CN101419175A - Method for detecting organic matter in soil - Google Patents

Abstract

The invention relates to measurement for organic substances in soil, in particular to a method for measuring organic substances in soil. The method comprises the following steps: using a digestion instrument to replace a heating device; using a digestion tube to replace a conical flask to receive samples and reagent solution; covering a small funnel with a bent part above the digestion tube when heating; timing from boiling of the solution; taking down the digestion tube after 6 to 8 minutes; cooling the digestion tube; and using sodium diphenylamine sulphonate as indicator to titrate residual K2Cr2O4. The method has the advantages of good repeatability, high reproducibility, simplicity and practicability.

Description

A kind of method of measuring soil with organic matter

Technical field

The present invention relates to the mensuration of soil with organic matter, a kind of specifically assay method that improves the soil organism.

Background technology

The soil organism is the various nutrients main source of nitrogen, phosphorus particularly in the soil, and it can make soil have keeping fertility and resiliency, make loosing soil and form structure, thereby have the ability of improving soil physico-chemical property, and be one of foundation of the classification of soils.In addition, the biological characteristics of soil also can change with the change of soil organism quality and quantity.Therefore, the content of organic matter be used as usually soil fertility level height important indicator (document 1: labor man Gui. handbook [M] is analyzed in soil agrochemistry. Beijing: agriculture publishing house, 1988:229-236; Document 2: Wen Xiaoqi. soil organism organon [M]. Beijing: agriculture publishing house, 1984:19-37; Document 3: Agricultural University Of Nanjing. soil agrochemistry analysis [M]. Beijing: agriculture publishing house, 1996:29-39).

The main method of measuring at present the soil organism comprises calcination method and potassium dichromate oxidation, and using maximum is potassium dichromate oxidation.The national standard method (GB9834-88) of measuring soil with organic matter is exactly a potassium dichromate oxidation.Its operation steps is: choose representative air-dry pedotheque, choose except that organic residual bodies such as plant roots leaves with tweezers, with waddy soil block is pressed carefully then, make it to sieve by 1mm.Fully behind the mixing, therefrom take out sample 10-20g, levigate, and all by the 0.25mm sieve, standby in the dress people port grinding bottle.Take by weighing the air-dried sample 0.05-0.5g for preparing, be accurate to 0.0001g, insert in the 150mL triangular flask, add the silver sulfate 0.1g of powdered, accurately add people 0.4mol/l potassium dichromate one sulfuric acid solution 10mL then and shake up.With the triangle that fills a sample bottled-simple and easy air set pipe, dislocation has been preheating in 200-230 ℃ the electric sand bath and has heated.When simple and easy air set pipe lower end falls first condensed fluid, begin to clock, disappear and boil 5 ± 0.5min.Disappear boil finish after, triangular flask is taken off cooling a moment from electric sand bath, water flushing condenser pipe inwall and the auspicious outer wall in the end thereof, make in the wash-bottle cumulative volume of solution should be controlled at 60-80ml and be advisable, add 3-5 and drip the phenanthroline indicator, with the remaining potassium dichromate of ferrous sulphate standard solution titration.Every Lot sample must be done 2-3 blank the demarcation simultaneously, gets the Powdered silicon dioxide of 0.500g and replaces sample, and other steps are identical with sample mensuration, get its mean value.But the author does overtesting, and electric sand-bath is heated inhomogeneous, and the time of beginning condensation is inconsistent, makes troubles to timing.

The national standard method GB7857-87 that measures the forest soil organic matter also is K ₂Cr ₂O ₄Volumetric method, operation steps is: claim soil sample (crossing the 0.25mm sieve) in the hard Boiling tube, to add 5ml0.8mol/l 1/6K with suction pipe with the decrement method ₂Cr ₂O ₄Standard solution, inject the 5ml concentrated sulphuric acid with syringe then, and careful rotation shakes up and is placed in the wire mesh cage, wire mesh cage is put into the oil bath pan that is heated to 185～190 ℃ in advance heat, temperature control is in 170～180 ℃, and makes solution keep boiling 5min, take out the iron wire cage, solution is shifted in the cooling back, is indicator with the phenanthroline, uses FeSO ₄Titration.But the enhancing with people's environmental consciousness of improving constantly along with the modern science means of testing, the analysis operation persons more and more feel the inadvisable property of oil bath heating means: (1) oil is volatile and pollute the laboratory air in conduction process, influences the healthy of operator; (2) if with naked light heating, easily ignite volatile oil and breaking out of fire danger; (3) the heating-up temperature undulatory property is big, influences the sample oxidation efficiency; (4) the sample hose outside surface is difficult to clean after adhering to grease, and can cause measurement result higher with in the grease lead-in tube outside the pipe in cleaning process as accidentally.

Summary of the invention

The purpose of this invention is to provide a kind of good reproducibility, reappearance height, and the method for the simple mensuration soil organism.

For achieving the above object, the technical solution used in the present invention is as follows:

A kind of method of measuring soil with organic matter,

1) it is levigate to get air-dry pedotheque 10-20g, and it is standby to cross the 0.25mm sieve, sample soil;

2) boil to disappearing and add sample soil 0.05-0.5g (being accurate to 0.0001g), Ag in the pipe successively ₂SO ₄0.15g, accurately add 10-20ml 0.10mol/lK with transfer pipet ₂Cr ₂O ₇-dense H ₂SO ₄Solution, boil in the pipe to disappear, put test tube then and disappear and boil in the aluminium ingot, pick up counting, take out test tube behind the 6-8min from boiling in being preheated to 170-180 ℃ in advance, after allowing it cool off automatically, break-even changing in the 250ml triangular flask washed test tube 2-3 time with distilled water, and the distilled water cleansing solution changes in the triangular flask equally, the volume of complete soln is 60-100ml in the final triangular flask, adds the H of 3-5ml mass concentration 85% ₃PO ₄With 0.1-0.3ml mass concentration 0.4-0.5% diphenylamine sulfonic acid sodium salt indicator, use 0.1-0.2mol/l FeSO then ₄Standard solution titration becomes to solution till the bright green, determines the FeSO that is consumed ₄The consumption of solution;

Get the Powdered silicon dioxide of 0.05-0.5g and replace sample soil to compare group, other steps are identical with sample soil test process, determine the FeSO that is consumed ₄The consumption of solution;

3) preparation antifebrin standard solution: get antifebrin reagent 0.1407 gram, add the redistilled water dissolving, be settled in the 1000ml volumetric flask, this solution contains organic carbon 100mg/l, is that mother liquor is diluted to organic carbon 10mg/l as the antifebrin standard solution with this solution; Replace sample soil carry out step 2 with this solution 5ml) operation, determine the FeSO that is consumed ₄The consumption of solution;

Replace the antifebrin standard solution to organize with distilled water 5.0ml, carry out aforesaid operations, determine the FeSO that is consumed as blank ₄The consumption of solution;

Calculate recovery rate:

Wherein: V _BlankThe FeSO that is consumed during-titration blank group ₄Liquor capacity, V _{Standard substance}The FeSO that consumes during-titration antifebrin standard solution ₄Liquor capacity, n _{Standard substance}The concentration of-standard substance, V _{Standard substance}The volume of-standard substance;

4) soil with organic matter content:

Wherein: V ₀The FeSO that consumes during-demarcation control group ₄Liquor capacity, V ₁The FeSO that-titration soil sample consumes ₄Liquor capacity, 1.724-organic carbon is changed into organic coefficient, m-air-dry quality of soil sample.

The principle of this test is as follows:

1) organic carbon and potassium dichromate react under the condition of heating:

2K ₂Cr ₂O ₇+8H ₂SO ₄+3C＝2K ₂SO ₄+2Cr ₂(SO ₄)3+3CO ₂↑+8H ₂O

2) remaining potassium dichromate and titrant ferrous sulphate react at normal temperatures during titration:

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

Before each the mensuration, FeSO ₄The concentration of solution all needs to demarcate again, and its process is,

Adopt conventional K ₂Cr ₂O ₇Oxidizing process is demarcated the concentration of FeSO4 solution, adds 1ml0.10mol/l K successively to triangular flask ₂Cr ₂O ₇, the dense H of 4ml ₂SO ₄With the dense H of 2ml ₃PO ₄, adding distil water 20ml carries out titration with FeSO4 solution;

Calculate the FeSO4 solution concentration:

$C_{{\mathrm{FeSO}}_4}=\frac{C_{K_2{\mathrm{Cr}}_2{O}_7}\×V_{K_2{\mathrm{Cr}}_2{O}_7}}{V_{{\mathrm{FeSO}}_4}}$

Wherein:

-K ₂Cr ₂O ₇Solution concentration, -K ₂Cr ₂O ₇Liquor capacity,

-FeSO ₄Solution concentration,

-FeSO ₄Liquor capacity.

Innovation part of the present invention is:

1. using disappears boils device and heats.The accuracy of boiling pipe heating of disappearing is very high, and edge effect is very little, and mixing material all wraps in the heating aluminium ingot, can guarantee that most solution come to life simultaneously, and offsets the temperature and time that boils easily and control.

2. add 0.15g Ag ₂SO ₄Ag ₂SO ₄Effect in this reaction has two: the one, and catalyzer, that play catalytic action is Ag ⁺The 2nd, screening agent is eliminated the Cl that may exist in the soil ^-Just interference to the test findings generation.The author adds 0.10g Ag by the discovery of doing experiment ₂SO ₄Can not well achieve the above object, and 0.15g can just satisfy above-mentioned requirements simultaneously.But Ag ₂SO ₄Amount again can not be too many, too much Ag ⁺May generate Ag ₂Cr ₂O ₇Precipitation influences measurement result.

3. add strong phosphoric acid (mass concentration 85%) during titration.The purpose that adds phosphoric acid: K ₂Cr ₂O ₇In acid solution, show very strong oxidability, therefore will add 1mol/L H ₂SO ₄, this moment Cr ₂O ₇ ^2-/ Cr ³⁺The condition electrode potential be 1.08V, can make Fe ²⁺Be oxidized to Fe ³⁺At 1mol/L H ₂SO ₄Middle E e ³⁺/ Fe ²⁺=+0.68V, the H of adding 1:3 (V/V) ₃PO ₄The back is because PO ₄ ^3-With Fe ³⁺Form stable colourless complex ion [Fe (PO ₄) ₂] ^3-, and make Fe ³⁺/ Fe ²⁺The right condition electrode potential of electricity reduces, so H is being arranged ₃PO ₄The H that exists ₂SO ₄Titration Fe in the medium ²⁺The time, the initial conditions electrode potential is minimum, and titration jump is the longest.

4. indicator is used sodium hisbenzene sulfonate instead.The oxidation state of diphenylamine sulfonic acid sodium salt is a purple, and it is colourless going back ortho states, and the condition electrode potential of variable color is 0.85V.Color change interval is 0.85 ± 0.059/2V, uses K ₂Cr ₂O ₇Titration Fe ²⁺The current potential of mutation range just in time the color change interval of indicator is included in, so during stoichiometric point, indicator is reduced into colourless by purple.Reaction equation is:

Diphenylbenzidine sulfonic acid purple (purple) diphenylbenzidine sulfonic acid (colourless)

The sodium hisbenzene sulfonate that adds is immediately by K ₂Cr ₂O ₇Be oxidized to the diphenylbenzidine sulfonic acid purple of purple, though the certain K of this reaction needed consumption ₂Cr ₂O ₇, along with the carrying out of titration, reversible reaction is carried out left, when arriving titration end-point, and K ₂Cr ₂O ₇All be released.Use the phenanthroline indicator then to need to consume titrant FeSO ₄, influence the accuracy of measurement result, so select to use instead sodium hisbenzene sulfonate.

Improving one's methods of using measured the soil organism, and following advantage is arranged:

1. heat satisfactory for result.Use disappears and boils device and heat, and its temperature fluctuation is little, and edge effect is minimum, and test tube is heated evenly, and does not produce testing laboratory's secondary pollution.

2. precision height, the accuracy degree is good.Aluminium ingot adds the heat energy better controlled and measures precision, well overcomes edge effect because aluminium ingot adds heat energy, and this is the indeterminable problem of oil bath and sand-bath.Use the sodium hisbenzene sulfonate indicator instead, can reduce the amount that participates in the redox reaction thing effectively, make measurement result more accurate.

3. instrument is simple, and is easy and simple to handle.Sand-bath needs condensing unit, has strengthened the cost and the complexity of test; Oil bath does not need condensing unit, complex operation and harmful.The present invention adopts simple to operate disappearing to boil device, disappears to boil to cover little funnel, and the effect of little funnel has two: the one, reduce heat dissipation, and play the effect of insulation; The 2nd, play the effect of partial reflux.

Embodiment

Adopt conventional K ₂Cr ₂O ₇Oxidizing process is demarcated the concentration of FeSO4 solution, adds 1ml0.10mol/l K successively to triangular flask ₂Cr ₂O ₇, the dense H of 4ml ₂SO ₄With the dense H of 2ml ₃PO ₄, adding distil water 20ml carries out titration with FeSO4 solution;

Calculate the FeSO4 solution concentration:

$C_{{\mathrm{FeSO}}_4}=\frac{C_{K_2{\mathrm{Cr}}_2{O}_7}\×V_{K_2{\mathrm{Cr}}_2{O}_7}}{V_{{\mathrm{FeSO}}_4}}$

Wherein:

-K ₂Cr ₂O ₇Solution concentration,

-K ₂Cr ₂O ₇Liquor capacity, -FeSO ₄Solution concentration,

-FeSO ₄Liquor capacity.

Embodiment 1

The soil pre-treatment is according to national standard method GB 9834-88.Choose representative air-dry pedotheque, choose except that organic residual bodies such as plant roots leaves, with waddy soil block is pressed carefully then, make it to sieve by 1mm with tweezers.Fully behind the mixing, therefrom take out sample 10-20g, levigate, and all by the 0.25mm sieve, standby in the dress people port grinding bottle.

The heating arrangement that the present invention improves one's methods is used instead to disappear and is boiled instrument, disappears to boil pipe and replace triangular flask splendid attire sample and reagent solution, disappears during heating and boils the little funnel of pipe top lid one afterbody bending, picks up counting from the solution boiling, will disappear behind the 6-8min to boil pipe and take off cooling.Make indicator with diphenylamine sulfonic acid sodium salt, use FeSO ₄The remaining K of titration ₂Cr ₂O ₄

Contrast the oil bath heating and disappear and boil the precision of two kinds of methods of device heating.

1) use improved method that the organic matter that contains in the pedotheque is measured.

Boil to disappearing and to add soil sample 0.3g (being accurate to 0.0001g), Ag in the pipe successively ₂SO ₄0.15g, accurately add 10ml0.10mol/l K with transfer pipet ₂Cr ₂O ₇-dense H ₂SO ₄Solution is put test tube then and is disappeared and boil in the aluminium ingot in being preheated to 170-180 ℃ in advance, picks up counting from boiling, takes out test tube behind the 6-8min, allows it automatically after the cooling, and break-even changing in the 250ml triangular flask with distilled water washing test tube 3 times, adds the H of 3ml 85% ₃PO ₄With 4 0.5% diphenylamine sulfonic acid sodium salt indicator, use 0.2000mol/lFeSO then ₄Standard solution titration becomes till the bright green to solution.

Get the Powdered silicon dioxide of 0.500g and replace sample to compare group, other steps are measured identical with sample.

Preparation antifebrin standard solution: get antifebrin reagent 0.1407 gram, add the redistilled water dissolving, be settled in the 1000ml volumetric flask, this solution contains organic carbon 100mg/l, is that mother liquor is diluted to organic carbon 10mg/l as the antifebrin standard solution with this solution; Replace sample soil carry out step 2 with this solution 5ml) operation, determine the FeSO that is consumed ₄The consumption of solution;

Replace the antifebrin standard solution to organize with distilled water 5.0ml, carry out aforesaid operations, determine the FeSO that is consumed as blank ₄The consumption of solution;

Calculate recovery rate:

Wherein: V _BlankThe FeSO that is consumed during-titration blank group ₄Liquor capacity, V _{Standard substance}The FeSO that consumes during-titration antifebrin standard solution ₄Liquor capacity, n _{Standard substance}The concentration of-standard substance, V _{Standard substance}The volume of-standard substance;

Soil with organic matter content:

Wherein: V ₀The FeSO that-demarcation control group consumes ₄Liquor capacity, V ₁The FeSO that-titration soil sample consumes ₄Liquor capacity, 1.724-organic carbon is changed into organic coefficient, m-air-dry quality of soil sample.

2) oil bath heating (national standard method GB7857-87):

In the hard test tube, add soil sample 0.3g (being accurate to 0.0001g) successively, add 5ml0.8mol/l 1/6 K with suction pipe ₂Cr ₂O ₄Standard solution, inject the 5ml concentrated sulphuric acid with syringe then, and careful rotation shakes up and is placed in the wire mesh cage, wire mesh cage is put into the oil bath pan that is heated to 185～190 ℃ in advance heat, temperature control is in 170～180 ℃, and makes solution keep boiling 5min, take out the iron wire cage, solution is shifted in the cooling back, is indicator with the phenanthroline, uses FeSO ₄Titration to solution is pink colour.

Get the Powdered silicon dioxide of 0.500g and replace sample, organize in contrast, other steps are measured identical with sample.

Soil with organic matter content:

$\mathrm{OM}=\frac{C_{\mathrm{FeS}{O}_4}\×(V_0-V_1)\×3\×{10}^{-3}\×1.724}{m}\×100$

Wherein: V ₀The FeSO that-demarcation control group consumes ₄Liquor capacity, V ₁The FeSO that-titration soil sample consumes ₄Liquor capacity, 1.724-organic carbon is changed into organic coefficient, m-air-dry quality of soil sample.

Use the method and the national standard method of invention as shown in table 1 to soil with organic matter Determination on content result.By the result as can be seen, the method precision of invention is significantly better than national standard method.

Table 1 inventive method and national standard method result contrast

National standard method (%)	Numbering	Inventive method (%)
			3.86	1	3.91
3.79	2	3.81
			3.74	3	3.74
3.90	4	3.71
			3.87	5	3.70
3.88	6	3.98
			3.84±0.06	The mean value fiducial interval	3.81±0.12

Annotate: the soil of numbering 1,2 disappears, and to boil temperature be 170 ℃, and the time of boiling that disappears is 8min; Numbering 3,4 soil disappears, and to boil temperature be 175 ℃, and the time of boiling that disappears is 7min; Be numbered 5,6 soil and disappear that to boil temperature be 180 ℃, the time of boiling that disappears is 6min.

Embodiment 2

Use content organic among the method bioassay standard soil sample GBW07412 of the present invention.

Specific implementation process:

Boil to disappearing and to add standard soil sample 0.4g (being accurate to 0.0001g), Ag in the pipe successively ₂SO ₄0.15g, accurately add 10ml0.10mol/l K with transfer pipet ₂Cr ₂O ₇-H ₂SO ₄Solution is put test tube then and is disappeared and boil in the aluminium ingot in being preheated to 180 ℃ in advance, picks up counting from boiling, takes out test tube behind the 6min, allows it automatically after the cooling, and break-even changing in the 250ml triangular flask with distilled water washing test tube 3 times, adds the H of 3ml85% ₃PO ₄With 4 0.5% diphenylamine sulfonic acid sodium salt indicator, use 0.2000mol/l FeSO then ₄Standard solution titration becomes till the bright green to solution.Get the Powdered silicon dioxide of 0.500g and replace sample, other steps are measured identical with sample.

Computation process is the same.

Use the method for invention that standard substance is measured 5 times, 5 times average result is as shown in table 2, and through the t-check relatively, measurement result conforms to reference value, illustrates with content results in the method mensuration soil of being invented accurately and reliably.

Table 3 uses the measurement result (n=5) of inventive method to the content of organic matter in the standard substance

Sample number into spectrum	Measured value (%)	Reference value (%)
			7412	1.822±0.082	1.820±0.090

Claims (2)

1. method of measuring soil with organic matter is characterized in that:

1) it is levigate to get air-dry pedotheque 10-20g, and it is standby to cross the 0.25mm sieve, sample soil;

2) boil to disappearing and add sample soil 0.05-0.5g, Ag in the pipe successively ₂SO ₄0.15g, add 10-20ml0.10mol/l K ₂Cr ₂O ₇-dense H ₂SO ₄Solution, boil in the pipe to disappear, put test tube then and disappear and boil in the aluminium ingot, pick up counting, take out test tube behind the 6-8min from boiling in being preheated to 170-180 ℃ in advance, after allowing it cool off automatically, change in the triangular flask, wash test tube 2-3 time with distilled water, the distilled water cleansing solution changes in the triangular flask equally, the volume of complete soln is 60-100ml in the final triangular flask, adds the H of 3-5ml mass concentration 85% ₃PO ₄With 0.1-0.3ml mass concentration 0.4-0.5% diphenylamine sulfonic acid sodium salt indicator, use 0.1-0.2mol/l FeSO then ₄Standard solution titration becomes to solution till the bright green, determines the FeSO that is consumed ₄The consumption of solution;

Get the Powdered silicon dioxide of 0.05-0.5g and replace sample soil to compare group, other steps are identical with sample soil test process, determine the FeSO that is consumed ₄The consumption of solution;

3) preparation antifebrin standard solution: get antifebrin reagent 0.1407 gram, add the redistilled water dissolving, be settled in the 1000ml volumetric flask, this solution contains organic carbon 100mg/l, is that mother liquor is diluted to organic carbon 10mg/l as the antifebrin standard solution with this solution; Replace sample soil carry out step 2 with this solution 5ml) operation, determine the FeSO that is consumed ₄The consumption of solution;

Replace the antifebrin standard solution to organize with distilled water 5.0ml, carry out aforesaid operations, determine the FeSO that is consumed as blank ₄The consumption of solution;

Calculate recovery rate:

Wherein: V _BlankThe FeSO that is consumed during-titration blank group ₄Liquor capacity, V _{Standard substance}The FeSO that consumes during-titration antifebrin standard solution ₄Liquor capacity, n _{Standard substance}The concentration of-standard substance, V _{Standard substance}The volume of-standard substance;

4) soil with organic matter content:

Wherein: V ₀The FeSO that consumes during-demarcation control group ₄Liquor capacity, V ₁The FeSO that-titration soil sample consumes ₄Liquor capacity, 1.724-organic carbon is changed into organic coefficient, m-air-dry quality of soil sample.

2. in accordance with the method for claim 1, it is characterized in that: before each the mensuration, the concentration of FeSO4 solution all needs to demarcate again, and its process is,

Adopt conventional K ₂Cr ₂O ₇Oxidizing process is demarcated the concentration of FeSO4 solution, adds 1ml0.10mol/l K successively to triangular flask ₂Cr ₂O ₇, the dense H of 4ml ₂SO ₄With the dense H of 2ml ₃PO ₄, adding distil water 20ml carries out titration with FeSO4 solution;

Calculate the FeSO4 solution concentration:

$C_{\mathrm{FeS}{O}_4}=\frac{C_{K_2{\mathrm{Cr}}_2{O}_7}\×V_{K_2{\mathrm{Cr}}_2{O}_7}}{V_{\mathrm{FeS}{O}_4}}$

Wherein:

-K ₂Cr ₂O ₇Solution concentration, -K ₂Cr ₂O ₇Liquor capacity,

-FeSO ₄Solution concentration,

-FeSO ₄Liquor capacity.