CN110865105B - Method for obtaining soil pH value in-situ calibration curve and application - Google Patents
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Abstract
The method for obtaining the soil pH value in-situ calibration curve and the application thereof comprise the following steps: the method comprises the steps of obtaining a pH buffer solution temperature coefficient equation, adjusting the pH value of soil to obtain soil with different pH values, obtaining a pH temperature coefficient equation for verifying the soil, obtaining a temperature coefficient equation for the pH value of the soil with different water contents, and obtaining a calibration curve of the pH value of the soil. The method for obtaining the soil pH calibration curve in the potentiometric in-situ determination is used for calibrating the soil pH in the potentiometric in-situ determination, and is suitable for all soil pH monitoring applying the potentiometric principle. The method converts the pH value obtained by in-situ measurement into the pH value measured according to the HJ962-2018 standard, and realizes the on-site rapid monitoring and prejudgment of the soil pH parameter.
Description
Technical Field
The invention belongs to the field of soil pH measurement, and particularly relates to a method for acquiring a soil pH value in-situ calibration curve and application thereof.
Background
The pH value is one of the most important basic properties of soil and is an important index of the soil formation process and the curing and fertilizing process. The pH value of Soil has important influence on the physical and chemical properties of Soil, the activity of microorganisms, the growth and development of plants, and the occurrence and effectiveness of nutrient elements and pollutants in Soil (Hao et al, Plant Soil 2019,434: 167-. The pH value of the soil is a general term of the acidity and alkalinity of the soil, and is determined by the activity of hydrogen ions and hydroxide ions in a soil solution to measure the acidity and alkalinity of the soil. According to a standard method for measuring the pH value of the soil by using an HJ962-2018 potential method, the selection of the pH value of the soil under the laboratory condition is regulated℃25℃And measuring the pH value of the soil suspension by a potential method when the soil-water ratio is 1: 2.5.
The pH is determined by+Index of activity, and H in solution+The activity is influenced by its concentration and temperature conditions, so changes in solution temperature reflect changes in pH (Ashton et al, TSP 2011,1: 1-7). The method for measuring pH by a potentiometric method is based on the Nernst principle: e ═ R × T/(n × F) × ln (C1/C2), this equation is expressed in terms of phasesThe relationship between the current potential of a defined electrode assembly and the chemical activity of the measured ion concentration is described for a simple form. Wherein E is the Nernst potential, i.e., the potential difference (V), R is the gas constant (8.31439J/mol/K), T is the Kelvin absolute temperature (K), and n is the number of charges measured on the ion (n)HF is the faraday constant (96495.7C/mol). When the temperature of the system is 20℃The pH change by one unit, C1/C2-10, can be calculated as E-58.16 mV. In addition, temperature also affects the electrodes for measurement (Ashton et al, TSP 2011,1: 1-7). Since ionic activity is temperature dependent, nernst potential is also temperature dependent, which is the principle of automatic temperature compensation used by commercial pH meters now on the market. But due to H in the soil solution+The activity is not only influenced by the temperature but also influenced by soil factors, the temperature coefficient of the pH value of the soil is possibly inconsistent with that of the soil in the solution, and the activity is not reported at home and abroad at present.
Generally, when the soil pH is measured in the field, due to harsh experimental conditions, factors such as soil water content and temperature affect the measurement result, and the soil pH in-situ observation data cannot be directly compared with the data obtained by HJ962-2018 standard measurement, so that the in-situ observation data can only be used as rough reference. How to calibrate soil pH data obtained by field measurement to make the soil pH data become a soil pH index which can be quantitatively described and compared with laboratory control conditions, and the method in the aspect is lacked at home and abroad at present.
The invention researches the influence of the soil temperature and the water content when the pH value of the soil is measured by a potentiometric method, and provides reference for the calibration of the pH value of the soil obtained by in-situ measurement.
Disclosure of Invention
The technical problem to be solved is as follows: the invention provides a method for obtaining a soil pH value in-situ calibration curve and application thereof, and the method provides a solution for in-situ calibration of soil pH value by a potentiometric method.
The technical scheme is as follows: the method for acquiring the soil pH value in-situ calibration curve comprises the following steps: (1) obtaining the temperature coefficient of the given pH buffer solution: preparing a series of buffer solutions with pH values of 3-10 respectively; the pH buffer solution is placed in a constant temperature incubator, the temperature is raised from 4 ℃ to 40 ℃, the temperature raising rate is 0.3-0.4 ℃/min, and the potential value change of the pH electrode in the buffer solution in the process is continuously monitored; performing linear fitting on the measured potential value and the solution temperature to obtain a pH buffer solution calibration curve; (2) obtaining pH temperature coefficients of different buffer solutions: plotting the pH value of the solution in the pH buffer solution calibration curve against the temperature coefficient to obtain a pH buffer solution temperature coefficient relation graph, and fitting the temperature coefficients of the buffer solution under different pH values by obtaining a linear equation y of-0.10 x +0.87 from the graph to realize the temperature calibration of the field pH electrode; (3) obtaining soil samples with different pH values: weighing 600g of soil sample, sieving with a 10-mesh sieve, adding 12 g of aluminum sulfate, 3 g of aluminum sulfate, 0.3 g of calcium hydroxide, 0.9 g of calcium hydroxide and 2.1g of calcium hydroxide respectively, adding deionized water to adjust the water content of the soil to 70% of the field water capacity, putting the soil into a constant-temperature incubator at 25 ℃ for culturing for at least 30 days, and keeping the water content unchanged; after the culture is finished, air-drying the soil sample and sieving the soil sample by a 10-mesh sieve for later use to obtain soil samples with different pH values; measuring the pH value of the series of culture soils at 25 ℃ according to the HJ962-2018 standard potential method; (4) obtaining the pH temperature coefficients of the soils with different water contents: taking 200g of the culture soil subjected to air drying and sieving in the step (2), respectively adding 40 mL, 60 mL and 80mL of deionized water, and uniformly mixing to ensure that the water content of the soil is respectively 20%, 30% and 40%; placing the soil sample in a constant temperature incubator, continuously heating the soil sample from 5 ℃ to 40 ℃, wherein the heating speed is 0.3-0.4 ℃/min, and monitoring the potential change of the pH electrode in the soil in the heating process; carrying out linear fitting on the potential value obtained by monitoring and the soil temperature value to respectively obtain the change curves of the pH electrode potential value of the soil with the water content of 20%, the water content of 30% and the water content of 40% along with the temperature; (5) acquiring a temperature coefficient equation of the soil with different pH values and different water contents: drawing a relation curve between the soil pH temperature coefficient and the soil pH; (6) obtaining a soil pH in-situ calibration curve: and according to the temperature coefficient equation of the pH buffer solution and the pH of the soil, performing equation fitting on the pH value of the soil obtained by in-situ measurement and the pH value measured according to the HJ962-2018 standard, wherein the temperature is 25 ℃, and the soil-water mass ratio is 1:2.5, so as to obtain an in-situ calibration curve of the pH of the soil.
The above buffer solutions with pH values of 3.09, 4.91, 5.63 and 7.69 were prepared: the pH value of the 3.09 buffer solution is 125mL, 0.2mol/L potassium hydrogen phthalate and 100mL, 0.1mol/L HCl, and the volume is determined to be 500 mL; the pH 4.91 buffer solution is 125mL of 0.2mol/L potassium hydrogen phthalate and 100mL of 0.1mol/L NaOH to be constant volume to 500 mL; the pH 5.63 buffer solution was a mixture of 61mL1/15mol/L potassium dihydrogen phosphate and 439mL 1/15mol/L disodium hydrogen phosphate; the pH 7.69 buffer solution was a mixture of 473.5mL 1/15mol/L potassium dihydrogen phosphate and 26.5mL 1/15mol/L disodium hydrogen phosphate; the acid-base buffer solution prepared by the method is verified by the 4 commercial pH buffer solutions to obtain an accurate solution pH value.
Preferably, the pH meter, the pH electrode and the temperature sensor in step (1) are 3 groups, each group of pH electrode, pH meter and temperature sensor is defined as a set of equipment, which is equipment 1, equipment 2 and equipment 3, respectively, the pH meter, the pH electrode and the temperature sensor in step (3) are 2 groups, each group of pH meter, pH electrode and temperature sensor is set as a set of equipment, which is equipment 4 and equipment 5, respectively; in the step (1), each sample is heated to 40 ℃ from 5 ℃ by three sets of equipment respectively, the potential value and the temperature change of the sample are measured in the process, in the step (3), each sample is heated to 40 ℃ from 5 ℃ by 2 sets of equipment respectively, and the heating speed is 0.3-0.4 ℃/min; and recording the potential values and temperature changes of the pH electrodes of the pH buffer solution and the soil sample in the process, and performing piecewise linear fitting on the obtained change curves of the temperature and the potential values to obtain a pH temperature coefficient equation of the buffer solution and the culture soil.
The method for obtaining the soil pH value in-situ calibration curve is applied to on-site rapid monitoring and prejudgment of soil pH parameters.
Has the advantages that: 1. after comparing 2 modes of manual temperature adjustment and automatic temperature control, the temperature coefficients of the soil and the solution are found to reach response balance when the temperature rising speed is 0.3-0.4 ℃/min, and the subsequent soil and solution temperature coefficient experiment adopts the temperature rising speed. 2. The pH value of the soil used for researching the temperature coefficient of the soil in the method is 3.4-8.5, and the pH value range of the soil in most cultivated lands in China is covered. 3. How to calibrate soil pH data obtained by field measurement to obtain quantitative parameters which can be compared with soil pH values obtained under laboratory control conditions is lacking at home and abroad at present. Therefore, the method for soil pH in-situ calibration fills the gap of domestic and foreign research.
Drawings
FIG. 1 shows the relationship between the temperature in the pH buffer solution and the potential value of the pH electrode (A is measured by device 1, B is measured by device 2, and C is measured by device 3);
FIG. 2 is a temperature coefficient relationship of a pH buffer solution;
FIG. 3.20% water content soil temperature and pH electrode potential relationship (A is measured by device 4, B is measured by device 5);
FIG. 4.30% water content soil temperature and pH electrode potential relationship (A for device 4 and B for device 5);
FIG. 5.40% water content soil temperature and pH electrode potential relationship (A for device 4 and B for device 5 measurements);
FIG. 6 is a graph showing the relationship between the pH value of the culture soil and the temperature coefficient;
FIG. 7 is a graph of in situ soil pH calibration.
Detailed Description
Verifying the correctness of the pH temperature coefficient relation of the soil through the pH temperature coefficients of the Yunnan brick red soil and Anhui moisture soil;
the method comprises the steps of converting the pH value of the soil under the saturated water content through in-situ measurement of Nanjing yellow brown soil, Anhui moisture soil and Hebei brown soil into a HJ962-2018 standard value, and comparing the standard value with the pH value of the soil measured according to the standard to verify the accuracy of the pH temperature coefficient of the solution, the pH temperature coefficient of the soil and the pH calibration curve of the soil.
pH buffered solutions of 4.01, 6.86, 9.18, and 10.01 were from: hanna and Thermo Fisher. The pH buffer solution and the soil pH are measured according to the HJ962-2018 standard, the pH electrode adopts a Raymagnetic E-201-C pH composite electrode with a zero point pH of 7.00, the electrode adopts a Raymagnetic E-201-Z conical pH composite electrode with a zero point pH of 7.00 when the soil in-situ pH is measured, the pH meter adopts a Saimer Feorion Star A211 type pH meter, the temperature sensor adopts an Orilong 927007MD electrode, and the constant temperature incubator adopts an LK-118L incubator (Longfei seed facility).
The invention relates to a method for acquiring a soil in-situ calibration curve for measuring soil pH by a potentiometric method, which comprises the following steps:
(1) obtaining pH temperature equations of different buffer solutions: pH buffer solutions with pH values of 3.09, 4.01, 4.91, 5.63, 6.86, 7.69, 9.18 and 10.01 are prepared. The pH buffer solution is placed in a constant temperature incubator to be heated from 5 ℃ to 40 ℃ (the heating rate is 0.3-0.4 ℃/min), and the potential value change of the pH electrode in the buffer solution in the heating process is continuously measured. The measured potential value and the solution temperature are subjected to linear fitting, so that a pH buffer solution calibration curve (figure 1) can be obtained. The potential values of the pH buffer solutions 3.09, 4.01, 4.91, 5.63 and 6.86 gradually increased with the increase of the incubation temperature, and the temperature coefficients decreased with the increase of the pH buffer solution. While the potential values of the pH buffer solutions of 7.69, 9.18 and 10.01 are basically kept unchanged or slightly reduced along with the increase of the culture temperature.
(2) Obtaining pH temperature coefficients of different buffer solutions: the pH of the solution of FIG. 1 is plotted against the temperature coefficient to obtain a temperature coefficient graph of the pH buffered solution (FIG. 2). The results show that the pH value and the temperature coefficient of the pH buffer solution are in an extremely significant negative correlation (R)2＝0.89，P<0.01). Temperature calibration of the field pH electrode can therefore be achieved by fitting the temperature coefficients of the buffer solution at different pH's to a linear equation (y-0.10 x + 0.87).
(3) Obtaining soil samples with different pH values: the soil samples which were air-dried and sieved after the culture were taken, respectively, and the pH value of the culture soil was measured according to the HJ962-2018 standard, and the pH results of the obtained culture soil are shown in Table 1.
TABLE 1 soil cultivation protocol and pH
(4) Obtaining the pH temperature coefficients of the soils with different water contents: 200g of Nanjing yellow brown soil cultured at 25 ℃ and with the pH values of 3.41, 3.72, 4.93, 5.80, 6.74 and 8.11 are respectively added with 40 g, 60 g and 80g of deionized water and mixed uniformly, so that the water content of the soil is maintained at 20%, 30% and 40%. And (3) placing the soil with different pH values and different water contents in a constant temperature incubator, raising the temperature from 5 ℃ to 40 ℃ at a temperature raising speed of 0.3-0.4 ℃/min, and continuously monitoring the potential value change of the pH electrode. And performing linear fitting on the obtained potential value and the soil temperature value to respectively obtain the change curves of the pH electrode potential value of the soil with the water content of 20% (figure 3), the water content of 30% (figure 4) and the water content of 40% (figure 5) along with the temperature. The result shows that the potential values of the pH electrodes in the soil with different pH values and different water contents are obviously increased along with the increase of the culture temperature. In addition, the stability of the in-situ pH value of the soil is poor at the water content of 20%, and the fluctuation is large, probably because the pH electrode sensitive film is not contacted with the soil solution to be loose under the water content, and the electrode potential is not easy to reach balance, so that the water saturation condition is recommended to be selected during field measurement; when the soil is dry, the electrode can be buried and then the water can be supplemented until the soil is saturated.
(5) Acquiring a temperature coefficient equation of the soil with different pH values and different water contents: the relation curve of the soil pH temperature coefficient and the soil pH is drawn, and the temperature coefficients of the soils with different pH values are found to be not very different when the water content of the culture soil is 30% and 40%. Therefore, when the soil pH is actually measured in the field, the soil is preferably prepared into a sample with saturated water. When the pH of the culture soil is high<At 5.0, the temperature coefficient decreased with increasing soil pH (fig. 6). The water content of the water-soluble polymer is 20 percent or 30 to 40 percent, and the water-soluble polymer are in extremely obvious negative correlation (R)2＝0.91，P<0.01；R2＝0.83，P<0.01). When the pH of the culture soil is high>At 5.0, the temperature coefficient of the soil pH electrode under the water content of 20 percent is reduced along with the increase of the pH value; the temperature coefficient of the soil with the water content of 30-40% does not basically change along with the increase of the pH value of the soil.
(6) Obtaining a soil pH in-situ calibration curve: and according to the temperature coefficient equation of the pH buffer solution and the pH of the soil, fitting the pH value of the soil obtained by in-situ measurement with the pH value measured according to the HJ962-2018 standard to obtain an in-situ calibration curve of the pH of the soil (figure 7). The results show that the slope between the soil pH value obtained by in-situ measurement converted at 25 ℃ and the pH value obtained by HJ962-2018 standard measurement is 1, and the intercept is 0.142.
Example 1
And (3) taking a Yunnan brick red soil sample which is air-dried and sieved by a 10-mesh sieve, and determining the pH value of the soil to be 5.30 according to the HJ962-2018 standard. Respectively adding 200g of soil sample into the soil to remove CO2Deionized water 60 and80g, and mixing uniformly to ensure that the water content of the soil is 30 percent and 40 percent respectively. Slowly heating the Yunnan brick red soil with different water contents in a constant temperature incubator (0.3-0.4 ℃/min), and continuously monitoring the potential value change of the pH electrode in the heating process of the Yunnan brick red soil. And performing linear fitting on the measured potential value and the soil temperature to obtain the pH temperature coefficient of the Yunnan brick red soil (the result is shown in figure 6). The result of measuring the temperature coefficient can be seen from the measuring result of the Yunnan brick red soil, which accords with the expectedness of the experiment and verifies the correctness of the obtained soil temperature coefficient.
Example 2
Taking an Anhui moisture soil sample which is air-dried and sieved by a 10-mesh sieve, and determining the pH value of the soil to be 7.78 according to the HJ962-2018 standard. Respectively adding 200g of soil sample into the soil to remove CO260 g of deionized water and 80g of deionized water are uniformly mixed, so that the water content of the soil is respectively 30% and 40%. The Anhui moisture soil with different water contents is placed in a constant temperature incubator to slowly rise the temperature (0.3-0.4 ℃/min), and the potential value change of a pH electrode of the Anhui moisture soil in the temperature rise process is continuously monitored. The pH temperature coefficient of Anhui moisture soil can be obtained by linear fitting the measured potential value and the soil temperature (the result is shown in FIG. 6). The result of measuring the temperature coefficient can be seen from the result of measuring moisture soil in Anhui province, and the accuracy of the obtained soil temperature coefficient equation is verified.
Example 3
In Nanjing soil research institute, national academy of sciences, one area was selected as a test site, and the potential values of the buffer solutions of pH 6.86 and 4.01 were measured to be 33.8 and 205.0mV, respectively, at temperatures of 31.2 ℃ and 31.1 ℃. Carefully burying the pH electrode in the soil of the test area, kneading the soil and covering the pH and temperature electrodes to remove CO2Deionized water is sprayed on the soil, and the pH electrode mV value and the temperature in the soil are measured to be 147.6mV and 29.6 ℃ respectively.
Temperature coefficients corresponding to pH 6.86 and 4.01 buffer solutions, respectively: k6.86＝-0.10×6.86+0.87＝0.184，K4.01-0.10 × 4.01+ 0.87-0.469. The potential values corresponding to the buffer solutions of pH 6.86 and 4.01 at 25 ℃ were found to be 33.8- (31.2-25). times.0.184 ═ 32.659mV, and 205.0- (31.1-25). times.0.469 ═ 2, respectively, by calculation02.139 mV. Meanwhile, the potential values corresponding to pH 6.86 and 4.01 buffer solutions at 29.6 ℃ were calculated to be 33.8- (31.2-29.6) × 0.184 ═ 33.5056mV and 205.0- (31.1-29.6) × 0.469 ═ 204.2965mV, respectively. The corresponding pH (147.6-444.6)/(-59.927) — (4.956) at 29.6 ℃ of the measured soil can be calculated from pH 6.86 at 29.6 ℃ and the potential value of 4.01 buffer solution.
The temperature coefficient Ks of the soil is 0.0217 × 4.956+0.8935 is 1.001, and the potential value corresponding to the soil at 25 ℃ is 147.6- (29.6-25.0). times.1.001 is 142.9954 mV. The pH of the soil should be (142.9954-440.6)/(-59.467) ═ 5.0054 at this time. From fig. 7, the soil pH was 1.1808 × 5.0045-0.8682-5.04 under the laboratory control conditions.
The soil sample is collected to a laboratory for air drying, ground and sieved by a 10-mesh sieve, the actually obtained soil sample pH value is determined to be 5.15 according to the HJ962-2018 standard, the difference between the soil pH value obtained in situ by the method and the national standard method is 0.11pH unit, and the feasibility of the soil pH calibration method is verified.
Example 4
In Anhui, a soil area with a certain moisture soil texture is selected as a test site, and the potential values of the pH 6.86 buffer solution and the 4.01 buffer solution are respectively 33.2 mV and 201.6mV, and the temperature of the solution is 26.6 ℃. Carefully burying the pH electrode in the soil of the test area, kneading the soil and covering the pH and temperature electrodes to remove CO2Deionized water is sprayed on the soil, and the pH electrode potential value and the temperature in the soil are measured to be-15.4 mV and 26.7 ℃ respectively.
Temperature coefficients corresponding to pH 6.86 and 4.01 buffer solutions, respectively: k6.86 ═ -0.10 × 6.86+0.87 ═ 0.184, K4.01 ═ -0.10 × 4.01+0.87 ═ 0.469. The potential values corresponding to the pH 6.86 and 4.01 buffer solutions at 25 ℃ were found to be 33.2- (26.6-25) × 0.184 ═ 32.91mV and 201.6- (26.6-25) × 0.469 ═ 200.85mV, respectively, by calculation. In this case, the potential values at 26.7 ℃ corresponding to pH 6.86 and 4.01 buffer solution were calculated to be 33.2- (26.6-26.7) × 0.184 ═ 33.22mV and 201.6- (26.6-26.7) × 0.469 ═ 201.65mV, respectively. Thus, the corresponding pH (-15.4-438.63)/(-59.098) ═ 7.70 at 26.7 ℃ in soil.
The temperature coefficient Ks of the soil is 0.0217 × 7.70+0.8935 ═ 1.06, and the potential value corresponding to the soil at 25 deg.C is-15.4- (26.7-25.0) × 1.06 ═ 17.20 mV. The pH of the soil at this point was (-17.20-437.15)/(-58.928) ═ 7.71. From fig. 7, the soil pH was found to be 1.1808 × 7.71-0.8682 ═ 8.24 under the control conditions of the fitting laboratory.
The soil sample is collected into a laboratory part, the sample is air-dried, ground and sieved by a 10-mesh sieve, the pH value of the actually obtained soil sample is measured according to the HJ962-2018 standard and is 8.17, the difference between the pH value of the soil obtained by the method in situ and the pH value obtained by the method in situ in a national standard method is 0.07pH unit, and the accuracy of the soil pH in situ measurement is improved.
Example 5
A certain soil area is selected as a test site in Hebei, and the potential values of the buffer solution with pH 6.86 and 4.01 are respectively 30.7 mV and 205.3mV, and the temperature is respectively 23.9 ℃ and 24.6 ℃. Carefully burying the pH electrode in the soil of the test area, kneading the soil and covering the pH and temperature electrodes to remove CO2Deionized water is sprayed on the soil, and the pH electrode mV value and the temperature in the soil are respectively 24.5mV and 24.3 ℃ through measurement.
Temperature coefficients corresponding to pH 6.86 and 4.01 buffer solutions, respectively: k6.86 ═ -0.10 × 6.86+0.87 ═ 0.184, K4.01 ═ -0.10 × 4.01+0.87 ═ 0.469. The potential values corresponding to the pH 6.86 and 4.01 buffer solutions at 25 ℃ were found to be 30.7- (23.9-25) × 0.184 ═ 30.9024mV and 205.3- (24.6-25) × 0.469 ═ 205.876mV, respectively, by calculation. Meanwhile, the potential values corresponding to a pH 6.86 and a 4.01 buffer solution at 24.3 ℃ were calculated to be 30.7- (23.9-24.3) × 0.184 ═ 30.7736mV and 205.3- (24.6-24.3) × 0.469 ═ 205.1593mV, respectively. The corresponding pH (24.5-450.52)/(-61.188) ═ 6.96 at 24.3 ℃ of the measured soil can be calculated from pH 6.86 at 24.3 ℃ and the potential value of the 4.01 buffer solution.
When the temperature coefficient of the soil is Ks 0.0217 × 6.9625+0.8935 is 1.0446, the potential value of the corresponding measured soil at 25 ℃ is 24.5- (24.3-25.0) × 1.0446 is 25.2312 mV. The pH of the soil should be (25.2312-451.13)/(-61.258) — 6.9525. From fig. 7, the soil pH was 1.1808 × 6.9525-0.8682-7.34 under the laboratory control conditions.
The soil sample is collected to a laboratory part, the sample is air-dried, ground and sieved by a 10-mesh sieve, the actually obtained soil sample pH value is determined to be 7.13 according to the HJ962-2018 standard, the difference between the soil pH value obtained in situ by the method and the national standard method is 0.21pH unit, and the feasibility of the soil pH calibration method is verified.
Claims (4)
1. The method for acquiring the soil pH value in-situ calibration curve is characterized by comprising the following steps:
(1) obtaining the temperature coefficient of the given pH buffer solution: preparing a series of buffer solutions with pH values of 3-10 respectively; the pH buffer solution is placed in a constant temperature incubator, the temperature is raised from 4 ℃ to 40 ℃, the temperature raising rate is 0.3-0.4 ℃/min, and the potential value change of the pH electrode in the buffer solution in the process is continuously monitored; performing linear fitting on the measured potential value and the solution temperature to obtain a pH buffer solution calibration curve;
(2) obtaining pH temperature coefficients of different buffer solutions: drawing the pH value of the solution in a pH buffer solution calibration curve to the temperature coefficient to obtain a pH buffer solution temperature coefficient relation graph, and obtaining a linear equation y = -0.10x +0.87 from the graph to fit the temperature coefficient of the buffer solution under different pH values so as to realize temperature calibration of the field pH electrode;
(3) obtaining soil samples with different pH values: weighing 600g of soil sample, sieving with a 10-mesh sieve, adding 12 g of aluminum sulfate, 3 g of aluminum sulfate, 0.3 g of calcium hydroxide, 0.9 g of calcium hydroxide and 2.1g of calcium hydroxide respectively, adding deionized water to adjust the water content of the soil to 70% of the field water capacity, putting the soil into a constant-temperature incubator at 25 ℃ for culturing for at least 30 days, and keeping the water content unchanged; after the culture is finished, air-drying the soil sample and sieving the soil sample by a 10-mesh sieve for later use to obtain soil samples with different pH values; measuring the pH value of the series of culture soils at 25 ℃ according to the HJ962-2018 standard potential method;
(4) obtaining the pH temperature coefficients of the soils with different water contents: taking 200g of the culture soil subjected to air drying and sieving in the step (2), respectively adding 40 mL, 60 mL and 80mL of deionized water, and uniformly mixing to ensure that the water content of the soil is respectively 20%, 30% and 40%; placing the soil sample in a constant temperature incubator, continuously heating the soil sample from 5 ℃ to 40 ℃, wherein the heating speed is 0.3-0.4 ℃/min, and monitoring the potential change of the pH electrode in the soil in the heating process; carrying out linear fitting on the potential value obtained by monitoring and the soil temperature value to respectively obtain the change curves of the pH electrode potential value of the soil with the water content of 20%, the water content of 30% and the water content of 40% along with the temperature;
(5) acquiring a temperature coefficient equation of the soil with different pH values and different water contents: drawing a relation curve between the soil pH temperature coefficient and the soil pH;
(6) obtaining a soil pH in-situ calibration curve: and according to the temperature coefficient equation of the pH buffer solution and the pH of the soil, performing equation fitting on the pH value of the soil obtained by in-situ measurement and the pH value measured according to the HJ962-2018 standard, wherein the temperature is 25 ℃, and the soil-water mass ratio is 1:2.5, so as to obtain an in-situ calibration curve of the pH of the soil.
2. The method for obtaining the soil pH value in-situ calibration curve according to claim 1, wherein the method comprises the following steps: the series of buffer solutions with the pH values of 3-10 are 4 buffer solutions with the pH values of 3.09, 4.91, 5.63 and 7.69, and the preparation method of the 4 buffer solutions comprises the following steps: the preparation method of 4 buffer solutions with pH values of 3.09, 4.91, 5.63 and 7.69 comprises the following steps: the pH value of the 3.09 buffer solution is 125mL, 0.2mol/L potassium hydrogen phthalate and 100mL, 0.1mol/L HCl, and the volume is determined to be 500 mL; the pH 4.91 buffer solution is 125mL of 0.2mol/L potassium hydrogen phthalate and 100mL of 0.1mol/L NaOH to be constant volume to 500 mL; the pH 5.63 buffer solution is a mixture of 61mL1/15mol/L potassium dihydrogen phosphate and 439mL 1/15mol/L disodium hydrogen phosphate; the pH 7.69 buffer solution was a mixture of 473.5mL 1/15mol/L potassium dihydrogen phosphate and 26.5mL 1/15mol/L disodium hydrogen phosphate; the buffer solution prepared by the method is verified by the 4 commercial pH buffer solutions to obtain an accurate solution pH value.
3. The method for obtaining the soil pH value in-situ calibration curve according to claim 1, wherein the method comprises the following steps: a pH meter and a temperature sensor are also adopted in the step (1), the pH meter, the pH electrode and the temperature sensor are all 3 groups, each group of the pH electrode, the pH meter and the temperature sensor is defined as a set of equipment which is respectively equipment 1, equipment 2 and equipment 3, the pH meter, the pH electrode and the temperature sensor in the step (3) are all 2 groups, each group of the pH meter, the pH electrode and the temperature sensor is set as a set of equipment which is respectively equipment 4 and equipment 5; in the step (1), each sample is heated to 40 ℃ from 5 ℃ by three sets of equipment respectively, the potential value and the temperature change of the sample are measured in the process, in the step (3), each sample is heated to 40 ℃ from 5 ℃ by 2 sets of equipment respectively, and the heating speed is 0.3-0.4 ℃/min; and recording the potential values and temperature changes of the pH electrodes of the pH buffer solution and the soil sample in the process, and performing piecewise linear fitting on the obtained change curves of the temperature and the potential values to obtain a pH temperature coefficient equation of the buffer solution and the culture soil.
4. The method for obtaining the soil pH value in-situ calibration curve according to any one of claims 1 to 3, is applied to the on-site rapid monitoring and prejudgment of soil pH parameters.
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