Find out the composition of the soil. What is soil made of? Find out the composition of the soil Inorganic components of the soil

What is soil made of? It would seem a simple question. We all know what it is. Every day we walk along it, planting plants in it that give us a harvest. We fertilize the soil, dig it up. Sometimes you can hear that the land is infertile. But what do we really know about soil? In most cases, only what is most upper layer earth's surface. And this is not so much. Let's figure out what components the earth consists of, what it can be and how it is formed.

Soil composition

So, the soil is the top fertile soil. It consists of various components. In addition to solid particles, it includes water and air, and even living organisms. Actually, the latter play a crucial role in its formation. The degree of its fertility also depends on microorganisms. In general, soil consists of phases: solid, liquid, gaseous and “living”. Let's look at what components form them.

Solid particles include various minerals and chemical elements. B includes almost the entire periodic table, but in different concentrations. The degree of soil fertility depends on the component of solid particles. The liquid components are also called soil solution. This is water in which chemical elements dissolve. There is liquid even in desert soils, but there are tiny amounts of it.

So, what is soil made of, besides these basic components? The space between solid particles is filled with gaseous components. Soil air consists of oxygen, nitrogen, carbon dioxide, and thanks to it, various processes occur in the soil, such as respiration of plant roots and rotting. Living organisms - fungi, bacteria, invertebrates and algae - actively participate in the process of soil formation and significantly change its composition by introducing chemical elements.

Mechanical structure of soil

What the soil consists of is now clear. But is its structure homogeneous? It's no secret that soil varies. It can be sandy and clayey or rocky. So, soil consists of particles different sizes. Its structure may include huge boulders and tiny grains of sand. Typically, particles in the soil are divided into several groups: clay, silt, sand, gravel. This is important for agriculture. It is the structure of the soil that determines the degree of effort that must be applied to cultivate it. It also determines how well the soil will absorb moisture. Good soil contains equal percentages of sand and clay. Such soil is called loamy. If there is a little more sand, then the soil is crumbly and easy to work with. But at the same time, such soil retains water and minerals less well. Clay soil is damp and sticky. It drains poorly. But at the same time, it contains the most nutrients.

The role of microorganisms in soil formation

Its properties depend on what components the soil consists of. But this is not the only thing that determines its qualities. Organic substances enter the soil from the dead remains of animals and plants. This happens thanks to microorganisms - saprophytes. They play a vital role in decomposition processes. Thanks to their active activity, so-called humus accumulates in the soil. This is a dark brown substance. Humus contains fatty acid esters, phenolic compounds and carboxylic acids. In the soil, particles of this substance stick together with clay. It turns out to be a single complex. Humus improves the quality of the soil. Its ability to retain moisture and minerals increases. In swampy areas, the formation of humus mass occurs very slowly. Organic residues are gradually compressed into peat.

Soil formation process

The soil forms very slowly. In order for a complete renewal of its mineral part to occur to a depth of approximately 1 meter, it takes at least 10 thousand years. What the soil consists of are the products of the constant work of wind and water. So where does soil come from?

First of all, these are particles of rocks. They serve as the basis of the soil. Under the influence of climatic factors, they are destroyed and crushed, settling on the ground. Gradually, this mineral part of the soil is populated by microorganisms, which, by processing organic remains, form humus in it. Invertebrates, constantly digging passages in it, loosen it, promoting good aeration.

Over time, the structure of the soil changes and it becomes more fertile. Plants also influence this process. As they grow, they change its microclimate. Human activity also influences soil formation. He cultivates and cultivates the land. And if the soil consists of infertile components, then a person fertilizes it by introducing both mineral and organic fertilizers.

by composition

In general, there is currently no generally accepted classification of soils. But it is still customary to divide them according to their mechanical composition into several groups. This division is especially relevant in agriculture. So, the classification is based on how much clay the soil consists of:

Loose sandy (less than 5%);

Cohesive sandy (5-10%);

Sandy loam (11-20%);

Light loamy (21-30%);

Medium loamy (31-45%);

Heavy loamy (46-60%);

Clayey (more than 60%).

What does the term “fertile” soil mean?

What parts the soil consists of affects the degree of its fertility. But what makes the earth such? The composition of the soil directly depends on many factors. This includes the climate, the abundance of plants, and the presence of living organisms that live in it. All this affects the chemical The degree of its fertility depends on which components are contained in the soil. Mineral components such as calcium, nitrogen, copper, potassium, magnesium, and phosphorus are considered very useful for high yields. These substances enter the ground during the decomposition of organic matter. If the soil is rich in mineral compounds, then it is fertile. Plants will bloom wildly on it. This soil is ideal for growing vegetable and fruit crops.

Chapter 4. SOIL ORGANIC MATTER AND ITS COMPOSITION

§1. Sources of organic matter and its composition

The most important component of the soil is organic matter, which is a complex combination of plant and animal residues at various stages of decomposition, and specific soil organic matter called humus.

A potential source of organic matter is considered to be all components of the biocenosis that fall on or into the soil (dying microorganisms, mosses, lichens, animals, etc.), but the main source of accumulation of humus in soils are green plants, which are annually left in the soil and on it. the surface contains a large amount of organic matter. The biological productivity of plants varies widely and ranges from 1–2 t/year of dry organic matter (tundra) to 30–35 t/year (humid subtropics).

Plant litter varies not only quantitatively, but also qualitatively (see Chapter 2). The chemical composition of organic substances entering the soil is very diverse and largely depends on the type of dead plants. Most of their mass is water (75–90%). The composition of dry matter includes carbohydrates, proteins, fats, waxes, resins, lipids, tannins and other compounds. The vast majority of these compounds are high molecular weight substances. The bulk of plant residues consists mainly of cellulose, hemicellulose, lignin and tannins, with tree species richest in them. Protein is most found in bacteria and legumes, the smallest amount is found in wood.

In addition, organic residues always contain some ash elements. The bulk of ash consists of calcium, magnesium, silicon, potassium, sodium, phosphorus, sulfur, iron, aluminum, manganese, which form organomineral complexonates in humus. The content of silica (SiO 2) ranges from 10 to 70%, phosphorus - from 2 to 10% of the ash mass. The name ash elements comes from the fact that when plants are burned, they remain in the ash rather than volatilize, as happens with carbon, hydrogen, oxygen and nitrogen.

In very small quantities microelements are found in the ash - boron, zinc, iodine, fluorine, molybdenum, cobalt, nickel, copper, etc. The highest ash content is found in algae, cereals and leguminous plants, the least amount of ash is contained in wood coniferous species. The composition of organic matter can be represented in the following way(Fig. 6).

§2. Transformation of organic matter in soil

The transformation of organic residues into humus is a complex biochemical process that occurs in the soil with the direct participation of microorganisms, animals, air oxygen and water. In this process, the main and decisive role belongs to microorganisms that participate in all stages of humus formation, which is facilitated by the huge population of soil microflora. Animals inhabiting the soil also actively participate in the conversion of organic residues into humus. Insects and their larvae, earthworms crush and grind plant residues, mix them with soil, swallow, process and throw away the unused part in the form of excrement into the soil.

When dying, all plant and animal organisms undergo decomposition processes into simpler compounds, the final stage of which is complete mineralization organic matter. The resulting inorganic substances are used by plants as nutrients. The rate of decomposition and mineralization processes of various compounds is not the same. Soluble sugars and starch are intensively mineralized; Proteins, hemicelluloses and cellulose decompose quite well; resistant - lignin, resins, waxes. Another part of the decomposition products is consumed by the microorganisms themselves (heterotrophic) for the synthesis of secondary proteins, fats, carbohydrates, which form the plasma of new generations of microorganisms, and after the death of the latter, they again undergo the process of decomposition. The process of temporary retention of organic matter in a microbial cell is called microbial synthesis. Some of the decomposition products turn into specific complex high-molecular substances - humic substances. The set of complex biochemical and physicochemical processes of transformation of organic matter, as a result of which specific soil organic matter is formed - humus, is called humification. All three processes occur in the soil simultaneously and are interconnected. The transformation of organic matter occurs with the participation of enzymes secreted by microorganisms and plant roots, under the influence of which biochemical reactions of hydrolysis, oxidation, reduction, fermentation, etc. are carried out. and humus is formed.

There are several theories of humus formation. The first to appear in 1952 was condensation theory developed by M.M. Kononova. In accordance with this theory, the formation of humus occurs as a gradual process of polycondensation (polymerization) of intermediate products of the decomposition of organic substances (first, fulvic acids are formed, and from them humic acids are formed). Concept biochemical oxidation developed by L.N. Alexandrova in the 70s of the XX century. According to it, the leading role in the process of humification is played by the reactions of slow biochemical oxidation of decomposition products, as a result of which a system of high molecular weight humic acids of variable elemental composition is formed. Humic acids interact with the ash elements of plant residues, released during the mineralization of the latter, as well as with the mineral part of the soil, forming various organomineral derivatives of humic acids. In this case, a single system of acids is split into a number of fractions that differ in the degree of solubility and molecular structure. The less dispersed part, which forms water-insoluble salts with calcium and sesquioxides, is formed as a group of humic acids. The more dispersed fraction, which produces predominantly soluble salts, forms the fulvic acid group. Biological The concepts of humus formation assume that humic substances are products of the synthesis of various microorganisms. This point of view was expressed by V.R. Williams, it was developed in the works of F.Yu. Geltser, S.P. Lyakh, D.G. Zvyagintsev and others.

In various natural conditions character and speed humus formation is not the same and depends on the interrelated conditions of soil formation: water-air and thermal conditions soil, its granulometric composition and physicochemical properties, composition and nature of the supply of plant residues, species composition and intensity of microorganism activity.

Transformation of residues occurs under aerobic or anaerobic conditions, depending on the water-air regime. IN aerobic conditions with a sufficient amount of moisture in the soil, favorable temperature and free access to O2, the process of decomposition of organic residues develops intensively with the participation of aerobic microorganisms. The most optimal conditions are temperature 25 - 30 ° C and humidity - 60% of the total moisture capacity of the soil. But under these same conditions, mineralization of both intermediate decomposition products and humic substances occurs rapidly, so relatively little humus accumulates in the soil, but many elements of ash and nitrogen nutrition of plants (in gray soils and other subtropical soils).

Under anaerobic conditions (with a constant excess of moisture, as well as at low temperatures and a lack of O2), the processes of humus formation proceed slowly with the participation mainly of anaerobic microorganisms. In this case, many low-molecular organic acids and reduced gaseous products (CH 4, H 2 S) are formed, which inhibit the vital activity of microorganisms. The decomposition process gradually fades, and organic residues turn into peat - a mass of weakly decomposed and undecomposed plant remains, partially preserving the anatomical structure. The most favorable conditions for the accumulation of humus are a combination of aerobic and anaerobic conditions in the soil with alternating periods of drying and wetting. This regime is typical for chernozems.

The species composition of soil microorganisms and the intensity of their vital activity also affect the formation of humus. Northern podzolic soils, as a result of specific hydrothermal conditions, are characterized by the lowest content of microorganisms with low species diversity and low vital activity. The consequence of this is the slow decomposition of plant residues and the accumulation of weakly decomposed peat. In the humid subtropics and tropics, intensive development of microbiological activity and, in connection with this, active mineralization of residues are observed. A comparison of humus reserves in different soils with different numbers of microorganisms in them indicates that both very weak and high soil biogenicity does not contribute to the accumulation of humus. Largest quantity humus accumulates in soils with an average content of microorganisms (chernozems).

The particle size distribution and physicochemical properties of the soil have an equally significant influence. In sandy and sandy loam soils that are well heated and aerated, the decomposition of organic residues proceeds quickly, a significant part of them is mineralized, there are few humic substances and they are poorly fixed on the surface of sand particles. In clay and loamy soils, the process of decomposition of organic residues under equal conditions occurs more slowly (due to a lack of O 2), humic substances are fixed on the surface of mineral particles and accumulate in the soil.

The chemical and mineralogical composition of the soil determines the amount of nutrients necessary for microorganisms, the reaction of the environment in which humus is formed, and the conditions for the fixation of humic substances in the soil. Thus, soils saturated with calcium have a neutral reaction, which is favorable for the development of bacteria and the fixation of humic acids in the form of calcium humates insoluble in water, which enriches it with humus. In an acidic environment, when soils are saturated with hydrogen and aluminum, soluble fulvic acids are formed, which have increased mobility and lead to a large accumulation of humus. Clay minerals such as montmorillonite and vermiculite also contribute to the fixation of humus in the soil.

Due to the difference in factors influencing the formation of humus, the quantity, quality and reserves of humus in different soils are not the same. Thus, the upper horizons of typical chernozems contain 10 - 14% humus, gray dark forest soils - 4 - 9%, soddy-podzolic soils - 2 - 3%, dark chestnut, yellow soils - 4 - 5%, brown and gray-brown semi-desert soils - 1 – 2%. Organic matter reserves in natural areas ah also different. The largest reserves, according to I.V. Tyurin, have various subtypes of chernozems, peat bogs, gray forest soils, medium - dark chestnut, red soils, low - podzolic, sod-podzolic, typical gray soils. The arable soils of the Republic of Belarus contain humus: clayey– 65 t/ha, in loamy– 52 t/ha, in sandy loam – 47 t/ha, in sandy– 35 t/ha. The soils of the Republic of Belarus, depending on the humus content in the arable layer, are divided into 6 groups (Table 3). In the soils of other natural zones there are gradations depending on the humus content.

Table 3

Grouping of soils of the Republic of Belarus according to humus content

In the Republic of Belarus, most of the land belongs to soils of groups II and III, about 20% to soils of group IV (Fig. 7).

§3. Composition and classification of humus

Humus is a specific high-molecular nitrogen-containing organic substance of acidic nature. It makes up the main part of the organic matter of the soil, which has completely lost the features of the anatomical structure of dead plant and animal organisms. Soil humus consists of specific humic substances, including humic acids (HA), fulvic acids (FA) and humin (see Fig. 6), which differ in solubility and extractability.

Humic acids– these are dark-colored high-molecular nitrogen-containing substances, insoluble in water, mineral and organic acids. They dissolve well in alkalis with the formation of colloidal solutions of dark cherry or brown-black color.

When interacting with metal cations, humic acids form salts - humates. Humates of monovalent metals are highly soluble in water and are washed out of the soil, while humates of di- and trivalent metals are insoluble in water and are well fixed in soils. The average molecular weight of humic acids is 1400. They contain C - 52 - 62%, H - 2.8 - 6.6%, O - 31 - 40%, N - 2 - 6% (by weight). The main components of the humic acid molecule are the core, side chains and peripheral functional groups. The core of humic substances consists of a number of aromatic cyclic rings. Side chains can be carbohydrate, amino acid and other chains. Functional groups are represented by several carboxyl (–COOH) and phenolhydroxyl groups, which play an important role in soil formation, as they determine the interaction of humic acids with the mineral part of the soil. Humic acids constitute the most valuable part of humus; they increase the absorption capacity of the soil and contribute to the accumulation of elements soil fertility and the formation of a water-resistant structure.

Fulvic acids is a group of humic acids that remains in solution after the precipitation of humic acids. These are also high-molecular organic nitrogen-containing acids, which, unlike humic acids, contain less carbon, but more oxygen and hydrogen. They have a light color (yellow, orange) and are highly soluble in water. Salts (fulvates) are also soluble in water and weakly fixed in the soil. Fulvic acids have a strongly acidic reaction and vigorously destroy the mineral part of the soil, causing the development of soil pod formation process.

The ratio between humic acids and fulvic acids varies in different soils. Depending on this indicator (C HA: C FC), the following types of humus are distinguished: humate(> 1,5), humate-fulvate (1,5 – 1), fulvate-humate (1 – 0,5), fulvic (< 0,5). Качество гумуса, плодородие почвы зависят от преобладания той или иной группы. К северу и к югу от черноземов содержание гуминовых кислот в почвах уменьшается. Относительно высокое содержание фульвокислот наблюдается в гумусе подзолистых почв и красноземов. Можно сказать, что условия, благоприятствующие накоплению гумуса в почвах, способствуют и накоплению устойчивой и наиболее агрономически ценной его части – гуминовых кислот. Соотношение С ГК: С ФК имеет наибольшее значение (1,5 – 2,5) в гумусе черноземов, снижаясь к северу и к югу от зоны этих почв. При интенсивном использовании пахотных земель без достаточного внесения органических удобрений наблюдается снижение как general content humus (dehumification) and humic acids.

Humin- this is part of the humic substances that do not dissolve in any solvent, are represented by a complex of organic substances (humic acids, fulvic acids and their organomineral derivatives), firmly associated with the mineral part of the soil. This is the inert part of soil humus.

The specificity and composition of humus complexes serves as the basis for the classification of humus types. R.E. Muller proposed a classification of forest forms of humus as a biological system of interaction between organic substances, microbiota and vegetation. Among these complexes, 3 types of humus are distinguished.

Soft humus - mul is formed in deciduous or mixed forests with intense activity of soil fauna under favorable hydrothermal conditions and the presence of a sufficient amount of bases, primarily calcium, in litter and soils, has a slightly acidic reaction, evenly permeates the mineral part of the soil and is easily mineralized. In mule soils, almost no litter accumulates, since the incoming litter is vigorously decomposed by the microbiota. Humic acids predominate in the composition of humus.

Coarse humus - pestilence, containing a large amount of semi-decomposed residues, is characteristic of coniferous forests, is formed with a low content of ash elements in the litter, a lack of bases and a high silica content in the soil, has an acidic reaction, is resistant to microorganisms, and mineralizes slowly with the participation of fungi. As a result of the slow development of humification and mineralization processes in soils, a thick litter peat-like horizon A 0 is formed, consisting of 3 layers: a) a layer of slightly decomposed organic matter (L), which is fresh litter, b) a semi-decomposed fermentation layer (F), c) a humified layer ( H).

Intermediate form - moder develops under conditions of fairly rapid mineralization of plant residues, where a significant role is played by the functional activity of soil animals that crush plant residues, which greatly facilitates their subsequent decomposition by soil microflora.

§4. The importance and balance of soil humus

The accumulation of humus is the result of the soil-forming process; at the same time, the humic substances themselves have a great influence on the further direction of the soil-forming process and the properties of the soil. The functions of humus in soil are very diverse:

1) formation of a specific soil profile (with horizon A), formation of soil structure, improvement of water-physical properties of the soil, increase in absorption capacity and buffering capacity of soils;

2) a source of mineral nutrients for plants (N, P, K, Ca, Mg, S, microelements), a source of organic nutrition for heterotrophic soil organisms, a source of CO 2 in the ground layer of the atmosphere and biologically active compounds in the soil, which directly stimulates growth and plant development, mobilizes nutrients, affects the biological activity of the soil;

3) performs sanitary-protective functions - accelerates the destruction of pesticides, fixes pollutants, reducing their entry into plants.

In connection with the diverse role of organic matter in soil fertility, the problem of humus balance in arable soils becomes of current importance. Like any balance, the humus balance includes items of income (receipt of organic residues and their humification) and expenditure (mineralization and other losses). Under natural conditions, the older the soil, the more fertile: the balance is positive or zero, in arable soils it is more often negative. On average, arable soils lose about 1 t/ha of humus per year. To regulate the amount of humus, systematic application of a sufficient amount of organic matter in the form of manure (from 1 ton of manure is formed ≈ 50 kg of humus), peat composts, sowing of perennial grasses, the use of green fertilizers (green manure), liming of acidic soils and gypsuming of alkaline soils is used.

The humus status of soils serves important indicator fertility and is determined by a system of indicators, including the level of content and reserves of organic matter, its profile distribution, enrichment with nitrogen (C: N) and calcium, the degree of humification, types of humic acids and their ratio. Some of its parameters serve as the object of environmental monitoring.

Soil organic matter- This a complex system all organic substances present in the profile in a free state or in the form of organomineral compounds, excluding those that are part of living organisms.

The main source of soil organic matter is the remains of plants and animals at various stages of decomposition. The largest volume of biomass comes from fallen plant debris; the contribution of invertebrate and vertebrate animals and microorganisms is much smaller, but they play an important role in enriching organic matter with nitrogen-containing components.

According to its origin, character and functions, soil organic matter is divided into two groups: organic residues and humus. The term “humus” is sometimes used as a synonym for the term “humus.”

Organic residues are represented mainly by ground and root litter of higher plants, which have not lost their anatomical structure. The chemical composition of plant residues in different cenoses varies widely. What they have in common is the predominance of carbohydrates (cellulose, hemicellulose, pectin substances), lignin, proteins and lipids. This entire complex complex of substances, after the death of living organisms, enters the soil and is transformed into mineral and humic substances, and is partially carried out of the soil with groundwater, possibly to oil-bearing horizons.

The decomposition of organic soil residues includes mechanical and physical destruction, biological and biochemical transformation and chemical processes. In the decomposition of organic residues, a major role is played by enzymes, soil invertebrate animals, bacteria and fungi. Enzymes are structured proteins that have many functional groups. The main source of enzymes are; plants. Acting as catalysts in the soil, enzymes accelerate the processes of decomposition and synthesis of organic substances millions of times.

Humus is the totality of all organic compounds, located in the soil, except for those that are part of living organisms and organic residues that have retained their anatomical structure.

The composition of humus includes nonspecific organic compounds and specific ones - humic substances.

Nonspecific is a group of organic substances of known nature and individual structure. They enter the soil from decomposing plant and animal residues and with root secretions. Nonspecific compounds are represented by almost all components that make up animal and plant tissues and intravital secretions of macro- and microorganisms. These include lignin, cellulose, proteins, amino acids, monosaccharides, waxes and fatty acids.

In general, the share of nonspecific organic compounds does not exceed 20% of the total amount of soil humus. Nonspecific organic compounds are products of varying degrees of decomposition and humification of plant, animal and microbial material entering the soil. These compounds determine the dynamics of rapidly changing soil properties: redox potential, content of mobile forms of nutrients, the number and activity of soil microorganisms, and the composition of soil solutions. Humic substances, on the contrary, determine the stability over time of other soil properties: exchange capacity, water-physical properties, air regime and color.

Specific organic part of soil - humic substances- represent a heterogeneous (heterogeneous) polydisperse system of high molecular weight nitrogen-containing aromatic compounds of an acidic nature. Humic substances are formed as a result of a complex biophysical and chemical process of transformation (humification) of decomposition products of organic residues entering the soil.

Depending on the chemical composition of plant residues and the factors of their decomposition (temperature, humidity, composition of microorganisms), two main types of humification are distinguished: fulvate and humate. Each of them corresponds to a certain fractional-group composition of humus. The group composition of humus refers to the set and content of various substances that are related in structure and properties of compounds. The most important groups are humic acids (HA) and fulvic acids (FA).

Humic acids contain 46 - 62% carbon (C), 3 - 6% nitrogen (N), 3-5% hydrogen (H) and 32-38% oxygen (O). Fulvic acids contain more carbon - 45-50%, nitrogen - 3.0-4.5% and hydrogen - 3-5%. Humic and fulvic acids almost always contain sulfur (up to 1.2%), phosphorus (tens and hundreds of fractions of a percent) and cations of various metals.

Fractions are distinguished within the groups HA and FC. The fractional composition of humus characterizes the set and content of various substances included in the HA and FA groups, according to the forms of their compounds with the mineral components of the soil. The following fractions are of greatest importance for soil formation: brown humic acids (BHA) associated with sesquioxides; black humic acids (BHA) bound to calcium; fractions I and Ia of fulvic acids associated with mobile forms of sesquioxides; HA and FA, tightly bound to sesquioxides and clay minerals.

The group composition of humus is characterized by the quantitative ratio of humic acids and fulvic acids. A quantitative measure of the type of humus is the ratio of the carbon content of humic acids (CHA) to the carbon content of fulvic acids (CFA). Based on the value of this ratio (CHA /CFA), four types of humus can be distinguished:

• — humate - more than 2;
• — fulvate-humate - 1-2;
• — humate-fulvate - 0.5-1.0;
• — fulvate - less than 0.5.

The group and fractional composition of humus changes naturally and consistently in the zonal genetic series of soils. In podzolic and turf- podzolic soils Humic acids are almost not formed and little of them accumulate. The ratio CHA/CFA is usually less than 1 and most often is 0.3-0.6. In gray soils and chernozems, the absolute content and proportion of humic acids is significantly higher. The ratio CHA/CFA in chernozems can reach 2.0-2.5. In soils located south of chernozems, the proportion of fulvic acids gradually increases again.

Excessive moisture, carbonate content of the rock, and salinity leave their mark on the group composition of humus. Additional moisture usually promotes the accumulation of humic acids. Increased humation is also characteristic of soils formed on carbonate rocks or under the influence of hard groundwater.

The group and fractional composition of humus also changes along the soil profile. The fractional composition of humus in different horizons depends on the mineralization of the soil solution and the pH value. Profile changes in the group composition of humus in most

soils are subordinated to one general pattern: with depth the proportion of humic acids decreases, the proportion of fulvic acids increases, the CHA / CFA ratio decreases to 0.1-0.3.

The depth of humification, or the degree of conversion of plant residues into humic substances, as well as the CHA / CFA ratio depend on the speed (kinetics) and duration of the humification process. The kinetics of humification is determined by soil-chemical and climatic characteristics that stimulate or inhibit the activity of microorganisms (nutrients, temperature, pH, humidity), and the susceptibility of plant residues to transformation depending on the molecular structure of the substance (monosaccharides, proteins are easier to transform, lignin, polysaccharides are more difficult) .

In humus horizons of temperate climate soils, the type of humus and the depth of humification, expressed by the ratio CHA/CFA, correlate with the duration of the period of biological activity.

The period of biological activity is a period of time during which favorable conditions are created for normal plant vegetation and active microbiological activity. The duration of the period of biological activity is determined by the duration of the period during which the air temperature consistently exceeds 10 ° C, and the supply of productive moisture is at least 1-2%. In the zonal series of soils, the value of CHA/CFA, which characterizes the depth of humification, corresponds to the duration of the period of biological activity.

Simultaneous consideration of two factors - the period of biological activity and the saturation of soils with bases - makes it possible to determine the areas of formation various types humus. Humate humus is formed only during a long period of biological activity and high degree soil saturation with bases. This combination of conditions is typical for chernozems. Strongly acidic soils (podzols, soddy-podzolic soils), regardless of the period of biological activity, have fulvic humus.

Humic substances in soil are highly reactive and actively interact with the mineral matrix. Under the influence of organic substances, unstable minerals of the parent rock are destroyed and chemical elements become more accessible to plants. In the process of organomineral interactions, soil aggregates are formed, which improves the structural condition of the soil.

Fulvic acids most actively destroy soil minerals. Interacting with sesquioxides (Fe 2 O 3 and Al 2 O 3), FAs form mobile aluminum and iron-humus complexes (iron and aluminum fulvates). These complexes are associated with the formation of illuvial-humus soil horizons in which they are deposited. Fulvates of alkaline and alkaline earth bases are highly soluble in water and easily migrate down the profile. Important Feature FC is their inability to fix calcium. Therefore, liming of acidic soils must be carried out regularly, every 3-4 years.

Humic acids, in contrast to FA, form poorly soluble organomineral compounds (calcium humates) with calcium. Due to this, humus-accumulative horizons are formed in the soils. Soil humic substances bind ions of many potentially toxic metals - Al, Pb, Cd, Ni, Co, which reduces dangerous influence chemical contamination of soils.

The processes of humus formation in forest soils have their own characteristics. The overwhelming majority of plant litter in the forest reaches the soil surface, where special conditions decomposition of organic residues. On the one hand, this is the free access of oxygen and the outflow of moisture, on the other hand, a humid and cool climate, a high content of difficult-to-decompose compounds in the litter, a rapid loss due to the leaching of bases released during the mineralization of the litter. Such conditions affect the vital activity of soil animals and microflora, which play an important role in the processes of transformation of organic residues: grinding, mixing with the mineral part of the soil, biochemical processing of organic compounds.

As a result of various combinations of all factors of decomposition of organic residues, three types (forms) of organic matter in forest soils are formed: mull, moder, and mor. The form of organic matter in forest soils refers to the entire set of organic substances contained both in the forest litter and in the humus horizon.

During the transition from mora to moder and mull, the properties of soil organic matter change: acidity decreases, ash content, the degree of saturation with bases, nitrogen content, and the intensity of decomposition of forest litter increase. In soil with the mull type, the litter contains no more than 10% of the total reserve of organic matter, and in the mora type, the litter accounts for up to 40% of its total reserve.

When organic matter of the mora type is formed, a thick three-layer litter is formed, which is well separated from the underlying mineral horizon (usually horizons E, EI, AY). Mainly fungal microflora takes part in the decomposition of litter. There are no earthworms, the reaction is strongly acidic. The forest litter has the following structure:

O L - the top layer about 1 cm thick, consisting of litter that has preserved the anatomical structure;

O F - middle layer of varying thickness, consisting of semi-decomposed light brown litter, intertwined with fungal hyphae and plant roots;

Oh - the lower layer of highly decomposed litter, dark brown, almost black, smeared, with a noticeable admixture of mineral particles.

In the moder type, the forest floor usually consists of two layers. Under the layer of weakly decomposed litter, a well-decomposed humus layer about 1 cm thick stands out, gradually turning into a clearly defined humus horizon with a thickness of 7-10 cm. Insects earthworms play an important role in the decomposition of litter. In the microflora, fungi predominate over bacteria. The organic matter of the humus layer is partially mixed with the mineral part of the soil. The reaction of the litter is slightly acidic. In forest soils with excessive moisture, the processes of decomposition of plant litter are inhibited and peat horizons are formed in them. The accumulation and rate of decomposition of organic matter in forest soils is influenced by the composition of the original plant residues. The more lignin, resins, tannins and the less nitrogen in plant residues, the slower the decomposition process and the more organic residues accumulate in the litter.

Based on the determination of the composition of plants from whose litter the litter was formed, a classification of forest litter was proposed. According to N.N. Stepanov (1929), the following types of litter can be distinguished: coniferous, small-leaved, broad-leaved, lichen, green moss, moss-grass, grass, long-moss, sphagnum, wet-grass, grass-marsh and broad-grass.

Humus status of soils- this is a set of general reserves and properties of organic substances, created by the processes of their accumulation, transformation and migration in the soil profile and reflected in a set of external characteristics. The system of indicators of humus status includes the content and reserves of humus, its profile distribution, nitrogen enrichment, degree of humification and types of humic acids.

The levels of humus accumulation are in good agreement with the duration of the period of biological activity.

The composition of organic carbon shows a natural increase in the reserves of humic acids from north to south.

The soils of the Arctic zone are characterized by low content and small reserves of organic matter. The process of humification takes place under extremely unfavorable conditions with low biochemical activity of soils. The soils of the northern taiga are characterized by a short period (about 60 days) and low level biological activity, as well as poor species composition of microflora. The processes of humification are slow. In zonal soils of the northern taiga, a coarse humus type of profile is formed. The humus-accumulative horizon in these soils is practically absent, the humus content under the litter is up to 1-2%.

In the subzone of soddy-podzolic soils of the southern taiga, the amount of solar radiation, moisture regime, vegetation cover, rich species composition of soil microflora and its higher biochemical activity over a fairly long period contribute to a deeper transformation of plant residues. One of the main features of the soils of the southern taiga subzone is the development of the sod process. The thickness of the accumulative horizon is small and is determined by the depth of penetration of the bulk of the roots of herbaceous vegetation. The average humus content in the AY horizon in forest soddy-podzolic soils ranges from 2.9 to 4.8%. The reserves of humus in these soils are small and, depending on the soil subtype and granulometric composition, range from 17 to 80 t/ha in a layer of 0-20 cm.

In the forest-steppe zone, humus reserves in the 0-20 cm layer range from 70 t/ha in gray soils to 129 t/ha in dark gray soils. Humus reserves in the chernozems of the forest-steppe zone in the 0-20 cm layer are up to 178 t/ha, and in the 0-100 cm layer - up to 488 t/ha. The humus content in horizon A of chernozems reaches 7.2%, gradually decreasing with depth.

In the northern regions of the European part of Russia, a significant amount of organic matter is concentrated in peat soils. Swamp landscapes are located mainly in the forest zone and tundra, where precipitation significantly exceeds evaporation. Peat contamination is especially high in the north of the taiga and in the forest-tundra. The oldest peat deposits, as a rule, occupy lake basins with sapropel deposits up to 12 thousand years old. The initial deposition of peat in such bogs occurred approximately 9-10 thousand years ago. Peat began to be deposited most actively around 8-9 thousand years ago. Sometimes there are peat deposits about 11 thousand years old. The HA content in peat ranges from 5 to 52%, increasing during the transition from high-moor to low-lying peat.

The humus content is associated with a variety of ecological functions of the soil. The humus layer forms a special energy shell of the planet, called humosphere. The energy accumulated in the humosphere is the basis for the existence and evolution of life on Earth. The humosphere performs the following important functions: accumulative, transport, regulatory, protective, physiological.

Accumulative function characteristic of humic acids (HA). Its essence lies in the accumulation of humic substances in its composition essential elements nutrition of living organisms. In the form of amine substances, up to 90-99% of all nitrogen accumulates in soils, more than half of phosphorus and sulfur. In this form, potassium, calcium, magnesium, jelly - 30 and almost all microelements necessary for plants and microorganisms are accumulated and stored for a long time.

Transport function This is due to the fact that humic substances can form complex organomineral compounds with metal cations, but they are soluble and capable of geochemical migration. Most microelements and a significant portion of phosphorus and sulfur compounds actively migrate in this form.

Regulatory function is due to the fact that humic substances take part in the regulation of almost all the most important soil properties. They form the color of humus horizons and, on this basis, their thermal regime. Humic soils are always much warmer than soils containing few humic substances. Humic substances play an important role in the formation of soil structure. They are involved in regulation mineral nutrition plants. Soil organic matter is used by its inhabitants as the main source of food. Plants take about 50% of their nitrogen from soil reserves.

Humic substances can dissolve many soil minerals, which leads to the mobilization of some mineral nutrition elements that are difficult for plants to access. The cation exchange capacity, ion-salt and acid-base buffer capacity of soils, and the redox regime depend on the amount of properties of humic substances in soils. Physical, water-physical and physical and mechanical properties soil Well-humused soils are better structured, have a more diverse species composition of microflora, and a greater number of invertebrate animals. Such soils are more permeable, easier to machine, better retain elements of plant nutrition, have a high absorption capacity and buffer capacity, and have a higher efficiency of mineral fertilizers.

Protective function is due to the fact that humic substances in the soil protect or preserve soil biota and plant cover in the event of various kinds of unfavorable extreme situations. Humus-rich soils are better able to withstand drought or waterlogging, they are less susceptible to erosion by deflation, and retain satisfactory properties longer when irrigated with increased doses or mineralized water.

Soils rich in humic substances can withstand higher technogenic loads. Under equal conditions of soil contamination with heavy metals, their toxic effect on plants on chernozems is less pronounced than on soddy podzolic soils. Humic substances quite firmly bind many radionuclides and pesticides, thereby preventing their entry into plants or other negative effects.

Physiological function is that humic acids and their salts can stimulate seed germination, activate plant respiration, and increase the productivity of cattle and poultry.

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Organic part soil represented by living organisms (living phase, or biophase), undecomposed, organic residues and humic substances (Fig. 1)

Organic part of the soil

Rice. 1. Organic part of the soil

Living organisms were discussed above. Now it is necessary to define organic residues.

Organic residues- these are organic substances, plant and animal tissues that have partially retained their original shape and structure. It should be noted that the different chemical compositions of different residues are different.

Humic substances represent all organic matter in the soil, with the exception of living organisms and their remains that have not lost their tissue structure. It is generally accepted to subdivide them into specific humic substances themselves and nonspecific organic substances of an individual nature.

Nonspecific humic substances contain substances of an individual nature:

a) nitrogenous compounds, for example, simple and complex, proteins, amino acids, peptides, purine bases, pyrimidine bases; carbohydrates; monosaccharides, oligosaccharides, polysaccharides;

b) lignin;

c) lipids;

e) tannins;

f) organic acids;

g) alcohols;

h) aldehydes.

Thus, nonspecific organic substances are individual organic compounds and intermediate products of the decomposition of organic residues. They constitute approximately 10-15% of the total humus content of mineral soils and can reach 50-80% of the total mass of organic compounds in peat horizons and forest litters.

Humic substances themselves are a specific system of high-molecular nitrogen-containing organic compounds of cyclic structure and acidic nature. According to many researchers, the structure of the humus compound molecule has complex nature. It has been established that the main components of the molecule are the core, side (peripheral) chains and functional groups.

It is believed that the core consists of aromatic and heterocyclic rings consisting of five- and six-membered compounds of the type:

benzene furan pyrrole naphthalene indole

Side chains extend from the core to the periphery of the molecule. They are represented in the molecule of humus compounds by amino acid, carbohydrate and other chains.

The composition of humic substances contains carboxyl (-COOH), phenolhydroxyl (-OH), methoxyl (-CH3O) and alcoholic hydroxyl. These functional groups determine the chemical properties of humic substances. Characteristic feature the system of humic substances itself is heterogeneity, i.e. the presence in it of components of different stages of humification. From this complex system, three groups of substances are distinguished:

a) humic acids;

b) fulvic acids;

c) humins, or, more precisely, non-hydrolyzable residue.

Humic acids (HA)– a dark-colored group of humic substances, extracted from the soil with alkaline solutions and precipitated by mineral acids at pH = 1-2. They are characterized by the following elemental composition: C content from 48 to 68%, H - 3.4-5.6%, N - 2.7-5.3%. These compounds are practically insoluble in water and mineral acids; they are easily precipitated from HA solutions by acids H+, Ca2+, Fe3+, Al3+. These are humic compounds of acidic nature, which is caused by carboxyl and phenolhydroxyl functional groups. The hydrogen of these groups can be replaced by other cations. The ability to substitute depends on the nature of the cation, pH of the environment and other conditions. In a neutral reaction, only hydrogen ions of carboxyl groups are replaced. The absorption capacity due to this property of HA ranges from 250 to 560 mEq per 100 g of HA. During an alkaline reaction, the absorption capacity increases to 600-700 mEq/100 g of HA due to the ability to replace hydrogen ions of hydroxyl groups. The molecular weight of HA, when determined by various methods, varies from 400 to hundreds of thousands. In the HA molecule, the aromatic part is most clearly represented, the mass of which prevails over the mass of the side (peripheral) chains.

Humic acids do not have a crystalline structure; the bulk of them are found in the soil in the form of gels, which are easily peptized by the action of alkalis and form molecular and colloidal solutions.

When HA interacts with metal ions, salts are formed, which are called humates. Humates NH4+, Na+, K+ are highly soluble in water and can form colloidal and molecular solutions. The role of these compounds in the soil is enormous. For example, humates Ca, Mg, Fe and A1 are generally poorly soluble, can form water-resistant gels, and at the same time pass into a stationary state (accumulation), and are also the basis for the formation of a water-resistant structure.

Fulvic acids (FA) - a specific group of humic substances, soluble in water and mineral acids. Characterized by the following chemical composition: C content from 40 to 52%; H - 5-4%, oxygen -40-48%, N - 2-6%. Fulvic acids, unlike HA, are highly soluble in water, acids and alkalis. The solutions are yellow or straw-yellow in color. This is where these compounds got their name: in Latin fulvus - yellow. Aqueous solutions of FA have a strongly acidic reaction (pH 2.5). The molecular weight of fulvic acids, determined by various methods, ranges from 100 to several hundred and even thousands conventional units masses.

The fulvic acid molecule has a simpler structure compared to humic acids. The aromatic part of these compounds is less clearly defined. The structure of the FA molecule is dominated by side (peripheral) chains. The active functional groups are carboxyl and phenolhydroxyl groups, the hydrogen of which enters into exchange reactions. The FA exchange capacity can reach 700-800 mEq per 100 g of fulvic acid preparations.

When interacting with the mineral part of the soil, fulvic acids form organo-mineral compounds with metal ions, as well as minerals. Fulvic acids, due to their strongly acidic reaction and good solubility in water, actively destroy the mineral part of the soil. In this case, salts of fulvic acids are formed, which have high mobility in the soil profile. Organo-mineral compounds of fulvic acids actively participate in the migration of matter and energy in the soil profile, in the formation, for example, of individual genetic horizons.

Non-hydrolyzable residue (humins) is a group of humic substances, which is the residue of alkali-insoluble soil organic compounds. This group consists of both humic substances themselves, for example, humins consist of humic acids tightly bound to minerals, and of tightly bound individual substances and organic residues of varying degrees of decomposition with the mineral part of the soil.

The soil is a complex system consisting of mineral and organic components. It serves as a substrate for plant development. For successful farming, it is necessary to know the characteristics and ways of soil formation - this helps to increase its fertility, i.e. it is of great economic importance.

Soil composition includes four main components:
1) mineral substance;
2) organic matter;
3) air;
4) water, which is more correctly called a soil solution, since certain substances are always dissolved in it.

Soil mineral matter

By chva consists of mineral components of different sizes: stones, crushed stone and “fine earth”. The latter is usually subdivided in order of particle enlargement into clay, silt and sand. The mechanical composition of the soil is determined by the relative content of sand, silt and clay in it.

Mechanical composition of the soil greatly influences drainage, nutrient content and soil temperature, in other words, soil structure from an agronomic point of view. Medium- and fine-textured soils, such as clays, loams and silts, are usually more suitable for plant growth, as they contain enough nutrients and are better able to retain water and dissolved salts. Sandy soils drain faster and lose nutrients as a result of leaching, but they are beneficial to use for early harvests; in the spring they dry out and warm up faster than clay ones. The presence of stones, i.e. particles with a diameter greater than 2 mm, is important from the point of view of wear of agricultural implements and the effect on drainage. Typically, as the rock content of soil increases, its ability to hold water decreases.

Soil organic matter

organic matter, as a rule, makes up only a small volume fraction of the soil, but it is very important because it determines many of its properties. This is the main source of plant nutrients such as phosphorus, nitrogen and sulfur; it promotes the formation of soil aggregates, i.e., a fine-lumpy structure, especially important for heavy soils, since as a result water permeability and aeration increase; it serves as food for microorganisms. Soil organic matter is divided into detritus, or dead organic matter (MOB), and biota.

Humus(humus) is the organic material formed when MOB is incompletely decomposed. A significant part of it does not exist in free form, but is associated with inorganic molecules, primarily with clay particles of soil. Together with them, humus makes up the so-called absorption complex of the soil, which is extremely important for almost all physical, chemical and biological processes occurring in it, in particular for the retention of water and nutrients.

Among soil organisms Earthworms occupy a special place. These detritivores, together with MOB, ingest large quantities of mineral particles. Moving between different layers of soil, worms constantly mix it. In addition, they leave passages that facilitate its aeration and drainage, thereby improving its structure and associated properties. Earthworms feel best in a neutral to slightly acidic environment, rarely occurring at a pH below 4.5.