Humus definition gost. Research methodology

The method of I. V. Tyurin is based on the oxidation of soil organic matter with chromic acid to the formation of carbon dioxide. The amount of oxygen consumed for the oxidation of organic carbon is determined by the difference between the amount of chromic acid taken for oxidation and the amount of it remaining unused after oxidation. As an oxidizing agent, 0.4 i. solution of K2Cr2O7 in sulfuric acid, previously diluted with water in a ratio of 1:1.
The oxidation reaction proceeds according to the following equations:

The rest of the chromic acid not consumed for oxidation is titrated with 0.1 N. Mohr's salt solution with indicator diphenylamine. Titration with Mohr's salt, which is a double salt of ammonium sulphate and ferrous sulphate - (NH4) 2SO4 FeSO4 6H2O, proceeds according to the following equation:

The completeness of oxidation of organic matter, subject to all the conditions of the method indicated below, is 85-90% of the value of oxidation by dry combustion (according to Gustavson).
The use of silver sulfate as a catalyst increases the completeness of oxidation to 95% (Komarov).
To obtain reliable results, it is necessary to pay attention to: 1) careful preparation of the soil for analysis and 2) exact observance of the boiling time during the oxidation of organic matter; the boiling of the oxidizing mixture itself should proceed calmly.
The method gives good convergence of parallel analyses, is fast, does not require special equipment (and therefore can be used in expeditionary conditions) and is currently generally accepted, especially when conducting mass analyses.
Soil preparation for analysis. When preparing the soil for analysis for humus content, special attention should be paid to the removal of roots and various organic residues of plant and animal origin from the soil.
From a soil sample taken in the field and brought to an air-dry state, an average sample of 50 g is taken, the roots and organic residues visible to the eye (insect shells, seeds, coals, etc.) are carefully selected with tweezers, soil clods are crushed with a wooden pestle with rubber tip and again carefully select the roots, using a magnifying glass.
Then the soil is ground in a porcelain mortar and passed through a sieve with a hole diameter of 1 mm, after which an average sample weighing 5 g is again taken from it and the selection of roots is repeated using the following method. A dry glass rod is vigorously rubbed with a dry cloth or woolen cloth and quickly passed at a height of about 10 cm above the soil, distributed in a thin layer over the surface of wax or parchment paper.
Thin small roots and semi-decayed plant residues, which could not be selected before due to their small size, adhere to the surface of the electrified stick and are thus removed from the soil. They are removed from the stick when it is rubbed again. It should not be held too low with a stick above the soil surface in order to avoid the removal of not only organic residues from the soil, but also fine earth.
In the process of selecting roots, it is necessary to repeatedly mix the soil and again distribute it in a thin layer. The operation should be carried out until only single roots are found on the stick. The purity of the selection of roots is controlled, in addition, by viewing the soil in a magnifying glass.
At the end of the selection of roots, the soil is again ground in a porcelain, jasper or agate mortar and passed through a sieve with a hole diameter of 0.25 mm. The entire 5 g sample should be prepared in the manner described above.
The soil prepared in the above way for analysis should be stored in parchment paper or wax bags or in test tubes with stoppers.
Analysis progress. A sample of air-dry soil for humus analysis is taken on an analytical balance. The sample size depends on the expected humus content in the soil, taking into account the type of soil (chernozem, podzolic, etc.) and the sampling depth.
With a humus content of 7 to 10%, IV Tyurin recommends a sample of 0.1 g; at 4-7% - 0.2 g; at 2-4% - 0.3 g; less than 2% - 0.5 g. In the case of sandy soils with a low humus content, the sample can be increased to 1 g.
With a very high content of humus (over 15-20%), its determination by the Tyurin method becomes unreliable, since complete oxidation is not achieved.
It is better to take the exact weights - 0.1; 0.2 g, which facilitates further calculations. To take accurate weights, you can use a calibrated watch glass with a diameter of 2.5-3 cm, from which the whole weight is transferred to a flask for burning using a small spatula and a brush for watercolors. The determination of humus according to Tyurin can be carried out simultaneously in 20-30 samples.
Samples are placed in dry conical flasks of 100 ml of ordinary glass, powdered silver sulfate is added to the same place at the tip of a knife. When performing mass analyzes, silver sulfate is not used. To be able to compare the results obtained in this case with the dry combustion method, IV Tyurin gives a coefficient of 1.17 (1936). Then, 10 ml of 0.4 N solution is poured into each flask. a solution of K2Cr2O7 prepared on a mixture of one part of H2SO4 (sp. weight 1.84) and one part of distilled water.
The potassium dichromate solution should be poured from the burette, measuring the required volume each time from zero and allowing the liquid to drain always at the same rate. You can also use a pipette, but always equipped with safety balls in the upper part.
In this case, a separating funnel made of refractory glass, adapted to work with strong acids, is very convenient. The use of such a funnel greatly speeds up the work and makes it safe.
After pouring the K2Cr2O7 solution into the neck of the flasks, funnels with a diameter of about 4 cm are inserted, the contents of the flasks are carefully mixed (making sure that the soil does not stick to their walls), after which the flasks are placed on an already hot eternite or sand electric stove, or on a tile with an exposed spiral, but covered with asbestos. You can also use gas burners, and in expeditionary conditions - a primus stove or a kerosene stove, placing a heating device under a sand bath (a frying pan with calcined quartz sand).
The contents of the flasks are brought to a boil and boiled for exactly 5 minutes. It is necessary to accurately mark the beginning of the boiling of the liquid, not mixing it with the appearance of small air bubbles at the beginning of heating. Boiling should be uniform and moderate; the release of steam from the funnel and the bouncing of the latter are unacceptable. Vigorous boiling should be avoided so as not to change the concentration of sulfuric acid, an increase in which can cause decomposition of chromic acid. To avoid too violent boiling, boiling on bare helix tiles is unacceptable.
After 5 minutes of boiling, the flasks are removed from the heating device, allowed to cool, the funnels above the flasks are washed on the inside and outside with distilled water from the wash, and the contents of the flasks are quantitatively transferred into 250 ml conical flasks, rinsing the flask in which oxidation was carried out several times. . The volume of liquid after transfer to a 250 ml flask should be 100-150 ml. The color of the liquid is orange-yellow or greenish-yellow; its greening indicates a lack of an oxidizing agent; analysis in this case must be repeated, reducing the sample.
8 drops of diphenylamine solution, which is an indicator, are added to the liquid, and the chromic acid remaining not consumed after the oxidation of the organic substance is titrated with 0.1 N. Mohr's salt solution. The indicator should be added immediately before titration. Titration is carried out in the cold. The red-brown color of the liquid, which appears after the addition of diphenylamine, when titrated with a solution of Mohr's salt, gradually turns into an intense blue, and then into a dirty purple. From this point on, the titration is carried out carefully, adding Mohr's salt 1 drop at a time and thoroughly mixing the contents of the flask. The end of the titration - a change in the dirty purple color of the solution to bottle green; after some standing (10-15 min.), the color of the liquid becomes green. The appearance of a bright green color during titration indicates an excess of Mohr's salt, i.e., that the solution has been overtitrated; analysis in this case must be repeated.
To eliminate the influence of ferric ions, which oxidize the indicator and cause a premature change in the color of the solution, 85% phosphoric acid is used. It is introduced into the flask before titration in the amount of 2.5 ml; the color change at the end of the titration in the presence of phosphoric acid is very sharp and is caused by 1-2 drops of Mohr's salt solution.
Simultaneously with the main analyzes in the same sequence, a blank is carried out (in triplicate) to establish the ratio between 10 ml of a chromium mixture solution and Mohr's salt solution. For uniform boiling of the liquid during a blank analysis, about 0.1-0.2 g of calcined pumice or soil, ground into powder, must be added to the flask before adding the solution of the chromium mixture. Otherwise, overheating occurs, which is inevitable when boiling a pure solution, which can cause decomposition of chromic acid. The rest proceed according to the described course of analysis.
When conducting large batches of analyzes for the content of humus according to the Tyurin method (30-60 analyzes at a time), you can take breaks at the following stages of work: taking samples - one day; oxidation, transfer to titration flasks and titration - the next day. Or, less desirable, sampling and oxidation on the same day, titration the next. In the latter case, the contents of the flasks after incineration must be diluted and transferred to titration flasks. Titration of blanks in this case should also be left until the next day. Each batch should always be titrated under the same lighting conditions (daylight or electric light).

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

	Definition
GENERAL CONCEPTS
1. Soil	An independent natural-historical organo-mineral natural body that arose on the surface of the earth as a result of prolonged exposure to biotic, abiotic and anthropogenic factors, consisting of solid mineral and organic particles, water and air and having specific genetic and morphological features, properties that create appropriate conditions for the growth and development of plants
2. Soil classification	The system of separation of soils by origin and (or) properties
3. Soil profile	The set of genetically conjugated and regularly changing soil horizons into which the soil is divided in the process of soil formation
4. Soil horizon	A specific layer of the soil profile formed as a result of the impact of soil-forming processes
5. Type of soil	The main classification unit, characterized by a commonality of properties due to the regimes and processes of soil formation, and unified system main genetic horizons
6. Soil subtype	Classification unit within a type, characterized by qualitative differences in the system of genetic horizons and in the manifestation of overlapping processes that characterize the transition to another type
7. Type of soil	Classification unit within the subtype, determined by the characteristics of the composition of the soil-absorbing complex, the nature of the salt profile, the main forms of neoplasms
8. Type of soil	Classification unit within a genus, quantitatively differing in the degree of expression of soil-forming processes that determine the type, subtype and genus of soils
9. Variety of soil	Classification unit that takes into account the division of soils according to the granulometric composition of the entire soil profile
10. Soil Discharge	Classification unit grouping soils according to the nature of soil-forming and underlying rocks
11. Ground cover	The totality of soils that cover the earth's surface
12. Structure of the soil cover	Spatial arrangement of elementary soil areas that are genetically related to each other to varying degrees and create a certain spatial pattern
13. Soil-forming factors	Elements of the natural environment: soil-forming rocks, climate, living and dead organisms, age and terrain, as well as anthropogenic activities that have a significant impact on soil formation
14. Elementary soil range	Primary component of soil cover, which is the area covered by soil in one of the lowest ranking units
15. Soil mapping Ndp. Mapping	Drawing up soil maps or maps of their individual properties
16. Soil fertility	The ability of the soil to meet the needs of plants in nutrients, moisture and air, as well as to provide conditions for their normal life
17. Soil passport
18. Soil evaluation	Comparative assessment in points of soil quality by natural properties
PHYSICAL PROPERTIES OF SOILS
19. Mechanical element of soil	Isolated primary particles of rocks and minerals, as well as amorphous compounds in soil
20. Soil aggregate	Structural unit of soil, consisting of soil mechanical elements connected to each other
21. Mechanical fraction of soil	A set of mechanical elements, the size of which is within certain limits
22. Soil Skeleton	The set of mechanical elements of the soil with a size of more than 1 mm
23. Fine earth	The totality of mechanical soil elements less than 1 mm in size
24. Silty soil fraction	The set of mechanical elements of the soil in size from 0.001 to 1.0 mm
25. Soil colloids	The set of mechanical elements of the soil in size from 0.0001 to 0.001 mm
26. Granulometric composition of the soil
27. Solid part of the soil	The totality of all types of particles that are in the soil in a solid state at a natural level of moisture
28. Soil structure	The physical structure of the solid part and the pore space of the soil, due to the size, shape, quantitative ratio, the nature of the relationship and the location of both mechanical elements and aggregates consisting of them
29. Pore space in soil	Gaps of various sizes and shapes between mechanical elements and soil aggregates occupied by air or water
30. Soil moisture	Water in the soil and released by drying the soil at a temperature of 105 ° C to constant mass
31. Soil moisture capacity	The value that quantitatively characterizes the water-holding capacity of the soil
32. Soil swelling	Increase in the volume of the soil as a whole or individual structural elements when moistened
33. Soil consistency	The degree of mobility of the particles that make up the soil under the influence of external mechanical influences at different soil moisture, due to the ratio of cohesive and adhesive forces
34. Soil density	The ratio of the mass of dry soil taken without disturbing the natural composition to its volume
35. Soil air capacity	Volume of pore space containing air at soil moisture corresponding to field capacity
36. Soil biological activity	The totality of biological processes occurring in the soil
37. Biological accumulation in soil	Accumulation in the soil of organic, organo-mineral and mineral substances as a result of the vital activity of plants, soil microflora and fauna
SOIL CHEMICAL COMPOSITION AND PROPERTIES
38. Chemical characteristics of the soil	Qualitative and quantitative description chemical properties soil and its chemical processes
39. Soil organic matter	The totality of all organic substances in the form of humus and the remains of animals and plants
40. Humus	Part of soil organic matter, represented by a combination of specific and non-specific organic substances of the soil, with the exception of compounds that are part of living organisms and their residues
41. Group composition of humus	List and quantitative content of groups of organic substances that make up humus
42. Fractional composition of humus
43. Specific humic substances	Dark-colored organic compounds that are part of humus and are formed in the process of humification of plant and animal residues in the soil
44. Humic acids	A class of high-molecular organic nitrogen-containing hydroxy acids with a benzoic nucleus, which are part of humus and are formed in the process of humification
45. Humic acids	A group of dark-colored humic acids, soluble in alkalis and insoluble in acids
46. ​​Hymatomelanic acids	Group of humic acids soluble in the standard
47. Fulvic acids	A group of humic acids soluble in water, alkalis and acids
48. Gumin	Organic matter that is part of the soil, insoluble in acids, alkalis, organic solvents
49. Organo-mineral compounds of the soil	Complex, heteropolar, adsorption and other products of the interaction of organic and mineral substances of the soil
50. Degree of humification of organic matter	The ratio of the amount of carbon of humic acids to total soil organic carbon, expressed in mass fractions
51. Mineralization of the soil solution
52. Easily soluble soil salts
53. Sparingly soluble soil salts
54. Mobility of chemical compounds in soil	The ability of compounds of chemical elements to pass from the solid phases of the soil into the soil solution
55. Soil acidity	The ability of the soil to exhibit the properties of acids
56. Soil alkalinity	The ability of the soil to exhibit the properties of the bases
57. Soil buffering	The ability of the soil to resist changes in its properties under the influence of various factors
58. Acid-base buffering of the soil	The ability of the soil to withstand changes in the pH of the soil solution when the soil interacts with acids and bases
ION EXCHANGE PROPERTIES OF SOILS
59. Soil absorption complex		The set of mineral, organic and organo-mineral particles of the solid phase of the soil, which have absorptive capacity
60. Ion exchange in soil		Reversible reaction of stoichiometric exchange of ions between the solid and liquid phases of the soil
61. Selectivity of metabolism in soil		Soil capacity for preferential absorption certain types ions
62. Soil cation exchange capacity		The maximum amount of cations that can be retained by the soil in the exchange state under given conditions
63. Soil anion exchange capacity		The maximum amount of anions that can be retained by the soil in the exchange state under given conditions
64. The amount of exchangeable cations in the soil		The total amount of exchangeable cations in the soil.
		Note. Exchangeable cations include: potassium, sodium, calcium, magnesium, etc.
65. Exchange bases of soil		Exchangeable cations that are part of the soil absorbing complex
66. Sum of exchangeable bases in soil		The total number of exchangeable bases in the soil
67. The degree of saturation of the soil with bases		The ratio of the sum of exchangeable bases to the sum of hydrolytic acidity and the sum of exchangeable bases
SOIL ANALYSIS
68. Soil analysis		A set of operations performed to determine the composition, physical-mechanical, physical-chemical, chemical, agrochemical and biological properties of the soil
69. Soil test site		Representative part of the study area, intended for sampling and detailed study of the soil
70. Single soil sample		A sample of a certain volume, taken once from a soil horizon, layer
71. Pooled soil sample Ndp. Mixed soil sample		Soil sample consisting of a given number of single samples
72. Absolutely dry soil sample		Soil sample dried to constant weight at 105°C
73. Air dry soil test		Soil sample dried to constant weight at laboratory temperature and humidity
74. Soil extract		An extract obtained after soil treatment with a solution of a given composition, which acted on the soil for a certain time at a certain soil-solution ratio
SOIL PROTECTION AND MANAGEMENT
75. Soil protection			A system of measures aimed at preventing the decline in soil fertility, their irrational use and pollution
76. Rational use soil			Economically, ecologically and socially justified use of soils in the national economy
77. Soil degradation			Deterioration of soil properties and fertility as a result of natural or anthropogenic factors
78. Soil erosion			Destruction and demolition of the upper most fertile soil horizons as a result of the action of water and wind
79. Depletion of the soil			Depletion of nutrients and a decrease in the biological activity of the soil as a result of its irrational use
80. Soil fatigue			The phenomenon observed in the monoculture of plants and is expressed in a decrease in yield with the introduction of full fertilizer and the preservation of favorable physical and mechanical properties of the soil
81. Soil leaching			Washing out of the soil of various substances by filtering solutions
82. Soil salinization			Accumulation of easily soluble salts in the soil
83. Migration of chemical compounds			Movement of chemical compounds within a soil horizon, profile, or landscape
84. Hummification			According to GOST 20432
85. Soil acidification Ndp. soil acidification			Changes in the acid-base properties of the soil caused by the natural soil-forming process, the entry of pollutants, the introduction of physiologically acidic fertilizers and other types of anthropogenic impact
86. Soil alkalization Ndp. Soil alkalization			Changes in the acid-base properties of the soil caused by the natural soil-forming process, the entry of pollutants, the introduction of physiologically alkaline ameliorants and other types of anthropogenic impact
87. Soil pollution			Accumulation in the soil of substances and organisms as a result of anthropogenic activities in such quantities that reduce the technological, nutritional and hygienic and sanitary value of cultivated crops and the quality of other natural objects
88. Global soil pollution			Soil pollution resulting from the long-range transport of a pollutant in the atmosphere over distances exceeding 1000 km from any source of pollution
89. Regional soil pollution			Soil pollution resulting from the transfer of a pollutant into the atmosphere at distances of more than 40 km from technogenic and more than 10 km from agricultural sources of pollution
90. Local soil pollution			Soil pollution near one or a combination of several sources of pollution
91. Background content of a substance in soil
92. Industrial source of soil pollution			Source of soil pollution caused by the activities of industrial and energy enterprises
93. Transport source of soil pollution			Source of soil pollution due to the operation of vehicles
94. Agricultural source of soil pollution			Source of soil pollution due to agricultural production
95. Household source of soil pollution			Source of soil pollution caused by human household activities
96. Soil pollution control			Checking the conformity of soil pollution in accordance with established norms and requirements
97. Soil pollution monitoring			System of regulatory observations, including observations of actual levels, determination of predictive levels of pollution, identification of sources of soil pollution
98. Soil pollutant			A substance that accumulates in the soil as a result of anthropogenic activities in such quantities that adversely affect the properties and fertility of the soil, the quality of agricultural products
99. Pesticide residue in soil			The amount of pesticide after due date expectations since its application
100. Soil self-purification			The ability of soil to reduce the concentration of a pollutant as a result of migration processes occurring in the soil
101. Soil self-purification time			The time interval during which the decrease occurs mass fraction soil pollutant by 96% of the initial value or its background content
102. Maximum allowable concentration of a soil pollutant			The maximum concentration of a soil pollutant that does not cause a negative direct or indirect impact on the natural environment and human health
103. Persistence of a soil pollutant			The duration of the persistence of the activity of a soil pollutant, characterizing the degree of its resistance to the processes of decomposition and transformation
104. Detoxify Soil Pollutant			Converting a soil pollutant into compounds that are non-toxic to organisms
105. Sanitary condition of the soil			The totality of physico-chemical, chemical and biological properties of the soil, which determine its direct impact on human and animal health

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

	Term number
Soil unit
Biological accumulation in soil
Soil biological activity
Soil analysis
Areal soil elementary
Soil appraisal
Soil buffering
Soil buffering acid-base
Specific humus substances
soil pollutant
Soil organic matter
Soil type
soil moisture
soil moisture capacity
Soil air capacity
Soil self-cleaning time
Soil extractor
soil leaching
soil horizon
Gumin
humification
Humus
soil degradation
Soil pollutant detoxification
soil anion exchange capacity
Soil cation exchange capacity
Soil pollution
soil pollution global
Soil pollution local
Soil pollution regional
soil acidification
Soil salinization
Soil alkalization
Soil use rational
Source of soil pollution industrial
Source of soil pollution agricultural
The source of soil pollution is transport
Source of household soil pollution
soil depletion
Mapping
soil mapping
Soil acidity
Hymatomelanic acids
Humic acids
Humic acids
Soil classification
The amount of pesticides in the soil is residual
Soil colloids
Soil absorption complex
soil consistency
Soil pollution control
The maximum permissible concentration of a soil pollutant
fine earth
Migration of chemical compounds
Mineralization of the soil solution
Soil pollution monitoring
soil swelling
Soil ion exchange
Soil bases are exchangeable
Soil protection
Soil passport
Soil pollutant persistence
soil fertility
soil density
Soil trial site
Mobility of chemical compounds in soil
Soil acidification
Soil subtype
Soil alkalization
Soil cover
The soil
soil fatigue
Soil sample absolutely dry
Soil sample air-dry
Single soil sample
Soil sample combined
Soil sample mixed
Pore ​​space in the soil
soil profile
soil type
soil discharge
Soil type
Soil self-purification
Selectivity of ion exchange in soil
soil skeleton
Soil organic-mineral compounds
Easily soluble soil salts
Soil salts, sparingly soluble
Composition of humus group
Fractional composition of humus
Soil composition granulometric
Soil condition sanitary
Degree of humification of organic matter
The degree of saturation of the soil with bases
Soil cover structure
Soil structure
The amount of exchangeable cations in the soil
The amount of exchangeable bases in the soil
soil type
Soil-forming factors
Soil fraction silty
Soil fraction mechanical
Fulvic acids
Soil chemical characteristics
Part of the soil is hard
Soil alkalinity
soil mechanical element
soil erosion

APPENDIX

Reference

	Definition
1. Soil-forming substrate	The weathered part of the earth's crust from which soil formed and develops
2. Type of soil-forming substrate	Classification unit of a soil-forming substrate that has similar characteristics in terms of texture and formation
3. Pedotop	Homogeneous soil spatial unit, the features of which vary within a certain interval
4. Podochore	A heterogeneous soil spatial unit consisting of several pedotopes that have a certain pattern of distribution
5. Soil shape	Classification unit of soils, defined by a combination of soil type or subtype and soil-forming substrate
6. Soil quality	Characteristics of the properties and composition of the soil, which determines its fertility
7. Heterogeneity of the soil cover	Spatial differentiation of soil cover characterized by differences in the properties and location of soils or pedotopes
8. Homogeneous (heterogeneous) soil cover	Ground cover containing at least 75% of the area with similar soil properties
9. Mechanical composition of the soil
10. Soil organisms	The totality of plant and animal organisms whose life takes place entirely or mainly in the soil
11. Soil reaction	The amount of free protons contained in the soil solution
12. Optimal content chemical in soil
13. Soil absorption capacity	A quantity that quantitatively expresses the ability of the liquid and solid phases of the soil to withstand a change in the reaction of the environment when a strong acid or alkali is added

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Method I.V. Tyurin is based on the oxidation of the carbon of humus substances to CO2 with a 0.4 N solution of potassium dichromate (K2Cr2O7). By the amount of chromium mixture used for the oxidation of organic carbon, its amount is judged. The purpose of the work: to learn how to determine the content of soil organic carbon by the method of wet ashing according to I.S. Tyurin. Materials and equipment: 1) 100 ml conical flasks, 2) funnels, 3) 0.4 N solution of K2Cr2O7 in dilute H2SO4 (1:1), 4) 0.1 N or 0.2 N Mohr's salt solution, 5) 0.2% phenylanthranilic acid solution, 6) titration burette, 7) hotplate or gas-burner. Progress of work: on an analytical balance, take a sample of soil 0.2-0.3 g. A sample of soil is carefully transferred into a 100 ml conical flask. 10 ml of chromium mixture is poured into the flask from the buret and the contents are gently mixed in a circular motion. A small funnel is inserted into the flask, which serves as a reflux condenser, the flask is placed on an asbestos mesh or an eternite tile, then the contents of the flask are brought to a boil and boiled for exactly 5 minutes from the moment large CO2 bubbles appear. Violent boiling is not allowed, as this leads to a distortion of the results due to the possible decomposition of the chromium mixture. For mass analyses, it is recommended to replace boiling by heating in an oven at 150°C for 30 minutes. The flask is cooled, the funnel and walls of the flask are washed out of the wash with distilled water, bringing the volume to 30-40 ml. Add 4-5 drops of a 0.2% solution of phenylanthranilic acid and titrate with 0.1N or 0.2N Mohr's salt solution.

The end of the titration is determined by the transition of the cherry-violet color to green. A blank determination is carried out, instead of weighing the soil using calcined soil or pumice (0.20.3 g). The content of organic carbon is calculated by the formula:

C \u003d (100 * (a - c) * KM * 0.0003 * KH2O) * P-1,

where C is the content of organic carbon, %; a - the amount of Mohr's salt used for blank titration; c - the amount of Mohr's salt used for titration of the potassium chromate residue; KM - correction to the titer of Mohr's salt; 0.0003 - the amount of organic carbon corresponding to 1 ml of 0.1 n solution of Mohr's salt, g (using 0.2 n solution of Mohr's salt, the amount of organic carbon corresponding to 1 ml of Mohr's salt is 0.0006 g); КН2О - coefficient of hygroscopicity for recalculation for absolutely dry sample of soil; P - sample of air-dry soil, g. The humus content is calculated based on the fact that its composition contains an average of 58% organic carbon (1 g of carbon corresponds to 1.724 g of humus):

Humus (%) \u003d C (%) * 1.724.

humic ashing titration

Tab. Fig. 1. Grouping of soils of forest nurseries in the taiga zone according to the availability of humus (scale of the Leningrad Research Institute of Forestry

Humus, % according to Tyurin	Degree of security
	Extremely poor
	Underserved
	Average wealthy
	well endowed

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The concept, features and process of humus formation. Humic substances as the main organic component of soil, water and solid fossil fuels. Significance and role of humification in soil formation. Chemical structure and properties of humic substances.

abstract, added 11/15/2010


Analysis of the soil cover within the boundaries of the licensed areas of the oil and gas complex of the Khanty-Mansiysk Autonomous Okrug - Yugra. Morphological description of gray forest soils. The process of transformation of plant residues in gray forest soils.

practice report, added 10/10/2015


Humus, its importance, ways to increase the content of humus in the soil. Crop rotation, meaning, classification. Technological operations performed during soil cultivation. Agricultural practices. Spring rapeseed. Meaning. Morphological and biological features.

test, added 05/20/2008


Interaction of humic substances with the mineral part of the soil. Aerobic anaerobic processes in the soil. Their role in fertility and plant life. Agronomic features of podzolic soils and their cultivation. The use of swamps and peat in agriculture.

test, added 01/12/2010


presentation, added 03/17/2014


Properties of the soil cover of Yakutia and its geography. Circulation of matter and energy. Soil formation factors. The air regime of the soil and the content of nutrients in it. Distribution of the land fund by soil categories. Farmland analysis.

Humus comes from lat. humus"earth, soil" - the main organic matter of the soil, containing the nutrients necessary for higher plants. Humus makes up 85-90% of soil organic matter and is an important criterion in assessing soil fertility. In the weight composition of the upper soil layer, the humus content varies from a fraction of a percent for steppe soils to 10-15% for chernozems. Humus consists of individual (including specific) organic compounds, products of their interaction, as well as organic compounds in the form of organo-mineral formations.

Humus is formed in the soil as a result of the transformation of plant and animal organic residues - humification.

To determine the content of organic matter in the soil, in soil analysis laboratories determine separately the amount of plant residues and humus. Plant residues are isolated from the soil in a dry or wet way, after which their amount is determined. To determine the amount of humus at soil chemical analysis it is necessary to determine the carbon content of decomposed organic matter in the soil - organic carbon. To determine organic carbon in soil analysis laboratories using the oxidometric method of analysis. Samples for soil chemical analysis for humus content are selected in accordance with GOST 17.4.3.01-83 “Nature protection. Soils. General requirements to sampling" .

The essence of the oxidometric method for determining humus in the soil is that organic matter is oxidized with potassium dichromate in a strongly acidic medium until carbon dioxide is formed, then the excess of potassium dichromate is titrated with a solution of Mohr's salt and the content of organic carbon in the soil is determined by the difference in the volumes of Mohr's salt consumed for titration of dichromate potassium in the experiment without soil and in the experiment with soil. The soil weight is taken depending on the approximate humus content: 0.05-1 gram for chernozems, about 1 gram for light gray soils.

Basic terms and definitions according to GOST: 27593-88 Soils. Terms and Definitions.

Humic acids- a class of high-molecular organic nitrogen-containing hydroxy acids with a benzoic nucleus, which are part of humus and are formed in the process of humification.

Humic acids(HA) - a group of dark-colored humic acids, soluble in alkalis and insoluble in acids.

Hymatomelanic acids(HMC) is a group of humic acids soluble in ethanol. Fulvic acids(FC)- a group of humic acids, soluble in water, alkalis and acids.

Gumin- organic matter that is part of the soil, insoluble in acids, alkalis, organic solvents.

Degree of humification of organic matter is the ratio of the amount of carbon in humic acids to the total amount of soil organic carbon, expressed in mass fractions.

Of the indirect methods for determining humus, the method of I.V. Tyurin, based on the oxidation of carbon of the organic matter of the soil with a sulfate solution of potassium dichromate, the excess of which is titrated with a solution of Mohr's salt, is most widely used. In fact, this method determines the oxidizability of humus. If we assume that the interaction of a solution of potassium dichromate with soil only oxidizes the carbon of humus and restores Cr 2 O 7 2- to Cr 3+, then the reaction can be schematically expressed by the following equation:

3С + 2K 2 Cr 2 O 7 + 8H 2 SO 4 → 3CO 2 + 2Cr 2 (SO 4) 3 + 2K 2 SO 4 + 8H 2 O

Since the potassium dichromate solution is poured into the sample of soil in excess, some part of it remains unused after the completion of the carbon oxidation reaction. The unreacted excess of Cr 2 O 7 2- is titrated with Mohr's salt solution (NH 4) 2 SO 4 ∙ FeSO 4 ∙ 6H 2 O:

K 2 Cr 2 O 7 + 6FeSO 4 + 7H 2 SO 4 → Cr 2 (SO 4) 3 + 3Fe 2 (SO 4) 3 + K 2 SO 4 + 7H 2 O

The volume of Mohr's salt solution used for titration is used to calculate the carbon content of the soil.

When interacting with humus, the Cr 2 O 7 2- ion reacts not only with carbon, but also with hydrogen, which is part of organic compounds:

12Н + 2K 2 Cr 2 O 7 + 8H 2 SO 4 → 2Cr 2 (SO 4) 3 + 2K 2 SO 4 + 14H 2 O

Since the product of hydrogen oxidation is water, it will not affect the results of carbon determination only if the ratio of hydrogen and oxygen atoms in the composition of soil humus is 2:1, as in H 2 O. If the ratio H:O >2 in humus, then more K 2 Cr 2 O 7 is consumed for its oxidation than is required for carbon oxidation, and the results are overestimated. With a ratio of H:O< 2 на окисление гумуса K 2 Cr 2 O 7 израсходуется меньше, чем необходимо для окисления углерода. В этом случае результаты будут заниженными.

Sulfuric acid solution of potassium dichromate reacts not only with humus, but also with some mineral components of the soil.

When analyzing soils containing free carbonates, sulfuric acid is partially neutralized, but this does not affect the results of determining humus carbon.

If the soils are saline and contain chloride ions, then the results of determining the total humus turn out to be overestimated, since along with carbon oxidation, Cr 2 O 7 2- is also consumed for the oxidation of chloride ions. The presence of reduced iron and manganese ions in hydromorphic soils also leads to overestimated results, since a part of Cr 2 O 7 2- goes to the oxidation of these ions. However, restrictions on the use of the Tyurin method for determining the humus content in hydromorphic soils apply only to freshly taken samples. It has been repeatedly noted in the literature that when analyzing samples of hydromorphic soils dried to an air-dry state, the results of determining humus obtained by the Tyurin method practically do not differ from the results obtained by the Knopp-Sabanin method. Therefore, the Tyurin method can also be used for the analysis of air-dry samples of hydromorphic soils.

The shortcomings of the Tyurin method include incomplete oxidation of organic matter, especially when analyzing samples from peaty horizons or enriched in decomposed plant remains. The humus content found by the Tyurin method is 85-95% of the amount determined by the dry combustion method according to Gustavson. For a more complete oxidation of carbon in organic compounds with a solution of potassium dichromate, I.V. Tyurin recommended using 0.1-0.2 g of Ag 2 SO 4 as a catalyst. In this case, 95–97% of the carbon of organic compounds is oxidized; however, in the practice of mass analyzes, a catalyst is usually not used.

Analysis progress. On an analytical (or torsion) balance, a sample of soil prepared for determining the total humus is taken, accurate to the third decimal place. It is recommended to adhere to the following weights (V.V. Ponomareva, T.A. Plotnikova, 1980):

Samples of soils are transferred into dry, clean 100 ml conical flasks and exactly 10 ml of a 0.4 N solution of a chromium mixture are added to them from a burette. It is a thick, viscous liquid, and if it is added quickly, some of the reagent will remain on the walls of the burette, which will lead to a large inaccuracy in the results of the analysis. The chromium mixture must be added slowly, at such a speed that falling drops can be seen. The nose of the burette should touch the neck of the flask to avoid splashing of the reagent when the drops fall freely.

The flasks are closed with small funnels or a stopper - a refrigerator and placed on a preheated tile. From the moment large bubbles of gas appear, the solution should boil moderately for exactly 5 minutes. It should not be taken as the beginning of boiling the intense release of small bubbles of air absorbed by the soil, which occurs even before boiling. The boil should always be more or less the same in intensity, neither too violent nor too weak, and the bubbles a little larger than a poppy seed. Boiling should not be accompanied by the release of steam from the funnel.

In the process of boiling, the solution of the chromium mixture changes its color from reddish-brown to brownish-brown, and sometimes green. The green color of the chromium mixture after the end of boiling indicates that potassium dichromate was not enough for the complete oxidation of soil humus. In this case, the analysis should be repeated with a smaller sample of soil.

After the boiling time, the flasks are removed from the stove and cooled. The funnel or stopper-refrigerator, as well as the walls of the flask, are washed from the rinse with distilled water, diluting the solution in the flask by 2-3 times. Add 5-6 drops of an indicator (0.2% solution of phenylanthranilic acid) and titrate the unreacted residue of the chromium mixture with 0.2 N. Mohr's salt solution until the brownish-brown color changes first to purple and then to green. The color of the chromium mixture, especially at the end of the titration, changes very sharply, so the titration must be done carefully and vigorously stir the contents of the flask all the time in a circular motion. The transition from purple to green comes from one drop of Mohr's salt. Reliable results are obtained when at least 10 ml of 0.2 N Mohr's salt solution is used to titrate the potassium dichromate residue.

Under strictly similar conditions, a blank determination is carried out in 2-fold repetition, adding about 0.1 g of calcined soil or pumice to the flask instead of the analyzed soil.

where V 1 is the amount of Mohr's salt solution used for titration of 10 ml of chromium mixture in a blank experiment, ml; V 2 is the amount of Mohr's salt solution used for titration of the chromium mixture of the analyzed sample, ml; n is the normality of the Mohr salt; 0.003 – molar mass of carbon equivalent, g/mol; m is the sample of soil, g; Kn 2 o - conversion factor for absolutely dry soil; 100 is a multiplier for conversion to 100 g of soil.

Calculation example. The sample of soil taken to determine humus is 0.305 g. 25.8 ml of Mohr's salt solution was used for titration of a blank sample, 22.3 ml of Mohr's salt solution was used for titration of the analyzed sample. The normality of Mohr's salt solution is 0.204. The conversion factor for absolutely dry soil is 1.072. The organic carbon content is:

Humus \u003d 0.96 ∙ 1.724 \u003d 1.66%.

The following reagents are used for analysis:

1. 0.4 n. solution of K 2 Cr 2 O 7 in dilute (1:1) sulfuric acid. 40 g of K 2 Cr 2 O 7 are dissolved in 500-600 ml of distilled water and filtered through a paper filter into a 1-liter volumetric flask. The solution is brought to the mark with distilled water and poured into a heat-resistant container with a capacity of 2.5-5 liters. To a solution of K 2 Cr 2 O 7 in a fume hood, poured in small portions (approximately 100 ml each) with careful and repeated stirring, 1 liter of concentrated H 2 SO 4 (pl. 1.84). When the solution is mixed with sulfuric acid, a strong heating of the liquid occurs, so you need to perform operations very carefully and use only heat-resistant dishes.

The prepared solution is closed with a funnel or glass and left to stand for complete cooling until the next day, then poured into a bottle with a ground stopper and stored in a dark place.

2. 0.2 n. Mohr's salt solution. Take 80 g of salt (NH 4) 2 SO 4 ∙ FeSO 4 ∙ 6H 2 O ( only blue crystals are used, brown ones are discarded) is placed in a flask filled with 650-700 ml of 1 N H 2 SO 4 solution and the solution is shaken until the salt is completely dissolved. The solution was then filtered into a 1 L volumetric flask and made up to the mark with distilled water. Mohr's salt solution is stored in a bottle insulated from the air with a Tishchenko flask with an alkaline solution of pyrogallol or a tube with Mohr's salt crystals.

The normality of Mohr's salt solution is established and checked by 0.1 N. KMnO 4 solution. Due to the fact that the normality of Mohr's salt changes rapidly, it should be checked after 1-2 days. To do this, 1 ml of H 2 SO 4 (density 1.84) is poured into a 250 ml conical flask with a measuring cylinder, 10 ml of Mohr's salt solution is measured with a burette, 50 ml of distilled water is added and titrated with 0.1 N. KMnO 4 solution (prepared from fixonal) to a slightly pink color that does not disappear within 1 min. The titration is repeated and the average value is taken. The normality of a solution of Mohr's salt is found by the formula:

V 1 ∙ N 1 = V 2 ∙ N 2

where V 1 and N 1 are the volume and normality of the Mohr salt solution, V 2 and N 2 are the volume and normality of the KMnO 4 solution.

3. 0.2% solution of phenylanthranilic acid C 13 H 11 O 2 N. Phenylatranilic acid is insoluble in water, so the indicator is prepared in a soda solution, for which 0.2 g of phenylanthranilic acid is dissolved in 100 ml of a 0.2% solution of anhydrous soda ( Na 2 CO 3). For better dissolution, a sample of phenylanthranilic acid is pre-moistened in a porcelain cup with a 0.2% soda solution to a creamy state and, in this form, is thoroughly mixed with a glass rod. After that, the rest of the soda solution is poured.

4. 1 n. H 2 SO 4 solution. In a 1 L volumetric flask filled with ~ 500 ml of distilled water, add 28 ml of concentrated H 2 SO 4 measured with a cylinder and mix. Allow the flask to cool to room temperature, dilute to the mark with distilled water and mix thoroughly.