With the arrival of spring, excavation work begins. I come to my grandmother’s village and help her plant potatoes and seedlings. In rural areas, all people are engaged in agriculture. This is their lifestyle. Soils are formed in different climates, under different vegetation and therefore have different fertility. In my area there is black soil, and this is the most fertile land.
Fertility is the main feature of the soil
Every day we walk on earth. She surrounds us everywhere. The soil feeds us! Have you ever wondered why you can grow vegetation in soil? And the answer is very simple. Next, I’ll just talk about this feature of soils.
Soil is the top layer earth's crust. It has its own peculiarity - fertility. And all because in the soil there is humus (humus). This is the top fertile organic layer, which is formed as a result of the death and decay of flora and animals. The more humus, the greater the fertility. It is measured on a 10-point scale - this is called quality. Thanks to this property, we have such vital food.
Our soil is unique. It has many basic and additional properties:
- grading– this is the ratio of different mineral elements in the soil composition;
- duty cycle– this is the presence of pores (gaps) in the composition of the earth;
- humidity– how much water the earth contains;
- hardness;
- stickiness.
But we need to know that about The main property of soil is fertility.
How the soil was formed
Soil is formed as a result Odeath and decomposition of organic matter (flora and fauna) and the action of inorganic nature (wind, water and temperature). It began to appear millions of years ago. This is a very complex geological and historical process. The main shells of the Earth and minerals began to form. Scientists claim that after the appearance of water and air, the first unicellular organisms and algae began to live on Earth. Volcanoes erupted, and then more complex living organisms appeared.
Alive and inanimate nature began to contact each other. As a result, the soil we needed appeared.
Absorbency. All soils contain colloidal particles (< 0,0001 мм). Они обладают многими специфическими свойствами. Поэтому от их количества зависит плодородие почвы. Содержанием коллоидных частиц прежде всего определяется поглотительная способность почвы - способность поглощать из окружающей среды и удерживать растворимые и взмученные в воде твёрдые вещества, пары воды и газа. Коллоидные и близкие к ним частицы почвы, обладающие способностью поглощения, называют почвенными поглощающим комплексом (ППК).
The doctrine of the absorption capacity of soils was developed by the Russian scientist K. K. Gedroits (1872-1932). There are several types of absorption: mechanical, physical (molecular), chemical, physicochemical and biological.
Mechanical absorption- the ability of soil to retain suspended particles during filtration that exceed the diameter of soil pores. Soil particles that fall into cracks that form on the soil surface are also mechanically retained. The more fine fractions of mechanical composition in the soil, the higher the mechanical absorption.
Physical absorption(or molecular adsorption) is based on the ability of soil colloids to attract molecules of a substance (water, solutions, gases, such as ammonia) to the surface and retain them on it without changing their properties.
Chemical absorption. Substances included in the soil solution and the solid phase of the soil enter into chemical interaction with salts in the soil to form slightly soluble or insoluble compounds in water.
Physico-chemical absorption, or exchange adsorption(exchange absorptivity). It is based on the ability of soil colloids to absorb cations from the soil solution and retain cations on the surface in exchange for other cations in the PPC.
The absorption energy of different cations depends on their valence and atomic mass: the higher the valence, and within the same valency, the higher the atomic mass, the higher the absorption energy. The exception is hydrogen (H). In order of increasing absorption energy, the cations are arranged in the following sequence:
Na< NH < K < Mg < H < Ca < Al < Fe
The amount of cations that soil can absorb is called cationic absorption capacity, or exchange capacity, and is expressed in milligram equivalents (mg-eq.) per 100 g of soil. The value of absorption capacity (T) varies from soil to soil and depends on the presence of mineral and organic colloids in the soil. Thus, in sandy loam soils it is only 5-10 mg-eq., in loamy low-humus soils - 15-20, and in loamy chernozems - 40-50 mg-eq. and higher.
The more clay particles and humus in the soil, the greater the absorption capacity.
The composition of absorbed bases is also very important for soil fertility. It may contain calcium, magnesium, hydrogen, potassium, sodium, ammonium, iron and aluminum. Divalent cations (Ca^, Mg^+) coagulate colloids well, promote 1ot_(x)1)1^om^1yu_s11^"kty11b1, create a normal or close to it soil reaction. Agronomically, these are the most valuable cations .
Monovalent cations (K+, _Ma+) disperse. soil-derived colloids, destroy the localized. yag.rega_ts)i-.-a_s_them and structure, in large quantities they cause an alkaline reaction. .
Absorbed hydrogen destroys soil collottes and acidifies the soil. Aluminum II can have an acidifying effect on the soil. Being repressed:.; from the absorbed state, it passes into the AlCl3 compound in the soil solution, which!! As a result of interaction with water, it forms hydrochloric acid.
Depending on the presence of hydrogen (II) and aluminum (Al) in the absorbed state, on the one hand, and divalent cations (Ca and Mg), on the other, saturated soils are distinguished. bases and not saturated with them. The first include nochs, in the absorbing complex of which; ".are
only calcium, magnesium, potassium cations and no hydrogen; the second group includes soils, the absorbing complex of which, along with other cations, includes hydrogen and aluminum. Chernozems, chestnut soils, gray soils are saturated with bases, but soddy-podzolic soils, red soils, and swamps are not saturated. Soils with high sodium saturation are solonetzes. They are structureless, blurred by rain, and when dry they float into a dense mass.
To characterize the agrochemical properties of soil, it is important to sum of absorbed bases(S). When determining it, the amount of cations contained in the absorbed state is taken into account.. (in podzolic soils Ca, Mg), with the exception of! hydrogen. This amount is also expressed in milligram equivalents per 100 g of soil. In different soils it ranges from 2 to 50 mEq. and higher. For example, on light soddy-podzolic soils S can be only 2-5 mg-eq., on light loam - 5-10, on heavy loams - 15--20, on forest-steppe soils and chernozem": from 20 to 50 mg-eq. The more S. the more agronomically valuable overnight
The amount of absorbed bases is related to the calculation degree of soil saturation with bases (V). It shows what part of the absorption capacity of the soil is occupied by absorbed bases, expressed as a percentage of the total absorption capacity, including the content of hydrogen ions (H), and is calculated by the formula:
It is believed that if the base saturation is less than 75%, then such soil must be limed.
Biological absorption. This type of absorption in the soil is carried out by the vital activity of plants and microorganisms. One of the important features of biological absorption is the selective ability of microorganisms and plants, manifested in the fact that they take from the soil mainly those substances that they need to build their body, for life.
Soil reaction. Forms of acidity. The reaction of the soil environment is directly related to the saturation of the soil with various cations.
Soils saturated with Ca and Mg (chernozems) have a neutral or slightly acidic reaction, favorable for most agricultural crops. Soils that are not saturated with bases are characterized by an acidic reaction. These are soddy-podzolic soils. Their high acidity can be harmful to many crops.
Soil acidity. In soils that are not saturated with bases, two forms of acidity are distinguished: actual and potential.
Current acidity is caused by the hydrogen ion present in the soil solution. It is usually observed in the presence of soluble organic acids, carbon dioxide, or compounds of aluminum and iron in the soil, which, when interacting with water, form an acid.
The reaction of the soil solution (water extract from the soil) is expressed by the pH value, which characterizes the concentration of hydrogen ions in it. The pH value itself is the negative logarithm of the concentration of hydrogen ions. The lower the pH, the higher the acidity of the soil. pH of strongly acidic soils 4.0-4.5; neutral 7.0; highly alkaline 8.0-9.0 *.
Potential acidity is detected when soil is treated with solutions of various salts, causing the displacement of hydrogen and aluminum ions from the absorbed state.
It is customary to distinguish between two forms of potential acidity: exchangeable and hydrolytic. Exchange acidity appears when soil is treated with 1 N. a solution of neutral salt, for example KCl. In this case, hydrogen nons (H+) are displaced from the soil.
* To determine the soil reaction, determination of the pH of the soil solution is still rarely used. More often, acidity is determined in salt extracts from the soil.
Metabolic acidity is expressed, like actual acidity, by the pH sign, but the “pH of salt extract” (or pH in KCl) must be indicated. The pH value of the salt extract for different soils is as follows:
very strongly acidic.........< 4,0
strongly acidic.......... 4.1-4.5
medium sour. .......... 4.6-5.0
slightly acidic. .......... 5.1-5.5
close to neutral.......... 5.6-6.0
neutral. .......... 6.0
alkaline......... 7-8
It is more accurate to express the exchangeable acidity of soils in milligram equivalents (mg-eq.) of hydrogen and aluminum (in total) per 100 g of soil.
Hydrolytic acidity is detected when the soil is treated with a hydrolytically alkaline salt (a salt of a strong base and a weak acid). Most often, 1 n is used to define it. sodium acetate solution (CHsCOONa).
The value of this form of acidity characterizes the ability of the soil to bind bases from solutions of hydrolytically alkaline salts. Hydrolytic acidity is expressed in milligram equivalents per 100 g of soil.
Hydrolytic acidity, as a rule, is greater than exchangeable and includes exchangeable and actual acidity, and exchangeable, in turn, includes actual acidity. Hydrolytic acidity depends on the type of soil; its absolute value ranges from 2 to 8-10 and even up to 15 mEq. per 100 g of soil.
Metabolic acidity is the most dangerous for plants. In practice, the use of liming and setting the dose of lime are widely justified by determining the pH of the soil solution.
Soil acidity can be reduced not only by liming, but also by other methods, for example, long-term, abundant manure using one of the soil cultivation techniques.
Soil alkalinity. The alkaline reaction of the soil solution appears when absorbed sodium interacts with the soil solution, which contains carbon dioxide or Ca(HCO3)2. Alkalinity is also distinguished between actual and potential. The first is due to the presence of a hydrolytically alkaline salt in the soil solution.
Depending on the content of exchangeable sodium (in% of the amount of absorbed bases), the following are distinguished:
salt licks. ............. 20
solonetzic soils......... 10-20
slightly solonetzic soils......... 5-10
Soils with more than 10% exchangeable sodium require gypsum and other improvement methods.
Soil buffering is the ability of soil to withstand sudden changes in its reaction. The buffering capacity depends on the absorption capacity, the composition of soil colloids and the presence of buffer mixtures, such as calcium bicarbonates, in the soil solution. Buffer is a very valuable property of soil.
Sandy, low-humus soils have very little buffering capacity; the reaction in them is easily shifted, for example, when applying acidic or alkaline forms of mineral fertilizers. Loamy soils rich in humus with a high degree of base saturation have a high buffering capacity: they resist well the influence of external factors that change the soil reaction.
Soil absorption capacity, base saturation, acidity, alkalinity play a very important role for the agronomic assessment of soils and are established during soil surveys. Corresponding indicators (pH, S, H obm, H hydr. T, U) are given in the characteristics of soils and serve as justification for certain methods of their improvement.
Soil structure. Soil particles can stick together and form structural lumps - aggregates that are not washed away by water. Soil with big amount units are called structural. Unstructured Soils are those in which individual mechanical elements (sand, dust) are not interconnected. The property of soil to form structural aggregates is called structure.
In agronomic terms, the most valuable is the finely lumpy and granular structure of the arable horizon with lump sizes from 1 to 5 mm. A very important quality of soil structure is its water resistance, i.e., the non-erosion of aggregates by water.
In structural soil, the best air-water regime is created and maintained, and, consequently, microbiological activity and nutritional regime. Textured soil is easier to cultivate.
However, the importance of soil structure cannot be overestimated. It is known, for example, that sandy soils are structureless, but with sufficient moisture and fertilizer they can produce very high yields.
Physical and physical-mechanical properties. TO physical properties soils include density, density of the solid phase of the soil, porosity, as well as water, air and thermal properties.
Soil density- the mass of a unit volume (1 cm cube) of dry soil in its natural state. The density of the arable layer of coarse-grained sandy soil is 1.8; podzolic loamy 1.2; typical chernozem 1.0. Based on the density of the soil, the mass of the arable layer per 1 hectare is calculated. For podzolic loams it will be 2.5-3 thousand tons (at a depth of 20 cm).
The density value is determined by the density of the solid phase of the soil and depends on its zonal characteristics.
Soil solid density- the ratio of the mass of the solid phase (soil particles) to the mass of the same volume of water at 4° C. The highest density of the solid phase is mineral soil, for example sandy with a high content of quartz (2.65), humus and peat have 1.6, so soils with a large amount of humus they have a lower density of the solid phase (for example, in thick chernozem it is 2.37).
Porosity or porosity. The soil consists of a solid phase (soil lumps) and spaces between them, or pores. The total volume of pores as a percentage of the total volume of the soil is called porosity, or porosity, of the soil. The pores can be occupied by water or air. The most favorable volume in agronomic terms is one in which the soil pores are approximately half occupied by water.
The duty cycle is distinguished capillary(volume of interstices of capillary section), non-capillary(spaces wider than capillaries) and general The latter in the arable layer is about 50%.
The physical and mechanical properties of the soil: cohesion, plasticity, stickiness, swelling and shrinkage are important during mechanical processing, since the resistivity of the soil to processing tools depends on them.
For agronomic characteristics of soil conditions, the term is used soil ripeness. Soil ripeness refers to its suitability for machining. It depends on the state of moisture, cohesion, plasticity, stickiness.
Ripe soil is easily processed with tools, does not stick to them, does not smear, does not form lumps, and crumbles into small lumps when processed.
An unfavorable combination of the listed physical properties of the soil can lead to the formation soil crust, worsening the living conditions of plants.
As a result of systematic compaction of the soil by a plow when plowing to the same depth, a dense layer of soil is formed in the upper part of the subsoil layer, the so-called plow sole. To prevent its occurrence, fields should be plowed to different depths and in different directions.
Water properties and water regime of soils. Water can be in the soil in different states and, depending on this, has different importance for plant nutrition. The following main forms of water in soil are distinguished.
Gravity water occupies large pores in the soil (non-capillary), moves from top to bottom under its own weight. This is the most accessible water for plants. However, if it fills all the pores, then waterlogging occurs. On sandy soils, gravitational water easily goes deep into an area inaccessible to roots.
Capillary water occupies soil capillaries. Along them it moves from a wetter layer to a drier one. As water evaporates from the soil surface, this upward flow can dry out the soil. Capillary water is quite accessible to plants.
Hygroscopic water is in the soil in the form of molecules in an absorbed state, retained by the surface of soil particles, almost inaccessible to plants, and moves between soil particles in the form of steam.
The named forms of water are not permanent. Water can move from one category to another. When the soil is waterlogged, all the spaces between its particles are occupied by water. When the soil dries out, free (non-capillary) water is consumed first, and then capillary water. If the reserves of capillary and non-capillary water are exhausted, then plants can hardly obtain it from the soil through the root system, since only water remains in the soil, which is inaccessible to plants. The degree of soil moisture at which plants begin to wither due to lack of moisture is called wilting moisture (ÂÇ). The wilting moisture content is usually equal to twice the maximum hygroscopicity on sandy soils; it is below 1% on sandy loam soils 1-3, on loamy soils 4-10, and on clay soils 15% and above.
The amount of water that soil holds firmly and plants cannot use is dead stock water. usually equal to one and a half maximum hygroscopicity.
In clay soils, whose water-holding capacity is very high, the dead moisture reserve is 10-15% of the soil mass, and in sandy soils it is less than 1%. This means that at the same humidity (let’s say 20%), clay and sandy soils have different amounts of water available to plants: clayey 5-10%, sandy 19%.
The water that is contained in the soil is super-humidity wilting (some consider it in excess of dead stock), i.e. greater than twice the maximum hygroscopicity is called productive (or available) moisture. The percentage of productive soil moisture is approximately the soil moisture expressed as a percentage minus twice the maximum hygroscopicity.
However, it is more accurate to calculate the amount of productive moisture in weight units. Each millimeter of precipitation corresponds to 10 tons of water per 1 hectare.
Productive moisture reserve (W) calculated taking into account the thickness and density of each soil layer using the formula: W = 0.1 P h (B - BЗ) ,
where 0.1 is the conversion factor into millimeters of water layer; /7 - soil density (in r per 1 cm cube); h- thickness of the soil layer for which the moisture reserve is calculated (in cm); IN- soil moisture and VZ- wilting moisture content (% of absolutely dry soil).
The soil is able to absorb and hold water and then release it to plants. To obtain a high yield, it is necessary that the soil always contains the amount of water the plants need. Grain crops spend 2-3 thousand tons of water per 1 hectare to create a harvest, and other plants spend more.
Water enters the soil primarily through precipitation, as well as from the atmosphere in the form of water vapor. The greatest amount of water that soil can hold (accommodate) when all pores are filled is called general, or total, moisture capacity (MC), It depends on the mechanical composition of the soil, the humus content in it and the overall porosity. For example, clay soils have a high moisture capacity (60-80 g of water per 100 g of soil), while sandy soils have a low capacity (15-25 g). It is especially high in peat soils. When the peat is completely saturated, its mass is several times greater than the mass of air-dry peat. The most favorable water regime for plants is created in mineral soils when they are saturated with water at 60-80% of their total moisture capacity.
They also distinguish field moisture capacity. The value of field moisture capacity (in % of dry soil mass) of sandy soils is 3-5, sandy loam 10-12, loamy and clayey 13-22. In the humus horizon of chernozem it can be 40-45%. Soil moisture that is higher is considered excessive.
The ability of soil to pass water through itself is called water permeability. If water permeability is poor, precipitation water flows over the soil surface. At the same time, with very high water permeability, such as sandy soils have, for example, precipitation penetrates very quickly through the soil and is not used by plants. The most favorable conditions for water permeability are in structural soils.
The water regime of the soil depends primarily on the amount of precipitation and on the amount of moisture consumed by evaporation and transpiration. The ratio of these values determines the type of soil water regime. He can be flushing(the ratio of precipitation to evaporation is greater than unity), transitional(this ratio is about one) and non-flushing(precipitation is less than the amount of evaporation). The flush type predominates in the forest-meadow zone, the non-flush type predominates in the steppe zone, and the transitional type predominates in the forest-steppe. When groundwater is close to each other, further effusion type of water regime, and at high groundwater levels - stagnant type.
Air and thermal properties of soil. The soil contains air, the composition of which differs from the atmospheric composition in a large amount of carbon dioxide and less oxygen. With a lack of air in the soil, seed germination slows down, the root system develops abnormally, and microbiological activity is suppressed.
It is important that there is a continuous intensive exchange of air between the soil and the atmosphere (aeration), so that air richer in oxygen enters the soil, and air poor in oxygen is removed from it.
Different soils have different thermal properties. Dark-colored soils are warmed up by the sun faster than light-colored soils. Soils with less water warm up more quickly in the spring, while waterlogged soils warm up and cool down slowly.
In farming practice it matters thermal conductivity soil Soils poor in organic matter have high thermal conductivity, while soils with a high content of organic matter, such as peat, have low thermal conductivity.
When planting a particular crop, you should not ignore the basic properties of the soil used, since the quality of the resulting crop depends on its fertility. We are used to using a wide variety of fertilizers, but few people think about what specific components are missing in the soil. Of course, this cannot be determined by eye, but it is simply necessary to know about the main characteristics of the substrate - we will analyze them further.
Basic soil properties
Soil is a whole system with its own rhythm of life and rules of development, so it is not surprising that its properties can be very different. Let's look at the main ones. 
Fertility
Soil fertility is usually understood as the entire set of its properties and processes occurring within it that contribute to the normal growth and development of plants. A substrate is considered fertile if it contains a huge amount of nutritional components, among which it is especially worth highlighting nitrogen, potassium, magnesium, copper, phosphorus, sulfur and, of course, humus (in good soils it is up to 10%).
All these components are closely related to each other, so you should not be surprised if the lack of one component or the disruption of any process provokes a change in all the others. Since time immemorial, people have assessed the quality of soil precisely from the point of view of fertility, on which the abundance of the harvest and the beauty of ornamental plants depend.Did you know? Soil is the second largest carbon store, behind the oceans.
Mechanical composition
Mechanical composition is another very important property that allows you to classify the soil as a certain variety. By and large, this concept refers to the texture or granular composition of the substrate, formed from millions of different elementary particles. 
This value is expressed as a percentage of the weight of completely dry soil. The features of the mechanical composition are based not only on the initial characteristics of the parent rock, but also on the parameters of the soil formation processes that constantly occur inside.
Physical properties
The mechanical composition directly affects the physical properties of the soil, such as water permeability (or density), porosity, and moisture capacity. Meanwhile, all of them are also very important factors in choosing a site when planting cultivated plants. We will talk more about these characteristics and their relationship further.
What does fertility depend on and how to increase it
Of course, for any agrarian or simple summer resident who grows various plants on his plot, the primary task will be to increase soil fertility, which should increase the amount of crops grown. Let's consider the main factors of soil maintenance and ways to achieve the desired result. 
Fertility Maintenance Factors
Fertility factors are understood as the totality of the amount of water, air, heat, zonal and nitrogen nutrition of plants, which directly affect their growth and development. At the same time, the organization of suitable conditions for fertility implies an integrated approach to the possibility of providing plants with the earthly growth factors they need.
The main such factors include:- amount of water in the soil;
- rainfall and irrigation (increased sodium accumulation can have a detrimental effect on the crop being grown);
- the value of total moisture evaporation, which will confirm the general increase in liquid volume throughout the year;
- sufficient level of nutrients.
Did you know? The process of soil formation occurs very slowly. Thus, it takes almost a century to form just 0.5–2 cm of its fertile layer.
Ways to increase fertility
To the very important conditions, on which fertility will depend, it is worth including temperature, nutritional, water-air, biochemical, physicochemical, salt and redox regimes. 
A person can influence the characteristics of some of them by taking the following measures:
- By organizing competent crop rotation by planting crops in the same place at five-year intervals. That is, no matter what you grow, it is advisable to change the place where the crop grows every five years.
- Sowing so-called “healing plants” on the site, among which garlic, wormwood, shepherd’s purse, and nettle stand out.
- Attracting earthworms. It has long been established that with a large accumulation of them, the soil produces higher yield volumes, which means their presence is very desirable (California species are distinguished by increased digestibility of various organic matter).
- Carrying out heat treatment for the destruction of all kinds of pests and weeds. Main disadvantage This method is impossible to use over large areas (more relevant for greenhouses and hotbeds).
- By introducing organic matter into the soil, especially manure, ash and compost.
- Carrying out mixed planting of crops. Along with the cultivated plant, experts recommend planting a suitable “neighbor” that will repel pests and prevent depletion of the substrate. For these purposes, you can plant basil, rosemary, chamomile, marigolds, which, among other things, will be very attractive to bees, thereby promoting plant pollination and increasing harvest volumes.
- Organizing periodic rest for each individual section of the territory. With constant, continuous cultivation of the same crops, any soil gets tired, so during the selected year it is better not to plant anything at all, doing only weeding, mulching and fertilizing. With the arrival of autumn, the site is dug up, trying to move the top layer down.
- Sowing green manure plants that have a high content of protein, starch and nitrogen. In this case, the ideal “residents” of your plot will be oats, rye, mustard, and sunflower. They are generally sown after harvest, although in some cases they are grown simultaneously with the main crops.
It is much easier to increase the fertility of closed soil than to achieve a similar result in an open area, so it is not surprising that many summer residents set up greenhouses and hotbeds on their territories, providing them with irrigation and ventilation systems, and sometimes even heating. Mechanical composition and its effect on the soil
At the beginning of the article, we already mentioned such a characteristic of soil as mechanical composition, and now we invite you to understand in more detail its characteristics and the distribution of soil into types in accordance with this criterion.
What is mechanical composition
The structure of the earth contains particles of very different sizes: like stones, remains rocks and mineral compounds (often reaching 10-12 cm in diameter), and very small elements invisible to the naked eye. Moreover, you cannot see some of them even with a regular microscope, so when studying soil mixtures you have to use a special electrical apparatus. 
The properties of the substrate, its richness and fertility largely depend on the sizes of these components, and if we perform a mechanical analysis of the substrate, we can attribute it to a specific type: physical clay (particle sizes are approximately 0.01 mm), physical sand ( particles reach sizes from 0.01 to 1 mm), colloidal components (size 0.0001 mm). Let us consider the most typical types of soils, identified on the basis of their mechanical composition.
Soil types depending on composition
Even if you do not have special equipment, and you cannot determine the type of soil mixture by eye, the following diagnostic methods (dry and wet) will tell you about its approximate mechanical composition.
Clayey
This substrate contains up to 50% pure clay and is characterized by such definitions as “damp”, “viscous”, “heavy”, “sticky” and “cold”. Clay soils allow water to pass through very slowly, retaining it on the surface, which makes it almost impossible to cultivate the area: wet clay sticks to gardening tools. 
In a dry state, it is very difficult to rub such soil with your fingers, but when you succeed, you get the feeling that you have a homogeneous powder in your hands. When wet, it begins to smear heavily, rolls perfectly into a cord and allows you to form a ring from the soil without any problems.
Sandy loam
Unlike the first option, dry sandy loam soils are easily rubbed with your fingers and in this state allow you to see small grains of sand with the naked eye. If you wet the substrate and try to load it into the string, you will only get a small part. In this case, along with clay, the substrate also contains sand, of which there is noticeably more (20% to 80%). 
Important! If the amount of sand in the soil mixture exceeds the specified value, then the quality of the soil as a whole will decrease.
Sandy
Such soils are formed exclusively by sand grains, with a small addition of clay or dust particles. This type of substrate is structureless and is not characterized by cohesive properties. 
Loamy
When you rub dry loam between your fingers, you obtain a fine powder with palpable grains of sand. Once moistened, it can be rolled into a cord that breaks when attempting to form a ring. Light loams will not allow you to form a ring, and the cord will crack when rolling. Heavy loamy substrates allow you to get a ring with cracks. Loamy soils themselves are already rich in mineral compounds, and they are also characterized by fairly high looseness, do not prevent the passage of moisture into the lower layers and ensure normal air circulation.
If the earth consists of small particles of silt and larger particles of sand, then it is of higher quality. To determine the proportions of these substances, you can conduct a small home study. Take a soil sample from your site, place it in a container of water and stir until it is not too liquid. First make a ball from the resulting solution, and then try to make a rope.
Of course, the final result plays the main role in this matter. That is, if you don’t get either a ball or a rope, then you have sand in front of you, and if you managed to form a ball, then you can assume the presence of sandy loam. Only loam is suitable for forming a rope, and if it folds into a ring, then it is most likely clay. The final and most accurate conclusion about the mechanical composition of the soil mixture can only be made based on the results laboratory tests during the office period. The influence of the composition on the future harvest
A lower or higher content of clay and sand in the soil will always affect the quality and quantity of the crop, so when choosing a site for planting seedlings of cultivated crops, it is important to take this nuance into account. On clay or completely sandy soils, most of the usual garden plants will be quite uncomfortable, if they can take root there at all. Planting in loamy or sandy loam soils can bring greater results, but they cannot compare with chernozems fertilized with organic matter and mineral compounds.
Physical properties of soil
The main physical properties of soil that you need to pay attention to first of all are density and porosity, and it cannot be said that they do not affect each other in any way. The denser the soil, the less its porosity, which means there is no need to talk about good water, air permeability or aeration. Let's look at this issue more carefully. 
Density (bulk mass)
Soil density is the mass of a unit volume, calculated in grams per cubic centimeter, or an absolutely dry soil mixture in its natural composition. Density determines the relative position of all constituent particles, taking into account the free space between them, and also affects moisture absorption, gas exchange and, as a consequence, the development of the roots of cultivated crops.
As for the level of soil density, it depends on the properties of the minerals that form the solid phase, granulometric components, content and structure of organic components. The optimal value for the density of the arable horizon for most of the vegetable crops grown in our country is considered to be 1.0-1.2 g per cubic meter. cm.
If we consider the density of soil mixtures in their dry state, we can distinguish the following degrees:
- Fused or very dense composition, when the soil is practically not amenable to the influence of a shovel (it can enter the ground no more than 1 cm). Basically, this option is typical for drained chernozem soils and columnar solonetzes.
- A dense structure in which the shovel penetrates the ground no more than 4-5 cm, and the substrate itself is difficult to break. Typical for heavy, clayey and uncultivated soils.
- Loose structure - agricultural tools easily go deep into the ground, and the soil itself is well structured. These are sandy loam soils and upper, well-structured loam horizons.
- The crumbly texture is characterized by the high flowability of the soil, the individual particles of which are loosely connected to each other. This option is typical for sandy loam and structureless substrates.
Important! The specific type of density depends not only on its mechanical, but also on its chemical composition and humidity. This property of soil has considerable practical value in the management of Agriculture, mostly in terms of the ability to process it.
Porosity
Porosity is the exact opposite of density above, and from a scientific point of view it is overall volume all free space (pores) between the solid components of the soil. It is expressed as a percentage of the total volume of the substrate, and for mineral varieties the range of these values will be in the range of 25–80%. In soil horizons, pores do not always have the same shape and diameter, therefore, based on their sizes, capillary and non-capillary types of soil are distinguished. The first is equal to the volume of all capillary pores in the soil, and the second is the volume of only large pores. 
The sum of the two values will be the total porosity. In many ways, this characteristic depends on the density, structure and mechanical composition, which we talked about earlier. In macrostructural substrates, pores will occupy more volume, in microstructural substrates - a smaller part of it. When a structureless substrate dries out, a soil crust forms on the surface of the earth, which negatively affects the growth and development of crops. Of course, it should be removed in a timely manner, and if possible, look for other, more successful places for planting.
10
once already
helped
Introduction……………………………………………………..…………………3
1. Soil………………………………………………………………………………4
2. Types of soils…………………………………………………………………………………5
3. Soil composition and properties………………………………………………………6
4. General physical properties of soil………………………………………….11
4.1 Water properties of soils………………………………………………………13
4.2 Thermal properties of soils…………………………………………………….16
4.3 Physical and mechanical properties……………………………………………………….18
4.4 Air properties of soils……………………………………………………………..20
5. Humus content……………………………………………………………………………….....22
6. Soil fertility………………………………………………………...…..23
7. Types of soil fertility…………………………………………………..…...25
8. Factors limiting soil fertility………………………………26
9. Reproduction of soil fertility……………………………………………………28
Conclusion………………………………………………………..……………..32
List of references………………………………………………………..34
List of accepted terms………………………..…………………………..35
Introduction
First scientific definition soil was given by V.V. Dokuchaev: “Soil should be called the “day” or outer horizons of rocks (no matter what), naturally changed by the combined influence of water, air and various kinds of organisms, living and dead.” He found that all soils on earth's surface are formed through “an extremely complex interaction of local climate, vegetation and animal life, the composition and structure of the parent rocks, the topography of the area and, finally, the age of the country.” These ideas of V.V. Dokuchaev were further developed in the concept of soil as a biomineral (“bio-inert”) dynamic system located in a constant material and energy interaction with the external environment and partially closed through the biological cycle.
The development of the doctrine of soil fertility is associated with the name of V.R. Williams. He studied in detail the formation and development of soil fertility in the course of natural soil formation, examined the conditions for the manifestation of fertility depending on a number of soil properties, and also formulated the basic principles about general principles increasing soil fertility when used in agricultural production.
Goal: To study the general physical properties of soil and their role in soil fertility
1.Show the importance of soil for plants and living organisms
2. Highlight the main property of soil - fertility
3. Foster a caring attitude towards nature in general
4. Get acquainted with the process of soil formation
5. Study of types of soil fertility
6.Study the role of humus for soil fertility
The soil
Soil is the most superficial layer of land on earth, resulting from changes in rocks under the influence of living and dead organisms (vegetation, animals, microorganisms), solar heat and atmospheric precipitation. Soil is a completely special natural formation, possessing only its own inherent structure, composition and properties. The most important property of soil is its fertility, i.e. the ability to ensure the growth and development of plants. To be fertile, the soil must have a sufficient amount of nutrients and a supply of water necessary to nourish plants; it is precisely by its fertility that the soil, as a natural body, differs from all other natural bodies (for example, barren stone), which are not capable of meeting the needs of plants for simultaneous and the joint presence of two factors of their existence - water and minerals.
Soil is the most important component of all terrestrial biocenoses and the Earth’s biosphere as a whole; through the Earth’s soil cover there are numerous ecological connections of all organisms living on and in the earth (including humans) with the lithosphere, hydrosphere and atmosphere.
The role of soil in the human economy is enormous. The study of soils is necessary not only for agricultural purposes, but also for the development of forestry, engineering and construction. Knowledge of soil properties is necessary to solve a number of problems in health care, exploration and mining of mineral resources, organization of green areas in urban areas, environmental monitoring, etc.
Soil types
Podzolic soil is formed under the canopy of a coniferous forest, on which there is insignificant herbaceous vegetation. The soil contains a small supply of humus (0.7 - 1.5%). The upper layer (humus) has a thickness of 2 to 15 cm. The deeper layer is structureless, podzolic, whitish, infertile, and has a thickness of 2 to 30 cm.
Sod-podzolic soil. It is a more fertile species.
This soil has a humus layer of 15–18 cm, under which another layer is infertile. Humus content is 1.5 - 1.8%. It has a dusty and easily destroyed lumpy structure. The soil solution has an acidic reaction.
Peat (marsh) soil. Forms on waterlogged soil. Peat soils have two types: highland and lowland, which differ greatly from each other. High peat bogs are formed in elevated areas that are waterlogged by soft groundwater and precipitation. Wild rosemary, cranberries, blueberries, and moss grow on it.
Floodplain soils. Located near rivers, they are considered the best for vegetable growing. They contain a small amount of humus, but have powerful humus capacity and a strong granular structure. Its disadvantage is that cold air stagnates in low areas; this is especially harmful in the spring. Floodplain soil has different acidity levels. According to its composition, the soil is divided into clayey, loamy, sandy and sandy loam.
Clay soil consists of clayey, small particles, the permeability of air and water is very poor. After rains, rapid compaction occurs by forming a crust on the surface.
Loamy soil consists of large sand and small clay particles. Such soil is more fertile than clay soil; it retains moisture accumulated in winter and spring well. In years with insufficient rainfall, it suffers less from drought.
sandy soil consists of larger particles. It causes rapid leaching of nutrients. Such soil easily allows water to pass through. Sandy soil has low fertility, but dries out and warms up quickly in the spring. Planting and sowing are carried out at great depths.
Sandy loam soil consists predominantly of large particles, the content of clay substances is about 20%. Compared to sandy soil, this soil retains water slightly better. A distinctive feature is low fertility. In sandy loam soil, little humus accumulates and the process of decomposition of organic matter occurs quickly.
Soil composition and properties
Soil is the surface layer of the earth's crust, which is formed and develops as a result of interactions, living microorganisms, rocks and is an independent ecosystem.
The most important property of the soil is soil fertility, i.e. the ability to ensure the growth and development of plants. This property is of exceptional value for human life and other organisms. Soil is an integral part of the biosphere and energy in nature and supports gas composition atmosphere.
Soil consists of solid, liquid, gaseous and living parts. Their ratio is different not only in different soils, but in different horizons of the same soil. There is a natural decrease in the content of organic substances and living organisms from the upper soil horizons to the lower ones and an increase in the intensity of transformation of the components of the parent rock from the lower and to the upper horizons. The solid part is dominated by minerals. Primary minerals (quartz, feldspars, hornblende, mica, etc.) form large fractions instead of rock fragments; secondary minerals (hydromicas, montmorillonite, kaolinite, etc.) formed during the weathering process are thinner. The looseness of soil composition is determined by the composition of its solid part, which includes particles of different sizes (from soil colloids, measured in hundredths of microns, to fragments with a diameter of several tens of cm). The bulk of soil is usually fine earth - particles less than 1 mm
Solid particles in their natural occurrence do not fill the entire volume of the soil mass, but only a certain part of it; The other part consists of pores - gaps of various sizes and shapes between particles and their aggregates. The total volume of pores is called soil porosity. For most mineral soils this value varies from 40 to 60%. In organic (peaty) soils it increases to 90%, in swampy, gleyed, mineral soils it decreases to 27%. The water composition of the soil (water permeability, water-lifting capacity, moisture capacity) and soil density depend on porosity. The pores contain soil solution and soil air. The ratio of their continuity changes due to the entry into the soil of the atmosphere of precipitation, sometimes irrigation and groundwater, as well as moisture consumption - soil runoff, evaporation (suction by plant roots), etc.
The pore space freed from water is filled with air. These phenomena determine the air and soil regime of the soil. The more pores are filled with moisture, the more difficult the gas exchange (especially O2 and CO2) between the soil and the atmosphere is, the slower the oxidation processes in the soil mass and the faster the reduction processes. Soil microorganisms also live in the pores. The density of the soil (or volumetric mass) in an undisturbed structure is determined by the porosity and average density of the solid phase. The density of mineral soils is from 1 to 1.6 g/cm 3 , less often 1.8 g/cm 3 , gleyed swampy soils - up to 2 g/cm 3 , peat soils - 0.1-0.2 g/cm 2 .
Dispersity is associated with a large total surface of solid particles: 3-5 m 2 /g for sandy soils, 30-150 m 2 /g for sandy loam soils, up to 300-400 m 2 /g for clayey soils. Due to this, soil particles, especially colloidal and silty fractions, have surface energy, which is manifested in the absorption capacity of the soil and the buffering capacity of the soil.
Mineral composition The solid part of the soil largely determines its fertility. There are few organic particles (plant residues), and only peat soils consist almost entirely of them. The composition of mineral substances includes: Si, Al, Fe, K, N, Mg, Ca, P, S; contains significantly less microelements: Cu, Mo, I, B, F, Pb, etc. The vast majority of elements are in oxidized form. Many soils, mainly in the soils of insufficiently moistened areas, contain a significant amount of CaCO3 (especially if the soils were formed on carbonate rock); in the soils of arid areas - CaSO4 and other more easily soluble salts; soils of humid tropical regions are enriched in Fe and Al. One reaction of these general patterns depends on the composition of soil-forming rocks, age of the soil, topography, climate, etc. For example, on basic igneous rocks soils richer in Al, Fe, alkaline earth and alkali metals are formed, and on acidic rocks - Si. In the humid tropics, on young weathered soil crust, soils are much poorer in iron and aluminum oxides than on older ones, and the content is similar to the soil of temperate latitudes. On steep slopes, where erosion processes are very active, the composition of the solid part of the soil differs slightly from the composition of the parent rocks. Saline soils contain a lot of chlorides and sulfates (less often nitrates and bicarbonates) of calcium and magnesium, which is associated with the initial salinity of the parent rock, with the supply of these salts from groundwater or as a result of soil formation.
The composition of the solid part of the soil includes organic matter, the main part (80 - 90%) of which is represented by a complex set of humic substances, or humus. Organic matter also consists of compounds of plant, animal and microbial origin containing fiber, lignin, proteins, sugars, resins, fats, tannins, etc. and intermediate products of their decomposition. When organic matter decomposes in the soil, the nitrogen it contains is converted into forms available to plants. Under natural conditions, they are the main source of nitrogen nutrition plant organisms. Many organic substances are involved in the creation of organomineral structural units (lumps). The emerging theoretical structure of the soil largely determines its physical properties, as well as water, air and thermal regimes. Organo-mineral compounds are represented by salts, clay-humus complexes, complex and intra-complex (chelates) compounds of humic acids with a number of elements (including Al and Fe). It is in these forms that the latter move into the soil.
The liquid part, i.e. soil solution is an active component of the soil that transports substances within it, removes them from the soil and supplies plants with water and dissolved nutrients. Usually contains ions, molecules, colloids and larger particles, sometimes turning into a suspension.
The gas part or soil air fills the pores not occupied by water. The quantity and composition of soil air, which includes N2, O2, CO2, volatile organic compounds, etc., are constant and are determined by the nature of the many chemicals occurring in the soil, biochemical processes. For example, the amount of CO2 in soil air varies significantly in the annual and daily cycles due to different rates of gas release by microorganisms and plant roots. Gas exchange between soil air and the atmosphere occurs primarily as a result of the diffusion of CO2 from the soil into the atmosphere and O2 in the opposite direction.
The living part of the soil consists of soil microorganisms (bacteria, fungi, actinomycetes, algae, etc.) and representations of many groups of invertebrate animals - protozoa, worms, mollusks, insects and their burrowing vertebrates, etc. The active role of living organisms in the formation of soil determines its identity to bioinert natural bodies - the most important components of the biosphere.
Chemical composition soil affects human health through water, plants and animals. The deficiency or excess of certain chemical elements in the soil can be so great that it leads to metabolic disorders and causes or contributes to the development of serious diseases. Thus, the widespread disease endemic (local) goiter is associated with a lack of iodine in the soil. A small amount of calcium with an excess of strontium causes urinary disease. Lack of fluoride leads to dental caries. With a high fluoride content (over 1.2 mg/l), diseases of the skeletal system (fluarosis) often occur.
Soil is a complex natural system where, under the influence of living organisms and other factors, the formation and destruction of complex organic compounds occurs. Mineral substances are extracted by plants from the soil, become part of their own organic compounds, and then are included in the organic substances of the body of first herbivores, then insectivores, and predatory animals. After the death of plants and animals, their organic compounds enter the soil. Under the influence of microorganisms, as a result of complex multi-stage decomposition processes, these compounds are transformed into forms available for absorption by plants. They are partly part of organic matter, retained in the soil or removed with filtered and wastewater. As a result, a natural cycle of chemical elements occurs in the system “soil - plants - (animals - microorganisms) - soil”. This cycle of V.R. Williams called it small, or biological. Thanks to the low cycle of substances in the soil, fertility is constantly maintained. In artificial agrocenoses, such a cycle is disrupted, since people withdraw a significant part of agricultural products, using them for their own needs. Due to the non-participation of this part of the production in the cycle, the soil becomes infertile. To avoid this and increase soil fertility in artificial agrocenoses, people apply organic and mineral fertilizers. By applying the necessary crop rotations, carefully cultivating and fertilizing the soil, people increase its fertility so significantly that most modern cultivated soils should be considered artificial, created with human participation. Thus, in some cases, human impact on soils leads to an increase in their fertility, in others - to deterioration, degradation and death.
General physical properties of soil.
Among physical soil properties distinguish its general physical, physical-mechanical, water, air and thermal properties. Physical properties influence the nature of the soil-forming process, soil fertility and plant development.
Common physical properties include soil density, solids density, and porosity.
Soil density is the mass of a unit volume of absolutely dry soil taken in its natural composition, expressed in grams per cubic centimeter. Soil density, g/cm3, is calculated using the formula
dv = m/V .
Where m- mass of absolutely dry soil, g; V- volume occupied by the soil sample, cm3.
Soil density depends on the granulometric and mineralogical compositions, structure, humus content and processing. After treatment, the soil is initially loose, and then gradually becomes compacted, and after some time its density changes little until the next treatment. The upper humified and structured horizons have the lowest density. For most agricultural crops, the optimal soil density is 1.0... 1.2 g/cm 3 .
Soil solids density is the mass of dry soil per unit volume of soil solids without pores. It is calculated, g/cm 3, using the formula
d = m/Vs.
Where m- mass of dry soil, g; V s- volume, cm 3.
In low-humus soils and in lower mineral horizons, the density of the solid phase is 2.6...2.8 g/cm 3 . With an increase in humus content, the density of the solid phase decreases to 2.4...2.5 g/cm3, and in peat soils - to 1.4...1.8 g/cm3. Solid density is used to calculate soil porosity.
The absorption of moisture, air exchange in the soil, the vital activity of microorganisms and the development of plant root systems depend on the density of the soil.
Soil porosity (porosity) is the total volume of all pores between particles of the soil solid phase. Porosity (total) is calculated based on soil density and solid phase density and is expressed as a percentage of the total soil volume:
Ptot. =(1-d v /d)100
Where d v- soil density, g/cm 3 ; d- density of the soil solid phase, g/cm3.
Porosity depends on the particle size distribution, structure, and organic matter content. In arable soils, porosity is caused by cultivation and cultivation techniques. With any loosening of the soil, porosity increases, and with compaction it decreases. The more structured the soil, the greater the overall porosity.
The sizes of the pores, which together form the overall porosity of the soil, vary from the finest capillaries to larger spaces that do not have capillary properties. Therefore, along with general porosity, capillary and non-capillary soil porosity are also distinguished. Capillary porosity is characteristic of undisturbed loamy soils, and non-capillary porosity is characteristic of structural and loose soils.
The pores can be filled with water or air. Capillary pores provide the water-holding capacity of the soil; the supply of moisture available to plants depends on them. Non-capillary pores increase water permeability and air exchange. A stable supply of moisture in the soil with simultaneous good air exchange is created when non-capillary porosity is 55...65% of the total porosity. Depending on the total porosity during the growing season for loamy and clayey soils, a qualitative assessment of soil porosity is given. The following is a qualitative assessment of soil porosity according to N.A. Kachinsky.
Soil porosity ensures the movement of water in the soil, water permeability and water-lifting capacity, moisture and air capacity. By the total porosity one can judge the degree of compaction of the arable soil layer. Soil fertility largely depends on porosity.
4.1 Water properties of soils. The most important water properties of soils include water permeability, water-lifting capacity, and soil moisture capacity.
Water permeability is the ability of soil to absorb and pass water through itself. The process of permeability involves absorbing moisture and filtering it. Absorption occurs when water enters the soil unsaturated with water, and filtration begins when most of the soil pores fill with water. During the first period of water entering the soil, water permeability is high, then it gradually decreases and by the time of complete saturation (at the beginning of filtration) it becomes almost constant. Water absorption is caused by sorption and capillary forces, filtration by gravity forces.
The degree of use of water resources depends on water permeability. With weak water permeability, part of the precipitation or irrigation water flows over the surface, which leads not only to unproductive consumption of moisture, but can cause soil erosion. Soils in which water penetrates to a depth of 15 cm during the first hour are considered well permeable. In moderately permeable soils, water passes from 5 to 15 cm in the first hour, and in weakly permeable soils - up to 5 cm. The highest water permeability is typical for sandy, also well-structured soils. soils, low - for clayey and structureless dense soils. Water permeability also depends on the composition of absorbed cations: sodium reduces water permeability, and calcium, on the contrary, increases it.
Water-lifting capacity is the ability of soil to lift water through capillaries. Water in soil capillaries forms a concave meniscus, on the surface of which surface tension is created. The thinner the capillary, the more concave the meniscus and, accordingly, the higher the water-lifting capacity. Loamy soils have the highest capillary rise (3...6 m). In sandy soils, the pores are large, so the height of the capillary rise is 3...5 times less than in loamy soils, and usually does not exceed 0.5...0.7 m. In dense clay soils, this figure decreases due to that very fine pores are filled with bound water.
The rate of capillary rise depends on the size of the capillaries and the viscosity of the water, determined by its temperature. In large pores, water rises faster, but reaches a small height. As the radius of the capillaries decreases, the speed decreases and the lift height increases. As the temperature increases, the viscosity of water decreases, so the rate of its capillary rise increases. Salts dissolved in water have a significant effect on the rate of capillary rise. Mineralized groundwater, unlike fresh water, rises to the surface through capillaries at a higher speed. Saline groundwater during its capillary rise often leads to soil salinization.
Water holding capacity is the ability of soil to hold water. Depending on the water-holding forces, they distinguish between maximum adsorption, capillary, maximum field and total moisture capacity.
Maximum adsorption moisture capacity (MAC) is the largest amount of moisture inaccessible to plants, which is firmly retained by the molecular forces of the soil (adsorption). It depends on the total surface of the particles, as well as on the humus content: the more silt particles and humus in the soil, the higher the maximum adsorption moisture capacity.
Capillary water capacity (KB) is the amount of water that is retained in the soil when capillary pores are filled above the groundwater level. Capillary moisture capacity depends on the height above the groundwater table. It is greatest near groundwater, and decreases as it rises to the surface.
Maximum field moisture capacity (FMC) is the amount of water that is retained in field conditions after the soil is completely moistened from the surface and excess water flows freely. Groundwater in this case does not affect soil moisture. The maximum field moisture capacity depends on the granulometric composition, density and porosity of the soil. It corresponds to the amount of capillary suspended water. A synonym for maximum field moisture capacity is the lowest moisture capacity (MC).
Full moisture capacity (MC) is the state of soil moisture when all pores are filled with water. Full moisture capacity is observed above impermeable horizons where groundwater is located. When the soil is completely saturated with water, there is no aeration, which makes it difficult for plant roots to breathe.
Soil moisture is divided into absolute and relative.
Absolute moisture is the total amount of water in the soil, expressed as a percentage of the soil's mass.
Relative humidity is the ratio of the absolute humidity of a given soil to its maximum field moisture capacity.
The availability of soil moisture to cultivated plants is determined by relative and absolute soil moisture.
Plant wilting humidity is the soil moisture at which plants show signs of wilting that do not disappear when the plants are placed in an atmosphere saturated with water vapor, that is, this is the lower limit of moisture availability to plants. Knowing the absolute humidity and the wilting humidity of plants, it is possible to calculate the supply of productive moisture.
Productive (active) moisture is the amount of water above the wilting moisture used by plants to create a crop. So, if the absolute moisture content of a given soil in the arable layer is 43%, and the wilting moisture content is 13%, then the reserve of productive moisture is equal to 30%.
For ease of determination, the amount of productive moisture is expressed in millimeters of water column. In this form, productive moisture is easier to compare with the amount of precipitation. Each millimeter of water on an area of 1 hectare corresponds to 10 tons of water.
4.2 Thermal properties of soils. The main thermal properties of soil include heat absorption capacity, heat capacity and thermal conductivity.
Heat absorption capacity is the ability of soil to absorb radiant energy from the Sun. The heat absorption capacity indicator is related to the albedo value.
Albedo is the ratio of reflected radiation to the total radiation reaching the Earth, expressed as a percentage. The lower the albedo, the more the soil absorbs solar radiation. This indicator depends on the color of the soil, moisture, structure, humus content and particle size distribution. Highly humus soils are dark in color, so they absorb radiant energy 10...15% more than low humus soils. Compared to sandy soils, clay soils are characterized by high heat absorption capacity. Dry soils reflect radiant energy 5...11% more than wet ones.
Heat capacity is the ability of soil to retain heat. There is a distinction between specific and volumetric heat capacity of soil.
Specific heat capacity is the amount of heat required to heat 1 g of dry soil by 1 °C (J/g per 1 °C).
Volumetric heat capacity is the amount of heat expended to heat 1 cm 3 of dry soil by 1 ° C (J/cm 3 per 1 ° C).
The heat capacity of the soil depends on the mineralogical and granulometric composition, as well as on the content of water and organic matter in it.
For dry soils, a small range of fluctuations in heat capacity is 0.170...0.200. When moistened, the heat capacity of sandy soils increases to 0.700, clayey soils - 0.824, and peaty soils - up to 0.900. Sandy and sandy loam soils are less moisture-holding, therefore they warm up faster and are called “warm”. Clay soils contain more water, which requires a lot of heat to heat, which is why they are called “cold” soils.
Thermal conductivity is the ability of soil to conduct heat. It is measured by the amount of heat in joules that passes through 1 cm 3 of soil in 1 s. The thermal conductivity of the main parts of the soil varies greatly. Thus, the thermal conductivity of quartz is 0.00984; granite - 0.03362; water - 0.00557; air - 0.00025 J cm 3 /s.
Since heat in the soil is transferred mainly through solid particles, water and air, as well as through the contact of particles with each other, thermal conductivity largely depends on the mineralogical and granulometric composition, humidity, air content and density of the soil. The larger the mechanical elements, the greater the thermal conductivity. Thus, the thermal conductivity of coarse sand with the same porosity and humidity is twice as high as that of the coarse silt fraction. The thermal conductivity of the solid phase of soil is approximately 100 times higher than that of air, so loose soil has a lower thermal conductivity coefficient than dense soil.
4.3 Physical and mechanical properties. The most important physical and mechanical properties of soil include plasticity, stickiness, swelling, shrinkage, cohesion, hardness and resistivity(processing resistance). The soil cultivation conditions and the operation of sowing and harvesting units depend on these properties.
The plasticity and stickiness of soil is due to the presence of clay particles and water in it.
Plasticity is the ability of soil to change its shape under the influence of force without disturbing the structure and to retain it after the removal of this force. The more silt particles in the soil, the more pronounced its plasticity. The greatest plasticity is characteristic of clay soils. Sandy soils have no plasticity. Plasticity also depends on the composition of absorbed cations and humus content. Thus, with a significant content of absorbed sodium cations in the soil, its plasticity increases, and with calcium saturation it decreases. As the humus content increases, the plasticity of the soil decreases.
Stickiness is directly related to plasticity and is also due to the presence of clay particles and water in the soil. Dry soils are not sticky. As moisture reaches approximately 80% of the lowest moisture capacity, stickiness increases and then begins to decrease.
Stickiness is determined by the force required to lift a piece of metal from the soil and is expressed in grams per square centimeter. Based on stickiness, soils are divided into extremely viscous (>15 g/cm2), highly viscous (5...15), medium viscous (2...5) and slightly viscous (<2г/см 2). Наибольшую липкость имеют глинистые почвы, наименьшую - песчаные. Почвы высокогуму-сированные и структурные не имеют липкости даже при увлажнении до 30...35 %. С липкостью связана физическая спелость почвы, то есть состояние влажности, при котором почва хорошо крошится на комки, не прилипая к орудиям обработки. Весной в первую очередь поспевают к обработке песчаные и супесчаные почвы, а при одинаковом гранулометрическом составе - более гумусированные.
Swelling is the increase in soil volume when moistened. The most swellable clay soils are those with a high content of colloids, on the surface of which moisture sorption occurs. Sandy soils with very low colloid content do not swell at all. Exchangeable sodium cations greatly increase the swelling properties of soils, which is why solonetzes are characterized by high swelling properties. With significant swelling, the soil structure is destroyed.
Shrinkage is the reverse process of swelling. When the soil dries out, cracks form, plant roots break, and moisture loss due to evaporation increases. The greater the swelling of the soil, the greater its shrinkage.
Cohesion is the ability of soil to resist external forces that tend to pull soil particles apart. Connectivity is expressed in grams per square centimeter. Clayey structureless soils have the greatest cohesion in the dry state, while sandy soils have the least cohesion. When clayey and loamy soils become structurized, their cohesion sharply decreases.
Hardness is the ability of soil to resist compression and wedging. Hardness and cohesion depend on the particle size distribution, humus content, composition of exchangeable cations, structure and degree of moisture. Soils with a high humus content, saturated with calcium and having a good cloddy-grained structure do not have high hardness and cohesion. Their processing requires less energy consumption.
Specific resistance is the force that is expended on cutting the layer, its rotation and friction against the working surface of the plow. It is characterized by the soil resistance in kilograms per 1 cm 2 of the cross-section of the soil layer lifted by the plow. Specific resistance depends on the physical and mechanical properties of the soil and ranges from 0.2...1.2 kg/cm 2.
To improve the physical and physical-mechanical properties of the soil, a set of measures is used: applying organic fertilizers, cultivating perennial grasses, sowing green manure, choosing the timing and methods of soil cultivation depending on the state of its moisture. When liming acidic soils and gypsuming alkaline soils, the composition of absorbed cations changes and the physical and mechanical properties improve. This is also facilitated by measures that reduce soil compaction by machines (minimizing tillage, deep loosening, etc.).
4.4 Air properties of soils. Soil is a porous body in which air is almost constantly present in varying quantities. It usually consists of a mixture of gases and fills the water-free pores of soils. Sources of soil air are atmospheric air and gases formed in the soil itself.
Most plants cannot exist without a constant flow of oxygen to the roots and removal of carbon dioxide from the soil - there must be a constant exchange with atmospheric air. The process of exchanging soil air with atmospheric air is called gas exchange or aeration.
With a lack of oxygen and an excess of carbon dioxide in the soil air, plant development is inhibited, the absorption of nutrients and water decreases, and root growth slows down. Lack of oxygen leads to plant death. All this necessitates constant soil aeration. Soil air can be in different states - free, adsorbed by the surface of soil particles and dissolved in the liquid phase of the soil. Free soil air is of great importance in soil aeration. It is usually found in non-capillary and capillary pores, is mobile and can exchange with atmospheric air.
The composition of soil air differs from atmospheric air in having less oxygen and more carbon dioxide.
In addition to the three main gases (N2, O2, CO2), small amounts of CH4, H2, etc. are found in the soil air.
During the growing season, the composition of soil air constantly changes as a result of the activity of microorganisms, plant respiration and gas exchange with the atmosphere. In arable, well-aerated soils with favorable physical properties, the CO2 content in the soil air during the growing season does not exceed 1–2%, and the O2 content does not fall below 18%.
The main factors influencing gas exchange are diffusion, changes in soil temperature, barometric pressure, soil moisture, and wind. All these factors act together in natural conditions, but diffusion must be considered the main one. As a result, gases move in accordance with their partial pressure.
The state of gas exchange is determined by the air properties of soils. These include breathability And air capacity.
Soil fertility. During its development, a plant needs nutrients, water, air and warmth. The soil that is able to satisfy these demands of the cultivated plant will be fertile soil.
Fertility is the main, basic property of the soil. This in turn depends on a number of other properties, which we will describe below.
Soil absorption capacity. The plant takes food from soil solutions with its roots. But in order for it to take the substances it needs, the solutions must be weak, that is, a very small amount of salts must be dissolved in a large amount of 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, plant roots are unable to absorb salts, and the plant dies, just as it would die from starvation.
But we know that the amount of water in the soil is constantly changing. There is more of it after rains, and less during drought. 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 humus soil regulate the strength of the solution within certain limits. When the strength of the solution increases, the soil absorbs some of the dissolved substances from it. On the contrary, after rains or artificial watering of the soil, when the amount of water in it increases significantly, some of the substances and salts found in the solid part of the soil again go into solution.
In many cases, exactly 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 salt, Glauber's salt, which is used as a laxative, and some other salts.
The ability of the soil, its solid part, to absorb from an aqueous solution and bind (in order to later release again) 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 a combination of both (organo-mineral particles). This part of the soil is called the part that absorbs it, or the complex that absorbs it.
The soil can even absorb some gases, such as ammonia, which smells so strongly in stables. Ammonia absorbed by the soil is converted into nitrate with the participation of bacteria.
But not all substances are absorbed equally well by the soil. For example, saltpeter, which is so valuable for plants, is very poorly 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 soils rich in humus can be safely fertilized with large quantities of nutrients. The excess will be absorbed by the soil and will not harm the plant, nor will it be washed away 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 greatest plant development.
Sandy soils have completely different properties. There is little clay and humus in these soils. Their absorption capacity is negligible. Water easily washes away the nutrient salts from them, and they disappear without a trace for the plants. In 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 added to sandy soils little by little, in several portions. It is also recommended not to leave sandy soils in pure steam, as water will wash away the soluble nutrients formed during the fallow process.
Fallow areas on sandy soils should be sown with lupine or seradella. By cultivating 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, sour humus) or alkalis (for example, soda) in the soil, then the cultivated plant dies. Most cultivated plants like the soil solution to be neither acidic nor alkaline; it should be average, neutral.
It turns out that the reaction of the soil greatly depends on what substances are absorbed by the soil. If the soil (its solid part) has absorbed aluminum or hydrogen, it will be acidic; soil that has taken sodium from the solution will be alkaline, and soil saturated with calcium will have a neutral, that is, 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 found in clay and other minerals.
In nature, different soils have different reactions: for example, swamp and podzolic soils, as well as red soils, are characterized by acidity, solonetzes - by alkalinity, and chernozems - by an average reaction.
Porosity, or porosity, of soil. If the soil has enough nutrients, but does not have enough water or air, the plant will die. Therefore, care must be taken to ensure that, along with food, there is always water and air in the soil, which are placed in soil voids, or wells. Soil wells occupy a very large volume, approximately 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 clayey 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 porosity is less - approximately 400-450 cubic centimeters per 1 liter of soil.
The size of voids and their shapes are very different, both in the same soil and even more so in different soils. For cultivated plants, it is advisable to create medium-sized wells, with a clearance from a few millimeters to tenths and hundredths of a millimeter. Holes in the soil that are too small, such as, for example, in the columnar horizon of solonetz or in the compacted horizon of podzolic soils, as well as holes that are too large (cracks) create unfavorable conditions for plants. Plant root hairs can penetrate only into wells with a diameter of at least 0.01 millimeters, and bacteria can only penetrate into wells with a diameter of at least 0.003 millimeters.
Soil permeability. Falling onto the soil surface in the form of precipitation, water, under the influence of gravity, seeps into the soil through large wells and is absorbed through thin wells, or capillaries, surrounding soil particles in a continuous layer.
The pores in sand are large, and water penetrates through them easily and quickly. On the contrary, it is absorbed with difficulty into clay soils with extremely small holes - tens and hundreds of times slower than into sand.
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 the individual small particles in it coagulate and stick together into porous grains and lumps. These grains and lumps, in the presence of lime and humus, are durable and difficult to wash away in water. In the soil between them, medium-sized pores are formed, like in sand, and somewhat larger. This (structural) clay soil has good water permeability, despite the fact that it consists of tiny particles.
Water holding capacity and soil moisture holding 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 with its surface. The closer the layer of water is to the soil particle, the stronger it is held by the soil, the more firmly it is bound by it.
The ability of soil to hold water is called its water holding capacity, and the amount of water that soil holds is called soil moisture holding capacity. The moisture holding 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 can 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.
Assimilable and non-absorbable water in the soil. The water contained in the soil varies in quality. We can distinguish five main categories of sharply different water in the soil: 1) bound, unfree water, which is strongly attracted by soil particles and is mostly inaccessible to plants; 2) capillary water, occupying medium-sized pores in the soil; 3) free, gravitational water that can flow from the soil; 4) steam water; 5) solid water (ice), which is formed in the soil when it freezes. Plants can absorb 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-inhabited soil layer without draining from it. This same water has the ability to move in the soil through capillaries in all directions: from bottom to top, top to bottom and to the sides. This is very important: when the root of a plant drinks water around itself, it can be sucked into it from neighboring, damper places.
But we must not forget that thanks to this same ability, the soil can dry out excessively. 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 along them and evaporates into the air.
The soil is dried more intensively even when the arable land is covered with a crust. This happens after the snow melts and after heavy rains. The crust has very well developed capillaries that strongly absorb water. If we strive to retain moisture in. soil, such a crust must be immediately broken using cultivators or harrows.
The less water in the soil that is bound and not absorbed by plants, 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, we must remember that although clay soils retain more water, they also contain more water that is inaccessible to plants than in sandy soils.
It’s bad when the soil dries out quickly and there is no water in it. The plants then die. But they cannot develop in soil overflowing with water. The average state of the soil is favorable for the plant, when some of the gaps in it are filled with water, and in other gaps there is air.
Soil air capacity. In dry soil, all wells are occupied by air. In this case, part of the air is forcefully attracted by the surface of the soil particles. This part of the air has weak mobility and is called absorbed air. The rest of the air placed in large pores will be free air. It has significant mobility, can be blown out of the soil and easily replaced by new portions of atmospheric air.
As the soil is moistened, the air from it is displaced by water and comes out, and some of it and other gases (for example, ammonia) dissolve in the 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, released during their respiration and during the smoldering of organic dead remains.
The air in the soil does not remain motionless. 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 (when cooling) contracts, and new portions of atmospheric air are sucked into the soil (“soil respiration”).
Soil air can be blown out by winds, or can be displaced from the soil by precipitation penetrating into it (water); can move when atmospheric (above-ground) pressure changes: when atmospheric pressure increases, part of the air enters the soil; when it decreases, 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 escapes, and drier and oxygen-rich atmospheric air penetrates into the soil pores.
The renewal of soil air in different climatic zones will occur more strongly, either from some of the above reasons, or from others. For example, in deserts, sudden changes in temperature during the day and night, as well as the blowing of soil air by the wind, will be more influential. 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 is constantly ventilated, “breathing easily”, so that the supply of oxygen is continuously restored in it.
Soil heat. Warmth is necessary for soil development and plant life. The soil receives heat from the sun, being heated by its rays. A small fraction 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 residues. 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 equally. Dark, humus-rich, and most importantly dry soils heat up much faster than light and damp soils. Wet soils heat up especially slowly; this happens because a lot of heat is spent 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, the location of the area is of great importance for heating the soil: soils lying on the southern slopes heat up 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 some depth. So one wave after another is sent into the soil every day. Soil particles either expand from heat or contract 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 is hidden under snow cover, when the water in it freezes, when instead of warm waves cold waves go into the depths, the life of the soil freezes to a large extent. All living things in the soil fall into winter hibernation and will awaken to a new vigorous life 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 located inside the lumps and in the capillaries between them, and air is located in large voids between the lumps, on their surface and partly in the lumps themselves - in large tubules and cells.
Structural soil also has good thermal properties. Microorganisms beneficial to plants develop favorably in it. The mineral part in such soil is more easily eroded 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, structural soil always produces higher crop yields.
But not every soil naturally has a good structure. Often you have to work hard to get structured arable land. In all soils, the creation of structure is helped by an artificial increase in humus in it, as well as saturation of the soil with calcium. For the latter purpose, lime is used on acidic soils, and gypsum is used on alkaline soils, for example, on solonetzes.
It is necessary to manure the soil, it is necessary to introduce perennial cereals and legumes into the crop rotation, mixed with each other, and on the sands - lupine and seradella. During life, grasses divide the soil into structural units with their roots. Leguminous grasses enrich the soil with nitrogen, and all herbs - legumes and cereals - enrich it with humus, since they have a powerful root system, several times larger than oats, rye, wheat and other field and garden plants.
Serious attention should be paid to timely tillage of the soil. When plowing dry soil, we destroy and disperse the structure; When plowing waterlogged soils, we press down on the structure and lubricate it. We should strive to plow, if possible, moderately moist soils, when they contain 50-70 percent of the moisture of their moisture capacity. Under this condition, the best quality structural arable land is obtained.
Structural arable land is an indicator of the cultivation of the field. The structure of the soil increases the yield and makes it stable in dry years.
If you find an error, please highlight a piece of text and click Ctrl+Enter.