GOST 27593-88

UDC 001.4:502.3:631.6.02:004.354

Group C00

INTERSTATE STANDARD

Terms and Definitions

soils. Terms and definitions

ISS 01.040.13

Date of introduction 01.07.88

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the State Agro-Industrial Committee of the USSR

2. APPROVED AND INTRODUCED BY Decree State Committee USSR according to the standards of 23.02.88 No. 326

3. The standard fully complies with ST SEV 5298-85

4. REPLACE GOST 17.4.1.03-84

5. REFERENCE REGULATIONS AND TECHNICAL DOCUMENTS

6. REPUBLICATION. November 2005

This International Standard establishes terms and definitions of concepts in the field of soil science.

The terms established by this standard are mandatory for use in all types of documentation and literature that are within the scope of standardization or use the results of this activity.

This standard should be used in conjunction with GOST 20432.

1. Standardized terms with definitions are given in Table. one.

2. One standardized term is established for each concept.

The use of terms - synonyms of the standardized term is not allowed. Synonyms that are unacceptable for use are given in Table. 1 as reference and marked with "Ndp".

2.1. For individual standardized terms in Table. 1 are given as reference short forms that are allowed to be used in cases that exclude the possibility of their different interpretation.

2.2. The above definitions can be changed, if necessary, by introducing derivative features into them, revealing the meaning of the terms used in them, indicating the objects included in the scope of the concept being defined. Changes should not violate the scope and content of the concepts defined in this standard.

Table 1

3. An alphabetical index of the terms contained in the standard in Russian is given in Table. 2.

4. Terms and definitions of concepts established in ST SEV 5298-85, but not used in the USSR, are given in the Appendix.

5. Standardized terms are in bold, their short form is in light, and invalid synonyms are in italics.

table 2

ALPHABETIC INDEX OF TERMS IN RUSSIAN LANGUAGE

APPENDIX

Reference

GOST 26213-91

Group C09

STATE STANDARD OF THE UNION OF THE SSR

Methods for determining organic matter

soils. Methods for determination of organic matter

OKSTU 9709

Introduction date 1993-07-01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the All-Union Production and Scientific Association "Soyuzselkhozkhimiya"

DEVELOPERS

L.M.Derzhavin, S.G.Samokhvalov (head of development), N.V.Sokolova, A.N.Orlova, K.A.Khabarova, V.G.Prizhukova, S.Ya.Privalenkova

2. APPROVED AND INTRODUCED BY Decree of the Committee for Standardization and Metrology of the USSR of December 29, 1991 N 2389

3. Term of verification - 1996

4. REPLACE GOST 26213-84

5. REFERENCE REGULATIONS AND TECHNICAL DOCUMENTS

This International Standard specifies photometric and gravimetric methods for the determination of organic matter in soils, overburden and wall rocks.

General requirements for analysis - according to GOST 29269.

1. DETERMINATION OF ORGANIC MATTER BY THE TYURIN METHOD IN THE CINAO MODIFICATION

1. DETERMINATION OF ORGANIC SUBSTANCE BY THE METHOD
TYURINA IN MODIFICATION TsINAO

The method is based on the oxidation of organic matter with a solution of potassium dichromate in sulfuric acid and the subsequent determination of trivalent chromium, equivalent to the content of organic matter, on a photoelectric colorimeter.

The method is not suitable for samples with a mass fraction of chloride greater than 0.6% and samples with a mass fraction of organic matter greater than 15%.

The limit values ​​of the relative error of the analysis results for a two-sided confidence level of 0.95 are in percent (rel.):

20 - with a mass fraction of organic matter up to 3%;

15 - St. 3 to 5%;

10 - St. 5 to 15%.

1.1. Sample selection

1.1.1. Sampling is carried out according to GOST 28168, GOST 17.4.3.01 and GOST 17.4.4.02 - depending on the objectives of the research.

1.1.2. A representative sample weighing 3-5 g is taken from the ground soil or rock for fine grinding. Before grinding, undecomposed roots and plant residues visible to the naked eye are removed from the sample with tweezers. Then the sample is completely crushed and passed through a wicker sieve with holes with a diameter of 0.25 mm. For fine grinding, mortars and grinding devices made of porcelain, steel and other hard materials are used.

1.2. Equipment and reagents

Photoelectrocolorimeter.

Bath water.

Torsion scales or others with an error of not more than 1 mg.

Heat-resistant glass test tubes with a capacity of 50 cm3 in accordance with GOST 23932.

Stand for test tubes.

Burette or dispenser for measuring 10 cm of chrome mixture.

Glass sticks 30 cm long.

Cylinder or dispenser for measuring 40 cm of water.

A rubber bulb with a glass tube or a device for barbation.

Burette with a capacity of 50 ml.

Volumetric flasks with a capacity of 1 dm.

Porcelain mug with a capacity of 2 dm.

Flask conical with a capacity of 1 dm.

Conical flasks or technological containers with a capacity of at least 100 ml.

Ammonium-iron (II) sulfate (Mohr's salt) according to GOST 4208 or iron (II) sulfate 7-water according to GOST 4148.

Potassium hydroxide according to GOST 24363.

Potassium dichromate according to GOST 4220.

Potassium permanganate, standard titer for preparing a solution of concentration (KMnO) = 0.1 mol / dm (0.1 N).

Sodium sulfite according to GOST 195 or sodium sulfite 7-water according to TU 6-09 5313.

Sulfuric acid according to GOST 4204 concentrated and concentration solution (HSO)=1 mol/dm.

Distilled water.

Ashless filters, with

blue tape.

1.3. Preparation for analysis

1.3.1. Preparation of the chromium mixture

(40.0 ± 0.1) g of finely ground potassium dichromate is placed in a volumetric flask with a capacity of 1 dm3, dissolved in water, bringing the volume to the mark, and poured into a porcelain mug. To the prepared solution is poured in portions of 100 cm 3 with an interval of 10-15 minutes 1 dm of concentrated sulfuric acid. The mug with the solution is covered with glass and left to cool completely.

The solution is stored in a dark glass bottle.

1.3.2. Preparation of a reducing agent solution - Mohr's salt solution of concentration [(NH)SOFеSO 6HO] ± 0.1 mol / dm or a solution of iron (II) sulfate 7-aqueous concentration (FeSO 7HO) = 0.1 mol / dm

(40.0 ± 0.1) g of Mohr's salt or (27.8 ± 0.1) g of 7-aqueous iron (II) sulfate is dissolved in 700 ml of sulfuric acid solution with concentration (HSO) = 1 mol / dm, filtered through double pleated filter into a 1 liter volumetric flask and dilute to volume with water.

The concentration of the solution is checked by titration against a solution of potassium permanganate concentration (KMnO) = 0.1 mol / dm, prepared from a standard titer. For titration in three conical flasks, 10 cm3 of the prepared reducing agent solution is measured with a burette, 1 cm3 of concentrated sulfuric acid and 50 cm3 of water are added, and the concentration is titrated with a solution of potassium permanganate until a faint pink color appears, which does not disappear within 1 min. To calculate the correction factor, use the arithmetic mean of the results of three titrations.

The correction factor () is calculated by the equation

where is the volume of potassium permanganate solution used for titration, cm;

- the volume of the reducing agent selected for titration, see

The solution is stored in a dark glass bottle, to which a burette is attached using a siphon. To protect the solution from oxidation by air oxygen, a Tishchenko bottle with an alkaline solution of sodium sulfite is attached to the bottle. The correction factor is checked at least every 3 days.

1.3.3. Preparation of an alkaline solution of sodium sulfite

(40.0±0.1) g of anhydrous or (80.0±0.1) g of 7-aqueous sodium sulphate is dissolved in 700 cm3 of water. (10.0±0.1) g of potassium hydroxide is dissolved in 300 ml of water. The prepared solutions are mixed.

1.4. Conducting an analysis

1.4.1. Oxidation of organic matter

The mass of a soil or rock sample for analysis is determined based on the expected content of organic matter, according to Table 1.

Table 1

Soil or rock samples are weighed with an error of not more than 1 mg and placed in test tubes installed in racks. 10 cm3 of chromium mixture is added to the samples. A glass rod is placed in each test tube and the sample is thoroughly mixed with the chromium mixture. The test tube racks are then lowered into a boiling water bath. The water level in the bath should be 2-3 cm higher than the level of the chromium mixture in the test tubes. The duration of suspension heating is 1 hour from the moment the water boils in the bath after the test tubes are immersed in it. The contents of the tubes are stirred with glass rods every 20 minutes. After 1 hour, the racks with test tubes are placed in a water bath with cold water. After cooling, 40 ml of water is poured into the test tubes. Then the sticks are removed from the test tubes, the suspensions are thoroughly mixed by air bubbling and left to settle solid particles and completely clarify the supernatant part of the solution. Instead of settling, it is allowed to filter suspensions through ashless filters (blue tape).

1.4.2. Preparation of reference solutions

Pour 10 ml of chromium mixture into nine test tubes and heat them for 1 hour in a boiling water bath together with the analyzed samples. After cooling, the volumes of distilled water and reducing agent solution indicated in Table 2 are poured into the test tubes. The solutions are thoroughly mixed by air bubbling.

table 2

1.4.3. Photometry of solutions

Photometry of solutions is carried out in a cuvette with a translucent layer thickness of 1-2 cm relative to reference solution N 1 at a wavelength of 590 nm or using an orange-red light filter with a maximum transmission in the region of 560-600 nm. The solutions are carefully transferred into the cuvette of the photoelectric colorimeter without disturbing the precipitate.

1.5. Results processing

1.5.1. The mass of organic matter in the analyzed sample is determined by the calibration curve. When constructing a calibration graph, the mass of organic matter in milligrams corresponding to the volume of the reducing agent in the reference solution is plotted along the abscissa axis, and the corresponding reading of the instrument is plotted along the ordinate axis.

1.5.2. The mass fraction of organic matter () in percent is calculated by the equation

where is the mass of organic matter in the analyzed sample, found from the graph, mg;

- correction factor for the concentration of the reducing agent;

- sample weight, mg;

100 - conversion factor to percent.

1.5.3. Permissible relative deviations from the certified value of the standard sample for a two-sided confidence level of 0.95 are shown in Table 3.

Table 3

2. GRAVIMETRIC METHOD FOR DETERMINING THE MASS FRACTION OF ORGANIC MATTER IN PEAT AND PEAT SOIL HORIZONS

The method is based on determining the mass loss of a sample after calcination at a temperature of 525 °C.

2.1. Sample selection

Sampling for analysis is carried out according to GOST 28168, GOST 27784.

2.5.2. The mass fraction of organic matter in percent is calculated by the formula

where is the mass fraction of ash content,%.

2.5.3. Control of the accuracy of the results of analyzes - according to GOST 27784.



The text of the document is verified by:
official publication
M.: Publishing house of standards, 1992

GOST 23740-79

Group G39

STATE STANDARD OF THE UNION OF THE SSR

SOILS

METHODS FOR LABORATORY DETERMINATION OF THE CONTENT

ORGANIC SUBSTANCES

soils. Methods of laboratory determination

of organic composition

Introduction date 1980-01-01

DEVELOPED by the USSR State Committee for Construction

PERFORMERS

G.V. Sorokina, Ph.D. tech. sciences; N.P. Betelev, Ph.D. geol.-miner. sciences; R.S. Ziangirov, Dr. geol.-miner. sciences; I.S. Bocharova; T.A. Kudinova

INTRODUCED by the USSR State Committee for Construction

Member of the Board V. I. Sychev

APPROVED AND INTRODUCED BY Decree of the State Committee of the USSR for Construction of June 20, 1979 No. 89

Reissue. June 1987

This International Standard applies to sandy and clayey soils and specifies methods for the laboratory determination of organic matter content when examining these soils for construction purposes.

1. GENERAL PROVISIONS

1.1. To determine the content of organic matter in the soil, it is necessary to establish separately the amount of plant residues and humus.

1.2. Plant residues should be isolated from the soil in a dry or wet way, and then their amount should be determined.

1.3. To determine the amount of humus, it is necessary to determine the carbon content of decomposed organic substances in the soil - organic carbon (Corg).

To determine organic carbon, the following methods should be used:

oxidometric;

dry combustion.

1.4. The oximetric method should be used to determine organic carbon in sandy and clayey soils containing less than 10% humus, and in soils containing chlorides after removal of the latter.

The method is not allowed to be used to determine organic carbon in sandy and clayey soils of marine, estuary, oxbow, lacustrine and marsh origin.

1.5. The method of dry combustion in oxygen should be used to determine organic carbon in soils of marine, estuary, oxbow, lacustrine, marsh origin and in soils containing more than 10% humus after removal of carbonates.

1.6. The content of organic carbon in the soil should be determined as a percentage of the dry matter of the sample and converted to the quantitative content of humus using a factor of 1.724.

1.7. Selection and transportation of undisturbed soil samples should be carried out in accordance with GOST 12071-84.

1.8. Organic matter should be determined for an average soil sample in an air-dry state.

The weight of the average soil sample must be at least 100 gf.

1.9. To carry out the test, it is necessary to prepare an air-dry soil sample by grinding in a porcelain mortar with a pestle with a rubber tip: to determine and isolate plant residues - up to the size of aggregates of 3-5 mm; to determine organic carbon - to a particle size of less than 0.25 mm, and then make a test for chlorides and carbonate content.

1.10. Sample weighing error should be no more than 0.01 gs when determining the amount of plant residues and no more than 0.0002 gs when determining organic carbon.

1.11. The number of parallel determinations of organic substances must be at least two.

The error of the results of parallel determinations should not exceed 2.5% of the average determined value. If the discrepancy between the results of two parallel determinations exceeds 2.5%, the number of determinations should be increased to three or more.

The arithmetic mean of the results of parallel determinations should be taken as the final result of the analysis.

1.12. The amount of organic substances should be determined to the second decimal place and recorded in a journal (see Appendix 2) indicating the method of determination (clauses 1.2 and 1.3).

1.13. The terms and definitions used in the standard are given in Appendix 1.

2. METHOD FOR DETERMINING PLANT RESIDUES

2.1. Plant residues should be isolated from an average air-dry soil sample and their amount determined as a percentage.

2.2. Equipment

Bath sand or water.

Glass funnel with a diameter of 14 cm according to GOST 25336-82.

Pear rubber.

Brush for sweeping particles from a sieve.

Magnifier.

Mixer.

Knife.

Tweezers.

Sieves with woven wire mesh No. 1 and 0.25 according to GOST 6613-86.

Sheet organic glass according to GOST 17622-72.

Cylinder (see Appendix 3).

Porcelain mortar according to GOST 9147-80, pestle according to GOST 9147-80 with a rubber tip.

Thermometer according to GOST 215-73, with measurement error up to 0.5°C.

Cloth or woolen fabric (a piece).

Porcelain cups according to GOST 9147-80.

Drying cabinet.

Spatula according to GOST 9147-80.

2.3. Conducting a test

2.3.1. The prepared soil should be thoroughly mixed and an average sample of at least 25 gauss should be taken using the square method. At the same time, a sample should be taken to determine the hygroscopic humidity in accordance with GOST 5180-84.

2.3.2. The sample taken must be placed on glass with paper placed under it (for the background). Plant residues should be carefully selected (under a magnifying glass), crushing lumps of soil with tweezers (dry method). To speed up the process of removing plant residues from the soil, an electrified organic glass plate should be used, and when large quantities plant residues, elutriate them in tap water (wet method).

A dry organic glass plate must be rubbed with a piece of woolen or cloth cloth and quickly held over the soil, distributed in a thin layer on glass or paper, making sure that clay particles are not attracted to the plate along with plant residues. The plate should be kept about 5 cm above the soil layer.

2.3.3. To elutriate plant residues, an average soil sample should be poured into a pre-weighed porcelain cup, weighed, moistened with water, and lightly rubbed with a pestle with a rubber tip so as not to damage plant residues. Then the sand should be clouded, for which the soil is poured with water, mixed and the top layer with clay particles is poured through a sieve with mesh No. 1 for 5-8 s into a large porcelain cup, making sure that no sand gets on the sieve. The operation must be repeated until the sand in the cup is completely washed out.

Plant residues on the sieve should be washed from clay particles and transferred to a weighed porcelain cup. Clay particles that have passed through a sieve should be shaken in a cup, allowed to settle, and plant residues that have passed through a sieve with mesh No. 1 should be poured through a sieve with mesh No. 0.25 into another cup.

Plant residues remaining on sieves with meshes No. 1 and 0.25 should be combined in one cup, and the water should be evaporated in a bath. All soil particles that have passed through the sieve should be transferred from the cup to the cylinder and the completeness of the release of plant residues should be checked (see Appendix 3).

2.3.4. Separated sand, clay particles and plant residues should be dried in an oven to constant weight at a temperature of 100-105°C and weighed with an error of not more than 0.01 gf.

2.4. Results processing

2.4.1. The amount of plant residues J(from) as a percentage should be calculated using the formula

where m(s0) is the weight of dry plant residues, gs;

m(s) - weight of dry soil, gf.

To recalculate the air-dry sample to dry, apply the coefficient

where W(g) - hygroscopic humidity in percent.

3. OXIDOMETRIC METHOD

3.1. The organic matter should be oxidized with potassium dichromate in a strongly acidic medium until carbon dioxide is formed, then the excess of potassium dichromate should be titrated with a solution of Mohr's salt and the content of organic carbon in the soil should be determined from the difference in the volumes of Mohr's salt spent on titration of potassium dichromate in the experiment without soil and in the experiment with soil.

3.2. Equipment and materials

3.2.1. Equipment

Bottles with lapped stoppers, 5000 ml.

10,000 ml bottle with ground stopper.

Burettes.

Laboratory scales according to GOST 24104-80 with weights according to GOST 7328-82.

Glass funnels according to GOST 25336-82 with a diameter of 3.5 and 10 cm.

Laboratory glass droppers according to GOST 25336-82.

Flat-bottomed conical flasks made of heat-resistant glass with a capacity of 100 and 2500-5000 ml.

Volumetric flask according to GOST 1770-74 with a capacity of 1000 ml.

Glass sticks.

Glass test tubes according to GOST 25336-82.

Flask type SPT (Tishchenko) in accordance with GOST 25336-82.

Watch glass.

Drying cabinet.

Porcelain cups according to GOST 9147-80 with a diameter of 5 and 9 cm.

Spatula according to GOST 9147-80.

3.2.2. materials

Potassium permanganate according to GOST 20490-75.

Nitric acid according to GOST 4461-77.

Phenylanthranilic acid.

Pyrogallol.

Sodium carbonate according to GOST 83-79.

Silver nitrate according to GOST 1277-75.

Salt of iron oxide and ammonium double sulphate (Mohr's salt) in accordance with GOST 4208-72.

3.3. Preparing for the test

3.3.1. An average sample weighing about 3 g should be taken by the method of squares from the soil (with removed plant residues and sifted through a sieve with mesh No. 1), pour distilled water and mix in a porcelain cup with a glass rod for 15 minutes.

3.3.2. The solution must be filtered into a test tube, acidified with a solution (1 N) of silver nitrate and mixed (by shaking). If a strong turbidity appears, chlorides should be removed from the soil before determining carbon by oxidation of organic matter with potassium dichromate.

3.3.3. To remove chlorides, it is necessary to take 25 g of soil prepared for analysis. A sample of soil should be placed in a glass, poured with distilled water, acidified with a few drops of sulfuric acid (1 N), and transferred to the filter by decantation.

Chlorides should be washed off in a dry sample of soil taken until the chlorine disappears (reaction to chlorine). The washed sample of soil from the filter should be transferred to a porcelain cup, dried to an air-dry state in a water bath and weighed after cooling.

To determine the carbon content, it is necessary to establish the ratio K1 between the initial weight of the soil taken and its weight after the removal of chlorides and drying

where m(1) is the weight of the air-dry sample taken to remove chlorides, gf;

m(2) - sample weight after removal of chlorides, g.

3.4. Conducting a test

3.4.1. An average sample weighing 10-20 gs should be further ground in a mortar to a particle size that completely passes through a sieve with mesh openings of 0.25 mm (to a state of powder), and thoroughly mixed.

The sample size should be from 0.05 to 1 g, depending on the expected humus content in accordance with the table.

3.4.2. At the same time, it is necessary to take a sample to determine the hygroscopic humidity in accordance with GOST 5180-84.

3.4.3. The soil sample should be weighed on a piece of tracing paper. The weight of the sample is determined by the difference between the weight of the tracing paper with the sample and the weight after pouring the sample into a 100 ml conical flask. The weighing error should be within ±0.0002 gs.

3.4.4. To a sample of soil with a burette, add 10 ml of a chromium mixture (0.4 N solution of potassium dichromate in dilute 1: 1 sulfuric acid). The solution from the buret is lowered from zero division drop by drop (slowly) observing the same time interval in parallel tests.

The contents of the flask should be gently stirred in a circular motion of the flask.

Flasks should be closed with funnels with a diameter of 3.5 cm to cool the water vapor and placed on a hot electric stove with a closed spiral or a sand bath*.

________________

* Boiling can be carried out in a thermostat for 30 minutes at a temperature of 150°C.

Boiling the solution should be continued for 5 minutes (without steam from the funnel); it should be barely noticeable, i.e., the release of carbon dioxide bubbles formed from the oxidation of soil organic matter should be plentiful, while the bubbles should be slightly larger than poppy seeds. The boiling time is counted from the moment the first relatively large gas bubble appears.

During boiling, the color of the solution should change from orange to brownish brown. If a green color appears, which indicates the complete consumption of chromic acid and its possible lack of humus oxidation, the experiment should be repeated, reducing the soil weight.

At the end of boiling, the flask should be removed from the stove (bath) or removed from the thermostat, rinse the funnel with a small amount of water, allow the flask to cool to room temperature and carry out titration.

3.4.5. Titration of excess chromium mixture should be carried out in the presence of phenylanthranilic acid. Before titration, it is necessary to wash the neck of the flask from the rinse with distilled water (the amount of water should not exceed 20 ml), add 5-6 drops of a 0.2% solution of phenylanthranilic acid and titrate with Mohr's salt solution (0.2 N) until the color changes to green. Mohr's salt solution at the end of the titration should be added dropwise, all the while stirring the solution with vigorous shaking.

3.4.6. Before the start or at the end of the test, it is necessary to conduct an experiment without soil to establish the ratio between solutions of the chromium mixture and Mohr's salt under conditions similar to paragraph 3.4.4. Pour 10 ml of chromium mixture into two conical flasks with a capacity of 100 ml, add about 0.2 g of calcined pumice stone ground into powder at the tip of a thin spatula for even boiling (sand is not allowed for this purpose) and boil the contents in the flasks for 5 minutes, as specified in clause 3.4.4.

After cooling, the boiled chromium mixture should be titrated with a 0.2 N solution of Mohr's salt in accordance with paragraph 3.4.5 and the average amount of Mohr's salt used for titration of 10 ml of the chromium mixture from two experiments should be determined.

3.4.7. Determination of organic carbon should be carried out in two parallel tests. It is advisable to first carry out one determination of organic carbon for a series of soil samples,

3.5. Results processing

The amount of organic carbon Corg in percent per dry sample of soil should be calculated using the formula

where a is the amount of Mohr's salt solution used to titrate 10 ml of the chromium mixture in the "experiment with pumice", ml;

b is the amount of Mohr's salt used to titrate the excess of the chromium mixture in the experiment with soil, ml;

n - the normality of the solution of Mohr's salt, established by its titration with a solution of permanganate (0.1 N);

0.003 - the value of 1 mgs.-eq. carbon*;

g - sample of dry soil, gf.

___________

To recalculate an air dry sample to a dry one, a coefficient is used

where W(g) is the hygroscopic soil moisture.

In the presence of chlorides in the soil, the coefficient K1 is used to recalculate Corg (clause 3.3.3).

4. DRY BURNING METHOD

4.1. Oxidation of the carbon-free sample of soil should be carried out by burning this sample in an oxygen flow at a temperature of 950-1000°C until the release of carbon dioxide, which is taken into account by the gas-volume method, ceases, with subsequent conversion to carbon.

4.2. Equipment and materials

4.2.1. Equipment

Autotransformer LATR-1 M.

Sand bath or water bath.

Cylinder oxygen with a reducer in accordance with GOST 13861-80.

Aneroid barometer.

Laboratory scales according to GOST 24104-80 with weights according to GOST 7328-82.

Gas analyzer GOU-1 according to GOST 10713-75.

Glass gasometer according to GOST 25336-82.

Funnels glass with a diameter of 10-14 cm in accordance with GOST 25336-82.

Kaliaapparat in accordance with GOST 25336-82 or a bottle with a nozzle CH (Drexel) in accordance with GOST 25336-82.

Columns for drying gases, 2 pcs.

Two-way valves according to GOST 7995-80.

Hook made of durable low-carbon wire.

Porcelain boats according to GOST 9147-80.

Electric tubular horizontal furnace, providing heating up to 1000 °C, type SUOL-025 1/12-M1.

Tile with a closed spiral.

Rubber stoppers according to GOST 7852-76.

The mesh is copper.

Wash bottles according to GOST 25336-82, 3 pcs.

Crucibles with a capacity of 50 cubic cm in accordance with GOST 9147-80.

Tube U-shaped according to GOST 25336-82.

The tube is quartz or porcelain, 750 mm long and 18-20 mm in inner diameter.

Rubber tube with an inner diameter of 3-4 mm.

Porcelain cups according to GOST 9147-80, 2 pcs.

Drying cabinet.

Desiccator according to GOST 25336-82 with calcium chloride 2-water according to GOST 4161-77.

4.2.2. materials

Chromic anhydride according to GOST 3776-78.

Ascarite with a grain size of 3-5 mm or soda lime.

Glass wool.

Distilled water according to GOST 6709-72.

Universal indicator paper or litmus.

Potassium oxide hydrate (potassium hydroxide).

Potassium dichromate (bichromate) according to GOST 2652-78.

Calcium chloride anhydrous.

Oxygen gaseous according to GOST 5583-78, obtained by deep air cooling.

Sulfuric acid according to GOST 4204-77.

Hydrochloric acid according to GOST 3118-77.

Methyl orange.

Sodium hydroxide (caustic soda) according to GOST 4328-77.

Quartz powder.

Filters.

4.3. Preparing the setup for testing

4.3.1. To prepare the installation (see drawing) for testing, vessel 17 and potassium apparatus 2 should be filled with a 40% solution of potassium oxide hydrate. Pour 450 ml of distilled water into equalizing flask 16, add a few drops of sulfuric acid and 2-3 drops of methyl orange (colored liquid). Distilled water should be poured into the jacket of the gas measuring burette 14 and the jacket of the refrigerator 10.

4.3.2. The gasometer 1 should be filled with oxygen, the column for drying gases 3 with soda lime or ascarite, the column for drying gases 4 with anhydrous calcium chloride. Glass wool should be placed in the U-shaped tube 7, and copper mesh should be placed in the porcelain tube 6 from the side facing the U-shaped tube. A solution of chromic anhydride in sulfuric acid should be poured into vessel 8 (see Appendix 5, item 3), and into vessel 9 - a solution of potassium dichromate in sulfuric acid (see Appendix 5, item 2).

4.3.3. The installation must be checked for leaks. The installation is hermetic if the levels of solutions in vessel 17 and measuring burette 14 remain unchanged for 10-15 minutes. If the installation is leaking, it should be disassembled, wipe all taps with a soft cloth, lubricate with Vaseline, reassemble and check for leaks again.

4.3.4. Porcelain tube 6 and boats for combustion should be calcined in a stream of oxygen at a temperature of 1000 ° C.

Boats should be stored in a desiccator.

The section of the desiccator cover should not be covered with lubricants, since oxygen is explosive when oils enter.

4.3.5. In case of tightness, oxygen should be passed through the installation for 15-20 minutes at an oven temperature of 1000 °C, after which the experiment should be carried out without a boat. The experiment without a boat should be carried out in the same way as incineration (see paragraph 4.4), but in this case, the indication of scale 15 after the absorption of gases by potassium caustic should be zero. If the liquid level in buret 14 after treatment with potassium gases became caustic above zero, the experiment without a boat should be repeated.

Installation for the determination of carbon of organic compounds by dry combustion

1 - gasometer with oxygen; 2 - potassium apparatus with potassium caustic; 3 - column for drying gases with ascarite or soda lime; 4 - column for drying gases with calcium chloride; 5 - electric tubular horizontal furnace; 6 - porcelain or quartz tube; 7 - U-shaped tube with glass wool to retain mechanical impurities; 8 - absorption vessel with a solution of chromic anhydride in sulfuric acid to retain sulfur oxides; 9 - absorption vessel with a solution of potassium dichromate in sulfuric acid, to retain nitrogen oxides; 10 - refrigerator; 11 - three-way valve; 12 - valve for connecting the gas measuring burette with the atmosphere; 13 - thermometer; 14 - gas measuring burette No. 2; 15 - movable scale of the gas measuring burette; 16 - leveling bottle; 17 - a vessel filled with a solution of caustic potash to absorb carbon dioxide

4.4. Sample preparation for testing

4.4.1. Before burning the soil, it is necessary to check it for carbonate content: for this, an average sample (1 gs) should be taken from the soil sample prepared for testing using the square method in a porcelain cup and 2-3 drops of 10% hydrochloric acid should be added. If there is no effervescence, there are no carbonates, the effervescence is strong and prolonged - less than 10% carbonates, the effervescence is violent and prolonged - more than 10% carbonates. The carbonates must be removed in a manner that does not decompose the organic matter.

4.4.2. To destroy carbonates, a solution of 5% sulfuric acid should be used.

In a porcelain crucible with a capacity of 50 ml, it is necessary to take an average sample of soil weighing 3 g using the square method, pour 3-4 ml of distilled water, stirring the soil with a glass rod. Then pour a solution of 5% sulfuric acid into the crucible from a buret or separating funnel. To avoid violent boiling and splashing of the suspension, the acid should be poured in small portions, stirring the soil all the time. When the release of gas bubbles formed during the reaction stops, it is necessary to check the pH of the suspension using universal indicator paper (pH 1-10). Bringing the reaction of the suspension to acidic (pH 5.5-5.0), add another 0.5 ml of a 5% sulfuric acid solution. After thorough mixing, remove the glass rod from the crucible and carefully rinse it with distilled water from the washer. Transfer the crucible to a plate with a closed spiral, boil the suspension for 5 minutes at low heat and check the reaction of the liquid using indicator paper.

If the pH of the suspension remains acidic, then the destruction of carbonates is complete.

In the presence of an alkaline reaction (pH> 7), a little more sulfuric acid is added and the suspension is boiled again for 5 minutes.

After the end of the destruction of carbonates, the crucible is removed from the plate. Neutralize the suspension and determine the reaction on indicator paper by adding dropwise 2% sodium hydroxide solution to pH 6.5.

The crucible should be transferred to a sand bath, the contents evaporated, and then dried in an oven for 5 hours.

After cooling in a desiccator, the crucibles with precipitates should be weighed with an error of ± 0.0002 g.

4.4.3. To calculate carbon, it is necessary to establish the ratio between the initial weight of the soil taken and its weight after the destruction of carbonates

where m(1) is the weight of the air-dry sample before the destruction of carbonates, gs;

m(2) is the weight of the dried sample after the destruction of carbonates, gs.

Notes:

1. In the process of acid treatment, the destruction of carbonate minerals and the formation of sulfate salts occur. In this case, the weight of the soil sample, as a rule, increases;

2. The dried sample should be stored in a desiccator until carbon is determined.

4.4.4. From non-carbonate pounded soil, a sample should be taken with an error of ± 0.0002 gauss to determine the carbon of organic compounds.

The sample size is determined by the estimated humus content:

for sands. . ............... 1 gs

for clay. . . .............. 0.5 gs

for soils with a humus content of more than 10% ... 0.01-0.03 gf

4.5. Conducting a test

4.5.1. Determination of carbon of organic compounds should be carried out using the installation (see drawing).

4.5.2. The gas-measuring burette 14 should be filled to the top with colored liquid from the equalizing bottle 16, for which purpose open the valve 12 and raise the equalizing bottle to the upper position, then close the valve 12.

4.5.3. A sample of soil should be placed in a pre-calcined boat, sprinkled with quartz powder on top to prevent flash and, using a hook, insert the boat into the central part of the porcelain tube 5, preheated to 950-1000 ° C, then quickly close the tube 6 with a stopper, through the hole in which oxygen for combustion, for which you should open the valve of the gas meter 1 and let oxygen in at a rate of 3-4 bubbles per second. Bubbles are counted in a caliper 2.

4.5.4. Valve 11, which connects porcelain tube 6 with measuring burette 14, should be kept closed for some time (~30 s) so that combustion starts under pressure. Then the valve 11 should be opened, connecting the porcelain tube 6 with the measuring burette 14. The gas mixture (oxygen and carbon dioxide) from the porcelain tube 6, passing through the vessels 7,8,9 and the refrigerator 10, enters the measuring burette 14, displacing the colored liquid. Filling the burette with gas takes about 3 minutes. Then it is necessary to stop the oxygen supply, close the valve of the gasometer 1 and close the valve 11 to seal the measuring burette.

4.5.5. By moving the equalizing bottle 16, it is necessary to set the surface of the liquid in it at the same level as the liquid in the burette 14 and to combine the zero division of the movable scale 15 of the burette 14 with these levels.

4.5.6. Having put the valve 11 in the position connecting the measuring burette 14 with the vessel 17, and raising the equalizing bottle 16 to the upper position, it is necessary to transfer the gas mixture from the burette 14 to the vessel 17; then, lowering the leveling bottle 16, you should transfer the gas from the vessel 17 back to the burette 14. This operation is repeated twice for better absorption of carbon dioxide.

4.5.7. Then you should close the valve 11 connecting the burette 14 with the vessel 17, and set the surface of the liquid in the equalizing bottle 16 at the same level with the liquid in the burette 14. Reading the position of this level on the scale 15 of the burette gives the amount of carbon dioxide absorbed in the vessel 17, i.e. carbon content in the analyzed sample.

4.5.8. After the transfer of gas from vessel 17 to burette 14, before reading the liquid level, it is necessary to establish the complete flow of liquid drops from the walls of the burette (usually about 1 min).

4.5.9. The operation of burning a sample of soil in an oxygen flow is repeated 4-6 times until the release of carbon dioxide ceases. To calculate the carbon content in a sample of soil, the amount of carbon dioxide released during its combustion should be summed up. After the test, it is necessary to measure the temperature of the gas in the buret 14 using a thermometer 13 and the atmospheric pressure using a barometer.

4.6. Results processing

4.6.1. The amount of organic carbon Corg in percent should be calculated using the formula

where a is the scale reading of the gas measuring burette (sum of readings) of the content of organic carbon in the sample, %;

p - correction factor for temperature and pressure, taken in accordance with the table in Appendix 6;

g - sample weight, gf.

To recalculate an air-dry sample to a dry one, the coefficient K should be applied (clause 3.5). The calculated C(lim) value for carbonate soil determines the percentage of organic carbon in the soil from which carbonates (insoluble residue) have been removed.

4.6.2. Recalculation of C (ogr) for carbonate soil should be carried out according to the formula

where K(2) is the content correction.

APPENDIX 1

TERMS AND DEFINITIONS

APPENDIX 2

JOURNAL OF THE DETERMINATION OF ORGANIC SUBSTANCES IN THE SOIL

1. Quantity log

plant debris in the ground

Journal checked "__" ___________19___________________________________________________

2. Log determination by oxidometric

soil organic carbon method

Executor___________________________________________________________________

(last name, first name, patronymic, signature)

The magazine checked "___" ________ 19_____ __________________________________________

(position, surname, name, patronymic, signature)

3. Dry burning log

the amount of organic carbon in the soil

Executor___________________________________________________________________

(last name, first name, patronymic, signature)

Journal checked "____" ___________ 19__ _______________________________________________

(position, surname, name, patronymic, signature)

APPENDIX 3

CHECKING THE PURITY OF HERBAL ISOLATION

RESIDUE FROM THE GROUND

To check the purity of the separation of plant residues from the soil, it is recommended that the clay sediment remaining in the porcelain cup (clause 2.3.3) be transferred by decantation through a sieve with a mesh No. 0.25 into a cylinder (see drawing) and topped up with water to the mark. Then you should measure the temperature of the water, shake the soil transferred into the cylinder with a stirrer for 1 min and pour a 100 mm suspension layer into a weighed porcelain cup through the upper fitting into a weighed porcelain cup after a time interval indicated depending on the temperature in the table.

Through the lower fitting, drain the lower layer of the suspension into another cup, if plant residues remain on the walls of the cylinder, collect them with your finger and add to the plant residues remaining on the sieve. Evaporate the suspensions collected in the dishes in a bath and check each fraction for the purity of the isolation of plant residues. The plant residues remaining on the walls of the cups during the evaporation process should be collected using an organic glass plate and added to the plant residues isolated earlier.

Table 1

Cylinder for checking the completeness of the extraction of plant residues

APPENDIX 4

Reference

ORGANIC SUBSTANCES IN GROUND BY OXIDATION

WITH POTASSIUM DICHROME

1. Preparation of a chromium mixture (0.4 N. solution of potassium dichromate in dilute 1: 1 sulfuric acid)

Dissolve 40 g of crystalline potassium dichromate ground in a porcelain mortar in 500-600 ml of distilled water and filter through a paper filter into a 1000 ml volumetric flask.

The solution is brought to the mark with distilled water and poured into a heat-resistant glass flask with a capacity of 2.5-5 liters.

To the solution is poured (under draft) in small portions (100 ml each) 1 liter of sulfuric acid (density 1.84 gf / cc) with careful and repeated stirring. The solution is closed with a funnel, left to stand for complete cooling until the next day, mixed again and poured into a bottle with a ground stopper. Store the solution in a dark place.

2. Preparation of 0.2 N solution of Mohr's salt

To prepare a 0.2 N solution, place 80 g of Mohr's salt (only blue crystals are used, strongly browned ones are discarded) in a 1-liter flask and pour a 1-N solution of sulfuric acid to about 2/3 of its volume. The solution is shaken until the salt is completely dissolved, filtered through a double folded filter, distilled water is added to the mark and mixed well.

The solution is stored in a bottle isolated from air (see drawing).

An alkaline solution of pyrogallol is placed in a Tishchenko flask.

To prepare an alkaline solution of pyrogallol, dissolve 12 g of pyrogallol in 50 ml of water and mix with a solution of caustic potash (180 g of potassium hydroxide per 300 ml of water).

The normality of Mohr's salt solution is established and checked by a 0.1 N solution of potassium permanganate. In a conical flask with a capacity of 250 ml, measure 10 ml of Mohr's salt solution with a burette, add 50 ml of distilled water and 1 ml of sulfuric acid (density 1.84 gf / cc, titrate with 0.1 N potassium permanganate solution until a slightly pink color does not disappear in for 1 minute Titration is carried out in triplicate.

where

3. Preparation of a solution of phenylanthranilic acid

Weigh out 0.2 g of phenylanthranilic acid and dissolve in 100 ml of 0.2% soda solution.

To improve the wetting of the indicator powder, the sample taken must first be mixed in a porcelain cup with a glass rod with several milliliters of a 0.2% soda solution to a pasty state. Then add the rest of the soda solution with thorough mixing.

Installation for storage of titrated solution of Mohr's salt

1 - safety tube with crystals of iron sulfate;

2 - Tishchenko bottle with an alkaline solution of pyrogallol

APPENDIX 5

Reference

PREPARATION OF SOLUTIONS FOR DETERMINATION OF THE CONTENT

ORGANIC CARBON COMPOUNDS IN THE GROUND

DRY BURNING

1. Preparation of a 40% solution of potassium hydroxide

Dissolve 40 weight parts of granulated potassium hydroxide in 60 weight parts of distilled water. The density of a 40% solution of potassium hydroxide is 1.40 gf / cc. If the density of the potassium hydroxide solution prepared according to the weight ratios of the components turned out to be lower than 1.40 gf / cc, more granulated potassium hydroxide is added, bringing the density of the solution to 1.40 gf / cc.

2. Preparation of a solution of potassium dichromate in sulfuric acid.

Dissolve 0.3 gs of crystalline potassium dichromate crushed in a porcelain mortar in 50 ml of sulfuric acid with a density of 1.84 gs / cc. If it is necessary to obtain a larger volume of solution, the amount of potassium dichromate and sulfuric acid is increased in the same ratio.

3. Preparation of a solution of chromic anhydride in sulfuric acid.

Take 30 ml of distilled water and add 12 gs of crystalline chromic anhydride ground in a porcelain mortar, dissolved in 15 ml of sulfuric acid with a density of 1.84 gs/cc.

If it is necessary to obtain a larger volume of solution, the amount of all three components is increased in the same ratio.

APPENDIX 6

Reference

Corrections for atmospheric pressure and temperature

to the gasometric determination of carbon

Note. The table contains correction factors for measuring burettes calibrated at 16°C and 760 mmHg. Art., using a 2% solution of sulfuric acid as a barrier liquid. For other measurement conditions (pressure below 730 and above 770 mm Hg), correction factors should be taken from Table. 1 attached to the device GOU-1.

The text of the document is verified by:

official publication

M: Standards Publishing House, 1987

Spectrophotometric determination of humus content in soil according to Orlov and Grindel

The method of volumetric determination of humus according to Tyurin, which is most often used in mass analyzes, is quite accurate with considerable simplicity and speed of determination. The introduction of a photometric end instead of titration makes it possible to further simplify the course of analysis due to the fact that there is no need to prepare titrated solutions in general, and instead of titration, optical density is measured on a photoelectrocolorimeter and spectrophotometer.

A number of options for the colorimetric and photometric determination of humus are proposed, which differ in the details of execution. Most authors resort to dilution and settling of the suspension after burning humus, followed by photometry in the red region of the spectrum. The oxidizing agent is usually a solution of potassium dichromate in sulfuric acid, but at different ratios. Since tri- and tetrachromate ions (Cr3O102- and Cr4O132-) are formed in sulfuric acid solutions, and when the solution is diluted, they depolymerize and the color becomes more stable over time (after 2-4 hours), photometry is recommended to be carried out several hours after dilution , which ensures the settling of the suspension and the constancy of color. Some authors recommend adding dry salt K2Cr2O7 to complete the oxidation of humus.

The mentioned methods differ little, varying in the amount and concentration of the oxidizing agent, boiling (heating) conditions, final volumes of the solution, and methods for measuring color.

The whole determination consists of two main operations: humus oxidation and photometry (colorimetry) of colors. It is advisable to carry out the oxidation of humus completely according to the Tyurin method. This ensures the comparability of the results obtained by volumetric and photometric methods. At the same time, the amount of dichromate spent on oxidation can be determined by any method without violating the continuity of the data. A common disadvantage of photometric methods is the need to prepare a scale. This lengthens the definition and detracts from the benefits of the photometric finish.

The principle of the method is that when humus is oxidized with dichromate, hexavalent chromium is reduced to trivalent: Cr2O72->2 Cr3+

Coloring pure solution potassium dichromate varies from yellow (in dilute solutions) to orange. The absorption band of Cr3+ is quite wide, and the absorption maximum falls on the region of 584-594 nm, having an average value at 588-590 nm.

The differences in the extinction coefficients of ate for the oxidized and reduced forms are very large. In the region of the maximum, the extinction coefficient of dichromate (calculated for a concentration equal to 1 mmol-eq / 100 cm3 is) 0.66, while the extinction coefficient of reduced chromium at the same wavelength is only 0.062, i.e. less than 11 times.

The use of the 590 nm region provides another important advantage. By measuring the optical density at 590 nm, we directly know the amount of reduced chromium, which is equivalent to the total amount of humus (reducing agent) in the analyzed sample. Thus, there is no need to determine "by difference", and, consequently, to establish the initial amount of dichromate in the oxidizing mixture. Moreover, due to the zero optical density of dichromate at l 590 nm, it is not necessary to titrate the initial oxidizing mixture; it can be prepared by taking a sample of salt on technical scales. In this case, the dichromate solution is poured into the sample of soil not from a burette, but with a measuring cylinder. The same circumstance even makes it possible to add dry salt to the oxidizing mixture, as mentioned above.

The height of the maximum, or optical density, at 590 nm depends only on the amount of the reducing agent - the dichromate introduced into the solution. The nature of the spectra shows that the region 588-592 nm is most favorable for quantitative determination, where the optical density is maximum, and there is a small horizontal section on the curve. This significantly reduces possible errors due to inaccurate measurement (establishment) of the wavelength.

C - concentration of Cr3 + ion,

l is the thickness of the absorbing layer (cell length), cm;

e590 - extinction coefficient at 590 nm.

If the concentration of the reducing agent is expressed in mmol-equiv / 100 ml of solution, then the extinction coefficient can be calculated:

e590 = 0.06983 meq-1 cm-1 100 ml.

The verification of the method showed that the determination of humus according to Tyurin and the measurement of its content on a spectrophotometer at 590 nm give good agreement between the results. The correlation coefficients of the results obtained by the spectrometric and volumetric methods are very high and reach 0.99.

Analysis progress. Take a sample of soil prepared for analysis - 0.3 g; this sample is suitable for humus content from 0.6-0.8 to 12-13%; with more or less humus, the sample is changed. Transfer the sample to a 100 ml conical flask, pour 20 ml of 0.4 N (for dichromate) oxidizing mixture, measuring the dichromate solution with a graduated cylinder. Carefully mix the contents, close the neck of the flask with a small funnel and boil on an electric stove with a thick asbestos mesh for exactly 5 minutes from the beginning of the boiling point. The mixture is cooled, transferred to a 100 ml graduated cylinder, rinsing the flask with distilled water, and bringing the volume to 100 ml by adding water. To speed up the analysis, you can dilute the mixture directly in the conical flasks. The cylinder (or flask) is stoppered, the mixture is well mixed and left overnight. The settled solution is carefully poured (without stirring up the sediment) into a photoelectrocolorimeter cuvette 3 or 5 cm long. With a humus content of up to 6-7%, you can use a 5 cm cuvette, with a higher humus content - a 3 cm cuvette.

The optical density of the solution is measured on a spectrophotometer (at 590 nm) or on a photoelectric colorimeter with a light filter (610 nm), setting the "zero" of the devices not by water, but by an idle solution (boiled and diluted solution of the oxidizing mixture).

where: D - optical density;

ate - repayment ratio;

l - cuvette length, cm;

t - sample of soil, g;

d - specific gravity of the solid phase of the soil.

The numerical coefficients take into account the dilution factor and the equivalent weight of carbon.

The change in volume due to the solid phase can be neglected at a sample size of 0.3-0.5 g. Then we get:

We obtain the final calculation formulas by substituting the numerical values ​​of el and l for spectrophotometers at l=590 nm:

cuvette 3 cm, %C = 1.43; cuvette 5 cm, %C = 0.86;

for photoelectric colorimeter, light filter with l = 610 nm:

cuvette 3 cm, %C = 1.82; cuvette 5 cm, %C = 1.09

New values ​​of the extinction coefficients are easy to find using a standard titrated solution of Mohr's salt.

For this purpose, 20 ml of a 0.4 N oxidizing mixture are taken into a series of flasks (accurately measuring with a burette), boiled for 5 minutes, and after cooling, 1, 3, 5, 10, 25 cm3 of a 0.2 N (titrated) solution are successively added to the flasks. Mora salts. The volume of the solution is adjusted to 100 cm3 (in volumetric flasks), and the optical densities of the solutions are measured with the light filter that is supposed to be used to determine humus. The repayment coefficient is found according to the formula of the BLB law for each solution separately, and then the average value is calculated.

Determination of the degree of humification of soil organic matter by the method of Robinson and Joyes

The principle of the method is that, when heated, a 6% solution of hydrogen peroxide destroys and partly dissolves some organic compounds, but does not affect others and, apparently, destroys precisely amorphous structureless compounds, while structural ones (cellulose, lignin) are not amenable to action of this reagent.

Definition progress. A 1-2 g sample of soil is placed in a glass with a capacity of 500 cm3, 60 cm3 of a 6% hydrogen peroxide solution is poured here and heated for 15 minutes at 100 ° C, and finally brought to a boil. If the reaction proceeded vigorously, then the operation with the addition of a new portion of hydrogen peroxide must be repeated until the hydrogen peroxide ceases to react with the soil. After that, the contents are filtered, the residue is washed several times with hot water, then washed off the filter into a weighed porcelain cup, dried to constant weight at 100 ° C and weighed. The dry residue is then calcined and weighed again. The difference between the mass of dry and calcined residue gives the amount of organic matter that has not been decomposed by hydrogen peroxide ("non-humified"), of course, together with chemically bound water.

More accurate results can be obtained by subtracting the mass of the dry residue of the same sample from the mass of a dry sample after it has been treated, according to the authors' description, with hydrogen peroxide; since the amount of water chemically bound to the mineral part of the soil and to that organic matter that has not been exposed to hydrogen peroxide should not change noticeably from the action of hydrogen peroxide, the indicated difference should give quite accurately the amount of humified organic matter of the soil, together with its chemically bound water.

Having determined the carbon content in the soil residue after its treatment with hydrogen peroxide by the Gustavson or Knop methods and knowing the content of the total carbon of the soil organic matter and the carbon of non-humified organic substances in the soil, we can find out the carbon content of humified organic compounds in the soil by the difference.

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Determination of soil organic matter by the method of I.V. Tyurina modified by Tsinao

Introduction

1. Soil, its structure and types

5. Practical part

Conclusion

Introduction

Soil organic matter refers to the totality of organic compounds present in soils. Among carbon compounds, they play the greatest role in soil formation and soil fertility.

The role of organic compounds is so great that the problem of soil organic matter has always occupied one of the central places in theoretical and applied soil science.

In the formation of soils and soil fertility, humus performs numerous functions. The optimal content of humus in the soil provides an agronomically valuable structure and a favorable water-air regime, improves soil warming. The most important physical and chemical indicators of soils are associated with humus, including high cation exchange capacity, acid-base buffering capacity of soils; acidity and the development of reduction processes depend on the quality and level of humus content. Therefore, at present, the quantitative analysis of humus in various soil types and the assessment of soil organic carbon reserves is important aspect to regulate the humus composition of soils used in agricultural production.

One of the quantitative methods for determining organic matter in soils is the photometric method of I.V. Tyurin, which is currently the main method and accepted in all laboratories. Therefore, the purpose of our work is to determine the amount of organic matter by the Tyurin method in the modification of Qingnao

1. Soil, its structure and types

Soil - the surface layer of the Earth, which has fertility. The soil is a multifunctional four-phase system formed as a result of weathering of rocks and vital activity of organisms. It is considered as a special natural membrane that regulates the interaction between the biosphere, hydrosphere and the Earth's atmosphere. It is formed under the influence of climate, topography, parent rock, as well as living organisms and changes over time. Soil is a mixture of solid particles, air and water.

Soil solids are:

a) mineral particles of large sizes, ranging from stones of considerable size to very small grains of sand. With the introduction of a large amount of water, these components are quickly deposited on the bottom of the vessel.

b) extremely small, dusty particles that can remain suspended in water for a long time. They are easily separated from the sand by soaking.

c) humic substances that were formed during the decay of dead organic bodies or waste products of organisms. Microorganisms (bacteria, fungi, monera, etc.) and earthworms play the main role in its formation. Many humic substances bear clear traces of their organic origin and give the soil a mostly black or brown color.

These three components are contained in almost all types of soil.

Part of the soil that does not pass through the mesh with 0.3 mm holes. It is called the soil skeleton (coarse sand, gravel, stones). The rest of the particles are called fine earth. Fine earth plays a major role in plant life. The admixture of stones and gravel significantly changes the physical properties of the soil.

Pore ​​volume. Mixing these constituent parts Soils, their relative quantitative relations and the way they are composed are very different in different types of soils. Soil particles leave small empty spaces (pores) between them. The sum of such spaces not filled with solid particles is called the pore volume of a given soil. The soil is very rich in such empty, interconnected spaces, which turn into capillaries as their opening narrows. This is of great importance for vegetation. Soil connectivity. The strength of the adhesion of soil particles to each other is very different. As an example, we will cite such extremes as dunes, the grains of sand of which, when dry, are not at all connected with each other, and such as clay soil. Chernozem also has little connectivity. Soil hairiness plays a very important role in its physical structure. It is mainly dependent on the size and mode of occurrence of the particles that make it up; hairiness is the greater, the smaller the grains and the more often they are located; cloddy soil has less capillarity than soil composed of individual grains. Stones and gravel in the soil also reduce its hairiness.

Based on the different composition of the soil, the following types of soil can be established: stony, sandy, calcareous, solonchak, clay, humus soils. These types are connected with each other by gradual transitions and innumerable intermediate members so that there are an innumerable number of soil types with the most diverse properties.

1) Rocky soil. The nature of the rock is decisive for which plants will grow on such soil. Differences in hardness, porosity, heat capacity and thermal conductivity are of primary importance here. Main rocks: granite, gneiss, limestone, dolomite, sandstone, shale, basalt, etc.

2) Sandy soil. The sand is made up of various minerals, predominantly quartz, as well as hornblende, feldspar, mica, and sometimes lime. Sandy soil belongs to loose soils, because the grains that make it up have little cohesion, the smaller, the larger the grains of sand.

3) Lime soil. Lime sand made from grains of carbonic lime contains more nutrients than quartz sand. It has a slightly higher water capacity and dries out less easily, but it also belongs to dry and warm soils. Marl is a very close combination of carbonic lime (about 8-45%, in lime marl about 75%) with clay (about 8-60%) and quartz sand. Its properties are dependent on the quantitative relations of its constituent parts and occupy a middle place between the properties of sand and clay.

4) Solonchak soil - soil characterized by the presence of easily soluble salts in the upper horizons in quantities that prevent the development of most plants, with the exception of halophytes, which also do not form a closed vegetation cover. They form in arid or semi-arid conditions with an effusion water regime; they are characteristic of the soil cover of steppes, semi-deserts and deserts.

The solonchak profile is usually poorly differentiated. From the surface lies a saline (salt) horizon containing from 1 to 15% of easily soluble salts (according to water extract). When dried, salt efflorescence and crusts appear on the surface of the soil. Secondary solonchaks, formed by the rise of mineralized groundwater as a result of an artificial change in the water regime (most often due to improper irrigation), can have any profile on which the solonchak horizon is superimposed.

5) Clay soil is almost the opposite of sand. Clay soil is characterized by high absorption capacity and hygroscopicity (it can absorb 5-6% of water vapor from the air). This is a dense and heavy soil, because the particles have a high cohesion. It is difficult to ventilate; this circumstance is unfavorable for plants and leads to the formation of acids and waterlogging of the soil. Clay soil is cold and wet, as it has a high water capacity (up to 90%) and capillarity; it sucks up a lot of water from the subsoil and is almost impermeable. In the case of supersaturation with water, it swells, the individual particles that make it apart move apart, and a porridge-like mass is obtained. Clay soil rich in water is plastic. Under the influence of a prolonged drought, it becomes hard as a stone, shrinks and cracks, which affects the vegetation. The unfavorable properties of clay soils can be eliminated by mixing with them substances with opposite properties, such as sand or lime.

soil carbon chemical organic

2. Features of the soil as an object of chemical research and indicators of the chemical state of soils

The soil can be considered as a complex chemical system, the study of the properties of which is carried out at different levels. The soil is studied as a natural formation, consisting of atoms of various chemical elements, and in the process of research their content is determined. This is the atomic or elemental level of studying the composition of soils. At the same time, soil scientists set themselves more complex tasks and study the composition of soils at higher levels (molecular, ionic, etc.).

Soil is a complex object of study. The complexity of studying the chemical state of soils is due to the peculiarities of their chemical properties and is associated with the need to obtain information that adequately reflects the properties of native soils and provides the most rational solution to both theoretical issues of soil science and issues of practical use of soils. A wide range of indicators is used to quantitatively describe the chemical state of soils. It includes indicators determined during the analysis of almost any objects and developed specifically for soil research. Indicators of the chemical state of soils are, for example, the mass fraction of humus in the soil, the pH of water or salt soil suspensions, the mass fraction of mobile compounds of chemical elements in the soil, and many others.

The set and subordination of indicators of the chemical state of soils are due to the characteristics of the soil as a chemical system and as an object of practical use. The features of the soil as a chemical system are heterogeneity, polychemistry, dispersity, heterogeneity, change and dynamics of properties, buffering, etc.

Soil polychemistry. In soils, the same chemical element can be part of various compounds: easily soluble salts, complex aluminosilicates, and organomineral substances. These components have different properties, which, in particular, determine the ability of a chemical element to pass from the solid phases of the soil to the liquid one, migrate in the soil profile and in the landscape, be consumed by plants, etc. Therefore, in the chemical analysis of soils, not only the total content of chemical elements is determined, but also indicators characterizing the composition and content of individual chemical compounds or groups of compounds with similar properties. These indicators make it possible to diagnose soil processes, to study the transformation of a chemical element in the process of soil formation, with the application of fertilizers and technogenic pollution, and to assess the fertility and ameliorative features of soils.

Soil heterogeneity. Soil consists of solid, liquid and gaseous phases. K.K. Gedroits wrote as early as 1906 that in order to determine the state of the soil system, it is necessary to study its solid phases and proceed to a systematic study of the liquid phase, depending, in particular, on the partial pressure of CO 2 in the soil air. Currently, when studying the chemical state of the soil and its individual components, indicators are determined that characterize not only the soil as a whole, but also its individual phases. Moreover, mathematical models have been developed that make it possible, for example, to evaluate the relationship between the levels of partial pressure of carbon dioxide in soil air, pH, carbonate alkalinity, and calcium concentration in soil solution.

Soil polydispersity. The solid phases of the soil are composed of particles different size from grains of sand to colloidal particles with a diameter of several micrometers. They are different in composition and have different properties. In special studies of the genesis of soils, indicators of the chemical composition and other properties of individual granulometric fractions are determined. The dispersity of soils is to some extent related to their ability to ion exchange, which, in turn, is characterized by a specific set of indicators - the capacity of cation and anion exchange, the composition of exchangeable cations, etc. Many chemical and physical properties of soils depend on the levels of these indicators.

Acid-base and redox properties of soils. The composition of soils includes components that exhibit the properties of acids and bases, oxidizing and reducing agents. When solving various theoretical and applied problems of soil science, agrochemistry, melioration, indicators characterizing the acidity and alkalinity of soils, their redox state are determined.

Heterogeneity, variability, dynamics, buffering of chemical properties of soils. Soil properties are not the same even within the same genetic horizon. When studying the processes of formation of a soil profile, the chemical properties of individual elements of the organization of the soil mass are evaluated.

Soil properties vary in space, change over time, and at the same time, soils have the ability to resist changes in their properties, i.e., they show buffering. Indicators and methods for characterizing the variability, dynamics, and buffering properties of soils have been developed.

Changes in soil properties. Various processes continuously occur in soils, which lead to changes in the chemical properties of soils. Practical use find indicators that characterize the direction, severity, speed of processes occurring in soils; the dynamics of changes in soil properties and their regimes are studied. The chemical properties of even isolated soil samples can change when they are dried, rubbed, or simply stored.

Variation in quality of soil composition. Different types and even types and varieties of soils can have such different properties that for them chemical characterization use not only different analytical techniques, but also different sets of indicators. For example, in podzolic, soddy-podzolic, gray forest soils, as a rule, the pH of aqueous and salt suspensions, exchangeable and hydrolytic acidity are determined, and exchangeable bases are displaced from soils by aqueous solutions of salts. At the same time, when analyzing saline soils, the pH of only aqueous suspensions is determined, and instead of acidity indicators, total, carbonate, and other types of alkalinity are determined. Exchangeable bases in saline soils cannot be determined by simply displacing them from the soil with aqueous salt solutions without the use of special analytical techniques.

The listed features of soils largely determine the fundamental principles of methods for studying the chemical state of soils, the nomenclature and classification of indicators of the chemical properties of soils and chemical soil processes.

3. Chemical and instrumental methods of soil analysis

In the chemical analysis of soils, almost any of the methods available to analysts can be used. In this case, either the directly desired value of the indicator is measured, or the value that is functionally related to it. For example, the concentration of salts in the liquid phases of water-saturated soil pastes and the degree of soil salinity can be estimated from the specific electrical conductivity of the filtrates from the pastes. This technique is used because it is easier to determine the electrical conductivity of a solution than the concentration in moles.

In the laboratory practice of soil analysis, classical chemical and instrumental methods are used. With classical chemical methods, the most accurate results can be obtained. The relative error of determination is 0.1--0.2%. The error of most instrumental methods is much higher - 2-5%. When analyzing soils, the errors may be higher than indicated. Classical chemical methods are now, with rare exceptions, mainly used to assess the correctness of the results of determinations obtained by instrumental methods.

Among the instrumental methods in soil analysis, electrochemical and spectroscopic methods are most widely used. Among the electrochemical methods, potentiometric, conductometric, coulometric and voltammetric methods, including all modern varieties of polarography, are used.

Among the spectroscopic methods, according to the nature of the interaction of radiation with matter, emission (emission), absorption (absorption), scattering, and reflection spectroscopy are distinguished. In addition, spectroscopy is divided into atomic and molecular. Soil analysis uses both atomic and molecular spectroscopy methods.

When choosing a measurement method, the characteristics of the chemical properties of the analyzed soil, the nature of the indicator, the required accuracy of determining its level, the possibilities of measurement methods, and the feasibility of the required measurements under the conditions of the experiment are taken into account. In turn, the accuracy of measurements is determined by the purpose of the study and the natural variability of the studied property. Accuracy is a collective characteristic of the method that evaluates the correctness and reproducibility of the results of the analysis. It must be taken into account that more accurate methods are usually more laborious. Despite the fact that classical chemical methods in many cases give way to more productive instrumental methods, it must be borne in mind that these methods, especially gravimetric ones, are the most accurate. Therefore, despite their laboriousness, they will certainly be used as standard arbitration methods in the development of new (including instrumental) methods of soil analysis and the creation of standard soil samples with a known (given) content of chemical elements. Standard samples of soil masses are used both to control the correctness of the obtained analysis results and to calibrate instruments.

4. Carbon in soils and methods for determining the carbon of organic compounds

Carbon in soils is part of both organic and inorganic compounds. Carbon, which is part of organic matter, is found in specific compounds characteristic only of soils - humic acids, fulvic acids, hymatomelanic acids, humin - and in non-specific compounds - lignin, amino acids, carbohydrates, fatty acids, alcohols, aldehydes, resins , waxes, etc. Mineral carbon compounds are represented by carbonates, the main part of which falls on relatively sparingly soluble calcium and magnesium carbonates. A small amount of carbon is in the form of easily soluble alkali carbonates and bicarbonates. In the gas phases of soils, carbon is represented by CO 2 , CH 4 , etc.

Difficulties in analyzing soils for the content of carbon in them, other things being equal, are associated with the need to separately determine the carbon of organic and mineral compounds.

All methods for determining carbon in organic compounds are based on its oxidation to carbon dioxide. Both direct and indirect methods of analysis are proposed. Direct methods are based on determining the amount of CO 2 formed during the oxidation of carbon in organic compounds; indirect methods - on determining the amount of the oxidizing agent used to convert the carbon of organic compounds into CO 2, or on determining the amount of the reduced form of the oxidizing agent used, formed during the analysis.

4.1 Carbon dioxide stripping methods

Using these methods, the carbon content is found by the amount of CO 2 released during the decomposition of soil organic matter. During the analysis, the amount of carbon dioxide is determined by a variety of direct or indirect methods. For this purpose, gravimetric, titrimetric, gas volumetric, coulometric and other methods of quantitative analysis are used.

The decomposition of organic matter to H 2 O and CO 2 can be carried out in two ways: by dry ashing when soil is heated and by wet ashing with solutions of strong oxidizing agents.

gravimetric methods. When determining the carbon of organic compounds by the gravimetric method, both dry and wet ashing of humus are used.

Soil scientists have studied the processes that occur when humic acids are heated. It was found that the destruction of the aliphatic part of the humic acid molecule occurs first, i.e. its peripheral or side chains. Then, at higher temperatures, the destruction of the aromatic nucleus, dehydrogenation, and, finally, the release of carbon in the form of CO 2 begins. At the stage preceding the release of CO 2 , the residue of humic acid is 80--90% carbon. The temperature at which certain processes occur varies depending on the experimental conditions - the heating rate, oxidizing conditions, the possibility of removing decomposition products, etc.

Gustavson's method is based on the dry ashing of soil organic matter at a temperature of 650-750°C. When the soil is heated, organic matter decomposes, and the carbon and hydrogen in their composition turn into carbon dioxide and water. Ashing of soils is carried out in a refractory tube through which oxygen or air deprived of CO 2 is continuously passed. For a more complete decomposition of humus, ashing is carried out in the presence of copper oxide. Copper oxide releases oxygen and, turning first into Cu 2 O and then into metallic copper, contributes to a more complete oxidation of the components of soil organic matter.

Soil volatile components and humus oxidation products are captured by special absorbers. To absorb water formed during the oxidation of hydrogen, calcium chloride or concentrated sulfuric acid, for the absorption of sulfur dioxide - lead chromate. A copper coil is used to reduce nitrogen oxides to free nitrogen, halogens are absorbed using a silver coil. Finally, ascarite (asbestos impregnated with NaOH) is used to absorb CO2. Ascarite is placed in U-shaped absorption tubes. The reaction proceeds according to the equation:

CO 2 + 2NaOH \u003d Na 2 CO 3 + H 2 O

Due to the fact that one of the reaction products is H 2 O, not only ascarite is placed in the absorption tube, but also calcium chloride, which quantitatively absorbs water:

CaC1 2 + nH 2 O \u003d CaC1 2 nH 2 O

The absorption tubes are weighed before and after the ashing of the organic matter and the carbon content of the soil is found from the mass increase due to CO 2 uptake.

Methods based on dry ashing and gravimetric determination of carbon dioxide are the most accurate of the methods for determining the carbon of organic compounds. During dry ashing, carbon is completely oxidized regardless of the type of organic compounds, and the gravimetric method is the most accurate of the methods for measuring the mass of CO 2. However, these methods are laborious and, moreover, cannot be used in the analysis of carbonate soils without special techniques. When soils containing carbonates are heated, decomposition of the latter is possible; therefore, when analyzing carbonate soils, the mass of absorption tubes can increase not only as a result of the absorption of carbon dioxide formed during the decomposition of organic matter, but also from CO 2 formed as a result of the decomposition of carbonates.

Gas volumetric methods are based on measuring the volume of carbon dioxide released during the ashing of humus and calculating the amount of carbon by the volume of CO 2 . Calculations are carried out taking into account the temperature and pressure at which the analysis was carried out. Gas volumetric determination of carbon in soils can be carried out using gas analyzers, including those designed to determine carbon in iron and steel. Ashing of the analyte is carried out in a heat-resistant tube in a muffle furnace in a stream of oxygen. During the analysis, the volume of the mixture of CO 2 and oxygen is measured. Then the mixture of gases is passed through a solution with a carbon dioxide absorber (CO 2 + 2KOH = K 2 CO 3 + H 2 O) and the volume of oxygen is measured. The volume of carbon dioxide formed as a result of the ashing of organic matter is calculated by the difference.

Titrimetric methods are also used to determine the carbon dioxide released during the ashing of humus. In this case, carbon dioxide is absorbed by the KOH solution. In an alkaline environment, carbon dioxide is transformed into COf "". The CO ion is precipitated with barium chloride in the form of BaCO3. The precipitate of barium carbonate is filtered off, washed with water and dissolved in a titrated solution of HCl, the excess of which is determined by titration with alkali. By the amount of HC1, which went to the dissolution of barium carbonate, the amount of carbon dioxide formed during the ashing of humus is judged.

Express methods. In recent decades, analyzers have been used to determine the carbon of organic compounds, allowing you to get a result within a few minutes.

One of the methods is based on the estimation of the CO 2 release rate. The method was developed specifically for soil analysis and makes it possible to separately evaluate carbon dioxide released during the decomposition of organic compounds and during the decomposition of carbonates.

As the sample of soil is heated in an oxygen flow to 700°C, the rate of CO2 release increases due to carbon oxidation. organic compounds, reaches a maximum and then decreases. The rate of decomposition of carbonates begins to increase at higher temperatures. The analyzer automatically records the rate curve of carbon dioxide release as the soil warms up and allows you to separately determine the carbon dioxide formed as a result of the decomposition of humus and carbonates.

4.2 Characteristics of the photometric method of analysis

Photometric method of analysis - a set of methods of molecular absorption spectral analysis based on the selective absorption of electromagnetic radiation in the visible, IR and UV regions by the molecules of the component being determined or its combination with a suitable reagent. The concentration of the component to be determined is determined according to the Bouguer-Lambert-Beer law. The photometric method includes visual photometry, spectrophotometry and photocolorimetry. The latter differs from spectrophotometry in that the absorption of light is measured mainly in the visible region of the spectrum, less often in the near UV and IR regions (i.e., in the wavelength range from ~ 315 to ~ 980 nm), and also in that for extraction the desired part of the spectrum (width 10-100 nm) use not monochromators, but narrow-band filters.

The devices for photocolorimetry are photoelectrocolorimeters (PEC), which are characterized by the simplicity of optical and electrical circuits. Most photometers have a set of 10-15 light filters and are two-beam devices in which a beam of light from a radiation source (an incandescent lamp, rarely a mercury lamp) passes through a light filter and a light beam divider (usually a prism), which divides the beam into two beams directed through cuvettes with test solution and reference solution. After the cuvettes, parallel light beams pass through calibrated attenuators (diaphragms), designed to equalize the intensities of light fluxes, and fall on two radiation receivers (photocells) connected in a differential circuit to a null indicator (galvanometer, indicator lamp). The lack of devices is the absence of a monochromator, which leads to a loss of measurement selectivity; The advantages of photometers are the simplicity of design and high sensitivity due to the large luminosity. The measured range of optical density is approximately 0.05-3.0, which makes it possible to determine many elements and their compounds in a wide range of contents - from ~ 10-6 to 50% by weight. For additional increase the sensitivity and selectivity of determinations, the selection of reagents that form intensely colored complex compounds with analytes, the choice of the composition of solutions and measurement conditions are essential. The determination errors are about 5%.

In the so-called differential photometric analysis, the optical density of the analyzed solution is measured relative to the optical density (which should not be less than 0.43) of the reference solution. The latter contains the component to be determined in a concentration close to the concentration of this component in the analyzed solution. This makes it possible to determine relatively high concentrations of substances with an error of 0.2-1% (in the case of spectrophotometry). In photometric titration, the dependence of the optical density of the titrated solution on the volume of the added titrant (titration curve) is obtained. The break in this curve determines the end point of the titration and, consequently, the concentration of the test component in the solution.

4.3 Photometric method for determination of carbon in organic compounds

The photometric method for determining the carbon of organic compounds is an indirect method. When using this method, the humus content is judged by the amount of Cr 3+ formed in the process of carbon oxidation. A variant of the photometric method used in Russia and other countries former USSR, was proposed by Tyurin.

When humus is oxidized with a solution of potassium dichromate, the carbon of organic compounds is converted into CO2, and Cr(VI) is reduced to Cr(III). The amount of Cr 3+ formed during the reaction is equivalent to the carbon content of organic compounds (and other reducing agents) in a sample of soil. Therefore, the carbon of organic compounds can be determined by the amount of Cr 3+ formed during the analysis. For this purpose, a photometric method is used.

Chromium belongs to the group of transition elements, the 3d-bital of which is not completely filled with electrons. Ions Cr 2 O 7 2- and Cr 3+ have their own color.

The color of a pure solution of KgCr 2 O 7, depending on the concentration, varies from yellow to reddish-orange, the color of solutions of Cr 2 (SO 4) 3 is green. The absorption spectra of the solutions, as well as the color of the solutions, are different.

Within the visible region of the spectrum (400--800 nm) on the light absorption curve of a solution of potassium dichromate there is one clearly defined maximum at a wavelength of 447 nm. As the wavelengths increase, the optical density decreases and reaches almost zero value in the wavelength range of 570–580 nm. The maximum on the light absorption curve of the Cr 3+ solution falls on the wavelength range 584–594 nm, i.e. to that section of the absorption spectrum of K 2 Cr 2 0 7 where the optical density of the solution is practically zero. The difference in the location of the maxima on the light absorption curves of solutions of Cr 2 O 7 2- and Cr 3+ allows the photometric method to determine the concentration of different valence forms of chromium in the joint presence in the solution.

It is convenient to determine the concentration of Cr 3+ in the wavelength range of 584 - 594 nm, since the light absorption of Cr 3+ solutions is maximum in it, and the optical density of K 2 Cr 2 0 7 solutions is practically zero and K 2 Cr 2 0 7 does not affect results of determination of Cr 3+ . The possibility of selective measurement of the optical density of Cr 3+ underlies the photometric method for determining the carbon of organic compounds.

After the interaction of potassium dichromate with soil, the optical density of the solution is measured in the wavelength range corresponding to the maximum absorption of Cr 3+ radiation (590 nm), the amount of Cr 3+ is determined, and the equivalent amount of carbon in organic compounds is calculated.

The use of the photometric method for the determination of organic carbon by the amount of Cr 3+ formed makes it possible not to establish the exact concentration and volume of the potassium dichromate solution taken for the analysis of a sample of soil. The volume of added solution can be measured using a graduated cylinder.

5. Practical part

In the experimental part, the determination of organic matter in soils was carried out according to the Tyurin method modified by Tsinao.

The method is based on the oxidation of organic matter with a solution of potassium dichromate in sulfuric acid and the subsequent determination of trivalent chromium, equivalent to the content of organic matter, on a photoelectric colorimeter.

The method is not suitable for samples with a mass fraction of chloride greater than 0.6% and samples with a mass fraction of organic matter greater than 15%

The limiting values ​​of the relative error of the analysis results for the two-sided confidence probability Р=0.95 are as a percentage:

20 - with a mass fraction of organic matter up to 3%

15 - over 3 to 5%

10 - over 5 to 15%.

Equipment and reagents

Photoelectrocalorimeter KFK 3-01

Water bath

Torsion scales or others with an error of not more than 1 mg.

Test tubes glass heat-resistant with a capacity of 50 ml. according to GOST 23932

Test tube rack

Burette or dispenser for measuring 10 ml. chrome mixture

Glass sticks 30 cm long.

Measuring cylinder 40 ml. water

Rubber bulbs with glass tube or barbation device

Burette with a capacity of 50 ml.

Volumetric flasks with a capacity of 1l.

Porcelain mug with a capacity of 2 liters.

Flask conical with a capacity of 1 l.

Conical flasks or technological containers with a capacity of at least 100 ml.

Ammonium-iron (II) sulfate (Mohr's salt) according to GOST 4208

Potassium dichromate according to GOST 4220

Potassium permanganate, standard titer for preparing a solution of concentration (1 / 5KMnO 4) \u003d 0.1 mol / l.

Sulfuric acid according to GOST 4204 concentrated and concentration solution (1/2 H 2 SO 4) = 1 mol / l.

Method of determination

The mass of a soil or rock sample for analysis is determined based on the expected content of organic matter according to Table 1.

Soil or rock samples are weighed with an error of not more than 1 mg and placed in test tubes installed in racks. Add 10 ml to the test tubes. chrome mixture. A glass rod is placed in each test tube and the sample is thoroughly mixed with the chromium mixture. The test tube racks are then lowered into a boiling water bath.

Table 1 - Dependence of the mass of the sample for the analysis of the mass fraction of organic matter

The water level in the bath should be 2-3 cm higher than the level of the chromium mixture in the test tubes. The duration of heating the suspension is 1 hour from the moment the water boils in the bath after the test tubes are immersed in it. The contents are stirred with glass rods every 20 minutes. After the expiration of the racks with test tubes, they are transferred to a water bath with cold water. After cooling, 40 ml of water is poured into the test tubes. Then the sticks are removed from the test tubes, the suspensions are thoroughly mixed by air bubbling and left until the solid particles settle and the supernatant part of the solution is completely clarified.

Then, reference solutions are prepared. 10 ml of the chromium mixture are poured into 9 test tubes and heated for 1 h, the volumes of distilled water and the reducing agent solution indicated in table 2 are poured into the test tubes. The solutions are thoroughly mixed by air bubbling.

Table 2 - Preparation of reference solutions

Photometry of solutions is carried out in a cuvette with a translucent layer thickness of 1–2 cm relative to the first reference solution at a wavelength of 590 nm or using an orange-red light filter with a maximum transmission in the region of 560–600 nm. The solutions are carefully transferred into the cuvette of the photoelectric calorimeter without disturbing the precipitate.

In this work, we used a chromium mixture, which was prepared from potassium dichromate K 2 Cr 2 O 7 of “Ch” grade.

Preparation of the chromium mixture

To prepare 500 ml of a chromium mixture, 10.0243 mg of finely ground potassium dichromate was placed in a 250 ml volumetric flask, dissolved in water, bringing the volume to the mark, and poured into a porcelain mug. 250 ml of concentrated sulfuric acid was added to the prepared solution in portions of 25 ml with an interval of 10–15 minutes. The mug with the solution was left until complete precipitation. The solution was then poured into a dark glass bottle.

Preparation of a solution of Mohr's salt with a concentration of 0.1 mol / l

A solution of the reducing agent - a solution of Mohr's salt with a concentration of 0.1 mol/l and a volume of 200 ml was prepared from a sample of Mohr's salt. A sample weighing 8.0153 mg was dissolved in 140 ml of sulfuric acid with a concentration of C (1/2H 2 SO 4) = 1 mol/l, filtered through a double pleated filter into a volumetric flask and 60 ml of water was added.

The concentration of the solution was checked by titration against the working solution of potassium permanganate with the exact concentration C(1/5KMnO 4)=0.0957 mol/l. For titration in three conical flasks, 10 ml of the prepared reducing agent solution was measured using a burette, 1 ml of concentrated sulfuric acid and 50 ml of water were added, and titrated with a solution of potassium permanganate until a faint pink color appeared, which did not disappear within 1 min. Then, the arithmetic mean of the results of three titrations was used to calculate the correction factor.

V1 (KMnO 4) \u003d 11.5 ml

V2 (KMnO 4) \u003d 11.7 ml V cf (KMnO 4) \u003d 11.6 ml

V3 (KMnO 4) \u003d 11.6 ml

where V cf is the volume of potassium permanganate solution used for titration, ml;

V - The volume of the reducing solution selected for titration, ml.

The object of analysis was the soil of the virgin lands of the city of Buzuluk. Sampling was carried out at a depth of 0-10, 10-20, and 20-30 cm. In the samples of soil horizons, the percentage of organic matter was determined, and three parallel determinations were made for each sample to obtain the greatest accuracy of the analysis results.

The mass of the sample for analysis (100 mg) was determined based on the expected content of organic matter (4-7%). Soil samples were weighed with an error of no more than 1 mg. The weighing results are presented in Table 3.

Table 3 - Sample weight for analysis.

Conducting an analysis

The analysis was carried out in accordance with the procedure. Each sample was placed in a 250 ml conical flask, 10 ml of chromium mixture was poured into each of the flasks, then the resulting mixture was thoroughly mixed with a glass rod and placed in an oven instead of a water bath for 20 minutes at a temperature of 120 0 C.

Exactly 20 minutes after reaching the required temperature, the flasks with the suspension were taken out, the contents were mixed and cooled. The slurry was then further agitated by air bubbling and allowed to settle for solid particles.

Then the reference solutions were prepared. 10 ml of chromium mixture were poured into nine conical flasks and heated for 20 min in an oven, similarly to the samples under study. After cooling, the volumes of distilled water and the reducing agent solution indicated in Table 2 were poured into the flasks.

Photometry of the analyzed solutions and reference solutions was carried out on a KFK 3-01 photoelectrocalorimeter in a cuvette with a translucent layer thickness of 1 cm relative to reference solution No. 1 at a wavelength of 590 nm.

The mass of organic matter in the analyzed sample was determined from the calibration curve. When constructing a calibration graph, the mass of organic matter in milligrams corresponding to the volume of the reducing agent in the reference solution was plotted along the abscissa axis, and the corresponding instrument reading was plotted along the ordinate axis.

Construction of a calibration graph

y \u003d 0.03x + 1.4 10 -4

The mass fraction of organic matter (X) in percent was calculated by the formula

where m is the mass of organic matter in the analyzed sample, found from the graph, mg;

K is the correction factor for the concentration of the reducing agent;

m 1 - sample weight, mg;

100 - conversion factor to percent.

The results of measuring the optical density, calculating the mass fraction of organic matter in the samples, as well as the determination error are presented in the summary table No. 4

Table 4 - Analysis results

Conclusion

As a result of our work, three samples of soils of virgin lands taken near the city of Buzuluk at a depth of 0-10, 10-20, 20-30 cm were analyzed for the content of organic matter. In this case, the mass fraction of humus, calculated based on the results of the analysis, was 5, nine; 4.75; 4.06 percent, respectively, the error of determination is 8.9; 4.6; 5.4 respectively for three soil samples. The calculated mass fraction confirms the assumption we made earlier that the mass fraction of humus in the samples studied by us varies in the range from 4 to 7 percent. Based on the data obtained, it can be concluded that this soil is medium-humus. This humus content is optimal for the soils of this region. With a lower humus content, crop yields fall, but increasing its content to a higher level does not lead to a noticeable increase in yield under the farming systems used.

List of sources used

1. Vorobieva A.A., Chemical analysis of soils: textbook. - M.: Publishing House of Moscow State University, 1998 - 270p.

2. Zvyagintsev D.G., Babieva I.P., Zenova G.M. Soil biology: Textbook - 3rd ed. correct and additional - M: Publishing House of Moscow State University, 2005-445s.

3. Ivanov D.N. Spectral analysis soils: Moscow "Kolos", 1974-270s.

4. Kreshkov A.P. Fundamentals of analytical chemistry. Book three. Ed. 2nd, revised. M., "Chemistry", 1977-488s.

5. Orlov D.S. Soil Chemistry: Textbook / D.S. Orlov, L.K. Sadovnikova, N.I. Sukhanov. - M.: Vyssh.shk., 2005.-558s.: ill.

6. Ponomareva V.V., Plotnikova T.A. Humus and soil formation. - L: Science, 1980 -438s.

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