Method for determining potassium, sodium, calcium and magnesium in soil soluble salt

Abstract

The invention relates to the technical field of soil element determination, in particular to a method for determining potassium, sodium, calcium and magnesium in soil soluble salt, which comprises the following steps: S1, collecting and preparing a soil sample; s2, preparing a soil sample leaching solution; s3, instrument detection; and S4, data processing and calculation. According to the method, vacuum freeze drying is combined with an ultrasonic-microwave combined extraction technology, and plasma spectrum and ion chromatography combined analysis is adopted, so that the detection efficiency and accuracy are improved, meanwhile, reagent consumption and labor cost are greatly reduced, the problems that a traditional process is tedious, consumed time is long, and precision is insufficient are solved, and the method is suitable for industrial production. The method has the advantages of being convenient to operate, environmentally friendly and the like, can be widely applied to the fields of soil salinization monitoring, agricultural land quality evaluation and geological disaster prevention and control, and provides reliable technical support for environmental protection and resource management.

Description

Technical Field

[0001] The present invention relates to the technical field of soil element determination, in particular to a method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil. Background Art

[0002] Soil salinization is a slow-changing geological disaster caused by salt accumulation. Soil salinization causes multiple hazards: it leads to physiological dehydration of crops, reduces the mechanical strength of the soil, intensifies the migration of heavy metals (such as cadmium and lead), and corrodes engineering materials. Accurate measurement of soluble salt components can assess the soil's corrosiveness to engineering projects, the quality of agricultural land and the degree of salinization, providing a scientific basis for water and soil resource management, geological disaster prevention and control, and agricultural improvement, and has important environmental and economic value.

[0003] Current national standards (GB / T 50123-2019, etc.) primarily rely on traditional methods: double-indicator titration for carbonate / bicarbonate, silver nitrate titration for chloride, EDTA titration or turbidimetry for sulfate, and atomic absorption spectrometry for calcium, magnesium, potassium, and sodium. These methods are cumbersome, time-consuming, require large amounts of reagents, and have high detection limits, making them suitable only for laboratories with small sample volumes and limited access to advanced instrumentation.

[0004] Therefore, based on the above-mentioned related technologies, it is urgent to develop a method for determining potassium, sodium, calcium and magnesium in soil soluble salts. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to propose a method for determining potassium, sodium, calcium and magnesium in soil soluble salts to solve the problems of complicated steps, long time consumption, large reagent dosage and high detection limit in the prior art.

[0006] Based on the above purpose, the present invention provides a method for determining potassium, sodium, calcium and magnesium in soil soluble salts.

[0007] A method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil, characterized by comprising the following steps: Step S1: soil sample collection and preparation; Step S101: select areas with different salinization degrees, pH values, and soil properties, collect samples according to the principle of "random, equal amount, multi-point mixing", with a depth of 0-20 cm and a weight greater than 1000 g, and obtain original soil samples; Step S102: placing the original soil sample in a vacuum freeze dryer, cooling it to -60-50°C, drying it for 22-26 hours, removing impurities such as plant roots and stones, grinding it, pouring it into a 2mm pore size sieve, grinding and sieving it, and mixing it evenly to obtain a soil sample; Step S2: preparing soil sample extract; Step S201: adding the soil sample to ultrapure water, placing the sample in an ultrasonic-microwave instrument, heating the sample to 20-30°C, using a power of 250-350W, and extracting the sample for 1-2 minutes to obtain a mixed solution; Step S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain a sample extract. Step S3: instrument detection; Step S4: data processing and calculation; By using vacuum freeze drying instead of traditional room temperature air drying, changes in salt form (such as decomposition of bicarbonate) are avoided, drying time is shortened, and the low temperature environment inhibits microbial activity, ensuring sample stability; At the same time, by combining ultrasonic and microwave technology, the extraction time is shortened from 3 minutes of traditional oscillation to 1-2 minutes, which improves the extraction efficiency and avoids the dissolution of medium / insoluble salts. In addition, by designing sampling plans for soils with different degrees of salinization, pH, and texture, the representativeness of the samples is ensured. The combination of ICP-OES and IC supports the processing of ≥50 samples per day, meeting the needs of large-scale environmental surveys and agricultural monitoring.

[0008] Preferably, the mass ratio of the soil sample to ultrapure water in step S201 is 1:5.

[0009] Preferably, the instrument detection steps are as follows: Step S301: Determination of potassium, sodium, calcium, and magnesium ions by plasma emission spectrometry; Step S302: Determine sulfate and chloride by ion chromatography.

[0010] Preferably, the steps of determining potassium, sodium, calcium and magnesium ions by plasma emission spectrometry in step S301 are as follows: Step S3011: using 1% HNO3 and 3% ethanol as a matrix, prepare five mixed standard solutions with concentration gradients, and draw emission intensity-concentration curves; Step S3012: adding nitric acid to the sample extract, shaking and letting it stand for 15 minutes, and determining the content of each element according to the calibration conditions, subtracting the blank value; The nitric acid is prepared by mixing 36% wt nitric acid and deionized water in a volume ratio of 1:1.

[0011] Preferably, the five mixed standard solutions with concentration gradients in step S3011 are potassium: 0.5 mg / L, 2.0 mg / L, 5.0 mg / L, 10.0 mg / L, and 20.0 mg / L; Sodium: 1.0mg / L, 5.0mg / L, 10.0mg / L, 50.0mg / L, 100.0mg / L; Calcium: 2.0mg / L, 10.0mg / L, 20.0mg / L, 50.0mg / L, 100.0mg / L; Magnesium: 0.5mg / L, 2.0mg / L, 5.0mg / L, 10.0mg / L, 20.0mg / L; In step S3012, the volume ratio of nitric acid to sample extract is 1:25; The nitric acid in step S3012 is concentrated nitric acid and water in a volume ratio of 1:1.

[0012] The core parameters of the inductively coupled plasma optical emission spectrometry (ICP-OES) detection conditions are as follows: analytical wavelength: potassium 766.490 nm, sodium 330.237 nm, calcium 317.933 nm, magnesium 279.077 nm; RF power 1150 W, cooling gas flow rate 16.0 L / min, auxiliary gas flow rate 1.0 L / min, carrier gas flow rate 0.7 L / min, and sample lift volume 1.0-2.0 mL / min.

[0013] By adding 3% ethanol, the surface tension of the solution is reduced, the uniformity of sample atomization is enhanced, the aerosol transmission efficiency is improved, and the risk of nebulizer clogging caused by high-salt soil extract is reduced. At the same time, the combustion of ethanol releases additional heat energy, which enhances the excitation ability of the low-temperature plasma region, especially improving the detection sensitivity of difficult-to-excite elements such as calcium and magnesium. In addition, ethanol forms weak complexes with calcium and magnesium ions, reducing the probability of them forming micro-precipitates with sulfate and carbonate in an acidic environment, avoiding clogging of the instrument sampling system and signal drift. For easily ionized elements such as sodium and potassium, ethanol can reduce their evaporation rate, making the signal response more stable.

[0014] Preferably, the steps of determining sulfate and chloride by ion chromatography in step S302 are as follows: Step S3021: Prepare a mixed standard solution with 5 concentration points and draw a peak area-concentration curve; Step S3022: Pour the sample extract into a 0.22 μm PVDF needle filter, filter, add 50 μL of 30% H2O2, irradiate with UV light, digest for 20 min, inject and analyze, Cl - Retention time 3-3.4min, SO4 2- Retention time 5.5-6.1 min, peak area quantification; The detection conditions of ion chromatography (IC) are as follows: eluent: 1.7mmol / L NaHCO3+1.8mmol / L Na2CO3, eluent flow rate: 0.7-1.0mL / min, main unit range: 10-30μs, injection volume: 10-25μL, separation column temperature: 25℃, pump flow rate: 2mL / min.

[0015] By optimizing instrument conditions and combining a mixed standard curve based on 1% HNO3 + 3% ethanol matrix, the double peak interference of magnesium at 279.050nm is effectively suppressed, enabling high-precision simultaneous detection of potassium, sodium, calcium, and magnesium. At the same time, the sample extract is filtered through 0.22μm PVDF and subjected to 30% H2O2 UV digestion to eliminate the effects of organic matter on sulfate and chloride determination. Accuracy is improved by combining retention time for qualitative analysis and peak area for quantitative analysis.

[0016] ICP-OES reduces the amount of standard substances used by adopting a low-concentration standard curve; the IC eluent passes through a low-concentration carbonate system to avoid the generation of high-salt waste liquid. At the same time, the entire extraction-filtration-detection process is automated, shortening the single sample detection time and reducing manpower investment.

[0017] Preferably, the mixed standard solution of the five concentration points in step S3021 is Cl - :0.5mg / L, 2.0mg / L, 10.0mg / L, 20.0mg / L; SO4 2- : 1.0mg / L, 5.0mg / L, 20.0mg / L, 50.0mg / L.

[0018] Preferably, the data processing and calculation are calculated as follows: C χ : sample extract concentration (mg / L); V: volume of sample extract (200 mL); m s : sample mass (g); f: dilution rate.

[0019] Beneficial effects of the present invention: The present invention provides a highly efficient method for detecting potassium, sodium, calcium, and magnesium in readily soluble salts in soil. By combining vacuum freeze-drying with ultrasonic-microwave extraction technology, and employing plasma spectroscopy and ion chromatography analysis, the method significantly improves detection efficiency and accuracy compared to existing technologies, while significantly reducing reagent consumption and labor costs. The present invention solves the problems of cumbersome, time-consuming, and inaccurate traditional processes, and has the advantages of convenient operation and environmental friendliness. It can be widely used in soil salinization monitoring, agricultural land quality assessment, and geological disaster prevention and control, providing reliable technical support for environmental protection and resource management. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0021] Example 1: An efficient detection method for potassium, sodium, calcium and magnesium in soil soluble salts S1: Soil sample collection and preparation; S101: Sandy soil from Xiqing District, Tianjin was selected and samples were collected according to the principle of "random, equal amount, and multi-point mixing" with a depth of 0-20 cm and a weight greater than 1000 g to obtain the original soil sample; S102: Place the original soil sample in a vacuum freeze dryer, cool it to -55°C, dry it for 24 hours, remove impurities such as plant roots and stones, grind it, pour it into a 2mm pore size sieve, grind it, sieve it, and mix it evenly to obtain a soil sample; S2: Preparation of soil sample extracts; S201: Add the soil sample to ultrapure water, place it in an ultrasonic-microwave instrument, raise the temperature to 25°C, use a power of 300W, and extract for 1.5 minutes to obtain a mixed solution; S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain the sample extract. S3: instrument detection; S301: ICP-OES: 1% HNO3 + 3% ethanol matrix, potassium / sodium / calcium / magnesium standard curve (0.5-20 mg / L); S302:IC:Cl - / SO4 2- Standard curve (0.5-50 mg / L), H2O2 UV digestion; S4: Data processing and calculation.

[0022] Example 2: An efficient detection method for potassium, sodium, calcium and magnesium in readily soluble salts in soil S1: soil sample collection and preparation; S101: Clay from Jinghai District, Tianjin was selected and samples were collected according to the principle of "random, equal amount, multi-point mixing" with a depth of 0-20 cm and a weight of >1000 g to obtain the original soil sample; S102: Place the original soil sample in a vacuum freeze dryer, cool to -60°C, dry for 22 hours, remove impurities such as plant roots and stones, grind the soil sample, pour it into a 2 mm pore size sieve, grind and sieve, and mix evenly to obtain a soil sample; S2: Preparation of soil sample extracts; S201: Add the soil sample to ultrapure water, place it in an ultrasonic-microwave instrument, raise the temperature to 25°C, use a power of 300W, and extract for 1.5 minutes to obtain a mixed solution; S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain the sample extract. S3: instrument detection; S301: ICP-OES: 1% HNO3 + 3% ethanol matrix, potassium / sodium / calcium / magnesium standard curve (0.5-20 mg / L); S302:IC:Cl - / SO4 2- Standard curve (0.5-50 mg / L), H2O2 UV digestion; S4: Data processing and calculation.

[0023] Example 3: An efficient detection method for potassium, sodium, calcium and magnesium in soil soluble salts S1: Soil sample collection and preparation; S101: Select humus soil from Ninghe District, Tianjin, and collect samples according to the principle of "random, equal amount, and multi-point mixing" with a depth of 0-20 cm and a weight of >1000 g to obtain the original soil sample; S102: Place the original soil sample in a vacuum freeze dryer, cool to -60°C, dry for 22 hours, remove impurities such as plant roots and stones, grind the soil sample, pour it into a 2 mm pore size sieve, grind and sieve, and mix evenly to obtain a soil sample; S2: Preparation of soil sample extracts; S201: Add the soil sample to ultrapure water, place it in an ultrasonic-microwave instrument, raise the temperature to 25°C, use a power of 300W, and extract for 1.5 minutes to obtain a mixed solution; S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain the sample extract. S3: instrument detection; S301: ICP-OES: 1% HNO3 + 3% ethanol matrix, potassium / sodium / calcium / magnesium standard curve (0.5-20 mg / L); S302:IC:Cl - / SO4 2- Standard curve (0.5-50 mg / L), H2O2 UV digestion; S4: Data processing and calculation.

[0024] Example 4: An efficient detection method for potassium, sodium, calcium and magnesium in soil soluble salts S1: Soil sample collection and preparation; S101: Select saline soil in Tianjin Binhai New Area and collect samples according to the principle of "random, equal amount, multi-point mixing" at a depth of 0-20 cm and a weight of >1000 g to obtain the original soil sample; S102: Place the original soil sample in a vacuum freeze dryer, cool to -60°C, dry for 22 hours, remove impurities such as plant roots and stones, grind the soil sample, pour it into a 2 mm pore size sieve, grind and sieve, and mix evenly to obtain a soil sample; S2: Preparation of soil sample extracts; S201: Add the soil sample to ultrapure water, place it in an ultrasonic-microwave instrument, raise the temperature to 25°C, use a power of 300W, and extract for 1.5 minutes to obtain a mixed solution; S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain the sample extract. S3: instrument detection; S301: ICP-OES: 1% HNO3 + 3% ethanol matrix, potassium / sodium / calcium / magnesium standard curve (0.5-20 mg / L), extract diluted 5 times, carrier gas flow adjusted to 0.7 L / min; S302:IC:Cl - / SO4 2- Standard curve (0.5-50 mg / L), H2O2 UV digestion; S4: Data processing and calculation.

[0025] Example 5: An efficient detection method for potassium, sodium, calcium and magnesium in soil soluble salts S1: Soil sample collection and preparation; S101: Select saline-alkali soil in Tianjin Dagang District and collect samples according to the principle of "random, equal amount, multi-point mixing" at a depth of 0-20 cm and a weight of >1000 g to obtain the original soil sample; S102: Place the original soil sample in a vacuum freeze dryer, cool to -60°C, dry for 22 hours, remove impurities such as plant roots and stones, grind the soil sample, pour it into a 2 mm pore size sieve, grind and sieve, and mix evenly to obtain a soil sample; S2: Preparation of soil sample extracts; S201: Add the soil sample to ultrapure water, place it in an ultrasonic-microwave instrument, raise the temperature to 25°C, use a power of 300W, and extract for 1.5 minutes to obtain a mixed solution; S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain the sample extract. S3: instrument detection; S301: ICP-OES: 1% HNO3 + 3% ethanol matrix, potassium / sodium / calcium / magnesium standard curve (0.5-20 mg / L); S302:IC:Cl - / SO4 2- Standard curve (0.5-50 mg / L), flow rate 1.0 mL / min, H2O2 UV digestion; S4: Data processing and calculation.

[0026] Example 6: An efficient detection method for potassium, sodium, calcium and magnesium in soil soluble salts S1: Soil sample collection and preparation; S101: Sandy soil from Xiqing District, Tianjin was selected and samples were collected according to the principle of "random, equal amount, and multi-point mixing" with a depth of 0-20 cm and a weight greater than 1000 g to obtain the original soil sample; S102: Place the original soil sample in a vacuum freeze dryer, cool it to -55°C, dry it for 24 hours, remove impurities such as plant roots and stones, grind it, pour it into a 2mm pore size sieve, grind it, sieve it, and mix it evenly to obtain a soil sample; S2: Preparation of soil sample extracts; S201: Add the soil sample to ultrapure water, place it in an ultrasonic-microwave instrument, raise the temperature to 20°C, set the power to 250W, and extract for 2 minutes to obtain a mixed solution; S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain the sample extract. S3: instrument detection; S301: ICP-OES: 1% HNO3 + 3% ethanol matrix, potassium / sodium / calcium / magnesium standard curve (0.5-20 mg / L); S302: IC: Cl- / SO42- standard curve (0.5-50 mg / L), H2O2 UV digestion; S4: Data processing and calculation.

[0027] Example 7: An efficient detection method for potassium, sodium, calcium and magnesium in soil soluble salts S1: Soil sample collection and preparation; S101: Sandy soil from Xiqing District, Tianjin was selected and samples were collected according to the principle of "random, equal amount, and multi-point mixing" with a depth of 0-20 cm and a weight greater than 1000 g to obtain the original soil sample; S102: Place the original soil sample in a vacuum freeze dryer, cool it to -55°C, dry it for 24 hours, remove impurities such as plant roots and stones, grind it, pour it into a 2mm pore size sieve, grind it, sieve it, and mix it evenly to obtain a soil sample; S2: Preparation of soil sample extracts; S201: Add the soil sample to ultrapure water, place it in an ultrasonic-microwave instrument, heat it to 30°C, use a power of 350W, and extract for 1 minute to obtain a mixed solution; S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain the sample extract. S3: instrument detection; S301: ICP-OES: 1% HNO3 + 3% ethanol matrix, potassium / sodium / calcium / magnesium standard curve (0.5-20 mg / L); S302: IC: Cl- / SO42- standard curve (0.5-50 mg / L), H2O2 UV digestion; S4: Data processing and calculation.

[0028] Performance testing: Comparative experimental data Examples 1-7 were compared using the new method with the current national standard GB / T 50123-2019, "Standard for Geotechnical Test Methods," to obtain measurement data. For each concentration sample, duplicate measurements were performed using both the new method and the comparative method. The averages of the duplicate measurements were recorded as the new method's measurement value (A) and the comparative method's measurement value (B), respectively. The paired difference (d) for the sample concentration (content) was then calculated.

[0029] The paired sample t-test method was used to determine whether the results of the two methods were significantly different. The arithmetic mean of the paired differences was obtained. , and the standard deviation Sd of the paired differences, calculate the test statistic: If the two-sided test P < α = 0.05, the measurement results of the two methods are significantly different; otherwise, the measurement results of the two methods are not significantly different.

[0030] Table 1 Comparison of the results of Examples 1-7 and the national standard method (unit: mg / 100g) project Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Potassium new method determination value 1.16 2.85 0.40 8.48 1.90 1.17 1.15 Potassium comparison method determination value 1.3 2.8 0.5 8.5 2.0 1.3 1.3 New method for determining sodium value 6.02 45.88 12.65 37.78 47.46 6.01 6.03 Sodium comparison method determination value 5.7 46.6 12.9 36.8 45.6 5.7 5.7 New method for determining calcium values 9.27 6.10 4.36 72.30 11.26 9.25 9.29 Calcium comparison method determination value 9.62 6.41 4.41 73.75 11.02 9.60 9.64 New method for determining magnesium value 2.86 3.66 1.25 22.53 5.00 2.84 2.88 Magnesium comparison method determination value 3.04 3.89 1.34 22.01 4.86 3.02 3.06 Sulfate new method determination value 6.63 29.77 3.37 91.26 33.15 6.66 6.60 Sulfate comparison method determination value 7.20 31.20 3.40 86.20 33.65 7.20 7.20 Chloride new method determination value 7.53 49.36 3.44 56.32 66.63 7.50 7.56 Chloride comparison method determination value 7.80 51.05 4.25 58.49 68.06 7.77 7.83 Table 2 Paired t-test analysis results

[0031] Precision verification The precision of the method was verified by using certified reference materials GBW(E)070031, GBW(E)070032 and GBW(E)070033 of three different concentrations or contents (high, medium and low) to perform seven parallel measurements on the samples according to the full sample analysis steps. Each sample was measured seven times in parallel according to the full procedure, and the mean value, standard deviation, relative standard deviation and other parameters of the samples at each concentration or content were calculated. Table 3 Units involved in verification analysis Serial number Laboratory Code Name of participating verification unit 1 C1 Guangxi Geology and Mineral Testing Research Center 2 C2 Heilongjiang Provincial Geological and Mineral Resources Experimental Testing Research Center 3 C3 Hunan Provincial Geological Experiment and Testing Center 4 C4 Liaoning Provincial Institute of Geology and Mineral Resources Co., Ltd. 5 C5 Testing Center of Shandong Bureau of China Metallurgical Geology Bureau 6 C6 Hebei Provincial Geological Experiment and Testing Center Table 4 Content range of certified reference materials

[0032] Table 5 Relative standard deviation between laboratories for samples 1-3

[0033] Note: —The average value of the samples tested at a certain concentration level by 6 laboratories; S' —inter-laboratory standard deviation; RSD'—Inter-laboratory relative standard deviation.

[0034] Data reliability verification Table 6 Cochran test table for outliers of samples 1-3

[0035] Calculation formula:

[0036] --Statistics; S i ---Laboratory standard deviation: S max -----The maximum value of the standard deviation in the laboratory; C 0.95 (7) / C 0.99 (7)------The data were obtained by consulting the Cochran test critical value table.

[0037] Data Analysis As can be seen from Table 1-2, all index paired t-tests satisfy P>0.05, confirming that the new method is statistically equivalent to the national standard method. The sulfate recovery rate of the humus soil sample (Example 3) is increased by 14% (3.37 vs 3.40), verifying that H2O2 UV digestion effectively eliminates organic interference. The sodium ion detection limit of the high-salt soil sample (Example 4) reaches 0.03 mg / 100 g (RSD=1.8%), proving the reliability of the dilution process.

[0038] As shown in Tables 3-5, the RSD' of potassium ions in low-concentration samples was 1.76%, the RSD' of calcium ions was 0.89%, and the RSD' of sulfate was 0.94%, indicating excellent stability of the low-concentration matrix; the RSD' of potassium ions in medium-concentration samples was 2.10%, the RSD' of calcium ions was 0.89%, and the RSD' of sulfate was 1.19%, and the detection standard composite met the requirements of LY / T 1251-1999; the RSD' of potassium ions in high-concentration samples was 1.00%, the RSD' of calcium ions was 0.60%, and the RSD' of sulfate was 1.82%, proving that the detection method of the present invention has strong resistance to high-salt interference, and the average RSD of the current national standard method is 5-8%, while the RSD' between laboratories of the present invention is <2.2%, and the precision is improved by more than 60%, so the present invention has high precision; As shown in Table 6, the Cochran outlier test shows that the statistic of potassium ion is 0.405, C 0.95 The critical value is 0.445, and its statistic is less than the critical value, so there is no outlier. The statistic of calcium ion is 0.344, and its data distribution is uniform. The statistic of chloride is 0.429, which can prove that there is no abnormality in the detection process of high-salt samples of the present invention, ensuring the accuracy of the detection results. At the same time, the C statistics of all indicators are less than the critical value (C 0.95 =0.445), confirming that the data from the six laboratories contained no outliers and the method was reproducible and reliable.

[0039] In summary, the present invention solves the three major pain points of traditional detection, namely, complicated procedures, insufficient precision, and low efficiency, through methodological innovation, and provides high-precision, high-throughput technical support for the prevention and control of soil salinization.

[0040] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0041] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil, characterized in that: The following steps are involved: Step S1: soil sample collection and preparation; Step S101: select areas with different salinization degrees, pH values, and soil properties, collect samples according to the principle of "random, equal amount, multi-point mixing" at a depth of 0-20 cm and a weight greater than 1000 g to obtain original soil samples; Step S102: placing the original soil sample in a vacuum freeze dryer, cooling it to -60-50°C, drying it for 22-26 hours, removing impurities such as plant roots and stones, grinding it, pouring it into a 2mm pore size sieve, grinding and sieving it, and mixing it evenly to obtain a soil sample; Step S2: preparing soil sample extract; Step S201: adding the soil sample to ultrapure water, placing the sample in an ultrasonic-microwave instrument, heating the sample to 20-30°C, using a power of 250-350W, and extracting the sample for 1-2 minutes to obtain a mixed solution; Step S202: Use a vacuum pump and a flat-bottom porcelain funnel to filter the mixed solution. If ∆EC is less than 1% and the filtrate is transparent, stop filtering to obtain a sample extract. Step S3: instrument detection; Step S4: Data processing and calculation.

2. The method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil according to claim 1, wherein: The mass ratio of the soil sample to ultrapure water in step S201 is 1:

5.

3. The method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil according to claim 1, wherein: The instrument detection steps are as follows: Step S301: Determination of potassium, sodium, calcium, and magnesium ions by plasma emission spectrometry; Step S302: Determine sulfate and chloride by ion chromatography.

4. The method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil according to claim 3, wherein: The steps of determining potassium, sodium, calcium and magnesium ions by plasma emission spectrometry in step S301 are as follows: Step S3011: using 1% HNO3 and 3% ethanol as a matrix, prepare five mixed standard solutions with concentration gradients, and draw emission intensity-concentration curves; Step S3012: adding nitric acid to the sample extract, shaking and letting it stand for 15 minutes, and determining the content of each element according to the calibration conditions, subtracting the blank value; The nitric acid is prepared by mixing 36% wt nitric acid and deionized water in a volume ratio of 1:

1.

5. The method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil according to claim 4, wherein: The five mixed standard solutions with concentration gradients in step S3011 are potassium: 0.5 mg / L, 2.0 mg / L, 5.0 mg / L, 10.0 mg / L, and 20.0 mg / L; Sodium: 1.0mg / L, 5.0mg / L, 10.0mg / L, 50.0mg / L, 100.0mg / L; Calcium: 2.0mg / L, 10.0mg / L, 20.0mg / L, 50.0mg / L, 100.0mg / L; Magnesium: 0.5mg / L, 2.0mg / L, 5.0mg / L, 10.0mg / L, 20.0mg / L; In step S3012, the volume ratio of nitric acid to sample extract is 1:25; The nitric acid in step S3012 is concentrated nitric acid and water in a volume ratio of 1:

1.

6. The method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil according to claim 3, wherein: The steps of determining sulfate and chloride by ion chromatography in step S302 are as follows: Step S3021: Prepare a mixed standard solution with 5 concentration points and draw a peak area-concentration curve; Step S3022: Pour the sample extract into a 0.22 μm PVDF needle filter, filter, add 50 μL of 30% H2O2, irradiate with UV light, digest for 20 min, inject and analyze, Cl - Retention time 3-3.4min, SO4 2- Retention time: 5.5-6.1 min, quantitative analysis by peak area.

7. The method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil according to claim 6, wherein: The mixed standard solution of the five concentration points in step S3021 is Cl - :0.5mg / L, 2.0mg / L, 10.0mg / L, 20.0mg / L; SO4 2- : 1.0mg / L, 5.0mg / L, 20.0mg / L, 50.0mg / L.

8. The method for determining potassium, sodium, calcium and magnesium in readily soluble salts in soil according to claim 1, wherein: The data processing and calculation formula is as follows: C χ : sample extract concentration (mg / L); V: volume of sample extract (200 mL); m s : sample mass (g); f: dilution factor.

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