Moisture is necessary for seed germination, without it the subsequent growth and development of the plant is impossible. With water, nutrients enter the plant from the soil, the evaporation of water from the leaves provides normal temperature conditions for the life of the plant.

SOIL WATER CAPACITY, a value that quantitatively characterizes the water-retaining capacity of the soil; the ability of the soil to absorb and retain a certain amount of moisture from running off by the action of capillary and sorption forces. Depending on the conditions that retain moisture in the soil, several types of water absorption are distinguished: maximum adsorption, capillary, least, and complete.

The maximum adsorption capacity of SOIL, bound moisture, sorbed moisture, approximate moisture - the largest amount of strongly bound water retained by sorption forces. The heavier the granulometric composition of the soil and the higher the content of humus in it, the greater the proportion of bound, almost inaccessible to grapes and other crops, moisture in the soil.

Water is an indispensable condition for soil formation and the formation of soil fertility. Without it, the development of soil fauna and microflora is impossible.

The processes of transformation, transformation and migration of substances in the soil also require a large amount of water.

To determine the needs of plants in water, an indicator is used - the transpiration coefficient - the number of weight parts of water spent on one weight part of the crop.

The degree of availability of soil moisture to plants and the state of the water regime are expressed by soil hydrolytic constants. The following soil-hydrological constants are distinguished:

• 1. Maximum adsorption capacity (MAV) - soil moisture corresponding to the highest content of strongly bound moisture inaccessible to plants.
• 2. Maximum hygroscopicity (MG) - soil moisture, corresponding to the amount of water that the soil can absorb from air completely saturated with water vapor. Moisture corresponding to MG is completely inaccessible to plants.
• 3. The moisture content of stable plant wilting (SW), corresponding to the content of water in the soil, at which plants show signs of wilting that do not disappear when the plants are placed in an atmosphere saturated with water vapor. The wilting moisture corresponds to soil moisture, when moisture from a state inaccessible to plants becomes available (the lower limit of soil moisture availability).
• 4. The lowest (field) soil moisture capacity (HB) - corresponds to the capillary-suspended saturation of the soil with water, when the latter is maximally available to plants.
• 5. Total moisture capacity (PV) - corresponds to such a moisture content in the soil when all its pores are saturated with water.

The ability of the soil to sustainably provide plants with water depends on the agrophysical factors of fertility.

Soil moisture capacity - called the ability of it to retain water. Distinguish between capillary, smallest (field) and full moisture capacity. Capillary capacity is determined by the amount of water contained in soil capillaries backed by an aquifer. The smallest moisture capacity is similar to capillary, but subject to the separation of capillary water from the water of the aquifer. Full moisture capacity - the state of moisture when all the pores (capillary and non-capillary) are completely filled with water.

Soil permeability is the ability to absorb and pass water through it. Water permeability depends on the granulometric composition, soil structure and degree of moisture. Water permeability is determined by passing water through the soil layer.

The water-lifting capacity of the soil is the ability of the capillary rise of water.

This property is due to the action of meniscus forces of the walls of soil capillaries moistened with water.

The conditions of the water regime in arable soil are constantly changing. A radical method of regulating the water regime of soils is melioration. Modern methods of hydrotechnical reclamation provide the possibility of two-way regulation of the water regime: irrigation with the discharge of excess water and drainage in combination with dosed irrigation.

The flow of moisture into the soil consists of absorption with partial filling of pores with water and water filtration. The totality of these phenomena is united by the concept of " soil permeability". According to the rate of water absorption, soils are distinguished by good, medium and slightly permeable soils. Soil filtration, i.e., the downward movement of moisture in the soil or soil when all water is filled, depends on many factors: mechanical composition, water resistance of aggregates, density, addition.

The amount of water that characterizes the water-holding capacity of the soil is called moisture capacity.Depending on the forces that retain moisture in the soil, there is a maximum adsorption capacity (moisture that is retained on the surface of the particles under the action of sorption forces), capillary (water reserve held by capillary forces), the smallest (field) and full capacity or water capacity (water content in soil when all pores are filled with water).

The concept of capillary fringe, which is important in agronomic science, is associated with capillary moisture capacity. capillary border the entire moisture layer between the groundwater level and the upper boundary of the soil wetting front is called.

The smallest (field) moisture capacity- this is the amount of moisture that is stored in the soil (or soil) in the absence of capillary inflow after the moaning of excess gravitational water. This is the maximum amount of water retained by the soil in natural conditions in the absence of evaporation and inflow of water from outside. The moisture capacity of the soil depends on the mechanical, chemical, mineralogical composition of the soil, its density, porosity, etc.

Aeration, water permeability, moisture capacity and other water-physical properties of the soil are important soil characteristics that affect soil fertility and its economic value.

Root extracts. Plants do not remain indebted to microorganisms - living plants feed soil microorganisms with their root secretions, and not only dying post-harvest residues, although the roots also make up about a third of the mass of the plant. Tatyana Ugarova gives a figure - up to 20% of the total mass of plants are root secretions. The composition of root secretions includes organic acids, sugars, amino acids and much more. According to T. Ugarova, a strong plant abundantly feeds soil microorganisms, while mass reproduction of the rhizosphere (root) beneficial microflora occurs. Moreover, plants stimulate the development of predominantly such microflora that nourishes plants, produces plant growth stimulants, and suppresses microflora harmful to plants.

Moisture capacity (moisture retention)- the property of the soil to absorb and retain the maximum amount of water that at a given time corresponds to the impact on it of forces and environmental conditions. This property depends on the state of moisture, porosity, soil temperature, concentration and composition of soil solutions, the degree of cultivation, as well as other factors and conditions of soil formation. The higher the temperature of the soil and air, the lower the moisture capacity, with the exception of soils enriched with humus. The moisture capacity varies according to the genetic horizons and the height of the soil column. In the soil column, as it were, a water column is enclosed, the shape of which depends on the height of the column of soil soil above the mirror and on the condition of moistening from the surface. The shape of such a column will correspond to the natural area. These columns in natural conditions change with the seasons of the year, as well as with weather conditions and fluctuations in soil moisture. The water column changes, approaching the optimal one, under the conditions of soil cultivation and reclamation. The following types of moisture content are distinguished:

• a) complete (PV);
• b) maximum adsorption (MAW);
• c) capillary (KV);
• d) the smallest field (HB)
• e) limiting field moisture capacity (PPV).

All types of moisture capacity change with the development of the soil in nature and even more - in production conditions. Even one treatment (loosening of ripe soil) can improve its water properties, increasing the field water capacity. And the introduction of mineral and organic fertilizers or other moisture-intensive substances into the soil can improve water properties or moisture capacity for a long time. This is achieved by incorporating manure, peat, compost and other moisture-intensive substances into the soil. The ameliorative effect can be exerted by the introduction of water-retaining highly porous moisture-intensive substances such as perlite, vermiculite, and expanded clay into the soil.

In addition to the main source of radiant energy, the heat released during exothermic, physicochemical and biochemical reactions enters the soil. However, the heat generated by biological and photochemical processes hardly changes the temperature of the soil. In summer, dry, heated soil can increase the temperature due to wetting. This warmth is known by the genus name heat of wetting. It manifests itself with weak wetting of soils rich in organic and mineral (clay) colloids. The very slight heating of the soil may be due to the internal heat of the Earth. Of the other secondary sources of heat, one should mention the “latent heat” of phase transformations, which is released in the process of crystallization, condensation and freezing of water, etc. Depending on the mechanical composition, humus content, color and moisture, warm and cold soils are distinguished. Heat capacity is determined by the amount of heat in calories that must be expended to raise the temperature of a unit mass (1 g) or volume (1 cm3) of soil by 1 ° C. The table shows that with increasing humidity, the heat capacity increases less for sands, more for clay, and even more for peat. Therefore, peat and clay are cold soils, while sandy soils are warm. Thermal conductivity and thermal diffusivity. Thermal conductivity- the ability of the soil to conduct heat. It is expressed as the amount of heat in calories passing per second through a 1 cm2 cross-sectional area through a 1 cm layer with a temperature gradient between the two surfaces of 1°C. Air-dry soil has a lower thermal conductivity than wet soil. This is due to the large thermal contact between individual soil particles united by water shells. Along with thermal conductivity, there are thermal diffusivity- the course of temperature changes in the soil. Thermal diffusivity characterizes the change in temperature per unit area per unit time. It is equal to the thermal conductivity divided by the volumetric heat capacity of the soil. During the crystallization of ice in the pores of the soil, a crystallization force is manifested, as a result of which the soil pores are clogged and wedged and the so-called frost heaving. The growth of ice crystals in large pores causes an inflow of water from small capillaries, where, in accordance with their decreasing size, freezing of water is delayed.

The sources of heat entering the soil and its expenditure are not the same for different zones; therefore, the heat balance of soils can be both positive and negative. In the first case, the soil receives more heat than it gives out, and in the second case, vice versa. But the heat balance of soils in any zone changes noticeably over time. The thermal balance of the soil can be regulated in the daily, seasonal, annual and long-term interval, which makes it possible to create a more favorable thermal regime of soils. The heat balance of soils in natural zones can be controlled not only through hydromelioration, but also through appropriate agromelioration and forest melioration, as well as some methods of agricultural technology. Vegetation averages the temperature of the soil, reducing its annual heat turnover, contributing to the cooling of the surface air layer due to transpiration and heat radiation. Large ponds and reservoirs moderate the air temperature. Very simple measures, for example, the cultivation of plants on ridges and ridges, make it possible to create favorable conditions for the thermal, light, water-air regime of the soil in the Far North. On sunny days, the average daily temperature in the root-inhabited soil layer on the ridges is several degrees higher than on the leveled surface. The use of electric, water and steam heating is promising, using industrial waste energy and inorganic natural resources. The regulation of the thermal regime and the thermal balance of the soil, together with the water-air balance, is of very great practical and scientific importance. The task is to manage the thermal regime of the soil, especially the reduction of freezing and the acceleration of its thawing.

soil moisture capacity- a value that quantitatively characterizes the water-holding capacity of the soil. Like moisture, moisture capacity is defined as a percentage of dry soil weight. Depending on the forces that retain moisture in soils, there are three main categories of moisture capacity: full, smallest and capillary.

Full moisture capacity - this is the maximum amount of water that the soil can hold using all the water-holding forces.

Lowest moisture capacity - this is the maximum amount of water that the soil can hold in chemical bonds and colloidal systems.

Capillary moisture capacity is the maximum amount of water that the soil can hold in its capillaries.

Materials and equipment

1) glass cylinders without a bottom; 2) gauze; 3) baths; 4) filter paper; 5) technical scales; 6) soil samples.

Progress

A glass cylinder without a bottom is tied with gauze from the lower end. In a cylinder pre-weighed on a technical scale, the soil is poured, slightly compacted by tapping, to a height of 10 cm. The mass of the cylinder with soil is determined. Next, the cylinder with soil is placed in a special bath of water - so that the bottom of the cylinder is on filter paper, the ends of which are lowered into the water.

Water through the pores of the paper is transferred to the soil, producing its capillary saturation. Every day, the cylinder is weighed on a technical balance until its mass ceases to increase. This will indicate that the soil has reached full capillary saturation. Capillary moisture capacity is calculated by the formula:

where HF– capillary moisture capacity, %; AT is the mass of soil in the cylinder after saturation, g;

M is the mass of absolutely dry soil, g.

Since the cylinder contains air dry hitch, and calculations are made on the mass absolutely dry soil, so the mass of absolutely dry soil must first be calculated using the value of the conversion factor obtained in the previous work (all laboratory work is performed with the same soil sample) according to the formula:

where M- the mass of absolutely dry soil, b is the weight of air-dry soil,

kH 2 O- coefficient of hygroscopicity.

Record the results in a table.

Lab No. 7

Determination of soil acidity

Basic information on the topic of work

Soil acidity - this is their ability to cause the acid reaction of the soil solution due to the presence of hydrogen cations in it. The most common source of soil acidity is fulvic acids, which are formed during the decomposition of plant residues. In addition to them, many low molecular weight acids are present in the soil - organic (butyric, acetic) and inorganic (carbonic, sulfuric, hydrochloric).

Acidity is a diagnostic parameter that has a significant impact on the life of the inhabitants of the soil and the plants growing on it. For most crops, the optimal acidity ranges are close to neutral, however, many natural soils are alkaline or acidic, so it becomes necessary to assess and, if necessary, correct their acidity.

Excessive acidity directly or indirectly has a negative effect on plants. Soil acidification leads to a violation of their structure, which in turn causes a sharp deterioration in aeration and capillary properties of the soil. Excess acidity inhibits the vital activity of beneficial microorganisms (especially nitrifiers and nitrogen fixers), enhances the binding of phosphorus by aluminum, which disrupts ion exchange processes in plant roots. Ultimately, these processes lead to blockage of the root vessels and the death of the root system.

There are two forms of acidity - actual and potential.

Actual acidity due to the presence in the soil solution of free hydrogen ions formed as a result of the dissociation of water-soluble organic and weak mineral acids, as well as hydrolytic acid salts. It directly affects the development of plants and microorganisms.

Potential acidity characterized by the presence of H + and Al 3+ ions in the soil-absorption complex, which, when the solid phase interacts with salt cations, are displaced into the soil solution and acidify it.

Determination of soil acidity is usually carried out potentiometric method. It is based on the measurement of the electromotive force in a circuit consisting of two half-elements: a measurement electrode immersed in the test solution and an auxiliary electrode with a constant potential value. A device for measuring pH is called a potentiometer or pH meter.

The results of potentiometric measurement of soil pH are evaluated using standard scales. In practical soil science, soils are classified according to the pH level of water extract (actual acidity) or salt extract (potential acidity) (Table 6).

Tab. 6. Classification of soils according to the level of acidity

Materials and equipment

1) chemical cups for 100-150 ml, 2) 1 N KCl solution, 3) potentiometer (pH meter), 4) technical scales; 5) soil samples.

Progress

To determine the actual acidity, 20 g of air-dry soil should be weighed on a technical scale. Place the sample in a 100-150 ml beaker and add 50 ml of distilled water. Mix the contents for 1-2 minutes and leave to stand for 5 minutes. Stir the suspension again before the determination, and then completely immerse the measurement electrode and the reference electrode in it. After 30-60 sec. read the pH value on the potentiometer scale corresponding to the measured acidity of the soil suspension.

To determine the potential acidity, 50 ml of 1N KCl solution is added to a 20 g sample of soil. The further course of the analysis is the same as in determining the actual acidity.

Record the results of the work in the table:

Lab #8

Water in the soil is one of the main factors of soil formation and one of the most important conditions for fertility. In terms of land reclamation, water becomes especially important as a physical system that is in complex relationships with the solid and gaseous phases of the soil and the plant (Fig. 9). The lack of water in the soil is detrimental to the crop. Only with the content of liquid water and nutrients in the soil necessary for the normal growth and development of plants under favorable air and thermal conditions can a high yield be obtained. The main source of water in the soil is precipitation, each millimeter of which per hectare is 10 m3, or 10 tons of water. The water cycle goes on continuously on Earth. This is a constantly ongoing geophysical process, including the following links: a) evaporation of water from the surface of the oceans; b) vapor transport by air currents in the atmosphere; c) cloud formation and precipitation over the ocean and land; d) the movement of water on the surface of the Earth and in its depths (accumulation of precipitation, runoff, infiltration, evaporation). The water content of the soil is determined by the climatic conditions of the zone and the water-holding capacity of the soil. The role of the soil in external moisture circulation and internal moisture exchange increases as a result of its cultivation, when moisture content, water permeability and moisture capacity increase markedly, but surface runoff and useless evaporation are reduced.

soil moisture

The water content in the soil ranges from severe desiccation (physiological dryness) to complete saturation and waterlogging. The amount of water currently in the soil and expressed as a weight or volume percentage in relation to the absolute dry soil is called soil moisture. Knowing the moisture content of the soil, it is not difficult to determine the stock of soil moisture. One and the same soil can be unequally moistened at different depths and in separate parts of the soil section. Soil moisture content depends on its physical properties, water permeability, moisture capacity, capillarity, specific surface and other moisture conditions. Changes in soil moisture and the creation of favorable conditions for moistening during the growing season are achieved by agricultural techniques. Each soil has its own moisture dynamics, which varies across genetic horizons. Distinguish between absolute humidity, which is characterized by the gross (absolute) amount of moisture in the soil at a given point at a given moment, expressed as a percentage of the weight or volume of the soil, and relative humidity, calculated as a percentage of porosity (total moisture capacity). Soil moisture is determined by various methods.

Soil moisture capacity

Moisture capacity - the property of the soil to absorb and retain the maximum amount of water that at a given time corresponds to the impact on it of forces and environmental conditions. This property depends on the state of moisture, porosity, soil temperature, concentration and composition of soil solutions, the degree of cultivation, as well as other factors and conditions of soil formation. The higher the temperature of the soil and air, the lower the moisture capacity, with the exception of soils enriched with humus. The moisture capacity varies according to the genetic horizons and the height of the soil column. In the soil column, as it were, a water column is enclosed, the shape of which depends on the height of the column of soil soil above the mirror and on the condition of moistening from the surface. The shape of such a column will correspond to the natural area. These columns in natural conditions change with the seasons of the year, as well as with weather conditions and fluctuations in soil moisture. The water column changes, approaching the optimal one, under the conditions of soil cultivation and reclamation. The following types of moisture capacity are distinguished: a) full; b) maximum adsorption; c) capillary; d) the smallest field and limiting field moisture capacity. All types of moisture capacity change with the development of the soil in nature and even more - in production conditions. Even one treatment (loosening of ripe soil) can improve its water properties, increasing the field water capacity. And the introduction of mineral and organic fertilizers or other moisture-intensive substances into the soil can improve water properties or moisture capacity for a long time. This is achieved by incorporating manure, peat, compost and other moisture-intensive substances into the soil. The ameliorative effect can be exerted by the introduction of water-retaining highly porous moisture-intensive substances such as perlite, vermiculite, and expanded clay into the soil.

In addition to the main source of radiant energy, the soil receives heat released during exothermic, physicochemical and biochemical reactions. However, the heat generated by biological and photochemical processes hardly changes the temperature of the soil. In summer, dry, heated soil can increase the temperature due to wetting. This heat is known as the heat of wetting. It manifests itself with weak wetting of soils rich in organic and mineral (clay) colloids. The very slight heating of the soil may be due to the internal heat of the Earth. Of the other secondary sources of heat, one should mention the “latent heat” of phase transformations, which is released in the process of crystallization, condensation and freezing of water, etc. Depending on the mechanical composition, humus content, color and moisture, warm and cold soils are distinguished. Heat capacity is determined by the amount of heat in calories that must be expended to raise the temperature of a unit mass (1 g) or volume (1 cm3) of soil by 1 ° C. The table shows that with increasing humidity, the heat capacity increases less for sands, more for clay, and even more for peat. Therefore, peat and clay are cold soils, while sandy soils are warm. Thermal conductivity and thermal diffusivity. Thermal conductivity - the ability of the soil to conduct heat. It is expressed as the amount of heat in calories passing per second through a 1 cm2 cross-sectional area through a 1 cm layer with a temperature gradient between the two surfaces of 1°C. Air-dry soil has a lower thermal conductivity than wet soil. This is due to the large thermal contact between individual soil particles united by water shells. Along with thermal conductivity, thermal diffusivity is distinguished - the course of temperature change in the soil. Thermal diffusivity characterizes the change in temperature per unit area per unit time. It is equal to the thermal conductivity divided by the volumetric heat capacity of the soil. During the crystallization of ice in the pores of the soil, a crystallization force is manifested, as a result of which the soil pores are clogged and wedged and the so-called frost heaving occurs. The growth of ice crystals in large pores causes an inflow of water from small capillaries, where, in accordance with their decreasing size, freezing of water is delayed.

The sources of heat entering the soil and its expenditure are not the same for different zones; therefore, the heat balance of soils can be both positive and negative. In the first case, the soil receives more heat than it gives out, and in the second case, vice versa. But the heat balance of soils in any zone changes noticeably over time. The thermal balance of the soil can be regulated in the daily, seasonal, annual and long-term interval, which makes it possible to create a more favorable thermal regime of soils. The heat balance of soils in natural zones can be controlled not only through hydromelioration, but also through appropriate agromelioration and forest melioration, as well as some methods of agricultural technology. Vegetation averages the temperature of the soil, reducing its annual heat turnover, contributing to the cooling of the surface air layer due to transpiration and heat radiation. Large ponds and reservoirs moderate the air temperature. Very simple measures, for example, the cultivation of plants on ridges and ridges, make it possible to create favorable conditions for the thermal, light, water-air regime of the soil in the Far North. On sunny days, the average daily temperature in the root-inhabited soil layer on the ridges is several degrees higher than on the leveled surface. The use of electric, water and steam heating is promising, using industrial waste energy and inorganic natural resources.

Thus, the regulation of the thermal regime and the thermal balance of the soil, together with the water-air balance, is of very great practical and scientific importance. The task is to manage the thermal regime of the soil, especially the reduction of freezing and the acceleration of its thawing.