The invention relates to soil science, land reclamation and agriculture. In the field where soil moisture observations are planned, first, once, at the beginning of the plant growing season, the density of the soil with an undisturbed structure is determined by the well-known method using a cutting ring or cylinder, after which, throughout the entire growing season, as necessary, using a drill that allows you to select the soil with an undisturbed structure, samples of a certain volume are taken along the horizons and weighed on technical scales, right in the field and without drying the sample in a thermostat (drying oven), soil moisture is determined as the difference in the densities of soils with an undisturbed structure in a wet and dry state, related to the density of the soil with an undisturbed structure and expressed as a percentage of the mass of dry soil. Simplification, acceleration and increased efficiency of determination are achieved. 1 salary files, 1 table.

The invention relates to soil science, land reclamation and agriculture and can be used to quickly determine soil moisture, assign dates for the next growing season irrigation of all crops, as in open ground, and in greenhouses.

There are several known methods (methods) for determining soil moisture and assigning dates for the next growing season irrigation of agricultural crops, which can be combined into the following groups:

Weighing (thermostatic-weighting), based on drying and weighing soil samples;

Strain gauge, based on measuring soil moisture tension by surface forces arising at the phase boundary;

Radioactive, which is based on a change in the intensity of radioactive radiation from radiation sources placed in the soil when interacting with water molecules or hydrogen atoms;

Electrical, in which the electrical resistance, conductivity, capacitance and inductance of the soil are measured, depending on its moisture content;

Optical, in which the degree of absorption or reflection of radiation energy is measured, depending on the humidity of the object;

Express methods: according to the condition of the plants, morphological characteristics, physiological indicators, organoleptic characteristics of the soil, by which the supply of plants with soil moisture and the degree of its moisture are determined (Plyusnin I.I., Golovanov A.I. Reclamation soil science / Edited by A.I. Golovanov. - M.: Kolos, 1983 . - P.61-62; Dospehov B.A., Vasiliev I.P., Tulikov A.M. Workshop on agriculture / Textbook for universities // 2nd edition, revised and supplemented - M.: Agroproizdat, 1987. - P.58-60; Workshop on soil science / Edited by I.S. Kaurichev. - 4th edition, revised and supplemented. - M.: Agropromizdat, 1986. - P.97-98; Piunovsky B.A. Workshop on reclamation agriculture. - 3rd edition, revised and expanded. - M.: Agropromizdat, 1986. - P.46-54; Dolgov S.I. Agrophysical methods for soil research. - M.: Nauka, 1966. - P.9-227; Verigo S.A., Razumova L.A. Soil moisture. - L.: Gidrometeoizdat, 1973. - 328 pp.; Rode A.A. Fundamentals of the doctrine of soil moisture. - T.1. Water properties soils and movement of soil moisture. T.2. Methods for determining the water regime of soils. - L.: Gidrometeoizdat, 1965, 1969. - 663 p. and 287 pp.; Discoveries, inventions, industrial designs and trademarks. G01N 5/02 a.s. No. 1196737, G01N 75/56 a.s. No. 898308, G01N 5/00 a.s. No. 1101718, G01N 22/04 a.s. No. 1101722, G01N 25/56 a.s. No. 1173283, G01N 23/24 a.s. No. 693184, G01N 23/00 a.s. No. 53/466, G01N 21/80 a.s. 1109610, G01J 1/04 a.s. 811084, G01N 21/86 a.s. No. 813209.

Disadvantages known methods determining soil moisture and the timing of vegetation irrigation is significant labor-intensive, energy-intensive and time-consuming process, the need to use a large amount laboratory equipment, electrical and radiation and other devices quite hazardous to health service personnel and surrounding people. A number of methods for determining soil moisture are characterized by low accuracy, which is insufficient for their practical use.

The closest technical solution Determining soil moisture and the timing of vegetation irrigation is a weight method (thermostatic-weight), in which soil samples to determine soil moisture in the field are taken with a special needle auger, from which the soil is transferred into a pre-weighed cup and covered with a lid. In the laboratory, wet soil in cups is weighed on technical scales and dried in a drying cabinet at a temperature of 105°C for 12-14 hours to a constant weight, controlling it on a scale with an accuracy of 0.01 g. Weighing cups with dry soil is carried out through 6 hours and then 8, 10, 12, 14 hours after the start of drying, until constant weight. Drying time depends on soil moisture and temperature regime in the drying cabinet. The differences in the mass of the cup with dry soil during the next weighing should not exceed 0.05 g.

Soil moisture is determined by the formula:

where β in is the desired moisture content, % of the mass of dry soil;

B is the mass of an empty aluminum cup, g;

B1 - mass of a cup with wet soil before drying, g;

B2 - mass of a cup with dry soil after drying, g.

(Dospehov B.A., Vasiliev I.P., Tulikov A.M. Workshop on agriculture / Textbook for universities // 2nd ed. revised and supplemented - M.: Agropromizdat, 1987. - P.57-58).

Disadvantage this method Determining soil moisture requires significant labor, time and energy, which is associated with repeated weighing of the soil sample and its prolonged drying in an oven for 12-14 hours until it reaches a constant weight.

The technical result achieved by the invention is to simplify the method for determining soil moisture, reduce labor, time and energy costs and the possibility of its rapid use in field conditions.

The result is achieved by the fact that in the field where observations of soil moisture are planned, first at the beginning of the plant growing season the density of dry soil with an undisturbed composition is determined using a well-known method, collecting wet samples using a cutting ring or cylinder, weighing them and drying them in a thermostat, and then throughout the entire growing season, if necessary, using a drill that allows you to select soil with an undisturbed structure along the horizons, take samples of moist soil of a certain volume and weigh them on technical scales, directly in the field and without drying the sample in a thermostat (drying cabinet), determine soil moisture, as the difference in the densities of soil with undisturbed composition in wet and dry states, related to the density of dry soil with undisturbed composition and expressed as a percentage of the mass of dry soil.

The method for determining soil moisture is that in a field where observations of soil moisture are planned previously at the beginning of the growing season, the density of dry soil with an intact structure is determined using a well-known method, taking wet samples using a cutting ring or cylinder, followed by weighing and drying in a thermostat . After this, throughout the entire growing season, as necessary, every day, every ten days, before and after precipitation and irrigation, samples of moist soil of a certain volume are taken along the horizons. Sampling for moisture content is carried out with a Negovelov drill, a TSHA cylinder drill, or any other drill that allows you to take soil samples with an undisturbed structure. These devices allow you to take samples of moist soil with an undisturbed structure of a certain volume. Selected samples of moist soil are weighed directly in the field on technical scales with an accuracy of 10 mg and the soil moisture is determined without drying in a thermostat (drying oven). It is found as the difference in the densities of soil with undisturbed composition in wet and dry states, related to the density of dry soil with undisturbed composition, expressed as a percentage of the mass of dry soil according to the formula:

where βв is soil moisture, % dry soil mass

p is the mass of the wet soil sample, g;

v is the volume of the wet soil sample corresponding to the volume of the drill, cm 3 ;

dv is the density of dry soil with undisturbed structure, g/cm 3 .

Research conducted in the laboratory of the Department of Soil Reclamation of the Novosibirsk State Medical Academy showed a sufficient degree of convergence of the results of determining soil moisture using the standard thermostat-weight and new methods (Table 1). The studies were carried out in quadruple repetition with two horizons of 0-20 and 20-40 cm, which had a density of dry soil with an undisturbed composition of 1.15 and 1.30 g/cm3, respectively. With a confidence probability of 95%, the accuracy of the experiment turned out to be quite high and amounted to 0.69%, and the smallest significant difference between the options turned out to be equal to 0.58% m.s.p. In accordance with this, the experimental error turned out to be insignificant and between the options amounted to 0.26-0.27% m.s.p. Consequently, the accuracy of determining soil moisture using the new method reaches 99%, the relative error is no more than 1%. This allows you to use new way determination of soil moisture for practical purposes in the field of reclamation, irrigated agriculture and crop production to monitor the dynamics of soil moisture, in water balance studies and in setting the timing of vegetation irrigation.

Table 1
Influence in various ways on the accuracy of soil moisture determination
Experience Options	Humidity, β% m.s.p.	Error, % m.s.p.	Relative error, %
The density of the soil with an undisturbed structure is 1.15 g/cm3. Thermostatic-weight method	27.50	-	-
The density of the soil with an undisturbed structure is 1.15 g/cm3. New way	27.23	0.27	1.00
The density of the soil with an undisturbed structure is 1.30 g/cm3. Thermostatic-weight method	27.81	-	-
The density of the soil with an undisturbed structure is 1.30 g/cm3. New way	27.55	0.26	0.99
Accuracy of experiment, m%	0.69	-	-
The smallest significant difference, NSR 095, % m.s.p.	-	0.58	-

A new accelerated method for determining soil moisture significantly reduces the cost of time, labor and energy when using it in comparison with the standard. When determining humidity by this method, there is no drying of the wet sample in a thermostat, which takes at least 12-14 hours and consumes a significant amount of electricity, approximately 15-20 square hours. There is no need to weigh the dried soil sample multiple times. The main advantage of the new method for determining soil moisture is the ability to quickly determine soil moisture directly in the field, without the use of bulky laboratory equipment.

1. A method for determining soil moisture, including sampling for analysis, weighing them, characterized in that in the field where soil moisture observations are planned, the density of dry soil with an undisturbed composition is first determined once at the beginning of the plant growing season using a well-known method, by taking wet samples with using a cutting ring or cylinder, followed by weighing and drying in a thermostat, after which, during the entire growing season, as necessary, using a drill that allows you to select soil with an undisturbed structure, samples of moist soil of a certain volume are taken along the horizons and weighed on technical scales, directly into field and without drying the sample in a thermostat (drying cabinet), soil moisture is determined as the difference in the densities of soil with undisturbed composition in a wet and dry state, related to the density of dry soil with undisturbed composition and expressed as a percentage of the mass of dry soil.

2. The method according to claim 1, characterized in that samples of moist soil with an undisturbed structure can be taken to determine soil moisture using a Negovelov drill or a TSHA cylinder drill.

SOIL MOISTURE. LEARNING TO MEASURE SOIL HUMIDITY

SOIL WATER CAPACITY

In the article on soil salinity, we wrote about water regimes. They are easy to understand, but they will not help in any way to calculate the watering rate. To do this, you will have to become familiar with the concepts of “humidity” and “moisture capacity” of the soil.

But first, let's look at the structure of the soil. Firstly, it consists of solid particles and pores. The first include sand, clay, humus - everything that is not a liquid or gas. And the voids that are between these solid particles are called pores. These pores are filled with gases (air) or water. On average, the optimal ratio is:50% solids to 50% pores.The size of these pores is also very important.The smallest pores“tunnels” are put together forwater - capillaries. This is veryan important part of the soil, becausecapillaries can risewater from deeper horizonsComrade It is believed that the root zonecan be moistened by soilwaters, if they are ondepth no more than 3 m. Then moisturefrom these horizons and risesup the capillaries. Besides,when the soil dries out, due tosurface forces, water canhold on in these sucksyeah, not letting the grounddry out too fast. Soil moisture is the percentage ratio of all soil moisture to dry soil. That is,soil moisture of 20% means that per 100 g of completely dry soil there is20 g of moisture (or 120 g of soil in your field 20 g of moisture). It is very important to remember that dry soil is used for calculations, not wet soil. For example, milk with a fat content of 4% means that 4 g of fat is found per 100 g of whole milk, and not skim milk (which, accordingly, is 96 g). While soil moisture of 4% is 4 g of moisture and 100 g of dry soil (or 104 g of soil with a moisture content of 4%).

Soil moisture capacity is maximum amount moisture that the soil can retain. There are several moisture capacities: PV (total moisture capacity) - the maximum amount of water that can fit in all the pores of the soil. In essence, this is a completely flooded field. In this case, the amount of air in the voids is zero; this situation on the field is extremely undesirable.

But the most important indicator is the lowest moisture capacity (MC), knowing the values of which, it is most convenient to determine the need for watering. This is the amount of moisture that the soil can “actively” retain with the help of various forces(adsorption, chemical bonds, hydro-colloids, capillaries, etc.). To put it simply, the lowest moisture capacity is achieved when, after complete saturation of the soil, water drains excess moisture which is not actively retained by the soil (water from large pores).

Therefore, it is more convenient to express the optimal soil moisture as a percentage of HB. This indicator shows not only the moisture content in your area, but also its shape. Free gravitational moisture is not available to plants, but only harms them. Too high NV (85% or more) is suitable for plant development, but increases the risk of developing root diseases.

As a rule, 100% NV is achieved at soil moisture from 20% (light soils) to 40% (loamy soils). In other words, if you have sandy loam soil, then the optimal 75% NV for most crops is achieved with soil moisture of 15%, and if it is heavy - up to 30%.

Moisture capacity is a fairly stable indicator. If there are no cardinal changes in the soil (as, for example, with a greenhouse substrate, where an intensive agricultural background is created), organic fertilizers, peat, ameliorants), then it is sufficient to measure this parameter once every few years. It is needed in order to correctly use the results of soil moisture measurements.

For example, if HW is 30% and soil moisture is 21%, then this soil moisture can be expressed as 70% of normal moisture capacity.

This can be expressed as: in order to fill a box with fruits by 60%, we first need to find out the capacity of this box (find out the NV of the soil). The next step is that we need to weigh the fruits that are already in the box (soil moisture). At the same time, in the same type of boxes the number of fruits can be different (it is enough to find out the NV of your soil once; the humidity changes constantly). And so, if we know that a box with a capacity of 10 kg contains 3.5 kg of fruit, then it is 35% filled, which means we need to add 2.5 kg of fruit. Let’s summarize the first results. To learn how to water plants correctly, you need to:

Determine the method by which soil moisture will be measured (once);

Measure the density, then the HV of your soil (once);

Measure your soil moisture (regularly);

Convert soil moisture into % of HB.

Make sure that the soil moisture does not go beyond certain limits. For example, it was not below 60% NV and above 80% NV. That is, you need to start watering at 60% NV.

HOW TO MEASURE THE MOISTURE CAPACITY OF SOIL?

The lowest moisture capacity of the soil is observed when, after abundant moisture (or flooding), all excess moisture goes into deep horizons. Therefore, in the field, this parameter can be measured during the occurrence of groundwater deeper than 3 m, otherwise they will constantly saturate the soil with new portions of moisture.

In early spring, when the soil is filled with melt water, choose typical site field (1.5x1.5 m), which is covered with film and straw to prevent moisture evaporation. On irrigated lands, analysis can be carried out after heavy watering. There is a third option - creating a small flood area. To do this, the selected area is surrounded by earthen ramparts (the earth is taken far from the site so as not to disturb the topography of the field), wooden or iron frames. To soak the soil, you need to use 200 liters of water per square meter if the soil is light, up to 300 for loamy soils. In the place where the water will be poured, you need to put plywood so as not to wash away the soil with the stream. Water must be poured in portions so that its layer is no more than 5 cm high. The next portion is served after the previous one is absorbed.

In all three cases, the ground is covered with oilcloth and straw. After a day, three days, and on loamy soils even after 10 days, soil samples are taken every 10 cm (0-10, 10-20, 20-30...) and the moisture content of the samples is measured. The obtained data are called HB1, HB3 and HB10, respectively. On sandy loam soils the most optimal parameter is NVZ, on heavy soils - NV10. HB1 is relevant where excess moisture drains within 24 hours (sand content is close to 100%, a large amount of coarse-grained fraction).

The indicator of the lowest moisture capacity will be the humidity of the sample. That is, if there are 27 g of water per 100 g of thermostat-dried soil in the sample, then 100% NV corresponds to 27% soil moisture.

SOIL MOISTURE MEASUREMENT

The most accurate method, which is also used by laboratories, is considered to be thermostat-gravity. It is very simple and uses only three types of equipment: scales, a thermostat and a drill, which can be replaced with a spatula. Almost any stove, oven or boiler, and a thermometer can serve as a thermostat volume. The disadvantage of this method is obvious - you can find out the soil moisture only 2-3 days from the moment the sample is taken, so it will be extremely difficult to determine the need for watering in this way. But other methods do not measure soil moisture, but other soil properties that depend on moisture. For example, the electrical conductivity of the soil depends on the concentration of the soil solution (for example, analysis using a TDS meter). On the one hand, it is higher if the humidity is lower, on the other hand, any application of fertilizers will greatly affect the result of the study.

Having decided how you plan to regularly measure soil moisture, it is recommended to use both the thermostat-weight method and the device you choose to determine the soil moisture content. This way you will perform a kind of calibration.

Let's look at an example. If the density of your soil is 1.1 g per cubic centimeter, according to the thermostat-weight method, the soil moisture content will be 30%, and according to the operational method - 25%, then the measurement error will be 165 tons of water per hectare . Therefore, when determining soil moisture with the selected device, it will be necessary to take a soil moisture of 25% as 100% NV.

Measuring humidity using electricalThe use of such instruments most often examines other properties of the soil: resistance, electrical conductivity, inductance, etc.

The most widely used devices are those that measure the dielectric properties of soil. Most often, a professional device weighs several hundred grams, equipped with a special probe. After “pricking” the soil with a probe, the device screen shows its moisture content as a percentage (after 3-5 seconds).

There are also simplified versions of such equipment for the private sector. The device, costing 200-800 hryvnia, can measure soil moisture (with an accuracy of 10%), its acidic environment, more expensive models - soil temperature. The hundred-gram water supply of eastern countries does not even always show the numbers; some models are limited to scales, such as the soil being “very dry”, etc. You shouldn't bet big on such electronics - they don't even always have the ability to be calibrated. There are also mini-modules on sale that can be part of a system for a budget automation system (for example, Ardunino).

TENSIOMETERS

The method of measuring humidity with a tensiometer is based on changes in pressure inside the tube of the device. The device consists of a ceramic vacuum tube and a vacuum manometer (a device for measuring pressure).

Before use, the tensiometer is charged by immersing it in water until the ceramic tube is completely saturated. Afterwards it is placed in the field (buried into the ground). It is recommended to use two tensiometers, for different depths (for example, 20 and 40 cm). The drier the soil becomes, the more it “pulls” water from the vacuum tube of the device, causing the pressure in it to drop. The second element of the tensiometer, a vacuum manometer, measures this drop. These data are already converted into actual soil moisture using special tables.

Since the device records the pressure drop, the needle deviates to the minus side (below zero). The further it moves from the zero mark, the lower the soil moisture. It is impossible to use the device data without tables, since when the moisture capacity is full, the arrow can show from - 10 centibars (note: centibar - 0.01 bar) on heavy soils to - 40 centibars on light soils. It is necessary to take into account the influence of other factors, including , soil temperature.

SO HOW MUCH SHOULD I WATER?

The last thing we need to do is calculate the watering rate. To do this, you can use the devices that are available (water until the device records the soil moisture we need) or calculate the norm using a mathematical method.

Everything is a little more complicated here. The first thing we need to know is specific gravity dry soil (mass of 1 cm 3 of soil in grams or 1 m 3 in tons), it is also called density. But our samples are not suitable for this - their volume will be damaged during drying. The easiest way to find out the specific gravity is from the tables, since this parameter is not too changeable and most of all depends on the granulometric composition of the soil. Of course, loosening reduces its specific gravity, but this will not affect the watering rate.

If we know that we need to add 25% of its capacity to our box, then we multiply this capacity by 0.25 (10 kg % 0.25 = 2.5 kg). Same with the soil. If you need to increase the soil moisture by 10%, then you need to multiply its mass by 0.1.

To find out the mass of soil on your site, you need its area in square meters multiply by 0.3 (the root zone is 30 cm or 0.3 m) and multiply by the specific gravity.

For a hectare it will be 10,000 m 2 x 0.3 m = 3000 m 3.

If 1 m 3 pounds weighs 1.1 tons, then we need to moisten: 3,000 m 3 x 1.1 t/m 3 = 3.3 thousand tons of soil. Then the irrigation rate (10% of this figure) will be 330 m3.

Well, the easiest way to determine soil moisture is to squeeze it in your hand. If water does not begin to penetrate through your fingers, but when you open your palm, the soil remains in a lump - this is satisfactory moisture. Will have to water it soon. How much should I water? This method will not answer such questions.

To measure soil moisture using the thermostat-weight method, you need to perform the following operations:

Prepare heat-resistant dishes for samples. In laboratory conditions, aluminum bottles with ground-in lids are used for this purpose. And a book. and cap have their own number, which is recorded to maintain the accuracy of the analysis. The dishes must be clean, pre-weighed with maximum accuracy (jug with lid together) - weight 1. Here you will have to either use precision scales(according to the method, scales should weigh up to 0.01 g, but they are also suitable with an accuracy of up to 0.1 g). If it is not possible to use such scales, samples are taken for analysis. more soil, but then it will take longer to dry.

Take a soil sample using a drill or shovel. Place them in the prepared bowl to fill half the volume (up to 2/3).

Weigh the container, lid and soil together - mass 2.

Place them to dry at a temperature of 100-105°C until the weight of the bottle stops changing. This way we find out mass 3.

Before the last weighing, close the container with a lid and let it cool in a tightly closed cabinet.

Drying allows you to find out how much water was in the soil sample (mass 2 minus mass 3) and the weight of the dry soil (mass 3 minus mass 1). The mass of water is divided by the mass of dry soil and multiplied by 100% - this is how the soil moisture is determined at the time of sampling.

First, let's look at the structure of the soil. Firstly, it consists of solid particles and pores. The first include sand, clay, humus - everything that is not a liquid or gas. And the voids that are between these solid particles are called pores. These pores are filled with gases (air) or water. On average, the optimal ratio is 50% solids to 50% pores. The size of these pores is also very important. The smallest pores form together “tunnels” for water - capillaries. This is a very important part of the soil, since water from deeper horizons can rise through capillaries. It is believed that the root zone can be moistened by groundwater if it is located at a depth of no more than 3 m. Then moisture from these horizons rises up through the capillaries. In addition, when the soil dries out, due to surface forces, water can be retained in these vessels, preventing the soil from drying out too quickly.

Soil moisture is the percentage of total soil moisture to dry soil. That is, 20% soil moisture means that there are 20 g of moisture per 100 g of completely dry soil (or 20 g of moisture in 120 g of soil in your field). It is very important to remember that dry soil is used for calculations, not wet soil. For example, milk with a fat content of 4% means that 4 g of fat is found per 100 g of whole milk, not skim milk (which, accordingly, is 96 g). While soil moisture of 4% is 4 g of moisture and 100 g of dry soil (or 104 g of soil with 4% moisture).

Soil moisture capacity - this is the maximum amount of moisture that the soil can hold.

There are several moisture containers:

PV (full moisture capacity) - the maximum amount of water that can be held in all the pores of the soil. In essence, this is a completely flooded field. In this case, the amount of air in the voids is zero; this situation on the field is extremely undesirable.

But the most important indicator is lowest moisture capacity (HW) , knowing the values of which, it is most convenient to determine the need for watering. This is the amount of moisture that the soil is able to “actively” retain through various forces (adsorption, chemical bonds, hydrocolloids, capillaries, etc.). To put it simply, the lowest moisture capacity is achieved when, after the soil is completely saturated with water, excess moisture drains away, which is not actively retained by the soil (water from large pores).

That's why optimal humidity soil and it is more convenient to express it as a percentage of NV. This indicator shows not only the moisture content in your area, but also its shape. Free gravitational moisture is not available to plants, but only harms them. Too high NV (85% or more) is suitable for plant development, but increases the risk of developing root diseases.

As a rule, 100% NV is achieved with soil moisture between 20% (light soils) and 40% (loamy soils). In other words, if you have sandy loam soil, then the optimal 75% NV for most crops is achieved with a soil moisture of 15%, but if it is heavy, up to 30%.

Moisture capacity- a fairly stable indicator. If there are no cardinal changes in the soil (as, for example, with a greenhouse substrate, where an intensive agricultural background is created, fertilizers, peat, and ameliorants are applied), then it is enough to measure this parameter once every few years. It is needed in order to correctly use the results of soil moisture measurements.

For example, if the HW is 30% and the soil moisture is 21%, then this soil moisture can be expressed as 70% of the normal water holding capacity.

This can be expressed as: in order to fill a box with fruits by 60%, we first need to find out the capacity of this box (find out the NV of the soil). The next step is we need to weigh the fruits that are already in the box (soil moisture). At the same time, in the same type of boxes the number of fruits can be different (it is enough to find out the NV of your soil once; the humidity changes constantly). And so, if we know that a box with a capacity of 10 kg contains 3.5 kg of fruit, then it is 35% full, which means we need to add 2.5 kg of fruit. Let's summarize the first results. To learn how to water plants correctly, you need to:

Determine the method by which soil moisture will be measured (once);
Measure the density, then the HV of your soil (once);
Measure your soil moisture (regularly);
Convert soil moisture to % of HB.
Make sure that soil moisture does not go beyond certain limits. For example, it was not below 60% NV and above 80% NV. That is, you need to start watering at 60% NV.

How to measure soil moisture capacity?

The lowest moisture capacity of the soil is observed when, after abundant moisture (or flooding), all excess moisture goes into deep horizons. Therefore, in field conditions, this parameter can be measured when groundwater is deeper than 3 m, otherwise it will constantly saturate the soil with new portions of moisture.

In early spring, when the soil is filled with melt water, a typical area of the field (1.5x1.5 m) is selected, which is covered with film and straw to prevent moisture evaporation. On irrigated lands, analysis can be carried out after heavy watering. There is a third option - creating small area flooding. To do this, the selected area is surrounded by earthen ramparts (the earth is taken far from the site so as not to disturb the topography of the field), wooden or iron frames. To soak the soil, you need to use 200 liters of water per square meter if the soil is light, up to 300 for loamy soils. In the place where the water will be poured, you need to put plywood so as not to wash away the soil with the stream. Water must be poured in portions so that its layer is no more than 5 cm high. The next portion is served after the previous one is absorbed.

In all three cases, the ground is covered with oilcloth and straw. After a day, three days, and on loamy soils even after 10 days, soil samples are taken every 10 cm (0-10, 10-20, 20-30...) and the moisture content of the samples is measured. The obtained data are called HB1, HB3 and HB10, respectively. On sandy loam soils the most optimal parameter- NVZ, for heavy ones - NV10. HB1 is relevant where excess moisture drains within 24 hours (sand content is close to 100%, a large number of coarse-grained fraction).

Soil moisture measurement

The most accurate method, which is also used by laboratories, is considered to be thermostat-gravity. It is very simple and uses only three types of equipment: a scale, a thermostat and a drill, which can be replaced with a spatula. Almost any stove, oven or boiler, and a thermometer can serve as a thermostat. The disadvantage of this method is obvious - you can find out the soil moisture only 2-3 days from the moment the sample is taken, so it will be extremely difficult to determine the need for watering in this way. But other methods do not measure soil moisture, but other soil properties that depend on moisture. For example, the electrical conductivity of the soil depends on the concentration of the soil solution (for example, analysis using a TDS meter). On the one hand, it is higher if the humidity is lower, on the other hand, any application of fertilizers will greatly affect the result of the study.

Let's look at an example. If the density of your soil is 1.1 g per cubic centimeter, according to the thermostat-weight method, the soil moisture content will be 30%, and according to the operational method - 25%, then the measurement error will be 165 tons of water per hectare. Therefore, when determining soil moisture with the selected device, it will be necessary to take a soil moisture of 25% as 100% NV.

Measuring humidity with electrical appliances most often studies other soil properties: resistance, electrical conductivity, inductance, etc.

There are also simplified versions of such equipment for the private sector; it can measure soil moisture (with an accuracy of 10%), its acidic environment, more expensive models - soil temperature. Instruments from eastern countries do not even always show numbers; some models are limited to scales such as “very dry” soil, etc. You shouldn't bet big on such electronics - they don't even always have the ability to be calibrated. There are also mini-modules on sale that can be part of a system for budget system automation (for example, Ardunino).

Tensiometers

The method of measuring humidity with a tensiometer is based on changes in pressure inside the tube of the device. The device consists of a vacuum ceramic tube and a vacuum manometer (a device for measuring pressure).

Before use, the tensiometer is charged by immersing it in water until the ceramic tube is completely saturated. Afterwards it is placed in the field (buried into the ground). It is recommended to use two tensiometers, for different depths (for example, 20 and 40 cm). The drier the soil becomes, the more it “pulls” water from the vacuum tube of the device, causing the pressure in it to drop. The second element of the tensiometer, the vacuum manometer, measures this drop. These data are already converted into actual soil moisture using special tables.

Since the device records the pressure drop, the needle deviates in the negative direction (below zero). The further it moves from the zero mark, the lower the soil moisture. It is impossible to use the device data without tables, since with full moisture capacity the arrow can show from - 10 centibar ( note: centibar - 0.01 bar) on heavy soils up to - 40 centibar on light soils. It is necessary to take into account the influence of other factors, including soil temperature.

So how much should you water?

Everything is a little more complicated here. The first thing we need to know is the specific gravity of dry soil (the mass of 1 cm3 of soil in grams or 1 m3 in tons), it is also called density. But our samples are not suitable for this - their volume will be damaged during drying. The easiest way to find out the specific gravity is from the tables, since this parameter is not too variable and most depends on the granulometric composition of the soil. Of course, loosening reduces its specific gravity, but this will not affect the watering rate.

If we know that we need to add 25% of its capacity to our box, then we multiply this capacity by 0.25 (10 kg % 0.25 = 2.5 kg). Same with the soil. If you need to increase soil moisture by 10%, then you need to multiply its mass by 0.1.

To find out the mass of soil on your site, you need to multiply its area in square meters by 0.3 (the root zone is 30 cm or 0.3 m) and multiply by the specific gravity.

For a hectare it will be 10,000 m2 x 0.3 m = 3000 m3.

If 1 m3 of soil weighs 1.1 tons, then we need to moisten: 3,000 m3 x 1.1 t/m3 = 3.3 thousand tons of soil. Then the irrigation rate (10% of this figure) will be 330 m3.

To measure soil moisture using the thermostat-weight method, you need to perform the following operations:

Prepare heat-resistant dishes for samples. In laboratory conditions, aluminum bottles with ground-in lids are used for this purpose. Both the bottle and the lid have their own number, which is recorded to maintain the accuracy of the analysis. The dishes must be clean, pre-weighed with maximum accuracy (a bottle with a lid together) - weight 1. Here you will either have to use precise scales (according to the methodology, scales should weigh up to 0.01 g, but will work with an accuracy of up to 0.1 g) . If it is not possible to use such scales, more soil is taken for analysis, but then it will take longer to dry.
Take a soil sample using a drill or shovel. Place them in the prepared bowl to fill half the volume (up to 2/3).
Weigh the container, lid and soil together - mass 2.
Place them to dry at a temperature of 100-105°C until the weight of the bottle stops changing. This way we find out mass 3.
Before the last weighing, close the container with a lid and let it cool in a tightly closed cabinet.
Drying allows you to know how much water was in the soil sample (mass 2 minus mass 3) and the weight of the dry soil (mass 3 minus mass 1). The mass of water is divided by the mass of dry soil and multiplied by 100% - this is how the soil moisture is determined at the time of sampling.

Material prepared by:

President of the Association of Gardeners of Russia (APYAPM), Doctor of Agricultural Sciences

D.s.-kh. Doctor of Science, Professor, Federal State Budgetary Educational Institution of Higher Professional Education "Saratov State Agrarian University named after. N.I. Vavilova"

Danilova T.A.
Specialist of the Association ASP-RUS, student of MichSAU

Using materials from Dr. Krzysztof Klamkowski,
Professor Waldemar Treder
Institute of Horticulture in Skierniewice

Methods for measuring soil moisture

Photo 1. Watering an intensive garden using drip irrigation

Fruit plants are characterized by a relatively high water content, which makes it necessary to irrigate gardens in our climatic conditions. Currently, the dominant plantings are those grafted on dwarf and semi-dwarf rootstocks, characterized by a poorly developed root system, thanks to which they absorb water from a smaller volume of soil. To optimize garden irrigation and obtain high yields with minimum consumption water, reliable criteria should be used to determine the irrigation regime.

It is advisable to monitor the water content in the soil and regulate its flow into plants only when necessary. Soil moisture levels should be monitored to avoid flooding of plants. Excessive irrigation leads to excessive water consumption, promotes leaching of minerals from the soil and restricts root respiration, which, in turn, can lead to stunted plant growth.

Photo 4. Drip irrigation transmission and control system

Properties of water in soil

The water properties of soil can be characterized by determining the amount of water it contains and measuring the force with which the water is bound (water potential). Potential values indicate the availability of water contained in the soil to plants. When soil water potential decreases, water becomes less available. There are a number of methods for measuring soil water content (or potential) values. Below is short review the most important and most frequently used methods for measuring soil moisture in horticultural practice.

Photo 5. Drip irrigation of an intensive apple orchard

Water potential measurement

Photo 6. Tensiometer

Tensiometer method

The tensiometer includes a ceramic filter, plastic pipe, vacuum pressure gauge (vacuum gauge). After it is filled with water, it is placed in the soil to determine the pressure. Water moves in ceramic element, which leads to a change in pressure in the pipe and changes in the meter reading. After hydration (or rain) in the soil, water does not enter the tube until a potential shift occurs between the soil and the tensiometer. Tensiometers are commercially available tubes of varying lengths for measuring water potential in soil at various depths. Tensiometers are often scaled from 0 to (-)100 centybarów (or other units of pressure). In practice, their readings are smaller and range from 0 (fully saturated soil water) to (-) 60 - 70 centibars (1 centibar corresponds to 1 kPa or 10 mbar).

The setup consists of a cavity with an opening close to the diameter of the tensiometer (for example, using a metal tube). The suspension with soil and water is poured into the hole of the tube, which is placed in the tensiometer.

Tensiometers are mainly used to decide when to start and stop irrigation. It is better to install them at different depths (for example, 20 cm and 40 cm). Based on the tensiometer readings, it is possible to determine the start time of irrigation (based on the readings of the tensiometer located closer to the surface) and the end time of irrigation (based on the data of the tensiometer located deeper).

Photo 7. Universal humidity controller with five sensors at different depths

Indications in the range of 10-30 centybarów correspond to the field moisture capacity at which soil moisture is optimal (for light soils - 30 -40 centybarów). Decrease in water potential (note that in measuring instruments the minus sign is often overlooked, as a result of which higher values are observed in the vacuum meter) indicates the condition of the soil, which needs less watering. Be sure to remove the tensiometer before winter sets in. IN last years A method has been developed that allows you to connect electronic tensiometers, with the help of which automatic accounting and data recording is carried out.

Photo 8. Humidity graph at various depths at drip irrigation using electronic tensiometers

Electrical resistance measurement

This method uses sensors (in the form of blocks, cylinders) made of porous material (gypsum), which house two electrodes connected to the meter. Electrical resistance the material depends on its water content, and this, in turn, determines the moisture content in the soil.

Photo 9. Electric humidity sensors

Holes are made in the soil to the required depth and sensors are placed in them. Close contact between the sensor element and the soil is essential (this applies to all moisture meters).
New types of sensors (gramilar matrix sensors) use a granular material that surrounds a special membrane and perforated covers made of steel or PVC. This ensures longer sensor life, faster response and more precise measurements. Sensors of this type can be used in automatic control systems for irrigation systems.

Measurements with dielectric probes TDR and EDR (capacitive)

Photo 10. TDR-100 sensor

Determination of soil moisture content using this method occurs by measuring the dielectric medium, which depends on soil moisture. Changes in the water content in the soil cause changes in its dielectric constant, which makes it possible to determine the relationship between these parameters.

With the development of technology, this method is becoming increasingly popular. Sensors of this type (particularly "displacement") are increasingly used to monitor soil moisture in the field and net moisture in substrates in protected crops. They are easy to use and the data they display is highly accurate. To improve the accuracy of the device, it must be calibrated to a specific soil type. According to the buyer's requirements, the manufacturer must provide a complete set of calibration various soils and substrates. Holes are dug in the garden and sensors are placed on the wall of the hole at the required depth. Soil moisture is determined by a portable meter. In recent years, such sensors have been found wide application in automatic irrigation control systems.

The advantage of this type of sensor is the ability to transmit measurements wirelessly (via radio or over long distances via mobile networks).

The soils are placed in a special PVC tube (several cm in diameter). The measurement is based on the movement of the probe along the tube (inserted and removed). Using a probe connected to the meter, you can read the water content in the selected soil profile (for example, 0 - 10 cm). The disadvantage of this method is that it is labor intensive. To give a correct assessment of the condition of the soil, one tube will not be enough. The more measurement points, the more reliable the information about the water content in the soil in the selected area will be.

There are also devices on the market in which probes are permanently placed in the pipe at a selected depth. The data is captured automatically and transmitted to the researcher. The cost of such devices is much higher.

Photo 11. Intensive garden with drip irrigation

It must be remembered that timely and correct determination of soil moisture allows you to reduce consumption. water resources and associated indirect costs of irrational use of fertilizers, crop loss and deterioration in product quality. Calculation methods and recommendations for optimal level humidification make it possible to determine exact amount water for plants, which prevents the leaching of fertilizers, stimulants and herbicides into the lower layers of the soil, and also eliminates water shortages for plants, allowing for a high yield of environmentally friendly products.

The thermostat-weight method is the main and most accurate method for determining soil moisture. This method is also simple and, despite a certain time investment, allows you to do without expensive equipment.

To determine humidity, the following tools and accessories are required:
1. A drill for taking samples 60-100 cm long (depending on the depth of the root layer of the soil), on which marks are applied every 10 cm. The photo shows the tip.
2. Heat-resistant cups (bugs), usually aluminum, which are pre-weighed and the empty weight is applied to the lid. It is convenient to choose a box where the cups are tightly placed for transportation to the field.
3. Scales with a division value of 0.1 g (or 0.01 g) and a maximum measurable weight of at least 200 g
4. Thermostat drying cabinet with a drying temperature of 105°C

The sampling process is as follows:

Going to required quantity cups, plate, knife and soil drill.
After arriving at the site for taking soil samples, a place is selected where there is a characteristic density of crops (plantings) of plants. For the accuracy of the experiment, it is necessary to choose a sampling location near the root system of the plant (in a row, if the plants grow on a ridge, on the ridge itself). After choosing a place, lightly trample it (but do not compact it), this is necessary in order to dry upper layer during the process it did not crumble inside the hole.
Then place a plate next to it and a cup for soil on it. You can do without a plate if the soil is dry and nothing sticks to the bottom of the cup.

Next, use a drill to pierce the soil to the first mark, turn the drill slightly and remove it. Using a knife, carefully pour the soil into a cup and immediately close it tightly to prevent moisture evaporation and place it in a box.
A second sample is taken to the next mark. After the drill has been removed, starting from the second mark, it is necessary to cut off the soil above the 10 cm mark, because This is the soil that crumbled or was cut off by the tip during the process of immersing the drill into the soil.
It should look like this:

It should be noted that the tip must be thoroughly cleaned of soil before each dive.
If the soil in the lower layers is moist and does not crumble (or the fence is carried out on heavy and medium soils), then to speed up the process, you can clean out the required layer and then throw away the remains.

Note. For the accuracy of the experiment, it is necessary to take samples at one point in triplicate.

After filling all the cups, they are carefully (so that they do not mix) transported to the laboratory where they are weighed and the data is entered into a log.

To automate and speed up calculations, we use MS Excel. Fill in the columns No. of the bottle, weight of the empty cup, weight of the cup with wet soil. open the glass and place it on the tray.

Next, the samples are placed in a drying cabinet in which the temperature is set to 105 degrees C, and dried for at least 6 hours.
After drying, remove the tray and immediately close the cups so that moisture from the air is not adsorbed into the soil. Then we cool the cups for 10-15 minutes and weigh them, filling in the column in the table with the weight of the cup with dry soil.

The calculation in the table is carried out as follows:
Column “Mass of dry soil (indicated O in the figure)” = “weight of the weighing bottle with dry soil (N)” - “weight of the weighing bottle (L)”
Column “mass of evaporated water (P)” = “weight of a bottle with wet soil (M)” - “mass of a bottle with dry soil (N)”
Column "percentage of moisture (R) = "weight of water (P)" / "weight of dry soil (O)" * 100%

To find out the amount of moisture in the soil as a percentage of the minimum moisture capacity, you need to know the amount of water that the soil layer is able to hold in its pores without being discharged into the lower layers. This is determined experimentally using flooded areas on which humidity is measured for 3-5 days (depending on the type of soil), when the relative humidity value is established at a more or less constant level - this should be considered the value of 100% NV (lowest moisture capacity or PPV - maximum field moisture capacity).

Current soil moisture value in %НВ = “rel. humidity (R)" / "rel. value humidity at 100% HB * 100%

To determine the soil moisture of the root layer, it is necessary to take the average value of all layers to the desired depth.
To speed up calculations of irrigation rates, you can create a table of moisture reserves (usually in t/ha or cubic m/ha) in different soil layers and at different meanings%NV. After this you can quickly calculate required amount irrigation water for the actual NV value and the planned NV value, the difference is the irrigation rate. At in different ways The watering rate must be increased slightly, taking into account losses due to evaporation, runoff, etc. You can learn more about the norms, techniques and methods of watering from ours.

Good luck in your work and high yields!

A.M. Menshikh, Ph.D.