physical properties soil

Questions

1. General concepts.

2. The solid phase of the soil and its effect on the resistivity during plowing.

3. Liquid and gaseous phases.

4. Characteristics of the soil structure.

5. Influence of compaction on the soil and ways to reduce it.

General concepts

The soil- the main means of production agriculture. Therefore, the responsibility of each generation of people for its condition is extremely great. The negligent attitude of previous generations to this wealth has led to the fact that we currently have only 14 ... 15 million km2. This is 1.5 times less than it was before active land cultivation (20 million km2).

Knowledge of the physical and mechanical properties of the soil allows the development and use of rational methods and systems of soil cultivation, which contribute to the preservation of its fertility.

The soil - this is the upper fertile part of the land of the earth's crust .

The soil is a heterogeneous medium, consists of solid, liquid and gaseous phases, see Fig. 1 - The structure of the soil composition.

Rice. one. The structure of the composition of the soil

There are physical and technological properties of the soil.

Physical- these are properties that characterize the state and structure of the soil (materials).

Physical properties of the soil: structure, mechanical composition, humidity, porosity (duty cycle) and density.

Technological are properties that appear when machining soil and influence the course of this process.

Technological properties include: soil hardness, coefficient of volumetric collapse, viscosity, stickiness, abrasiveness.

The solid phase of the soil and its influence on the resistivity during plowing

solid phase presented Stony inclusions are particles larger than 1 mm and fine earth - particles smaller than 1 mm.

Stony Soils is the ratio of the mass of stony inclusions to the mass of fine earth in percent.

The soil is considered non-stony if the content of stones in it does not exceed 0.5%;

Slightly stony - 0.5 ... 5.0% of stones;

medium stony - 5.0 ... 10% of stones;

Strongly stony - more than 10% of stones.

The last two soil types require a special tillage system.

The mechanical composition of the soil is determined by the results of the analysis of fine earth, which is divided into "physical sand" (particle size more than 0.01 mm) and "physical clay" - (particle size less than 0.01 mm). Depending on the content of "physical clay" soils are divided into:

sandy (sand) - the content of "physical clay" up to 10%;

· sandy loam (sandy loam) – 10…20% of “physical clay”;

· loamy (loam) – 20…50% of “physical clay”;

Clay (clays) more than 50% of “physical clay”.

The clay particles contain cementing inclusions, due to which the soil is held together.

There are heavy and light soils.

heavy – These are soils that contain a lot of clay .

Their properties: when wet, they stick to the working bodies of machines, and when dry, they form lumps. These soils do not absorb moisture well, but retain it well.

Lungs – These are soils that contain a lot of sand particles. . Properties: they are not sticky and not plastic, because they do not contain binding inclusions. Sandy soils absorb moisture well, but retain it poorly.

Sandy and loamy soils in their properties occupy an intermediate position in comparison with clay and sandy soils. It turns out " golden mean”, so these soils are characterized by high yields.

The mechanical composition of soils has a direct impact on the workability of soils, which is characterized by soil resistivity Kud. Coefficient resistivity soil is determined only during plowing. This is the ratio of the drag force of the plow to the cross-sectional area of ​​the formation.

Rice. 2. To the calculation of soil resistivity.

,

Where Rsopr. – plow resistance force, N;

BUT– plowing depth, cm;

AT– body capture width, cm;

N- the number of buildings.

The dependence of soil resistivity on its mechanical composition can be expressed graphically:

Rice. 3. Graph of Soil Resistivity

(particle size less than 0.01 mm).

According to the resistivity of the soil are divided into five groups, see Table 1

The solid phase of the soil can be Structural and Structureless.

The structure of the soil is determined by a set of aggregates of different sizes, shapes, density, water capacity and porosity. Aggregates consist of individual mechanical particles held together by clay and humus.

Structureless soils consist of solid elements occurring in a continuous mass.

The structure of the soil can be:

blocky (aggregates larger than 10 mm);

lumpy (3…10 mm) macroaggregate;

granular (0.25…3 mm) macroaggregate;

dusty (less than 0.25 mm) - microaggregates.

From an agronomic point of view, aggregates with sizes of 0.25 ... 10 mm are considered valuable, they are called macroaggregates. Units smaller than 0.25 mm are called Microaggregates.

The most resistant to the eroding effect of water are aggregates from 1 to 10 mm.

Aggregates smaller than 1 mm are erosive. If the upper soil layer (0...5 cm) contains more than 50% of such particles, and there is no living and non-living vegetation, then at a wind speed of more than
12 m/s wind erosion takes place (dust storms are formed). For the south of Ukraine, the most dangerous period in this respect is January-April.

Structural soils yield more than unstructured soils. Frequent tillage, as well as its compaction by the running wheels of machines, leads to the destruction of the soil structure.

Assessment of the content of aggregates in structural soil different sizes produced by determining the aggregate composition of the soil (Fig. 4).

Rice. 4.

Liquid and gaseous phases

Liquid phase It is represented in the soil by water and solutions of various substances.

The water is divided into gravitational And capillary.

gravitational moisture contained in large voids. Feature: It moves freely from upper layers soil to the bottom by gravity. With low soil moisture, gravity water can be absorbed by the capillaries of the upper layers of the soil.

capillary moisture, Contained in small capillary voids. Feature: in capillary voids, this moisture moves in any direction and spreads from more humid layers to less humid ones. This water is available to all plants and constitutes the main reserve of soil moisture.

The amount of water that is placed in the soil is judged by absolute humidity ( Wa, %):

, (1)

Where M In and MS are the masses of wet and dry soil, respectively.

Absolutely dry soil is called, dried at a temperature of 105 ° C to constant weight.

When comparing the degree of moisture in soils of different mechanical composition, it is determined by the value Relative Humidity (Wo, %):

, (2)

where Wp– field moisture capacity of the soil; %.

Field moisture capacity of the soil- This maximum amount moisture in percent that the soil is able to hold in itself (soil moisture at the moment of its complete saturation).

Field capacity various soils varies in wide aisles: 100 g of dry clay soil can hold 50 g of water, while 100 g of sandy soil can hold only 5 ... wet impression Wo= 75%, and clay is almost dry because Wo = 30%.

;

;

;

..

Soil moisture has a greater impact on the quality and energy intensity of its cultivation (Fig. 5).

Rice. 5.

When plowing (Fig. 5) dry soils (segment AB) blocks are formed with a diameter of up to 0.5 m or more. When plowing waterlogged soils (section VG), there is a strong sticking and unloading of the soil in front of the plow body. This leads to an increase in soil resistivity and poor incorporation of plant residues. With a further increase in humidity (segment DG) water acts as a lubricant and Co. decreases.

From the graph (Fig.5) best performance processing takes place at an absolute humidity of 15 ... 30%. It has been established that in this case the soils are not only preserved, but new structural aggregates are formed.

gaseous phase in the soil it is represented by air and gases - ammonia, methane, etc. Air is in the soil in Free and pinched state. Free air is located in large voids, and “pinched” in capillaries.

The “pinched” air increases the elasticity of the soil and reduces its water permeability.

The movement of free air leads to the loss of moisture from loose soil. During processing, the soil is compressed and a significant part of the free air goes into a “pinched” state. In this case, potential energy is accumulated, which, after the termination of compression, breaks the bonds between soil lumps, contributing to the structuring of the soil.

Soil structure characteristics

The main characteristics of soil structure are its Porosity and Density(bulk weight).

All types of soil are permeated with pores filled with air, water or organic inclusions.

Porosity called the volume of voids in the soil filled with water and air.

Soil total porosity R, % is determined from the formula:

, (3)

Where Vblank- the volume of voids that can be filled with air and water;

Vprob. is the volume of the studied soil.

Porosity depends on the structure, degree of compaction, moisture content, as well as on the mechanical composition of the soil. . In clays and loams it is 50...60%, in sandy soils - 40...50%.

The porosity of the same soil is a variable dependent on moisture. In moist soil, the particles appear to be, as it were, moved apart by layers of water; when the soil dries, they come closer.

soil density

Distinguish valid, In a natural state and density solid phase.

Actual Density is the ratio of mass M From absolutely dry soil to volume V Prob. of the test sample taken without disturbing its natural composition:

Density in natural state- represents the ratio of the mass of soil in its natural state to the volume of the test sample taken without disturbing its natural composition:

. (5)

Usually, the actual density of the soil and the density in the natural state are determined by the cutting cylinder method, which consists in taking soil samples in the natural state (without disturbing its structure) (Fig. 6).

Rice. Fig. 6. Scheme for determining soil density by the “cutting cylinders” method: 1 – soil; 2 – cutting cylinder; 3 - knife.

Solid density equal to the ratio of the mass of absolutely dry soil to its volume in a compressed state.

. (6)

In practice, the density of the solid phase is found by the pycnometric method, in which the mass M is determined by weighing, and the volume is found as the volume of water displaced by the soil sample.

The density of the solid phase varies from 2.4 (chernozems) to 2.7 g/cm3 (red soils).

The density value depends on the mechanical composition, humus content and soil porosity. The density of the arable layer varies over a wide range - from 0.9 to 1.6 g/cm3. The subsurface horizons of the soil have a higher density - 1.6...1.8 g/cm3.

Experiments have shown that for each type of plant there are optimal densities. When the soil is compacted above the optimal yield value ( At) decreases, and if the compaction is too high, it is completely absent (Fig. 7).

Rice. 7.

Soil density is considered a very important fertility factor. It is regulated by mechanical tillage in accordance with the requirements for individual plant species.

Impact of compaction on the soil and ways to reduce it

Consequences of overconsolidation of the soil:

1. Degrades its structure, aeration, nitrifying ability, etc.; worsens the microrelief of the agricultural background and the conditions for subsequent technological operations;

2. Reduces the effectiveness of mineral fertilizers;

3. Promotes the development of erosion processes;

4. Increases the traction resistance of tillage machines, resulting in an increase in the specific energy and fuel consumption by 10 ... 17%;

5. Causes a decrease in the performance of units by 8 ... 12% or more;

6. Leads to a decrease in crop yields by 15% or more;

Reducing the compacting effect of MTA propellers on the soil is carried out: due to technological operations and constructive measures.

Technological operations:

1. Carrying out field work in the most optimal agrotechnical terms (the period of “ripeness” of the soil);

2. Combination of operations (with a flat cutting foot) performed in one pass of the unit;

3. The introduction of chisel tillage, which is less energy-intensive compared to moldboard plowing, destroys the plow track and allows almost twice as much to accumulate and retain moisture in the soil;

4. Introduction of zero tillage (sowing with a stubble seeder, cross-breeding wheat with wheatgrass, etc.);

5. Cultivation of agricultural crops using a permanent technological track (track system of agriculture).

Structural measures:

1. Wide introduction of traction-driven units (bridge technology of cultivation of agricultural crops);

2. The use of wide profile (arch) tires with low internal air pressure.

3.Equipment of energy facilities with twin or triple wheels;

4. The use of caterpillar and half-track power vehicles in the main field work;

5. The introduction of rubber-reinforced caterpillars to reduce their mass, and hence the total pressure of the tractor on the soil.

Literature

1. M55 Mechanical and technological power of the agricultural materials: Navch. helper/O. M. Tsarenko, S. S. Yatsun, M. Ya. Dovzhik, G. M. Oliynik; Ed. S. S. Yatsuna. - K.: Agrarna osvita, 2000.-243p.:il. ISBN 966-95661-0-7

2. Mechanical and technological power of the agricultural materials:

Podruchnik / O. M. Tsarenko, D. G. Voytyuk, V. M. Shvaiko et al.; Ed. S.S.

Yatsuna.-K.: Meta, 2003.-448s.: il. ISBN 966-7947-06-8

3. Mechanical and technological power of agricultural materials. Workshop: Navch. helper/D. G.Voytyuk, O.M. Tsarenko, S.S. Yatsun ta in.; For ed. S.S. Yatsuna: -K.: Agrarian education, 2000.-93 p.: il.

4. Haylis G. A. et al. Mechanical and technological properties of agricultural materials - Lutsk. LGTU, 1998. - 268 p.

5. Kovalev N. G., Khaylis G. A., Kovalev M. M. Agricultural materials (types, composition, properties). - M.: IK "Rodnik", magazine "Agrarian Science", 1998.-208 p., ill. 113.-(Textbooks and textbooks, manuals for higher education, institutions).

6. Physical and mechanical properties of plants, soils and fertilizers. - M.: Kolos, 1970.

7. Skotnikov V. A. et al. Workshop on agricultural machines. - Minsk: Harvest, 1984. - 375 p.

8. Methods for studying the physical and mechanical properties of agricultural plants. M.: VISKHOM, 1960. -–269 p.

9. Karpenko A. N., Khalasky V. M. Agricultural machines. – M.: “Agropromizdat”, 1983. – 522 p.

Voronezh State Medical Academy named after N.N. Burdenko

Institute of Nursing Education

Department of Higher Nursing Education

TEST

DISCIPLINE: Hygiene

SUBJECT:

1) The composition and properties of the soil. Soil self-purification.

2) Food storage and preservation.

COMPLETED: 3rd year student

304 groups (d/o)

CHECKED:

Voronezh

PLAN

1. SOIL COMPOSITION.

2. SOIL FORMING FACTORS.

3. SOIL TYPES.

4. SOIL PROPERTIES.

5. SOIL SELF-CLEANING.

6. CRITERIA FOR QUALITATIVE SANITARY AND HYGIENIC ASSESSMENT OF SOIL.

7. FOOD STORAGE.

8. FOOD PRESERVATION.

9. FOOD STORAGE REQUIREMENTS.

10. LIST OF USED LITERATURE.

SOIL COMPOSITION

The soil- the outer layer of rocks modified under the influence of water, air and various organisms.

The soil consists of solid (mineral and organic), liquid and gaseous phases. All soils are characterized by a decrease in the content of organic matter and living organisms from the upper soil horizons to the lower ones.

Horizon A1 is dark-colored, contains humus, is enriched in minerals and is of the greatest importance for biogenic processes.

Horizon A2 - eluvial layer, usually has ashy, light gray or yellowish grey colour.

Horizon B is an eluvial layer, usually dense, brown or brown in color, enriched in colloidal dispersed minerals.

Horizon With parent rock altered by soil-forming processes.

Horizon B is the parent rock.

The solid part of the soil consists of mineral and organic substances. By dispersion, mineral substances are divided into two groups: with a diameter of more than 0.001 mm (fragments of rocks and minerals, mineral neoplasms) and less than 0.001 mm (weathering particles of clay minerals, organic compounds). The polydispersity of particles of a solid soil particle determines its friability. Part of the soil volume filled with air or water is called soil porosity, which is 40-60%, sometimes up to 90% (peat), sometimes up to 27% (loam).

The composition of the mineral part of the soil includes Si, Al, Fe, K, Na, Mg, Ca, P, S and others chemical elements, which are mainly in the oxidized state (SiO2, A12O3, Fe2O3, K2O, Na2O, MgO, CaO), as well as in the form of salts: carbonic, sulfuric, phosphoric, hydrochloric.

The solid part of the soil includes organic matter(mainly in humus), which contains carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and other elements. Many elements are dissolved in soil moisture, which fills part of the pores, while the rest of the pores contain air, which in upper layers(15-30 m) consists of N2 (78-60%), O2 (11-21%), CO2 (0.3-8.0%).

SOIL FORMING FACTORS

Soil-forming factors: There are at least 6 soil-forming factors. In general, the process of soil formation began when the first microorganisms and unicellular algae appeared.

The first soil-forming factor is the parent rock, it is subdivided into three types: igneous rocks (these are the rocks that were formed as a result of the cooling of magmatic masses during the eruption of volcanoes (granites, basalites)), metamorphic rocks are those rocks that were formed as a result of the action high temperatures and pressure, sedimentary rocks - those rocks that were formed as a result of weathering and crushing. Sedimentary rocks are the main soil-forming rocks. Sedimentary rocks were affected by living organisms, the process of soil formation was going on.

The second soil-forming factor- Soil age. The earlier the soil formation process began, the thicker the soil layer.

Surface relief. On mountain slopes, the soil layer is slipping.

Climate.

soil organisms. Both the amount of soil and its quality depend on the set and number of organisms.

Human activity. As a result of human activity, transport, industry, the soil becomes the cause of changes in the state of human health.

Currently, the soil is considered as a self-developing system that ensures the circulation of substances in nature. In the soil, all types of waste are neutralized (soil self-purification function).

SOIL TYPES

Different types of soils were formed in connection with the predominance of one or another soil-forming factor. On the territory of Russia allocate the following soils:

tundra soils.

· weakly podzolic and podzolic soils (comprise most of the soils of Russia).

· gray forest soils (characteristic of the southern region of Russia).

Chernozems (beginning in the Tambov region) occupy a small area.

chestnut soils.

Brown, solonchak soils are characteristic of the southern steppe and desert areas.

Soil types matter mainly for agriculture.

It is preferable to build houses, buildings on dry, sandy soils, because these soils will be favorable in terms of self-cleaning, there will be no

swamps will be created, there will be no mosquitoes, etc.

The hygienic properties of the soil largely depend on its mechanical composition (on the granulometric composition). It is determined mainly by those rocks on which the soil was formed. In each soil, a mineral and an organic part are distinguished. There is a whole classification of soils according to their mechanical composition. We use the Kaczynski classification according to which soils are divided into structural (large structures prevail) and structureless (small soil structures prevail). Depending on whether the soil is structured or unstructured, many physical properties of the soil are determined, which are important in hygienic terms.

SOIL PROPERTIES

The physical properties of soil include:

1. Porosity (depending on the size and shape of the grains) coarse-grained soils

porosity reaches 85%, on clay soil the porosity is 40-

2. Soil capillarity. The ability of soil to hold moisture. Capillarity is higher in fine-grained soils, which means that the height of uplift ground water, say, in chernozem is higher than on sandy soil. Therefore, construction is more favorable on coarse-grained soils, less dampness, lower groundwater.

3. Soil moisture capacity- that is, the ability of the soil to retain moisture: black soil will have high humidity, less podzolic and even less sandy soil. This is important for creating an optimal microclimate in terms of humidity inside buildings. It is believed that soils with high water holding capacity are unhealthy.

4. Soil hygroscopicity is the ability to attract water vapor from the air. Coarse-grained soils, free from pollution, have minimal hygroscopicity.

5. Soil air. It fills the pores of honey with soil particles, being in direct contact with atmospheric air, it differs in composition from atmospheric. If in the atmospheric air the oxygen content reaches 21%, then in the soil air the oxygen content is much less - 18-19%. Clean soil contains mainly oxygen and carbon dioxide, while polluted soils contain hydrogen and methane. The more oxygen in the soil air, the better the self-purification processes in the soil. For example, in a heap of garbage, where there is no access to oxygen, the processes of humus predominate, and if the waste is neutralized in uncontaminated soil (that is, there is little waste, a lot of clean soil), then the self-purification processes go to the end, ending with mineralization humification, that is, the formation of humus.

6. Soil moisture- exists in a chemically bound, liquid and gaseous state. Soil moisture affects the microclimate and the survival of microorganisms in the soil.

7. Chemical composition of the soil. Soil can contain all chemical elements. The human body by qualitative composition contains the same macro and microelements as the soil, since the soil is involved in the cycle of substances in nature, which means that the soil affects the state of human health.

healthy soil called easily permeable, coarse-grained uncontaminated soil. The soil is considered healthy if the content of clay and sand in it is 1:3, there are no pathogens, helminth eggs, and trace elements are contained in quantities that do not cause endemic diseases.

According to the world element composition, 3 types of soils are distinguished:

soils with normal microelement composition, with excessive and insufficient microelement composition. Such territories that characterize normal, excessive or insufficient microelement composition are called provinces. These are natural geochemical provinces. There are provinces with insufficient fluorine content, such areas are endemic for caries. Provinces with excess fluorine are endemic for fluorosis. Provinces with insufficient iodine content - endemic goiter and Graves' disease are registered on them. There are also natural territories where such a symptom complex as Urov's disease, or Kashin-Peck's disease, or chondroosteodystrophy is noted. This disease is associated with an imbalance of strontium and calcium. There are provinces with a high content of molybdenum. They show such diseases as molybdenosis or endemic gout.

This video lesson is intended for self-study of the topic "Soil and its composition." During this lesson, you will be able to get acquainted with the main property of the soil - fertility. The teacher will talk about the composition of the soil, thanks to which plants can obtain from it the elements necessary for their growth.

If you drop a piece of dry soil into a glass of water, how can you explain the appearance of air bubbles in the water? This experience shows that the composition of the soil includes air.

After lowering the soil into a glass of water, you need to stir and let it settle. Using a pipette, a few drops of this water are taken and placed on a glass slide. Now you need to heat the glass over the fire of the candle. After the water evaporated, a thin layer remained on the glass white coating are mineral salts. This experience showed that the soil contains mineral salts that can dissolve in water.

You can put the soil in the lid, then it should be heated over a candle flame. Glass is held above the soil. The glass first becomes wet, and then droplets of water appear on it. This is the water that is contained in the soil, when heated, it evaporates. Water vapor rises, meets cold glass on its way, cools down and turns into tiny droplets of water (Fig. 2).

Rice. 2. Experiments on the soil ()

This experience shows that water is present in the soil. If you continue to heat the soil, then soon there will be smoke and bad smell. This burns part of the soil, which consists of decaying remains of plants and small animals. This is component soil - humus. If the soil is calcined for a very long time on fire, then the humus will completely burn out and the soil will turn gray. This proves that humus gives the soil a dark color.

If you dip some soil into a glass of water, mix it and let it settle, you will see how a layer of sand settles to the bottom, a layer of clay on top of it, and a layer of dark color on top is humus. This proves that the soil contains sand and clay (Fig. 3).

Rice. 3. Experiments on the soil ()

What are the results of the experiments and observations? We learned that the composition of the soil includes air, water, mineral salts, humus, sand and clay.

In the soil there is always Live nature: plant roots, bacteria, earthworms, ants, dung beetles and many others. They gnaw on the roots of plants, grind something, drag it, and collect it.

What do plants get from the soil? First, air, the roots of plants breathe the air that is in the soil. Second, water. Plants absorb nutrients along with water. The remains of dead plants and animals are processed by bacteria and insects that are in the soil. So, the soil is constantly replenished with humus and mineral salts. This is a real storehouse of plant nutrients. In addition, animals living in the soil loosen it, and air and water penetrate the soil better.

When they say that the earth is the breadwinner, they mean the soil. Plants take water and nutrients from the soil. Many animals eat plants. Insects eat plant roots, stems, leaves (Fig. 4), granivorous birds regale on fruits. Vegetable food is eaten by cows, horses, moose.

Herbivorous animals become prey for predators. Consequently, predatory animals depend on soil fertility.

A person on earth grows grains, vegetables, legumes, fruits and berries and ornamental plants. fertile soil provides people with clothes made of cotton and linen, pets with food, and they give people milk, meat, eggs, honey, wool and many other products. The soil is the most important wealth of the country, so farmers take care of increasing its fertility and protect it.

How do people take care of the soil? In order for the soil to better pass air and retain water, it is dug up and loosened annually. During autumn digging after harvesting, clods of earth do not break, in winter snow lingers between them, so in spring the soil is better saturated with water. Loosen the soil in the spring, just before sowing (Fig. 5). In loose soil, seeds germinate better, sprouts break through faster, and the root system develops well.

Rice. 5. Loosening the soil ()

There are very few dissolved salts in the soil, so it is necessary to replenish the salt reserves annually. Plants produce fertilizers that contain all the mineral salts necessary for plant growth. But there are also very good natural fertilizers, such as peat and manure. They are applied to the soil in the fall. The richer the soil in humus, the more fertile it is. Due to the dark color, the soil warms up better in the sun.

What is damaging the soil? Damage to the soil is caused by ravines (Fig. 6), strong winds, heavy rains, wheels of passing cars, household garbage. But people have learned to deal with ravines, for example, their slopes are plowed not along, but across.

The sprouts hold water so it doesn't run down the slope and erode the soil. Also, to stop the growth of ravines, shrubs and trees are planted on the tops and slopes of the ravine. In places where strong winds are frequent, people plant windbreaks and sow grass.

Today in the lesson you learned about the composition of the soil. You also learned the importance of soil for human life.

Bibliography

1. Vakhrushev A.A., Danilov D.D. The world 3. - M.: Ballas.
2. Dmitrieva N.Ya., Kazakov A.N. The world around 3. - M .: Publishing house "Fedorov".
3. Pleshakov A.A. The world around 3. - M .: Education.

1. Krugosvet.ru ().
2. Zaiko-mich.narod.ru).
3. Schemo.RF ().

Homework

1. What is the main property of soil?
2. Soil composition?
3. How do people take care of the soil?

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

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

Soil absorption capacity. The plant takes its food from soil solutions with its roots. But in order for it to be able to take the substances it needs, the solutions must be weak, that is, a large number of a very small amount of salts should be dissolved in water (no more than 2-3 grams of nutrient salts per 1 liter of water). True, there may be too little salt, and then the plant starves, but it also dies when the aqueous solution is too strong. From such a concentrated aqueous solution, the roots of plants are not able to absorb salts, and the plant dies, as it would die from starvation.

But we know that the amount of water in the soil is constantly changing. After the rains it is more, in the drought - less. This means that the strength of the soil solution must also change, and at the same time the plant must suffer. It turns out that the properties of the soil that feeds it, and mainly its clay particles and humus, come to the aid of the plant.

Clay particles and soil humus to some extent regulate the strength of the solution. When the strength of the solution increases, the soil absorbs some of the dissolved substances from it. On the contrary, after rains or artificial irrigation of the soil, when the amount of water in it increases significantly, some of the substances, salts that are in the solid part of the soil, again go into solution.

In many cases, just those substances that the plant needs are absorbed, such as potassium, calcium, phosphoric acid, lime, and some others. However, along with them, the soil also absorbs sodium, which sharply worsens all its properties. Sodium is found in table (edible) salt, in Glauber's salt, which is used as a laxative, and in some other salts.

The ability of the soil, its solid part, to absorb from an aqueous solution and bind (in order to give it back later) certain substances and salts is called the absorption capacity of the soil.

The absorption capacity of the soil depends mainly on the content of the smallest colloidal particles in the soil - mineral, organic, and the combination of both (organo-mineral particles). This part of the soil is called its absorbing part, or its absorbing complex.

The soil can even absorb some gases, such as ammonia, which smells so strongly in the stables. The ammonia absorbed by the soil is converted into saltpeter with the participation of bacteria.

But not all substances are absorbed by the soil equally well. For example, saltpeter, so valuable for plants, is very weakly absorbed by it, and therefore saltpeter is more easily washed out of the soil by water than other substances.

Since the absorption capacity of soils increases with the content of clay and humus in the soil, clayey, humus-rich soils can be safely fertilized with large amounts of nutrients. The excess will be absorbed by the soil and will not damage the plant, nor will it be washed out with water. This should not be done only with saltpeter, which is poorly absorbed by clay soils. Therefore, in practice, saltpeter is usually applied in two portions: one - before sowing and the other - during the period of the greatest development of plants.

Sandy soils have completely different properties. There is little clay and humus in these soils. Their absorption capacity is negligible. Water easily leaches nutritious salts from them, and they disappear without a trace for plants. In a drought, when the soil solution becomes very strong, the sandy soil is unable to absorb excess salts, and plants, if the soil is excessively fertilized with water-soluble substances, die (burn out). Therefore, in order not to thicken the soil solution and not lose nutrients, fertilizers are applied to sandy soils little by little, in several portions. It is also recommended not to leave sandy soils in pure fallow, as the water will wash out the soluble nutrients formed during the fallowing process.

Fallow areas on sandy soils should be sown with lupine or seradella. By plowing these plants during their flowering period, we will enrich the soil with valuable humus. Seradella can also be used as an excellent livestock feed.

Along with clay particles and humus, a significant role in the absorption capacity of the soil is played by the microorganisms inhabiting it, which either absorb a number of substances to build their body, or release them when dying and looping.

A similar absorption and release of nutrients is observed during the life and death of plants.

Soil reaction. If there are a lot of acids (for example, acidic humus) or alkalis (for example, soda) in the soil, then the cultivated plant dies. Majority cultivated plants likes the soil solution to be neither acidic nor alkaline; it should be medium, neutral.

It turns out that the reaction of the soil is highly dependent on what substances are absorbed by the soil. If the soil (solid part of it) has absorbed aluminum or hydrogen, 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, an average reaction. Hydrogen is found in water and various acids. In addition, hydrogen is apparently released into the soil solution by the roots of living plants. Calcium is found in lime, gypsum and other salts, aluminum is abundant in clay and other minerals.

In nature, different soils also have different reactions: for example, marsh and podzolic soils, as well as red soils, are acidic, solonetzes are alkaline, and chernozems are of medium reaction.

Openness, or porosity, soil. If there is enough nutrients in the soil, but there is not enough water or air in it, the plant dies. Therefore, one has to take care that, along with food, there is always water and air in the soil, which are located in soil voids, or wells. Soil wells occupy a very large volume, about half of the total soil volume. So, if you cut out 1 liter of soil without compacting it, then the voids in it will be about 500 cubic centimeters, and the rest of the volume will be occupied by the solid part of the soil. In loose loams and clay soils, the number of wells per 1 liter of soil can reach 600 and even 700 cubic centimeters, in peat soils- 800 cubic centimeters, and in sandy soils, the duty cycle is less - about 400-450 cubic centimeters per 1 liter of soil.

The size of the voids and their shape are very different both in the same and even more so in different soils. For cultivated plants, it is desirable to create wells of medium size, with a clearance from a few millimeters to tenths and hundredths of a millimeter. Too small holes in the soil, as, for example, in the columnar horizon of solonetz or in the compacted horizon of podzolic soils, as well as too large ones (cracks), create unfavorable conditions for plants. Root hairs of plants can penetrate only into boreholes with a diameter of at least 0.01 mm, and bacteria - into boreholes of at least 0.003 mm.

Soil permeability. Falling on the surface of the soil in the form of precipitation, water seeps into the soil through large wells under the influence of gravity and is absorbed through thin wells, or capillaries, surrounding the soil particles with a continuous layer.

In the sands, the pores are large, and water penetrates through them easily and quickly. On the contrary, in clay soils with extremely small holes, it is absorbed with difficulty - tens and hundreds of times slower than in the sands.

Water permeability of structural soil. However, what has been said about clay soils is true only for structureless soils. If the clay soil is rich in lime and humus, then individual small particles in it coagulate, stick together into porous grains and lumps. These grains and lumps, in the presence of lime and humus, are durable and hardly erode in water. In the soil between them, pores of medium size are formed, as in sand, and somewhat larger. Such (structural) clayey soil has good water permeability, despite the fact that it consists of tiny particles.

Water holding capacity and soil moisture capacity. Getting into the soil, water wets its particles, surrounding them in many layers. Water sticks to the soil, and the soil firmly holds it on its surface. The closer the water layer is to the soil particle, the stronger it is held by the soil, the stronger it is bound by it.

The ability of the soil to hold water is called its water-holding capacity, and the amount of water that the soil holds is called the soil moisture capacity. The moisture capacity of different soils is different: 100 grams of clay soil rich in humus can hold 60-70 grams of water, while 100 grams of sandy soil only hold 10 to 25 grams of water. In most cases, the arable layer of loamy and clay soils can hold 30 to 40 grams of water (30-40 percent) per 100 grams of soil.

Digestible and indigestible water in the soil. The water contained in the soil varies in quality. Five main categories of sharply different water in the soil can be distinguished: 1) bound, non-free water, which is strongly attracted by soil particles and for the most part is inaccessible to plants; 2) capillary water, which occupies medium-sized pores in the soil; 3) free, gravitational water that can drain from the soil; 4) vaporous water; 5) solid water (ice), which is formed in the soil when it freezes. Plants can assimilate the second and third categories of water with their roots, and capillary water is especially important in this case, since it is retained in the root layer of the soil without draining from it. The same water has the ability to move in the soil through capillaries in all directions: from bottom to top, from top to bottom and to the sides. This is very important: when the root of a plant drinks water around it, it can be sucked to it from neighboring, more damp places.

But we must not forget that due to the same ability, the soil can dry out too much. This happens when the field is poorly loosened or not loosened at all from the surface. In such areas, soil capillaries extend to the very top. Water rises through them and evaporates into the air.

The soil is also strongly dried in the case when the arable land is covered with a crust. It happens after the snow melts and after heavy rains. Capillaries are very well developed in the crust, strongly sucking water. If we strive to keep moisture in. soil, such a crust must be immediately broken with cultivators or harrows.

The less bound, indigestible water in the soil, the better. In clay soil, there are 10-15 grams of such water per 100 grams of soil, while in sandy soil it is only 1-2 grams. Thus, it must be remembered that although clay soils retain more water, there is more water inaccessible to plants than in sandy soils.

It is bad when the soil dries out quickly and there is no water in it. The plants then die. But they cannot develop either: in soil overflowing with water. For a plant, the average state of the soil is favorable, when part of the gaps in it are filled with water, and air is in other gaps.

Soil air capacity. In dry soil, all wells are filled with air. At the same time, part of the air is attracted by the surface of soil particles with force. This part of the air has low mobility and is called absorbed air. The rest of the air placed in large pores will be free air. It has considerable mobility, can be blown out of the soil and can be easily replaced by new portions of atmospheric air.

As the soil becomes moist, air is displaced from it by water and comes out, and part of it and other gases (for example, ammonia) dissolve in soil water.

Oxygen is mainly consumed from the air in the soil. As already 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 consumed by various bacteria during respiration, decomposition and oxidation of plant and animal residues. Instead of the oxygen consumed by living beings, the air in the soil is enriched with carbon dioxide, which is released during their respiration and during the smoldering of dead organic residues.

The air in the soil does not remain in it without movement. It constantly exchanges with atmospheric air. This is primarily facilitated by the heating and cooling of the soil, due to which the soil air either expands and leaves the soil, or (during cooling) contracts, and new portions of atmospheric air are sucked into the soil (“soil breathing”).

Soil air can be blown out by winds, can be displaced from the soil by precipitation penetrating into it (water); can be set in motion when atmospheric (above ground) pressure changes:, with an increase atmospheric pressure part of the air enters the soil; when it decreases, the soil air escapes into the atmosphere.

Air renewal can occur even in the absence of wind, rain and temperature changes.

At the same time, soil air, rich in carbon dioxide and water vapor, gradually comes out, and drier and richer in oxygen atmospheric air penetrates into soil pores.

Soil air renewal in various climatic zones will occur stronger now from one of the above reasons, then from others. 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, will be more affected. In places rich in precipitation, for example, in the taiga zone, a change in air will noticeably occur when water seeps into the soil, etc.

For the "normal" development of cultivated plants, it is necessary that the soil be constantly ventilated, "breathe easily", so that the supply of oxygen is continuously restored in it.

soil heat. Warmth is essential for soil development and plant life. The soil receives heat from the sun, heating up with its rays. A small proportion of heat comes to the soil surface from the internal, heated layers of the earth, and is also released during the respiration of living beings and during the decomposition of plant and animal remains. Sometimes the soil is warmed by warm springs flowing to the surface of the earth from its deep heated layers.

Not all soils are heated by the sun in the same way. Dark, humus-rich, and most importantly dry soils heat up much faster than light and damp soils. Wet soils heat up especially slowly; this is because a lot of heat is spent on heating and evaporating the water in them. Sandy soils are drier than clay soils, and therefore they heat up faster.

In addition to color, humus and water content, great importance for heating the soil, the location of the terrain has: the soils lying on the southern slopes are heated better than others, somewhat weaker - on the eastern and western slopes, and worst of all - on the northern slope.

The heat received by the soil is gradually transferred to the lower layers through soil particles, water and air. At night, the soil will cool from the surface, and the warm daytime wave will move to a certain depth. So one wave after another every day goes into the soil. Soil particles either expand from heat or shrink from cold. This contributes to their greater and faster weathering.

Warm soils are favorable for the development of plants and other living creatures inhabiting the soil.

In winter, when the soil hides under a cover of snow, when water freezes in it, when instead of warm waves cold waves go into the depths, the life of the soil to a large extent freezes. All living things in the soil fall into hibernation and to a new vibrant life will wake up only next spring.

Once again about the importance of soil structure. All soil properties important for the development of agricultural plants are best expressed in structural soils. Structural soil contains both water and air. Water in such soil is placed inside the lumps and in the capillaries between them, and air is in large voids between the lumps, along their surface, and partly in the lumps themselves - in large tubules and cells.

Structural soil also has good thermal properties. It favorably develops beneficial microorganisms for plants. The mineral part in such soil is more easily weathered and releases nutrients. 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, structured soil will always produce a higher crop yield.

But not every soil naturally has a good structure. Often you have to work hard to get structural arable land. On all soils, the creation of a structure is helped by an artificial increase in humus in it, as well as saturation of the soil with calcium. For the last target acidic soils lime is used, on alkaline, for example, on salt licks - gypsum.

Soils must be cultivated, perennial cereals and legumes must be introduced into the crop rotation, mixed with each other, and on the sands - lupine and seradella. During life, grasses dismember the soil into structural units with their roots. legume herbs enrich the soil with nitrogen, and all herbs - legumes and cereals - enrich it with humus, as they have a powerful root system, several times greater than oats, rye, wheat and other field and garden plants.

Serious attention should be paid to the timely cultivation of the soil. When plowing dry soil, we destroy, pulverize the structure; when plowing waterlogged soils - we crush the structure, lubricate it. It is necessary to strive to plow, if possible, moderately moist soils, when they contain 50-70 percent of moisture from their moisture capacity. Under this condition, the best quality structural arable land is obtained.

Structural arable land is an indicator of the cultural character of the field. The structure of the soil increases the yield and makes it stable in dry years.

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Chemical (content of macro and microelements, pH)

The chemical properties of gray forest soils reflect the conditions of their formation. The described soils have an acidic or slightly acidic reaction of the soil solution, not very high soil saturation with bases, a reduced amount of silt particles in the A 1 A 2 horizon (or A 2 in light gray soils) with an increased hydrolytic acidity compared to other soil horizons.

Signs of podzolization are relatively easy to determine by soil morphology and are confirmed by chemical analysis data. In dark gray soils, a significant accumulation of humus is noticeable, humic acids predominate over fulvic acids, calcium is accumulated in the upper horizon, and the soils are completely saturated with bases. The content of humus in gray forest soils increases from north to south and from west to east [Zelikov]. Chemical composition and physico-chemical properties. The data of the bulk analysis (Table 3) of gray forest soils show that their upper horizons are depleted in sesquioxides and enriched in silicic acid. This pattern of changes in the bulk composition along the profile of gray forest soils indicates a noticeable podzolization. It is most clearly expressed in light gray soils and to a lesser extent in dark gray ones. The content of humus and nitrogen along the profile indicates a more intense manifestation of the soddy process in dark gray forest soils and its weakest development in light gray ones. The total reserves of humus in a meter layer are on average 200 tons per 1 ha, with fluctuations from 100 - 150 tons in light gray to 300 tons in dark gray soils. Light gray and gray soils under the forest often in the upper horizon (A 1) still have some predominance of fulvic acids over humic acids, but already in the horizons A 1 A 2 and B 1 humic acids predominate.

The physicochemical properties of gray forest soils well reflect the features of their genesis (Table 2). Light gray soils are acidic, not saturated with bases (V=70-80%). Absorption capacity in the humus horizon of loamy varieties is 14 -18 m = equiv. and increases in the illuvial horizon due to its enrichment in the clay fraction.

The subtype gray forest soils is also characterized by an acid reaction and some unsaturation with bases, although to a somewhat lesser extent than light gray soils. Absorption capacity, depending on the mechanical composition and humus content in the horizon A 1 (A p) ranges from 18 - 30 m. = Eq.

Table 3. Gross chemical composition and physicochemical properties of gray forest soils

more favorable physicochemical characteristics in dark gray soils. Absorption capacity in the upper horizon ranges from 15 - 20 to 35-45 m - eq. They have a higher base saturation (V=80 - 90%). The reaction of the salt extract is often slightly acidic. In contrast to light gray soils, gray and dark gray soils are characterized by the highest absorption capacity in the upper horizons, which is associated with a higher humus content and less depletion of silt in the upper horizons.

Hydrolytic acidity in the type of gray forest soils is usually 2 - 5 meq. per 100 g of soil.

Gray forest soils are slightly acidic or almost neutral reaction(pH of water extract 5.5...6.5, saline - 5...6). In the upper horizons, a slight accumulation of silicic acid is observed, and in horizon B, sesquioxides are observed (Table 4).

Dark gray forest soils differ from gray and light gray ones in a higher content of humus, nitrogen, phosphorus, and potassium, a less clearly defined illuvial horizon, and greater base saturation.

Table 4. Analysis data for gray forest loamy soil (according to N.P. Remezov)

Horizon	Sample depth, cm				% on soil					Degree of saturation with bases, %	suspension pH
A1	2...10	4,4	80,5	8,6	3,4	20	8	6	34	82	6,5	5,5
A1A2	20...30	1,8	80,3	8,5	4,5	16	6	4	26	85	6,2	5,7
B1	40...50	0,7	75,4	8,2	5,4	18	6	2	26	92	6,0	5,8
IN 2	70...80	0,4	75,6	10,1	5,7	17	6	1	24	91	6,2	6,0
IN 3	100...110	0,4	76,2	9,8	5,5	9	6	1	26	96	6,3	6,0

Light gray forest soils contain slightly less plant nutrients, have a lower uptake capacity, are somewhat more acidic, have a well-defined illuvial horizon, and have a relatively high amount of silicic acid in the upper layer.

The physical properties of gray forest soils are determined primarily by the mechanical composition, the nature of the absorbing complex, and the content of humus. The structure of soils, their water and air regime, composition, etc., depend on these indicators. On the whole, the physical properties of gray forest soils should be considered quite satisfactory in agronomic terms. The soils have a rather high total duty cycle: 50...55% in the upper horizons, 40...45% in the lower ones. Their field moisture capacity is 45% in horizon A and 35...40% in horizon B. Such data determine the effective duty cycle of gray forest soils at 10...13%. These indicators give grounds to conclude that gray forest soils are water-intensive, well-permeable to water, and well aerated.

Physical

The density of the solid phase of gray forest soils increases down the profile, which is associated with a decrease in the humus content. Dark gray soils, being more humus-rich, also have a lower density of the solid phase. The density is the lowest in dark gray soils due to their better structure and higher humus content. All gray forest soils are characterized by a high density of compacted illuvial horizons (1.5-1.65 g/cm3). The total porosity varies from 50 - 60% in the upper horizons to 40 - 45% in the illuvial and rock. In light gray soils, capillary porosity sharply prevails over non-capillary.

The unfavorable physical properties of light gray soils determine their noticeably worse water permeability compared to other subtypes. Dark gray soils, due to their better physical properties, are characterized by greater moisture capacity and a higher content of moisture available to plants.

The agrophysical properties of gray forest soils, especially light gray ones, are not very favorable. The low content of humus, depletion in silt, and enrichment in silt fractions contribute to the rapid destructuring of the upper horizon during plowing, so such soils float and form a crust. The state of maturity in gray forest soils for the conditions of the same farm and region occurs somewhat later than in chernozems.

The subtypes of gray forest soils significantly differ from each other in terms of the water resistance of the macrostructure of plow horizons. In light gray soils, the content of water-stable aggregates larger than 0.25 mm is the same as in soddy-podzolic soils - 20-30%, so the arable horizon is prone to rapid compaction and the formation of a crust on the surface after rains. In gray and dark gray soils, the structural state is more favorable; water-resistant aggregates larger than 0.25 mm in their arable layers, respectively, about 40 and 50%, and in subarable - about 60 and 80% (Kovrigo).

Biological

Some microorganisms produce strong mineral acids (nitrifiers, sulfur oxidizing bacteria) that destroy minerals. Many bacteria, as well as mold fungi, secrete organic acids that decompose minerals or give chelate compounds with their components. The word "chelates" comes from the Greek "hela", which means "claw", since the paired combined bonds that capture the metal in the noted compounds can be figuratively compared in form and function with the claw of cancer.

Microorganisms take an active part in the formation of humus. Humus begins to accumulate in the soil layer from the first stages of the development of the soil-forming process. The term humus unites a whole group of related macromolecular compounds, the chemical nature of which has not yet been precisely established. Humus makes up 85-90% of all soil organic matter. It accumulated a significant amount of nitrogen, phosphorus and other elements. Humus is formed from plant decay present on the soil surface and the dead root system of plants.

Degree of susceptibility to erosion processes

As a result of plowing gray forest soils, an arable layer was created in place of the A 1 and partially A 1 A 2 horizons. The natural vegetation cover is disturbed, so this soil is highly susceptible to wind and water erosion. The long-term use of the three-field farming system with grain crops and a fallow field left a significant imprint on the properties of the soil. This was reflected in a decrease in the content in the arable layer, especially due to the mineralization of the most mobile (active) constituents, humus substances, mechanical destruction of the agronomically valuable granular structure during soil cultivation. Of importance was the destruction of the structure by raindrops falling on the soil surface unprotected by forest litter. All this led to the destructurization of the arable layer, a decrease in the effective duty cycle and water permeability, the appearance of surface runoff after snowmelt and heavy rainfall, soil washout and erosion. To increase the fertility of gray forest soils, it is necessary to take measures to create a structural and deep arable layer, eliminate erosion, and restore soils damaged by erosion. On virgin soils, the development of erosion processes is observed to a lesser extent, because. the soil layer is protected by natural vegetation cover.