Method for detecting biochemical fulvic acid in mixed fertilizer

Abstract

The invention relates to a method for detecting biochemical fulvic acid in a mixed fertilizer, which comprises the following steps of: establishing a standard chart based on the relationship among the content of mineral source fulvic acid, the total content of fulvic acid and the content of biochemical fulvic acid in a standard composite fulvic acid sample, and fitting a linear equation; taking a to-be-detected sample, determining the total content of mineral source fulvic acid and fulvic acid on the basis of ash content, and finally determining the content of biochemical fulvic acid in the to-be-detected sample on the basis of the linear equation and the standard diagram. According to the method, the content of the biochemical fulvic acid in the composite fulvic acid can be accurately estimated on the premise that mineral source fulvic acid and the biochemical fulvic acid do not need to be distinguished, and the authenticity of the marked content of the composite fulvic acid commodity for marking the content of the biochemical fulvic acid can be more efficiently verified.

Description

Technical Field

[0001] This application belongs to the field of fulvic acid detection technology, and specifically relates to a biochemical fulvic acid detection method in mixed fertilizers. Background Technology

[0002] Fulvic acid is a type of humic acid, mainly divided into mineral-derived fulvic acid and biochemical fulvic acid. Mineral-derived fulvic acid is derived from the alkali extracts of lignite, weathered coal, and peat, possessing strong soil-improving and metal-chelating abilities. Therefore, it is often used as a soil conditioner in combination with water-soluble fertilizers such as potassium and phosphate fertilizers. Biochemical fulvic acid is derived from the microbial fermentation products of organic waste such as molasses and straw, exhibiting high plant growth promotion activity and being more easily absorbed by plants. To comprehensively utilize the effects of mineral-derived and biochemical fulvic acid, some manufacturers blend them according to their primary and secondary effects to prepare compound fulvic acid fertilizers, clearly indicating the content or proportion of different fulvic acids for differentiated application. However, due to the significant difference in price and manufacturing cost between mineral-derived and biochemical fulvic acid, some unscrupulous manufacturers falsify the mixed content. Furthermore, for soil conditioners, excessive mixing with biochemical fulvic acid can lead to a decline in the soil-improving performance of the fertilizer. To accurately detect the content of biochemical fulvic acid in compound fertilizers, current technologies typically employ an alkaline extraction and acid precipitation method to detect mineral-derived fulvic acid, followed by fluorescence spectroscopy to determine the actual content ratio of mineral-derived and biochemical fulvic acid. However, the alkaline extraction and acid precipitation method for mineral-derived fulvic acid is prone to overestimation due to residues, and the absorbance ranges of mineral-derived and biochemical fulvic acid overlap, easily leading to measured values ​​higher than the actual values. Furthermore, both methods involve cumbersome instrumentation and experimental procedures, hindering efficient content determination. Summary of the Invention

[0003] Based on the aforementioned technical needs, this application provides a method for detecting biochemical fulvic acid in mixed fertilizers, which can improve the accuracy and efficiency of detecting the biochemical fulvic acid content in mixed fertilizers.

[0004] To achieve the above objectives, the technical solution of this application is as follows:

[0005] A method for detecting biochemical fulvic acid in mixed fertilizers includes the following steps:

[0006] S1. Prepare group a of composite fulvic acid standard samples by mixing mineral-derived fulvic acid and biochemical fulvic acid with a calibration purity of not less than 90%. Each group includes f portions. Determine the total fulvic acid content of each group. S2. Plot a standard curve for biochemical fulvic acid determination with the total fulvic acid content of each group as the vertical axis and the corresponding biochemical fulvic acid content as the horizontal axis; S3. Take the sample to be tested and determine its mineral fulvic acid content and total fulvic acid content; S4. Input the mineral fulvic acid content and total fulvic acid content of the sample to be tested into the standard curve for biochemical fulvic acid determination to obtain the biochemical fulvic acid content of the sample to be tested.

[0007] Preferably, step S4 includes: in the biochemical fulvic acid calculation model, based on the standard lines adjacent to the mineral fulvic acid content and / or total fulvic acid content of the sample to be tested, a reference line is proposed for the total fulvic acid content of the sample to be tested relative to the biochemical fulvic acid content; the mineral fulvic acid content and total fulvic acid content of the sample to be tested are input into the reference line to obtain the biochemical fulvic acid content of the sample to be tested.

[0008] Preferably, in any group of composite fulvic acid standard samples in step S1, the content of mineral-derived fulvic acid is the same, and the ratio of the content of biochemical fulvic acid to the content of mineral-derived fulvic acid gradually increases.

[0009] Preferably, the step of taking the sample to be tested and determining its mineral-derived fulvic acid content includes the following steps: S31. Take several samples with known mineral-derived fulvic acid content and weight. Standard mineral fulvic acid samples with a purity of not less than 90% were placed in crucibles and ignited to constant weight, then transferred to a desiccator to cool, and subsequently weighed quickly to obtain the ash content. Based on the formula Calculate the ash content of each standard sample; S32. Plot a standard curve with the humic acid content of each standard mineral-derived fulvic acid sample as the abscissa and the corresponding ash content as the ordinate, and fit a linear equation; S33. Take the weight as... The sample to be tested was placed in a crucible and heated to constant weight, then transferred to a desiccator to cool, and then quickly weighed to obtain a mass of [missing value]. The ash content, based on the formula The ash content of the sample to be tested is calculated, and the mineral humic acid content of the sample to be tested is obtained based on the standard curve and the ash content of the sample.

[0010] Preferably, in step S31, the calcination temperature of the standard sample is 550±10℃, the calcination time is not less than 4h, and the drying and cooling time is not less than 30min.

[0011] Preferably, the determination of the total fulvic acid content of the sample to be tested includes the following steps: taking a sample of weight n and placing it in a centrifuge tube, adding fulvic acid extract and deionized water for culture, then performing a first centrifugation, taking the supernatant and adding pH adjustment solution, performing a second centrifugation, taking the precipitate after standing, ultrafiltration, washing and drying the precipitate to obtain the dried product, and obtaining the total fulvic acid content based on the ratio of the weight of the dried product to the weight of the sample to be tested.

[0012] Preferably, the taking supernatant and pH adjusting liquid is adding pH adjusting liquid drop by drop into the supernatant until PH = 1 ± 0.1.

[0013] Preferably, the ratio of the sample to be tested to the fulvic acid extract is , the volume ratio of the fulvic acid extract to deionized water is , the first centrifugation is 1000 rpm for 15 min; the volume ratio of the pH adjusting liquid to the supernatant is , the second centrifugation is 1000 rpm for 10 min; the ultrafiltration is first dissolving the precipitate using a dissolving agent, then ultrafiltrating the dissolved liquid with 3KDa; the washing is first resuspending the ultrafiltrated filtrate using a precipitant, then taking the precipitate after the third centrifugation, and using a washing agent to wash the precipitate for no less than three times; the drying is 40℃ drying to constant weight.

[0014] Preferably, the third centrifugation is 1000 rpm for 5 min.

[0015] Preferably, the ratio of the dissolving agent to the precipitate is to .

[0016] By adopting the above technical solution, compared with the prior art, the present application has at least the following beneficial effects:

[0017] The present method does not need to directly measure the biochemical fulvic acid content in the composite fulvic acid, but by pre-establishing the corresponding relationship model of the total fulvic acid content and the biochemical fulvic acid, and then estimating the total fulvic acid content and the mineral source fulvic acid content of the sample, the content of the biochemical fulvic acid can be correspondingly output, and there is no need to separately distinguish the biochemical fulvic acid and the mineral source fulvic acid, avoiding the problem that the measurement error of the biochemical fulvic acid is large due to the influence of the residual mineral source fulvic acid in the separation process, thereby improving the detection accuracy of the biochemical fulvic acid content compared with the prior art; and since the estimation process does not need to use fluorescence spectrum, the efficiency is higher and the cost is lower when a large number of detections are performed. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a standard line graph for determining biochemical fulvic acid in the embodiment.

[0019] Figure 2 It is a standard line graph for determining mineral source fulvic acid in the embodiment.

[0020] Figure 3 It is an operation schematic diagram of the mineral source fulvic acid content and the total fulvic acid content detection method in the embodiment.

[0021] (Note: Figure 1The fitting equations corresponding to each standard line are arranged from low to high according to the height distribution of the standard lines DETAILED DESCRIPTION

[0022] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The technical solutions of the present application will be further described below in combination with the drawings of the embodiments of the present application. The present application is not limited to the following specific embodiments.

[0023] It should be understood that the same or similar reference numerals in the drawings of the embodiments correspond to the same or similar components. In the description of the present application, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "inner", "outer", "left", "right", "front", "back", "top", "bottom", etc. are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the structures or components referred to must have a particular orientation, be constructed and operated in a particular orientation. Therefore, the terms describing the positional relationship in the drawings are used only for exemplary illustration, and cannot be understood as a limitation on the present patent. For those skilled in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0024] The technical solutions of the present application will be further described below in combination with the drawings of the embodiments of the present application. The present application is not limited to the following specific embodiments. Figure 1 to the drawings Figure 3 The present application will be further described in detail below in combination with the specific embodiments.

[0025] The present application discloses a method for detecting biochemical fulvic acid in a mixed fertilizer, which is used to solve the problem that it is inconvenient to separately determine the biochemical fulvic acid and the mineral fulvic acid in the composite fulvic acid. Based on the high accuracy of the potassium dichromate oxidation method for determining the total content of fulvic acid, and considering that the natural inorganic salts and other minerals contained in the mineral fulvic acid are still in the form of ash after burning due to the source (such as the alkali extract of lignite, weathered coal, and peat), which are difficult to be removed by purification, the content of the mineral fulvic acid in the composite fulvic acid can be accurately calibrated based on the inverse trend of the content relationship between the two, and thus the content of the biochemical fulvic acid can be determined based on the corresponding relationship between the content of the biochemical fulvic acid, the content of the mineral fulvic acid, and the total content of fulvic acid. The method comprises the following steps:

[0026] Step 1: Prepare a composite fulvic acid standard sample with a quantity of a groups by using mineral fulvic acid and biochemical fulvic acid whose purity has been determined and is not less than 90%, wherein each group of composite fulvic acid standard sample comprises f parts, and the total content of fulvic acid in each group of composite fulvic acid standard sample is determined by using the potassium dichromate oxidation method , the determination method is as follows: put any one of the composite fulvic acid standard sample into a centrifuge tube, add enough potassium dichromate solution, then slowly add enough concentrated sulfuric acid, after adding acid, heat the solution in water bath, after the reaction is complete (the solution changes from orange red to green), transfer the completely cooled reaction solution to a conical flask, dilute with enough distilled water, then add o-phenanthroline indicator dropwise, make the reaction solution orange red, then titrate with ferrous sulfate standard solution to the endpoint (the color of the reaction solution changes from orange red to dark green and then to light green), record the amount of ferrous sulfate consumed to reach the endpoint ; treat the blank group without adding composite fulvic acid standard sample by the above method, and record the consumption of ferrous sulfate ; calculate the organic carbon content based on the formula , wherein represents the concentration of ferrous sulfate solution, and M represents the mass of the composite fulvic acid sample; then calculate the fulvic acid content value by the formula , assuming that the fulvic acid content of the composite fulvic acid standard sample is 100%, the fulvic acid content value is equal to the organic matter content value.

[0027] After step 1, the source fulvic acid mass, biochemical fulvic acid mass, and total fulvic acid content of each composite fulvic acid standard sample after determination are as follows:

[0028] (Note: the first row in the table corresponds to the content of biochemical fulvic acid in the composite fulvic acid, unit: g, the first column corresponds to the group number, the second column corresponds to the content of source fulvic acid, unit: g, the third to twelfth columns correspond to the total fulvic acid content determination value of 12 parts in each group, unit: g).

[0029]

[0030] Among them, the content of source fulvic acid in the first group is 0, and the content of biochemical fulvic acid is determined by potassium dichromate oxidation method, which is used as a blank control, aiming to verify the accuracy and sensitivity of the potassium dichromate oxidation method for determining the content of biochemical fulvic acid; according to the test results of each group, although the total fulvic acid content measured by the potassium dichromate oxidation method is slightly lower than the actual total value, it increases linearly with the change of the ratio, so it has reference value.

[0031] Preferably, since the content of source fulvic acid and the total content of fulvic acid are relatively easier to be determined than biochemical fulvic acid in the prior art, and it is difficult to completely separate the mixed source fulvic acid and biochemical fulvic acid in the prior art, in order to clearly reflect the relationship between biochemical fulvic acid and total fulvic acid, the content of source fulvic acid added in each group of composite fulvic acid standard sample is the same, and the content of biochemical fulvic acid gradually increases compared with the content of source fulvic acid, that is, the amount of biochemical fulvic acid added shows an increasing trend.

[0032] Step 2, seeFigure 1 The total content of fulvic acid in each group of the above table is taken as the vertical coordinate, and the corresponding biochemical fulvic acid content of each part is taken as the horizontal coordinate. The standard line graph for determining the biochemical fulvic acid content of each group of composite fulvic acid samples is drawn.

[0033] Step 3: Determine the mineral source fulvic acid content and total fulvic acid content of the test sample.

[0034] Step 4: Input the mineral source fulvic acid content and total fulvic acid content of the test sample into the standard line graph for determining biochemical fulvic acid, and output the biochemical fulvic acid content corresponding to the total fulvic acid content.

[0035] Preferably, in step 3, the present application provides a specific embodiment for determining the mineral source fulvic acid content and total fulvic acid content of the test sample, as follows:

[0036] Method for determining the mineral source fulvic acid content of the test sample:

[0037] Step S31: Prepare 10 samples with known true mineral source fulvic acid content as standard samples. The purity of the mineral source fulvic acid in each standard sample is not less than 90% after calibration. Weigh 1g of each standard sample for standby, place the crucible in a muffle furnace at 550°C for 1 hour, take it out after drying and cooling, and weigh it to ensure that the weight before and after heating is consistent; take one of the standard samples and place it in a crucible and heat it to carbonization using an electric stove at 250°C, then transfer it to a muffle furnace at 550°C for 4 hours, then transfer it to a desiccator for cooling and drying for 30 minutes to reduce the temperature of the ash to 200-250°C, then quickly weigh the ash to obtain the ash mass of the standard sample The ash content of the standard sample is obtained based on the formula Repeat step 10 times to calculate the ash content of each prepared standard sample.

[0038] The comparative relationship between the mineral source fulvic acid content and the ash content of each standard sample is as follows:

[0039]

[0040] Step S32:

[0041] 1. Establish a linear fitting equation: based on the mineral source fulvic acid content and ash content of the standard samples in the above table, a first-order equation is obtained by least squares fitting: , where X represents the mineral source fulvic acid content and Y represents the ash content.

[0042] 2. Verify the fitting results based on the above table, and the results are as follows:

[0043] ​

[0044] Therefore, it can be seen that the fitting equation has high prediction accuracy for the ash content of samples with a source fulvic acid content of less than 93%.

[0045] 3. A standard line graph of source fulvic acid content-ash content is drawn with the source fulvic acid content of each standard sample as the abscissa and the actual ash content corresponding to each standard sample as the ordinate (see FIG. 2). Figure 2

[0046] Step S33, weigh 1 g of the sample to be measured for standby, place the crucible in the muffle furnace at 550°C for 1 hour, take it out and dry and cool it and weigh it to ensure that the weight of the crucible before and after heating is consistent; take one of the samples to be measured and place it in the crucible and use the electric furnace to heat it to carbonization at 250°C, then transfer the crucible to the muffle furnace at 550°C for 4 hours, then transfer it to the dryer for cooling and drying for 30 minutes to reduce the ash temperature to 200-250°C, then quickly weigh the ash to obtain the ash mass of the sample to be measured, repeat step 3 several times until the ash mass collected reaches the ash mass in step 1 above, based on the formula calculate the ash content of the sample to be measured, and find the source fulvic acid content value corresponding to the ash content based on the above standard line graph, which is the source fulvic acid content of the sample to be measured.

[0047] Preferably, the present embodiment also provides a method for determining the total content of fulvic acid in a sample to be measured:

[0048] Take n grams of the sample to be measured corresponding to the ash mass obtained above and place it in a centrifuge tube, add ml of fulvic acid extraction solution and ml of deionized water to the centrifuge tube and incubate for 2 h, then centrifuge the culture solution at 1000 rpm for the first time for 15 min, take out the supernatant after standing and layering, add PH adjusting solution drop by drop to the supernatant, and monitor the pH value of the supernatant in real time until it is adjusted to the range of 1±0.1, then centrifuge the supernatant at 1000 rpm for the second time for 10 min, take the precipitate after standing and layering, and perform ultrafiltration and washing, wherein the precipitate is first dissolved with a dissolving agent during the ultrafiltration process, and the ratio of the amount of dissolving agent to the amount of precipitate is to ​, to ensure that the precipitate is completely dissolved in the dosage ratio range, the solution is subjected to ultrafiltration using a 3KDa ultrafiltration membrane, the filtration pressure is set to 0.2MPa to 0.4MPa to avoid damage to the filter membrane due to excessive pressure while ensuring that the filtration volume is not less than 90%, and the macromolecular impurities and humic acid in the solution are filtered out to ensure that the fulvic acid with a molecular weight of less than 3KDa is in the filtrate; then the precipitant is added to the filtrate to precipitate and resuspend the fulvic acid, and then the suspension is centrifuged at 1000rpm for the third time for 5min, and the precipitate is taken after standing and detergent is added, the precipitate is taken after stirring and resuspension, and the suspension is centrifuged at 1000rpm for 5min, and the washing process is repeated for not less than 2 times, and the wet precipitate is dried to a constant weight at 40℃, and the obtained dry substance is weighed, and the total content of fulvic acid in the sample to be tested is obtained by the formula The total content of fulvic acid in the sample to be tested is obtained.

[0049] Specifically, in the above method for determining the total content of fulvic acid in the sample to be tested, the fulvic acid extract solution used is 0.1mol / L NaOH solution; the pH adjusting solution is 1mol / L HCL solution, the dissolving agent is 0.05mol / L The solution has a pH of 8.1 to 8.5, which can avoid the precipitation of fulvic acid and the dissolution of humic acid; the washing agent is 0.1mol / L HCL solution.

[0050] Based on the above steps for determining the source fulvic acid content and the total content of fulvic acid in the sample to be tested, 2g of the sample to be tested is taken, and 0.28g of ash content is obtained by step 31, the ash content is 14% by the formula The source fulvic acid content is 63.6% by the formula The source fulvic acid content is 63.6% by the formula

[0051] In one embodiment of step 4: in the above biochemical fulvic acid determination standard line graph, since the source fulvic acid content is close to 1g, the corresponding total content of fulvic acid is brought into the biochemical fulvic acid determination standard line with a source fulvic acid content of 1g, and the output biochemical fulvic acid content is 0.81g.

[0052] But it is known that the potassium dichromate oxidation method for determining the content of biochemical fulvic acid generally gives a lower value, and the content of biochemical fulvic acid obtained by step 4 using the standard line with a source fulvic acid content of 1g will be lower than the actual measured value. To further accurately determine the content of biochemical fulvic acid, a reference line of the total content of fulvic acid relative to the content of biochemical fulvic acid is drawn adjacent to the standard lines with a fulvic acid content of 1 and 2 based on the source fulvic acid content of 1.27g, see the attached Figure 1 ​The linear equation fitted to the reference line is y = 1.0382x + 0.0974 (R2= 0.9987), and the total content of fulvic acid of the sample to be tested is 1.82g, so the content of biochemical fulvic acid is about 1.66g. Combined with the attached Figure 1 It can be seen that the value is closer to the actual value.

[0053] In summary, the method for detecting the content of mineral fulvic acid in the water-soluble fertilizer has the following beneficial effects:

[0054] The method does not directly measure the content of biochemical fulvic acid in the compound fulvic acid, but establishes a corresponding relationship model between the total content of fulvic acid and biochemical fulvic acid in advance, and then estimates the total content of fulvic acid and the content of mineral fulvic acid in the sample, so as to output the content of biochemical fulvic acid. It is not necessary to separately distinguish biochemical fulvic acid and mineral fulvic acid, which avoids the problem that the measurement error of biochemical fulvic acid is large due to the influence of residual mineral fulvic acid in the separation process, thereby improving the detection accuracy of the content of biochemical fulvic acid compared with the prior art. Since the estimation process does not use fluorescence spectrum, the efficiency is higher and the cost is lower when a large number of detections are performed.

[0055] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, those skilled in the art can make other different forms of changes or modifications. Here, all the embodiments cannot be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for detecting biochemical fulvic acid in mixed fertilizers, characterized in that, Includes the following steps: S1. Prepare group a of composite fulvic acid standard samples by mixing mineral-derived fulvic acid and biochemical fulvic acid with a calibration purity of not less than 90%. Each group includes f portions. Determine the total fulvic acid content of each group. ; S2. Plot the standard curve of biochemical fulvic acid determination with the total fulvic acid content of each group as the vertical axis and the corresponding biochemical fulvic acid content as the horizontal axis. S3. Take the sample to be tested and determine its mineral-derived fulvic acid content and total fulvic acid content; S4. Input the mineral fulvic acid content and total fulvic acid content of the sample to be tested into the standard curve chart for biochemical fulvic acid determination to obtain the biochemical fulvic acid content of the sample to be tested.

2. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 1, characterized in that, Step S4 includes: in the biochemical fulvic acid calculation model, based on the standard lines adjacent to the mineral fulvic acid content and / or total fulvic acid content of the sample to be tested, a reference line is proposed for the total fulvic acid content of the sample to be tested relative to the biochemical fulvic acid content. The mineral fulvic acid content and total fulvic acid content of the sample to be tested are input into the reference line to obtain the biochemical fulvic acid content of the sample to be tested.

3. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 1, characterized in that, In any group of composite fulvic acid standard samples in step S1, the content of mineral-derived fulvic acid is the same, and the ratio of the content of biochemical fulvic acid to the content of mineral-derived fulvic acid gradually increases.

4. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 1, characterized in that, The determination of the mineral-derived fulvic acid content in the sample to be tested includes the following steps: S31. Take several portions of mineral-derived fulvic acid with known content and weight. Standard mineral fulvic acid samples with a purity of not less than 90% were placed in crucibles and ignited to constant weight, then transferred to a desiccator to cool, and subsequently weighed quickly to obtain the ash content. Based on the formula Calculate the ash content of each standard sample; S32. Using the fulvic acid content of each standard mineral source fulvic acid sample as the abscissa and the corresponding ash content as the ordinate, draw a standard line graph and fit a linear equation. S33. Take the weight as The sample to be tested was placed in a crucible and heated to constant weight, then transferred to a desiccator to cool, and then quickly weighed to obtain a mass of [missing value]. Ash content, based on formula The ash content of the sample to be tested is calculated, and the mineral humic acid content of the sample to be tested is obtained based on the standard curve and the ash content of the sample.

5. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 4, characterized in that, In step S31, the calcination temperature of the standard sample is 550±10℃, the calcination time is not less than 4h, and the drying and cooling time is not less than 30min.

6. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 1, characterized in that, The determination of the total fulvic acid content of the sample to be tested includes the following steps: a sample of weight n is placed in a centrifuge tube, fulvic acid extract and deionized water are added and cultured, then centrifuged for the first time, the supernatant is taken and pH adjustment solution is added, centrifuged for the second time, the precipitate is taken after standing, the precipitate is ultrafiltered, washed and dried to obtain the dried matter, and the total fulvic acid content is obtained based on the ratio of the weight of the dried matter to the weight of the sample to be tested.

7. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 6, characterized in that, The step of adding pH adjustment solution to the supernatant involves adding the pH adjustment solution dropwise to the supernatant until the pH is 1 ± 0.

1.

8. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 6, characterized in that, The ratio of the sample to be tested to the humic acid extract is: The volume ratio of the humic acid extract to deionized water is: The centrifugation is performed at 1000 rpm for 15 minutes; the volume ratio of the pH adjustment solution to the supernatant is... The secondary centrifugation is centrifugation at 1000 rpm for 10 min; the ultrafiltration is to first dissolve the precipitate with a solvent, and then perform 3 kDa ultrafiltration on the solution; the washing is to first resuspend the ultrafiltration filtrate with a precipitant, and then take the precipitate after a third centrifugation, and wash the precipitate with a detergent at least three times; the drying is drying at 40°C to constant weight.

9. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 8, characterized in that, The third centrifugation was performed at 1000 rpm for 5 minutes.

10. The method for detecting biochemical fulvic acid in mixed fertilizers as described in claim 8, characterized in that, The ratio of solvent to precipitate is: to .

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