A method for determining organic phosphorus components of high organic matter soil

Abstract

The application discloses a method for determining organic phosphorus components of high-organic-matter soil, which comprises a decoloring step: adding KMnO4 solution drop by drop into a liquid to be decolored until the liquid to be decolored is purple red, then adding ascorbic acid solution to neutralize the excessive KMnO4, completing the decoloring, and obtaining a decolored liquid. The application can oxidize and dissolve organic matters in the liquid to be measured by adding KMnO4 solution, then neutralize the excessive KMnO4 with ascorbic acid solution, so that the liquid to be measured becomes colorless and clear, and the decoloring purpose is achieved. The use of ascorbic acid to neutralize the excessive potassium permanganate can not introduce other substances into the liquid to be measured, so that other possible errors can be avoided. The application can more accurately determine various forms of Pi by KMnO4 decoloring, so that more accurate soil organic phosphorus components can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry and relates to soil analysis methods, particularly to methods for determining organic phosphorus components in soil. Background Technology

[0002] Peat soil, marsh soil, meadow soil, etc. are all types of soil with high organic matter content.

[0003] Soil phosphorus classification is of great significance for understanding the composition of soil phosphorus forms and assessing phosphorus availability. However, the chemical forms of phosphorus compounds in soil are extremely complex, making it quite difficult to distinguish their specific chemical composition.

[0004] In existing technologies, a chemical grouping method is used to classify phosphorus-containing compounds in soil with similar chemical composition and similar biological availability into the same component, which is called soil phosphorus classification.

[0005] Among the methods for classifying soil organic phosphorus, the most classic is the Bowman and Cole method (BC method) proposed in 1978. This method classifies soil organic phosphorus into the following four components: active organic phosphorus (L-Po), moderately active organic phosphorus (ML-Po), moderately stable organic phosphorus / fulvic acid phosphorus (MR-Po), and highly stable organic phosphorus / humic acid phosphorus (HR-Po).

[0006] L-Po was extracted using NaHCO3 solution, and its main components are easily decomposed and mineralized substances such as nucleic acids and phospholipids, exhibiting high bioavailability. ML-Po was extracted using H2SO4 solution, and the extracted components include substances such as calcium phytate and magnesium, with bioavailability second only to L-Po. After extraction with NaOH solution, the extract was acidified with HCl. The acid-soluble component was MR-Po (fulvic acid phosphorus), while the acid-insoluble component was HR-Po (humic acid phosphorus).

[0007] In the process of realizing this invention, the inventors discovered that at least one of the following technical problems exists in the prior art:

[0008] a) The BC method is not suitable for organic phosphorus classification in soils with high organic matter content. After extraction with solutions such as NaHCO3 and NaOH, the organic matter dissolves, causing the test solution to turn yellowish-brown or dark brown, which seriously affects the subsequent molybdenum-antimony colorimetric process and causes measurement errors.

[0009] (b) For the reasons mentioned above, it is necessary to decolorize the extraction solution. Conventional techniques use activated carbon for decolorization. However, since activated carbon itself has an adsorption effect on phosphorus, the measured value will be lower than expected.

[0010] c) Activated carbon has a poor decolorization effect on soils with high organic matter content, which also affects the subsequent molybdenum-antimony colorimetric analysis and causes measurement errors.

[0011] In the existing technology, there is no literature on the analysis and determination of organic phosphorus components in soils with high organic matter content. Summary of the Invention

[0012] Therefore, the present invention aims to provide a method for accurately determining the organic phosphorus components in soils with high organic matter content.

[0013] Through long-term exploration and experimentation, and continuous reform and innovation, the inventors have provided a method for determining the organic phosphorus component of high-organic-matter soils to solve the above-mentioned technical problems. This method includes a decolorization step.

[0014] Add KMnO4 solution dropwise to the solution to be decolorized until the solution turns purple-red. Then add ascorbic acid solution to neutralize the excess KMnO4, thus completing the decolorization and obtaining the decolorized solution.

[0015] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soils of the present invention, the decolorization step specifically comprises:

[0016] Add 0.1 mol·L⁻¹ dropwise to the solution to be decolorized. -1 KMnO4 solution is added until the decolorized solution turns purplish-red. After 3-5 minutes, 10% ascorbic acid solution is added to neutralize the excess KMnO4, thus completing the decolorization and obtaining the decolorized solution.

[0017] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soil of the present invention, the organic matter content in the high-organic-matter soil is 100 g / kg or more.

[0018] According to one embodiment of the method for determining the organic phosphorus component of high organic matter soils of the present invention, the high organic matter soils include peat soils, marsh soils, or meadow soils.

[0019] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soils of the present invention, the organic phosphorus includes active organic phosphorus, and the determination steps for the active organic phosphorus are as follows:

[0020] S11. Take the air-dried soil powder, add NaHCO3 solution and shake to extract. After shaking, immediately centrifuge and filter with phosphorus-free filter paper to obtain the first precipitate and the first supernatant.

[0021] S12. Take a first preset amount of the first supernatant into the first colorimetric container, add H2SO4 to the colorimetric container, shake well to make the solution acidic and remove CO2, and obtain the first test solution.

[0022] S13. The first test solution is a decolorizing solution. The first test solution is decolorized to obtain the first decolorized solution.

[0023] S14. The active inorganic phosphorus in the first decolorizing solution was determined by the molybdenum-antimony colorimetric method.

[0024] S15. Take the first supernatant of the second preset amount, evaporate it to dryness in a container, add concentrated H2SO4, digest it, and prepare test solution A after digestion. The total active phosphorus of test solution A is determined by colorimetric determination using the molybdenum antimony colorimetric method.

[0025] The difference between total active phosphorus and active inorganic phosphorus is active organic phosphorus.

[0026] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soils of the present invention, the organic phosphorus further includes stable organic phosphorus; the determination steps for stable organic phosphorus are as follows:

[0027] S21. Take the first precipitate, extract it by shaking with NaOH solution, centrifuge and filter to obtain the second supernatant and the second precipitate;

[0028] S22. Take the first preset amount of the second supernatant into the second colorimetric tube, add H2SO4 and shake well to make the solution acidic, and obtain the second test solution;

[0029] S23. The second test solution is a decolorizing solution. The second test solution is decolorized to obtain a second decolorized solution.

[0030] S24. The stable inorganic phosphorus in the second decolorizing solution was determined by the molybdenum-antimony colorimetric method.

[0031] S25. Take the second preset amount of the second supernatant, evaporate it to dryness in a container, add concentrated H2SO4, digest it, and prepare test solution B after digestion. The stable total phosphorus of test solution B is determined by colorimetric determination using the molybdenum antimony colorimetric method.

[0032] The difference between stable total phosphorus and stable inorganic phosphorus is the stable organic phosphorus.

[0033] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soils of the present invention, the organic phosphorus further includes fulvic acid phosphorus; the determination steps for fulvic acid phosphorus are as follows:

[0034] S31. Take the third preset amount of the second supernatant, add concentrated H2SO4 to adjust the pH to acidic, let it stand to precipitate, take the preset amount of the third supernatant, put it in the third colorimetric tube, and obtain the third test solution.

[0035] S32. Take the first preset amount of the third test solution as the decolorizing solution and perform decolorization treatment to obtain the third decolorized solution;

[0036] S33, the MR-Pi of the third decolorizing solution was determined by the molybdenum-antimony colorimetric method;

[0037] S34. Take the second preset amount of the third test solution, evaporate it to dryness in a container, add concentrated H2SO4, digest it, and prepare test solution C after digestion. MR-Pt of test solution C is determined by colorimetric analysis using the molybdenum antimony colorimetric method.

[0038] The difference between MR-Pt and MR-Pi is fulvic acid phosphorus.

[0039] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soils of the present invention, the organic phosphorus further includes moderately active organic phosphorus, and the determination steps for the moderately active organic phosphorus are as follows:

[0040] S41. Take the second precipitate, add H2SO4 solution, shake to extract, centrifuge, filter, and obtain the fourth supernatant;

[0041] S42. Take the fourth supernatant of the first preset amount as the fourth test solution, and measure ML-Pi by the molybdenum-antimony colorimetric method.

[0042] S43. Take the second preset amount of the fourth supernatant, evaporate it to dryness in a container, add concentrated H2SO4, digest and boil it, and prepare the D test solution after digestion. The ML-Pt of the D test solution is measured by colorimetric determination using the molybdenum antimony colorimetric method.

[0043] The difference between ML-Pt and ML-Pi is the medium-activity organophosphorus compound.

[0044] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soils of the present invention, the specific steps of evaporating to dryness in a container, adding concentrated H2SO4, and digesting are as follows:

[0045] Place the container on a boiling water bath to evaporate to dryness, add concentrated H2SO4, shake well, then add HClO4 dropwise and shake well. Place a small curved-neck funnel at the mouth of the bottle and heat it on a hot plate until the solution becomes colorless and transparent. After the sulfuric acid fumes and refluxes, remove it. After the digestion solution cools, wash it with distilled water into a volumetric flask, make up to volume, and shake well.

[0046] According to one embodiment of the method for determining organic phosphorus components in high-organic-matter soils of the present invention, the molybdenum-antimony colorimetric method is specifically operated as follows:

[0047] Add dinitrophenol indicator to the colorimetric container, adjust the pH with dilute H2SO4 and dilute NaOH solution until the solution is just slightly yellow, add molybdenum antimony colorimetric solution, dilute to volume with water, and shake well; place at room temperature above 15℃ for 30 min, and then measure colorimetrically at a wavelength of 700 nm.

[0048] Compared with the prior art, one of the above technical solutions has the following advantages:

[0049] a) This invention decolorizes the test solution by adding KMnO4 solution to oxidize dissolved organic substances, followed by neutralizing excess KMnO4 with ascorbic acid solution, thereby making the test solution colorless and clear. Neutralizing excess potassium permanganate with ascorbic acid prevents the introduction of other substances into the test solution system, thus avoiding potential errors.

[0050] b) After decolorization treatment, the color of the soil extract is significantly reduced, which is more conducive to the subsequent pH adjustment and colorimetric process.

[0051] c) The present invention enables more accurate determination of various forms of Pi through KMnO4 decolorization, thereby obtaining more accurate soil organic phosphorus composition. Detailed Implementation

[0052] The following description is based on specific embodiments.

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the present invention.

[0054] The soil samples used in this embodiment were collected from marsh soil (No. 1) and peat soil (No. 2) in the Ruoergai Wetland Nature Reserve on the northeastern edge of the Qinghai-Tibet Plateau. The basic physicochemical properties of the soil are shown in Table 1.

[0055] Table 1. Basic physicochemical properties of the tested soils

[0056]

[0057] In this embodiment, organic substances dissolved in KMnO4 solution are oxidized, and then excess KMnO4 is neutralized with ascorbic acid solution, thereby turning the test solution colorless and clear, achieving the purpose of decolorization. Neutralizing excess potassium permanganate with ascorbic acid prevents the introduction of other substances into the test solution system, thus avoiding potential errors. Furthermore, experiments have shown that the decolorization effect of KMnO4 solution / ascorbic acid is significantly better than that of activated carbon decolorization.

[0058] The reagents used in this embodiment are as follows:

[0059] 0.1 mol·L -1KMnO4 solution: Weigh 15.8034g of potassium permanganate (KMnO4, analytical grade) and dissolve it in 1000ml of distilled water.

[0060] 10% Ascorbic Acid Solution: Weigh 10g of ascorbic acid (C6H8O6, levorotatory, optical rotation +21°~+22°, analytical grade) and dissolve it in 100ml of distilled water.

[0061] Molybdenum-antimony stock solution: Slowly pour 153 ml of concentrated sulfuric acid into 400 ml of distilled water while stirring, and allow to cool slightly. Separately, dissolve 10 g of ammonium molybdate in 300 ml of distilled water. Slowly pour the prepared sulfuric acid solution into the ammonium molybdate solution while stirring. Then add potassium antimony tartrate (5.0 g·L⁻¹). -1 Add 100ml of solution and then dilute with water to a final volume of 1000ml. Pour into a brown bottle and store away from light.

[0062] Molybdenum-antimony anti-chromic reagent: Add 1.50g to 100ml of molybdenum-antimony stock solution. This reagent must be prepared and used immediately.

[0063] Example 1

[0064] Take 1.00 g of air-dried soil sample with a particle size <0.15 mm, and add 50 mL of 0.5 mol·L⁻¹ solution. -1 Extract with NaHCO3 solution by shaking for 0.5 h. After shaking, immediately centrifuge and filter with phosphorus-free filter paper to obtain the first precipitate and the first supernatant. Take 10 mL of the first supernatant into a 25 mL colorimetric container (colorimetric tube) and add 2 mL of 2 mol·L⁻¹ solution. -1 The H2SO4 was shaken well to make the test solution acidic and remove CO2, thus obtaining the first test solution.

[0065] Add 0.1 mol·L⁻¹ dropwise to the first colorimetric container. -1 The KMnO4 solution was applied until the first test solution turned purple-red. After 5 minutes, 10% ascorbic acid solution was added to neutralize the excess KMnO4. At this point, the decolorization of the test solution was complete, yielding the first decolorized solution. For comparison, activated carbon decolorization was added, replacing this step with activated carbon decolorization: 15 ml of the first supernatant was taken, 1.5 g of phosphorus-free activated carbon was added, and the mixture was shaken at 28°C for 10 minutes at a shaking rate of 200 times / min. After shaking, the mixture was filtered through phosphorus-free filter paper, and 10 ml of the filtrate was used for colorimetric analysis. The remaining steps were the same as the method of this invention. A non-decolorization treatment was added for comparison: after centrifugation and filtration, 10 mL of the first supernatant was directly taken for colorimetric analysis.

[0066] The color of the soil extracts from the three treatments was detected using the dilution factor method (HJ1182-2021), and the results are shown in Table 2.

[0067] Table 2 Color of soil extracts under different decolorization treatments

[0068]

[0069] Compared to non-decolorization treatment and activated carbon decolorization treatment, the soil extract treated with KMnO4 showed a significant reduction in color. This is more beneficial for subsequent pH adjustment and colorimetric processes.

[0070] Add 2 drops of dinitrophenol indicator to the first colorimetric container, adjust the pH with dilute H2SO4 and dilute NaOH solution until the solution is just slightly yellow, add 2.5 mL of molybdenum antimony colorimetric solution, shake well, and dilute to volume with water.

[0071] The active inorganic phosphorus (L-Pi) was determined by colorimetric measurement at a wavelength of 700 nm after being placed at room temperature above 15°C for 30 min.

[0072] Take another 10 mL of the first supernatant into a 100 mL Erlenmeyer flask, evaporate it to dryness on a boiling water bath, add 3 mL of concentrated H2SO4 and shake well, then add 10 drops of HClO4 and shake well. Place a small bent-neck funnel at the mouth of the flask and heat it on a hot plate until the solution becomes colorless and transparent. After the sulfuric acid fumes and is refluxed, remove it (the total digestion time is about 30 min). After the digested solution cools, wash it with distilled water into a 50 mL volumetric flask, make up to volume, and shake well. Finally, take 10 mL of the digested solution A into a 25 mL colorimetric tube and determine the active total phosphorus (L-Pt) by colorimetric determination using the molybdenum antimony colorimetric method.

[0073] The difference between L-Pt and L-Pi is the active organophosphate (L-Po).

[0074] The results of phosphorus component detection in the soils of the three treatments are shown in Table 3. Table 3: Content of active inorganic phosphorus, total active phosphorus, and active organic phosphorus in soils under different decolorization treatments.

[0075]

[0076] Note: Each treatment was repeated 5 times.

[0077] As shown in Table 3, the difference in total active phosphorus content between the two tested soils under different decolorization treatments was less than 0.5%, indicating that decolorization treatment had no effect on total phosphorus content. However, different decolorization treatments had a significant impact on the content of various forms of Pi in the soil, manifested as an increase in Pi measurement values ​​after decolorization. Compared with the untreated soil, the L-Pi content of soil 1 increased by 49.8% and 30.4% after KMnO4 decolorization and activated carbon decolorization, respectively; the L-Pi content of soil 2 increased by 59.6% and 30.3% after KMnO4 decolorization and activated carbon decolorization, respectively. Furthermore, the standard deviation of the Pi content measured after decolorization was smaller than that after untreated soil, indicating that the Pi data measured after decolorization was more accurate and reliable. In both decolorization treatments, the Pi content of the soil after KMnO4 decolorization was also increased to varying degrees compared to that after activated carbon decolorization, and the standard deviation was also smaller. Therefore, the KMnO4 decolorization method is more advantageous for accurate determination of L-Pi.

[0078] In summary, the KMnO4 decolorization method is a more accurate and effective decolorization method for determining organic phosphorus components in soils with high organic matter content.

[0079] Example 2

[0080] The first precipitate was prepared using 50 mL of 0.1 mol·L⁻¹ solution. -1 Extraction with NaOH solution by shaking for 6 hours, followed by centrifugation and filtration to obtain the second supernatant and the second precipitate. Take 5 mL of the second supernatant into a 25 mL second colorimetric container and add 0.2 mL of 2 mol·L⁻¹ solution. -1 The H2SO4 was shaken well to make the test solution acidic, thus obtaining the second test solution.

[0081] Add 0.1 mol·L⁻¹ dropwise to the second colorimetric container. -1 The KMnO4 solution was applied until the test solution turned purple-red. After 5 minutes, 10% ascorbic acid solution was added to neutralize the excess KMnO4. At this point, the second test solution was decolorized, yielding the second decolorized solution. For comparison, activated carbon decolorization was added, replacing this step: 15 ml of the second supernatant was taken, 1.5 g of phosphorus-free activated carbon was added, and the mixture was shaken at 28°C for 10 minutes at a shaking rate of 200 times / min. After shaking, the mixture was filtered through phosphorus-free filter paper, and 10 ml of the filtrate was used for colorimetric analysis. The remaining steps were the same as in this embodiment. A non-decolorization treatment was added for comparison: after centrifugation and filtration, 10 ml of the second supernatant was directly used for colorimetric analysis.

[0082] The color of the soil extracts from the three treatments was detected using the dilution factor method (HJ1182-2021), and the results are shown in Table 4.

[0083] Table 4 Color of soil leachate under different decolorization treatments

[0084]

[0085] Compared to non-decolorization treatment and activated carbon decolorization treatment, the soil extract treated with KMnO4 showed a significant reduction in color. This is more beneficial for subsequent pH adjustment and colorimetric processes.

[0086] Stable inorganic phosphorus (R-Pi) was determined by colorimetric analysis at a wavelength of 700 nm using the molybdenum-antimony colorimetric method.

[0087] Take another 5 mL of the second supernatant into a 100 mL Erlenmeyer flask, and digest it with H2SO4-HClO4 as described in Example 1. Then determine the stable total phosphorus (R-Pt) using the molybdenum antimony colorimetric method.

[0088] The difference between R-Pt and R-Pi is the stable organophosphate (R-Po).

[0089] The results of the detection of stable inorganic phosphorus, stable total phosphorus, and stable organic phosphorus content in the three treatment soils are shown in Table 5.

[0090] Table 5. Contents of stable inorganic phosphorus, stable total phosphorus, and stable organic phosphorus in soils under different treatments.

[0091]

[0092] Note: Each treatment was repeated 5 times.

[0093] The difference in stable total phosphorus content between the two tested soils under different decolorization treatments was less than 0.5%, indicating that the decolorization treatment had no effect on the total phosphorus content. In the RP extraction step, R-Pi could not be measured without decolorization, therefore R-Po could not be obtained. For soil 1, KMnO4 decolorization increased R-Pi by 60.2% compared to activated carbon decolorization; for soil 2, KMnO4 decolorization increased R-Pi by 67.5% compared to activated carbon decolorization, and the standard deviation was also smaller. Therefore, the KMnO4 decolorization method is more suitable for accurately determining R-Pi.

[0094] Example 3

[0095] Take the second supernatant, add concentrated H2SO4 to adjust the pH to 3.0, let it stand to precipitate, and then take 5 mL of the third supernatant into a 25 mL third colorimetric container to obtain the third test solution.

[0096] Add 0.1 mol·L⁻¹ dropwise to the third colorimetric container. -1The KMnO4 solution was applied until the test solution turned purple-red. After 5 minutes, 10% ascorbic acid solution was added to neutralize the excess KMnO4. At this point, the decolorization of the test solution was complete, yielding the third decolorized solution. For comparison, activated carbon decolorization was added, replacing this step with activated carbon decolorization: 15 ml of the third supernatant was taken, 1.5 g of phosphorus-free activated carbon was added, and the mixture was shaken at 28°C for 10 minutes at a shaking rate of 200 times / min. After shaking, the mixture was filtered through phosphorus-free filter paper, and 10 ml of the filtrate was used for colorimetric analysis. The remaining steps were the same as in this embodiment. A non-decolorization treatment was added for comparison: 10 mL of the third supernatant was directly used for colorimetric analysis.

[0097] The color of the soil extracts from the three treatments was detected using the dilution factor method (HJ1182-2021), and the results are shown in Table 6.

[0098] Table 6 Color of soil extracts under different decolorization treatments

[0099]

[0100] Compared to non-decolorization treatment and activated carbon decolorization treatment, the soil extract treated with KMnO4 showed a significant reduction in color. This is more beneficial for subsequent pH adjustment and colorimetric processes.

[0101] MR-Pi was determined by colorimetric analysis at a wavelength of 700 nm using the molybdenum-antimony colorimetric method.

[0102] Take 5 mL of the third supernatant into a 100 mL Erlenmeyer flask, digest it with H2SO4-HClO4 as described in Example 1, and then measure MR-Pt using the molybdenum antimony colorimetric method.

[0103] The difference between MR-Pt and MR-Pi is fulvic acid phosphorus (MR-Po).

[0104] The results of the detection of MR-Pt, MR-Pi, and MR-Po contents in the soil of the three treatments are shown in Table 7.

[0105] Then subtract MR-Po from R-Po to obtain HR-Po.

[0106] Table 7. Contents of MR-Pt, MR-Pi, and MR-Po in soils under different treatments

[0107]

[0108] Note: Each treatment was repeated 5 times.

[0109] As shown in Table 7, the difference in MR-Pt content between the two tested soils under different decolorization treatments was less than 0.5%, indicating that the decolorization treatment had no effect on the total phosphorus content. However, different decolorization treatments had a significant effect on the soil MR-Pi content, manifested as an increase in the Pi measurement value after decolorization. Compared with the untreated soil, the MR-Pi of soil 1 increased by 138.8% and 53.9% after KMnO4 decolorization and activated carbon decolorization, respectively; the MR-Pi of soil 2 increased by 36.8% and 14.3% after KMnO4 decolorization and activated carbon decolorization, respectively. Furthermore, the standard deviation of the Pi content measured after decolorization was smaller than that after untreated soil, indicating that the Pi data measured after decolorization was more accurate and reliable. In both decolorization treatments, the Pi content of the soil after KMnO4 decolorization was also increased to varying degrees compared to the Pi content after activated carbon decolorization, and the standard deviation was also smaller. Therefore, the KMnO4 decolorization method is more advantageous for accurately determining MR-Pi.

[0110] In summary, the KMnO4 decolorization method is a more accurate and effective decolorization method for determining organic phosphorus components in soils with high organic matter content.

[0111] Example 4

[0112] The second precipitate was treated with 50 mL of 1 mol·L⁻¹ solution. -1 Extract with H2SO4 solution by shaking for 1 hour, centrifuge, and filter to obtain the fourth supernatant. The fourth supernatant is a colorless and transparent liquid and does not require decolorization. Take 5 mL of the fourth supernatant into a 50 mL colorimetric tube, and the ML-Pi can be directly measured using the molybdenum-antimony colorimetric method.

[0113] Take another 5 mL of the fourth supernatant into a 100 mL Erlenmeyer flask, and digest it with H2SO4-HClO4 as in Example 1. Then measure the ML-Pt using the molybdenum antimony colorimetric method.

[0114] The difference between ML-Pt and ML-Pi is ML-Po.

[0115] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining the organic phosphorus component in high-organic-matter soils, characterized in that, The organic matter content in the high-organic-matter soil is above 100g / kg. The organic phosphorus includes active organic phosphorus, moderately active organic phosphorus, fulvic acid phosphorus, and humic acid phosphorus. The determination steps for the active organophosphorus compounds are as follows: S11. Take the air-dried soil powder, add NaHCO3 solution and shake to extract. After shaking, immediately centrifuge and filter with phosphorus-free filter paper to obtain the first precipitate and the first supernatant. S12. Take a first preset amount of the first supernatant into the first colorimetric container, add H2SO4 to the colorimetric container, shake well to make the solution acidic and remove CO2, and obtain the first test solution. S13. The first test solution is a decolorizing solution. The first test solution is decolorized to obtain the first decolorized solution. S14. The active inorganic phosphorus in the first decolorizing solution was determined by the molybdenum-antimony colorimetric method. S15. Take the first supernatant of the second preset amount, evaporate it to dryness in a container, add concentrated H2SO4, digest it, and prepare test solution A after digestion. The total active phosphorus of test solution A is determined by colorimetric determination using the molybdenum antimony colorimetric method. The difference between total active phosphorus and active inorganic phosphorus is the active organic phosphorus; The steps for determining stable organophosphorus compounds are as follows: S21. Take the first precipitate, extract it by shaking with NaOH solution, centrifuge and filter to obtain the second supernatant and the second precipitate; S22. Take the first preset amount of the second supernatant into the second colorimetric tube, add H2SO4 and shake well to make the solution acidic, and obtain the second test solution; S23. The second test solution is a decolorizing solution. The second test solution is decolorized to obtain a second decolorized solution. S24. The stable inorganic phosphorus in the second decolorizing solution was determined by the molybdenum-antimony colorimetric method. S25. Take the second preset amount of the second supernatant, evaporate it to dryness in a container, add concentrated H2SO4, digest it, and prepare test solution B after digestion. The stable total phosphorus of test solution B is determined by colorimetric determination using the molybdenum antimony colorimetric method. The difference between stable total phosphorus and stable inorganic phosphorus is the value of stable organic phosphorus. The steps for determining fulvic acid phosphorus are as follows: S31. Take the third preset amount of the second supernatant, add concentrated H2SO4 to adjust the pH to acidic, let it stand to precipitate, take the preset amount of the third supernatant, put it in the third colorimetric tube, and obtain the third test solution. S32. Take the first preset amount of the third test solution as the decolorizing solution and perform decolorization treatment to obtain the third decolorized solution; S33, the MR-Pi of the third decolorizing solution was determined by the molybdenum-antimony colorimetric method; S34. Take the second preset amount of the third test solution, evaporate it to dryness in a container, add concentrated H2SO4, digest it, and prepare test solution C after digestion. MR-Pt of test solution C is determined by colorimetric analysis using the molybdenum antimony colorimetric method. The difference between MR-Pt and MR-Pi is fulvic acid phosphorus; The difference between stable organophosphorus phosphorus and fulvic acid phosphorus is equal to that between humic acid phosphorus and stable organophosphorus phosphorus. The steps for determining the active organophosphorus compounds are as follows: S41. Take the second precipitate, add H2SO4 solution, shake to extract, centrifuge, filter, and obtain the fourth supernatant; S42. Take the fourth supernatant of the first preset amount as the fourth test solution, and measure ML-Pi by the molybdenum-antimony colorimetric method. S43. Take the second preset amount of the fourth supernatant, evaporate it to dryness in a container, add concentrated H2SO4, digest and boil it, and prepare the D test solution after digestion. The ML-Pt of the D test solution is measured by colorimetric determination using the molybdenum antimony colorimetric method. The difference between ML-Pt and ML-Pi is the medium-activity organophosphorus phosphorus. The decolorization treatment specifically involves adding 0.1 mol·L⁻¹ of the solution to be decolorized dropwise. -1 KMnO4 solution is added until the decolorized solution turns purplish-red. After 3-5 minutes, 10% ascorbic acid solution is added to neutralize the excess KMnO4, thus completing the decolorization and obtaining the decolorized solution.

2. The method for determining organic phosphorus components in high-organic-matter soils according to claim 1, characterized in that, The high organic matter soils include peat soils, marsh soils, or meadow soils.

3. The method for determining organic phosphorus components in high-organic-matter soils according to claim 1, characterized in that, The specific steps for evaporating to dryness in a container, adding concentrated H2SO4, and digesting are as follows: Place the container on a boiling water bath to evaporate to dryness, add concentrated H2SO4, shake well, then add HClO4 dropwise and shake well. Place a small curved-neck funnel at the mouth of the bottle and heat it on a hot plate until the solution becomes colorless and transparent. After the sulfuric acid fumes and refluxes, remove it. After the digestion solution cools, wash it with distilled water into a volumetric flask, make up to volume, and shake well.

4. The method for determining organic phosphorus components in high-organic-matter soils according to claim 1, characterized in that, The specific operation of the molybdenum-antimony colorimetric method is as follows: Add dinitrophenol indicator to the colorimetric container, adjust the pH with dilute H2SO4 and dilute NaOH solution until the solution is just slightly yellow, add molybdenum antimony colorimetric solution, dilute to volume with water, and shake well; place at room temperature above 15℃ for 30 min, and then measure colorimetrically at a wavelength of 700 nm.

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