Soil formation and fertility mainly depend on vegetation, microorganisms and soil fauna.

Dying roots are the main source of organic matter entering the soil, from which humus is formed, coloring the soil dark to the depth of mass distribution of root systems in it. By extracting nutrients from a depth of several meters and dying, plants, together with organic matter, accumulate elements of nitrogen and mineral nutrition in the upper horizons of the soil. At the same time, herbaceous plants extract more minerals from the soil than woody plants.

Each plant formation corresponds to a complex of microorganisms of different species composition, changing with changes in soil formation. There is a close connection between the soil-forming process and soil organisms.

The roots of plants, like a muff, are covered with a living layer of microbial cells - bacteria and fungi, beneficial and harmful. By selecting appropriate plants in crop rotation, it is possible to combat unwanted soil microorganisms.

Dying green vegetation is decomposed by bacteria and fungi. Microorganisms energetically change not only the organic, but also the mineral part of the soil. Their life activity depends on a set of soil conditions that can either promote or retard the development of microbes.

The number of microorganisms in the soil reaches enormous values. In 1 g of virgin soil there are 0.5 - 2, in cultivated soils - 2 - 3 or more billion microbes. Their dry weight reaches 0.1-0.3 t/ha or more.

Most microorganisms are found in the surface soil horizons (10 cm). Downwards their number decreases; at a depth of several meters the soil is relatively sterile.

The most favorable temperature for microbiological processes is from 20 to 40 o. There are more microorganisms in well-treated cultivated soil than in untreated soil; there are more of them in fresh neutral and calcareous soils and less in saline soils.

Worms and larvae mix the soil, bringing the soil up from the deep layers and enriching it with organic matter. The soil mass that passes through the intestines of earthworms is enriched with nitrogen and calcium and acquires a greater absorption capacity. Consequently, earthworms improve the chemical and physical properties of the soil, increasing its porosity, aeration and moisture holding capacity. There are no earthworms in highly acidic and alkaline, swampy or very dry soils.

Finally, the soil is inhabited by vertebrate animals, mainly rodents (gophers, boars, marmots, hamsters, ferrets, mice, mole rats, moles), forming in places numerous burrows. Filled burrows of shrews, which look like oval spots of different diameters on the soil section, are known as hollows. Over-digging of the soil often negatively affects its properties, increasing carbonate content and water permeability to a very large loss of water due to filtration. Deep tillage and surface leveling reduce the harmful effects of earthmovers.

Significant factors In soil formation are animal and plant organisms - special components of the soil. Their role consists of enormous geochemical work. Organic compounds soils are formed as a result of the vital activity of plants, animals and microorganisms. In the “soil-plant” system, there is a constant biological cycle of substances, in which plants play an active role. The beginning of soil formation is always associated with the settlement of organisms on the mineral substrate. Representatives of all four kingdoms of living nature live in the soil - plants, animals, fungi, prokaryotes (microorganisms - bacteria, actinomycetes and blue-green algae). Microorganisms are prepared biogenic fine earth- a substrate for the settlement of higher plants - the main producers of organic matter.

The main role here belongs to vegetation. Green plants are practically the only creators primary organic substances. Absorbing carbon dioxide from the atmosphere, water and minerals from the soil, and using the energy of sunlight, they create complex organic compounds rich in energy.

The phytomass of higher plants strongly depends on the type of vegetation and the specific conditions of its formation. The biomass and annual productivity of woody vegetation increase as one moves from high latitudes to lower ones, while the biomass and productivity of herbaceous vegetation of meadows and steppes noticeably decreases, starting from the forest-steppe and further to dry steppes and semi-deserts.

The same amount of energy is concentrated in the humus layer of the Earth as in the entire land biomass, and the energy assimilated in plants due to photosynthesis is accumulated. One of the most productive components of biomass is litter. In a coniferous forest, litter decomposes very slowly due to the specificity of its chemical composition. Forest litter together with coarse humus forms a type of litter pestilence, which is mineralized mainly by fungi. Mineralization process annual shedding mainly occurs during the annual cycle. In mixed and deciduous forests, the litter of herbaceous vegetation takes a greater part in humus formation. The bases released during the mineralization of litter neutralize the acidic products of soil formation; humate-fulvate humus of the type more saturated with calcium is synthesized moder. Gray forest or brown forest soils are formed with a less acidic reaction than podzolic soils and a higher level of fertility.

Under the canopy of grassy steppe or meadow vegetation, the main source of humus formation is mass of dying roots. The hydrothermal conditions of the steppe zone contribute to the rapid decomposition of organic residues.

Forest communities provide the greatest amount of organic matter, especially in the humid tropics. Less organic matter is created in tundra, desert, swampy areas, etc. Vegetation influences structure and character soil organic matter, soil moisture. The degree and nature of the influence of vegetation as a soil-forming factor depends on:

• plant species composition,
• the density of their standing,
• chemistry and many other factors

Main function of animal organisms in soil - transformation of organic matter. Both soil and terrestrial animals take part in soil formation. In the soil environment, animals are represented mainly by invertebrates and protozoa. Vertebrates (for example, moles, etc.) that constantly live in the soil are also of some importance. Soil animals are divided into two groups:

• biophages that feed on living organisms or tissues of animal organisms,
• saprophages that use organic matter for food.

The bulk of soil animals are saprophages (nematodes, earthworms, etc.). There are more than 1 million protozoa per 1 hectare of soil, and dozens of worms, nematodes and other saprophages per 1 m2. A huge mass of saprophages, eating dead plant remains, throws excrement into the soil. According to the calculations of Charles Darwin, the soil mass completely passes through the digestive tract of worms within several years. Saprophages influence the formation of the soil profile, humus content, and soil structure.

The most numerous representatives of the terrestrial animal world involved in soil formation are small rodents(voles, etc.).

Plant and animal residues entering the soil undergo complex changes. A certain part of them disintegrates into carbon dioxide, water and simple salts (mineralization process), others pass into new complex organic substances of the soil itself.

Microorganisms(bacteria, actinomycetes, fungi, algae, protozoa). In the surface horizon, the total mass of microorganisms is several tons per 1 hectare, and soil microorganisms constitute from 0.01 to 0.1% of the total land biomass. Microorganisms prefer to settle on nutrient-enriched animal excrement. They participate in humus formation and decompose organic matter into simple end products:

• gases (carbon dioxide, ammonia, etc.),
• water,
• simple mineral compounds.

The main mass of microorganisms is concentrated in the upper 20 cm of soil. Microorganisms (for example, nodule bacteria of leguminous plants) fix nitrogen 2/3 from the air, accumulating it in soils and maintaining nitrogen nutrition of plants without the application of mineral fertilizers. The role of biological factors in soil formation is most clearly manifested in the formation of humus.

Microorganisms and their role in soil formation. General informationDenia. Soil formation is a biological process, and a variety of groups of living organisms are directly involved in its development. Among them, microorganisms that are widely distributed in nature are of great importance. They are found in the soil, air, on high mountains, on bare rocks, in deserts, in the depths of the Arctic Ocean, etc.

Microbes are especially widespread in the soil, which is the only natural environment where all the necessary conditions exist for their normal development.

Good soil always contains a sufficient amount of organic and mineral substances, often has the necessary moisture and reaction of the soil solution, is sufficiently supplied with oxygen and protects microorganisms from the harmful effects of direct sunlight.

The development of microorganisms in the soil is closely related to organic matter. The richer the soil is in plant residues, the more microbes it contains (Table 4).

IN 1 G soddy-podzolic soils contain about 500 million bacteria, 1 G chestnut-1 -1.5 billion; in chernozems, characterized by a high content of organic matter, the number of microorganisms reaches 2-3 billion per 1 G soil, and in well-cultivated chernozems there are much more microorganisms.

Despite the negligible size of microbes, their total weight in soils reaches a significant value. So, if we take the average cell sizes to be 1X2 microns and their number in 1 g of soil is 5 billion, then in a 25-centimeter layer 1 ha soil, the live weight of microbes will be about 1-3 tons.

Cultivated soils that are well cultivated and fertilized with manure are especially rich in microorganisms.

This entire mass of microbes in the soil layer is distributed unevenly. Surface horizons are the richest in microorganisms to a depth of 25-35 cm; As you go deeper, the number of microbes becomes less and less, and at a considerable depth they are found in negligible quantities. The root system of plants has a great influence on the distribution of microflora in the soil environment. Roots constantly release various types of organic compounds into the external environment, which serve as a good source of nutrition for microorganisms; in the root zone of plants there are usually favorable conditions for microorganisms. This zone is called the rhizosphere. In the rhizosphere, as many studies show, the number of microbes is tens and hundreds, and sometimes thousands of times greater than outside the root zone. Microbes cover the root system of plants with an almost continuous layer.

Abundant microflora in the rhizosphere, as well as throughout the entire soil layer, plays an important role in the development of soil fertility. Microorganisms can develop intensively only under certain temperature conditions, with appropriate humidity and environmental reaction.

Temperature is of great importance for their life.

Experiments show that the minimum temperature at which the vital activity of most soil microbes is still possible is approximately + 3°. Below this temperature their development usually stops. Maximum temperature is about +45°. As for the optimal temperature, it is most often within the range of +20-35°.

The influence of temperature on the vital activity of microorganisms is closely related to humidity. Moisture is as much a necessary factor for the development of microbes as heat. If the temperature of the decomposing mass is quite favorable, but the humidity is insufficient or excessive, then decomposition will be difficult.

Likewise, decomposition will be difficult if moisture conditions are optimal but temperature conditions are unfavorable. Decomposition processes usually reach their greatest intensity when soil moisture is about 60% of total moisture capacity. In accordance with this, the decomposition of plant residues in nature occurs unevenly throughout the year.

The most vigorous decomposition occurs most often in the first half of summer, when thermal conditions and humidity are in the most favorable combination. During the hot summer months, when the soil dries out greatly, the activity of microorganisms decreases and the decomposition process is minimized. Decomposition also slows down as the heat decreases in the autumn, and with the onset of frost this process stops completely.

As for the reaction of the environment, different groups of microorganisms have different requirements in this regard. Thus, all bacteria can develop only in a neutral, slightly acidic or slightly alkaline environment. The acid reaction has a depressing effect on bacteria. The strongest obstacle to the life of bacteria is also the tannins contained in woody vegetation.

Mushrooms, on the contrary, freely tolerate a clearly expressed acid reaction. Unlike bacteria, fungi develop well on plant residues containing tannins.

The vital activity of microorganisms is associated with the decomposition of dead plants and animals and their transformation into humus, or humus, the processes of mineralization of organic matter, the fixation of atmospheric nitrogen, the processes of ammonification, nitrification, denitrification and the processes of synthesis of complex organic compounds.

Microorganisms are of great importance in the destruction and synthesis of minerals, as well as in regulating redox conditions in the soil.

The huge microscopic population of the soil includes bacteria, actinomycetes, fungi, algae, protozoa (protozoa) and various ultramicroscopic creatures - phages, bacteriophages and actinophages.

Bacteria. Bacteria constitute the most abundant and diverse group of soil microflora; these are microscopic single-celled organisms that have a cell membrane, are rich in nucleoproteins and lack chlorophyll and plastids. Bacteria do not have a cell nucleus and reproduce by simple division. Bacteria are very small in size, usually not exceeding a few microns. They have different shapes - round, rod-shaped and curved.

Based on the type of nutrition, bacteria are divided into two groups - autotrophic and heterotrophic.

In relation to air, bacteria are divided into aerobic and anaerobic. Aerobic bacteria can develop only in conditions of free access of air, anaerobic bacteria do not require molecular oxygen for respiration. Among anaerobes there are conditional, facultative bacteria, which can develop both without oxygen and in its presence, and unconditional, obligate microbes, which can live and multiply only in the absence of free access to air.

Autotrophic bacteria use only carbon from carbon dioxide for nutrition and do not require complex organic substances. To convert carbon dioxide into organic compounds in their bodies, they use either solar energy (photosynthesis) or chemical energy from the oxidation of a number of mineral substances (chemosynthesis).

The category of bacteria with the ability to photosynthesize includes only colored, green and purple sulfur bacteria. The nutrition of microbes through chemosynthesis is much more widely developed in nature. The most common chemotrophic bacteria in soil are nitrifying, iron, thionic and hydrogen bacteria.

Nitrifying bacteria, which are associated with the nitrification process, are of great importance in soil formation.

The process of nitrification, i.e. the process of converting ammonia into salts of nitric acid, occurs under the influence of two types of bacteria. One of them (Nitrosomonas, Nitrocystus, Nitrosospira) oxidize ammonia to nitrous acid: 2N.H.+3 O 2 =2 HNO 2 +2 H 2 O + 158 kcal Other bacteria (Nitrobacter) continue the oxidation reaction, resulting in the formation of nitric acid: 2HNO 2 + O 2 = 2 HNO 3 + 48 kcal

Nitric acid, meeting in the soil with various bases, immediately gives a number of nitrate salts: NaNO 3 , KNO 3 And Ca( NO 3 ) 2 . Salts of nitric acid are the most convenient form of nitrogen nutrition for plants, therefore the nitrification process is of great production importance.

It should be noted that nitrification in soils occurs with the joint, rather than sequential, activity of the nitrifying microbes noted above, which is why it is not possible to detect a significant content of nitrous acid salts in the soils.

The nitrification process develops best in well-aerated soils with a neutral or alkaline reaction (pH from 6.2 to 9) in the presence of a significant amount of humus and sufficient moisture content. Anaerobic conditions and acidic environments are detrimental| for nitrifying bacteria.

Rational mechanical tillage, liming of acidic soils, and application of fertilizers are the most important measures that can help create the most favorable conditions for nitrification. Nitrification is an oxidative process, so aeration is a necessary condition for the intensive formation of nitrogen salts in the soil.

Sulfur bacteria, which include Thiobacillus thiooxydans, Thiobacillus thioparusetc., cause the process of sulfofification, i.e. the oxidation of hydrogen sulfide to sulfuric acid. The sulfofification process is carried out in two stages - the oxidation of hydrogen sulfide to sulfur and the oxidation of sulfur to sulfuric acid:

The sulfuric acid formed in this process, meeting in the soil with various bases, turns into salts of sulfuric acid, from which plants take sulfur for nutrition.

All sulfur bacteria are aerobes, therefore conditions that favor the nitrification process also promote the sulfofification process. The looser the soil and the more favorable the gas exchange conditions in it, the more vigorously the transformation occurs. H 2 Sinto sulfuric acid. In soils that are poorly aerated, compacted, and deprived of air flow, the sulfofification process gives way to the so-called desulfofication process, in which sulfuric acid salts are reduced back to H 2 S.

Iron bacteria are represented in soils mainly by filamentous (Crenothrix, Leptothrix) and unicellular (Gallionella, Siderocapsa) bacteria. The vital activity of iron bacteria is associated with the process of oxidation of ferrous salts into oxide salts:

Some iron bacteria are also capable of oxidizing manganese salts, thereby forming ferromanganese nodules in the soil.

Heterotrophic bacteria absorb carbon from organic compounds, so they can only develop in the presence of organic matter. They are represented in soils by various physiological groups, which together carry out the process of destruction of all organic compounds to the stage of their complete mineralization. The processes of ammonification, butyric acid fermentation, fermentation of pectin substances, cellulose, protein decomposition, denitrification and desulfification are associated with the vital activity of heterotrophic bacteria.

Nitrogen-fixing bacteria, which play a huge role in the nitrogen cycle in nature, also belong to this category of microorganisms. In relation to air oxygen, heterotrophs are divided into aerobic and anaerobic bacteria.

Ammonification, i.e. the process of decomposition of organic nitrogenous substances with the formation of ammonia, is caused by the vital activity of very diverse groups of microorganisms. Ammonia is released during the decomposition of proteins, peptones, amino acids, urea, uric and hypuric acids.

Typical representatives of ammonifying bacteria are Bact. vulgare, Bact. putidum, Bact. subtilis, Bact. mesentericus And Bact. mycoides.

The first stage of protein breakdown is hydrolysis to form free amino acids; Some of them are used by microbes to build the body, the other part can undergo further decomposition with the release of nitrogen in the form of ammonia.

Chemically this process can be expressed by the following scheme:

The process of protein ammonification can occur under both aerobic and anaerobic conditions. The hydrolytic breakdown of urea occurs predominantly under aerobic conditions under the influence of mainly the following bacteria: Micrococcus ureae, Saroina ureae, Urobacterium pasteurii, Urobacillus miqueliiand etc.

Schematically, the process of ammonia fermentation of urea can be represented as follows:

The resulting ammonium carbonate, as a chemically fragile substance, then easily breaks down into carbon dioxide, water and ammonia:

Meeting various acids in soil conditions, ammonia reacts with them and forms ammonium salts. For example, when ammonia reacts with sulfuric acid, ammonium sulfate can be formed:

Nitrogen in the form of ammonia compounds is quite available for plant nutrition. Since the process of ammonification is carried out by aerobic and anaerobic microorganisms, the formation of ammonia nitrogen can occur in soils that are well aerated and in compacted soils with difficult gas exchange.

It should be noted that the accumulation of ammonia in the soil and the further process of its oxidation or nitrification occur when the C to N ratio in the decomposing material is less than 20:1; when the C to N ratio is greater than 20:1, all the ammonia formed is intercepted by microorganisms that decompose nitrogen-free organic substances and is used by them to build their plasma protein. The presence in the soil of a large amount of undecomposed organic matter rich in carbohydrates (for example, straw) inhibits the accumulation of ammonia in the soil (L.N. Aleksandrova).

The breakdown of carbohydrates occurs under the influence of butyric acid bacteria Clostridium pasteurianum, Clostridium butricumand etc.

Butyric acid fermentation is accompanied by the formation of butyric acid, carbon dioxide and hydrogen:

Cellulose fermentation is caused by the activity of specific cellulose-decomposing bacteria, typical representatives of which are Cytophaga hutchinsonii, You. omelianskii and etc.

The biochemical process of cellulose or fiber breakdown occurs under both aerobic and anaerobic conditions.

Fermentation of pectin substances, which are intercellular substances of plant tissues, occurs under aerobic and anaerobic conditions under the influence of pectin-decomposing bacteria Clostridium pectinovorumand etc.

Hydrolytic breakdown of fats occurs under the influence of microorganisms possessing the enzyme lipase. The most energetic fat destroyers are Pseudomonas. fluorescens And Bact. pyocyaneum.

Very common microorganisms in the soil are denitrifying bacteria, which cause the process of denitrification - the reduction of nitrates to free nitrogen.

The most energetic denitrifiers are predominantly non-spore-bearing bacteriaPseudomonas fluorescens, Bact. stutzeri, Bact. denitrificans and etc.

Denitrifying bacteria belong to facultative anaerobes, which, although they can develop in the presence of atmospheric oxygen, develop more intensively when access to air is difficult or even in its complete absence. Without receiving air oxygen or receiving it in limited quantities, these bacteria take it away from nitrates and nitrites and oxidize nitrogen-free organic substances with it. Part of the nitrogen released in this case is irretrievably evaporated into the atmosphere, while the other part goes to build the plasma of denitrifiers.

For agriculture, denitrification is in most cases harmful, since it is associated with the loss of nitrogen, the most important nutrient element for plants. However, this process can develop intensively only in soils with poor air permeability, compacted and waterlogged soils. In cultivated and well-cultivated soils, the vital activity of denitrifying bacteria is greatly inhibited and their negative role does not appear.

Bacteria that assimilate atmospheric nitrogen. The process of fixation, or binding, of atmospheric nitrogen is of great importance in the accumulation of nitrogen compounds in soils.

The essence of this process lies in the fact that a certain group of bacteria, the so-called nitrogen fixers, binds free nitrogen from the atmosphere and, turning it into complex compounds in their body, thereby enriches the soil layer with it. Thus, along with the processes of decomposition of complex organic nitrogen substances in the soil, processes of creation, or synthesis, of nitrogenous compounds occur at the expense of free atmospheric nitrogen.

Note that the reserves of nitrogen in the atmosphere are practically inexhaustible. Above every square meter of the earth's surface hangs a column of gaseous nitrogen weighing 8 tons. Meanwhile, atmospheric nitrogen is completely inaccessible directly to higher plants; it can be used only after its preliminary binding by special nitrogen-fixing microorganisms.

There are two groups of nitrogen-fixing microbes in soil. Some of them, the so-called nodule bacteria (Bacterium radicicola), are able to develop only on the roots of various legumes, while others live freely in the soil environment.

Of the free-living microbes, some are aerobic (Azotobacter chroococcum), others - anaerobic organisms (Clostridium pasteurianum).

The most important in agriculture are nodule bacteria and free-living ones - Azotobacter, as for bacteria of another type - Clostridium pasteurianum, then they, being anaerobic, are usually suppressed in cultivated, well-cultivated soils, as a result of which their role in the accumulation of nitrogen in the soil is relatively insignificant.

Nodule bacteria, capable of living only in symbiosis with leguminous plants, are represented in soils by several species. Each type of nodule bacteria can develop only on one specific species or on several types of leguminous plants. Under favorable conditions, as observations show, the amount of nitrogen bound by nodule bacteria can reach 100 and even 120 kg per hectare during one growing season.

As for free living bacteria (Azotobacter), then the most necessary condition for their existence is the presence of humus substances in the soil as a source of carbon compounds from which these organisms draw the energy they need.

The total amount of nitrogen that can be accumulated in the soil by Azotobacter during the summer reaches an average of 30-35 kg per hectare. These figures speak very eloquently about the enormous role played by nitrogen-fixing bacteria in soil fertility. Nitrogen accumulated in the bodies of microorganisms undergoes the same transformations in the soil as nitrogen in other organic compounds. After the death of nitrogen-fixing bacteria, their bodies decompose under the influence of ammonification and nitrification processes and the nitrogen contained in them passes into ammonium and then into nitrate compounds, which serve as food for plants.

Mushrooms. Along with bacteria, fungi, which are heterotrophic saprophytic organisms that feed on ready-made organic matter, take a large part in soil-forming processes.

Fungal microflora in soils is very diverse and is represented by a large number of species. The most common of these are molds, which reproduce either by the formation of conidia from conidiophores, or sporangia, on special thickened cells. Representatives of the genera belong to the group of mold fungi Penicillium, Trichoderma, Aspergillus, Cladosporium, Rhizopus.

Algae fungi are also widespread in soils (Phycomycetes), marsupial mushrooms (Ascomycetes), including yeast fungi (Saccharomycetes), and then higher (Basidio– mycetes) and imperfect fungi (Fungi imperfecti).

Many types of fungi are capable of forming mycorrhiza on the roots of green plants, causing a special mycotrophic type of plant root nutrition.

Mycorrhiza usually refers to the coexistence of many plants with special soil fungi, called mycorrhizal fungi. There are ectotrophic, or external, mycorrhiza and endotrophic, or internal, mycorrhiza; hyphae of the ectotrophic mycorrhiza fungus spread mainly on the surface of the root, forming a kind of special cover around it; hyphae of the endotrophic mycorrhiza fungus penetrate into the root, spreading in its tissues.

In this symbiosis, mycorrhizal fungi use carbohydrates, in particular sugar, as well as some hydroxy acids and amino acids coming from the leaves to the roots of plants, and at the same time supply green plants with nitrogen, since fungi are able to absorb nutrients, including nitrogen, directly from organic compounds of soil humus, forest litter and semi-decomposed peat residues.

Mycorrhizal fungi are the most widespread among woody plants, and each plant species is characterized by a specific type of fungus. Yes, mushroom Boletus elegausgives mycorrhiza in larch and is found only where this tree grows; Boletus luteussettles on pine roots, etc.

All fungal microflora have a fairly high oxygen demand, so the surface layers of the soil are richest in fungi. Most mushrooms develop at temperatures from 5 to 40°, with an optimum of about 25-30°. An essential feature of mushrooms is that they develop well in both neutral and acidic environments, therefore the decomposition of woody residues in the forest, which are characterized by an acidic reaction, occurs mainly under the influence of fungal microflora.

The vital activity of fungal microflora in the soil is associated with various processes of decomposition of fiber, fats, lignin, proteins and other organic compounds. Fungi from the genera take the greatest part in the decomposition of fiber Trichoderma, Aspergillus, Fusariumand others; of fungi that decompose pectin can be called Mucor stolonifer, Aspergillus niger, Cladosporiumand others; many molds (Oidium lactis, different types Aspergillus And Penicillium) energetically decompose fats,

Open-chain hydrocarbons, as well as aromatic hydrocarbons, are oxidized to CO 2 and H 2 O under the influence of a number of fungi; Many molds and imperfect fungi cause ammonification of proteins. Fungi play a particularly important role in the formation and decomposition of humus substances, which make up the most essential part of the soil.

Actinomycetes. Actinomycetes, or radiant fungi, are widespread in soils (Actynomycetes), which are a transitional form between bacteria and fungi (Table 5).

A characteristic feature of actinomycetes is a unicellular branched mycelium, which has two parts: one of them is immersed in a nutrient substrate, and the other rises up in the form of aerial mycelium, on which spores are formed. Actinomycete colonies are often pigmented and colored pink, red, greenish, brown and black.

All actinomycetes are typical aerobes and develop best at a temperature of 30-35°. Among them, antagonists that inhibit the development of bacteria by releasing antibiotics are widespread.

The role of actinomycetes in soil-forming processes is very significant. They take an active part in the decomposition of nitrogen-free and nitrogenous organic substances, including the most persistent compounds that make up soil humus, or humus.

Seaweed. Algae occupy a significant place among soil microflora. The most common algae found in soil are flagellated algae (Flagellatae), green algae (Chlorophyseae), blue-green (Cyanophyceae) and diatoms (Diatomae). On the soil surface, as well as in the arable layer to a depth of 30 cm the number of algae cells can reach 100 thousand per 1 G soil.

Algae actively participate in the weathering processes of rocks and minerals, such as kaolinite, decomposing it into free oxides of silicon and aluminum.

Being chlorophyll-containing organisms, they are capable of photosynthesis and during their development enrich the soil layer with some amount of organic matter.

Blue-green algae (Nostoc, Phormidium) are capable of assimilating nitrogen gas. In this regard, they are of interest to agriculture. At the same time, the abundant development of algae enriches the soil with carbohydrates and stimulates the development of nitrogen-fixing bacteria such as Azotobacter.

Lichens. Along with bacteria, fungi and algae, lichens, which are complex symbiotic organisms consisting of fungi and algae, take a significant part in soil-forming processes.

Lichens are able to grow directly on rocks and rocks, so they are usually the pioneers of plant life on exposed rock surfaces. The most common of them are crustose or crustose lichens, followed by foliose and fruticose lichens. Most lichens have the ability to penetrate into rocks using fungal hyphae and cause active destruction of all rocks exposed to the surface. They belong to Rhizocarpon geographicum, different kinds Lecarona, Aspicilia, Halmatommaetc. Lichens of the genera are widespread Cladonia, Alectoriaand others in the tundra, forest zone and high mountain areas.

Developing on igneous, especially silica-rich rocks, lichens form on their surface very characteristic, variegated covers of red, yellow, black, gray, brown and other colors.

Lichens emit carbon dioxide and specific lichen acids, which cause the destruction of minerals; many lichens produce antibiotics that inhibit the development of bacteria.

As a result of the vital activity of lichens, a thin layer of primitive soil is formed on the surface of rocks, in which a certain amount of humus accumulates, as well as phosphorus, potassium, sulfur and other elements. Rock mosses, and later some higher green plants, settle on this primitive soil.

Protozoa ( Protozoa). Representatives of the simplest animal organisms, which have received the common name Protozoa. These include rhizomes

( Rhizopoda), flagellates (Flagellatata) and ciliated or ciliates (Ciliata). Most protozoa are aerobes, and only a few are anaerobes.

The most favorable temperature conditions for their development lie in the range of 18-22°, the best reaction is neutral, however, good development of protozoa is also observed with an acidic reaction. In terms of their feeding method, protozoa are mostly heterotrophs; They feed primarily on other organisms - bacteria, algae, as well as fungal embryos and other microorganisms.

Among the protozoa there are saprophytic organisms, in particular flagellates and some ciliates that feed on soluble organic substances. Among flagellates there are autotrophic protozoa. Some representatives of protozoa live in symbiosis with green algae. Protozoa are distributed mainly in the surface 15-centimeter layer of soil. IN 1 G There are up to 1.5 million of them in the soil. The richer the soil is in organic matter, the more protozoa it contains, especially amoebas.

In the process of life activity, protozoa transform complex organic compounds into simpler ones and thereby contribute to an increase in the supply of substances in the soil that are more accessible to higher plants. Often more soluble nitrogen compounds are found in soils rich in amoebae than in similar soils less populated by amoebae.

Animals and their role in soil formation. IN lives in the soil a large number of invertebrate and vertebrate animals that take a constant and active part in soil-forming processes.

Of significant importance in this regard are, first of all, representatives of invertebrates - the larvae of various insects, ants, and especially earthworms, which, crushing organic residues and passing them along with mineral particles of the soil through the digestive apparatus, often produce very profound changes in the chemical and physical properties soil

The importance of various kinds of animals inhabiting the soil in the soil-forming process is eloquently demonstrated, for example, by the fact that earthworms alone are capable of passing several tons of soil mass through their bodies annually in area 1 ha. It follows that long before the soil was cultivated with agricultural tools, it was continuously “plowed up” by worms. These lowly organized creatures play an important role in soil development. In cultivated irrigated gray soils, according to the research of N.A. Dimo, earthworms are thrown annually onto the surface 1 ha about 123 T processed soil.

Worm excrement, or coprolites, are well-glued, water-resistant lumps of soil enriched with microorganisms, organic matter, nitrogen, calcium and other elements. Thus, earthworms not only improve the physical properties of the soil - porosity, aeration, water permeability, but to a certain extent also its chemical composition.

Other animals also do significant work in this regard. Moles, mice, hamsters, gophers and others, making various passages in the soil - molehills - and mixing organic substances with minerals, noticeably increase the water and air permeability of the soil, which undoubtedly enhances and accelerates the processes of decomposition of plant residues, and create a kind of tuberculate microrelief, very characteristic For steppe regions.

Thus, burrowing and digging animals constantly loosen, mix and move the soil, which, undoubtedly, most noticeably affects the intensification of the processes of decomposition of organic residues, as well as the weathering of its mineral part.

The idea of ​​the participation of animals in the decomposition of organic matter will become even more complete if we take into account that vegetation serves as food for various herbivores and that, before entering the soil, a significant part of the organic residues undergoes significant processing in the digestive organs of animals.

Green plants and their role in soil formation. MainThe role in soil formation belongs to green plants, which, using solar energy, synthesize organic matter by assimilation of carbon dioxide from the air, water, nitrogen compounds and ash elements of the soil. The remains of dead plants entering the soil become food for microorganisms, which in the process of life synthesize soil humus and form mineral and organomineral compounds, which in turn serve as a source of food for new generations of green plants.

The division of the soil profile into horizons is closely related to vegetation.

Thanks to the ability to release carbon dioxide and a number of organic acids by their roots, plants enhance the weathering process of poorly soluble minerals and thereby contribute to the formation of easily mobile compounds in the soil.

Vegetation cover is also of great importance as a factor capable of changing climatic conditions in the smallest areas and greatly preventing the development of erosion processes, i.e., soil washout and blowing away.

Thus, as a result of the vital activity of green vegetation on the continents of the globe, soils develop that contain humus, or humus, mineral and organomineral compounds.

Green plants are divided into woody and herbaceous.

Woody plants are perennial, their lifespan is often measured in tens of years, and sometimes many centuries.

A characteristic feature of woody plants is that only part of the organic mass formed over the summer dies off each year. The other part, often more significant, remains in the living plant, providing material for the growth of the stem, branches and roots. Dead remains in the form of leaves, needles and branches are deposited mainly on the soil surface, forming a layer of forest litter. In the soil layer, trees leave a relatively small portion of dead organic matter, since their root system is perennial.

Herbaceous vegetation has a large network of thin roots that densely penetrate the soil, after the death of which the soil mass is enriched with a significant amount of organic matter. In annual herbaceous plants, all vegetative organs usually exist only for one year; the plants die off entirely every year, with the exception of only ripe seeds.

Dying plants deposit dead organic matter both on the soil surface and within the soil mass at varying depths. Thanks to this, decomposition processes occur directly in the soil layer, and the soil is annually enriched with humus and elements of ash and nitrogen food.

Mosses, which are widely found under the forest canopy and in swamps, play a unique role in soil formation. Mosses lack a root system and absorb nutrients through the entire surface of their organs, attaching to the substrate with hair-like formations, or rhizoids.

Mosses are distinguished by their enormous moisture capacity. Where they settle, anaerobiosis is created, the processes of decomposition of organic residues slow down and waterlogging and peat accumulation begin.

The considered features inherent in one or another group of green plants directly affect the soil-forming process, and, consequently, the nature and quality of the resulting soils.

But no matter how individual groups of green plants differ in one or another characteristics, their main significance in soil formation always comes down to the synthesis of organic matter from mineral compounds. Organic matter, which plays a large role in soil fertility, can only be created by green plants.

The decomposition of organic remains of various plant formations is carried out by different microorganisms. In one case, this process is caused by the activity of mainly fungi, in the other - by bacteria.

Thus, woody debris in the forest decomposes mainly with the dominant participation of mold fungi. Bacteria here develop somewhat weaker due to the fact that the wood pulp contains tannins and has an acidic reaction. Bacteria are usually included in the process of decomposition of wood residues after fungi destroy tannins, which retard the development of many groups of bacteria. Conditions are favorable for fungal decomposition in the forest, since elastic woody remains lie loosely on the soil surface and the air flow to them is not limited.

An essential feature of the fungal decomposition of woody plant residues is that a significant amount of fulvic acids is formed here, which play a large role in the development of soddy-podzolic soils.

Organic remains of meadow herbaceous vegetation with insufficient aeration are decomposed mainly by anaerobic bacteria. Only in the upper parts of the soil, where oxygen penetrates, do aerobic decomposition processes occur.

Anaerobic decomposition is very slow. This explains the fact that in meadows under grass vegetation a rather thick, slightly decomposed turf is often formed, entwined with roots.

In the same way, under the influence of anaerobic microorganisms, significant accumulations of peat are gradually formed in swamps and marshy soils, widespread in the northern and central parts of our country.

Unlike meadows and wetlands, all dead remains of steppe plants are decomposed mostly by aerobic bacteria.

This is explained, firstly, by the fact that steppe vegetation dies off in the summer, when the soil is most dried out and well aerated; secondly, the grass vegetation in the steppe that dies in summer does not form a continuous dense felt, but usually lies in a loose layer, which also cannot serve as an obstacle to the penetration of oxygen into the soil.

The process of aerobic decomposition of all organic substances proceeds very quickly and completely; This explains the situation that plants of the steppe formation, especially in dry steppe conditions, after they die, usually do not leave large deposits of humus in the soil.

- Source-

Garkusha, I.F. Soil science / I.F. Garkusha.- L.: Publishing house of agricultural literature, magazines and posters, 1962.- 448 p.

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He identified five factors of soil formation: parent (soil-forming) rock; climate; plants; animal organisms; relief and time. Currently, they have been replenished with two more: water (soil and groundwater) and human economic activity.

Soil-forming rocks(or parent) are the rocks from which soils are formed. The soil-forming 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 certain specificity to each type of soil.

Soil-forming rocks differ in origin, composition, structure and properties. They are divided into igneous, metamorphic and sedimentary rocks.

The mineralogical, chemical and mechanical composition of rocks determines the conditions for plant growth and 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, promotes the formation of a humus horizon and its structure. On acidic rocks these processes are much slower. An increased content of water-soluble salts leads to the formation of saline soils. Depending on the mechanical composition and nature of the composition of the rocks, they differ in water permeability, moisture capacity, and porosity, which predetermines their water, air, and thermal regimes during the development of soils.

Meaning relief in the formation of soils and the development of soil cover is large and diverse. 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.

Thus, in the mountains, vertical zonation of climate, vegetation and soil occurs 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 reaching 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.

The rocks from which soil is formed are called soil-forming or parent rocks.

Soil-forming rocks are characterized by their origin, composition, structure and properties. The soil-forming rock is the material basis of the soil and transfers to it its mechanical, mineralogical and chemical composition, as well as physical and chemical properties, which are subsequently gradually change to varying degrees under the influence of the soil-forming process.

The properties and composition of parent rocks influence the composition of settling vegetation, its productivity, the rate of decomposition of organic residues, the quality of the resulting humus, the characteristics of the interaction of organic substances with minerals and other aspects of the soil-forming process.

The main soil-forming rocks are loose sedimentary rocks.

Sedimentary rocks - deposits of weathering products of massively crystalline rocks or remains of various organisms. They are divided into clastic, chemical and biogenic sediments.

The most common sedimentary rocks include continental Quaternary deposits: glacial, fluvioglacial, loess and loess-like loams, eluvial, alluvial, colluvial, proluvial, aeolian, less common lacustrine and marine. They differ in the nature of their composition, moisture capacity, water permeability, and porosity, which determines the water-air and thermal regimes.

Biological factor of soil formation

The biological factor of soil formation is understood as the diverse participation of living organisms and their metabolic products in the soil-forming process.

The most powerful factor influencing the direction of the soil-forming process are living organisms. The beginning of soil formation is always associated with the settlement of organisms on a mineral substrate. Representatives of all four kingdoms of living nature live in the soil - plants, animals, fungi, prokaryotes. Pioneers in the development and transformation of inert mineral matter in the soil are various types of microorganisms, lichens, and algae. They do not yet create soil, they prepare biogenic fine earth - a substrate for the settlement of higher plants - the main producers of organic matter. It is they, higher plants, as the main accumulators of matter and energy in the biosphere, who play the leading role in soil formation processes

The role of woody and herbaceous, forest and steppe or meadow vegetation in soil formation processes is significantly different.

Under the forest, litter, which is the main source of humus, comes mainly to the soil surface. To a lesser extent, the roots of woody vegetation participate in humus formation.

In a coniferous forest, litter, due to the specificity of its chemical composition and high mechanical strength, very slowly undergoes decomposition processes. Forest litter together with coarse humus forms a “mor” type litter of varying thickness. The process of decomposition in the litter is carried out mainly by fungi; humus has a fulvate character.

In mixed and, especially, deciduous forests, leaf litter is softer, contains a high amount of bases, and is rich in nitrogen. The process of mineralization of annual litter mainly occurs during the annual cycle. In forests of this type, litter of herbaceous vegetation takes a large part in humus formation. The bases released during the mineralization of litter neutralize the acidic products of soil formation, and humus of the humate-fulvate type, more saturated with calcium, is synthesized.

A different pattern of entry of organic residues and chemical elements into the soil is observed under the canopy of grassy steppe or meadow vegetation. The main source of humus formation is the mass of dying root systems and, to a much lesser extent, above-ground mass (steppe felt, plant seeds, etc.). This is explained by the fact that the root biomass of herbaceous vegetation (as opposed to woody vegetation) usually significantly predominates over the above-ground biomass. The litter of herbaceous vegetation, in contrast to the litter of tree species, is characterized by a finer structure, lower mechanical strength, high ash content, and rich in nitrogen and bases.

The soil-forming process occurring under the influence of herbaceous vegetation is called sod process.

Along with higher vegetation, numerous representatives of soil fauna - invertebrates and vertebrates that inhabit various soil horizons and live on its surface - have a great influence on soil formation processes.

The functions of invertebrate and vertebrate animals are important and varied; one of them is the destruction, grinding and consumption of organic residues on the surface of the soil and inside it.

The second function of soil animals is expressed in the accumulation of nutrients in their bodies and mainly in the synthesis of nitrogen-containing protein compounds. After the completion of the animal’s life cycle, tissue disintegrates and the substances and energy accumulated in the animal’s bodies are returned to the soil.

The activity of burrowing animals has a great influence on the movement of masses of soil and soil, on the formation of a unique micro- and nanorelief. In some cases, soil dug up and emissions to the surface reach such proportions that it becomes necessary to introduce special definitions into the nomenclature of soils (for example, carbonate dug up chernozem). The profile of such soils has a loose, cavernous structure; soil horizons are often displaced and transformed.

Thus, three groups of organisms participate in soil formation - green plants, microorganisms and animals that form complex biocenoses on land. At the same time, the functions of each of these groups as soil formers are different.

Green plants are the only primary source of organic substances in the soil, and their main function as soil formers should be considered the biological cycle of substances - the supply of nutrients and water from the soil, the synthesis of organic mass and its return to the soil after the completion of the life cycle.

The main functions of microorganisms as soil formers are the decomposition of plant residues and soil humus to simple salts used by plants, participation in the formation of humic substances, and in the destruction and new formation of soil minerals.

The main functions of soil animals are loosening the soil and improving its physical and water properties, enriching the soil with humus and minerals.

Course of lectures “Soil Science”

LECTURE 3. Soil properties and structure

1. Morphological characteristics of soils 34

1.1.Soil structure 34

1.2. Soil coloring 38

1.3.Granulometric composition of soils and its agronomic significance 40

2. Organic and organomineral substances in soils 43

2.1. The influence of soil formation conditions on humus formation 43

2.2.Composition of humus 44

2.3. Humus status of soils 48

Brief summary of Lecture 3 49

1. Morphological characteristics of soils

During the process of soil formation, the rock acquires a multi-level morphological organization. There are morphons of 1,2, 3, 4,5 orders. To identify morphons, there is a system of morphological soil characteristics.

Morphological characteristics of soil are a system of indicators that allows one to distinguish morphological elements from one another.

External morphological characteristics include:

structure,

thickness of the profile and individual horizons,

grading,

structure,

addition,

neoplasms,

inclusions.

1.1.Soil structure

Any soil is a system of successively replacing each other vertically. genetic horizons- layers into which the original is differentiated parent rock in the process of soil formation.

This vertical sequence of horizons is called soil profile.

A soil profile is a certain vertical sequence of genetic horizons within a soil individual, specific for each type of soil formation.

The soil profile represents the first level of morphological organization of the soil as a natural body, the soil horizon is the second.

The soil profile characterizes the change in its vertical properties associated with the impact of the soil-forming process on the parent rock. The main factors in the formation of the soil profile, i.e., differentiation of the original soil-forming rock into genetic horizons, are

these are, firstly, vertical flows of matter and energy (descending or ascending depending on the type of soil formation and its annual, seasonal or long-term cyclicity)

and, secondly, the vertical distribution of living matter (plant root systems, microorganisms, soil-dwelling animals).

The structure of the soil profile, i.e., the nature and sequence of its constituent genetic horizons, is specific to each soil type and serves as its main diagnostic characteristic. This means that all horizons in the profile are mutually connected and conditioned.

The soil horizon, in turn, is also not homogeneous and consists of morphological elements of the third level - morphones, by which we mean intrahorizon morphological elements.

At the fourth level of morphological organization there are soil aggregates, into which soil naturally breaks down within genetic horizons.

The next, fifth level of soil morphological organization can only be detected using a microscope. This is the microstructure of soil, studied within the framework of soil micromorphology.