Soil moisture capacity and methods for its determination. Soil moisture capacity Total field moisture capacity

In several (4-5) places typical for a given field, if this was not done in advance, in the irrigation strip, closer to the droppers (at a distance of 30-40 cm from them), soil samples are taken in a layer of 0.2-0.3 m and 0.5-0.6 m) samples from each depth are mixed with each other and two average samples are obtained from depths of 20-30 cm and 0-60 cm. Each average sample with a volume of 1.5-2.0 liters of soil is sifted after a little drying to remove roots and other random inclusions.

Then the sifted earth in the above volumes is placed in a drying cabinet for 6-8 hours at a temperature of 100-105°C until completely dry.

It is necessary to prepare a cylinder without a bottom with a set volume of 1 liter of soil (you can use a PET water bottle, carefully cutting off the bottom and top neck) and weigh the empty vessel. The bottom of the vessel is tied with cloth (several layers of gauze), placed on a flat surface and filled with 1 liter of soil, lightly tapping the walls to eliminate voids, then weigh and record the weight of 1 liter of soil.

A vessel with soil is lowered into a prepared container with water 1-2 cm below the bottom level for the capillary volume of water. After water appears on the surface of the soil in the vessel by capillary action, the vessel is carefully removed from the water so that the bottom covered with fabric does not fall off, then the excess water is allowed to drain. Weigh the vessel with the soil and determine the amount of capillary water in grams per 1 liter of soil (1 ml of water = 1 g).

The level of water evaporation from the soil is a factor that determines the rates and intervals of watering. The amount of evaporation depends on two factors: evaporation from the soil surface and evaporation of water by the plant. The larger the vegetative mass, the greater the amount of water evaporation, especially with significant dry air and high temperature air. The relative dependence of these two factors results in greater water evaporation during the growing season. It especially increases during the period of increasing fruit mass and their ripening (see Table 12.23). Therefore, when calculating the irrigation rate, an evaporation coefficient is introduced that takes these factors into account.

Plant evaporation coefficient (Cevaporation coefficient) is the ratio between actual transpiration and potential evaporation from a unit of water surface per unit of time.

Daily evaporation E is defined as evaporation from an open water surface of 1 m2 per day and is expressed in mm, l/m2 or m3 Da.

Daily evaporation E day by a plant is determined by the formula:

E day = E and x K use

For example, 9 l/m2/day x 0.6 = 5.4 l/m2/day. This is one of the ways to determine the daily irrigation norm or the amount of evaporation.

In cultivated soil, the mineral part is approximately 45%, soil organic matter - up to 5%, water - 20-30%, air - 20-30% of the soil volume. From the moment the soil is saturated with moisture (irrigation, precipitation) in a fairly short period, often within a few days, as a result of evaporation and drainage, many pores open, often up to 50% of the total volume in the root zone.

These indicators are different on different soils. The higher bulk density soil, the higher the water supply at LV 100%; on heavy soils there is always more of it than on light soils. Application of systems drip irrigation determines the distribution of water in soils of different mechanical composition. On heavy soils, a stronger horizontal distribution of water is observed, the wet “onion” - the shape of the distribution of water from one dropper - is wider, the ratio of width and depth is approximately equal, while on light soils the “onion” has a vertical

new shape, its width is 2-3 times less than its length; on soils of average mechanical composition, the “onion” has an intermediate shape.

The assessment of productive moisture reserves in millimeters is carried out taking into account the limited depth of the soil layer (see Table 12.24).

Methods for determining irrigation norms

It is necessary to organize daily accounting of water evaporation per unit area. Knowing the reserve of productive water in the soil on a certain date and its daily consumption for evaporation, the irrigation rate for a certain period of time is determined. This is usually 1-3 days for vegetable crops, 7 or more days for fruit crops and grapes, which is specifically calculated for each crop. Typically, in fertigation practice, two methods are used to determine irrigation rates: evaporimetric and tensiometric.

Evaporimetric method. At weather stations they install a special

a device - an evaporimeter for determining daily evaporation from a unit of water surface area, for example 1 m 2. This indicator is the potential evaporation E and from 1 m 2 in mm/day, l/day. However, to convert to the actual evaporation of plants per unit area, a conversion factor K rast is introduced, the value of which takes into account the evaporation of plants during periods of their growth, i.e., taking into account the degree of foliage of plants, as well as the soil (see Table 16). For example, for tomatoes in July E n = 7.6 l/m 2, K grow = 0.8.

The daily evaporation of plants under these conditions is equal to:

E day = E and x K grow, = 7.6 l/m2 x 0.8 = 6.1 l/m2

For 1 hectare of area this will be 6.1 mm= 61 mUga of water. Then a recalculation is made to the actual moisture strip within 1 hectare.

This is the standard method for determining irrigation rates adopted by the FAO -

international agricultural organization. This method is highly accurate, but requires equipment for a weather station on the farm and daily accounting.

Theisiometric method. Currently, introducing new systems

drip irrigation on various crops, they are beginning to use different types foreign-made tensiometers that determine soil moisture anywhere in the field and at any depth of the active soil layer. There are water, mercury, barometric, electrical, electronic-analog and other tensiometers. All of them are equipped with a tube that passes into a ceramic porous vessel, through which water flows through the pores into the soil, creating a vacuum in the tube, hermetically connected to a water-measuring device - mercury or other barometer. When the tube is completely filled with water and the insert tube is hermetically inserted into it on top, the mercury barometer or air pressure gauge shows zero (0), and as water evaporates from the soil, it passes from the ceramic tube into the soil, creating a vacuum in the tube, which changes the pressure reading in device,

by which the degree of moisture in the soil is judged.

The degree of pressure reduction of the manometer is determined in the following units: 1

Bar = 100 centibars - approximately 1 atm. (more precisely 0.99 Bar).

Since part of the soil volume must be filled with air, taking this into account, the instrument readings are interpreted as follows:

* 0-10 centibars (0-0.1 atm.) - the soil is waterlogged;

* 11-25 centibar (0.11-0.25 atm.) - optimal conditions humidity,

there is no need for irrigation;

* 26-50 centibars - there is a need to replenish water reserves in the soil, in the zone of the main mass of roots, taking into account layer-by-layer moisture.

Since with a change in the mechanical composition of the soil, the lower limit of its required moisture content does not change significantly, in each specific case, before watering, a lower, but sufficient, degree of soil moisture supply is determined within 30 centibars (0.3 atm.) and a nomogram is drawn up for operational calculation irrigation norm or use, as indicated above, data on daily water evaporation taking into account the transpiration coefficient.

Knowing the initial soil moisture, i.e. from the start of the countdown - 11 centibars

(0.11 atm), daily decrease in tensiometer reading to 26-30 centibars

(0.26-0.3 atm.) on vegetables, and slightly lower, up to 0.3-0.4 atm. on grapes and fruits, where the depth of the root layer reaches 100 cm, the irrigation rate is determined, that is, the amount of water required to bring the optimal soil moisture to the upper level. Thus, solving the problem of managing the drip irrigation regime based on the tensiometric method comes down to maintaining optimal soil moisture and the corresponding range of suction pressure during the growing season. The suction pressure values are set for fruit crops according to tensiometer readings at different thresholds of pre-irrigation humidity in the humidification circuit at a depth of 0.3 and 0.6 m at a distance of 0.3-0.4 m from the dripper.

The lower limits of optimal moisture content are 0.7-0.8 (HB) And, accordingly, tensiometric readings range from 30-20 centibars (0.3-

0.2 atm.). For vegetable crops, the lower limit will be at 0.25-0.3 atm.

When using tensiometers, certain rules must be observed.

Fork: The location of the tensiometer should be typical for the field. Usually 2 tensiometers are placed at one point. For vegetable crops - one at a depth of 10-15 cm, and the second - 30 cm, at a distance of 10-15 cm from

droppers. On fruit and grapes, one tensiometer is placed at a depth of 30 cm, and the second - 60 cm, at a distance of 15-30 cm from the dropper.

In order for the dropper's performance to be within normal limits, it is necessary to regularly ensure that it is not clogged insoluble salts and algae. To check the performance of droppers, the number of flowing drops is usually counted in 30 seconds at different places in the field and at the place where the tensiometer is installed.

Tensiometers are installed after watering the site. To install them, use a hand drill or a tube with a diameter slightly larger than the standard diameter of the tensiometer (> 19 mm). Having installed the tensiometer at the desired depth, the free space around it is carefully compacted so that there are no air cavities. In heavy soil, make a hole to the desired depth with a thin tube, wait for water to appear, then place a tensiometer and compact the soil around it.

It is necessary to take tensiometer readings in the early morning hours, when

The temperature is still stable after the night. It should be taken into account that after watering or rain when high humidity soil tensiometer readings will be higher than previous readings. Soil moisture penetrates through the porous part (sensor) into the tensiometer flask until the pressure in the tensiometer equals the water pressure in the soil, as a result of which the pressure in the tensiometer decreases, down to the initial value of 0 or slightly lower.

Water flow from the tensiometer occurs continuously. However, sharp changes may occur when the evaporative capacity of the soil is high (hot days, dry winds), and a high transpiration coefficient is observed during periods of flowering and fruit ripening.

During or after watering, add water to the device to replenish what previously leaked. For irrigation, you must use only distilled water, adding 20 ml of 3% sodium hypochloride solution per 1 liter of water, which has sterilizing properties against bacteria and algae. Pour water into the tensiometer until it begins to flow out, that is, to the entire volume of the lower tube. Typically up to 1 liter of distilled water is required per tensiometer.

You need to make sure that no dirt gets into the device, including from your hands. If, due to operating conditions, a small amount of distillate is added to the device, then an additional 8-10 drops of a 3% solution of sodium hypochloride, calcium are added to the device prophylactically, which protects the ceramic vessel (sensor) from harmful microflora.

At the end of the irrigation season, carefully remove the device from the soil with a rotating motion, wash the ceramic sensor under running water and, without damaging its surface, wipe it with a 3% hypochloride solution with a cleaning pad. When washing, hold the device only vertically with the sensor down. Store tensiometers in a clean container filled with a solution of distilled water with the addition of a 3% hypochloride solution. Compliance with the rules of operation and storage of the device is the basis for its durability and correct indications during operation.

When tensiometers operate, at first after their installation, a certain period of adaptation passes until a cor-

The new system and roots will not come into contact with the sensor of the device. During this period, it is possible to irrigate taking into account transpiration factors using the gravimetric method from the water surface.

When the root system has sufficiently formed around the device (young roots, root hairs), the device shows the real need for water. During this time, sudden changes in pressure may occur. This is observed with a sharp decrease in humidity and is an indicator for the start of irrigation. If the plants are well developed, have a good root system and are sufficiently leafy, then the pressure drop, i.e., the decrease in soil moisture, will be stronger.

A small change in the pressure of the soil solution and, accordingly, the tensiometer indicates a weak root system, poor absorption of water by the plant or its absence. If it is known that the place where the tensiometer is installed does not correspond to the typical site due to plant disease, excessive salinity, insufficient soil ventilation, etc., then the tensiometers must be moved to another place, and the sooner the better.

In addition to tensiometers, soil solution extractors should be used. These are the same tubes with a porous vessel at the bottom (sensor), but without pressure gauges and without filling them with water. Through a porous ceramic tube, the soil solution penetrates into it, and then using an extractor syringe with a long pipe lowered to the bottom of the vessel, the soil solution is sucked out for field express determination of pH, EC (salt concentration in millisiemens for further recalculation of their amount in the solution ), determining the amount of Na, C1 using indicator solutions. This solution can also be analyzed in laboratory conditions. Such control allows optimizing growing conditions during

throughout the growing season, especially during the fertigation period. When using ion-selective electrodes or other methods of express analysis, the presence of nitrogen, phosphorus, potassium, calcium, magnesium and other elements in the soil solution is monitored.

Extraction devices must be installed next to tensiometers.

CALCULATION OF IRRIGATION RATE

Determination of the value of irrigation norms based on tensiometer readings is carried out using graphs of the dependence of the suction pressure of the device on soil moisture. Such graphs in specific soil conditions allow you to quickly determine irrigation rates.

For fruit and grapes, a tensiometer installed at a depth of 0.3 m characterizes average value humidity in the soil layer is 0-50 cm, and at a depth of 0.6 m - in a layer of 50-100 cm.

The moisture deficit is calculated using the formula:

Q = 10h (Q nv - Q pp), mm water column,

where h is the depth of the calculated soil layer, mm; Q nv - volume humidity

soils, NV; Q pp - pre-irrigation moisture content of the soil volume, % HB. 459

Watering rate, l/plant, is determined by the formula:

V = (Q 0-50 + Q 50-100) XS

where V is the irrigation rate; Q 0-50 - soil moisture, mm, in a layer of 0-50 cm,

Q 50-100 in a layer of 50-100 cm; S is the size of the humidification circuit, m2.

For example, 1.5 m x 1.0 m = 1.5 m 2.

Accounting can be kept for a day or another period of time. To simplify calculations, use a nomogram - a graph that takes into account the dependence of suction pressure on soil moisture separately for each layer. For example, O-25, 26-50, 51-100 cm. On the nomogram, along the abscissa axis, the value of suction pressure is plotted for the layer 0-50 cm at the point 30 cm (PS 1 and for the layer 51-100 cm at the point 60 cm (PS 2) with an interval of 0.1 atm along the ordinate axis. The graph will show the estimated amount of water in liters per plant, l/m 2 or m 3 |ha.

Determining the irrigation rate using a nomogram comes down to calculating the volume of water V using the PS values measured by tensiometers. and PS 2.

The irrigation rate per 1 ha is determined:

M(m 3 |ha) = 0.001 V X N,

where M is the irrigation rate; N is the number of plants (drippers) per 1 ha.

A similar calculation is carried out for vegetable crops, but usually on these crops tensiometers are placed at a shallow depth and they give rapidly changing readings of soil moisture, that is, watering is carried out more often. The duration of watering is determined by the formula:

T= V: G,

where G is water consumption by the dropper, l/h; V - irrigation norm, l; T is the duration of irrigation, h, depending on the volume of water and the productivity of the drippers. "

Using certain types of tensiometers, the irrigation process can be automated. In this case, the irrigation system pump is turned off a little earlier (which should be programmed) than the upper limit of the required humidity is reached.

To calculate the irrigation interval in days, it is necessary to divide the irrigation rate V by the daily irrigation rate (mm/day), determined tensiometrically. The irrigation rate can be expressed in mm/ha or in l/m2, within the range between the maximum and lower humidity thresholds. The irrigation rate for a period of time within these humidity limits, divided by the daily irrigation rate, gives the value of the interval between waterings.

WATER FOR IRRIGATION

AND REGULATION OF ITS QUALITY

In irrigation practice, various water sources are used. These are primarily river waters, reservoirs, mine waters, well waters, etc.

Ukraine's water potential is very rich. 92 rivers flow through its territory, there are 18 very large reservoirs, 362 large lakes and ponds. Three quarters of all water resources Dnepr River. The largest reservoirs were created on the basis of the Dnieper water: Kievskoye, Kanevskoye, Kremenchugskoye, Dneprodzerzhinskoye, Zaporozhye and Kakhovskoye, which are sources of water for various purposes, including irrigation

The pH value of the water of the Kyiv Reservoir is influenced by humus discharges from the Pripyat River. In summer, 5-10 mg/l CO 2 accumulates in the bottom sediments of reservoirs, sometimes up to 20-45 mg/l, so the pH value drops to 7.4. The difference in pH between surface and bottom waters can reach 1-1.5 pH. In autumn, due to the attenuation of photosynthesis, the value of Rns decreases due to acidification of CO 2. In summer, CO 2 is absorbed during the process of photosynthesis, so pH reaches 9.4. The amount of NH 4 varies from 0.2 to 3.7 mg/l, NO 3 is maximum in winter - 0.5 mg/l, P - from 0 to 1 mg/l, since it is adsorbed by Fe, total nitrogen - 0, 5-1.5 mg/l, soluble iron from 1.2 mg/l in winter to 0.4 mg/l in summer (maximum), and usually 0.01-0.2 mg/l. Seasonal changes in pH values are caused mainly by carbonate equilibrium in water. The minimum pH value in winter is 6.7-7.0; maximum in summer - up to 9.7.

The Northern Donets and the rivers of the Azov region, including the Northern Donets reservoirs (Isaakovskoye, Luganskoye, Krasnooskolskoye), are characterized by high levels of calcium and sodium, chlorine - 36-124 mg/l, total mineralization - 550-2,000 mg/l. These waters contain NO 3 - 44-77 mg/l (a consequence of their pollution). Groundwater is moderately mineralized -600-700 mg/l, pH - 6.6-8, water is hydrocarbonate-calcium and magnesium.

The wells provide water from low-mineralized drinking water to highly saline water, especially in the coal-mining regions of Donbass.

The waters of the Bug Estuary near the city of Nikolaev are characterized by high mineralization - 500-3,000 mg/l, containing HCO 3 - 400-500 mg/l, Ca - 50-120 mg/l, Mg - 30-100 mg/l, sum ions - 500-800 mg/l, Na + K - 40-

70 mg/l, C1 - 30-70 mg/l.

In Crimea, in addition to the North Crimean Canal, which irrigates the Steppe Crimea with the waters of the Kakhovka Reservoir, there are a number of reservoirs: Chernorechenskoe, Kachinskoe, Simferopolskoe, as well as the waters of the mountainous Crimea.

The waters of the mountainous Crimea have a mineralization from 200-300 to 500-800 mg/l,

HCO 3, from 150-200 to 300 mg/l, SO 4, - from 20-30 to 300 or more mg/l, C1 - from 6-10 to 25-150 mg/l, Ca - from 40-60 to 100-150 mg/l, Mg - from 6-10 to 25-40

mg/l, Na + K - from 40 to 100-200 mg/l. Reservoir waters have a mineralization from 200 to 300-400 mg/l, HCO 3 - from 90-116 to 220-270 mg/l, SO 4 - from 9-14 to 64-75 mg/l, C1 - from 5- 8 to 18-20 mg/l, Ca - 36-87 mg/l, Mg - from 1-2 to 19-23 mg/l, Na + K - from 1-4 to 8-24 mg/l.

461 The given figures should be taken into account when organizing drip irrigation; it is advisable to analyze the water according to the above parameters once every 2-3 months. The analysis should include an assessment of the levels of physical, chemical and biological contamination of water. Typically, water quality laboratories of sanitary and environmental control stations carry out such a standard analysis.

When using water from reservoirs, especially reservoirs of Dnieper water, usually shallow, well heated in summer, with a greater prevalence of blue-green and other algae and bacteria that form gelatinous mucus and clog nozzles, it is necessary to regularly clean them (see chlorination process active chlorine).

If it is necessary to regulate the amount of algae and bacteria in the water, as well as their metabolic products - mucus, active chlorine should be continuously introduced into the irrigation water so that at the exit from the irrigation system its concentration in the irrigation water is at least 0.5-1 mg/ l, in the working solution - up to 10 mg/l C1. Another method can be used - periodically introduce cleaning doses of active chlorine of 20 mg/l in the last 30-60 minutes of the irrigation cycle.

Precipitated CaCO 3 and MgCO 3 can be removed by acidifying the irrigation water to a pH level of 5.5-7. At this level of water acidity, these salts do not precipitate and are removed from the irrigation system. Acid cleaning precipitates and dissolves sediments formed in irrigation systems - hydroxides, carbonates and phosphates.

Typically, technical acids are used that are not contaminated with impurities and do not contain gypsum and phosphate deposits. For this purpose, technical nitric, orthophosphoric or perchloric acid is used. The usual working concentration of these acids is 0.6% of the active substance. The duration of acid irrigation of about 1 hour is quite sufficient.

If the water is heavily contaminated with iron compounds or iron-containing bacteria, the water is treated with active chlorine in an amount of 0.64 of the amount of iron in the water (taken as one), which promotes the precipitation of iron. If necessary, chlorine is supplied to the filter system, which should be checked and cleaned regularly.

Control of hydrogen sulfide bacteria is also carried out using active chlorine in a concentration 4-9 times higher than the concentration of hydrogen sulfide in irrigation water. The problem of excess manganese in water is eliminated by adding chlorine in a concentration exceeding the concentration of manganese in water by 1.3 times.

Thus, in preparation for irrigation, it is necessary to assess the water quality and prepare necessary solutions to bring water, if necessary, to certain conditions. Sulfur oxide can be chlorinated by periodic or continuous addition of 0.6 mg/l C1 per 1 mg/l S.

The process of chlorination with active chlorine. To dissolve organic matter, the pipe system is filled with water containing increased doses - 30-50 mg/l C1 (depending on the degree of contamination). The water must remain in the system for at least 1 hour without leaking through the droppers. At the end of the treatment, the water must contain at least 1 mg/l of Cl; at a lower concentration, repeat the treatment. Increased doses of chlorine are usually used only to flush the system after the end of the growing season. An overdose of chlorine may disrupt the stability of the sediment, causing it to move towards the droppers and clog them. Chlorination should not be carried out if the iron concentration exceeds 0.4 mg/l, since sediment may clog the droppers. When chlorinating, avoid using fertilizers containing NH 4, NH 2, with which chlorine reacts.

Chemicals for water treatment. Various acids are used to improve the quality of irrigation water. It is sufficient to acidify the water to pH 6.0, at which the precipitates of CaCO 3, calcium phosphate, and iron oxides dissolve. If necessary, carried out special cleaning irrigation systems with a duration of 10-90 minutes of acidification to pH 2 with water, followed by rinsing. The cheapest are nitric and hydrochloric acids. At significant quantities iron more than 1 mg/l) phosphoric acid cannot be used for acidification. Treating water with acid open ground is carried out periodically. At pH 2 - short-term treatment (10-30 min), at pH 4 - longer rinses.

When the concentration of iron in water is more than 0.2 mg/l, preventive flushing of the systems is carried out. At an iron concentration of 0.3 to 1.5 mg/l, iron bacteria can develop and clog the injectors. Sedimentation and aeration of water before use improves the precipitation of iron, this also applies to sulfur. Aeration of water and its oxidation with active chlorine (1 mg/l S requires 8.6 mg/l C1) reduces the amount of free sulfur entering

reaction with calcium.

OPERATION OF DRIP

IRRIGATION SYSTEMS

In addition to water filtration, systematic flushing of main and drip lines is used. Washing is carried out by simultaneously opening the end caps (plugs) on 5-8 drip lines for 1 minute to remove dirt and algae. When chlorinating with an active chlorine concentration of up to 30 mg/l, the duration of the treatment process is no more than 1 hour. When periodically treating with acid against inorganic and organic deposits in drip irrigation systems, various acids are used. At a concentration of HC1 - 33%, H 3 PO 4 - 85%, HNO 3 -60%, a working solution with a concentration of 0.6% is used. In terms of the active substance, this will be: HC1 - 0.2% active ingredient, H,PO^ - 0.5% active ingredient. H 3 PO 4 - 0.36% active ingredient, which should be taken into account when using acids with different concentrations. The duration of acid treatment is 12 minutes, subsequent washing is 30 minutes.

Soil moisture capacity is a value that quantitatively characterizes the water-holding capacity of the soil. Depending on the conditions of moisture retention, moisture capacity is distinguished as total, field, maximum field, minimum, capillary, maximum molecular, maximum adsorption, of which the main ones are the smallest, capillary and total.
Determination of field soil moisture capacity. To determine the field moisture capacity (MC) in a selected area, areas of at least 1x1 m in size are enclosed with a double row of rollers. The surface of the area is leveled and covered with coarse sand with a layer of 2 cm. When performing this analysis, you can use metal or dense wooden frames.
Near the site according to genetic horizons or separate layers(0-10, 10-20 cm, etc.) soil samples are taken with drills to determine its porosity, moisture and density. Using these data, the actual water supply and porosity of the soil are determined in each individual layer and in the total thickness of the soil under study (50 or 100 cm). By subtracting the volume occupied by water from the total volume of pores, the amount of water required to fill all the pores in the studied layer of water is determined. To ensure complete soaking, the amount of water is increased by 1.5 times.
The calculated amount of water is evenly supplied to the site and the protective strip so that its layer on the soil surface is 2-5 cm thick.
After all the water has been absorbed, the platform and protective strip are covered with plastic film, and on top with straw, sawdust or other mulching material. Subsequently, every 3-4 days, samples are taken to determine soil moisture every 10 cm to the entire depth of the layer under study until more or less constant moisture is established in each layer. This humidity will characterize the field moisture capacity of the soil, which is expressed as a percentage of the mass of absolutely dry soil, in mm or m3 in a layer of 0-50 and 0-100 cm per 1 ha.
Records and calculations when determining PV are carried out in the form established for determining soil moisture by the gravimetric method. The PV value is subsequently used to calculate the irrigation water norm. If the PV and the water reserve in the arable soil layer Vp (m3) are known, then the irrigation rate Pn = PV - Vp.
Using the same data, it is possible to determine the leaching norm for saline soils.
Determination of moisture capacity in laboratory conditions. Moisture capacity in laboratory conditions is determined on monoliths with a volume of 1000-1500 cm3 with natural soil composition. The monoliths are placed in a bath or on a table covered with oilcloth, so that their surfaces assume a horizontal position, and covered with filter paper. Then the monolith is watered from above with water so that it does not stagnate on its surface and does not flow down the sides. After soaking the soil sample to 3/4 of its height, watering is stopped, the monolith is covered with oilcloth and left in this position for gravitational water to flow into its lower part. The duration of water drainage depends on the mechanical properties of the soil and its density: for sandy soils 0.5 hours is enough, for light and medium loams - 1-3 hours, for heavy loams and clays - 8-16 hours.

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Progress of the analysis. Large roots are removed from air-dry soil. The soil is lightly kneaded, sifted through a sieve with 3 mm holes and poured into a glass tube with a diameter of 3-4 cm, a height of 10-20 cm, the lower end of which is tied with cotton cloth or gauze with a filter. The closer the soil layer lies to the water supply surface, the greater the capillary moisture capacity, and, conversely, the further the soil is from the water level, the less the moisture capacity. Therefore, the length of the tube must be taken according to the size of the vessels in which the experiment is carried out. Pour in the soil, compacting it by lightly tapping the bottom on the table so that the height of the soil column is 1-2 cm below its upper end. All subsequent operations and calculations are the same as in the method for determining the moisture capacity of soil with an undisturbed structure.[...]

Potatoes love well-drained soil, so watering is required only after applying dry fertilizers, during the dry period of summer (once every 7-10 days), and most importantly, during the formation of tubers, which begins in the budding and flowering phase. During these periods, soil moisture should be no lower than 80-85% of the total moisture capacity of the soil.[...]

The method for establishing the nitrification capacity of soil according to Kravkov is based on creating the most favorable conditions for nitrification and subsequent determination of the amount of nitrates. To do this, a sample of soil is composted in the laboratory for two weeks at optimal temperature (26-28°) and humidity (60% of the capillary moisture capacity of the soil), free access of air, in a well-ventilated thermostat. At the end of composting, the amount of nitrates in the water extract from the soil is determined colorimetrically. [...]

The total (according to N.A. Kachinsky) or the smallest (according to A.A. Rode) soil moisture capacity or the maximum field (according to A.P. Rozov) and field (according to S.I. Dolgov) - the amount of moisture that the soil retains after humidification with free outflow of gravitational water. The diversity of names of this important hydrological constant creates a lot of confusion. The term “lowest moisture capacity” is unsuccessful, since it contradicts the fact of the maximum moisture content in the soil. The other two terms are also not entirely successful, but since there is no more suitable name, henceforth we will use the term “total moisture capacity”. N.A. Kachinsky explains the name “general” by the fact that soil moisture at this hydrological constant includes all the main categories of soil moisture (except gravitational). The constant characterizing the total moisture capacity is widely used in reclamation practice, where it is called field moisture capacity (FC), which, along with the total moisture capacity (WC), is the most common term.[...]

With an increase in soil moisture, the herbicidal activity of the preparations, as a rule, increased, but to varying degrees and up to a certain limit. The greatest phytotoxicity of the preparations when incorporated into the soil appeared at a humidity of 50-60% of the total moisture capacity of the soil. [...]

Green manure like others organic fertilizers, plowed into the soil, slightly reduces its acidity, reduces the mobility of aluminum, increases buffering capacity, absorption capacity, moisture capacity, water permeability, and improves soil structure. ABOUT positive impact green fertilizer on the physical and physico-chemical properties of the soil is evidenced by data from numerous studies. Thus, in the sandy soil of the Novozybkovsky experimental station, at the end of four rotations of crop rotation with alternating fallows - winter crops - potatoes - oats, depending on the use of lupine as an independent crop in the fallow and a stubble crop after winter crops, the humus content and the value of capillary moisture capacity of the soil were different ( table 136).[...]

The vessels were watered at the rate of 60% of the total moisture capacity of the soil. The experiment was launched on May 8, 1964[...]

An effective agrochemical method for increasing the fertility of eroded soils and protecting them from erosion, especially on washed away soils, is to cultivate crops on them at green manure. IN different zones In Russia, annual and perennial lupine, alfalfa, clover, broad beans, white mustard, vetch, etc. are used for this. The effect is achieved by plowing green mass, when the water permeability and moisture capacity of the soil increases, microbiological processes intensify, and the agrophysical properties of the land improve.[... ]

Humidity in vessels with holes in the bottom is maintained at the level of the soil's full moisture capacity. To do this, the vessels are watered daily until the first drop of liquid flows into the saucer. There is no need to water when it rains; one should even take care that the rain does not overfill the saucer, because then nutrient solution will be lost. That is why the volume of the saucer should be at least 0.5 liters, preferably up to 1 liter. Before watering the vessel, pour all the liquid from the saucer into it. If there is too much, pour until the first drop seeps out.[...]

The preparatory work is to determine the hygroscopic water and moisture capacity of the soil.[...]

Then the irrigation rate is determined, the value of which depends mainly on the field moisture capacity of the soil, its moisture content before watering and the depth of the wetted layer. The value of soil moisture capacity is taken from the explanatory note to the soil reclamation map. In farms where water-physical properties have not been determined, reference material is used to calculate the irrigation rate (the moisture capacity of most irrigated soils is well known). [...]

It has been established that the optimal moisture content for nitrification is 50-70% of the total moisture capacity of the soil, optimal temperature is 25-30°.[...]

When placing clover in crop rotation, it should be taken into account that it sharply reduces the yield by acidic soils. Good conditions for clover are created on neutral, moisture-absorbing soils. As a moisture-loving plant, clover does not grow well on loose sandy soils that have poor moisture retention. Acidic peat and excessively moist soils with high level groundwater.[...]

After establishing direct current water, the device is disconnected from the measuring cylinder and removed from the soil. To do this, part of the soil near the enclosing element is removed and the soil sample is cut from below with a spatula. The device is removed by holding the soil in it with a spatula. Carefully tilt the device and drain the water from it through the hole in the float chamber cover. Then the device along with the spatula is placed on the table, the float chamber is disconnected and placed in a thermostat to dry. The enclosing element from below is covered with a swab of 2-3 layers of gauze and placed on air-dry soil, previously sifted through a sieve with 0.25 or 0.5 mm holes, for 1 hour to suck out easily moving water from it. After an hour, the cartridge with the soil is removed and weighed together with the float chamber. After this, a sample is taken with a small drill to determine the moisture content (capillary moisture capacity) of the soil; the same as when the soil in the cartridges is saturated from below. At this point all weighing is completed, the device is freed from the soil, washed, dried and lubricated.[...]

Laying composts. Preparatory work when laying composts comes down to taking soil samples in the field (see page 79), determining soil moisture (see page 81) and its moisture capacity, taring glasses, analyzing and weighing fertilizers and checking temperature fluctuations in the thermostat. Methods for determining soil moisture capacity are already known to technical school students from practical classes in soil science. Below is how to find out the capillary moisture capacity (see page 253).[...]

Potential nitrogen fixation activity is determined in freshly selected or air-dried soil samples. To do this, 5 g of soil, freed from roots and sifted through a sieve with a cell diameter of 1 mm, is placed in a penicillin bottle, 2% glucose is added (by weight of absolutely dry soil) and moistened with sterile tap water to a humidity of approximately 80% of full moisture capacity. The soil is thoroughly mixed until a homogeneous mass is obtained, the bottle is closed with a cotton stopper and incubated for 24 hours at 28°C. [...]

Determination of OM in samples of disturbed composition. When setting up vegetation experiments, it is necessary to know the moisture capacity of the soil, since the soil moisture in the vessels is set as a percentage of the moisture capacity and is maintained at a certain level during the experiment.[...]

The formation of microbiological cenoses and the intensity of microorganism activity depend on the hydrothermal regime of the soil, its reaction, the quantitative and qualitative residue of organic matter in the soil, aeration conditions and mineral nutrition. For most microorganisms, the optimum hydrothermal conditions in the soil are characterized by a temperature of 25-35 ° C and a humidity of about 60% of the total moisture capacity of the soil.[...]

If water is supplied from below, then after capillary saturation of the sample to a constant mass, the capillary moisture capacity of the soil can be established in the same way.[...]

A significant part of the peat bogs of the North arose on the site of former pine and spruce forests. At some stage of leaching of forest soils, woody vegetation begins to be scarce nutrients. Moss vegetation, which does not require nutritional conditions, appears and gradually displaces woody vegetation. The water-air regime in the surface layers of the soil is disrupted. As a result, conditions favorable for waterlogging are created under the forest canopy, especially with flat terrain, close aquifers and moisture-intensive soils. Green mosses, in particular cuckoo flax, are often harbingers of forest waterlogging. They are replaced by various types of sphagnum moss - a typical representative of bog mosses. Old generations of trees gradually die off and are replaced by typical swamp woody vegetation.[...]

The repeatability of the experiment with spring wheat was 6-fold, with sugar beets - 10-fold. Plants were watered with tap water up to 60% of the soil's total moisture capacity after one day by weight.[...]

There are two types of vessels: Wagner's vessels and Mitscherlich's vessels. In metal vessels of the first type, watering is carried out by weight up to 60 - 70% of the total moisture capacity of the soil through a tube soldered to the side, in glass vessels- through a glass tube inserted into the vessel. In Mitscherlich vessels there is an oblong hole at the bottom, closed at the top by a groove.[...]

The weight of the equipped glass, which it should have after watering, is calculated as follows. Let’s say a container (a glass with a tube and glass) weighs 180 g, a sample of soil (with a humidity of 5.6%) - 105.6 g, the weight of water (with a capillary moisture capacity of the soil of 40%) to bring the soil to a moisture content of 24%, which corresponds 60% of the given moisture capacity is 24 g, but slightly less is poured into a glass with soil (minus the amount of water already in the soil - 5.6 g) - 18.4, or only 304 g[...]

Excessive moisture can be eliminated by creating a thick, well-cultivated arable layer and loosening the subarable horizon, which increases the moisture capacity of the soil and allows moisture to penetrate into the lower layers. This moisture during dry critical periods of the growing season serves as an additional reserve for the plants being grown.[...]

The moisture content increases sharply, starting from the upper boundary of the capillary fringe and up to the groundwater level. At the upper boundary of the border it usually corresponds to the total or maximum field moisture capacity. However, for irrigation purposes it is necessary to determine the moisture capacity of the soil even when water is supplied from above.[...]

After all the water has been absorbed, the platform and protective strip are covered with plastic film, and on top with straw, sawdust or other mulching material. Subsequently, every 3-4 days, samples are taken to determine soil moisture every 10 cm to the entire depth of the layer under study until more or less constant moisture is established in each layer. This humidity will characterize the field moisture capacity of the soil, which is expressed as a percentage of the mass of absolutely dry soil, in mm or m3 in a layer of 0-50 and 0-100 cm per hectare.[...]

In order to preserve SEDO, coastal areas of watercourses, seasonal drains, ponds, wetlands and areas of terrain with a slope of no more than 1-2%, which are flooded during floods and rainfalls, including areas with moisture-absorbing soils, are left undeveloped.[...]

The experiments were carried out in the vegetation house of the Institute of Biology. Sowing was carried out with spring wheat seeds of the Lutescens 758 variety. Experimental plants were grown in containers with a capacity of 8 kg of soil-sand mixture. Watering was carried out by weight, at the rate of 65% of the total moisture capacity of the soil.[...]

Humus is defined as a complex and fairly stable mixture of brown or dark brown amorphous colloidal materials that are formed from the tissues of numerous dead organisms of matter - from the remains of decomposed plants, animals and microorganisms. The peculiar physicochemical properties make humus the most important component of the soil, determining its fertility; it serves as a source of nitrogen, phosphorus, sulfur and microfertilizers for plants. In addition, humus increases the cation exchange capacity, air permeability, filterability, moisture capacity of the soil and prevents its erosion [1].[...]

A very important operation for caring for plants during the growing season is watering. The vessels are watered daily, in the early morning or evening hours, depending on the topic of the experience. It should be noted that watering with tap water is not suitable when conducting experiments with liming. Watering is carried out by weight until the optimal humidity established for the experiment. To establish the required soil moisture, the total moisture capacity and its moisture content when filling the vessels are first determined. The weight of the vessels for irrigation is calculated based on the desired optimal humidity, which is usually 60-70% of the total moisture capacity of the soil, summing up the weights of the container, sand added from below and above the vessel during filling and sowing, frame, dry soil and required quantity water. The weight of the vessel for watering is written on a label pasted on the cover. IN hot weather you have to water the vessels twice, once giving a certain volume of water, and the other time bringing it to a given weight. In order to have more equal lighting conditions for all vessels, they are swapped daily during watering, and also moved one row along the trolley. The vessels are usually placed on trolleys; in clear weather they are rolled out into the open air under a net, and at night and in bad weather they are taken under a glass roof. Mitscherlich vessels are installed on fixed tables under a mesh.

SOIL MOISTURE CAPACITY - the ability of the soil to hold alaga; expressed as a percentage of the volume or mass of the soil.[...]

MOISTURE CAPACITY OF SOIL. The maximum amount of water that soil can hold. The total moisture capacity of the soil is the maximum amount of water that can be contained in the soil when the water surface is at the same level as the soil surface, when all soil air is replaced by water. The capillary moisture capacity of the soil is the amount of water that the soil can hold due to capillary rise above the level of the free water surface. The lowest field moisture capacity of the soil is the amount of water that the soil can retain when the free water surface is deep and the capillary saturation layer overlying it does not reach the root-inhabited soil layer. [...]

Light soils with a high content of, for example, sand or lime dry out very quickly. Frequent application of well-rotted organic material - rotted leaves, peat or compost - increases the moisture capacity of the soil without causing it to become waterlogged due to the formation of humus, which has a high absorption capacity. [...]

Soil moisture is determined by drying in an oven at 105°C to constant weight. Calculate the moisture capacity of the soil.[...]

Peat bogs have the highest moisture capacity (up to 500-700%). The moisture capacity is expressed as a percentage of the weight of dry soil. The hygienic importance of soil moisture capacity is due to the fact that high moisture capacity causes dampness in the soil and the buildings located on it, reduces the permeability of the soil to air and water, and interferes with the purification of wastewater. Such soils are unhealthy, damp and cold.[...]

Determination of field soil moisture capacity. To determine field moisture capacity (MC) in a selected area, areas of at least 1×1 m in size are fenced off with a double row of rollers. The surface of the area is leveled and covered with coarse sand with a layer of 2 cm. When performing this analysis, you can use metal or dense wooden frames. [...]

Increasing the depth of soil cultivation contributes to better absorption of precipitation. The deeper the soil is processed, the more moisture it can absorb in a short time. Therefore, with an increase in the depth of soil cultivation, conditions are created to reduce surface runoff, and with a reduction in the volume of runoff, in turn, the potential danger of soil erosion is reduced. However, the anti-erosion effectiveness of deep plowing depends on numerous factors: the nature of precipitation that forms surface water runoff, the state of water permeability and moisture capacity of soils during runoff, the steepness of the slope, etc. [...]

The method for establishing the nitrification capacity of soil according to Kravkov is based on creating the most favorable conditions for nitrification in the studied soil and subsequent determination of the amount of nitrates. To do this, a sample of soil is composted in the laboratory for two weeks at optimal temperature (26-28°) and humidity (60% of the capillary moisture capacity of the soil), free access of air, in a well-ventilated thermostat. At the end of composting, the amount of nitrates in the water extract from the soil is determined colorimetrically. [...]

Green fertilizer, like other organic fertilizers, plowed into the soil, slightly reduces its acidity, reduces the mobility of aluminum, increases buffering capacity, absorption capacity, moisture capacity, water permeability, and improves soil structure. The positive effect of green fertilizer on the physical and physicochemical properties of the soil is evidenced by data from numerous studies. Thus, in the sandy soil of the Novozybkovsky experimental station, at the end of four rotations of crop rotation with alternating fallows - winter crops - potatoes - oats, depending on the use of lupine as an independent crop in the fallow and a stubble crop after winter crops, the humus content and the value of capillary moisture capacity of the soil were different ( Table 136).[...]

The vessels were watered at the rate of 60% of the total moisture capacity of the soil. The experiment was launched on May 8, 1964[...]

An effective agrochemical method for increasing the fertility of eroded soils and protecting them from erosion, especially on washed away soils, is cultivating crops on them for green manure. In different zones of Russia, annual and perennial lupine, alfalfa, clover, broad beans, white mustard, vetch, etc. are used for this purpose. The effect is achieved by plowing green mass, when the water permeability and moisture capacity of the soil increases, microbiological processes intensify, and the agrophysical properties of the land improve.[ …]

Humidity in vessels with holes in the bottom is maintained at the level of the soil's full moisture capacity. To do this, the vessels are watered daily until the first drop of liquid flows into the saucer. There is no need to water when it rains; You should even take care that the rain does not overfill the saucer, because then the nutrient solution will be lost. That is why the volume of the saucer should be at least 0.5 liters, preferably up to 1 liter. Before watering the vessel, pour all the liquid from the saucer into it. If there is too much, pour until the first drop seeps out. [...]

The preparatory work is to determine the hygroscopic water and moisture capacity of the soil.[...]

It has been established that the optimal humidity for nitrification is 50-70% of the total moisture capacity of the soil, the optimal temperature is 25-30°. [...]

When placing clover in crop rotation, it should be taken into account that it sharply reduces yield on acidic soils. Good conditions for clover are created on neutral, moisture-absorbing soils. As a moisture-loving plant, clover does not grow well on loose sandy soils that have poor moisture retention. Acidic peat and excessively moist soils with a high groundwater level are unsuitable for it.[...]

After establishing a constant flow of water, the device is disconnected from the measuring cylinder and removed from the soil. To do this, part of the soil near the enclosing element is removed and the soil sample is cut from below with a spatula. The device is removed by holding the soil in it with a spatula. Carefully tilt the device and drain the water from it through the hole in the float chamber cover. Then the device along with the spatula is placed on the table, the float chamber is disconnected and placed in a thermostat to dry. The enclosing element from below is covered with a swab of 2-3 layers of gauze and placed on air-dry soil, previously sifted through a sieve with 0.25 or 0.5 mm holes, for 1 hour to suck out easily moving water from it. After an hour, the cartridge with the soil is removed and weighed together with the float chamber. After this, a sample is taken with a small drill to determine the moisture content (capillary moisture capacity) of the soil; the same as when the soil in the cartridges is saturated from below. At this point all weighing is completed, the device is freed from the soil, washed, dried and lubricated.[...]

Potential nitrogen fixation activity is determined in freshly selected or air-dried soil samples. To do this, 5 g of soil, freed from roots and sifted through a sieve with a mesh diameter of 1 mm, is placed in a penicillin bottle, 2% glucose is added (by weight of absolutely dry soil) and moistened with sterile tap water to a humidity of approximately 80% of the full moisture capacity. The soil is thoroughly mixed until a homogeneous mass is obtained, the bottle is closed with a cotton stopper and incubated for 24 hours at 28°C. [...]

The formation of microbiological cenoses and the intensity of microorganism activity depend on the hydrothermal regime of the soil, its reaction, the quantitative and qualitative residue of organic matter in the soil, the conditions of aeration and mineral nutrition. For most microorganisms, the optimum hydrothermal conditions in the soil are characterized by a temperature of 25-35 ° C and a humidity of about 60% of the total moisture capacity of the soil. [...]

If water is supplied from below, then after capillary saturation of the sample to a constant mass, the capillary moisture capacity of the soil can be established in the same way.[...]

A significant part of the peat bogs of the North arose on the site of former pine and spruce forests. At some stage of leaching of forest soils, woody vegetation begins to lack nutrients. Moss vegetation, which does not require nutritional conditions, appears and gradually displaces woody vegetation. The water-air regime in the surface layers of the soil is disrupted. As a result, conditions favorable for waterlogging are created under the forest canopy, especially with flat terrain, close aquifers and moisture-intensive soils. Green mosses, in particular cuckoo flax, are often harbingers of forest waterlogging. They are replaced by various types of sphagnum moss - a typical representative of bog mosses. Old generations of trees gradually die off and are replaced by typical swamp woody vegetation.[...]

The repeatability of the experiment with spring wheat was 6-fold, with sugar beets - 10-fold. Plants were watered with tap water up to 60% of the total moisture capacity of the soil after one day by weight.[...]

There are two types of vessels: Wagner's vessels and Mitscherlich's vessels. In metal vessels of the first type, watering is carried out by weight up to 60 - 70% of the total moisture capacity of the soil through a tube soldered to the side, in glass vessels - through a glass tube inserted into the vessel. In Mitscherlich vessels there is an oblong hole at the bottom, closed at the top by a groove.[...]

Excessive moisture can be eliminated by creating a thick, well-cultivated arable layer and loosening the subarable horizon, which increases the moisture capacity of the soil and allows moisture to penetrate into the lower layers. During dry critical periods of the growing season, this moisture serves as an additional reserve for the plants being grown. [...]

In order to preserve SEDO, coastal areas of watercourses, seasonal drains, reservoirs, wetlands and areas of terrain with a slope of no more than 1-2%, which are flooded during floods and rainfalls, including areas with moisture-absorbing soils, are left undeveloped.[...]

A very important operation for caring for plants during the growing season is watering. The vessels are watered daily, in the early morning or evening hours, depending on the theme of the experiment. It should be noted that watering with tap water is not suitable when conducting experiments with liming. Watering is carried out by weight until the optimal humidity established for the experiment. To establish the required soil moisture, the total moisture capacity and its moisture content when filling the vessels are first determined. The weight of the vessels for irrigation is calculated based on the desired optimal humidity, which is usually 60-70% of the total moisture capacity of the soil, summing up the weights of the container, sand added from below and above the vessel during filling and sowing, frame, dry soil and the required amount of water. The weight of the vessel for watering is written on a label pasted on the cover. In hot weather, you have to water the vessels twice, once giving a certain volume of water, and the other time bringing it to a given weight. In order to have more equal lighting conditions for all vessels, they are swapped daily during watering, and also moved one row along the trolley. The vessels are usually placed on trolleys; in clear weather they are rolled out into the open air under a net, and at night and in bad weather they are taken under a glass roof. Mitscherlich vessels are installed on fixed tables under a mesh.[...]

WATER PROPERTIES OF SOIL

The main water properties of soils are water holding capacity, water permeability and water-lifting capacity.

Water-holding capacity is the property of soil to retain water due to the action of sorption and capillary forces. The greatest amount of water that the soil can hold by one force or another is called moisture capacity.

Depending on the form in which the moisture retained by the soil is, there are total, minimum, capillary and maximum molecular moisture capacity.

For soils with normal moisture, the moisture state corresponding to full moisture capacity may occur after snowmelt, heavy rains, or when irrigated with large amounts of water. For excessively wet (hydromorphic) soils, the state of full moisture capacity can be long-term or permanent.

With a long-term state of soil saturation with water to full moisture capacity, anaerobic processes develop in them, reducing its fertility and plant productivity. Considered optimal for plants relative humidity soils within 50-60% PV.

However, as a result of swelling of the soil when it is moistened and the presence of trapped air, the total moisture capacity does not always exactly correspond to the total porosity of the soil.

The lowest moisture capacity (LC) is the maximum amount of capillary-suspended moisture that the soil can retain for a long time after abundant moistening and free drainage of water, provided that evaporation and capillary moistening due to groundwater are excluded.

Soil permeability is the ability of soils to absorb and pass water through itself. There are two stages of water permeability: absorption and filtration. Absorption is the absorption of water by the soil and its passage through soil that is not saturated with water. Filtration (seepage) is the movement of water in the soil under the influence of gravity and pressure gradient when the soil is completely saturated with water. These stages of water permeability are characterized by absorption and filtration coefficients, respectively.

Water permeability is measured by the volume of water (mm) flowing through a unit area of soil (cm 2 ) per unit of time (h) with a water pressure of 5 cm.

This value is very dynamic, depending on the particle size distribution and chemical properties soils, their structural state, density, porosity, humidity.

In soils of heavy granulometric composition, water permeability is lower than in light soils; the presence of absorbed sodium or magnesium in the PPC, which contributes to the rapid swelling of soils, makes the soils practically waterproof.

Water-lifting capacity is the ability of soil to cause upward movement of the water contained in it due to capillary forces.

The height of water rise in soils and the speed of its movement are determined mainly by the granulometric and structural composition of soils and their porosity.

The heavier and less structured the soil, the greater the potential height of water rise, and the slower its rise rate.

WATER REGIME OF SOIL

The water regime is understood as the totality of the phenomena of moisture entering the soil, its retention, consumption and movement in the soil. It is expressed quantitatively through the water balance, which characterizes the flow of moisture into the soil and the flow out of it.

Professor A. A. Rode identified 6 types of water regime, dividing them into several subtypes.

1. Permafrost type. Distributed in permafrost conditions. The frozen layer of soil is waterproof and is an aquifer, over which the supra-permafrost perch flows, which causes the upper part of the thawed soil to become saturated with water during the growing season.

2. Flushing type (KU > 1). Characteristic of areas where the amount of annual precipitation is greater than evaporation. The entire soil profile is annually subjected to through wetting to groundwater and intensive leaching of soil-forming products. Under the influence of the leaching type of water regime, soils of the podzolic type, red soils and yellow soils are formed. When groundwater occurs close to the surface and the soils and soil-forming rocks have low water permeability, a bog subtype of water regime is formed. Under its influence, bog and podzolic-marsh soils are formed.

3. Periodically flushing type (KU = 1, with fluctuations from 1.2 to 0.8). This type of water regime is characterized by an average long-term balance of precipitation and evaporation. It is characterized by alternating limited wetting of soils and rocks in dry years (non-flushing conditions) and through wetting (flushing regime) in wet years. Soil washing by excess precipitation occurs 1-2 times every few years. This type of water regime is characteristic of gray forest soils, podzolized and leached chernozems. Soil water supply is unstable.

4. Non-flush type (KU< 1). Характеризуется распределением влаги осадков преимущественно в верхних горизонтах и не достигает грунтовых вод. Связь между атмосферной и groundwater carried out through a layer with very low humidity, close to the air intake. Moisture exchange occurs through the movement of water in the form of steam. This type of water regime is typical for steppe soils - chernozems, chestnut, brown semi-desert and gray-brown desert soils. In this series of soils, the amount of precipitation decreases and evaporation increases. The humidification coefficient decreases from 0.6 to 0.1.

Moisture circulation covers a thickness of soil and soil from 4 m (steppe chernozems) to 1 m (desert-steppe, desert soils).

The moisture reserves accumulated in steppe soils in the spring are intensively spent on transpiration and physical evaporation and by autumn they become negligible. In semi-desert and desert zones, farming is impossible without irrigation.

5. Exhaustive type (KU< 1). Проявляется в степной, полупустынной и пустынной зонах при близком залегании грунтовых вод. Преобладают восходящие потоки влаги по капиллярам от грунтовых вод. При высокой минерализации грунтовых вод в почву поступают легкорастворимые соли, происходит ее засоление.

6. Irrigation type. It is created by additionally moistening the soil with irrigation water. With proper rationing of irrigation water and compliance with the irrigation regime, the water regime of the soil should be formed according to the non-flushing type with a WC close to unity.

Lowest moisture capacity (according to P.S. Kossovich)

One of the main water properties of soil is moisture capacity, which refers to the amount of water retained by the soil. It is expressed as a percentage of the mass of absolutely dry soil or its volume.

The most important characteristic of the water regime of soils is its lowest moisture capacity, which is understood as greatest number suspended moisture that the soil is able to retain after abundant moisture and drainage of gravitational water. At the lowest moisture capacity, the amount of moisture available to plants reaches the maximum possible value. E. Mitscherlich called the amount of water in the soil, minus that part of it that constitutes the so-called dead reserve, “physiologically available soil moisture.”

The lowest moisture capacity is determined in field conditions with natural soil formation using the flooded pad method. The essence of the method is that the soil is saturated with water until all the pores are filled with it, and then the excess moisture is allowed to drain under the influence of gravity. The established equilibrium humidity will correspond to HB. It characterizes the water-holding capacity of the soil. To determine the NV, select an area of at least 1 x 1 m in size, around which a protective edge is created, enclosed in a double ring of compacted earth rollers 25-30 cm high, or wooden or metal frames are installed. The soil surface inside the site is leveled and covered with coarse sand with a 2 cm layer to protect the soil from erosion. Soil samples are taken near the site along genetic horizons or individual layers to determine its porosity, moisture and density. Based on these data, the actual water reserve in each of the horizons (layers) and porosity are determined. By subtracting the volume occupied by water from the total pore volume, the amount of water required to fill all the pores in the studied layer is determined.

Calculation example. Area of the pouring area S = 1 x 1 = 1 m2. It has been established that the thickness of the arable layer is 20 cm or 0.2 m, soil moisture W is 20%; density d - 1.2 g/cm3; porosity P - 54%.

a) volume of the arable layer: V arable = hS = 0.2 x 1 = 0.2 m3 = 200 l.

b) the volume of all pores in the layer under study:

Vpore = Vsoil (P/100) = 200 (54/100) = 108 l

c) the volume of pores occupied by water at a humidity of 20%

V water = V smell (W/100) S = 200 (20/100) 1 = 40 l

d) Volume of water-free pores

Vfree = Vpor - Vwater = 108 - 40 = 68 l.

To fill all the pores in the topsoil within the flood area, 68 liters of water will be required.

In this way, the amount of water is calculated to fill the soil pores to the depth to which the NV is determined (usually up to 1-3 m).

To better guarantee complete soaking, the amount of water is increased by 1.5 times for lateral spreading.

Having determined the required amount of water, they begin to fill the site. A stream of water from a bucket or hose is directed at some solid object to avoid disturbing the soil structure. When the entire specified volume of water is absorbed into the soil, its surface is covered with a film to prevent evaporation.

The time for excess water to drain and establish equilibrium moisture content corresponding to HB depends on the mechanical composition of the soil. For sandy and sandy loam soils it is 1 day, for loamy soils 2-3 days, for clayey soils 3-7 days. More precisely, this time can be determined by observing the soil moisture in the area for several days. When fluctuations in soil moisture over time are insignificant, not exceeding 1-2%, then this will mean achieving equilibrium moisture, i.e.

Field soil moisture capacity

In laboratory conditions, NI for soils with disturbed composition can be determined by saturating soil samples with water from above, by analogy with determining the structure of the arable soil layer.

An approximate idea of NV values can also be obtained using the method of A.V. Nikolaev. To do this, an arbitrary amount of soil, passed through a sieve with a mesh diameter of 1 mm, is moistened with water with thorough mixing until a fluid mass is formed, then part of it (20-30 ml) is poured onto a gypsum plate and kept until wet surface the soil will not become dull due to the absorption of excess water by the plate. After this, the soil is removed from the gypsum plate and placed in a bottle to determine the humidity, which, with a certain convention, will correspond to the HB.

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Maximum hygroscopic humidity, maximum molecular moisture capacity, lower and upper limits of plasticity are directly related to the granulometric and mineralogical composition of soils and soils, therefore they influence to some extent the cohesion and water resistance of the structure and, consequently, their anti-erosion resistance. However, this influence is usually difficult to detect due to the influence of other more powerful factors.[...]

Maximum molecular moisture capacity (MMC) corresponds to the highest content of loosely bound water retained by sorption forces or forces of molecular attraction. [...]

According to a number of authors (Vadyunina, 1973, for chestnut soils, Umarov, 1974, for gray soils), the value of the maximum molecular moisture capacity corresponds to the capillary rupture humidity (CBR). The term was introduced into soil hydrophysics by A. A. Rode and M. M. Abramova. However, the method direct definition There is no VRK. In practice, the term MMV is more common. It is also used in hydrogeology.[...]

Depending on the form in which the moisture retained by the soil is, a distinction is made between total, minimum, capillary and maximum molecular moisture capacity. [...]

Quaternary rocks of the territory of the AGKM are represented by sands, sandy loams, loams, clays, characterized by significantly individual physicochemical and water properties - specific and volumetric gravity, porosity, maximum molecular moisture capacity, plasticity and filtration coefficients. [...]

Loosely bound water. This is the second form of physically bound, or sorbed, water, called film water. It is formed as a result of additional (to MG) sorption of water molecules upon contact of solid colloidal soil particles with liquid water. This occurs because soil particles that have sorbed the maximum number of hygroscopic water molecules (from water vapor) are not completely saturated and are still capable of retaining several dozen layers of oriented water molecules, forming a water film. Film, or loosely bound, water is weakly mobile (it moves slowly from a soil particle with a thicker film to a particle with a thinner film).

It is inaccessible to plants. The maximum amount of loosely bound (film) water held by the forces of molecular attraction of dispersed soil particles is called the maximum molecular moisture capacity (MMC).[...]

So high values humidity, at which municipal wastewater sediments retain their given shape, significantly distinguishes them from other dispersed materials, such as ore concentrates. For the latter, these values usually do not exceed 10-12%.[...]

Total moisture capacity (Wmax)- this is the soil moisture, expressed in fractions of units, when its pores are completely filled with water.

Maximum molecular moisture capacity (Wm)– the ability of soil to retain film or hygroscopic water, closely associated with soil particles.

From the difference between the total and maximum molecular moisture capacity, the amount of water that can be released by the soil during drainage is determined. In sands, this difference is called water yield (WВ). It characterizes the water abundance of sandy soil saturated with water and should be taken into account when calculating groundwater production.

where Wв – water loss of loose rocks, %;

Wmax – total moisture capacity (water capacity), %;

Wm – maximum molecular moisture capacity, %.

It characterizes what part of the water (%) of its total content in the rock flows freely.

For quantitative characteristics of water loss it is also used water loss coefficient Kv, equal to the ratio of the volume of flowing water to the volume of rock, expressed in fractions of a unit.

Let's transform formula 1.15 and get an expression for calculating the water loss coefficient - formula 1.16:

(1.16)

where Kv is the coefficient of water loss of loose rocks, fractions of units;

ε – rock porosity coefficient, fraction of units;

ρs – density of the mineral part of the rock at natural humidity, g/cm3;

ρw – density of formation water, g/cm3.

Wm – maximum molecular moisture capacity, fractions of units.

Characteristics of soil water permeability is the filtration coefficient (Kf), i.e. the speed of water passing through the soil with a pressure gradient equal to unity. The filtration coefficient is expressed in cm/sec or m/day.

Capillary moisture capacity– the ability of soil to fill only capillary pores as a result of capillary water rising from below, from the free water level.

Total and capillary moisture capacity for the same type of soil can vary significantly depending on its density, nature of composition and structure.

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The moisture capacity of soil is understood as its ability to hold a certain amount of water for a long time. Depending on the conditions of filling and retention, a distinction is made between maximum adsorption moisture capacity, minimum (field) moisture capacity, or water permeability.

The smallest (field) moisture capacity is the maximum amount of capillary-suspended water that can be retained by the soil by meniscus or capillary forces after all the gravitational water has drained off.

Moisture capacity depends on the granulometric composition of the soil, on the structure of the soil, on the amount of humus, saline content, and salinity. It is expressed in weight and volume percentages, m 3 per 1 hectare, mm.

Determination of the smallest (field) moisture capacity in the field. Students determine the lowest field moisture capacity in the vicinity of the agricultural institute.

An experimental site measuring 3 x 3 m is laid on the selected site. Satisfactory results are also obtained with a site size of 1.5 x 1.5 and 1 x 1 m.

The surface of the site is leveled, treated in the same way as the entire field, and filled with water in the amount necessary to displace air from the pores of the volume of soil planned for inspection. To protect against the spreading of water when pouring, the site is surrounded by two earthen ramparts 20--25 cm high, spaced 0.4--0.6 m apart. You can mark the site with branches, and fill it at a distance of 0.5 m from it There is an earthen rampart around.

To determine the amount of water needed to fill the site, a soil section is made nearby, a morphological description of the soil is carried out, and the volumetric, specific gravity, moisture and porosity of the soil are determined. The total porosity and the actual water reserve in the soil layers are calculated. The results are recorded using the form below. IN in this example To completely saturate a soil layer of 0-30 cm, 111.6 mm or 1116 m 3 of water per 1 ha is needed. Its actual reserve is 405 m 3 per 1 hectare. Consequently, to saturate the soil, 1116 - 405 = 711 m 3 per 1 hectare is required, and for an area of 2 m 2 - 0.142 m 3 or 142 liters. Taking into account the loss of water due to spreading, its rate is increased by 1.5-2.0 times. With a meter depth of soaking, pour 200-300 liters per 1 m2.

The calculated volume of water is supplied to the site with a constant water pressure of 5 cm. A layer of water of 5 cm is maintained until the entire water supply is used up. When all the water has been absorbed into the soil, the area is covered with oilcloth or plastic film, and on top is a half-meter layer of straw to prevent evaporation and is left to drain by gravity. Sandy loam and sandy soils withstand 24 hours, loamy soils 2-3 days, clayey soils 3-5 days. After this period, soil moisture samples are taken with a drill every 10 cm, no less than three times. As soon as constant humidity is established with slight fluctuations within 0.5-0.7%, this humidity is taken as the value of field moisture capacity.

The results of determining soil moisture before and after watering are recorded in a notebook in the following form:

Calculation of moisture capacity is carried out using the formulas:

NV% = ((a - b) / (b - c)) * 100; NV m = NV %

The lowest field moisture capacity is used when calculating irrigation rates, leaching rates for saline soils, and planning crop irrigation regimes.