General physical properties of the soil. Soil Composition Soil Properties 3

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Soil is a special natural formation that serves as the main resource for the development of agriculture in any country. What are the main factors in soil formation, and what are their types?

What is soil?

V. I. Dahl in his dictionary indicates the genesis of this term from the Old Russian word to rest (lie). What is soil in a scientific context?

Soil (or soil) is a specific natural formation, the upper layer of the planet’s hard shell (lithosphere), which has a systemic structure. The study of this unique natural body is a separate science - soil science. The father of this discipline can be considered the great Russian researcher Vasily Dokuchaev. In the second half of the XIX century, it was he who made a lot of efforts in order to answer the question as accurately as possible: "What is the soil?"

It is difficult to imagine that for several tens of kilometers one soil stretches with the same properties. Scientists distinguish several types of soils, each of which has its own set of features. However, any of them is formed under the influence of two main processes:

Weathering rocks.
The activity of living organisms.

Soil structure

The internal structure of any soil includes several components. It:

mineral part (mother rock);
organic matter (or humus);
water;
soil air;
alive organisms;
neoplasms and inclusions.

It is humus that determines the key property of the soil - its fertility. It should not be assumed that the soil is an exclusively “dead” and abiotic formation. Many living organisms live in it - from bacteria to ticks and earthworms. Even the representatives of the family Mammals (for example, mole) live in the soil environment.

Properties and significance in nature

It is impossible to correctly answer the question of what soil is without telling about its basic properties. It is equally important to know about its role in nature and human life.

So, the main properties of the soil are:

water permeability (soil is a porous formation that passes water well, however, this property depends on the structure and mechanical composition of a particular soil);
moisture capacity (on the other hand, the soil is able to retain a certain amount of moisture, thereby nourishing the roots of plants);
water loss (the ability of the soil to lift water up the soil pores).

However, the most important (and unique) property of this natural formation is its fertility - the ability to saturate the roots of plants with nutrients and water, which, in turn, ensures their vital activity. With the help of rational methods of land cultivation, a person can increase the fertility of a particular soil.

The role and place of soil in nature is difficult to overestimate. After all, it, in fact, is precisely that “bridge” that ensures the interaction of all four shells of the Earth - the lithosphere, hydrosphere, atmosphere and biosphere.

Soil formation process

As mentioned above, soil is formed as a result of two processes: weathering of rocks and vital activity of organisms.

The factors of soil formation include the following:

climatic features of the region;
relief;
parent rock;
biota (plants and animals);
human activities.

However, the main factor in soil formation is precisely the climate of the territory. It affects not only the formation of soils, but also their distribution over the planet (latitudinal zonality of soils).

Climatic processes affect the formation of soil directly, largely determining its mode and structure, as well as indirectly (through vegetation and animal organisms).

Main types and zones of soil

Soils, like many other components of nature, are subject to geographical (latitudinal) zoning. So, we can distinguish the following (main) soils:

Red earth and yellow earth are soil types that form in the subtropical and tropical climates, in conditions of high humidity.
Podzolic soils are poor soils that form under coniferous and mixed forests. These soils are common in the temperate latitudes of Europe and North America.
Gray-brown soils are a special type of soil that forms under deserts and semi-deserts. They are distinguished by high salinity, common in Central Asia.
Black earth is the most fertile soil type. Formed in the steppe and forest-steppe zone of Eurasia and America.

Depending on the mineral composition and structure, the soil can also be: clay, sandy, rocky, sandy-clay, etc.

Clay soil contains about 40-60% clay. It differs in specific properties: viscosity, dampness and ductility. The permeability of such a soil is usually not very high. That is why clay soil is extremely rarely completely dry.

Conclusion

Soil is a special natural body, with certain properties and structure. However, the main, key feature is its fertility. The properties of the soil determine its very important place in the geographical envelope. After all, it is she who provides the interaction of all its structural elements. Moreover, it is an important economic resource on which the food security of any country in the world depends.

In general, the soil is a surface layer of the hard shell of our planet, characterized by fertility.

One of the foundations for soil formation is rocks.
For many years, the rocks that make up the plains, the bottoms of water bodies, as well as the mountains themselves, were destroyed under the influence of air masses, water, heat from the sun, and living organisms.

How the soil is formed

In principle, the process of soil formation should be considered from the point of view of the direct relationship between animate and inanimate nature - as a result of the vital activity of organisms and weathering of rocks.

Needles, tree branches, dry fallen leaves and grass accumulate in the ground and become six months old; beneath them, in turn, are pebbles, clay and sand, humus, the remains of animals and insects - ladybugs, ants.

Mushrooms and bacteria are also found in the soil ...
Earthworms and moles generally spend most of their lives in the soil, only occasionally appearing outside.
May bugs in the soil lay eggs.
For snails and frogs, the soil is a salvation from hot weather.

Earth bumblebee in the winter winters.

Beetles can penetrate the soil to a depth of two meters;
ants and even more - up to three meters;
and moles - up to five meters;
Well, earthworms in this regard are the “champions" - up to eight meters.

Air and water enter the soil thanks to the passages that animals make during their life, thereby enriching it.

And animals grind plant residues in the soil, and bacteria turn them into humus.
The main property of the soil is fertility.

Fertility means the presence of substances in the soil that determine the growth and development of plants.

How to determine the composition of the soil?

Experience No. 1. Air

Dip a small lump of soil (dry) into a glass of water. And, you will see how bubbles will rise on the surface of the water, which indicates the presence of air in the soil.

Experience No. 2. Mineral salts, clay, sand

Dip the soil in a glass of water, stir and leave for a while. Then drip a couple of drops of clouded water on a glass and heat it. When the water evaporates, then on the glass you will see a white coating, indicating the presence of mineral salts in the soil.

In the glass itself, over time it will be possible to observe the following: sand settles at the bottom, clay is deposited on it, and humus is already deposited on the clay itself.

Experience No. 3. Water

Place the crushed soil lumps on some tin surface and heat it; while holding a glass over the soil: the glass will fog up first, and then drops of water will appear on it. which means that the soil contains water.

Experience No. 4. Humus

In continuation of the previous: do not stop heating the soil, and you will feel a nasty smell. The fact is that the burning rotting remains of animals and plants (humus) give a similar smell.
And if you continue heating, the humus will burn up and the soil will turn gray. It turns out that it is humus that determines the dark color of the soil.

The plant in its development needs nutrients, water, air and heat. That soil, which is able to satisfy these demands of a cultivated plant, will be fertile soil.

Fertility is the main, main property of the soil. It, in turn, depends on a number of other properties, which we will describe below.

Soil absorption capacity. The plant takes its roots from soil solutions. But so that it can take away the substances it needs, the concentration of solutions should be weak (no more than 2-3 gnutrient salts per 1 l water). True, there may be too little salt, and then the plant will go hungry, but it will die if the aqueous solution is too strong. From a concentrated aqueous solution, the plant roots are not able to absorb salts, and the plant dies, as would die of starvation.

But we know that the amount of water in the soil is constantly changing. After the rains there are more, less during the drought. This means that the strength of the soil solution is also different, which cannot but affect the state of the plant. But the properties of the soil that feeds it come to the aid of the plant, and mainly its clay particles and humus, which, within certain limits, regulate the strength of the solution. When the concentration of the solution increases, the soil absorbs some of the substances from it. This happens for various reasons. Some substances are more firmly absorbed by the solid part of the soil, forming together with it new hardly soluble compounds and salts. This can be said about iron, phosphoric and carbonic acids, etc. Others, such as calcium, potassium, sodium, magnesium, are only attracted from the solution to the surface of soil particles (this is an “absorbing soil complex”), they are concentrated in water layers that are closest to these particles (in the so-called diffuse layer), and other elements are forced out of them. So, calcium is absorbed from the solution, and magnesium and sodium are displaced into the solution. Maybe the other way around. Usually those elements that are more in the soil solution are absorbed. Finally, in the case of a significant increase in the concentration of the soil solution, third substances can precipitate from it in the form of crystals: lime in chernozem soils, lime and gypsum in chestnut soils, etc.

In many cases, the substances necessary for the plant are absorbed - potassium, calcium, phosphoric acid, lime. However, along with them, the soil also absorbs sodium, significant amounts of which in the absorption complex dramatically worsen all its properties.

The ability of the soil, its solid part, to absorb from an aqueous solution and bind some substances and salts is called the absorption capacity of the soil.

Soil absorption capacity depends mainly on the content of colloidal particles in it (finer than 0.0001 mm) - mineral, organic and organo-mineral. This part of the soil is called its absorbing complex. The more such particles, the better the absorption capacity of the soil. Consequently, clay and loamy, especially humus-rich soils will always have greater absorption capacity than sandy-loamy and sandy soils, and even more so - poor in humus. So, in clay chernozem, the amount of absorbed calcium and magnesium reaches 1% or more by weight of the soil, whereas in sandy podzolic soils of the same substances only tenths and hundredths of a percent are observed in the absorbed state.

The soil does not take the absorbed materials irrevocably. They only remain in it until the moment when the amount of water increases and when the plant requires them through its root system. With an increase in soil moisture, part of the substances will certainly go back to the soil solution.

The fact that the soil really absorbs various substances from water is easy to verify. We will dissolve some salt in water, for example barium chloride, and shake it together with soil (preferably clay, rich in humus). After a while we filter the water using a funnel and a paper filter and determine the amount of barium in it. It turns out that barium became less in solution, as it was absorbed by the soil, and instead of it, the calcium content in the water increased.

The soil can even absorb some gases, for example ammonia, a sharp-smelling gas that forms ammonia when combined with water. Ammonia absorbed by the soil with the participation of bacteria is converted to nitrate.

But not all substances are absorbed by the soil equally well. It is very poorly absorbed by it, so valuable for plant nitrate, and therefore it is easier than other substances to be washed out of the soil with water. In addition, as we noted, not all soils differ in the same absorption capacity. Well absorb soil substances rich in clay particles and humus. In such soils, nutrients are better fixed and therefore more difficult to wash out with water. And the strength of the aqueous solution in these soils, if they are not salted, is maintained approximately the same, which is of great importance for plant nutrition.

Clay rich, humus-rich soils can be safely fertilized with the necessary amounts of nutrients for plants (for example, superphosphate), as their excess, if they appear, will be absorbed by the soil and will not destroy the plants, and also will not be washed with water. This should not be done only with nitrate. Therefore, in practice, it is usually introduced into the topsoil in two portions: one during sowing, and the other during the period of the greatest development of plants.

Sandy soils have completely different properties. Clay and humus are few in them, their absorption capacity is negligible. Water easily leaches nutrient salts from them, and they disappear without a trace for plants.

In drought, when the concentration of the soil solution rises significantly, sandy soil is not able to absorb excess salts, and plants, if the soil is fertilized with water-soluble substances, can die: they burn out. Therefore, in order not to create unnecessary strength of the soil solution and not to lose nutrients, fertilizers are introduced into sandy soils little by little, in several portions. It is also impossible to leave these soils in a clean pair, since water will wash nutrients out of them. During the fallow season in the podzolic zone, these soils should be inoculated with seradella or lupine. Seradella is an excellent fodder for livestock, and lupine, if it is smelled during the flowering period, enriches the soil with humus, nitrogen and improves its physical properties.

Domestic experts and agricultural leaders have proposed that, on heavy soils, fertilizers be added that are readily soluble in water under fractional portions under plants, several times a season, taking into account the stage of plant development. This technique, which in practice came to be called plant nutrition, significantly increases the yield of crops.

Along with clay particles and humus, the microorganisms inhabiting it play a significant role in the absorption capacity of the soil. Propagating in the soil, they absorb various nutrients from the soil solution to build their body. After death, the bodies of microorganisms decay and the substances absorbed by them again return to the soil, to the soil solution and can be used by plants. A similar phenomenon is observed during the life and death of the plants themselves.

Soil reaction. If the soil contains too many acids (carbonic acid, fulvic acids in gley-podzolic soils) or alkalis (soda in solonetzes), then the cultivated plant develops poorly or even dies. For the favorable development of most cultivated plants, it is necessary that the soil solution is neither acidic nor alkaline, but medium, neutral.

It turns out that the soil reaction (acidity, alkalinity) to a great extent depends on what substances are absorbed by it. If the soil (its solid part) has absorbed hydrogen or aluminum, it will be acidic; the soil that has taken sodium from the solution will be alkaline, and the soil saturated with calcium will have a neutral, that is, medium, reaction.

In nature, different soils have different reactions. For example, marsh and podzolic, as well as red soils, are acidic, solonetzes are alkaline, and chernozems are medium-sized. We will learn more about these soils in subsequent chapters of our book.

The porosity, or duty cycle, of the soil. If there is enough nutrients in the soil but not enough water or air, the plant dies. Therefore, it is necessary to ensure that along with food in the soil there are always water and air, which are located in soil voids. Voids (pores, or wells) of the soil occupy about half of the total soil volume. So if you cut 1 l soil from the arable layer without compaction, then the voids in it will be about 500 cm 3(50% by volume), and the remaining volume will be occupied by the solid part of the soil. In loose loam and clay soils, the number of wells per 1 d of soil can reach 600 and even 700 cm 3;in peat soils - 800 cm 3;in sandy soils, the duty cycle is less - about 400-450 cm 3.

The size of the voids and their shape are very different both in the same soil and in different soils. Small wells have a gap of a hundredth, thousandth of a millimeter and even smaller, large voids, such as cracks, in the soil can have a gap of several centimeters. Too small wells in the columnar horizon of solonetzes (inside the columns), as well as very large ones (cracks) create unfavorable conditions for plants. So, root hairs of plants can penetrate only into wells with a diameter of at least 0.01 mm, and bacteria - in wells no smaller than 0.003-0.001 mmFor cultivated plants, it is desirable to create medium-sized wells in the soil by processing and structuring - with a clearance from a few millimeters to tenths and hundredths of a millimeter, and they should be evenly distributed throughout the entire thickness of the soil. In this case, even in moist soil, large pores will contain air necessary for respiration of the soil population and for oxidative processes, and in thin ones - water - an indispensable condition for the existence of all living things.

Water permeability of the soil. Falling to the soil surface in the form of precipitation, water, under the influence of gravity, seeps into it through large wells and dissolves through thin wells, or capillaries, surrounding the soil particles in a continuous layer. The larger the soil particles (for example, in sand), the greater the passages between them and the easier water will penetrate through such soil. On the contrary, in soil (for example, clayey) rich in tiny particles, the passages between them are extremely small. Water seeps into clay soils hundreds of times slower than sandy soils. In this case, it penetrates the soil mainly through cracks, wormholes, and along the courses of old decayed roots.

However, the foregoing is true only with respect to clay structureless soils. If such soil is rich in humus and lime, then individual small particles in it (especially colloidal particles) coagulate, stick together, stick together into porous grains and lumps, which, in the presence of humus and lime, are mechanically very strong and resist long-term erosion with water. In the soil between them pores of medium size are formed, as in sand, and somewhat larger. This (structural) clay soil has good water permeability, despite the fact that it consists of tiny particles.

In fig. 46 shows various wells in structural and non-structural soils. In particular, lumps of structural soil are shown here as completely capillary. However, in the best soils, such as chernozems, as well as in the cultivated arable layer of other soils and inside the lumps themselves, there are non-capillary cells and tubules, which are quite accessible to air even in moist, capillary-saturated soil with water. These voids are formed as a result of insect activity, root decay, tillage, etc. Such lumps are especially valuable. They and between them simultaneously contain water and air. They are easily permeable to bacteria and fungi, to the roots of plants. They provide soil fertility (Fig. 47).

The water permeability of the soil is easily determined in the field. To do this, in the soil to a depth of 6-7 cmembed a wooden or metal square (area 50 × 50 cm).Its lower part is made with a wedge and, if it is wooden, is upholstered with tin. The square must be installed firmly so that there are no gaps between its walls and the soil. It is better to embed not one, but two squares into the soil, as shown in Fig. 48, outdoor (50 × 50 cm)and internal (25 × 25 cm).

Pour water into both squares in a layer of 5 cm and then, maintaining it at a constant level and taking into account the flow of water, they monitor the speed of its penetration into the soil. Counts should be made on the inner square, from which the water will fall almost vertically downward, while from the outer square it will spread to the sides.

Then calculate the water permeability of the soil in millimeters of water per unit time, for example, in 1 minSince the water permeability of the soil changes over time (usually decreases), it is advisable to extend observations over it for several hours (6-8 hour).

When determining water permeability, the temperature of the water should be taken into account. The higher the temperature, the lower the viscosity of the water and it penetrates the soil faster. In the final calculation (according to the special Hazen formula), the water permeability of the soil is brought to a temperature of 10 ° C. This allows us to compare the water permeability of different soils obtained at different water temperatures.

Moisture content of the soil. Once in the soil, water, as already mentioned, moistens the soil particles, surrounding them with many layers. Water adheres to the soil, and the soil holds it firmly by virtue of its surface energy. The closer the layer of water to the soil particle, the more strongly it is held by the soil, the stronger it is bound by it. In addition, water is retained in soil capillaries.

The ability of the soil to retain water under conditions of free runoff is called the water holding capacity of the soil, and the amount of water that under the same conditions preserves the soil is the moisture capacity of the soil.

The moisture capacity of different soils is different. 100 g clay soil rich in humus can hold 50 g water (50%) and more, and 100 g sandy soil - only 5 to 25 g (5-25%). In most cases, the arable layer of loamy and clay soils holds 100 g soil from 30 to 40 g water (30-40%); peat soils are characterized by high moisture capacity: 100, 200, 300% and more.

The water resistance of the soil. If the soil is lined with a waterproof layer, then with heavy rain or artificial irrigation, all its pores are filled with water. The soil is, as it were, poured by it. The greater the soil duty cycle, the more water will fit in it. This amount of water will correspond to the water capacity of the soil.

It is clear that the water capacity of the soil in volume is equal to its duty cycle. The water capacity should be distinguished from the moisture capacity of the soil, which is understood as the amount of water held by the soil after completely soaking it and free draining of water through the pores down or to the side along the slope.

Various forms of water in the soil. The water contained in the soil is not the same in quality. Six main categories can be distinguished.

Water is tightly bound, not free, which is strongly attracted by soil particles and plants are almost completely inaccessible. In nature, there are two forms of such water: hygroscopic and maximally hygroscopic. The first is found in air-dry soil. It is absorbed by completely dry soil from the atmosphere or remains in the soil when it is dried in an atmosphere not fully saturated with water vapor (relative humidity<100%). Вторая форма прочносвязанной адсорбированной воды (максимально гигроскопическая) поглощается почвой из атмосферы, полностью насыщенной парами (относительная влажность воздуха 100% или близко к этому). Обе эти формы воды в почве передвигаются лишь в виде пара, поэтому они переносчиками солей быть не могут.

On top of the shell of the most hygroscopic water covering the soil particles, a film of loosely bound water is formed in more moist soil: this is film water. It has a high voltage, and although it can move in soil in liquid form, its intensity of movement is extremely slow. Therefore, film water is a weak carrier of salts, and it is difficult for plants to access. .

Capillary water occupies medium-sized pores in the soil. The water is free, gravitational, flows from the soil down or to the side along a slope. Steamy water is contained in soil air. Solid water (ice) is formed in the soil upon freezing. Intracellular (osmotic) water is contained in the cells of dead, but underdeveloped plants.

When there is a lot of water in the soil, the soil binds only part of it to its surface. The rest of the water is free, and plants can easily absorb it from the roots: it is gravitational and capillary water. Especially valuable in this case is capillary water; Being easily assimilated by the plant, it is at the same time held in the root-inhabited soil layer, not draining from it. The same water has the ability to move through the capillaries in the soil in all directions. When the root of the plant drinks water around it, it can be sucked into it from neighboring, more moist places. It is important that capillary water does not occupy all pores completely, but alternates with larger pores occupied by air, which is necessary for the respiration of plant roots and the entire living population of the soil.

When the soil dries up, there is little water in it. It is located in thin layers around the soil particles, and they attract it with great force to themselves. As already noted, bound water is also heterogeneous in composition. Its outer films are more friable. They are less strongly retained by the soil. The plant can still perceive this part of bound water (loose-bound, or film-like water) with its roots, but it is difficult to absorb and slowly. With this soil moisture, the plant consumes more water, evaporating it through the leaves and stems, rather than absorbing it by the roots. As a result, it loses its elasticity (turgor, as they say) and begins to fade. The soil moisture at which the plant withers is called the plant wilting moisture. This form of water is attracted to the surface of the soil with a force of 15-20 atm.

With further drying of the soil, when the outer loose layers of bound water are used up, only the finest water films around the soil particles will remain in it. This dense, firmly bound soil, water already known to us is hygroscopic and maximally hygroscopic. The force with which it is held by the soil is greater than the suction capacity of the root, and therefore the plant cannot perceive it. If there is only such water in the soil, the plant dies. The more colloidal particles in the soil, the stronger it holds water and the greater part of it will be inaccessible to plants. On clay soils containing many of these particles, plants die from drought already when at 100 g soil accounts for about 10-15 gwater (15% by weight of dry soil). In sandy soils of silt (particles finer than 0.001 mm) very little, and therefore almost all of the water from them can be taken by the plant. A plant on sandy soil dies only when at 100 g soil remains 1-2 gwater (1-2%) and even less.

Thus, it must be remembered that, although clay soils retain water in themselves more strongly, water in them is more inaccessible to plants than in sandy soils.

The forms of water described by us are located in soil pores, not being part of the solid matter of soils. They are adjoined by intracellular water contained in plant cells whose shells have not yet been destroyed, for example, in underdeveloped peat, in freshly plowed turf.

But there are two forms of water that make up the solid phase of the soil - chemically bound water, or constitutional, and crystallized water, or crystalline hydrate.

The first is most strongly associated with solid particles, including disrupted water molecules in the form of hydroxyl ions (OH ions), for example, during the interaction of iron oxide with water. The reaction Fe 2 O 3 + 2H 2 O -\u003e 2Fe (OH) 3 produces two molecules of iron oxide hydrate.

The second is also part of a solid molecule, but already whole water molecules. For example, gypsum contains two water molecules: CaSO 4 2H 2 O.

There are a lot of chemically bound water in clay minerals and a little in sand and sandy loam. It is removed from the soil at a red-hot temperature (400-800 ° C); moreover, the original mineral decomposes. The calcined residue remains.

Crystal hydrate water is removed from the soil at lower temperatures. For example, one molecule of water is removed from gypsum if the sample is heated to 107 ° C, and the second molecule is heated to 170 ° C. Dehydrated gypsum (anhydrite) in this case does not decompose, but its physical properties change. A lot of crystallization water is found in salt marshes.

Determination of soil moisture capacity. For practical purposes, it is important to know how much soil can retain water and how much it is inaccessible to plants. One and the other value is easy to determine. To do this, a plot of about 1 m 2 well watered and covered with oilcloth, tarpaulin, and straw or grass is placed on top to prevent evaporation of water. They wait one to two days so that free water that cannot be held by soil can drain or dissolve . Then a moistened area is opened and a soil incision is made across it, from the wet wall of which at various depths, soil samples are taken into a glass or jar (20 grams each). Wet soil must be weighed, then dried in an oven and weighed again. The difference in weight will show how much water was in the soil. If water permeability of the soil was determined in the field using frames, as described above, then at the end of work in the same area, soil moisture capacity can be determined (Fig. 49).

Determination of water inaccessible to plants. Water inaccessible to plants can be determined as follows. A laboratory sample of soil (grams 50-100) is scattered under laboratory conditions with a thin layer on paper and left for 10 days to allow the soil to dry. After drying, there will still be moisture invisible to the eye, the so-called hygroscopic water. If such soil is first weighed (in a glass or on a saucer), then dried in an oven and weighed again, then you will notice that its weight has decreased. This evaporated hygroscopic water. Knowing the weight of the soil before drying and after drying, you can calculate how much water was. If you double the found value, you get about the amount of water for a given soil, not digestible by the plant. This is the so-called maximum hygroscopic water. Both moisture capacity and non-digestible water are more convenient to calculate as a percentage of the weight of dry soil. For example, if we say that the moisture capacity of the soil is 50%, and that the digestible water in it is 10%, then this means that 100 g dry soil during irrigation can hold 50 g water, and of these 50 g plants can use 40 and the rest 10 g will be inaccessible to him. The moisture of the wilting of the plants, i.e. the moisture of the soil at which the plant still lives, but is already beginning to wither, is equal to approximately one and a half supply of water not absorbed by the plants. So, if not assimilated, or "dead", the water supply in the soil is 10%, then the plants will begin to wither when the moisture content of this soil decreases to 15%.

In a drought, there is little water in the soil and it is located only in shallow wells and thin films around soil particles. When there is a lot of water, it fills larger pores and passages. In addition, water can saturate substances such as humus and clay, and they swell greatly. Especially a lot of water trap humus and semi-decayed plant residues.

When the soil dries quickly and there is little water in it, the plants die. But they cannot develop in soil overflowing with water; here they lack air. For most plants, the average soil condition is favorable when some of the pores in it (about 3/4) are filled with water, and air is in other spaces. Some plants, such as rice, develop well in moist soil.

Ground water. If there is a lot of water in the soil, then, as noted, it seeps down. Penetrating through soil or mother rock, water meets a greater or lesser depth of the waterproof layer (cohesive clay or rock), stagnates on this layer or flows in the direction where it is inclined. This will already be groundwater, which feeds wells, lakes, rivers, and with a high occurrence, water also plants in a drought. If groundwater comes too close to the surface of the soil (by 1 m and closer), then she swamps her. In fig. 50 shows various forms of free, capillary, and bound water in soil.

Water capacity of the soil. Water in the soil can move not only from top to bottom, but also to the sides, as well as from bottom to top. It is not difficult to verify this. Take a mug with a perforated bottom, pour earth into it and put it in water so that it covers only the bottom of the mug. A day or two will pass (and for some soils only a few hours or even minutes), and you will notice that the soil has wetted to the very top. Water rises in the smallest gaps between the soil particles. These gaps are so narrow that they are called hair gaps or capillaries. Water adheres to the walls of the capillaries. Its layers on opposite walls of the capillary merge and fill its entire volume. In the upper part of such a water column, where water is attracted to the walls of the capillary, a concave water meniscus forms. Directly under such a meniscus, the pressure in the water is less than 1 atm.The smaller the diameter of the capillary, the more concave the meniscus formed in it and the weaker the pressure underneath. Under a flat water surface, the pressure is 1 atm.If the soil capillary with its lower end is immersed in “free” water, a concave meniscus forms in it and the water is sucked into the capillary as if by a pump. It will rise in the capillary to such a height, while the weight of the raised column of water does not balance the difference in pressures under the flat surface of the “free” water and under the concave meniscus. The column of water raised in the capillary in this case is called capillary water, “backed” groundwater or temporary overhead water. The smaller the capillaries, the higher the water rises along them, and the thinnest it rises to a height of 2-7 m

In clay soils, which have minute gaps between soil particles, water is strongly attracted to the latter. It would seem that such soils most strongly raise water through the capillaries. In fact, this is not observed. When clay particles absorb water, this “bound” water fills a significant part of the lumen of the smallest wells, and its new portions have nowhere to push. In sand, on the contrary, the wells are too wide and the attraction of water by soil particles is weak, and therefore the water rises through the capillaries quickly, but to a small height. It is best to transport upward water the soils with average mechanical composition, namely medium loamy soils, for example, Ukrainian loess.

Capillary water can linger and move in the soil even when it does not communicate with groundwater or temporary high water, for example after rain or artificial irrigation of the soil. It will be capillary “suspended” water (suspended on water menisci). It can move in any direction from more moistened capillaries, where the menisci are less concave, into the zone of narrower capillaries with more concave menisci, under which the “negative” is more pronounced (less than 1 atm.)pressure.

The ability of the soil to absorb and raise water from a certain depth, and also to conduct it from one layer to another and to the sides along the capillaries, is of great importance for plant life. If the soil did not have this ability, a lot of water in it would be completely useless, and we know how expensive water is for plants, especially in arid areas. During droughts, when the soil from the surface is not completely moistened, the plants live solely due to the water moving along the capillaries and the film water.

The rise and resorption of water through the capillaries is possible not only in the presence of groundwater or a top water, as shown in Fig. 50, but also in the absence thereof. In this case, large capillary wells filled with water play the role of shallow reservoirs supplying a network of thinner soil pores (Fig. 51).

Thus, the water-raising capillary capacity of the soil enables plants to better and more fully use moisture.

Evaporative ability of the soil. However, one must not forget that the water-lifting capacity of the soil can also cause excessive drying of it. This happens when the field is poorly loosened or not at all loosened from the surface. In such areas, the soil capillaries extend to the very top. Water rises through them and evaporates into the air. By loosening the soil, we break, break the capillaries. Water rising from below will reach only the loosened layer and will not go higher, but will accumulate and remain under it.

The soil is dried out intensely even when the arable land is covered with a crust. It happens after the rains. Thin capillaries are very well developed in the crust, which strongly suck in water. To preserve moisture in the soil, such a crust should be immediately broken with cultivators or harrows.

So, thanks to the numerous tubules, passages and gaps in the soil, water moves in it in all directions, washing out various salts, including those necessary for plants. Water with salts dissolved in it is food for plants and other inhabitants of the soil.

Air regime of the soil. In dry soil, all wells are occupied by air. Part of it is attracted with force by the surface of soil particles. This part of the air has poor mobility and is called absorbed air. The rest of the air located in large pores is considered free. It has significant mobility, can be blown out of the soil and easily replaced with new portions of atmospheric air.

As the soil is moistened, the air is forced out by the water and goes outside, and part of it and other gases dissolve in the soil water. Ammonia dissolves especially well in water (in 1 l water several hundred liters). Other gases, such as carbon dioxide, oxygen and nitrogen, also dissolve in water, but are much weaker than ammonia. For the successful growth of most cultivated plants, it is necessary that both air and water are in the soil. At the same time, water occupies small and medium pores, and air - larger ones.

Of the air in the soil, oxygen is mainly consumed. As mentioned above, it is spent on the respiration of the roots of plants and animals inhabiting the soil, combines with various substances in the soil, such as iron, and is mainly used by various bacteria in the respiration, decomposition and oxidation of plant, animal and some mineral residues. Instead of the oxygen consumed by living things, the air in the soil is enriched with carbon dioxide, which is released during their breathing and during the decay of organic residues. From soil air, carbon dioxide enters both the soil solution and the atmosphere.

The air in the soil does not remain without movement. In the afternoon, when the soil warms up by the sun's rays, the air inside it also warms up. It expands, and part of it comes out. At night, the soil and the air it contains cool down. A rarefied space forms in the soil, and new air from the outside fills it. It will take several days, and the entire composition of the air in the soil will be updated.

Air changes in the soil also occur for other reasons. It can be blown away by the wind, replaced by water seeping into the soil, and in both cases, the air removed from the soil is replaced by new portions of fresh atmospheric air. Soil air also moves when atmospheric pressure changes; an increase in this pressure causes the introduction of some part of the soil air into the soil. On the contrary, its decrease is accompanied by the release of part of the soil air to the outside. Finally, the change of air in the soil can occur even in the absence of wind, rain and at constant atmospheric pressure. At the same time, soil air, rich in carbon dioxide and water vapor, gradually comes out, and drier and rich in atmospheric oxygen penetrates into the soil pores (gas diffusion occurs).

The intensity of soil air renewal in various climatic and soil zones depends on various reasons. For example, in deserts, a sharp change in temperature during the day and night, as well as the blowing of soil air by the wind, are more affected. In an area rich in precipitation, for example, taiga, air change will noticeably occur when water seeps into the soil, etc.

Since soil air is almost always wetter than atmospheric air, replacing it with the latter leads to drying out the soil. Consequently, the soil can evaporate and lose water not only by its surface, but also through the inner layers and pores. Such evaporation, unlike surface evaporation, is called subsoil. It causes great harm to those soils into which the wind easily penetrates (lumpy, fractured, freshly plowed in hot windy weather). Therefore, in arid areas in order to avoid moisture loss, deep plowing the soil in the heat is not recommended. And if plowing is done, then the arable land after the plow must be carefully barred and leveled (with a drag or rear of the harrow).

Not all soils exchange air equally freely. For example, sandy soils are characterized by large passages between soil particles. Air penetrates these soils easily and to great depths. The roots of plants breathe freely, in the presence of water, plant and animal residues quickly decompose. A different picture is observed in unstructured clay, wet soils. The gaps between the soil particles are small, and even those are often occupied by water. Air penetrates into such soil with difficulty and in small quantities. The soil dries up slowly. Plant and animal residues decompose poorly. Various substances in the soil, such as iron, not only do not oxidize, but lose the oxygen that they have accumulated before. Having lost some of the oxygen, iron becomes toxic to plants. In such soil, bacteria that create saltpeter cannot live. But the bacteria that destroy it begin to develop.

In a word, the soil "lives an abnormal life" and, as it were, "suffocates." Such soil is gradually swamped. To correct the soil, you need to drain it, loosen the surface layer, smell lime, manure in it, apply mineral fertilizers under the plants.

Heat in the soil. For the development of soil and plant life, heat is needed. The soil receives heat from the sun, directly heated by its rays, or from air and precipitation. A little heat comes to the soil surface and from the internal heated layers of the Earth, and also is released during the breathing of living creatures, decomposition of plant and animal residues, the interaction of some components of the soil with each other, when the vapors are condensed into liquid water, and water freezes. Sometimes the soil is warmed by warm springs flowing to the surface of the Earth from its deeply heated layers. Such sources are known, for example, in Iceland, the USSR - in Kamchatka, the North Caucasus (Goryachevodsk), in Dagestan, Georgia (Tbilisi), Azerbaijan (near Lankaran) and in other places.

Not all soils are equally heated by the sun. Dark, rich in chernozem, and most importantly dry soils warm up much faster than light and moist. Damp soils are especially slowly heated. This is because a lot of heat is spent on warming and evaporating the water in them. Sandy soils are drier than clay soils and therefore heat up sooner.

In addition to the color and content of humus and water, the location of the area is of great importance for heating the soil: the soils lying on the southern slopes heat better than others, somewhat weaker on the eastern and western, and worst of all on the northern.

The heat received by the soil is gradually transmitted through soil particles, water and air are transferred to the lower layers. Solid particles of soil and water conduct heat better. A very weak conductor of heat is air.

At night, the soil cools from the surface, and a warm day wave moves to a certain depth. So the waves one after another every day go into the soil. Soil particles expand from heat, then shrink from cold. This contributes to a larger and faster weathering.

Warm soils are favorable for the development of plants and other soil inhabitants.

In winter, when the soil is hidden under snow cover, when water freezes in it and instead of warm deep waves go cold, its life freezes to a significant extent. All life in the soil falls into hibernation and wakes up only the next spring.

The electrical conductivity of the soil depends on its moisture content, quantity and quality of salts, density (or porosity) and temperature. The electrical conductivity of dry soil is close to zero. As humidity increases and salts dissolve in water, the soil's electrical resistance drops sharply, and its electrical conductivity increases. Those salts that dissociate in an aqueous solution, turning into an ionic state, especially increase the electrical conductivity of the soil. For example, sodium chloride in solution gives a sodium ion with a positive electric charge (Na +) and a chlorine ion with a negative electric charge (C1 -). Chains of interacting ions in a solution are conductors of electricity.

Numerous attempts have been made to measure the moisture and salt content in the soil by its electrical conductivity. However, the exact values \u200b\u200bare not obtained, since the electrical conductivity depends on several reasons. So, with increasing humidity, the electrical conductivity initially increases, but with humidity above the moisture capacity of the soil, it again falls, since the soil solution of salts becomes very diluted.

But in a number of cases where it is required to ascertain sharp changes in soil moisture or temperature, the soil's electrical resistance or its inverse value, electrical conductivity, is used in soil works, for example, in determining soil water permeability by the method of isolated columns. A soil column is dug in the soil in the form of a prism and wrapped with oilcloth so that water does not flow from it to the sides. Brass or copper electrodes are driven into the wall of the column, from which insulated wires are brought out and connected to the electrical network (with a voltmeter or ammeter). The soil section is buried. Outside, a wooden or metal square is installed on the column, into which water is poured to level 5 cm from the soil surface, then the amount of absorbed water is calculated. In parallel with this, starting from the upper pair of electrodes, the soil resistance to the action of electric current is determined. Dry soil has a very high resistance (tens of thousands ohm).But when the wetted layer spreads to the depth of the electrodes, the soil resistance decreases by tens of thousands of times, and the electrical conductivity increases accordingly. This will be instantly noted by a voltmeter or ammeter. So, without digging up the soil, you can precisely determine when and at what depth it got wet, what is important to know when studying the water permeability of the soil, after rain, during artificial irrigation and in other scientific and practical observations.

Using a similar installation, without breaking the soil, it is possible to establish the depth of its freezing: in frozen soil, the electrical conductivity decreases sharply.

Once again about the structure of the soil. All soil properties that are important for the development of agricultural plants get the best expression in structural soils that contain both air and water. Water is placed inside the lumps and at the joints between them, and air is in large voids between the lumps, along their surface and partly inside the lumps, in large channels and pores (see Fig. 47). Structural soil has good thermal properties. Microorganisms useful for plants are favorably developed in it. The mineral part in such soil is more easily eroded and releases the nutrients needed for plants. In it, on the surface of the lumps, plant and animal residues decompose better, and the inner, less ventilated part of the lumps is a "laboratory" where high-quality neutral ("sweet") humus accumulates. Ultimately, structural soil always provides a higher yield of agricultural plants. Therefore, the expression is true: cultural soil (loamy and clayey) is a structural soil. But not in any soil by nature is a good structure. Often you have to work hard to get structural arable land. On all soils, the creation of the structure is helped by the artificial increase in humus in it, as well as the saturation of the soil with calcium. For the latter purpose, lime is used on acid soils, and on gypsum (for example, on solonetzes) gypsum or lime and gypsum substitutes.

It is necessary to manure the soil, introduce annual and perennial cereal and bean herbs into the crop rotation, and lupine and seradella on the sands. Legumes enrich the soil with calcium and nitrogen, and all herbs - legumes and cereals - provided they are plentifully enriched with humus, as they have a root system several times larger than oats, rye, wheat and other field and garden plants (rice . 52). In addition, well-developed herbs with a dense network of their roots divide the soil into grains and lumps much stronger than cereals or vegetables with a weak root system. When introducing herbs into crop rotations, one cannot be limited to a well-known pattern. It is necessary to test and boldly introduce new crops into the crop mixtures of crop rotations. For example, in the non-chernozem zone, along with clover and timothy, ryegrasses, fescue, and hedgehog deserve great attention; in the dry steppes along with alfalfa and wheatgrass - clover, chickpea and Sudanese, in the humid subtropics - lupine, horse bean, horned lamb, etc.

Serious attention must be paid to timely tillage. When plowing dry soil, we destroy, spray the structure; when plowing waterlogged soils, press the structure, lubricate it. If possible, you should strive to plow optimally moistened soil when it is not lubricated and does not adhere to the implements; under this condition, the best quality structural soil is obtained.

Experience in using polymers for soil structuring. As can be seen from the foregoing, the main methods of soil structuring at present are processing, introducing crop rotation with herbs, applying organic and mineral fertilizers, liming acidic soils, gypsum plating of solonetzes, or using lime and gypsum substitutes. The correct systematic use of these techniques cultivates and structures the soil and ultimately improves their fertility.

The structure of the arable layer can be quickly improved by cultivating it at optimal humidity. However, if there are no durable, water-resistant, and porous aggregates in the initial soil before treatment, then it is possible to improve its physical condition due to treatment for a short time. The loosened arable land quickly sits down, and in the event of heavy rain or watering, it is disengaged. Lumps and grains are washed away by water, the soil is covered with a harmful crust.

A much more fundamental soil structuring is achieved as a result of cultivation of grasses, especially perennial ones, in crop rotation. The structure created under herbs (with a high yield and well-developed root mass) is preserved for several years and only gradually (after 4-5 years) is lost under row crops and especially cereal crops. It would seem that this method fully satisfies agricultural production. However, it is not. Significant soil structuring, for example podzolic soils, is achieved under grasses (a mixture of red clover with timothy) only after two years of use, and the maximum structuring effect of a more complex grass mixture in pasture crop rotations (4-5-component) is observed after 4-5 years of grass growth. Thus, the time required for soil structuring in the field of crop rotation is about half that time, which subsequently lasts the effect of structuring. The result is very modest. Therefore, the search for faster and more effective methods for improving the physical properties of the soil by introducing any ameliorating substances into it is natural.

The first attempt to prepare artificial glue for soil structuring was made by K. Fadeev and V.R. Williams at the end of the XIX century. They received an ammonia humic extract from the northern chernozem and used it in an experiment to structure a mixture of Vorobev tertiary sand and silt fraction from Gzhel clay. A similar attempt was made by S. Oden (1915) and then N.I. Savvinov (1936), receiving an alkaline extract from peat.

From 1932 to 1936, extensive research in the field of artificial soil structuring was carried out under the supervision of Academician A.F. Ioffe in Leningrad, at the Physics and Agronomy Institute. Similar work was later performed in the United States and other foreign countries. Various adhesives for soil structuring have been proposed (peat glue, viscose, etc.). However, the first experiments in this regard were unsuccessful. The proposed cement adhesives structured the soil only for a short time (a year or two), and their quantity for the structuring was required large (tens of tons per hectare). Therefore, these preparations were not included in agricultural practice.

A new direction in solving this problem was determined in the last two decades, when polymers, collectively called krilliums, were used for soil structuring.

Krilliums are mainly derivatives of three organic acids: acrylic, methacrylic and maleic. The molecules (primary particles) of these acids and their derivatives have the ability, interacting with each other, to form chains (polymers), which include thousands and even millions of individual simple molecules. These substances are soluble in water. If they are introduced into the soil with powder, mix thoroughly with the soil and then moisten it with water, the polymers impregnate the wetted layer 1. Interacting with soil particles, they will begin to coagulate, harden and, like cement, will bind soil particles. At this time, you need to wait until the soil dries to the optimum moisture, and loosen it so as to create a structure of the right size and optimal porosity (lumpy-grained). When the soil dries, its lumps and grains will acquire mechanical strength and water resistance. They will be resistant to spraying during processing and against spreading during rains or irrigation. So in a few days, you can structure the soil, which, if properly processed, subsequently lasts 5-6 years.

To date, a number of countries have proposed various polymer preparations, which, when tested, have proven themselves to be good structural agents; for example, in the USA - preparations “Gipan”, “Separan” and others, in the German Democratic Republic - “Verdikunk AN”, in the USSR - several drugs, of which the polymer “K-4” proposed by the colloid chemistry laboratory of the Academy of Sciences of the Uzbek SSR has the highest structural ability (Fig. 53).

The use of polymers for soil structuring in agricultural production is still very limited. The reason for this is the high cost of polymers needed in agriculture. We need a special plant that manufactures them for agricultural purposes. When krillium preparations are produced not in hundreds of kilograms, but in millions of tons, their price will decrease many times. It should be remembered that krilliums can be widely used to combat water and wind erosion of soils, to fix bottoms and slopes on channels, to combat dustiness at airfields and stadiums, and for other purposes.

Krilliums need to be cooked humus-like. After all, humic acids, especially humic and ulmic, are themselves natural polymers, which explains their high structural role in the soil.

In addition, synthesizing krillia, you need to take care not only of their structural role, but also to provide them with fertilizing qualities. The named polymer preparations are long-acting nitrogen fertilizers. In addition, during the synthesis, it is necessary to introduce potassium and phosphorus into them. Observing these conditions and introducing polymers into the soil, we will not only structure it, but will also provide complete fertilizer - nitrogen, potassium, phosphorus.

But while krilliums are not available on a large scale for agriculture, it is necessary to structure the soil in all other ways previously described: cultivating the soil, using grass crop rotations, etc. It should always be remembered that structural arable land on loamy and clay soils is an indicator of the field’s culture. The structural nature of the soil increases the yield and makes it sustainable.

Agriculture is based on the use of soil as the main production tool. Soil in crop production is a medium for cultivating plants. The crop depends on the quality of the soil. Soil has the most important property - fertility.

Soil fertility is the ability of the soil to provide plants throughout the entire period of their growth and development with nutrients, water and air. Therefore, the work of the farmer is aimed not only at obtaining high yields, but also at maintaining and improving soil fertility.

The composition of the soil is divided into two parts - mineral and organic.

The mineral part of the soil includes mainly sand and clay. Depending on the content of mechanical particles - sand and clay - the soils are divided into clay, loamy, sandy and sandy loam (Fig. 8). In agronomic terms, loamy and sandy loamy soils are the best. Loamy soils retain water well, have a sufficient content of nutrients and air for the normal development and growth of plants, and are easier to process than clay ones. Sandy loam soils retain moisture less, but are easily processed and quickly warmed up in the spring.

Fig. 8. The mechanical composition of the soil: a - sand; b- sandy loam; in - light loam; g - medium loam; d - heavy loam; e - clay

The organic part of the soil consists of the remains of plants and animals. Upon decomposition of organic residues, humus (humus) is formed. Bacteria and microorganisms take part in the formation of humus. Humus improves the physical properties of the soil (creates a lumpy-grained structure necessary for plants) and enriches it with nutrients: salts of nitrogen, potassium and phosphorus.

The soil consists of individual lumps (aggregates) and, from an agronomic point of view, can be structural and structureless.

The structural soil is slightly sticky, so it is easy to dig and plow, even if it is very moist. From the structural soil, plants absorb nutrients well.

Unstructured soil does not absorb moisture well. Water runoff over the surface leads to soil erosion. After rains or watering, such soils “float”, become denser, and become difficult to process.

To create and maintain the soil structure, in addition to the systematic application of fertilizers, it is necessary to sow perennial grasses (for example, clover, alfalfa), leaving behind a large amount of organic residues.

Soil deposits have developed over hundreds of thousands of years. These processes took place in a wide variety of conditions. Therefore, the soils of different geographical regions are not identical in structure and properties. On the territory of Russia, more than one hundred different types of soils are noted, the most common of which are: podzolic, sod-podzolic, sod, gray forest, chernozems and chestnut soils.

Podzolic soils formed under the canopy of a closed coniferous forest with moss cover, poor grass vegetation or without it. The fertile layer of podzolic soils is low, about 10 cm. Under it is a grayish-white layer similar to ash, so this soil is called podzolic.

Sod-podzolic soils formed under meadow and bog vegetation. Their fertile layer is 20 cm.

Soddy soils formed under meadow vegetation and forests, which had significant grass cover. The fertile layer of sod soils reaches 25 cm.

Gray forest soils were formed as a result of the vital activity of broad-leaved forests and meadow steppes. Their fertile layer exceeds 50 cm.

Black soil soils accumulated under the cover of grassy meadow-steppe and steppe vegetation. Rich vegetation leaves behind a significant amount of root residues. This contributes to the accumulation of a large amount of humus in the soil. Chernozem soils are highly fertile, their fertile layer is highest - 80-100 cm.

Chestnut soils formed in an arid climate, under the sparse grassy vegetation of the dry steppes. The fertile layer of these soils is 30-40 cm.

As you can see, the fertility of different soils is not the same. But a person, by properly cultivating the fields, using timely fertilizers and alternating planting crops, can significantly increase soil fertility.

Practical work No. 3
Determination of soil mechanical composition on a school site

You will need: soil samples, plastic bags, scoop, water, cups.

Safety Rules

Take soil samples with a scoop.
Sprinkle the soil gently without spraying.
Wash your hands when finished.

Work order

Collect soil samples (about two glasses each) from the vegetable plot, garden and greenhouse in bags.
Put the soil of each sample in a cup and moisten it with water.
Soften the soil with your fingers to a doughy state.
Roll out well-softened soil into a cord about 3 cm thick.
Try folding the cord into a ring.
Determine the mechanical composition of the soil (see. Fig. 8):
- heavy loam - the cord easily rolls, when rolled into a ring, it cracks;
- medium loam - the cord is easily formed, but when collapsed into a ring it breaks up;
- light loam - the cord breaks into pieces at the slightest attempt to twist it into a ring;
- sandy loam - the cord breaks into pieces when rolling;
- sand-cord is not formed.
7. Tidy up the workplace, wash dishes and hands.

New concepts

Fertility; soil types: podzolic, sod-podzolic, sod, gray forest, chernozem, chestnut; clay, loamy, sandy and sandy loamy soils; structural and structureless soils; humus (humus).

test questions

What is the most important property of soil?
What is fertility?
What are the main soil types?
Which soils are highly fertile?
How to divide the soil depending on the content of mechanical particles?
Determine the soil texture in your garden.
What is the difference between structural soil and structureless soil?

Soil is a loose surface layer of land with fertility. Fertility of the soil Fertility of the soil, i.e., its ability to provide plants with the necessary set and amount of nutrients, water, air, is one of the most basic properties of the soil.

Human activities Human activities Climate Climate Mother rock Plants Plants soil topography Animals Determines the nature of the effect of soil, melt and rainwater on the soil, and the migration of water-soluble substances. It affects the thermal and water conditions of soils. Determines the thermal and water conditions of soils. Changes the properties of the soil. Organic residues are supplied to the soil, as a result a special substance is formed - humus. Rocks on which soils are formed. They affect soil properties and their fertility. The larger the age of the territory, the more powerful the soil layer. Convert organic to inorganic

In 1886, he defined the soil as a fertile surface layer of the Earth created by the combined action of all components of nature. More than 100 years ago, V.V. Dokuchaev established that the distribution of the main soil types is subject to the law of latitudinal zoning on the plains and altitudinal zonation in the mountains. VV Dokuchaev called climate change, its main characteristics, the moistening regime and temperature regime, to be the most important reason for the zoning of soils. What did Dokuchaev mean by calling the soil “a mirror of the landscape?” () The soil determines the vegetation cover and depends on it

Soil fertility depends on the thickness of accumulation horizon 1. The most important property of soil is its fertility, i.e. ability to provide growth and development of plants. 2. Humus is important for fertility, in which the chemical elements necessary for nutrition are accumulated. A1A1A1A1 A2 B C Accumulation horizon Washout horizon Washout horizon Mother rocks

C B A2A2 A1A1 Ao Mother rock Illuvial horizon (washout zone) Elluvial horizon (washout zone) Humus-accumulative (humus horizon) Forest litter Meadow felt Soil profile - vertical section of the soil from the Surface to the parent rock

1. What are the conditions of soil formation known to you. Try to highlight the main ones for the soils of our region. 2. What soil properties are known to you? Remember what you know about the properties of soils from botany. 3. Knowing what the soil fertility depends on, make a characteristic of the climate, topography, and vegetation of the territory where fertile soils could have formed. 4. What determines the diversity of soils in our country?

A b BB 2. What is soil fertility? The ability of the soil to produce high crop yields. The ability of the soil to provide plants with the necessary set and amount of nutrients, water, air, high humus yield. Next question Next question