Vegetation as a factor of soil formation. The role of microorganisms, higher plants and animals in soil-forming processes Which organisms are most important for soil formation

Allocated five factors of soil formation: parent (parent) rock; climate; plants; animal organisms; relief and time. Currently, they have been replenished with two more: waters (soil and ground) and human economic activity.

Parent rocks(or parent) are rocks from which soils are formed. The parent rock is the material basis of the soil and transfers to it its mechanical, mineralogical and chemical composition, as well as physical, chemical and physicochemical properties, which subsequently gradually change to varying degrees under the influence of the soil forming process, giving a certain specificity to each type of soil.

Parent rocks differ in origin, composition, structure and properties. They are classified into igneous, metamorphic and sedimentary rocks.

The mineralogical, chemical and mechanical composition of rocks determines the conditions for the growth of plants, has a great influence on humus accumulation, podzolization, gleying, salinization and other processes. Thus, the carbonate content of rocks in the taiga-forest zone creates a favorable reaction of the environment, contributes to the formation of the humus horizon, its structure. In acidic rocks, these processes are much slower. The increased content of water-soluble salts leads to the formation of saline soils. Depending on the mechanical composition, the nature of the composition of the rocks, they differ in water permeability, moisture capacity, porosity, which predetermines in the process of soil development their water, air, and thermal regimes.

Meaning relief in the formation of soils and the development of the soil cover is large and varied. The relief acts as the main factor in the redistribution of solar radiation and precipitation, depending on the exposure and steepness of slopes and affects the water, thermal, nutrient, redox and salt regimes of soils.

So, in the mountains, vertical zoning of climate, vegetation and soils arises due to a decrease in air temperature with height and changes in moisture. Air masses, approaching the mountains, slowly rise and gradually cool, which contributes to the achievement of the dew point and precipitation. Having crossed the mountains, the same air masses, descending, heat up and become dry. Differences in hydration cause changes in nutritional, redox and salt regimes.

Biological factor of soil formation- Three groups of organisms are involved in soil formation - green plants, microorganisms and animals that make up complex biocenoses.

Vegetation. Plants are the only primary source of organic matter in the soil. Their main function as soil formers should be considered the biological cycle of substances - the synthesis of biomass due to carbon dioxide of the atmosphere, solar energy, water and mineral compounds coming from the soil. Plant biomass in the form of root residues and ground litter is returned to the soil. The nature of the participation of green plants in soil formation is different and depends on the type of vegetation and the intensity of the biological cycle (Table 5.1).

All living organisms on Earth form biological communities (cenoses) and biological formations, with which the processes of formation and development of soils are inextricably linked,

The theory of plant formations from the point of view of soil science was developed by VR Williams. As the main criteria for the separation of plant formations, he took such indicators as the composition of plant groups, the peculiarities of the input of organic matter into the soil and the nature of its decomposition under the influence of microorganisms with different ratios of aerobic and anaerobic processes.

At present, when studying the role of plant cenoses in soil formation, the character and intensity of the biological cycle of substances are additionally taken into account; This makes it possible to expand the theory of plant formations from the point of view of soil science and to give a more detailed division of them.

According to N.N. Rozov, the following main groups of plant formations are distinguished:

1. woody vegetation: taiga forests, deciduous forests, humid subtropical forests and rainforests;
2. transitional woody - herbaceous vegetation formation: xerophytic forests, savannas;
3. herbaceous vegetation formation: dry and swampy meadows, grassy prairies, temperate steppes, subtropical shrub steppes;
4. desert plant formation: vegetation of the subboreal, subtropical and tropical soil - climatic zones;
5. lichen - moss vegetation: tundra, raised bogs.

Forest vegetation is a perennial vegetation; therefore, its remains come mainly to the soil surface in the form of ground litter, from which forest litter is formed. Water-soluble decomposition products enter the mineral soil. A feature of the biological cycle in the forest is the long-term conservation of a significant amount of nitrogen and ash elements of plant nutrition in perennial biomass and their exclusion from the annual biological cycle. In different natural conditions different types of forest are formed, which determines the nature of the soil-forming process, and, consequently, the type of forming soils.

Herbaceous vegetation forms a dense network of thin roots in the soil, intertwining the entire upper part of the soil profile, the biomass of which usually exceeds the biomass of the terrestrial part. Since the terrestrial part of herbaceous vegetation is alienated by humans and eaten by animals, the roots are the main source of organic matter in the soil under the herbaceous vegetation. Root systems and products of their humification structure the upper root-inhabited part of the profile, in which a humus horizon, rich in nutrients, is gradually formed. The intensity of the processes is determined by natural conditions, since, depending on the type of herbaceous formations, the amount of biomass formed and the intensity of the biological cycle are different. Therefore, in different natural conditions, different soils are formed under herbaceous vegetation. Moss - lichen vegetation is characterized by the fact that, with a high moisture capacity, it has little activity in the biological cycle. This is the reason for the conservation of dying plant residues, which, with sufficient and excess moisture, turn into peat, and with constant drying, they are easily fluttered by the wind.

Microorganisms. (The role of microorganisms in soil formation is no less significant than the role of plants. Despite their small size, due to their abundance, they have a huge total surface area and therefore actively contact the soil. According to E.N. bacteria reaches 5 million m 2. Due to the short life cycle and high reproduction rate, microorganisms relatively quickly enrich the soil with a significant amount of organic matter) According to I.V. Tyurin's calculations, the annual input of dry microbial matter into the soil can be 0.6 tha. (This biomass, rich in proteins, containing a lot of nitrogen, phosphorus, potassium, is of great importance for soil formation and the formation of soil fertility.

Microorganisms are the active factor with the activity of which the processes of decomposition of organic substances and their transformation into soil humus are associated. Microorganisms fix atmospheric nitrogen. They secrete enzymes, vitamins, growth and other biological substances. The entry of plant nutrients into the soil solution, and, consequently, soil fertility, depends on the activity of microorganisms.

The most common type of soil microorganism is bacteria. Their number ranges from several hundred thousand to billions per gram of soil. Depending on the way of feeding, bacteria are divided into heterotrophic and autotrophic.

Heterotrophic bacteria use the carbon of organic compounds, decomposing organic residues to simple mineral compounds.

Autotrophic bacteria assimilate carbon from air carbon dioxide and oxidize undeoxidized mineral compounds formed during the activity of heterotrophs.

According to the type of respiration, bacteria are divided into aerobic, which develop in the presence of molecular oxygen, and anaerobic, which do not require free oxygen for their evolution.

The vast majority of bacteria develop best when the environment is neutral. In an acidic environment, they are inactive.

Actinomycetes (mold bacteria, or radiant fungi) are found in soils in smaller quantities than other bacteria; however, they are very diverse and play an important role in the soil-forming process. Actinomycetes decompose cellulose, lignin, humus substances of the soil, participate in the formation of humus. They thrive best in neutral to slightly alkaline soils, rich in organic matter and well cultivated.

Mushrooms- saprophytes are heterotrophic organisms. They are found in all soils. Having branching mycelium, fungi densely intertwine organic debris in the soil. Under aerobic conditions, they break down fiber, lignin, fats, proteins, and other organic compounds. Mushrooms are involved in the mineralization of soil humus.

Fungi are able to enter into symbiosis with plants, forming internal or external mycorrhiza. In this symbiosis, the fungus receives carbon nutrition from the plant, and itself provides the plant with nitrogen formed during the decomposition of nitrogen-containing organic soil compounds.

Seaweed distributed in all soils, mainly in the surface layer. They contain chlorophyll in their cells, thanks to which they are able to assimilate carbon dioxide and release oxygen.

Algae are actively involved in the weathering of rocks and in the primary process of soil formation.

Lichens in nature, they usually develop on poor soils, stony substrates, pine forests, tundra and desert.

Lichen is a symbiosis of fungus and algae. Lichen algae synthesizes organic matter, which the fungus uses, and the fungus provides the algae with water and minerals dissolved in it.

Lichens destroy the rock biochemically - by dissolving and mechanically - with the help of hyphae and thalli (the body of the lichen), firmly growing together with the surface.

From the moment lichens settle on rocks, more intensive biological weathering and primary soil formation begins.

The simplest are represented in the soil by the classes of rhizopods (amoeba), flagellates and ciliates. They feed mainly on microorganisms that inhabit the soil. Some protozoa contain chlorophyll diffusely dissolved in protoplasm and are able to assimilate carbon dioxide and mineral salts. Separate types can break down proteins, carbohydrates, fats and even fiber.

Outbreaks of protozoa activity in the soil are accompanied by a decrease in the number of bacteria. Therefore, it is customary to consider the manifestation of the activity of protozoa as an indicator that is negative for fertility. At the same time, some data indicate that in some cases, with the development of amoebas in the soil, the amount of assimilable forms of nitrogen increases.

Microorganisms in the soil form a complex biocenosis, in which their various groups are in certain relationships that change depending on changes in soil formation conditions.

The nature of microbial biocenoses is influenced by the conditions of water, air and thermal regimes of soils, the reaction of the environment (acidic or alkaline), the composition of organic residues, etc. Thus, with an increase in soil moisture and deterioration of aeration, the activity of anaerobic microorganisms increases; with an increase in the acidity of the soil solution, bacteria are inhibited and fungi are activated.

All groups of microorganisms are sensitive to changes in external conditions, therefore, during the year their activity is very unequal. At very high and low air temperatures, biological activity in soils dies down.

(By regulating the conditions for the vital activity of microorganisms, one can significantly influence the fertility of the soil. Providing a loose composition of the arable layer and optimal moisture conditions, neutralizing the acidity of the soil, we favor the development of nitrification and accumulation of nitrogen, the mobilization of other nutrients and, in general, create favorable conditions for the development of plants.)

Animals... The soil fauna is quite numerous and varied; it is represented by invertebrates and vertebrates.

The most active soil formers among invertebrates are earthworms. Beginning with Charles Darwin, many scientists have noted their important role in the soil-forming process.

Earthworms are widespread almost everywhere in both cultivated and virgin soils. Their number ranges from hundreds of thousands to several million per hectare. Moving inside the soil and feeding on plant debris, earthworms are actively involved in the processing and decomposition of organic debris, passing a huge mass of soil through themselves during digestion.

According to NA Dimo, on irrigated cultivated gray soils, worms annually throw up to 123 tons of processed soil on the surface of 1 hectare in the form of excrement (coprolites). Coprolites are well-aggregated lumps enriched in bacteria, organic matter, and calcium carbonate. The researches of SI Ponomareva established that the emissions of earthworms on soddy-podzolic soil have a neutral reaction, contain 20% more humus and absorbed calcium. All this suggests that earthworms improve the physical properties of soils, make them looser, more airy and permeable, thereby increasing their fertility.

Insects- ants, termites, bumblebees, wasps, beetles and their larvae are also involved in the process of soil formation. Making numerous moves in the soil, they loosen the soil and improve its water-physical properties. In addition, feeding on plant residues, they mix them with the soil, and when they die off, they themselves serve as a source of soil enrichment with organic substances.

Vertebrates- lizards, snakes, marmots, mice, ground squirrels, moles - do a great job of mixing the soil. Making holes in the soil, they throw a large amount of earth to the surface. The formed passages (mole holes) are filled with a mass of soil or rock and on the soil profile have a rounded shape, distinguished by color and degree of compaction. In the steppe regions, earth-moving animals mix the upper and lower horizons so much that a tubercle microrelief is formed on the surface, and the soil is characterized as dug (molehill) chernozem, dug chestnut soil or gray soil.
read the same

Chapter 2. FACTORS OF SOIL FORMATION. GENERAL SCHEME OF THE TILLAGE PROCESS

§1. The concept of soil formation factors

Under factors of soil formation the components of the natural environment external to the soil are understood, under the influence and with the participation of which the soil cover of the earth's surface is formed. For the first time this close causal relationship between natural conditions, the nature of soil formation and soil properties was established by V.V. Dokuchaev. He also identified the main factors of soil formation, which are: soil-forming rocks, climate, relief, living organisms, human economic activity and time. The listed factors in their various combinations create a great variety of soil types, their combinations, a unique mosaic of the soil cover. VV Dokuchaev noted that all soil-forming agents are equal and take an equal part in soil formation, the absence of one of them excludes the possibility of a soil-forming process. At certain stages or in specific conditions of soil development, any one of the factors can act as a determining factor.

Parent rocks. The significance of the parent, or parent, rock as a factor of soil formation lies in the fact that it is the source material from which the soils are formed, and the environment where the activity of living organisms is manifested. However, the parent rock is not an inert soil skeleton. It takes a direct part in the processes developing on it, determining the granulometric, mineralogical and chemical composition of soils and thereby influencing the physical, physicochemical, water-air properties, thermal, nutrient and water regimes of the soil. All these properties directly affect the speed, direction and nature of soil-forming processes: mineralization and humification of plant residues, the rate of accumulation and movement of substances in the soil mass, as well as the formation and level of soil fertility.

Under the same natural conditions, but on different soil-forming rocks, completely different soils can form. So, for example, in the taiga-forest zone, low-fertile, podzolic soils are formed on an aluminosilicate moraine, and fertile soils with a high humus content, an agronomically valuable structure and a favorable neutral reaction are formed on a carbonate moraine. In the same zone, poor and dry sandy soils are formed on fluvioglacial sands, and floodplain soddy, fertile soils are formed on alluvium.

By origin, rocks are divided into three groups:

1) magmatic, formed during intrusion into the earth's crust or eruption on the surface of magma (basic - basalt, gabbro; acidic - granite; ultrabasic - peridonite, dunite);

2) sedimentary rocks formed by mechanical or chemical deposition of the products of destruction of igneous and metamorphic rocks, as well as the vital activity of organisms;

3) metamorphic rocks formed from pre-existing rocks under the influence of metamorphic factors (high temperatures, pressure, the action of gases). The most widespread are schists, phyllites, gneisses, quartzites, and marbles.

In most of the Earth, soils have formed on sedimentary rocks. They cover about 75% of the surface of the continents. According to genetic characteristics, sedimentary rocks are distinguished: clastic, or mechanical, chemical and organogenic.

Mechanical, or fragmental, deposits were formed during mechanical crushing (crushing) of various rocks under the influence of thermal weathering, as well as their destruction by glaciers and snow waters.

Eluvium- weathering products remaining at the place of their formation. This material is made up of debris different sizes... In mountainous terrain, eluvium is found on elevations. Soils formed on eluvial deposits are characterized by low fertility, low thickness, as well as rubble and stony.

Deluvium Are friable weathering products carried by temporary insignificant water currents flowing down the slopes during rains and spring snowmelt. This fine earthy material is deposited at the base and in the lower part of the slopes. On deluvial deposits, soils of fairly high fertility are formed.

Alluvium- sediments of river constant water flows. These deposits are formed in river valleys during floods and are characterized by stratification and grading. They can be different in particle content - sandy in the near-river part of the floodplain and silty in the near-terrace part.

Lacustrine sediments- sapropel, lake silts, marl. They are characterized by a clayey, less often fine sandy composition with a significant amount of silt, carbonates, or readily soluble salts. Quite fertile soils are being formed.

Swamp sediments consist of peat and bog silt.

Marine sediments found in the Caspian lowland, on the coast of the northern seas. These rocks are sorted, of different granulometric composition, layered and contain salts. Saline soils are formed on marine sediments.

Aeolian deposits are formed during the transfer and deposition of sandy material by the wind. Sandy deposits occupy large areas in deserts. They form such forms of relief as dunes, dunes, hillocks.

On the vast plains, sediments of the Quaternary period are mainly distributed - glacial deposits, weathering products of various rocks, displaced and deposited by the glacier. They also prevail in the composition of the parent rocks of Belarus and are divided into moraine, water-glacial, lacustrine-glacial. For moraines characterized by unsorted, heterogeneous texture, boulders, enrichment with primary minerals, red-brown, yellow-brown colors. Water-glacial deposits are associated with the movement and redeposition of moraine material by glacial flows beyond the edge of the glacier. They are characterized by sorting, flat relief, boulderlessness, poor in chemical composition, mostly sandy. Lacustrine-glacial are deposits of shallow glacial lakes. Characterized by a high content of silt fractions, boulderlessness, rich chemical composition, loam and sandy loam in mechanical composition, often carbonate, compacted, prone to waterlogging.

Loess-like loams and loess have a different genesis. They are characterized by fawn or brownish-fawn coloration, carbonate content, loose constitution, they are rich in chemical composition, more often light loams, are prone to erosion and the formation of ravines.

Chemical sedimentary rocks arise by the deposition of matter on the bottom of water bodies from solutions as a result of chemical reactions or changes in water temperature. Carbonate rocks are formed at the bottom of the seas in part by the deposition of calcium carbonate from the water, which enters with the river water. Most of the calcium carbonate deposited on the seabed is a product of the activity of some organisms. So, in the Cretaceous period of the Mesozoic era, there was an accumulation of chalk deposits due to microscopic shell amoebas (foraminifera, etc.).

Organogenic breeds consist of the waste products of animals and plants, as well as of their undecomposed remains (peat). Many carbonate rocks (coral, shell limestones, etc.) are formed with the participation of organisms, the skeletal or protective part of which contains calcium carbonate.

When assessing soils, all parent rocks are divided (Fig. 2) into saline and non-saline... Saline rocks are deposits of long-dried sea basins or lakes; saline soils (salt marshes, salt licks) can develop on them. On carbonate rocks, soils develop with a neutral reaction of the environment, which contributes to the accumulation of humus in the soil (sod-carbonate, etc.).

The most valuable parent rocks are loesses, loesslike loams and other carbonate rocks (glacial and lacustrine deposits), as well as alluvial loams in river floodplains. The less valuable are carbonate-free mantle loams, and the poorest are quartz sands (aeolian deposits).

Based on the characteristics of the parent rock, P.S. Kosovich (1911) made two conclusions:

1. Different soils can form on the same rocks, if other factors of soil formation differ from each other. A soddy soil is formed on a loamy rock under herbaceous vegetation, and soddy-podzolic or other forest soil is formed under a forest.

2. The same soils can be formed on different rocks, if the other factors of soil formation are the same. Sod-podzolic soils are formed under a mixed coniferous-deciduous forest on sandy, sandy loam, loamy rocks.

However, exceptions are possible: the more active the process of soil formation, the weaker the influence of the rock, but if the chemical composition and physical properties of the rock are expressed sharply (carbonate rock), it has a long-term effect.

Climate is a long-term weather regime of a particular area. In various natural conditions, the climate obeys the law of zoning. It depends on latitude, altitude, landforms and distance from seas and oceans. Temperature, precipitation, wind and air humidity have the greatest impact on soil formation. These elements, in combination with other factors of soil formation, determine a certain pattern in the distribution of the soil cover.

The provision of the soil with energy is associated with the climate - heat and, to a large extent, with water. The activity of biological processes and the development of the soil-forming process depend on the value of the annual amount of incoming heat and moisture, the characteristics of their daily and seasonal distribution.

The characteristics of the climate in terms of temperature indicators and humidification conditions are of great importance. The following climatic groupings are distinguished according to the indicators of the sum of temperatures above 10 о С for the growing season: cold polar< 600 о, холодно-умеренные – 600 – 2000 о, тепло-умеренные – 2000 – 3800 о, теплые субтропические – 3800 – 8000 о, жаркие тропические >8000 about... These climate groups are located in the form of latitudinal belts and are called soil-biothermal belts, which are characterized by certain types of vegetation and soils. According to the conditions of humidification, climatic groups are distinguished: very wet- moisture coefficient> 1.33, humid humid - 1.00 - 1.33, semi-humid - 0,55 – 1 , 00, semi-dry - 0.33 - 0.55, dry arid - 0.12 - 0.33, very dry -< 0,12. Humidification coefficient (HCP) Is the ratio of precipitation to evaporation. The abundance of precipitation contributes to the washing of the soil and the removal of readily soluble salts, including minerals, formed during the decomposition of organic residues into the lower horizons. In an arid climate, these compounds are not only not carried out, but, on the contrary, are capable of accumulating in the upper layers of the soil, leading to its salinization.

The climate has direct and indirect influence on the nature of the soil-forming process. The direct impact is related to the direct impact on the soil of precipitation, heating and cooling. The indirect influence of climate is manifested through the impact on flora and fauna.

Thus, the climate strongly influences the thermal, air and other soil regimes. The type of vegetation and the composition of phytocenoses, the rate of formation and transformation of organic matter, the rate of enzymatic reactions, the metabolic and functional activity of microbiota, plants and animals, and the processes of wind and water erosion depend on the combination of temperature conditions and moisture.

Relief. The influence of the relief on the soil-forming process is mainly indirect, through the redistribution of heat and water that enter the land surface. A significant change in the height of the terrain entails a significant change in temperature conditions and changes in moisture. The air masses, rising to the mountains, are cooled, which causes precipitation, and the air, having passed through the mountains, heats up again and becomes dry. This is associated with the phenomenon of vertical zoning of climate, vegetation and soils in the mountains.

The relief influences the redistribution of solar energy and precipitation depending on the exposure, steepness and shape of the slopes. Slopes of different steepness and shape redistribute moisture, regulate the ratio of flowing, percolating and accumulating precipitation. From elevated relief elements, water flows down the slopes and accumulates in depressions. On a concave slope, water collects in the soil, on a convex slope, it flows down. Slopes of different exposure receive different amounts of solar energy. The southern slopes are always warmer and drier than the northern ones. In the best conditions are the southeastern slopes, which are warmed by the sun in moist soil. The greatest temperature differences are observed in summer and can reach 5 - 7 o C on different slopes. The maximum temperatures are observed on the southwestern slopes, as the sun heats up the already dried soil. Windward slopes receive more moisture than leeward slopes. All this creates differences in moisture and affects the nature of the water, nutritional and air regimes. These factors create different conditions for the growth of vegetation, differences in the synthesis and decomposition of organic matter, the transformation of soil minerals, which leads to the formation of different soils into different conditions relief.

The relief also affects the intensity of erosion. In the case of a leaching water regime, slope landforms are a condition for the occurrence of water erosion of soils; in an arid climate, plain forms favor the occurrence of wind erosion.

There are three groups of landforms: macrorelief- plains, mountain systems, plateaus that determine the general appearance and affect the climate of a large territory, mesorelief- average landforms against the general background of macrorelief: hills, ravines, valleys, slopes, under the influence of which the local climate is formed and the structure of the soil cover is determined within a particular landscape, microrelief- landforms with height fluctuations of about 1 m: hillocks, hummocks, depressions, saucers, creating patchiness of the soil cover.

Biological factors... Plants, microorganisms and animals play a leading role in soil formation and soil fertility. Each of these groupings fulfills its role, but only when they joint activities the parent rock turns into soil.

The role of plants in soil formation is multifaceted. First, green plants synthesize organic matter. After the end of the life cycle of plants, part of the biomass in the form of root residues and ground litter returns to the soil annually. In the upper horizons, the processes of transformation of organic matter take place and nutrients are accumulated, the soil profile develops and soil fertility is formed. For each natural area specific combinations of herbaceous, shrubby and woody vegetation are characteristic, which differ greatly both in productivity and in the ratio and quantity chemical elements in plant material. Therefore, the roles of woody and herbaceous vegetation in soil formation processes differ significantly.

In forests, the total biomass is the highest, however, the annual growth, and, consequently, litter in them is much less than in meadow steppes, where the main source of organic matter is the mass of dying root systems and, to a lesser extent, the aboveground mass. Litter of woody vegetation falls mainly on the surface of the soil, while that of herbaceous vegetation - in the soil, which prevents its loss and leads to better and faster interaction with the mineral part of the soil and microorganisms. Coniferous litter due to its chemical characteristics (low ash content in combination with a small amount of calcium, the content of a large amount of difficult-to-decompose compounds such as lignin, tannins, resins) undergoes decomposition very slowly, mainly by fungal microflora. Coarse humus of the fulvate type is formed. The litter of herbaceous vegetation is characterized by a finer structure, lower mechanical strength, high ash content (10 - 12%), rich in nitrogen and bases, and is rapidly decomposed, mainly by bacteria. Formed "soft" saturated with calcium humus, predominantly humate type. These factors are the reason for the low fertility of forest soils, while the biomass returning to the soil in meadow phytocenoses forms a powerful humus horizon and fertile soil.

The process of soil formation under coniferous forests under the conditions of a leaching water regime is most often of the type podzolization... The forming soils are characterized by high acidity, low humus content, unsaturation with bases, low content of nutrients, low biological activity and low fertility (podzolic, sod-podzolic). The soil-forming process under the influence of herbaceous vegetation is called sod. As a result of this process, soils with a high humus content, saturated with calcium, with a neutral or close to neutral reaction of the environment, rich in nutrients, are formed, are distinguished by high natural fertility (chernozems, sod and various meadow soils). Under the cover of mixed and deciduous forests, gray forest or brown forest soils are formed with a less acidic reaction than in podzolic soils, the degree of saturation with bases increases, the nitrogen content increases, and fertility increases.

Due to root secretions, plants enhance the process of destruction and transformation of sparingly soluble minerals and contribute to the formation of readily mobile compounds in the soil mass. All this is the result direct the influence of vegetation on the soil-forming process. Indirect the effect on the soil is manifested in a change in the thermal and water regime.

A large and varied soil fauna plays a significant role in soil formation. These are protozoa (flagellates, ciliates, rhizopods), invertebrates (arthropods (ticks, springtails, etc.), earthworms), insects (beetles, ants, etc.), vertebrates (rodents). They crush organic residues, change their chemical and physical properties, accelerating their decomposition. Animals living in the soil, making various moves and mixing organic and mineral substances, increase the air and water permeability of the soil, and form the structure of the soil.

Microorganisms, which are the main destroyers of dead organic matter to simple end products (water, gases, mineral compounds), play a completely unique and extremely important role in the processes of soil formation. Microorganisms are involved in the formation of salts from organomineral complexes, in the destruction and formation of minerals, in the movement and accumulation of soil formation products. Microorganisms are an important factor in the biological cycle of substances, their metabolic activity affects the processes of transformation of organic matter, regulates the nutrient and air regime of the soil, and determines the development of soil fertility. By the number, species composition of microorganisms, the biological activity of soils, reserves of organic matter, the content of nutrients, air and moisture supply are judged. The greatest number of them is in chernozem soils, the smallest - in tundra soils. Each type of soil has its own specific profile distribution of microorganisms, the bulk is concentrated in the upper humus layers within 25 - 35 cm.The biomass of fungi and bacteria in the arable layer is 3 - 5 t / ha, the number of bacteria reaches 5 - 8 billion CFU / g soil, actinomycetes - tens of millions per gram of soil, the length of fungal hyphae - up to 1000 m / ha.

Various groups of microorganisms have a differentiated effect on soil formation. Bacteria are the most common group that performs various transformations of organic matter in the soil, actively decomposing protein-rich residues, and fixing gaseous nitrogen. According to the need for free oxygen in the air, aerobic, anaerobic and facultative bacteria are released, according to the way of nutrition - autotrophic and heterotrophic bacteria. Autotrophic bacteria, according to the method of obtaining energy, are divided into photosynthetic and chemosynthetic (nitrifying, sulfur bacteria, iron bacteria)... Heterotrophic bacteria use ready-made organic matter for nutrition; under their influence, the most important soil formation processes occur - the decomposition of organic residues and the biosynthesis of humus. Actinomycetes and fungi decompose cellulose, lignin, waxes, resins, and actively participate in the formation of humus.

Algae are autotrophic photosynthetic organisms that are involved in weathering and primary soil-forming processes. Lichens are symbiotic organisms, hyphae are introduced into rocks, as a result, more intense biological weathering and primary soil formation begins, primitive soils are formed.

Age. Since the natural process of soil formation takes place in time, the age of soils is of great importance in their evolution. Time itself cannot change the nature of soil formation, but the effect of the influence of each factor or their combination is manifested precisely in the temporal aspect. Thus, the soil as a natural-historical body has an age. There are absolute and relative soil ages. Absolute age Is the time elapsed from the beginning of soil formation to the stage of its development. The earlier the territory was freed from the sea or glacier and, therefore, the earlier the parent rock of this area began to be destroyed, the older the soils will have. Conversely, young will be soils where the soil-forming process began relatively later. The oldest are soils of southern latitudes (South America, Southeast Asia - 2-30 million years), younger - middle and northern latitudes (10 thousand years), the youngest are soils on alluvial deposits along river banks, on shallows. Relative age characterizes the differences in the rate of soil formation of soils of one territory with the same absolute age, depending on the relief and nature of the parent rocks, on the targeted impact of the anthropogenic factor. Therefore, they can be at different stages of development.

Human production activity. The ways and means of influencing the soil are extremely varied. Mechanical processing with heavy agricultural machines, application of organic and mineral fertilizers, plant protection products, drainage and irrigation, man-made disturbances - all this leads to a change in physical, chemical, biological and even morphological properties, and these changes occur much faster than in natural conditions. The water, air, food regime of the cultivated soils is changing. In general, human activity is aimed at creating cultural highly fertile soils where their natural fertility is low, and maintaining high productivity of soils with high fertility, which is exhaustible. If production activity is carried out without taking into account the conditions of development and properties of soils, then such negative consequences as salinization, erosion, waterlogging, pollution, dehumification of soils, etc.

All factors of soil formation have a specific effect on the soil and cannot be replaced with each other, i.e. they are equivalent. Each of them plays a role in the exchange of matter and energy between the soil and the environment. However, the leading factor in soil formation should still be considered a biological one. In addition, the soil itself has a certain effect on the factors of soil formation, causing certain changes in them.

§2. Geological and biological cycles of substances

The formation and life of the soil are inextricably linked with the processes of the cycle of substances. Before the appearance of green plants, various geological processes took place on the planet and existed geological circulation of substances, which is a set of processes of exchange of matter between land and sea and consists of:

1) continental weathering of rocks, resulting in the formation of mobile joints; 2) the transfer of these compounds from land to seas and oceans; 3) deposition of sedimentary rocks at the bottom of the oceans of the seas with their subsequent transformation; 4) a new outcrop of marine sedimentary and metamorphic rocks on the day surface.

The geological cycle has been going on for millions and billions of years, covering up to several kilometers of the lithosphere. Weathering is its driving force. The process of mechanical destruction and chemical change of rocks and their constituent minerals under the influence of the atmosphere, hydrosphere and biosphere is called weathering. Living organisms, atmospheric water, gases and temperature jointly affect the rock. All these factors have a destructive effect on her at the same time. Depending on the predominant factor, three forms of weathering are distinguished: physical, chemical and biological.

Physical weathering is the mechanical destruction of rocks into fragments of various sizes without changing the chemical composition of the minerals that form them. The main factor physical weathering - fluctuations in daily and seasonal temperatures, the effect of freezing water, wind. When heated, the minerals included in the rock expand. And since different minerals have different coefficients of volumetric and linear expansion, local pressures arise that destroy the rock. This process takes place at the contact points of various minerals and rocks. When heating and cooling alternate, cracks form between crystals. Penetrating into small cracks, water creates such capillary pressure that even the hardest rocks are destroyed. When water freezes, these cracks enlarge. In hot climates, water gets into the cracks together with dissolved salts, the crystals of which also have a destructive effect on the rock. Thus, for a long time, many cracks are formed, leading to its complete mechanical destruction. The destroyed rocks acquire the ability to pass and retain water. As a result of crushing massive rocks, the total surface area with which water and gases come into contact is greatly increased. And this determines the course of chemical processes.

Chemical weathering leads to the formation of new compounds and minerals that differ in chemical composition from the primary minerals. The factors of this type of weathering are water with salts and carbon dioxide dissolved in it, as well as atmospheric oxygen. Chemical weathering includes the following processes: dissolution, hydrolysis, hydration, oxidation. The dissolving effect of water increases with increasing temperature. If the water contains carbon dioxide, then in an acidic environment, minerals are destroyed faster. As a result of the weathering of igneous rocks, residual formations, redeposited sediments and soluble salts are obtained.

Before the emergence of life on the globe, the destruction of rocks proceeded only in the two above-mentioned ways, but with the advent of organic life, new weathering processes arose - biological.

Biological weathering is the mechanical destruction and chemical change of rocks under the influence of living organisms and their metabolic products. This type of weathering is associated with soil formation. If during physical and chemical weathering only the transformation of igneous rocks into sedimentary rocks occurs, then during biological weathering soil is formed, and nutrients for plants and organic matter are accumulated in it.

Bacteria, fungi, actinomycetes, green plants, as well as various animals are involved in the soil-forming process. Numerous microorganisms, especially chemosynthetic ones, decompose rocks. Thus, nitrifying bacteria form strong nitric acid, and sulfur bacteria form sulfuric acid, which vigorously decompose aluminosilicates and other minerals. Silicate bacteria, releasing organic acids and carbon dioxide, destroy feldspars, phosphorites and convert potassium and phosphorus into a form available to plants. Algae (diatoms, blue-green, green, etc.), mosses and lichens also destroy rocks.

Green plants secrete organic acids and other biogenic substances, which interact with the mineral part, forming complex organo-mineral compounds. Root systems selectively assimilate ash elements, and after the plants die off, nitrogen, phosphorus, potassium, calcium, sulfur and other biogenic elements accumulate in the upper soil horizons. In addition, the roots of plants, especially woody ones, penetrating deep into rocks through cracks, put pressure on the rocks and destroy them mechanically. Thus, under the influence of physical, chemical and biological weathering, rocks, collapsing, are enriched with fine earth, clay and colloidal particles, acquire moisture capacity, absorbency, become water and air permeable; they accumulate plant nutrients and organic matter. This leads to the emergence of an essential property of the soil - fertility, which rocks do not have.

Against the background of a large geological circulation of substances, there is a small biological the cycle of substances, which is the exchange of matter in the "soil - plant" system. A feature of this cycle is the selectivity of the absorption of substances by organisms, cyclicity, short duration, covers meter layers of the lithosphere, the driving force is soil formation. The biological cycle of substances is at the heart of agricultural production.

The cycles of substances are interconnected with each other, the biological one goes against the background of the geological one, therefore substances can get from one cycle to another. To maintain soil fertility, it is necessary to create conditions under which the biological cycle would receive the most complete expression, and the geological cycle would be limited in its manifestation.

§3. General scheme of the soil-forming process

Soil-forming process - it is a set of phenomena of transformation and movement of substances and energy flowing in the soil mass (A.A. Rode). Soil formation begins from the moment living organisms settle on rocks or the products of their weathering. Any soil-forming process, according to A.A. Rode, is composed of a set elementary soil-forming processes(EPP) of the first and second order. The first-order EPP, or general soil-forming processes, include:

1) synthesis of organic matter ↔ destruction and mineralization of organic matter;

2) synthesis of secondary minerals and organomineral complexes ↔ destruction of mineral compounds;

3) biological accumulation of elements ↔ leaching of mineral and organic compounds;

4) input of moisture into the soil ↔ consumption of moisture from the soil;

5) receipt of radiant energy on the soil surface and heating ↔ radiation of energy by the soil and cooling.

The first three pairs of elementary processes determine food, the fourth pair - water, the fifth pair - the thermal regimes of the soil. The soil-forming process is qualitatively the same in all soils, but quantitatively (by the rate of flow) it differs, i.e. in different soils, the process of soil formation is different, and even in the same soil at different depths, it proceeds in different ways. Therefore, any soil is a series of successively replacing each other vertically genetic horizons- layers into which the parent rock is divided in the process of soil formation. The entire cumulative sequence of horizons is called soil profile... Horizons are called genetic because they are linked by a common origin.

EPPs have their own characteristics at different stages of the emergence and development of the soil, which allows us to speak about a number of stages soil-forming process. The genesis of any soil consists of three successive stages:

1) initial soil formation(primary soil-forming process). It coincides with the settlement of the first living organisms on a rock, is characterized by low activity and volume of the biological cycle, active nonbiological first-order EPPs (dissolution, precipitation, hydration, diffusion, etc.), a weak connection of these processes with each other, therefore, the parent rock at this stage has no pronounced soil features, and the profile is very weakly divided into horizons;

2) stage of soil development characterized by an increase in the activity and volume of biological circulation through activity higher plants, nutrients are accumulated. Therefore, the intensity and direction of the development of soil formation processes here depends primarily on the nature of the vegetation. At this stage, EPP of the second order, or particular soil-forming processes (meso- and macroprocesses), prevail. Under their influence, the specific material composition of the soil and its physical properties are formed. By the end of this stage, the process gradually slows down (comes to a certain equilibrium state), a mature soil with a characteristic profile and a set of properties is formed. The development stage can last for hundreds, thousands or more years.

The main private soil-forming processes include:

● turfy- the process of intensive humus formation and accumulation of biogenic elements. It develops under perennial herbaceous vegetation in a moderately humid climate, most intensively with a non-flush type of water regime on carbonate rocks in the steppe zone, where ordinary chernozems are formed. Typical chernozems are formed in the forest-steppe, in the taiga-forest zone on the flooded meadows of the river floodplain - soddy floodplains, outside the floodplains on carbonate rocks - soddy-calcareous, on carbonate-free - soddy-podzolic soils;

● podzolization- the process of removal from the upper soil horizons of the products of destruction of primary and secondary minerals into the underlying or ground waters with a relative accumulation of silica. In its pure form, it develops under the canopy of a coniferous forest with a poor herbaceous cover in a humid climate with a leaching type of water regime on carbonate-free rocks and causes the formation of podzolic soils;

● lessivage- a complex process associated with podzolization of the removal of silty substances without destruction in the form of suspensions from the upper horizons with their accumulation in the lower ones. Flows under deciduous forests;

● swampy- develops under the influence of marsh vegetation in conditions of constant excessive moisture with the course of the process of peat formation and gleying. In the conditions of Belarus, as a result of the bog process, bog-podzolic, peat-bog, sod and sod-podzolic boggy, alluvial boggy are formed. The process takes place under anaerobic conditions with the obligatory participation of fungi and bacteria;

● peat formation - biochemical process of transformation and conservation of organic residues with their slight humification and mineralization, leading to the formation of surface peat horizons of varying degrees of thickness;

● gleying- the process of biochemical reduction of iron and manganese compounds, accompanied by their transition to a mobile form during waterlogging of soils under anaerobic conditions with the participation of microorganisms. The soil acquires bluish, gray-gray, greenish shades and, if the color is characteristic of the entire horizon, then such a horizon is called gley, if the color is only spots - gley;

● lateritic - the process of accumulation of iron and aluminum compounds in the soil and leaching of silica in a humid and warm climate. On such soils, there is also an intensive soddy process with the formation of red soils and yellow soils in the subtropics and ferralitic soils in the humid tropics;

● solonetzic - the process of accumulation of readily soluble salts (chlorides, sulfates, etc.) in the soil profile during the effusion type of water regime under conditions of saline groundwater or saline soil-forming rocks. Salt marshes are formed, with desalinization - salt licks, with further washing - malt;

3) equilibrium stage(formed soil) occurs when, according to the main parameters (the amount of humus, the power of genetic horizons, the amount of basic nutrients, etc.), a dynamic equilibrium with the existing complex of soil formation factors is achieved, lasts indefinitely. At this stage, the biological cycle proceeds in such a way that each next cycle practically repeats the previous one. All micro-, meso- and macroprocesses are coordinated in time and space and form a complex biogeochemical cycle that promotes the renewal natural properties soil.

§4. Morphological features of soils as a reflection of the processes of their formation and development

In the process of development, the soil acquires a number of external, or morphological, features that distinguish it from the parent rock. They indicate the direction and severity of the soil-forming process. These features include: 1) the structure and thickness of the profile; 2) the nature of the transition of horizons; 3) boiling from 10% HCl; 4) granulometric composition; 5) coloring; 6) humidity; 7) structure; 8) addition; 9) neoplasms and inclusions.

The structure and thickness of the soil profile. Each soil type has a certain vertical sequence of genetic horizons, the whole set of which is called a soil profile. The formation of horizons is associated with the movement of various substances (ascending or descending current) along the soil mass and the layer-by-layer distribution of living organisms. Genetic horizons are represented by homogeneous horizontal soil layers differing in morphological characteristics, composition and properties. Each horizon has its own name and is indicated by the initial letters of the Latin alphabet. The horizon can be subdivided into sub-horizons, to designate which and reflect their specific properties, additional digital and alphabetic indices are used.

Below is a system for identifying the main types of soil horizons.

A - humic - the surface horizon of accumulation of organic matter, humus and nutrients are accumulated in it. Depending on its nature, the following stand out:

A O - forest litter, consisting of decaying forest litter (leaves, needles, branches, etc.);

A d - turf - surface horizon, strongly intertwined and held together by the roots of herbaceous vegetation;

A 1 - humus-eluvial a horizon in which, along with the accumulation of humus, destruction and partial leaching of organic and mineral substances occur;

And groin - arable- surface humus horizon, transformed by periodic tillage in agriculture.

In boggy soils, the upper horizon consists of peat - a mass of semi-decomposed plants.

T 1 - peat, not decomposed - plant residues have completely retained their original shape;

T 2 - peat medium decomposed - plant remains only partially retained their shape in the form of scraps of tissue;

T 3 - peat decomposed - continuous organic spreading mass without visible traces of plant residues;

TA - peat mineralized - arable peat horizon modified by drainage and cultivation.

A 2 - podzolic (eluvial) - horizon of intensive destruction of the mineral part of the soil and leaching of the products of destruction. It is located under the humus horizon and has a light color (gray, whitish, pale yellow); by origin may be podzolic(acid hydrolysis of minerals and removal of degradation products), solodized(alkaline hydrolysis of minerals). Under the A2 horizon (in podzolic, gray forest soils, solods), the B horizon is formed, which differs in its properties from any surface horizon.

V - illuvial horizon, into which the products of soil formation are washed in and where partially accumulate. Depending on the washed out substances, the following types of illuvial horizon are distinguished:

B h - illuvial-humus the horizon is coffee-colored due to the content of ferruginous-humic substances;

B f - glandular illuvial horizon of ocher or brown color, containing ferruginous products of destruction of the mineral part of the upper horizon;

In Ca - illuvial-carbonate horizon, often containing carbonate new formations in the form of loose accumulations of calcium carbonates.

In soils without an eluvial horizon (in chernozems, chestnut soils), in which there is no vertical movement of substances, horizon B is called transitional from humus-accumulative to parent rock.

G - gley horizon - is formed in boggy and boggy soils in conditions of constant excessive moisture. It is colored in bluish, bluish tones by the ferrous compounds of iron (II) and manganese formed here. Differs in structurelessness and low porosity.

Under conditions of temporary excessive moisture, gley can also appear in other horizons of the profile. In this case, the letter "g" is added to the base index, for example A 2 g, B g.

WITH - parent rock - horizon, poorly affected by soil-forming processes and not showing signs of the above-described soil horizons.

D - underlying rock - It stands out in the case when the soil horizons were formed on one rock, and below there is another rock that differs in lithological properties.

The transition from one horizon to another in different soils can be different: sharp, clear, noticeable or gradual. That's why nature of the transition between the soil horizons in the profile is of diagnostic value and often indicates the direction and intensity of soil formation.

Soil power Is the vertical extent of its horizons from the surface to the source rock. For different types of soils, the average thickness ranges from 40-50 to 100-150 cm. In the harsh natural conditions of the tundra, the soil-forming process can only take place in the upper part of the rocks, above the permafrost, therefore the thickness of the entire soil is insignificant (20-30 cm). In the steppes under lush herbaceous vegetation, the thickness of chernozems can reach 200 - 300 cm.

The thickness of individual horizons characterizes the genesis and agronomic value of soils. Thus, a thick humus horizon indicates a significant development of accumulation, weak leaching and, therefore, about large stocks nutrients. Poverty and low production value, for example, of podzolic soils is determined by a pronounced eluvial horizon, from which nutrients are washed out.

Field studies can reveal the presence of carbonates in the soil and the depth of their occurrence using 10% HC1. To do this, an acid solution is dripped onto the wall of the soil cut and the depth from which it begins is determined. boiling, and its intensity.

Soil color is of great diagnostic value, since it reflects its chemical and mineralogical composition, is the basis for dividing the soil layer into horizons. All the variety of soil colors can be reduced to three basic colors: black, white and red.

The black and dark color is due to the humus content: the more humus, the darker the color of the soil. At 9 - 12% humus content, the soil is black, at 4 - 6% - dark gray, dark brown or chestnut. Soils with a low humus content have a color characteristic of the parent rock. The intensity of the black color will also be affected by the type of humus; soils with the same quantitative humus content of the fulvate type will be lighter than the soils of the humate type. Some soils are black colored by dark primary minerals, sulfides, manganese hydroxides.

The white color and light tones of other colors are due to the presence of quartz, lime, alumina hydrates and salts in the soil. The red color of the soil is caused by the accumulation of iron (III) oxides. With a high content of it, the soil has a red, rusty or red-brown color, with a small amount - yellow or orange. The bluish, bluish and greenish tones of color are caused by the formation of ferrous iron compounds under anaerobic conditions with excessive moisture. Soils of this color are referred to as gley or gley soils. Inhomogeneous, mottled color is a consequence of the alternation of oxidation and reduction processes. When describing morphological characters, they usually indicate the degree of color (dark brown, light chestnut) or note a shade (whitish with a yellowish tinge). It should be borne in mind that it depends on moisture: moist soil is darker than dry. In terms of moisture, the soil can be dry(dusty) , fresh(hand cold), wet (when squeezed in the hand, moisture is felt, the paper pressed to the ground gets wet) and wet(water flows). All processes occurring in the soil and the shade of color are associated with the amount of water.

The ability of the soil to disintegrate into individual aggregates is called structure, and the aggregate of aggregates is the soil structure. Distinguish between structureless soils (mechanical elements are not connected in aggregates) and structural. Unstructured soils have many unfavorable properties: low water and air permeability, when it rains, they float, become viscous, when they dry, they quickly lose moisture, merge into one mass that is difficult to cultivate. Structural in the agronomic concept is the soil, which is dominated (not less than 55%) by aggregates of medium size (0.25 - 10 mm), characterized by properties opposite to the structureless soil.

According to the shape of the aggregates, three types of structure are distinguished:

1) cuboid- the aggregates are equally developed along all three axes and resemble a cube; they are divided into nut-like, lumpy, granular, lumpy;

2) prismatic- the aggregates are developed along the vertical axis and resemble a prism, subdivided into pillar and prismatic;

3) plate-like- the aggregates are developed along the horizontal axis, sometimes platy and scaly.

A cuboid structure is more valuable agronomically, as it creates the most valuable water-air regime. One of the main conditions for the formation of a structural soil is the presence in it of a sufficient amount of silty and colloidal particles and humus. The former are "glue", the latter impart water resistance to soil aggregates.

Each type of soil and even each soil horizon has its own structure. For acidic soils, a platy structure is inherent, for alkaline soils it is prismatic, for neutral and close to neutral soils, it is cuboid.

Addition - these are external signs of the nature of porosity and the degree of soil density. It depends on the properties of the parent rock, particle size distribution, soil structure, as well as the activity of the soil fauna and plant roots. According to the degree of density, a very dense, dense, loose and crumbly constitution is distinguished.

Loose addition is characteristic of sandy soils devoid of humus. Under mechanical stress, even small, they are characterized by flowability, i.e. break up into separate elements.

Loose the composition is inherent in loamy and clayey soils with a well-defined structure, as well as in the upper horizons of sandy and sandy loamy soils enriched with humus. The arable horizons have such a constitution after processing them in a ripe state. The shovel easily enters such soil.

Dense the addition is characteristic of the illuvial horizons of most loamy and clayey soils. When digging with a shovel, considerable effort is required.

Very dense or merged, addition is characteristic of cohesive clayey structureless soils, as well as illuvial horizons of some solonetz soils. It is impossible to dig such soils with a shovel; you have to use a crowbar or a pickaxe.

The composition of the soil is an important agronomic characteristic that determines the duty cycle and, therefore, aeration, water permeability, as well as soil resistance during cultivation.

Neoplasms – These are accumulations of substances that differ from the enclosing soil material in composition and composition. They are formed as a result of physical, chemical and biological soil-forming processes. TO chemical neoplasms include readily soluble salts, gypsum, carbonic lime, iron compounds, silica and other substances.

Easily soluble salts typical for saline soils. They are found in the form of white crusts on the soil surface or in the form of deposits, veins, grains in the thickness of the profile. Gypsum occurs in chestnut, brown, saline soils and gray soils in the form of white, gray and yellowish veins, accumulations of crystals on the soil surface. Neoplasms CaCO 3 white are found in the form of sharply outlined white spots, in the form of mold, dense accumulations of lime of various shapes. They are determined by boiling with 10% hydrochloric acid solution.

Iron hydroxides found in podzolic, sod-podzolic and waterlogged soils in the form of dark brown rounded solid nodules, blurry spots. Sandy soils are characterized by ortsands - brown cemented layers of iron hydroxide. Iron compounds of a bluish, bluish or greenish color are characteristic of gley and gley soils.

Silica forms a white powder on the surface of structural units of gray forest soils, podzolized chernozems and solonetzes

To neoplasms biological origin include: coprolites - excrement of worms and larvae in the form of glued water-resistant lumps; molehills - moles, ground squirrels, marmots, hamsters, covered with soil; roots - traces of rotten large roots; wormoins - moves of worms; dendrites - dark imprints of small roots in the form of a pattern.

Each soil has its own specific set of neoplasms with their specific position in the profile

Inclusions - these are various objects (fragments of stones, boulders, pieces of brick, glass, shells, animal bones, etc.) that are not genetically related to the soil-forming process.

The role of microorganisms in soil formation and soil fertility is extremely complex and varied; Microbes, being the oldest organisms on the globe, existing for billions of years, are the most ancient soil-formers, acting long before the appearance of higher plants and animals. The consequences of the vital activity of microorganisms go far beyond the soils inhabited by them and largely determine the properties of sedimentary rocks, the composition of the atmosphere and natural waters, the geochemical history of elements such as carbon, nitrogen, sulfur, phosphorus, oxygen, hydrogen, calcium, potassium, and iron.
Microorganisms are polyfunctional in biochemical terms and are capable of carrying out processes in the biosphere and soils that are inaccessible to plants and animals, but which are essential part biological circulation of energy and substances. These are the processes of nitrogen fixation, oxidation of ammonia and hydrogen sulfide, reduction of sulfate and nitric acid salts, precipitation of iron and manganese compounds from solution. This also includes the microbial synthesis in the soil of many vitamins, enzymes, amino acids and other physiologically active compounds.
By carrying out these amazing reactions, autotrophic bacteria, like plants, can synthesize organic matter themselves, but without using the energy of the sun. That is why there is every reason to believe that the primary soil-forming process on Earth was carried out by communities of autotrophic and heterotrophic microorganisms long before the appearance of green plants. It should be noted that bacteria and fungi are very strong destroyers of primary minerals and burnt rocks, agents of the so-called biological weathering.
However, the main feature of microorganisms is their ability to bring the processes of decomposition of plant and animal organic matter to complete mineralization. Without this link, the normal spiral cyclicity of biological processes in the biosphere could not exist and life itself would not be possible. This is a deep fundamental difference between the role of microorganisms in the biosphere and the role of plants and animals. Plants synthesize organic matter, animals perform the primary mechanical and biochemical destruction of organic matter and prepare it for future humus formation. Microorganisms, completing the decomposition of organic matter, synthesize soil humus, and then destroy it. Synthesis of physiologically active compounds, humus formation and complete mineralization of organic residues - main function microorganisms in soil processes and biological circulation.
Microorganisms are sometimes found at depths of tens and hundreds of meters. But their main mass is concentrated in the root-inhabited soil horizons and especially in the upper 10-20 cm. The total weight of the wet mass of various microorganisms can be up to 10 t / ha in the upper 25-cm soil layer. Macca microorganisms account for 0.5-2.5% of the weight of humus in soils. At the same time, per 1 g of soil, the number of microorganisms is tens and hundreds of millions of specimens, and in the rhizosphere of plants - tens of billions. The higher the level of fertility of natural soils, the richer and more diverse microorganisms are represented in them. Highly fertile cultivated soils are the richest in a variety of microorganisms. With the development of new methods of studying microorganisms, it turns out that our modern knowledge is still extremely insufficient. Apparently, the role, number and function of microorganisms in soil formation is much greater than we now imagine.
Among the soil microorganisms are both representatives of the plant world and representatives of the animal world (Fig. 52). The microflora contains the most numerous fungi, actinomycetes and bacteria. Algae are much less common. The microfauna is dominated by amoebas and flagellates. Ciliates and micronematodes in soils are also sometimes found in large numbers. More and more data are accumulating on the presence of non-cellular forms of microorganisms (bacteriophages, viruses) in soils.

Soil algae

Soil mushrooms

Bacteria

Viruses (bacteriophage)

The leading role in soil formation and the formation of soil fertility belongs to three

groups of living organisms - terrestrial plants, microorganisms and soil animals. Each of these groups

organisms fulfills its role, but only with their joint activity does the parent rock turn into soil. The dominant position in soil formation belongs to green plants, which extract ash elements and nitrogen from the rock, synthesize organic matter in the process of photosynthesis, which, together with ash elements, enters the soil through litter. Role different types vegetation is significantly different, and this is the main reason for the diversity of soils in nature. Microorganisms (bacteria, fungi, algae and lichens) are the first to settle on the rock, actively participating in its biological weathering. They play the main role in the processes of decomposition of plant residues of green plants and their mineralization to simple salts available to plants. They participate in the processes of humification and mineralization of humus, in the destruction and formation of soil minerals, affect the composition of soil air, regulating the ratio between O 2 and CO 2 in it.

The number, species composition and activity of microorganisms depend on soil fertility and hydrothermal conditions. The most common bacteria in the soil, the number of which can reach 3 billion pieces. in 1 g of soil. Soil animals are also involved in the formation of soil, represented by nematodes, insects, earthworms, ants, moles, rodents, etc. All of them use organic residues in the form of food, promote its decomposition, accelerate the humification of plant residues, improve the physical properties of the soil. Invertebrates (nematodes, insects, worms, etc.) predominate among the soil fauna. A special role is played by earthworms, which pass through themselves up to 600 tons of fine earth per year. It has been established that many soils are 50, sometimes 89% composed of dilapidated aggregates created by worms.

Soil-forming process- the process of soil formation, the essence of which is the interaction of organisms and products of their decay with rocks and products of their weathering.

Thus, the soil-forming process occurs at the contact of the lithosphere and biosphere as a result of their interpenetration. Along with the lithosphere and biosphere, the atmosphere and hydrosphere are the source of substances involved in the soil-forming process. The main source of energy of the soil-forming process is solar energy, both direct and condensed in the remains of organisms, water seeping through the soil, etc. The soil-forming process is very complex, it includes a variety of chemical, physical and biological phenomena occurring simultaneously and in different directions ... These phenomena can be grouped into 3 groups - decomposition, synthesis and movement... In the soil, there is a decay of plant and animal organisms, various minerals and fragments of rocks; it synthesizes special forms of organic matter (humus) and various secondary minerals (mainly clay minerals, mineral oxides and simple salts); the products of decomposition and synthesis in the form of true and colloidal solutions, as well as suspensions, move down the profile, and with a close occurrence of soil-groundwater and upward with their capillary and film currents. The indicated main groups of processes, in turn, are diverse.