Tropical belt.It is the largest in the area (5.6 billion g.), Which is about 42% of the surface of the sushi. Mountain areas within this belt occupy about 13% of the area. Semi-hydromorphic, hydromorphic, paleohydromorphic, floodplain soils make up 15.5% of the belt area. In a tropical belt, three rows of soil-bioclimatic areas can be distinguished: 1. Tropical wet and variable wet forests (humid and seven media); 2. Tropical arid xerophyte forest and savanna (semi-samid); 3. Tropical semi-desert and deserted (arid).
Stay three wet forests tropical regions: American, African and Australia-Asian. Ferrallitic and differentiated and undifferentiated soils are dominated in the soil cover of these areas. For wet forest areas, combinations of ferromallic soils of watersheds, ferromallic glying and gluened soils of the lower parts of the slopes and tropical marshes in depressions are characterized.
Tropical xerophyte forest and savanna areas occupy an area of \u200b\u200b1,7 mld. and distributed mainly in the eastern hemisphere: Indo-
African and Australian regions. In Western Hemisphere, this is the Antilles and small territories in South America. Mountain areas within the regions under consideration are 16.2% of the area. The hydromorphic conditions of the soil formation (19.5% of the territory) are widespread. Two types of soils dominate in soil cover: brown-red and red-brown savanna. The first are predominantly a ferallite composition, and the second is a fersilation. Among these soils are vertisoli. In the tropical belt, four semi-desert and desert areas can be distinguished: Afro-Asian, Australian, South African, South American, which are closed with subtropical desert areas. Gorgeous areas occupy 6.3% of their area, and hydromorphic soils are about 2.4%. Deserted sandy spaces spread over 24% of the area of \u200b\u200bthe region.
General features tropical soil formation.Since redo-color deposits are widespread in the territory of the ancient sushi, they are the most typical soil-forming rocks of the tropics. Laterithic and carbonate cortions are minorial to the soil formation and life of plants, so their outputs are usually deprived soil cover And fruitless.
Ancient weathered crust is usually buried under younger education and as well-forming rocks are rare. By virtue of the prevalence of red-color deposits among the soil-forming rocks, many tropical soils have a red or close color to it, which is reflected in the names of these soils, which are referred to as red, orange, yellow. It should be emphasized that these colors inherit soils, the formation of which can occur in different modern bioclimatic conditions. Despite the fact that red-color education may have a clay composition, the absorption capacity of these sediments and the soil developed on them is very small. In the process of forming red-color formations on the surface of clay minerals, FE (III) hydroxides are firmly fixed, which not only causes red
the color of clay particles, but also significantly reduces their absorption capacity.
The most important feature tropical belt - stable heat air, therefore special meaning Acquires the nature of atmospheric moistening. Since evaporation in the tropics is high, then the annual amount of precipitation does not give the ideas about the degree of atmospheric moistening. Even with a very significant annual amount of precipitation in tropical soils throughout the year, there may be a change in the molded regime. Therefore, in the tropics, in addition to soils of sustainable atmospheric moistening (automorphic) and permanent soil
common moisturizing (hydromorphic), there is an extensive group of soils developing in seasonal hydromorphism conditions.
Temperature conditions Tropics determine the possibility of vegetation _________ vegetation all year, therefore, with optimal moisture migration chemical elements In the soil system - plants in tropical landscapes proceeds more intensively than in high landscapes. In this case, the capacity of the annual biological cycle of chemical elements and the biomass of plants in the tropics is much larger than in other conditions. Studying tropical soils is quite complex problem. The issues of genesis, the Nomenclature of the IR Lassification of tropical soils are under development.
Such soils are usually called red and red-brown soilssavannan and dry tropical marriage (Feroshams).
The humus horizon of gray or grayish-reddish fourth, often light mechanical composition, in the upper part more or less acouted (A1 + D), with a capacity of 10-15 cm, with a liner structure. The surface of the soil is often covered with ferrous or silicon chubble or rounded ferrous concrete, accumulating as the fine-seated mixture or washed. The transition to the underlying horizon is gradual.
The transition humus-metamorphic horizon of AVMF is a grayish-red color, more brightly colored than the previous one, the mechanical composition is heavier, the structure is the continuing, which is. Horizon power 30-40 cm.
Illuvial - metamorphic Horizon BFMf is a heavier mechanical composition than the overlying horizons, more compact addition, with a pronounced lining and nut structure. Persons of structural separate parts are visible in places the thin glossy colloidal films. The color of the horizon is brighter than the previous one - brick-red or orange with dark glands and manganese specs. It begins at a depth of 50-60 cm from the surface and continues to a depth of 100-150 cm.
Maternal breed of siallit or sially alleged composition. In case of occurrence of weathering products in situ retains the structure of rocks. Sometimes at the bottom of the profile above the horizon of the soil-forming breed lies the carbonate concretion horizon of SUMO3.
Among the minnous minerals of furrosions, there are a significant proportion of Illitis, hydroslides and mixed-layered minerals. The share of kaolinitis accounts for 20-30%. Therefore, in the shaft analysis of a closer fraction, the ratio SiO2 / Al2O3 is 3.0-3.2. The maximum of a certain fraction is observed at the bottom of the profile - in the History of VTMF.
Although many ferozes of bright red color, the gross content of iron in them is small -3-7%. Only in latiticized (enriched with ferrous specifics) soils, the FE2O3 content reaches 20%. Bright soil painting is associated with the predominance of low-water hydrates of iron oxides. The content of humus is usually low: 2-3% in the upper horizon. The composition of humus is not studied. Single analyzes show a humate-voltage or fulvant-humatic composition, the ratio of SG / SF is close to one.
The reaction of soils in the upper part of the profile is weakly acidic or neutral, in the lower - weakly alkaline. In many cases, calcium carbonates are present in the deep part of the profile (more than 1.5 m). Absorption capacity of 10-20 mg.EKV per 100 g of soil. The degree of unsaturation in the upper horizons is about 15-25%. Soil is well aggregated. Farrors family studied extremely not enough.
In bright tropical forests and highly harvested savannas in the soil comes annually from 70 to 120 c / ha plant residues (I.A. Denisov, 1971). Thanks to the strong development of herbs, a significant part of the dead organic matter is in the soil, which contributes to their fastest humification. Total content Gumus in soils from 1 to 4% or more. Soil reaction is a weakly acidic, often neutral.
Despite the fact that the soils often have a heavy mechanical composition, their absorption capacity is small, from 10 to 20 MG-eq on the city of red soils of highly old savannas and bright tropical forests Wide used in tropical agriculture. Great danger When processing presents their lightweight erodority.
Wet tropics and subtropics make up 23% of the sushi surface. The most large arrays are common in both northern and in southern hemispheres, while the largest arrays are located in the eastern prophetic areas. In the northern hemisphere of the soil wet subtropics are common in the south of Pl. Korea, on southern Islands Japan, in Central and Southeast China. IN North America They occupy southern zones Appalachians and the plains adjacent to them, most of the Florida paradise. IN southern Hemisphere The soil of wet subtropics of a narrow strip are placed in the northeast of Australia, Tasmania, New Zealand and the southeastern coast of Africa. In the western hemisphere of the soil of wet subtropics locally housed in the south of Bulgaria, Yugoslavia, Spain, Italy, Greece, Turkey, on the Islands of the Mediterranean, in the Black Sea champion of the Caucasus, in Lenkrani. Soil wet subtropics and equatorial forests widespread in South America (Amazon Delta), Africa (Congo Congo, Cameroon, Gulf Coast), on New Guinea Islands, Ceylon, Philippines, Indonesia, South-East Asia, in the north of Australia.
Relief. The soils of wet subtropics and tropics are developing in the conditions of the dissected relief of the previations and low mountains, as well as allegedly undermined ancient accumulative terraces. Powerful relief dismemberment contributes to widespread development.
Climate. In wet subtropics The climate is wet and warm. Mid annual temperature air from + 13 ° C to + 15 ° C, the coldest month + 5 ° C - + 7 ° C, warm month + 21 ° C - + 23 ° C. The amount of precipitation is 1000-2500 mm, which fall out in the fall and winter. In the tropics, the average monthly air temperatures range from + 18 ° C to + 25 ° C. The amount of precipitation for the year 2000-3000 or more.
Vegetation Subtropics presented deciduous forests With the predominance of the count, beech, oak, chestnut with an evergreen undergrowth of Rhododendron, lambist, interlaced by lianans and wild grapes. Tropical forest is different large variety and multi-tiered wood and shrub breeds, sent by Lianami. The development of grassy vegetation depends on illumination. At the clarified areas, a lush herbal coating can develop, but uniform.
Soil-forming breeds Presented predominantly red-color crust of weathered massively crystalline rocks, very high power: in India - 12-15 m, Australia - 5-15 m, Africa - about 50 m, which is explained by the high intensity of all types of weathering.
Soil. A group of types of types are attributed to a group of fulvato-ferry soils: red-made, yellow-bearing subtropical forests, red, red-yellow and yellow ferry wet tropical forests and equatorial forests.
Soil processes. For the formation of fulvant soils are necessary the following conditions: wet, warm or hot climate; poor grounds, but rich in one-hour oxides and clay minerals of the kaolin group; forest vegetation, rich and many years of OPED; Large capacity of biological circulation; The relief that provides free drainage and removal of moving weathering (bases and part of the silica).
Ferralitis - This is a process in which most of the primary minerals decomposes (with the exception of quartz) and secondary minerals are formed by a group of one-time oxides and clay minerals of the kaolinite group and haloup. Weathered occurs in free drainage conditions, so moving products of destruction of minerals - Ca, Mg, k, Na, part of SiO2 - are taken out of the stratum of weathering.
Hydrates of iron oxides, aluminum, which are exempted during weathelation, are low-modular in the medium, poor organic acids. They accumulate B. large quantities and evenly stain in the breed from bright red to yellow color Depending on their quantity, the ratio and degree of hydration. Under the influence of iron hydroxides, a stable waterproof small -comed structure is formed.
In tropical I. subtropical forests It comes mainly on the surface of the soil and to a much lesser extent in the thickness of the upper horizons due to the dying of the root systems. The decay of the organic matter goes very quickly, which contributes to high temperatures and constantly high humidity Soil, optimal for the development of microorganisms. Most of Organic residues are mineralized completely and therefore the amount of humus is low. The composition of humus ultrafulvate; Dissolving fractions of fulvocuslot in the medium depleted bases penetrate deeply into the soil. Therefore, the concentration of humus in the upper horizon is insignificant. Usually it is redistributed by the profile at a significant glybine.
Tropical belt. Two vary soil zones: 1. Tropical wet forest areas.
→ red-Yellow Ferrallite Soil Zone
- formed in more wet and warm conditions; climatic seasons not expressed, almost no fluctuations in the temperature of the day and night; very deep washing of soils, Intensive development of soil erosion. → Red Ferrallite Soil Zone
- in variable-wet rainforests and highly harvested savannas. 2. Tropical xerophyte forest and savannah regions:
→Brown-red soils
- form under dry tropical parel and thickets of shrubs. Have a predominantly ferallization composition→Red-brown soils
- in dry savannas, with a slightly smaller moisture. During drought, trees are discharged by foliage and herbs burn out → organic substances Mineralized on the surface of the soil. Soils have a ferry rally.
Subtropical belt. Brown soils
- immense water regime; In the humidity time of the year there is intensive weathelation with the formation of secondary minerals.SERO-brown soils
- Maximum precipitation falls for winter and soil deeply missed and exempted from easily soluble salts. Black subtropical soils
- on weathering products and reverseage of major breeds. Similar to chernozem (significant accumulation of humus, immense water regime, the presence of illuvial-carbonate horizon)
Subboroneal (moderate) belt. Brown forest soil
- dominate under wide forests in deep injection conditions; Weak profile differentiation, with the exception of humus horizon and clarified appearance horizons. Brown forest gley soils
- with weakened surface drain and wagge. Black soil
- no forest cover, there is a rich dispersion and humus horizons like Chernozem,But!: Unlike Chernozem, they have a wash water mode, Chernozem
- In the profile, a powerful dark-colored humus layer (35-150 cm), the grainy and lumpy structure of the humus layer + opead is rich in the ash elements and nitrogen - annual powerful income. Strengthened the process of humification.Chestnut soils
- in conditions of dry climate; The humus horizon is less powerful; In the illuvial carbonate horizon, carbonates are highlighted in the form of bright white spots of white-eyed; Network Type water regime; Since there are little precipitation.Brown semi-desert soils
- the humus-eluvial horizon of grayish-brown color is distinctly distinguished, often a very thin crust is peeling from the surface, the climate is continental, dry, low productivity of vegetation; The humification process is short-lived (spring).
cold- temperate zone. Podzolic soils
- They are formed as a result of the development of a podzolic process (that is, the destruction of the upper part of the profile of the primary and secondary minerals and the removal of the destruction of the fracture is below the underlying horizons and in groundwater). Dernovo-podzolic soils
- develop under the influence of podzolic and turf (that is, the process of forming soils with a well-developed humus horizon, which flows under the influence of herbal vegetation) processes. Merzlotically taiga soil
– perennial Merzlota, weak bockers of substances.
Polar (cold) belt. Arctic dernea soils
- different in chemical features depending on the composition of the breeds and drainage conditions; Characteristic of combustion and cracking; Not a big intake of organic residues, a low-power humus horizon ,. Tundra gley soils
- in the profile allocate an organogenic horizon (depending on the degree of decomposition from peat to humus) and the mineral horizon, varying degrees Cooked.
Tropical zone.Under the tropics here is meant the territory between the northern and southern tropics, i.e. Parallel with latimes 23 ° 07 "Northern and South latitude. This territory includes tropical, subequatorial and equatorial climatic belts.
Tropical soils occupy more than 1/4 surfaces of the world sushi. The conditions for soil formation in the tropics and high latitudes are sharply different. The most notable distinguishing features of tropical landscapes are climate, vegetable and animal world, but these differences are not limited. Most of the tropical territory ( South America, Africa, Peninsula, Industan, Australia) It is the remains of the oldest sushi (Gondwana), on which the weathering processes were walking for a long time - starting from the lower Paleozoa, and sometimes even from the Precambria. Therefore, some important properties of modern tropical soils are inherited from ancient weathering products, and separate processes of modern soil formation are complexly related to the processes of the ancient steps of hypergenesis (weathered). Traces of the most ancient phase of hypergenesis, the formation of which is widespread in many areas of the ancient sushi, are presented with a powerful weathered bark with a differentiated profile. These ancient bark of tropical territory, as a rule, do not serve as the soil-forming rocks, are usually buried under later formations. In areas of deep faults, cutting into the Cenozoic sections of the ancient sushi and accompanied by powerful volcanic eruptions, these barks are covered with powerful cover of Love. However, on an immeasurably larger area, the surface of the ancient crate of weathered is covered with peculiar coating sediments of red. These red-colored sediments, reducing the huge territory of the tropical sushi, are a completely special hypergenic education, which arose in other conditions and is significantly more time than the ancient weathelation bark. Red color sediments have a sled-loom composition, their power varies from several decimeters to 10 m or more. These deposits were formed in sufficiently wet conditions, conducive to high geochemical activity of iron. As part of these sediments there is iron oxide, it is he gives deposits a red color. These red color deposits are the most typical soil-forming tropic rocks, so many tropical soils have a red or close color to it, which is reflected in their names. These colors inherit the soil, the formation of which can occur in various modern bioclimatic conditions. Along with red color sediments, lake loams, having gray, light yellow sandy alluvial deposits, brown, can act as the soil-forming rocks. volcanic ash et al., Therefore, the soils formed in the same bioclimatic conditions are not always the same color. The most important feature of the tropical belt is a steady high air temperature, therefore, the nature of atmospheric moistening becomes of particular importance. Since evaporation in the tropics is high, then the annual amount of precipitation does not give the ideas about the degree of atmospheric moistening. Even with a significant annual amount of precipitation in tropical soils, throughout the year, a dry period is changed (with the amount of precipitation less than 60 mm per month) and the wet period (with the amount of precipitation more than 100 mm per month). In accordance with moisturizing in soils, there is a change of irregular and flushing regimes. one. Soil landscapes of rain (constantly wet) rainforest. Constantly wet rainforests are common on large territory In South America, Africa, in Madagascar, in Southeast Asia, Indonesia, in the Philippines, in New Guinea and Australia. Under these forests, soils are formed for which at different times were offered different names – red-yellow lathe , ferrallitic and others. The climate of these forests is hot and wet, average temperatures of more than 20 ° C. The annual amount of precipitation is 1800-2000 mm, although it reaches 5000-8000 mm in separate places. The duration of the dry period does not exceed 1-2 months. Significant moisturizing is not accompanied by the use of soil with water and no fear. The abundance of heat and moisture determines the largest biomass among the biocenoses - about 5000 c / ha and the mass of the annual patch - 250 c / ha. There is almost no forest litter, since almost all OPEDs are destroyed throughout the year due to the intensive activities of soil animals and microorganisms. Most of the released elements released as a result of the decomposition immediately captured the complex root rain forest system and again involved in the biological circulation. As a result of these processes, there is almost no humus accumulation in these soils. Gumus Rain Forest Soil Horizon gray, very low (5-7 cm) and contains only a few percent of humus. It is replaced by the transition horizon of A / B (10-20 cm), during which humus hue completely disappears. The peculiarity of these biocenoses is that almost the entire mass of the chemical elements necessary for the nutrition of plants are contained in the plants themselves and only due to this is not washed away with heavy atmospheric precipitation. When cutting rainy tropical forest, Atmospheric precipitates very quickly blur the upper thin fertile soil layer and fruitless land remains under the forest. 2. Soil tropical landscapes of seasonal atmospheric moistening. Without constantly wet forests, a variety of landscapes, atmospheric moisturizing on which are unevenly uneven, and temperature conditions are changed for the largest area, and the temperature conditions are changed slightly (average monthly temperatures are close to 20 ° C). With a duration of a dry period from 3 to 6 months a year at the annual amount of precipitation from 900 to 1500 mm, landscapes of seasonally wet bright rainforests and highly harvested savannes are developing. Light tropical forests are characterized by free arrangement of trees, abundance of light and, as a result of this, lush cover of cereal herbs. High-retard savannahs are various combinations of grassy vegetation with the islands of the forest or separate specimens of trees. Soils that are formed under these landscapes are called red or ferallotic soils of seasonally wet rainforest and highly harvested savannah . The structure of the profile of these soils: the humus horizon (a) is located on top, in the upper part more or less accepted, with a capacity of 10-15 cm, dark gray. The following is the transitional horizon (B) below, during which the gray shade is gradually disappeared and the red color of the soil-forming rock is enhanced. The power of this horizon is 30-50 cm. The total content of humus in the soil from 1 to 4%, sometimes more. Soil reaction is a weakly acidic, often almost neutral. These soils are widely used in tropical agriculture. The main problem when using them is a slight destruction of soil under the action of erosion. With the duration of the dry period from 7 to 10 months a year and the annual amount of precipitation 400-600 mm, xerophytic biocenoses develop, which are a combination of dry wood-shrub thickets and low herbs. Soils, forming under these landscapes, are called red-brown soils dry savannah. The structure of these soils: under the humus horizon A, with a capacity of about 10 cm, a weakly gray shade, a transition horizon in 25-35 cm is located. At the bottom of this horizon, there are sometimes carbonate spraying. Next follows the soil-forming breed. The content of humus in these soils is usually small. The soil reaction is low-alkaline (pH \u003d 7.0-7.5). These soils are widespread in Central and Western regions of Australia, in some areas tropical Africa. For agriculture, they are unsuitable and used mainly under pastures. With the annual amount of precipitation less than 300 mm, the soils of arid tropical (semi-desert and deserted) landscapes are formed , having common features with gray-brown soils and serosms. They have a low-power and carbonate weakly differentiated profile. Since the red-forming rocks in many areas are red-colored products [neogenic] weathered, these soils have a reddish color. The zone of tropical islands.A special group forms the soil of the ocean islands of the tropical belt of the World Ocean, among them the most peculiar soil coral islands – atollles. Soil-forming rocks on such islands serve snow-white coral sands and reef limestone. Vegetation is represented by thickets of shrubs and forests of coconut palm with intermittent cover from low cereals. Here are the most common atoll humus-carbonate sand soils With a low-power humus horizon (5-10 cm), characterized by the content of gumus 1-2% and pH about 7.5. Often an important factor for soiling on the islands is Ornithofauna. The colonies of birds are laying huge amounts of litter, which enriches the soil with organic matter and contributes to the emergence of special wood vegetation, thickets of high herbs and ferns. In the soil profile, a powerful peat-humus horizon with an acidic reaction is formed. Such soils are called atoll melano-humus-carbonate. Gumus-carbonate soils are an important natural resource of numerous island states of the quiet and Indian OceanovBeing the main plantation for coconut palm. Mountain area zone.Mountain soils occupy more than 20% of the entire surface of the sushi. IN mountainous countries In the main features, the same combination of soil formation factors are repeated, as on the plains, therefore many soils of the type of automorphic soils of the plated territories are common in the mountains: podzolic, chernozem, etc. However, the formation of soils in mountain and equible areas has certain differences, therefore the same type of soils formed In the plains and mountain areas, clearly differ. Highlight mining and podzolic, mountain Chernozem and DR. Besides, in mountain areas There are such conditions in which specific mountain soilwho have no analogues on the plains (for example, gorn-meadow soils). One of distinctive features Mountain soil structures are low-power genetic horizons and all soil profiles. The power of the mountain soil profile may be 10 or more times less than the power of the profile of similar flat soil, while maintaining the structure of the flat soil profile and its features. For mountainous areas, the vertical zonality (or explanation) of the soil cover is characteristic, under which the natural change of alone soils is understood as it raises from the foot to the vertices of high mountains. This phenomenon is due to a natural change in hydrothermal conditions and composition of vegetation with a height. The lower belt of the mountain soil belongs to that natural zone, in the square of which are mountains. For example, if mining system It is located in the desert zone, then gray-brown desert soils will be formed on its lower belt, but with a rise upside down, they will alternately replace the mountain-chestnut, mining and chernozem, mining and mountain-meadow soils. However, under the influence of local bioclimatic features, some natural zones may fall out of the structure of the vertical zonality of soil cover. Inversion of soil zones may be observed, when one zone turns out to be higher than it should be done with horizontal.
Tropical belt occupies the most large square (more than 5.6 billion hectares, which is 42% of the sushi surface). Mountain areas account for 0.7 billion hectares or 12.8% of the belt area.
The tropical belt is located on all continents. The climate is hot average temperature The air of the coldest month is at least 20-22 ° C. There is a uniformity of temperature distribution by season of the year. Due to the similarity of thermal conditions, the soil distribution is due to the main moisture and features of the soil-forming rocks, which in the process of weathering acquire a ferallite composition.
In the rain period there is a solid wasting of the soil, in a dry period - its strong drainage. Great importance Acquires the duration of the moisture period. Since the tropics are characterized by high evaporation, the annual precipitation amount does not give the idea of \u200b\u200bthe degree of atmospheric moistening. Even with a very significant annual amount of precipitation in tropical soils throughout the year there may be a change in the washing type of water regime by irregular. It is considered to be dry months with quantity atmospheric oyphans <60 мм, а влажными - >100 mm. Number of precipitation<60 мм в месяц составляет величину, которая меньше испаряемости. Вся вода расходуется на транспирацию, поэтому в это время почва не только не промывается, но даже теряет запас воды, доступной для растений, и высыхает. В периоды дождей, наоборот, процессы транспирации не в силах уравновесить количество выпадающей атмосферной влаги. В результате усиленного поверхностного стока и подъема уровня грунтовых вод понижения рельефа и низменные равнины на некоторое время заболачиваются.
By differences in atmospheric moisture mode, the tropical belt can be divided into four areas: humid (characteristic is constantly wet, hot climate), semi-humid (variable-wet, hot climate), semi-diaride (characterized by a dry climate) and arid (characterized by a hot and arid climate).
Currently, the most common soils in the tropical belt are ferallic soils. tropical humid regions (Three wet areas are allocated: American, covering Central America and most of South America; African, including the Congo River pool and the Gulf Coast; Australia-Asian, which occupies the Peninsula of South Asia (part of the Industan and Indochina), the North Coast of Australia and all Islands, located between these continents).
Ferrallitic soils Characterized by an acidic reaction of the medium, low absorption capacity. The degree of saturation of the bases of 15-25%. Ferrallitic soil character is manifested in high content of iron and aluminum oxides and low /
To the most common soils tropical semi-human regions (in the northern hemisphere they stand out in Central America; in the northern part of South America; in the Western, Central and Eastern part of Africa; on the Peninsulas of South Asia (part of the Indogen and Indochina); Southern Hemisphere Tropical SemiGumidal Oblas occupy the central part of South America, extensive territories of Western , central and eastern Africa, North Australia) are red red ferritic Soil. By the nature of the soil formation, they are close to the soils of tropical humid regions, but there are some differences:
1) soil deeply enhance in a dry period;
2) upper horizons due to warming up in a dry period
provided red as a result of thermal dehydration of iron oxides;
3) the humus horizon has a dark brown color; increase
its power (up to 30-40 cm), the content of humus (up to 4%); The composition of humus is predominantly fulviving;
4) the possibility of falling out the specific forms of iron hydroxides increases.
In Soil Pokrov tropical semi-samide regions (Indo-African, Australian, Central American, South American) highlights brown-red soils of xerophytic forests and red-brown soils dry savannah.
Brown-red Soils are formed in conditions that are characterized by a significant amount of precipitation (about 1000 mm) and the winter dry season duration of the month. The soil formation takes place under dry tropical gentlemen and shrubs (in Australia, this was mostly overgrown acacia, in the pool, the r. San Francisco is a prickhecker-cactus formation.
The soil is formed with a periodically washing type of water regime. Brown-red soils are characterized by a humus horizon with a capacity of 25-30 cm containing 3-4% humus of the humanity-valve composition. They have a weakly acidic medium (pH 5.0-6.0), are saturated with the grounds.
Red-brown soils form under the influence of the ferallization process in its typical manifestation. The humus horizon is less developed (20-25 cm), is characterized by a low content of humus (about 1%), the reaction of the medium from weakly acid to weakly alkaline.
In the lower parts of the profile there is an illuvial-carbonate horizon.
The formation of ferrous concretions is less intense than in brown-red soils; Ferrous surface crusts are rarely formed.
In semi-desert zones arid regions (Afro-Asian, embracing South Sahara and the southern part of the Arabian Peninsula; Australian, which occupies a significant part of the mainland; South Africa (Kalahari Desert); South American) Under low-fat deserted savanna, reddish-brown soils are developed. They are formed with a weak effect of the ferallization process.
From red-brown soil, they are characterized by a lesser degree of ferrity, more drier color, low content of humus (about 1%). The soil is characterized by a weakly alkaline medium reaction (pH 7.0-7.5), the presence of carbonates and the absence of easily soluble salts.
Red-brown soils occupy approximately 33% of the territory of the arid tropical regions. The rest is represented by sandy and stony desert soils, as well as black tropical arid. In the relief slides, allyuvial soils, salt marshes and salt soils are often formed in the river policies.
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