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, fluvio-glacial, 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.
The national economic significance of soil as a universal means of production is determined by its qualities and properties. In agricultural production, the main quality of the soil is of great importance - fertility, and for industrial sectors, physical and physical-mechanical properties...
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INTRODUCTION
1 Rocks as soil-forming factors
3. Climate as a soil formation factor
4. Relief as a soil formation factor
5. Time as a factor in soil formation
6. Human production activity as a soil-forming factor
Conclusion
Literature
INTRODUCTION
Earth is priceless folk wealth and the main means of production in agriculture.
Soil is the main resource of every society, the main means of agricultural production and the spatial basis for the location and development of all sectors of the national economy. The national economic significance of soil as a universal means of production is determined by its qualities and properties. In agricultural production, the main quality of the soil - fertility - is of great importance, and for industrial sectors, physical and physical-mechanical properties.
The outstanding Russian scientist V.V. Dokuchaev first gave the following definition of soil[ 2, p.17 ]: “Soil should be called the “daytime,” or outer, horizons of rocks (no matter what), naturally modified by the combined action of water, air and various kinds of organisms, living and dead.”
It is known that the earth provides all the necessary food products for humans, as well as various types of raw materials for industry. The earth is the source of life. That is why the land must be protected and its productivity must be consciously and purposefully increased. It belongs not only to us, but also to the next generation.
In agricultural production, one cannot ignore the properties of the soil, the characteristics of living organisms, weather conditions, etc. In-depth knowledge of soils and their properties is of great importance for the effective implementation of agronomic and reclamation measures on them.
The soil cover of Ukraine is one of the main indicators of its wealth, the basis for the settlement of human society and the main means of production in agriculture. The quantity and quality of soil resources and their use determine the level of well-being of society.
Rational use of land and specialization of agricultural sectors are possible only on the basis of deep knowledge of the characteristics of the soil cover, the specifics of soil fertility, and their environmental properties.
Taking into account the characteristics of soils and climatic conditions, zoning of agricultural production and its specialization are carried out. The fulfillment of socio-economic objectives depends on the use of soil cover.
The process of soil formation is the process of transforming rocks into a qualitatively new state - soil under the influence of a complex of factors.
The doctrine of soil formation factors was created by V.V. Dokuchaev. He showed that soil is formed under the influence of climate, vegetation, soil-forming rocks, relief and time. These factors act throughout the land area, which is why they are called global soil formation factors. Later V.R. Williams identified another factor in soil formation - human production activity. Human production activity is a locally operating factor.
V.V. Dokuchaev wrote that all soil-forming agents have the same importance in the process of soil formation. In order to study the soil, knowledge of all soil-forming factors is necessary.The development of the soil-forming process and the formation of specific types of soils occur under certain natural conditions. The conditions on which the soil-forming process depends were called soil-forming factors by V.V. Dokuchaev [ 13, p.220].
The combination of soil-forming factors is a combination of environmental conditions for the development of the soil-forming process and soils. The study of each soil formation factor involves characterizing it according to certain parameters and assessing its role in soil formation.
- Rocks as soil-forming materials th factor.
The role of soil-forming materials rocks as a soil formation factor consists of in that they are the material from which soil is formed. Parent rocks transfer their granulometric, mineralogical and chemical composition.
The main soil-forming rocks are products of weathering of rocks.
Weathering (hypergenesis ) - the process of destruction of rocks and minerals under the influence of certain natural factors (air, water, temperature fluctuations and living organisms). In this case, other rocks are formed and new minerals are synthesized. Weathering is a set of complex and diverse processes, quantitative and qualitative changes in rocks. The horizons of rocks where the weathering process occurs are called weathering crust. Its thickness varies from a few centimeters to 2-10 m.
The nature of rock destruction and, as a rule, the composition of weathering products depend on environmental conditions and on the mineralogical composition of the rock itself. Geochemical studies have proven that the weathering of acidic rocks forms sands and sandy loams, medium rocks - loams and basic rocks - heavy loams and clays. All of the above-mentioned loose deposits have certain physical and physical-mechanical properties that allow soil formation processes to occur. This distinguishes them from non-vitreous rocks.
As a rule, modern soils are formed on complex complexes of weathering products. The most common soil-forming rocks are loose sediments of the Quaternary period. They are diverse in composition, structure, and properties, which affects soil formation and the level of soil fertility. The most common soil-containing rocks are discussed below.
Eluvial deposits are products of weathering of bedrock of various compositions remaining at the site of formation.
V. A. Kovda (1973) lists eight varieties of eluvial rocks. The most common of them are dribnozem carbonate eluvium. Primary eluvium is common on igneous rocks, particularly in Mongolia, Armenia and Crimea; secondary (neoluvium) - over a large area of Europe and Asia in the form of loess, loess-like and syrt loams. They cover the underlying bedrock like a blanket and therefore are called cover rocks. The forests have a fawn or brownish-fawn color and a silty-loamy mechanical composition. They are characterized by carbonate content, porosity, mealiness, and good water permeability. The chemical composition and physical properties of wood are very favorable for plant growth.
Loess-like loams contain less carbonates, and there are also non-carbonate ones. They are coarse-grained, often layered, with less mealiness and porosity. Forests are distributed mainly in Ukraine, the southern regions of Russia, Central Asia, and the center of North America; loess-like loams - in Belarus, the Central Non-Chernozem Zone of Russia and in other areas. Chernozem, gray forest, chestnut and gray desert-steppe soils were formed on these rocks.
Proluvial and deluvial sediments are formed in the foothills and at the foot of the mountains. Various soils form on them. In the Carpathian region and the Carpathians, brown forest soils are formed on such deposits.
Glacial deposits (moraine) form small islands on elevated elements of the relief of Ukrainian Polesie. These deposits occupy large areas in the north of the European part of Russia and Western Siberia. Glacial deposits are formed from heterogeneous clastic material, predominantly of a loamy composition with the inclusion of gravelly sand, pebbles, and boulders. According to the chemical composition, moraine can be either carbonate or non-carbonate. Soddy-carbonate, weakly and medium-podzolic soils are formed on the carbonate moraine. On non-carbonate soils there are medium and highly podzolic soils. In the presence of a large number of boulders, the agronomic properties of the soil deteriorate significantly.
Water-ice-fluvioglacial deposits occupy a large area in the taiga-forest zone of the European part of Russia, Belarus, Poland, and the Baltic states. In Ukraine they occupy 10.5% of the republic's territory. Their formation is associated with the activity of powerful glacial flows.
Fluvioglacial deposits are layered sorted material of sandy, sandy loam, and in places loamy mechanical composition of light yellow or light gray color. Their main component is quartz with admixtures of feldspar grains. Some of the sandy mass contains layers of small pebbles and boulders of crystalline rocks. The mechanical and chemical composition of these deposits is unfavorable for the formation of highly fertile soils.
Lacustrine-glacial deposits are common in the northwestern part of European Russia. They were formed in depressions of the ancient relief and have a clayey mechanical composition (layered ribbon clays of lakes near the lakes). The formation of lake sediments was accompanied by the accumulation of water-soluble salts, carbonates and gypsum. When lakes dry up, salt marshes form.
Alluvial deposits are common in river floodplains (floodplain alluvium). Modern and ancient alluvial deposits are distinguished by age. They are characterized by differentiation in particle size and layering. The mechanical composition of alluvial deposits depends on their position relative to the river bed. Thus, in the riverbed part of the floodplain, gravel-pebble and sandy deposits are formed, in the central part - sandy, in the near-terrace - sandy loam-clayey. Highly fertile floodplain soils are formed on alluvial deposits. In Ukraine they occupy about 9% of the territory.
Clays of various origins on the territory of Ukraine are also often found in soil-forming rocks. They are mainly common on the slopes of beams, terraces, river valleys and the like.
In addition, the soil-forming rocks in Ukraine are weathering products of hard carbonate rocks (Southern Coast of Crimea), loose weathering products of igneous rocks (Azov and Dnieper uplands), weathering products of sandstones (Donbass, Crimea, Carpathians), weathering products of clay shales (Donbass, Crimea , Carpathians)
The mechanical composition of soil-forming rocks is important in the process of soil formation. In addition, the mineralogical and chemical composition directly affects the course of elementary processes occurring in the soil. Depending on this, the soil acquires certain physical and physical-mechanical properties that predetermine its agricultural production characteristics.
The mechanical and chemical composition of these deposits is unfavorable for So, sandy and sandy loam soils are easy to process with agricultural machines. That's why they are called light soils. They have a favorable air regime, high water permeability, and warm up quickly. At the same time, they have a number of negative properties, namely: low content of humus and nutrients (due to intensive washing), low degree of structure, insignificant capacity for removing cations, and are easily subject to erosion.
Soils formed on clay rocks are called difficult. They have high moisture capacity and water-holding capacity. As a rule, they are rich in humus and easily accessible nutrients. In such soils, in the presence of the necessary conditions, the process of formation of structural aggregates occurs intensively.
If clay soils are structureless for one reason or another, they have unfavorable physical properties. Radical improvement of the mechanical composition of the soil is carried out by claying sandy and sanding clay soils with the simultaneous application of high doses of organic fertilizers.
The mineralogical and chemical (elementary) composition of soil-forming rocks significantly influences the nature and direction of chemical reactions, the redistribution of chemical elements along the soil profile, i.e. on the geochemistry of soil formation. All this in a certain way influences other soil formation processes. As a result, in a limited area that has areas covered with various soil-forming rocks, different types or subtypes of soils are formed.
2. Biological factors of soil formation
The process of soil formation begins from the moment living organisms settle on rock. They assimilate elements of the lithosphere, water and atmospheric elements, incorporate them into metabolism and return them to the soil in forms and ratios. So, as a result of life activityIn the organism, a small biological cycle of substances occurs, as well as ground cycles of the circulation of a number of chemical elements (C, O, H, N, P, S, etc.).
The vital activity of all organisms inhabiting the soil (microorganisms, plants, animals) and the products of their vital activity carry out the most important elementary processes of soil formation - the synthesis and decomposition of organic matter, the destruction and new formation of minerals, the redistribution and accumulation of substances. All this determines the general course of the process of soil formation and the formation of soil fertility.
The soil is simultaneously inhabited by representatives of all four kingdoms of living nature - prokaryotes, fungi, plants, animals. However, the functions of organisms of each kingdom in soil formation are different.
Microorganisms inhabiting the soil are very diverse in composition and in the nature of biological activity. Therefore, their role in soil formation is extremely complex and diverse. Microorganisms have existed on Earth for a billion years; they are the most ancient soil formers, because they appeared on earth long before the appearance of higher plants and animals. In addition to soil formation, their activity largely determines the properties of sedimentary rocks, the composition of the atmosphere and natural waters, the geochemical history of many elements (C, O, H, N, P, S, etc.). In the biosphere they carry out processes such as fixation of atmospheric nitrogen , oxidation of ammonia and hydrogen sulfide, reduction of sulfates and nitrates, accumulation of iron and manganese compounds, synthesis of biologically active substances in soils - enzymes, vitamins, amino acids, etc. Microorganisms are directly involved in the destruction of minerals and rocks in the process of biological weathering.
However, the main function of microorganisms in soil formation is the decomposition of organic residues of plant and animal origin into humus formation and complete mineralization.
The bulk of microorganisms are concentrated in the horizon of root systems at a depth of 10-20 cm. Their number in 1 g of soil is tens and hundreds of millions of pieces. The total mass of microorganisms in the arable horizon (25-30 cm) is 10 t/ha. Highly fertile cultivated soils contain the most microorganisms.
In the process of life, plants carry out biogenic migration of chemical elements in the soil-plant-soil system. At the same time, a significant part of the ash elements, as well as nitrogen, accumulates in the upper horizon, hundreds of millions of pieces. The total mass of microorganisms in the arable horizon (25-30 cm) is 10 t/ha. Highly fertile cultivated soils contain the most microorganisms.
The process of soil formation involves bacteria, algae, lichens, amoebas, micronematodes, flagellates, ciliates, fungi and actinomycetes. There is evidence of the presence of non-cellular forms of microorganisms (viruses, bacteriophages) in soils.
Higher plants. Familiarization with the role of microorganisms in soil formation indicates that they themselves do not yet create soil. Soil formation is possible only when producers of organic matter settle on the parent rock. Higher plants are such producers on the globe. It is these organisms that play the leading role in soil formation processes. The dead remains of higher plants, transformed by microorganisms and animals, make up the bulk of the organic part of the soil. Consequently, green plants are the main source of organic matter for soil formation.
Green land plants annually produce about 5.3 1011 tons of biomass. Part of this biomass in the form of dead remains of roots and above-ground organs enters the soil annually. The amount of biological mass entering the soil depends on the type of vegetation and climatic conditions. Part of the plant litter is decomposed by microorganisms, and the second part accumulates in the form of forest litter and steppe felt.
The absorption of soil chemical elements by the roots of higher plants, the synthesis of organic substances, their return to the soil and their decomposition by microorganisms are the main links in the biological cycle of substances. From the previously mentioned it is clear that green plants are the main agent of the biological cycle, and the soil acts as its arena. This is the second function of plants as soil formers.
In the process of life, plants carry out biogenic migration of chemical elements in the soil-plant-soil system. At the same time, a significant part of the ash elements, as well as nitrogen, accumulates in the upper horizonsoil. In this case, plants act as concentrators of chemical elements. This is the function of plants in soil formation.
Animals. Representatives of the following types of animals participate in soil formation processes: protozoa, worms, mollusks, arthropods and mammals. Based on size, soil fauna is divided into four groups: nano-, micro-, meso- and macrofauna. Each group of animals is adapted to certain living conditions, to a certain interaction with the environment. The total reserves of zoomass in soils in terms of phytomass are insignificant - on average 1-2%.
The main function of animals in the biosphere and soil formation is consumption, primary and secondary destruction of organic substances, redistribution of energy reserves and its conversion into thermal, mechanical and chemical.
Among the animals inhabiting the soil, invertebrates predominate. Their total biomass is 1000 times higher than the total biomass of vertebrates. The soils are inhabited by earthworms, enchytraids, mites, springtails, etc. By eating plant debris, they significantly accelerate the biological cycle of substances.
Among invertebrates, earthworms play a particularly important role in soil formation. They are common in soils of various soil-climatic zones. Their number per 1 hectare of soil can reach several million individuals.
The activities of earthworms in soil formation are varied; they form a dense network of passages in the soil, improving its physical properties: porosity, aeration, moisture capacity. The waste products of earthworms - caprolites - improve the structure of the soil and increase the water content of structural aggregates. Soil rich in earthworms has low acidity, high humus content and other positive qualities. It is estimated that earthworms mix the entire surface soil horizon in 50 years.
A significant number of larvae of various insects, termites, ants, etc. live in soils. They also intensively mix the soil mass,form a large number of passages in it and thereby improve the water and physical properties of the soil.
Among vertebrate animals, steppe rodents (voles, marmots, moles, gophers, etc.) take an active part in soil formation processes. They build deep burrows and long passages in the soil. The volume of soil they mix reaches several hundred cubic meters per hectare. Intensive mixing of the soil mass by digging animals leads not only to physical, but also profound chemical changes. The soil mass brought from the depths to the surface changes the chemical composition of the upper soil horizons.
1.3 Climate as a soil formation factor
Climate is one of the main factors in soil formation and geographic distribution of grants. Its versatile influence on soil formation was noted by V.V. Dokuchaev. It is now known that climate influences soil formation both directly (determines the hydrothermal regime of the soil) and indirectly - through vegetation, microorganisms and animals.
The main climatic factors that influence soil formation processes are solar radiation, precipitation and wind.
Solar radiation. Sunlight, which brings thermal energy to the surface of the globe, is the main source of energy for life and soil formation. Solar energy absorbed by the soil is spent on processes such as heating, evaporation, transpiration, photosynthesis, humus synthesis, etc.
The thermal conditions of soil formation on our planet are very diverse, but in general terms they are determined by the values of the radiation balance, which correlate with such indicators as the average annual temperature and the sum of active temperatures (Table 1).
High average annual temperatures (+32; +35°C ) are typical for the tropics, the lowest are for the polar regions. The difference in average annual temperatures on Earth reaches 60-70°C.
The sum of active temperatures is used for agronomic and soil assessment of the territorial thermal regime. Temperatures above +5 are active for herbaceous vegetation°C , for forest - above +10°C.
Table 1
Planetary thermal zones
|
Belt |
Average annual temperature air, °C |
Radiation balance, kJ/(cm 2 year) |
Sum of active temperatures, °C, per year at the southern border of the zones |
|
Polar |
23 - 15 |
21 - 42 |
400 500 |
|
Boreal |
4 + 4 |
42 - 84 |
2400 |
|
Subboreal |
84 - 210 |
4000 |
|
|
Subtropical |
210 - 252 |
6000 8000 |
|
|
Tropical |
252 - 336 |
8000 - 10000 |
The average annual temperature, the value of the radiation balance and the sum of active temperatures per year increase from the polar regions to the tropical ones. Naturally, in the same direction, the intensity of weathering and the synthesis of organic mass increase, and the vital activity of animals and microorganisms becomes more active. In the same direction, the intensity of soil-forming processes increases: destruction of minerals, decomposition of organic residues, synthesis of humic acids, etc. At high average annual temperatures, more clay particles are formed as a product of intense weathering.
Soil temperature affects the rate of chemical reactions. According to van't Hoff's rule , with a temperature increase of 10°C the speed of chemical reactions increases by 2-3 times. Therefore, in areas with high average annual temperatures, geochemical processes occur significantlyfaster than in cold latitudes. This determines the annual rate of weathering, the formation of different weathering crusts and, as a consequence, the varied chemical composition of soils. In addition, the degree of dissociation of chemical compounds in aqueous solutions depends on temperature. When the temperature rises from 0°C to 50 °C dissociation increases 8 times.
Temperature affects the dissolution of gases in the soil solution, the rate of coagulation and peptization and other physicochemical processes.
Atmospheric precipitation The effective influence of heat and light on biological and soil-forming processes is possible only if there is a sufficient amount of moisture. Therefore, the importance of precipitation in soil formation is very high. Soil formation is influenced in a certain way by both the amount and seasonal distribution of atmospheric precipitation.
Atmospheric precipitation entering the soil dissolves mineral and organic compounds, moves them to lower horizons (leaches), transfers mobile forms of compounds and mechanical particles from elevated to lower relief elements. These processes are carried out by surface and underground water.
Under the influence of atmospheric precipitation, the processes of hydrolysis of primary minerals and the formation of secondary clay minerals occur. Atmospheric precipitation brings dust particles, dissolved salts, acids, nitrogen, ammonia, CO2, and toxic compounds to the soil surface. Moisture from atmospheric precipitation is retained in the pores and capillaries of the soil and is used by plants to synthesize organic matter, which in the future is used to replenish the supply of humic substances and is a source of energy and nutrients for animals and microorganisms. Thus, precipitation directly and indirectly affects humification processes.
The downward movement of water ultimately forms the genetic horizons of the soil - humus, eluvial, illuvium, etc. Intensive runoff of atmospheric precipitation causes water erosion of soils.
The nature of precipitation in a given area affects the thermal regime of soils.
The degree of soil moisture is determined by their chemical composition. In arid regions, soils with a high content of carbonates and water-soluble salts, low humus content, and low absorption capacity are formed. In humid landscapes, soil leaching increases, the content of humus, clay minerals and soil absorption capacity increases. Under waterlogged conditions, soil acidity increases significantly, humus content and absorption capacity decrease.
When assessing the role of climate as a soil formation factor, one should simultaneously take into account the influence of precipitation and temperature. Soil scientists have long been looking for a form to express the combined influence of heat and precipitation on soil formation. An original approach to solving this problem was the concept of hydrothermal series, developed by V. R. Volobuev (1956). He proved the planetary connection between precipitation, average annual temperatures, radiation balance, evaporation and soil cover characteristics. Based on an analysis of the relationship between these factors, the hydrothermal conditions for the formation of the main types of soils were established and their climatic areas were identified.
Based on hydrothermal conditions, soils are divided into two categories.
1. Soils in which biological processes are suppressed. They formed in regions with low humidity (500 mm per year), but in different thermal zones. This category includes desert gray soils, chestnut and tundra soils.
2. Soils formed in warm and temperate tropical latitudes. This category of soils was formed under limited thermal conditions, but in a wide range of precipitation amounts (1000-5000 mm per year). These are brown forest soils, yellow soils of the subtropics and lateritic soils of the humid tropics.
Conventionally, soils are classified into moisture series (hydraulic series) and thermal series. Hydroseries combine soils that are formed in different thermal conditions.conditions, but under conditions of almost identical moisture. Thermal series, on the contrary, combine soils formed under conditions of different moisture content, but in similar thermal conditions. In total, seven hydroseries are designated (desert (A), gray soil (B), chestnut (C), chernozem (D), three podzolic (E, F, G) and seven thermoseries (arctic (I), subarctic (II), moderate cold (III), temperate (IV), warm temperate (V), subtropical (VI) and tropical (VII).
The net effect of the combined effects of precipitation and temperature on soil formation is very complex. The nature of the soil formation process, in addition, depends on the combination of hydrothermal conditions with relief, geochemical balance of substances and other factors.
Wind. In addition to solar radiation and precipitation, wind also influences soil formation. It transports mineral and organic particles from one area to another, redistributes precipitation, enhances evaporation and thus participates in the formation of the mechanical, chemical composition and water regime of the soil.
All processes of destruction, transfer and deposition of mechanical particles of rocks and soils that occur under the influence of wind are called aeolian. There are aeolian deflation, aeolian corrosion and aeolian accumulation.
The intensity of soil blowing is determined by many factors: wind speed, the presence of vegetation cover, the mechanical and structural composition of the soil, topography, etc. With strong deflation, dust storms occur.
As a result of deflation, the top fertile layer is blown away and soil fertility decreases. In places where wind-blown substances accumulate (ravines, ravines, forest belts, populated areas, agricultural lands), perennial plants and crops die, fertile lands, irrigation canals, roads, etc. are covered.
So, aeolian processes cause significant harm to agriculture, water and other sectors of the national economy. Both denudation and accumulation sharply disrupt the normal course of soil formation processes.
1.4 Relief as a soil formation factor
Relief is a unique factor of soil formation. Its significance in the formation and geographical distribution of soils is great and varied. It acts as the main factor in the redistribution of solar radiation and precipitation. Depending on the exposure and steepness of the slopes, it affects the water, thermal, nutrient and salt regimes of the soil, determines the structure of the soil cover and is the basis of soil cartography.
In the practice of field soil research, it is customary to use the following taxonomy of relief types:
1) macrorelief;
2) mesorelief;
3) microrelief;
4) nanorelief.
Each of these types of relief plays a certain role in soil formation and soil geography, in the formation of the structure of the soil cover .
Macrorelief - large landforms that determine the general appearance of a large area of the earth's surface: mountain ranges, plateaus, valleys, etc. The emergence of macrorelief forms is associated mainly with tectonic phenomena in the earth's crust.
The forms of macrorelief primarily influence the redistribution of solar heat and precipitation over vast territories and predetermine the horizontal and vertical zonation of soils.
On large plains there is a change in bioclimatic zones, which are characterized by a certain type of vegetation, type of water and temperature regimes. Thus, a certain combination of soil formation factors acquires a zonal character. As a result, soil zones and subzones are formed, which is a manifestation of the law of horizontal zoning.
Mountain systems also redistribute atmospheric precipitation, which causes changes in plant and soil zones. High mountains act as a barrier to warm, humid air masses. Therefore, a large amount of precipitation falls on the windward slopes, and an arid climate forms on the slopes of the opposite exposure. It is clear that the soil cover of wet and dry slopes is not the same.
In addition to the redistribution of solar heat and precipitation in mountainous areas, soil formation is influenced by the absolute altitude of the area. As the altitude of the area changes, all climatic factors change: temperature, air humidity, precipitation, pressure, insolation, etc. As you ascend into the mountains, the atmosphere thins, the content of water vapor and dust particles in the air decreases, solar radiation increases, the influx of ultraviolet rays and, at the same time, heat radiation. Such climate changes cause differentiation of vegetation and soils, that is, the emergence of natural zonality. Soil zones that regularly replace each other form vertical soil structures.
Mesoreliefs are forms of medium size in height and length (several square kilometers). Examples of such forms are ravines, beams, basins, terraces, stream valleys, mounds, etc. They arose as a result of geological processes of denudation, the formation of continental sediments, etc.
Microrelief is small forms of relief that occupy small areas and are details of large forms. These include tubercles, depressions, hummocks, small depressions, swelling, karst sinkholes, coastal ramparts, etc.
Elements of meso- and microrelief redistribute solar energy and moisture from atmospheric precipitation in a given area.
The redistribution of solar energy is determined by the presence of slopes of unequal steepness and exposure. At any time of the year throughout the Northern Hemisphere, northern slopes receive less heat than southern slopes and are therefore cold. The difference in soil temperature in summer between the northern and southern slopes, with the same steepness, can reach 5-8°C.
Features of the thermal regime on slopes of different exposures have different effects on their water regime and the nature of vegetation. Thiscauses the formation of different types of soils. On southern slopes, soils are formed under conditions of relatively less moisture and more contrasting temperature conditions. In this regard, agriculture tends to develop on the southern slopes, while the northern slopes remain undeveloped.
Uneven terrain determines the flow of surface water. Precipitation water flows down slopes from elevated relief elements to lower ones. As a result, elevated areas lose some moisture, and low-lying soils receive additional moisture.
The redistribution of moisture across relief elements is associated with the migration of solid and water-soluble products of weathering and soil formation. Flowing down slopes, rain and melt water carry with them soil particles and dissolved compounds, which accumulate in low areas. Thus, soil formation on various relief elements occurs under different hydrothermal and geochemical conditions.
Based on their position on the relief and the nature of the redistribution of atmospheric precipitation, three groups of soils are distinguished, which are called genetic series of moisture.
On elevated relief elements under conditions of free flow of surface water and deep groundwater, that is, in autonomous landscape-geochemical conditions, automorphic soils are formed under the influence of the downward movement of water along the profile.
Hygromorphic soils are formed in low-lying areas of relief under conditions of prolonged stagnation of surface water or in shallow (less than 3 m) groundwater, which is enriched with chemical elements and compounds brought from elevated elements. These soils are formed depending on landscape and geochemical conditions under the influence of the upward movement of water.
Soils that form in autonomous conditions, but are briefly flooded by surface water or are formed when groundwater is shallow (3 - 6 m), are called hydromorphic soils (meadow-chernozemic soils).
Soils that form under conditions of seasonal ground moisture are called automorphic-hydromorphic.
The dependence of hygromorphic soils on the chemical composition of rocks and soils of elevated relief elements is called the geochemical communication of soils.
The close connection between relief elements and characteristic differences in soils became the basis for the development of the method of reference areas ("keys") when mapping soils. The essence of this method is that, in a typical area for a given area, a connection is established between relief elements with plant groups, with the composition of soil-forming rocks and characteristic soil features. To do this, lay the required number of soil sections on different relief elements and establish the relevance of soil declinations to them. The obtained data are the hypsometric basis for mapping the soils of the area.
1.5 Time as a factor in soil formation
In his works, V.V. Dokuchaev pointed out that modern soils are the product of a long and complex geological history of the earth’s surface. Soil cannot appear instantly, remain unchanged for a long time, and then suddenly disappear. It takes a certain amount of time for soil to form.
The process of soil formation, like any natural process, has its beginning, stages of development, a certain speed and completion time.
Soil formation begins from the moment living organisms settle on loose weathered rock.
According to the observations of many scientists, 1 cm of the humus horizon of the soil in the temperate zone is formed in 100-200 years, and the full profile of modern soil takes from several hundred to several thousand years.
A sign of the completion of soil formation and its achievement of a mature state is a clear differentiation of the profile into genetic horizons. Soils that have not achieved complete differentiation and full profile development are called immature (young).
Soils on the earth's surface began to form with the appearance of living organisms. The first organisms on Earth were bacteria, which appeared in the Lower Paleozoic period (more than 500 million years ago). Scientists suggest that under their influence, primitive soils were formed, similar to those that form in our time in the highlands.
At the end of the Silurian period, when psilophyte plants appeared on Earth (400 million years ago), a new stage of soil formation began on the planet. Under their influence, moist soils were formed on the waterlogged coasts of the seas. These soils are the oldest on Earth. Fossil remains of these soils have survived to this day (oil shale of the Leningrad region and Estonia).
350-360 million years ago, at the end of the Devonian period, psilophytes disappeared and were replaced by ferns and horsetails. They had a root system and in the Carboniferous occupied large areas of land with a tropical and subtropical climate. Under such conditions, ferrallitic soils were formed, similar to modern subtropical and tropical soils. When mining coal in the Donbass, soils were discovered that are more than 300 million years old, but they have the characteristics and properties of modern soils.
During the Permian period (285 - 240 million years ago), sharp climatic changes occurred. In large areas of land, an arid, desert climate was established, and in others, a cold, humid climate. It is believed that intense evaporation and cryogenic processes caused the formation of desert, saline, frozen soils. In a moderately cold, humid climate, soils similar to podzolic ones began to form. Over the next 120-130 million years there were no conditions for the emergence of new soils. Only in the Eocene did new natural landscapes emerge - steppes. During this period, chernozems and chestnut soils began to form.
At the beginning of the Quaternary period, tundra formed, and somewhat later sphagnum bogs arose. During this period, tundra soils and peat bogs began to form.
Thus, in the process of evolution of the organic world on Earth, the process of the emergence of new soils and an increase in their diversity can be traced.
The modern soil cover of the earth is of different ages. Year zero has those areas of land that have only been freed from water as a result of marine regression (Caspian Sea, Aral Sea region), drainage of river deltas, during the construction of polders (Holland). Surfaces covered with volcanic ash from modern volcanic eruptions and outcrops of embankment quarries also have zero age.
The age of soils in Eastern Europe corresponds to the period of the end of the last continental glacial period (about 10 thousand years ago) and the beginning of the Caspian-Black Sea regression. In this regard, the age of chernozems is 8-10 thousand years, and the age of chestnut soils is 5-6 thousand years. years.
1.6 Human production activity as a soil-forming factor.
The factors of soil formation discussed earlier - rocks, climate, living organisms, relief and time - are global. They influence soil formation processes throughout the land area.
In addition to global factors, there are a number of locally operating factors. These factors include human production activity.
In the process of production activities, humans, using powerful means, influence the environment, including the soil, which leads to significant changes in natural ecological systems and changes in the process of soil formation.
By developing virgin lands, people create favorable conditions for the development of cultivated plants. However, this disrupts the dynamic balance of all components of the natural landscape: the nature of vegetation, the composition of microorganisms and zoofauna, the nature of metabolism and energy in the soil-plant system changes. The influence of other soil formation factors changes: climate, relief, parent rock .
Soil cultivation, water regime regulation (drainage, irrigation, snow retention, fertilization, chemical and other types of reclamation radically change the chemical composition of the soil, its physical, thermal and water properties.
Thus, with the beginning of cultivation of virgin soil, the nature of soil formation begins to change. The soil passes from the natural to the cultural phase of its development, before the cultural process of soil formation. The essence of this process is aimed at the formation of a powerful humus horizon, which must have high biological activity, high humus content, favorable structural composition, optimal nutritional, thermal, water and air conditions.
The main factors influencing the soil at all stages of cultural soil formation are cultivated plants, mechanical tillage, fertilizers and various reclamation measures. The role of these factors in soil formation is studied in detail in the course of agronomic soil science.
Systematic improvement of soil properties and increasing its fertility through the use of agrotechnical measures is called soil cultivation. Cultivated soils create favorable conditions for the growth and development of plants.
7. Interrelation of soil formation factors.
Soil formation factors have a specific effect on soil formation and cannot be replaced by each other. In this sense they are equivalent. Each of them plays its role in the processes of exchange of matter and energy between the soil and its natural environment.
At the same time, the entire complex set of processes that characterize the soil-forming process as a consequence of the interaction of soil-forming factors can be combined into 3 groups (according to A.A. Rode): those occurring as a result of the activity of living organisms; developing due to the products of the vital activity of living organisms and phenomena of an abiotic nature that are not directly related to the first two. Moreover, the first two groups cover the most essential aspects of the soil formation process and it is their consequence that is the emergence and development of a specific soil property - fertility. Therefore, in natural soil formation, the biological factor should be considered the leading one.
At the same time, the factors of soil formation in nature are closely related, and their division given above is to a certain extent abstracted for understanding the elementary phenomena of soil formation. In fact, they are combined in nature into ecological complexes, determined by the conjugate development of their components.
Dokuchaev emphasized that soil is formed as a result of the interaction of soil-forming factors. When factors interact, they influence each other and, as a result of this influence and interaction, micro-, meso- and macro processes of soil formation develop. Under their influence, soil is formed with a set of genetic horizons and specific properties.
There are two main cycles in the development of natural ecosystems, landscapes, and soils - bioclimatic and biogeomorphological.
The bioclimatic cycle of development is determined by cosmic and planetary phenomena, the distribution of solar radiation on the surface and the dynamics of the atmosphere; Vegetation and soils in this cycle evolve along with the climate.
The biogeomorphological development cycle is determined by geological, geomorphological and geochemical processes; in it, the development of vegetation and soil cover is associated with the formation of relief and surface deposits.
Recently, the third cycle has become increasingly important in life - human production activity, which, on the one hand, adapts to the main cycles, and on the other, greatly changes them through the replacement of natural vegetation with cultivated vegetation and through the transformation of soil cover using methods of agricultural technology, land reclamation, reclamation, as well as through the creation of cultural landscapes.
Conclusion
Thus, the process of soil formation is a set of various elementary soil processes that form the composition of the solid phase of the soil, solution and soil air, the structure and properties of the soil.
The processes of development of soils and soil cover, as well as the process of formation of their fertility, are associated with natural factors of soil formation, as well as with the diverse activities of human society, with the development of its productive forces, environmental, economic and social conditions. Living organisms play a special role in soil formation. In the process of their life activity, organic and organo-mineral substances are formed in the upper layer of the rock, which creates conditions for retaining moisture, increasing gas exchange with the atmosphere, absorbing radiant energy from the Sun, etc.
On a global scale, the geographic patterns of soil formation on its individual continents are associated with zonal changes in climate and vegetation in the latitudinal direction (north south). Differences in the soil cover of small areas are due to the influence of relief (hills, valleys, etc.), composition and properties of rocks on vegetation and soil-forming processes.
Using soil as a means of production, a person significantly changes the conditions of soil formation, influencing both directly its properties, regime and fertility, and the natural factors that determine soil formation. Planting and cutting down forests and cultivating crops change the appearance of natural vegetation; drainage and irrigation change the humidification regime. No less dramatic effects on the soil are caused by methods of soil cultivation, the use of fertilizers and chemical reclamation agents (liming, gypsum). Consequently, the soil is not only the subject of labor, but, to a certain extent, the product of this labor. This directly affects the ecological situation on Earth.
Literature
- Dobrovolsky V.V. Geography of soils with the basics of soil science: Textbook. for ped. Inst.-M.: VLADOS, 2001.-384 p.: ill.-(Textbook for universities).
- Chorny I.B. Geography of soils with the basics of soil science: Navch. Pos_bnik. K.: Vishcha School, 1995. 240 p.
- Loze J., Mathieu K. Explanatory dictionary of soil science: Transl. from French M.: Mir, 1998. 398 p.
- Atlas of soils of the Ukrainian SSR / Ed. N.K. Krupsky, N.I. Half pan. K.: Harvest, 1979.
- Vedenichev P.F. Land resources of the Ukrainian SSR and their economic use. K.: Naukova Dumka 1979.
- Bilyavsky G.O., Padun M.M., Furduy R.S. Fundamentals of underground ecology. K.: Libid, 1993. 300 p.
- Bilyavsky G.O., Furduy N.S. Workshop on foreign ecology. K.: Libid, 1997.
- Safranov T.A. Ecological foundations of nature management. Lviv: “New World”, 2003. 248 p.
- Laboratory and field workshop in ecology / Ped. ed. V.P. Zamostyana, that Ya.P. Didukha. Kiev: Phytosociocenter, 2000. 216 p.
- Perelman A.I. Geochemistry of the biosphere. M.: Nauka, 1973. 168 p.
- Yakushova A.F., Khain V.E., Slavin V.I. General geology. M.: Publishing house. Moscow State University, 1988. 448 p.
- Lapin A.G., Usov M.A. Fundamentals of agronomy.-L.: Gidrometeoizdat, 1990-292 p.
- Van't Hoff's rule/|Material from Wikipedia the free encyclopedia.// Electronic resource]. Access mode:http://uk.wikipedia.org/wiki/Van't Hoff_Rule
- Kovrigo V.P., Kaurichev I.S., Burlakova L.M. Soil science with fundamentals of geology. K.: Kolos, 2000-416 p.
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Chapter 2. SOIL FORMATION FACTORS. GENERAL SCHEME OF SOIL FORMING PROCESS
§1. The concept of soil formation factors
Under soil formation factors refers to the components of the natural environment external to the soil, 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 varied combination create a great variety of soil types, their combinations, and a unique mosaic of soil cover. V.V. Dokuchaev noted that all soil-forming agents are equivalent and take an equal part in soil formation; the absence of one of them excludes the possibility of the soil-forming process. At certain stages or under specific conditions of soil development, any one of the factors may act as a determining factor.
Soil-forming rocks. The importance of soil-forming, or parent, rock as a factor in soil formation lies in the fact that it is the source material from which soils are formed and the environment where the activity of living organisms occurs. However, the soil-forming rock is not the inert skeleton of the soil. 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, physico-chemical, 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, 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. For example, in the taiga-forest zone, low-fertility, 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.
Based on their origin, rocks are divided into three groups:
1) magmatic, formed when magma penetrates into the earth’s crust or erupts onto the surface (basic - basalt, gabbro; acidic - granite; ultrabasic - peridonite, dunite);
2) sedimentary rocks formed by mechanical or chemical deposition of 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, action of gases). The most common are schists, phyllites, gneisses, quartzites, and marbles.
In most of the Earth, soils were formed on sedimentary rocks. They cover about 75% of the surface of the continents. According to genetic characteristics, sedimentary rocks are divided into: clastic, or mechanical, chemical and organogenic.
Mechanical, or clastic, deposits were formed during the mechanical grinding (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 site of their formation. This material consists of fragments of different sizes. In mountainous terrain, eluvium is found at elevations. Soils formed on eluvial deposits are characterized by low fertility, low thickness, as well as gravelly and rockiness.
Diluvium- These are loose weathering products carried by temporary minor water flows flowing down the slopes during rains and spring snowmelt. This fine earth material is deposited at the base and bottom of slopes. Soils of fairly high fertility are formed on colluvial deposits.
Alluvium– deposits of river permanent water flows. These deposits are formed in river valleys during floods and are characterized by layering and sorting. There may be different particle contents - sandy in the near-river part of the floodplain and silty in the near-terrace part.
Lake sediments– sapropel, lake silts, marl. They are characterized by a clayey, less often fine-sandy composition with a significant amount of silt, carbonates or easily soluble salts. Quite fertile soils are formed.
Swamp sediments consist of peat and marsh silt.
Marine sediments found in the Caspian lowland, on the coast of the northern seas. These rocks are sorted, have different granulometric compositions, are layered and contain salts. Saline soils form on marine sediments.
Aeolian deposits are formed when sandy material is transported and deposited by the wind. Sand deposits occupy large areas in deserts. They form landforms such as dunes, dunes, and mounds.
On the vast plains, deposits of the Quaternary period are mainly widespread - glacial deposits, weathering products of various rocks transported and deposited by a glacier. They predominate in the composition of the soil-forming rocks of Belarus and are divided into moraine, water-glacial, and lacustrine-glacial. For moraines characterized by unsorting, heterogeneous mechanical composition, bouldering, enrichment in 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, smooth relief, boulder-free, poor in chemical composition, predominantly sandy. Lacustrine-glacial are deposits of shallow periglacial lakes. Characterized by a high content of silt fractions, boulder-free, rich in chemical composition, loam and sandy loam in mechanical composition, often carbonate, compacted, prone to waterlogging.
Loess-like loams and loess have different genesis. They are characterized by fawn or brownish-fawn color, carbonate content, loose composition, they are rich in chemical composition, often light loams, prone to erosion and the formation of ravines.
Chemical Sedimentary rocks arise by the deposition of substances at the bottom of reservoirs from solutions as a result of chemical reactions or changes in water temperature. Carbonate rocks are formed on the bottom of the seas partly during the precipitation of calcium carbonate salt from water, which comes along with river water. Most of the calcium carbonate deposited on the seabed is a product of the activity of certain organisms. Thus, in the Cretaceous period of the Mesozoic era, chalk deposits accumulated due to microscopic testate amoebae (foraminifera, etc.).
Organogenic rocks consist of waste products of animals and plants, as well as their undecomposed remains (peat). Many carbonate rocks (coral limestones, shell limestones, etc.) are formed with the participation of organisms whose skeletal or protective parts contain calcium carbonate.
When assessing soils, all parent rocks are divided (Fig. 2) into salted and unsalted. Saline rocks are deposits of long-dried sea basins or lakes; saline soils (salt marshes, solonetzes) can develop on them. On carbonate rocks, soils develop with a neutral reaction of the environment, which promotes the accumulation of humus in the soil (soddy-carbonate, etc.).
The most valuable soil-forming rocks are loess, loess-like loams and other carbonate rocks (glacial and lake sediments), as well as alluvial loams in river floodplains. The less valuable are non-carbonate cover loams, and the poorest are quartz sands (eolian 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 soil formation factors differ. On loamy rock, under herbaceous vegetation, soddy soil is formed; under forest, soddy-podzolic or other forest soil is formed.
2. The same soils can form on different rocks if other soil formation factors are the same. Under mixed coniferous-deciduous forest, soddy-podzolic soils are formed on sandy, sandy loam, loamy rocks.
However, exceptions are possible: the more active the soil formation process is, the weaker the influence of the rock, but if the chemical composition and physical properties of the rock are pronounced (carbonate rock), it has a long-lasting effect.
Climate is the long-term weather pattern of a particular area. In various natural conditions, the climate obeys the law of zonation. It depends on geographic latitude, altitude above sea level, landforms and distance from seas and oceans. Soil formation is most strongly influenced by temperature, precipitation, wind and air humidity. These elements, in combination with other soil-forming factors, determine a certain pattern in the distribution of soil cover.
Climate is related to the provision of energy to the soil - heat and, to a large extent, water. The activity of biological processes and the development of the soil-forming process depend on the annual amount of incoming heat and moisture and the characteristics of their daily and seasonal distribution.
Characteristics of the climate in terms of temperature and moisture conditions are of great importance. The following climatic groups are distinguished based on the sum of temperatures: above 10 o C 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 o. These climate groups are located in the form of latitudinal zones and are called soil-biothermal zones, which are characterized by certain types of vegetation and soils. Based on moisture conditions, climatic groups are distinguished: very wet– moisture coefficient> 1.33, humid humid – 1.00 – 1.33, semi-moist – 0,55 – 1 .00, semi-dry – 0.33 – 0.55, dry arid – 0.12 – 0.33, very dry –< 0,12. Humidity coefficient (HTC) is the ratio of precipitation to evaporation. The abundance of precipitation contributes to the washing of the soil and the removal of easily soluble salts to the lower horizons, including mineral substances formed during the decomposition of organic residues. In an arid climate, these compounds are not only not carried out, but, on the contrary, are able to accumulate 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. Direct effects are due to the direct effects of precipitation, heating and cooling on the soil. The indirect influence of climate is manifested through its impact on vegetation and fauna.
Thus, climate greatly influences the thermal, air and other soil regimes. The type of vegetation and 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 relief on the soil-forming process is mainly indirect, through the redistribution of heat and water that reaches the land surface. A significant change in the altitude of the area entails a significant change in temperature conditions and changes in moisture. Air masses, rising into the mountains, cool, which causes precipitation, and the air, having flown over the mountains, heats up again and becomes dry. This is associated with the phenomenon of vertical zonation of climate, vegetation and soils in the mountains.
Relief affects 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 and regulate the ratio of flowing, seeping 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, and on a convex slope, it flows off. Slopes of different exposures receive different amounts of solar energy. The southern slopes are always warmer and drier than the northern ones. The best conditions are found on the south-eastern slopes, which are warmed by the sun and moist soil. The greatest differences in temperatures are observed in the summer and can reach 5 - 7 o C on different slopes. Maximum temperatures are observed on the southwestern slopes, as the sun heats the already dry soil. Windward slopes receive more moisture than leeward ones. All this creates differences in hydration and affects the nature of the water, nutrient and air regimes. These factors create different conditions for the growth of vegetation, differences in the synthesis and decomposition of organic matter, and the transformation of soil minerals, which leads to the formation of different soils in different relief conditions.
Relief also affects the intensity of erosion. In a leaching water regime, slope forms of relief are a condition for the occurrence of water erosion of soils; in arid climates, flat forms favor the occurrence of wind erosion.
There are three groups of landforms: macrorelief– plains, mountain systems, plateaus that determine the general appearance and influence the climate of a large territory, mesorelief– average forms of relief against the general background of the 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 specific landscape, microrelief– landforms with height fluctuations of about 1 m: hillocks, hummocks, depressions, saucers, creating spotty soil cover.
Biological factors. The leading role in soil formation and the formation of soil fertility belongs to plants, microorganisms and animals. Each of these groups plays its role, but only through their joint activity does the parent rock turn into soil.
The role of plants in the formation of soils is multifaceted. Firstly, green plants synthesize organic matter. After the completion of the plant life cycle, part of the biomass in the form of root residues and ground litter returns annually to the soil. In the upper horizons, processes of transformation of organic matter take place and nutrients accumulate, the soil profile develops and soil fertility is formed. Each natural zone is characterized by specific combinations of herbaceous, shrub and woody vegetation, which vary greatly both in productivity and in the ratio and quantity of chemical elements in the plant material. Therefore, the roles of woody and herbaceous vegetation in soil formation processes are significantly different.
In forests, the total biomass is the greatest, but the annual growth, and therefore the litterfall, 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 above-ground mass. The litter of woody vegetation falls mainly on the soil surface, while that of herbaceous vegetation falls into the soil, which prevents its loss and ensures better and faster interaction with the mineral part of the soil and microorganisms. Coniferous litter, due to its chemical characteristics (low ash content combined with a small amount of calcium, containing a large number 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. Litter of herbaceous vegetation is characterized by a finer structure, lower mechanical strength, high ash content (10–12%), rich in nitrogen and bases, and quickly decomposes, mainly by bacteria. A “soft” calcium-rich humus, predominantly of the humate type, is formed. These factors are the reason for the low fertility of forest soils, while the biomass returning to the soil in meadow phytocenoses forms a thick humus horizon and fertile soil.
The process of soil formation under coniferous forests under leaching water conditions most often follows the type podzol formation. Emerging soils are characterized by high acidity, low humus content, unsaturation with bases, low content of nutrients, reduced biological activity and low level of fertility (podzolic, sod-podzolic). The soil-forming process occurring under the influence of herbaceous vegetation is called turf. As a result of this process, soils are formed with a high humus content, saturated with calcium, with a neutral or close to neutral reaction environment, rich in nutrients, and characterized by high natural fertility (chernozems, turf and various meadow soils). Under the cover of mixed and broad-leaved forests, gray forest or brown forest soils are formed with a less acidic reaction than podzolic soils, the degree of base saturation increases, the nitrogen content increases, and fertility increases.
Thanks to root secretions, plants enhance the process of destruction and transformation of sparingly soluble minerals and contribute to the formation of easily mobile compounds in the soil. All this is the result direct influence of vegetation on the soil-forming process. Indirect the impact on the soil is manifested in changes in thermal and water regimes.
Numerous and diverse soil fauna play a significant role in soil formation. These are protozoa (flagellates, ciliates, rhizomes), 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, forming the structure of the soil.
A completely unique and extremely important role in the processes of soil formation is played by microorganisms, which are the main destroyers of dead organic matter into simple final products (water, gases, mineral compounds). Microorganisms participate in the formation of salts from organomineral complexes, in the destruction and new 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 mass, regulates the nutrient and air regime of the soil, and determines the development of soil fertility. The number and species composition of microorganisms are used to judge the biological activity of soils, reserves of organic matter, content of nutrients, air and moisture availability. 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.
Different groups of microorganisms have a differential effect on soil formation. Bacteria are the most common group that carry out various transformations of organic matter in the soil, actively decomposing protein-rich residues, and fixing nitrogen gas. According to the need for free oxygen in the air, aerobic, anaerobic and facultative bacteria are distinguished; according to the method of nutrition, autotrophic and heterotrophic bacteria are distinguished. Autotrophic bacteria are divided into photosynthetic and chemosynthetic according to the method of obtaining energy. (nitrifying, sulfur bacteria, iron bacteria). Heterotrophic bacteria use ready-made organic matter for nutrition; under their influence, the most important processes of soil formation occur - the decomposition of organic residues and the biosynthesis of humus. Actinomycetes and fungi decompose fiber, lignin, waxes, resins, and actively participate in the formation of humus.
Algae are autotrophic photosynthetic organisms that participate in weathering processes and the primary soil-forming process. Lichens are symbiotic organisms, they penetrate into rocks with hyphae, as a result, more intense biological weathering and primary soil formation begin, and primitive soils are formed.
Age. Since the natural process of soil formation occurs over 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 each factor or their combination is manifested precisely in the temporal aspect. Thus, the soil as a natural-historical body has age. There are absolute and relative ages of soils. 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 soil will be. Conversely, soils where the soil-forming process began relatively later will be young. The most ancient are the soils of the southern latitudes (South America, Southeast Asia - 2 - 30 million years), the youngest are the middle and northern latitudes (10 thousand years), the youngest are the soils on alluvial deposits along the banks of rivers, on shallows. Relative age characterizes differences in the rate of soil formation of soils of the same 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 may be at different stages of development.
Human production activity. The ways and means of influencing the soil are extremely diverse. Mechanical processing with heavy agricultural machines, the application of organic and mineral fertilizers, plant protection products, drainage and irrigation, man-made disturbances - all this leads to changes in physical, chemical, biological and even morphological properties, and these changes occur much faster than in natural conditions. The water, air, and food regimes of cultivated soils change. In general, human activity is aimed at creating cultivated highly fertile soils where their natural fertility is low, and maintaining high productivity of soils with high fertility, which is exhaustible. If production activities are carried out without taking into account the development conditions and soil properties, then such negative consequences as salinization, erosion, waterlogging, pollution, soil dehumification, etc. arise.
All soil formation factors have a specific effect on the soil and cannot be replaced by 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 biological. In addition, the soil itself has a certain influence on soil formation factors, causing certain changes in them.
§2. Geological and biological cycles of substances
The formation and life of soil are inextricably linked with the processes of substance circulation. Before the appearance of green plants, various geological processes took place on the planet and there was geological the cycle of substances, which is a set of metabolic processes between land and sea and consists of:
1) continental weathering of rocks, resulting in the formation of mobile compounds; 2) transfer of these compounds from land to seas and oceans; 3) deposits of sedimentary rocks on the bottom of the oceans of the seas with their subsequent transformation; 4) new exposure of marine sedimentary and metamorphic rocks to the surface.
The geological cycle goes on for millions and billions of years, covering up to several kilometers of the lithosphere. Its driving force is weathering. 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. Rocks are jointly affected by living organisms, atmospheric water, gases and temperature. All these factors have a destructive effect on it 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 of physical weathering is fluctuations in daily and seasonal temperatures, the effect of freezing water, and wind. When heated, the minerals 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 occurs at points of contact between various minerals and rocks. When alternating heating and cooling, cracks form between the crystals. Penetrating into small cracks, water creates such capillary pressure that even the hardest rocks are destroyed. When water freezes, these cracks widen. In hot climates, water gets into the cracks along with dissolved salts, the crystals of which also have a destructive effect on the rock. Thus, over a long period of time, many cracks form, leading to its complete mechanical destruction. Destroyed rocks acquire the ability to pass and retain water. As a result of the fragmentation of massive rocks, the total surface area with which water and gases come into contact greatly increases. And this determines the occurrence 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 dissolved salts and carbon dioxide, as well as air oxygen. Chemical weathering includes the following processes: dissolution, hydrolysis, hydration, oxidation. The solvent effect of water increases with increasing temperature. If the water contains carbon dioxide, then minerals are destroyed faster in an acidic environment. As a result of weathering of igneous rocks, residual formations, redeposited sediments and soluble salts are obtained.
Before the emergence of life on the Earth, the destruction of rocks took place only in the two above-mentioned ways, but with the advent of organic life, new weathering processes arose - biological ones.
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 plant nutrients and organic matter accumulate in it.
The soil-forming process involves bacteria, fungi, actinomycetes, green plants, and various animals. 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 accessible to plants. Algae (diatoms, blue-greens, greens, etc.), mosses and lichens also destroy rocks.
Green plants secrete organic acids and other nutrients that interact with the mineral part, forming complex organomineral compounds. Root systems selectively absorb ash elements, and after the plants die, nitrogen, phosphorus, potassium, calcium, sulfur and other biogenic elements accumulate in the upper soil horizons. In addition, the roots of plants, especially trees, penetrating deep into rocks through cracks, exert pressure on the rocks and destroy them mechanically. Thus, under the influence of physical, chemical and biological weathering, rocks, when destroyed, become enriched with fine earth, clay and colloidal particles, acquire moisture capacity, absorption capacity, and 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 cycle of substances, there is a small biological the cycle of substances, which is the exchange of substances in the “soil-plant” system. The peculiarity of this cycle is the selectivity of 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 underlies agricultural production.
The cycles of substances are interconnected, the biological goes against the background of the geological, so substances can fall 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 formation process – this is a set of phenomena of transformation and movement of substances and energy occurring in the soil layer (A.A. Rode). Soil formation begins from the moment living organisms settle on rocks or their weathering products. Any soil-forming process, according to A.A. Roda, is composed of a combination elementary soil-forming processes(EPP) of the first and second order. 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) moisture entry into the soil ↔ moisture consumption from the soil;
5) the arrival of radiant energy on the soil surface and heating ↔ radiation of energy by the soil and cooling.
The first three pairs of elementary processes are determined by food processes, the fourth pair by water, and the fifth pair by thermal regimes of the soil. The soil-forming process is qualitatively the same in all soils, but differs quantitatively (by the rate of occurrence), i.e. In different soils, the process of soil formation is different, and even in the same soil at different depths it proceeds differently. Therefore, any soil is a series of sequentially replacing each other vertically. genetic horizons– layers into which the parent rock is divided during the process of soil formation. The entire cumulative sequence of horizons is called soil profile. Horizons are called genetic because they are connected by a common origin.
ESPs have their own characteristics at different stages of soil emergence and development, which allows us to talk 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 the rock, is characterized by low activity and volume of the biological cycle, active non-biological EPP of the first order (dissolution, precipitation, hydration, diffusion, etc.), a weak connection of these processes with each other, therefore the parent rock at this stage does not have clearly defined soil characteristics, and the profile is very weakly divided into horizons;
2) soil development stage characterized by an increase in the activity and volume of the biological cycle through the activity of higher plants, nutrients accumulate. Therefore, the intensity and direction of development of soil formation processes here depends primarily on the nature of the vegetation. At this stage, second-order EPP, or private soil-forming processes (meso- and macroprocesses), predominate. 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), and a mature soil with a characteristic profile and set of properties is formed. The development stage can last hundreds, thousands or more years.
The main private soil-forming processes include:
● turf– the process of intensive humus formation and accumulation of nutrients. It develops under perennial herbaceous vegetation in a moderately humid climate, most intensively under non-percolative water regime on carbonate rocks in the steppe zone, where ordinary chernozems are formed. In the forest-steppe, typical chernozems are formed, in the taiga-forest zone on the floodplain meadows of the river floodplain - soddy floodplain soils, outside the floodplains on carbonate rocks - soddy-carbonate soils, on non-carbonate soils - soddy-podzolic soils;
● podzolization– the process of removal of destruction products of primary and secondary minerals from the upper soil horizons into underlying or groundwater with a relative accumulation of silica. In its pure form, it develops under the canopy of a coniferous forest with poor grass cover in a humid climate with a leaching type of water regime on non-carbonate rocks and causes the formation of podzolic soils;
● lessivage– associated with podzolization, a complex process of 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;
● swamp– develops under the influence of marsh vegetation in conditions of constant excess moisture with the process of peat formation and gleying. In the conditions of Belarus, as a result of the swamp process, swamp-podzolic, peat-swamp, sod and sod-podzolic swamps, alluvial swamps are formed. The process takes place under anaerobic conditions with the obligatory participation of fungi and bacteria;
● peat formation – biochemical process of transformation and preservation 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 when soils are waterlogged under anaerobic conditions with the participation of microorganisms. The soil acquires bluish, 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 under humid and warm climates. On such soils there is also an intensive turf process with the formation of red soils and yellow soils in the subtropics and ferrallitic soils in the humid tropics;
● solonetzic – the process of accumulation of easily soluble salts (chlorides, sulfates, etc.) in the soil profile under the effusion type of water regime under conditions of mineralized groundwater or saline soil-forming rocks. Salt marshes are formed, with desalinization - solonetzes, with further washing - malt;
3) stage of equilibrium functioning(formed soil) occurs when, according to the main parameters (the amount of humus, the thickness of genetic horizons, the amount of basic nutrients, etc.), a dynamic equilibrium is achieved with the existing complex of soil formation factors, and lasts indefinitely. At this stage, the biological cycle proceeds in such a way that each subsequent cycle practically repeats the previous one. All micro-, meso- and macroprocesses are coordinated in time and space and form a complex biogeochemical cycle that contributes to the restoration of the natural properties of the soil.
§4. Morphological characteristics 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, characteristics that distinguish it from the parent rock. They indicate the direction and degree of expression of the soil-forming process. These features include: 1) 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.
Structure and thickness of the soil profile. Each soil type has a certain vertical sequence of genetic horizons, the entirety of which is called a soil profile. The formation of horizons is associated with the movement of various substances (upward or downward current) through the soil layer and the layer-by-layer distribution of living organisms. Genetic horizons are represented by homogeneous horizontal layers of soil that differ in morphological characteristics, composition and properties. Each horizon has its own name and is designated by the initial letters of the Latin alphabet. A horizon can be divided into subhorizons, to designate which and reflect their specific properties, additional digital and letter indices are used.
Below is a system for identifying the main types of soil horizons.
A - humus - the surface horizon of accumulation of organic matter, humus and nutrients accumulate in it. Depending on its nature, the following are distinguished:
A O – forest floor, consisting of decaying forest litter (leaves, pine 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 occurs;
And the groin - arable– surface humus horizon transformed by periodic cultivation in agriculture.
In bog soils, the upper horizon consists of peat - a mass of semi-decomposed plants.
T 1 – undecomposed peat – plant remains have completely retained their original shape;
T 2 – peat medium decomposed – plant remains only partially retained their shape in the form of tissue scraps;
T 3 – decomposed peat – a solid organic spreadable 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 destruction products. It is located under the humus horizon and has a light color (gray, whitish, fawn); origin may be podzolic(acid hydrolysis of minerals and removal of destruction products), lonesome(alkaline hydrolysis of minerals). Under the A2 horizon (in podzolic, gray forest soils, malts), horizon B is formed, which differs in its properties from any surface horizon.
IN - illuvial horizon into which soil formation products are washed and partially accumulate. Depending on the washed-in substances, the following types of illuvial horizon are distinguished:
B h – illuvial-humus the horizon is coffee-colored due to the content of ferrous-humic substances;
B f – illuvial-ferruginous an ocher or brown horizon containing ferruginous products of destruction of the mineral part of the upper horizon;
In Sa – illuvial-carbonate horizon, often containing new carbonate formations in the form of a loose accumulation of calcium carbonates.
In soils without an eluvial horizon (chernozems, chestnut soils), in which vertical movement of substances does not occur, horizon B is called transitional from humus-accumulative to parent rock.
G – gley horizon - is formed in swampy and swampy soils under conditions of constant excess moisture. It is colored in bluish, bluish tones by the ferrous compounds of iron (II) and manganese formed here. It is characterized by its structurelessness and low porosity.
Under conditions of temporary excess moisture, gleying may also appear in other horizons of the profile. In this case, the letter “g” is added to the main index, for example A 2 g, B g.
WITH - parent rock – a horizon that is weakly affected by soil-forming processes and does not have the characteristics of the soil horizons described above.
D – underlying rock - stands out when soil horizons were formed on one rock, and below lies another rock with different lithological properties.
The transition from one horizon to another in different soils can be different: abrupt, clear, noticeable or gradual. That's why nature of the transition between soil horizons in a profile has 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 parent 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 occur in the upper part of the rocks, above the permafrost, so the thickness of the entire soil here is insignificant (20–30 cm). In the steppes, under lush grassy 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, consequently, large reserves of nutrients. The poverty and low production value of, for example, podzolic soils is determined by the clearly defined eluvial horizon from which nutrients have been washed away.
Field studies can reveal the presence carbonates in the soil and their depth using 10% HC1. To do this, drop an acid solution onto the wall of the soil cut and determine the depth from which boiling, and its intensity.
Soil coloring has great diagnostic significance, since it reflects its chemical and mineralogical composition and is the basis for dividing the soil mass into horizons. All the variety of soil colors can be reduced to three main 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% it is dark gray, dark brown or chestnut. Soils with low humus content have a color characteristic of the soil-forming rock. The intensity of the black color will also be affected by the type of humus; soils with the same quantitative content of humus with the fulvate type will be lighter than soils with the humate type. Some soils are given a black color by dark primary minerals, manganese sulfides, and 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 excess moisture. Soils of this color are classified as gleyic or gleyed. Heterogeneous, spotty coloring is a consequence of alternating processes of oxidation and reduction. When describing morphological characteristics, they usually indicate the degree of color (dark brown, light chestnut) or note the shade (whitish with a yellowish tint). It should be borne in mind that it depends on humidity: wet soil is darker than dry soil. Soil moisture content can be dry(gathers dust) , fresh(cools the hand), wet (when squeezed in the hand, moisture is felt, the paper pressed to the soil 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 soil to break down into separate aggregates is called structure, and the set of aggregates is the soil structure. There are structureless soils (mechanical elements are not combined into aggregates) and structural ones. Structureless soils have many unfavorable properties: low water and air permeability, when it rains they float, become viscous, when dry they quickly lose moisture, and merge into one mass that is difficult to process. Structural in the agronomic concept is soil in which medium-sized aggregates (0.25 - 10 mm) predominate (at least 55%) and are characterized by properties opposite to structureless soil.
Based on the shape of the aggregates, three types of structure are distinguished:
1) cuboid– aggregates are developed equally along all three axes and resemble a cube, divided into nut-shaped, lumpy, granular, blocky;
2) prism-shaped– the aggregates are developed along the vertical axis and resemble a prism, divided into columnar and prismatic;
3) plate-shaped– aggregates are developed along a horizontal axis, and can be plate-like or scaly.
Agronomically, the cube-shaped structure is more valuable, as it creates the most valuable water-air regime. One of the main conditions for the formation of structural soil is the presence in it of a sufficient amount of silt 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. Acid soils have a plate-like structure, alkaline soils have a prism-shaped structure, and neutral and close to neutral soils have a cuboid structure.
Addition – These are external signs of the nature of porosity and degree of soil density. It depends on the properties of the parent rock, particle size distribution, soil structure, as well as the activity of soil fauna and plant roots. Based on the degree of density, a distinction is made between very dense, dense, loose and crumbly.
Crumbly the composition is characteristic of sandy soils devoid of humus. Under mechanical influence, even a small one, they are characterized by flowability, i.e. break down into individual elements.
Loose the composition is characteristic of loamy and clayey soils with a well-defined structure, as well as the upper horizons of sandy and sandy loam soils enriched with humus. This is the structure of arable horizons after cultivation in a ripe state. A shovel penetrates such soils easily.
Dense the composition is typical for the illuvial horizons of most loamy and clayey soils. Digging with a shovel requires significant effort.
Very dense or merged, the composition is characteristic of cohesive clayey structureless soils, as well as illuvial horizons of some solonetzic soils. It is impossible to dig such soils with a shovel; you have to use a crowbar or a pick.
Soil composition is an important agronomic feature that determines porosity and, consequently, aeration, water permeability, and soil resistance during cultivation.
Neoplasms – These are accumulations of substances that differ from the soil material containing them in composition and composition. They are formed as a result of physical, chemical and biological soil-forming processes. TO chemical neoplasms include easily soluble salts, gypsum, lime carbonate, iron compounds, silica and other substances.
Easily soluble salts characteristic of saline soils. They occur in the form of white crusts on the soil surface or in the form of deposits, veins, and grains in the thickness of the profile. Gypsum found 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 in color are found in the form of sharply defined white spots, in the form of mold, dense accumulations of lime of various shapes. They are determined by boiling with a 10% solution of hydrochloric acid.
Iron hydroxides found in podzolic, soddy-podzolic and swampy soils in the form of dark brown rounded solid nodules and vaguely shaped spots. Sandy soils are characterized by ortzands - brown cemented layers of iron hydroxide. Iron compounds of bluish, bluish or greenish color are characteristic of gleyic 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 origins include: coprolites - excrement of worms and larvae in the form of glued water-resistant lumps; molehills - passages of moles, gophers, marmots, hamsters, covered with soil; roots - traces of rotten large roots; wormholes - wormholes; dendrites - dark imprints of small roots in the form of a pattern.
Each soil has its own special set of new formations 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 the formation of soils and soil fertility is extremely complex and diverse; microbes, being the oldest organisms on the globe, existing for billions of years, are the most ancient soil formers, operating long before the appearance of higher plants and animals. The consequences of the vital activity of microorganisms go far beyond the soils they inhabit and largely determine the properties of sedimentary rocks, the composition of the atmosphere and natural waters, and the geochemical history of elements such as carbon, nitrogen, sulfur, phosphorus, oxygen, hydrogen, calcium, potassium, and iron.
Microorganisms are biochemically multifunctional in their properties and are capable of carrying out processes in the biosphere and soils that are inaccessible to plants and animals, but which are an essential part of the biological cycle of energy and substances. These are the processes of nitrogen fixation, oxidation of ammonia and hydrogen sulfide, reduction of sulfate and nitrate salts, and precipitation of iron and manganese compounds from solution. This also includes 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 rocks, agents of so-called biological weathering.
However, the most important 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 the 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. The synthesis of physiologically active compounds, humus formation and complete mineralization of organic residues is the main function of 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 wet weight of various microorganisms can be up to 10 t/ha in the upper 25-centimeter soil layer. Macca microorganisms account for 0.5-2.5% of the weight of humus in soils. Moreover, 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 the microorganisms present in them. Highly fertile cultivated soils are the richest in a variety of microorganisms. As new methods for studying microorganisms develop, it becomes clear that our current knowledge is still extremely insufficient. Apparently, the role, number and functions of microorganisms in soil formation are much greater than we currently imagine.
Among soil microorganisms there are both representatives of the plant world and representatives of the animal world (Fig. 52). The most numerous microflora are fungi, actinomycetes and bacteria. Algae are much less common. The microfauna is dominated by amoebas and flagellates. Ciliated and micronematodes are also sometimes found in large numbers in soils. More and more data are accumulating on the presence of non-cellular forms of microorganisms (bacteriophages, viruses) in soils.
Soil algae
Soil algae are single- and multicellular microorganisms (sometimes mobile) that have specific pigments such as chlorophyll, which ensure the assimilation of carbon dioxide and photosynthesis of organic matter. Algae, unlike most other microorganisms, contribute to the enrichment of soils with organic matter and oxygen.
Algae inhabit mainly the upper illuminated soil horizons, although occasionally they can be found at a depth of up to 30-50 cm. Depending on the type of pigments, algae are distinguished as green, blue-green, purple, and yellow. In 1 g of soil there can be up to 300 thousand unicellular algae. The role of unicellular microalgae is especially evident on the surface of barren clayey soils of deserts - takyrs, on solonetzes, on fresh alluvial deposits in shallow waters. Using the emerging moisture, microalgae enrich the surface with fresh organic matter, cause increased destruction of primary minerals, and increase the dispersion of the solid phase. Some algae play a significant role in the transformation of silica compounds (diatoms) and calcium in the soil, others have the ability to fix nitrogen.
Blue-green algae (India, Japan, Indonesia) living in rice fields and alluvial soils of river valleys in the tropics are especially important in the balance of soil nitrogen. They supply nitrogen and oxygen to the soils and plants of these lands in significant quantities, maintaining their fertility. Compared to other microorganisms, the importance of algae in soil formation is still relatively limited. This is explained by the fact that the total amount of algae biomass averages 0.5-1 t/ha.
Soil mushrooms
Bacteria
Bacteria are the most numerous and most diverse tiny single-celled organisms that inhabit soils. Their size is very small - 0.5-2 microns.
Bacteria, together with algae, fungi and protozoa in soils, perform the function of humus formation and complete mineralization of organic matter. About 50 genera and up to 250 species of soil bacteria have been described. Among the many groups of bacteria, two or three are of special importance in soil formation: true bacteria, actinomycetes and myxobacteria. True bacteria are divided into two groups - non-spore and spore. The nonspore group includes autotrophic bacteria that themselves synthesize organic matter and therefore can exist in an environment where any form of organic matter is completely absent. These are bacteria that oxidize hydrogen (Bacterium hydrogenius), carbon compounds (Bact. methanicus), iron bacteria and sulfur bacteria that oxidize iron and sulfur, nitrifying bacteria that oxidize ammonia into nitrites and the latter into nitrates (Table 29). The role of autotrophic bacteria was especially significant before the emergence of algae and green plants that synthesize organic substances.
The same group of non-spore bacteria includes the so-called semiautotrophs, which fix nitrogen from the soil air, but at the same time require organic matter. Nitrogen-fixing bacteria live either freely or in symbiosis with leguminous plants, forming peculiar nodules and nodules on the roots. Bacteria of the genus Phizobium Azotobactcr and Clostridium live freely in the soil and fix nitrogen in the soil air. Over the course of a year, these microorganisms can accumulate up to 50-300 kg/ha of nitrogen in the soil, destroying and oxidizing a proportional amount of organic matter. This is the basis for the practice of adding plant matter (straw, leaves, green fertilizers, etc.) to the soil, which provides “feeding” of nitrogen fixers and activates their activity. To enhance nitrogen fixation in the fields, special bacterial fertilizers are used.
Actinomycetes are considered as organisms transitional between bacteria and fungi. They are typical heterotrophic organisms. In shape, they are branched unicellular organisms, somewhat larger in size than true bacteria. The thinnest hyphae (less than 1 micron) are quite long. From this group of bacteria, Waksman isolated strains of streptomycetes that produce the famous antibiotic streptomycin, which has enormous activity. Some species of actinomycetes are used to produce vitamins. Actinomycetes give soils the characteristic smell of freshly plowed soil. In soil, actinomycetes are closely associated with decaying organic matter, breaking down and consuming fiber, hemicellulose, proteins and, apparently, even lignin. Actinomycetes are aerobic microorganisms and play a major role in soils of dry, hot climates.
Spore-bearing bacteria are, according to S.N. Mishustin, a sensitive indicator of the direction of the soil-forming process, the age of soils, and the degree of their cultivation. Some microbiologists introduced the concept of soil biogenicity and the bioorgano-mineral complex of soils. The latter includes surface layers of minerals, organic and organomineral colloids, microorganisms, water and gases. The higher the soil biogenicity, the higher their fertility. Cultivated and irrigated soils always have relatively higher biogenicity. Active production of carbon dioxide in soils is one of the indicators of their biogenicity. Carbon dioxide is a universal metabolic product of soil organisms. The annual production of CO2 in soil can reach 3-4 and even 8 thousand l/ha. Carbon dioxide in ground air is a product of the metabolism of soil organisms and the result of mineralization of organic compounds.
Agricultural plants on highly biogenic soils such as chernozems and valley meadow soils, thanks to the work of microorganisms, are provided with physiologically active compounds, nitrogen and phosphorus nutrition and a relatively increased concentration of carbon dioxide, which is so necessary for photosynthesis. Cultivated soils, as a rule, are rich in bacterial microorganisms, contain active forms of Azotobacter and are enriched with physiologically active compounds. In the frozen acidic soils of the north and in peats, due to the low activity of microorganisms, plants are poorly provided with hormonal and vitamin nutrition, as well as mineral compounds of nitrogen and phosphorus. Surface air in the Arctic has a 2 times lower concentration of carbon dioxide (according to A.A. Grigoriev - 0.16% instead of 0.03%). This significantly reduces the soil fertility of the north as a whole. The soils of deserts, especially subtropical and tropical ones, due to dryness and heating to 70-80 ° C, are also depleted in bacteria.
Viruses (bacteriophage)
Microorganisms are invisible to the eye, and therefore people tend to underestimate their role in the biosphere and soil formation. Meanwhile, from what is stated above, it is obvious that microorganisms are an essential component of any natural biogeocenosis. Both trophic chains and ecological pyramids, illustrating the process of destruction of biomass and redistribution of energy accumulated in the phytomass and zoomass of each landscape, include complex links in the world of microorganisms.
Unlike the animal world, many autotrophic microorganisms replenish to some extent biomass and accumulated energy reserves, extending the biogenic cycle of biosphere substances in its soil part. Microbiomass in terrestrial soils by weight is in absolute numbers about 1 * 10 9 t, which in relation to phytobiomass is equal to only 0.0001%, however, the amazing rate of reproduction and generational changes in microorganisms is so high that the geochemical and soil significance of the activity of microorganisms in biosphere is equivalent to the value of plant activity and, perhaps, even exceeds it.
18. The role of higher plants in soil formation
Higher plants play a colossal role in soil formation. Biological cycle. Plants absorb nutrients at the ion level and absorb nutrients from aqueous solutions.
The role of higher plants in soil formation
The main part of the living matter of land is formed by higher plants, including woody vegetation. Higher plants as generators of organic matter. The formation of organic matter is mainly associated with photosynthesis, a process carried out in the green parts of plants with the participation of chlorophyll. Plants, absorbing carbon dioxide from the atmosphere and water, synthesize organic matter according to the scheme:
Light, chlorophyll
6СО 2+ 6H 2 O + 674 kcal → C 6 H 12 O 6 + 6O 2
To carry out this complex reaction, the energy of sunlight is used. A variety of compounds are created in plant cells - carbohydrates, fats, proteins, etc. Every year, higher sushi plants synthesize about 10 10 T dry organic matter. The amount of annual vegetation productivity varies greatly depending on geographical conditions. At the same time, the spatial and genetic connection between communities of higher plants and certain soils has long attracted attention and was noted by M. V. Lomonosov.
From perennial tree species, only a small part of their biological mass enters the soil each year in the form of litter of dying parts, mainly above-ground ones. Shrub vegetation annually loses a significantly larger part of its biomass, and herbaceous vegetation dies off almost completely.
To assess the dynamics of organic matter in the plant-soil system, the following indicators are used:
Biological mass (biomass) is the total amount of living organic matter of plant communities. The structure of biomass is important - the ratio of organic matter in the above-ground parts and roots of plants.
Dead organic matter is the amount of organic matter contained in dead parts of plants, as well as in litter products accumulated on the soil (forest litter, steppe felt, peat horizon).
Annual growth is the mass of organic matter growing in the underground and above-ground parts of plants per year.
Decay-the amount of annually dying organic matter per unit area (usually in centners per hectare).
The dying organic matter of forest communities is represented mainly by above-ground parts (needles, branches, bark), while roots are important in the composition of litter in herbaceous communities.
The ratio of litter to biomass shows how firmly organic matter is retained by a given plant community. Calculations show that temperate forests hold organic matter most firmly. For example, spruce forests of the northern taiga spend 4% of organic matter of biomass on litter, spruce forests of the southern taiga - about 2%, and oak forests - only 1.5%. In tropical rainforests, 5% of the biomass is lost to litter, in savannas - 17%, the herbaceous vegetation of the steppes spends 43-46% of the total biomass on litter.
Higher plants as concentrators of ash elements and nitrogen. Through their vital activity, plants determine an extremely important process - biogenic migration of chemicals elements.
(The main chemical elements of all organic substances are carbon, oxygen and hydrogen, constituting about 90% of the weight of the dry matter of plants. Plants obtain these elements from the atmosphere and water. But plants contain nitrogen, phosphorus, potassium, calcium, sodium, magnesium, chlorine , sulfur and many others, i.e. almost all currently known chemical elements. They are not random impurities and contaminants, but have a certain physiological significance. Chemical elements contained in plants in fairly significant quantities are part of common organic compounds . Unlike carbon, oxygen, hydrogen and nitrogen, most of the chemical elements contained in plants remain in the ash when burned and are therefore called ash elements. Ash elements are extracted by plants from the soil and are part of organic matter. After dying, the organic matter enters soil, where it undergoes deep transformation under the influence of microorganisms. In this case, a significant part of the ash elements passes into forms available for absorption by plants, and partially re-enters the growing organic matter, while some is retained in the soil or removed with filtered water. As a result, there is a natural migration of ash chemical elements in the soil - vegetation - soil system, called by V. R. Williams the biological (or small) cycle.
In the process of long evolution, various groups of plants have developed the ability to absorb certain chemical elements. Therefore, the chemical composition of the ash of different plants has significant differences. For example, increased accumulation of silicon was found in the ash of cereals, potassium in the ash of umbellifers and legumes, and sodium and chlorine in the ash of quinoa. The famous Soviet soil scientist and geochemist V. A. Kovda calculated the composition of ash elements of various groups of plants.
The unequal chemical composition of plant ash causes differences in the composition of ash elements in the litter of the main plant communities.
No matter how important the redistribution of chemical elements in the biological cycle system is for soil formation, the role of higher plants in soil formation is not limited to this. It is known how important vegetation is for regulation of runoff and soil erosion! although different plant groups do not equally protect the soil from water and wind erosion.
Participation of animals in soil formation. The main function of soil animals is the transformation of organic matter. This process is carried out thanks to food chains. Herbivores synthesize zoomass, which is subsequently consumed by predators and animals that exist through the use of metabolic products and death. Since at each link of the food chain from 50 to 90% of the energy contained in the consumed biomass is lost, so-called ecological pyramids are formed. Therefore, the amount of zoomass is significant less amount of phytomass and amounts to several billion tons.
The smaller the organisms, the greater their number in the soil. Protozoa are found in numbers of more than a million copies in 1 G soil.
The digging activity of soil animals is also important for soil formation.
Worms are one of the most common groups of soil animals. They are kept in numbers of many thousands and even up to several million individuals per 1 ha. Charles Darwin attached great importance to the activity of worms. According to his calculations, the soil mass completely passes through the organisms of worms within several years. It has been established that worms can process 1 ha up to 50-380 T soil, creating a fine-lumpy structure and in a certain way changing plant residues in quantities of up to 5 t/ha.
In steppe soils, significant work is carried out by rodents - shrews. In some cases, the passages of shrews are so numerous that “mole black soils” are mentioned in the literature.
Microelements in plant and animal organisms
Some chemical elements are part of special compounds that can regulate vital biochemical processes. These are vitamins, enzymes and hormones. These substances play the role of natural catalysts in living organisms. A number of important biological processes are possible only in the presence of these compounds. Thanks to these elements, vitamins, enzymes and hormones acquire their special activating properties.
Chemical elements that are part of organic compounds as biochemical activators are called microelements. Among them, many trace elements are known (molybdenum, copper, cobalt, etc.), as well as chemical elements contained in the earth’s crust in quantities significantly greater than 0.01% (for example, iron).
The vigorous absorption of trace elements by plants is reflected in their increased content in the upper part of the soil, enriched with dead remains of plant and animal organisms.
Not only vegetation, but also soil animals contribute to the accumulation of certain chemical elements in the soil. The analyzes showed that the soil fauna accumulates certain elements