestible) N, P, K. low level fertility, cold soils. Typical for sowing Taiga In the West Siberian province and East European.

The desert only at first glance may seem like a lifeless territory. In fact, it is inhabited by unusual representatives of the animal and flora able to adapt to difficult climatic conditions. The natural zone The desert is very extensive and occupies 20% of the earth's land area.

Description of the natural zone of the Desert

The desert is a vast flat area with a monotonous landscape, poor soil, flora and fauna. Such landmasses are found on all continents except Europe. The main symptom of the desert is drought.

To the features of the relief natural complex Desert include:

plains;
plateaus;
arteries of dry rivers and lakes.

This type of natural area extends over most of Australia, a relatively small part South America, located in subtropical and tropical zones northern hemisphere. On the territory of Russia, deserts are located in the south of the Astrakhan region in the eastern regions of Kalmykia.

The largest desert in the world is the Sahara, which is located on the territory of ten countries. African continent. Life here is found only in rare oases, and on the territory of over 9,000 thousand square meters. km, only one river flows, communication with which is not available to everyone. Characteristically, the Sahara consists of several deserts, similar in their climatic conditions.

Rice. 1. The Sahara Desert is the largest in the world.

Desert types

Depending on the type of surface, the desert is divided into 4 classes:

Climate features

In terms of describing deserts, it is worth mentioning the features of the climate separately. This natural area is characterized by:

high day temperature , which can drop to 0 degrees Celsius at night. In the northern desert, this mark can reach -40 degrees. Such sharp temperature fluctuations indicate continental climate most deserts.
Exceptional dry air . Humidity ranges from 5-20%, which is much lower than normal. The reason for this is extremely rare precipitation, which can fall once every few months or even years. The deserts of South America are considered the driest.

Often in the desert there is a so-called "dry rain". Water droplets drip from ordinary rain clouds, but when they collide with highly heated air, they evaporate even in the layers of the atmosphere, without reaching the ground.

Flora and fauna of the desert

Deserts and semi-deserts are characterized by poor vegetation. As a rule, these are thorny shrubs that have adapted to seek moisture deep in the soil with the help of a powerfully developed root system.

Desert animals are presented small predators and rodents, reptiles and reptiles.

What are the soils in deserts and semi-deserts?

Peculiarities of soil formation on sands are due to a sharp predominance (90% or more) of sandy fractions (1.0 ... 0.05 mm), structurelessness. Therefore, they have high air permeability (total porosity 38.2...44.2%) and water permeability (more than 100 mm/h), insignificant height of capillary rise from 30...60 cm to 70...80 cm above ground level. water, low water-holding capacity (HB 2.5 ... 10.0%), significant thermal conductivity and the lowest heat capacity, low absorption capacity (1 ... 5 mg eq / 100 g of sand).
The period of time favorable for soil formation is 1.0...1.5 spring months when microbiological activity is highest.

Desert sandy soils are formed in the southern deserts under the main soil-forming plant, sedge, with a slight admixture of ephemera and shrubs. They have a thin profile (less than 50...70 cm), poorly differentiated into horizons, in which the content of physical clay and carbonates often differs little from the eolian sandy soil-forming rocks. Humus accumulates in them less than 0.4%; humus type is fulvate. A feature of soil formation here is its discontinuity due to the drift of sand sediment, since its upper layer (3 ... rhizomes, holding the sand together, is located in a layer from 3 ... 8 to 15 ... 20 cm. This horizon is called radicular. It is distinguished by a greater grayishness against a general yellowish background. Below it lies a more compressed and slightly compacted yellowish horizon with brownish and barely noticeable whitishness from carbonates, with abundant vertical sedge roots. In addition to such full-profile soils, incompletely developed and underdeveloped soils are widespread. There are especially many such soils in the Karakum Desert.

Yellowish-gray desert (slightly differentiated desert) soils are the main soil type in the desert zone. These are loose-sandy (physical clay lt; 2.5%), weakly cohesive sandy (2.5 ... 5.0%), cohesive sandy (5 ... 10%) soils. They are predominantly formed on quartz-calcite-feldspar, feldspar-calcite-quartz, gypsum-calcareous, marl and residual saline sands, on sandy-loamy sandy-gravel eluvium of dense bedrocks (sandstones, limestones).
Pale gray desert poorly differentiated (loose sandy, weakly cohesive sandy, cohesively sandy) soils are found in northern deserts. large areas they occupy in the Taukums, Muyunkums, Sary-Ishikotrau, on the Sam massifs, the Caspian Karakum, the Buzachi peninsula, in the Arkala desert, at the foot of the Tarbagatai. Primitive (3...10 cm), thin (10...40 cm), medium-thick (40...70 cm) and rarely thick (70...100 cm) soils were identified among them. In these soils, a change in the mineralogical composition is noticeable. The amount of physical clay increased from 0.6...0.8% in barchan sand to 3...5% in horizon A, and humus, respectively, from 0.02...0.07 to 0.3...0 ,4 %. Carbonates are randomly distributed along the profile.

On eolian sands under wormwood-shrub-ephemeral vegetation, soils have been formed with the following structure: horizon A (0...10 cm) light gray with brownish, silty-cohesive sandy, contains many roots, loose; horizon B (10...36 cm) grayish-brownish with paleness and yellowishness, weakly compacted, silty-cohesive-sandy, contains plant roots, structureless; horizon BC (36...80 cm) yellowish-brown with pale pale, slightly compacted, sandy, with a small number of roots; horizon C yellowish, sandy, carbonate. However, the area of such soils is insignificant, because due to overgrazing of animals, they are deformed to varying degrees, sometimes to the formation of dune sands.
ordinary
Soil cover of semi-deserts

Desert soil cover
sand, sand, one fucking sand...
Soil cover of semi-deserts
The soil cover of the semi-deserts of the CIS, located mainly in the Lower Trans-Volga region and Central Kazakhstan, is formed by automorphic humus-poor solonetsous light chestnut and solonetsous brown desert-steppe soils in combination with solonetzes. Where groundwater is close, solonchaks are formed, in flat depressions, depressions, or estuaries, meadow-chestnut soils, in which there is more humus and less soluble salts than in brown and light chestnut soils.
Semi-desert soils occupy about 6% of the territory of the CIS.
Of the features of the soil cover of the semi-deserts of the CIS, it should be noted, as especially characteristic, the complexity and solonetzization. Complexity is expressed in frequent shift at a short distance soils different types and subtypes, in the mosaicity of the soil cover: at a distance of several meters one can observe complexes of chestnut, light chestnut solonetsous soils and solonetzes.
The complexity and alkalinity of semi-desert soils prevent the development of these provinces for agriculture. Agriculture without irrigation on these soils is impossible (excluding light chestnut sandy loamy and dark-colored soils of depressions and estuaries, water regime which is more favorable). Basically, semi-deserts are used as pastures for local and distant pastures.

Desert soil cover

The soil cover of the deserts of the CIS is mainly represented by automorphic gray-brown soils and gray soils, and in places where groundwater is close to meadow-gray soils, solonchaks and takyrs. The total area of desert soils is about 8% of the territory of the CIS.
The main massifs of serozems gravitate towards foothill loss plains. Central Asia with their mild, unstable winters, hot and dry summers, with a predominance of ephemers, ephemeroids, saltworts, and desert shrubs in the sparse vegetation cover. A. N. Rozanov considers serozem soils subtropical semi-deserts.
Gray-brown soils rich in gypsum are confined mainly to the northern provinces of the deserts. They are most often distributed on the tertiary plateaus of Ustyurt and Betpak-Dala, where wormwood, saltwort, and ephemera predominate in the vegetation cover. Gray-brown soils and most gray soils are the poorest soils in terms of humus reserves.
Takyrs, almost devoid of vegetation, develop in flat shallow depressions, the genesis of which is still unclear. Of the other soils, the most widespread in the deserts of the CIS are solonchaks, rich in readily soluble salts, predominantly of sulfate-chloride and chloride types of salt accumulation. (Kovda, 1946, 1947). The possibility of removal of salts formed here and brought from outside is very limited. However, in the serozems of southern deserts, readily soluble salts are found in large quantities no closer than 1.52 m from the soil surface, which is due to the loss of most of the precipitation during the cold period of the year, when evaporation is small, and soil wetting is deep enough.
Finally, in irrigated oases, cultivated serozems are formed, enriched with sediments of irrigation water. Serozems are quite fertile if they are irrigated and fertilized. Due to the low content of humus in desert soils, the introduction of nitrogen is very effective.

natural zone forest-steppe tundra

The semi-desert zone enters the Russian Plain only in the southeast, occupying here the Ergeni upland and the northern half Caspian lowland. Its southern border to the west of the Volga runs at a distance of about 150 km from the coast of the Caspian Sea; in the Volga-Ural interfluve, it moves away from the sea even further and passes here along the line: Lake Baskunchak - Lake Aralsor - the mouths of the Small and Big Uzen - the Ural River south of Kalmykov.

The position in the southeast of the Russian Plain in the depths of the Eurasian continent determines the sharply continental, dry climate of this zone. Summer in the semi-deserts is hot and sunny. The average temperature in July reaches 23--25 °, in the city of Novouzensk during warm period 85 days happens with dry winds. Winter is as cold as ever Kola Peninsula: average temperature January -7--8° in the southwest of the zone and -13--14° in its northeast. The snow cover is thin - from 10 to 30 cm. The total annual amount of precipitation is 300 - 200 mm; this is three to four times less than the volatility. For example, in the city of Novouzensk, the annual precipitation is 250 mm, and the evaporation rate is 910 mm.

Surface runoff in the semi-desert is negligible, so its own river network is not developed in it. Ground water is saline and mostly not suitable for drinking.

In addition to the climate, the geological and geomorphological features of the territory have the strongest impact on the landscape of the zone - a small absolute height, flatness, weak erosional dissection, the presence of saline bedrock and Quaternary rocks. There are few ravines and gullies in the zone. Instead of these erosional forms, closed basin-depression forms are widespread - steppe depressions, estuaries, sors, etc. Their genesis is different - from suffusion-subsidence to karst and tectonic (some estuaries).

The continental climate, flat terrain and saline soils contribute to the accumulation of salts in the soils of semi-deserts, including easily soluble ones. Salt licks are as typical for semi-deserts as are light chestnut soils, which are zonal here. Lack of moisture and salinity of soils lead to discontinuous, clump distribution of vegetation. The abundance of hollow-depression forms causes extraordinary diversity, complexity of vegetation and soil cover. With a lack of moisture, even the most insignificant depressions - 10 - 20 cm deep - lead to drastic changes in soils and vegetation. It can be said that a semi-desert is a zone of complexes in which the grassy steppe along the depressions, the wormwood-saltwort desert on solonetzes and the fescue-chamomile proper semi-desert on light chestnut soils are closely intertwined.

In the animal world of semi-deserts, an outstanding role belongs to rodents. Among them, in terms of abundance and impact on the landscape, ground squirrels are distinguished, represented here by two species - a small ground squirrel that lives on loamy plains, and a yellow ground squirrel that inhabits the sands. The occurrence of gophers is very high. In some places on one hectare you can count up to 740-750 ground squirrel holes. Ground squirrel ejections create a hillock microrelief characteristic of the Caspian Sea, which further enhances the complexity of the soil and vegetation cover.

In addition to ground squirrels, jerboas, gerbils, voles, steppe lemmings, and mice are common rodents in the semi-desert. Within the zone, the saiga antelope is found, which previously inhabited the steppe and forest-steppe zone Russian plain. In some places, wild boar is found in the reed thickets of river valleys. Of the predators, the wolf, the corsac fox, and the steppe polecat are common.

The composition of birds (steppe eagle, harrier, larks), reptiles and insects is also quite diverse.

Most of the semi-desert zone is used as pasture. Firth and irrigated agriculture is developed in places.

The southern third of the Caspian lowland belongs to the desert zone. Due to the small size of the territory and the uniformity of geological and geomorphological conditions, the desert zone on the Russian Plain belongs to one landscape provinces -- provinces sandy and clay-saline deserts of the Caspian Sea. The features of dryness and continental climate, characteristic of the southeast of the Russian Plain, reach their maximum in the desert zone. The annual amount of precipitation in deserts is less than 200 mm. In the city of Astrakhan, on average, 170 mm of precipitation falls per year, with an evaporation rate of 936 mm. Winter is extremely snowless, even by the end of its snow depth does not reach 10 cm. For this reason, the Caspian desert, especially to the west of the Volga (Black Lands), where the winter is warmer, is a good winter pasture.

Surface runoff in the deserts is so low (less than 0.5 l/sec) that no local river crosses the province.

Geologically, the territory of the Caspian desert is very young; its coastal parts have turned into dry land quite recently. In contrast to the semi-desert, the desert zone in the Quaternary was flooded by all three transgressions of the Caspian Sea, including the Khazar one. Almost the entire territory of the province lies below sea level.

Huge areas in the desert are occupied by sands of marine (Late Khvalynian Sea) and alluvial-deltaic origin. The area of the Volga-Ural sands alone is about 50 thousand km3.

On the coast of the Caspian Sea, and especially near the Volga delta and to the west of it, there are Baer knolls. More precisely, these are low (6–20 m) and long (from several hundred meters to 5–6 km) sandy ridges, mainly in the latitudinal direction. First described by academician K.M. Baer, the mounds later served as the object of special study more than once. Regarding their genesis, various hypotheses were put forward - eolian, tectonic, water-erosion, water-accumulation, and many others. Most likely, their formation should be associated with the accumulation and movement of sediments by the waters of the ancient sea basins retreating to the south. Later, part of the hillocks underwent eolian processing. AT soil cover deserts, brown desert-steppe soils appear, salt marshes stretch in a wide strip along the shores of the Caspian Sea. Vegetation is closely dependent on soils. On saline clay soils, wormwood-saltwort groups are represented. Vegetation looks more diverse sandy deserts, characterized by a shallow occurrence of fresh groundwater. It is formed by grass-wormwood groups with the participation of bluegrass (Poa bulbosa), Siberian couch grass (Agropyrum sibiricum), prutnyak, and milkweed. In the northwest of the Volga-Ural sands in the Urda sands, rich fresh water, small groves of poplar and aspen survived, they are bred orchards and melons.

Deserts are used as pastures and grasslands. Horticulture, horticulture and melon growing are developed in the wide Volga-Akhtuba floodplain. The area of floodplain lands used for agriculture is still small and can be successfully increased many times over.

semi-deserts temperate zone – natural area temperate zone, which has transitional features from steppes to deserts. A sharply continental climate is characteristic, evaporation is 3-4 times greater than the amount of precipitation. The annual amount of precipitation varies between 150-250 mm.

In semi-deserts, brown semi-desert-steppe soils are formed, as well as light chestnut soils poor in humus. Along with them, salt licks are very widespread.

In the semi-deserts, sparse wormwood-cereal vegetation grows, which is torn in nature.

The fauna of the semi-deserts is not distinguished by its originality; it includes species of the steppe and desert zones. An exceptional role in the animal world is played by rodents.

The deserts of the temperate zone occupy the plains of Eurasia from the Caspian Sea in the west to Central China in the east, the largest of them are the Karakum and Kyzylkum deserts in Central Asia. AT North America- These are the arid regions of the Great Basin, in South America - Patagonia.

The desert climate is characterized by extreme aridity and continentality, with sharp contrasts between very hot summers and cold winter. The amount of precipitation varies from 75 to 150 mm per year.

The soil cover is dominated by brown and gray-brown desert soils, often saline. Takyrs are characteristic - specific formations of clay deserts, which are a cracked dry clay surface.
Vegetation cover is sparse and dominated by perennial subshrubs and ephemera (annual herbaceous plants that bloom during a short rainy period). Of the shrubs, the leading role belongs to various types wormwood and saltwort. In some places there are "forests" of saxaul - a small leafless tree, the roots of which go to a depth of 20 m. At the height of summer, the deserts of the temperate zone differ little from tropical deserts, but they have a short but stormy flowering period - early spring. It happens that the desert is covered with a real flowering carpet.

The fauna is mainly represented by reptiles (snakes, lizards). Many desert animals can long time to be without food and water, such as a domesticated camel. Of the birds, various larks, plover, bustard-beauty, desert warbler, etc. are common.

Deserts of the subtropical and tropical zones

subtropical and tropical desert located in the north-west of India, in Pakistan, Iran, Asia Minor. They cover the Arabian Peninsula and the entire north of Africa, West Coast South America for almost 3500 km and central part Australia.

The climate in the deserts is sharply continental. Summer is very dry and hot, during the day the air temperature in the shade rises above 40 0С. At night, the heat subsides, the temperature often drops to 0 0C. Precipitation falls no more than 180 mm per year. Chile's Atacama Desert receives less than 10 mm of precipitation per year.

The soil cover is represented mainly by brown desert soils, but soils are completely absent in vast areas. Salt marshes form in places where groundwater is shallow. Large territories occupy rocky deserts. Clay deserts, located, as a rule, in relief depressions, are almost devoid of vegetation. They are easily flooded during intermittent rains and look like lakes, although the depth of these "lakes" is only a few millimeters. The clay layer does not absorb water - it quickly evaporates in the sun, the dry surface of the earth cracks, and takyrs are formed. Clay areas are replaced by spaces of moving sand with eolian relief forms - dunes, "crescent" or "sickle" shape, reaching a height of 12 m, and dunes.

Desert plants usually have a well developed root system. Mostly thorny bushes, cacti and some herbs grow here. Other plants - ephemera - survive the drought in the form of seeds, having time to germinate and bloom in a couple of months after a rare rain.

The fauna of the deserts is represented by a wide variety of reptiles (snakes, lizards, turtles), birds (eagles, crows, sparrows, owls, etc.) and mammals (cheetah, kulan, camel, etc.).

Human life in deserts is possible only in oases.