A soil water potential equivalent measurement system and calibration and correction method

Abstract

The present invention discloses a system for equivalently measuring soil water potential and a calibration and correction method, belonging to the technical field of soil water potential measurement. The method includes the following steps: establishing a model of the soil to be measured, covering all soil water potential measurement environments; selecting a porous medium material as the measurement conversion target according to the measurement environment, and using the capacitance and resistance parameters of the porous medium material to replace the total water potential parameter and solute potential parameter in the soil water potential to be measured; and designing a measurement circuit to equivalently represent the entire measurement process, and directly calculating and correcting the capacitance and resistance of this material. Compared with the traditional soil water potential measurement method, the present invention has a wide measurement range, strong adaptability to the measurement environment, little influence of the measurement result by the environment, accurate measurement result, and low production cost of the entire device.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil water potential measurement, and particularly relates to a soil water potential equivalent measurement system and a calibration and correction method. Background Technique

[0002] The water in the soil contains different amounts and forms of energy, and the movement of water in the soil follows the law of potential energy from high to low. Measuring or calculating the soil water potential is required in the study of plant physiology, the water available to plants in the soil, and the process of soil water movement flux. Currently, the in-situ methods for measuring soil water potential include the tensiometer method (such as the negative pressure gauge), the thermocouple hygrometer (such as the PSYPRO dew point water potential meter), the heat capacity method, and the resistance method (such as the WaterMark), etc.

[0003] The tensiometer measures the soil water potential by measuring the principle of negative pressure, and often has an upper working limit of 85 kPa. Under conditions exceeding 85 kPa, it may not work properly even at normal temperature, and the requirements for the water filled in the tensiometer are very high. Bubbles in the tube or dissolved gases in the water will affect the water potential measurement results. The thermocouple hygrometer can measure the soil water potential within the range of 2000 kPa. Although it has been applied within a certain range at present, due to the high precision requirements for the micro-signal of this instrument, a precision microvoltmeter must be equipped, but the microvoltmeter is expensive and not yet popular. Another major limitation of the thermocouple hygrometer is that its accuracy in measuring the water potential in soils with high water content is poor. In soils with high water content, the sensitivity of the thermocouple hygrometer to moisture decreases. The heat capacity method is a thermal pulse type that actively emits a part of energy to capture the temperature rise process to distinguish the humidity of the ceramic equilibrium material, that is, the higher the water potential, the lower the temperature rise, and the lower the water potential, the higher the temperature rise. In unsaturated soils, the soil water potential includes the matrix potential and the solute potential. Although the thermocouple hygrometer measures the total water potential, in soils with high salt content, this method cannot obtain the matrix potential. The resistance method uses nylon material or gypsum material to wrap the electrodes and measures the resistance of the overall material to measure the matrix potential, but the resistance method is often greatly affected by temperature and cannot work properly in the nearly saturated section of the soil. Summary of the Invention

[0004] In order to solve the technical problems existing in the above background technique, the present invention provides a soil water potential equivalent measurement system and a calibration and correction method.

[0005] The present invention adopts the following technical solutions: A soil water potential equivalent measurement system, comprising:

[0006] Establish a measurement soil model, and select a corresponding water potential equilibrium material according to the properties of the soil to be measured based on the measurement soil model;

[0007] A soil water potential equivalent circuit, which is configured to measure the equivalent parameters of the water potential equilibrium material;

[0008] Pre - establish a mapping relationship, and calculate the actual water potential parameters of the soil to be measured based on the mapping relationship and the equivalent parameters of the water potential balance material.

[0009] Among them, the water potential balance material is a porous medium material.

[0010] In a further embodiment, the soil measurement model includes: a non - salinized soil measurement model and a saline - alkali soil measurement model;

[0011] The actual soil water potential parameters of the non - salinized soil measurement model at least include: matrix potential a;

[0012] The actual soil water potential parameters of the saline - alkali soil measurement model at least include: matrix potential a and solute potential b.

[0013] In a further embodiment, the bubble pressure value of the porous medium material is at least 1000 hPa, and its pore size is: 0.45 μm - 1 μm; 2 to 4 electrodes are embedded inside the porous medium material.

[0014] In a further embodiment, the equivalent circuit includes: an AC signal source U1, a first amplifier U2, a second amplifier U3, a resistor R1, a variable resistor R2, a resistor Rf, an equivalent circuit Rx, a capacitor C1, and a capacitor C2; their connection relationship is: one end of the AC signal source is connected to one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the resistor R1, the other end of the resistor R1 is connected to pin 2 of the variable resistor R2, pin 3 of the variable resistor R2 is connected to the other end of the AC signal source, pin 1 of the variable resistor R2 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to one end of the equivalent circuit Rx and is also connected to pin 3 of the amplifier U2, pin 2 of the amplifier U2 is connected to pin 1 of the amplifier U2; the other end of the equivalent circuit Rx is connected to pin 2 of the amplifier U3, and both pin 1 and pin 3 of the amplifier U3 are connected to the other end of the AC signal source; one end of the resistor Rf is connected to pin 2 of the amplifier U3 and the other end is connected to pin 2 of the amplifier U3;

[0015] Among them, the equivalent circuit Rx can be equivalent to the state after the moisture in the porous medium material reaches equilibrium. The equivalent circuit Rx includes: a DC component U, a capacitor C A and a resistor R A ; among them, the positive pole of the DC component U is connected to pin 3 of the amplifier U2, the capacitor C A and the resistor R AConnected in parallel, one end is connected to the negative pole of the DC component U, and the other end is connected to pin 2 of U3.

[0016] In a further embodiment, the capacitor C A has a capacitance value denoted as C, and the resistor R A has a resistance value denoted as R; the porous medium material is calibrated before use, and after calibration, there is the following formula: the capacitance value of the capacitor C A can be expressed as the total water potential C, and the resistance value of the resistor R A can be expressed as the solute potential R.

[0017] In a further embodiment, the calibration work includes: calibration of the capacitance value C; using the porous medium material to establish a suction model of 0 - 10000 kPa, simulating the calibration of the total water potential and capacitance value in the soil model, and the calibration points are 6 - 7, and the calibrated capacitance value C is denoted as K1C.

[0018] In a further embodiment, the calibration work includes: calibration of the resistance value R; placing the porous medium material sensor in KCl solutions of different standards such as 0.001 mol / L, 0.01 mol / L, 0.1 mol / L, and 1 mol / L, establishing a multi - point conductance model, simulating the calibration of the solute potential and resistance value in the soil model, and the calibration points are 4, and the calibrated resistance value R is denoted as K2R.

[0019] In a further embodiment, based on the mapping relationship, the matrix potential a = K1C - K2R, and the solute potential b = K2R.

[0020] In a further embodiment, it further includes: a thermal resistance measurement circuit, which is used to synchronously measure the temperature of the corresponding soil model.

[0021] A method for equivalent determination of soil water potential includes the following steps:

[0022] Step 1. Parameter setting: The AC voltage between pin 1 and pin 2 of the amplifier U2 is U f , and the AC voltage between pin 1 and pin 3 of the amplifier U3 is U0; when the equivalent circuit is measured, data at least at two different frequency moments are recorded to calculate the capacitance value C and the resistance value R; among them, when a sinusoidal AC current with a lower frequency is input, U f is measured as U fl ; U0 is measured as U 0l ; when a sinusoidal AC current with a higher frequency is input, U f is measured as U fh ; U0 is measured as U 0h ;

[0023] Step 2. When the AC voltage value U fl is not equal to the U fh value, the capacitance value C and the resistance value R should be corrected. Set the voltage correction coefficient as , and the frequency correction coefficient ; = = , = ;

[0024] Step 3. Calculate the corrected capacitance value C and resistance value R. Since there is a 90° phase difference in the current flowing through the capacitor C A and the resistor R A , complex numbers need to be used for calculation. Taking the current as the basic calculation formula, the correction process of the resistance value R is as follows:

[0025]

[0026] Also, there is the capacitive reactance formula: ; ; Therefore ;

[0027] ;

[0028] Then the correction process of the capacitance value C is as follows: ;

[0029] At the same time

[0030] Because of the capacitive reactance formula: , so:

[0031] = .

[0032] Advantages of the present invention: The present invention adopts a porous medium material design in combination with an equivalent circuit to measure and correct the soil water potential. Compared with the traditional water potential measurement method, the measurement method of the present invention has strong environmental adaptability, and can accurately measure the decisive parameters of relevant soil moisture in both non-salinized soil and saline-alkali soil, and is less affected by environmental factors. The present invention can be normally measured in the range of -10,000 kPa to 0 kPa, and has a wider application range. Compared with the traditional measurement method, which can often only measure a single parameter in the soil water potential and the accuracy of the measured parameter is poor, the present invention designs a correction method after measurement to ensure the accuracy of the measurement result. Moreover, the design of the entire measurement device is plug-and-play, easy to operate, and the overall production cost is low. Description of the Drawings

[0033] Figure 1 This is a schematic structural diagram of the equivalent circuit of the present invention. Specific embodiments

[0034] The present invention will be further described below in conjunction with embodiments and the accompanying drawings.

[0035] The methods for measuring soil water potential in the prior art are as follows: Method 1, the tensiometer method, which measures by the principle of measuring negative pressure, often has an upper limit of 85 kPa. Under conditions exceeding 85 kPa, it may vaporize and cannot work properly even at normal temperature. Moreover, the requirements for the water filled in the tensiometer are very high. Bubbles in the tube or dissolved gases in the water will affect the measurement result of water potential. Method 2: The thermocouple hygrometer can measure soil water potential within the range of 2000 kPa. Although it has been applied in some scientific research at present, because this instrument has high precision requirements for weak signals, it must be equipped with a precision microvoltmeter, which is expensive and not yet popularized. Another major limitation of the thermocouple hygrometer is that its accuracy in measuring water potential in soils with high water content is poor. In soils with high water content, the relative humidity in the soil is almost 100%, so the sensitivity of the thermocouple hygrometer to moisture decreases. Method 3, the heat capacity method, the thermal pulse actively emits a part of energy to capture the temperature rise process to distinguish the humidity of the ceramic equilibrium material, that is, the higher the water potential, the lower the temperature rise, and the lower the water potential, the higher the temperature rise. In unsaturated soils, soil water potential includes matrix potential and solute potential. Although the thermocouple hygrometer measures the total water potential, in soils with high salt content, this method cannot obtain the matrix potential. Method 4, the resistance method, wraps nylon material or gypsum material in the electrode and measures the resistance of the whole material to measure the matrix potential, but the resistance method is often greatly affected by temperature and cannot work properly in the nearly saturated section of the soil.

[0036] Embodiment 1

[0037] Based on the defects existing in the above methods, in order to solve the existing technical problems, this embodiment provides a new method for measuring soil water potential. The principle of this measuring device and measuring method is different from various previous measuring methods. A soil water potential equivalent measuring system includes: establishing a measured soil model, and selecting a water potential equilibrium material according to the measured soil model; a soil water potential equivalent circuit, which is arranged to measure the equivalent parameters of the water potential equilibrium material;

[0038] Among them, the water potential balance material is set as a porous medium material; there is a mapping relationship between the actual soil water potential parameters in the soil model and the equivalent parameters of the balance material. Since traditional measurement methods are often difficult to accurately measure in saturated soil and saline-alkali soil, the present invention first establishes a soil model that encompasses all soil types to be measured, which serves as the basis for calibration detection, ensuring that the measurement device and method can be applied to all environments and enhancing the applicability and practicality of the present invention. In the application of the present invention, the water potential balance material is a porous medium material, specifically the porous medium material ED21 produced by Nanjing Smart Sensor Co., Ltd. The characteristics of this porous medium material are: the bubble point pressure ≥ 1000 hPa, the pore size: 0.45 μm - 1 μm porous material. The bubble point pressure is the gas pressure that presses out the liquid from the largest pore in the completely wetted bubble point membrane. The liquid used for the experiment must completely wet the membrane, and at this time, the membrane pores will be filled with liquid. When the gas pressure is greater than the capillary pressure and surface tension in the membrane pores, the liquid can be pressed out of the membrane pores. The bubble point pressure of ED21 designed by Smart is 0.1 MPa for the bubble pressure, corresponding to a pore size of approximately 1 μm. According to the use environment and requirements for data results, its pore size can be set smaller. In a further embodiment, 2 to 4 electrodes are embedded inside the porous medium material.

[0039] In a further embodiment, the measured soil model includes: a non-salinized soil measurement model and a saline-alkali soil measurement model; the actual soil water potential parameters of the non-salinized soil measurement model include: matrix potential a;

[0040] The actual soil water potential parameters of the saline-alkali soil measurement model include: matrix potential a and solute potential b. For non-salinized soil, in research, the solute potential is often not distinguished from the soil matrix potential, but the solute potential is attributed to the matrix potential. Generally, it is considered that the matrix potential of saturated soil is 0, and the water potential has only two types: gravitational potential and pressure potential; for unsaturated soil, the pressure potential is 0, and the water potential has only gravitational potential and matrix potential. For relatively dry soil, the pressure potential is 0, the weight potential can be ignored, and soil moisture is mainly determined by the matrix potential. Therefore, the water potential of non-salinized soil moisture is mainly affected by the matrix potential a; for saline-alkali soil, due to the high salt content in the soil, the solute potential b cannot be ignored, so it is the matrix potential a and the solute potential b that determine the moisture state and movement of saline-alkali soil.

[0041] In a further embodiment, because the information in the soil cannot be accurately obtained, the present invention measures capacitance and resistance by synchronous dual-frequency, and the conversion is established through a porous medium material. The measured capacitance and resistance are the capacitance and resistance of the porous medium material after the soil water balance is stable. The capacitance of the porous medium material can characterize the total water potential of the soil, and the resistance value of the porous medium material can characterize the solute potential of the soil; however, it is not necessarily linear. Therefore, during calibration detection, it is necessary to simulate 6 to 8 suction points and measure the actual capacitance output value, so that it can be calibrated to the soil water potential (suction) value for measurement; and the resistance value of the porous medium material can characterize the solubility of the solute in the porous medium material, which is essentially equivalent to the solute potential in the soil solution. The solute potential can be looked up in the table of physical chemistry books corresponding to the resistance (conductivity) of a specific KCl solution.

[0042] In a further implementation, the specific calibration work is as follows. Before the actual use of the porous medium material, the calibration work of capacitance value C and capacitance value R should be carried out. For the calibration of capacitance value C, use the porous medium material to establish a suction model of 0 - 10000 kPa, and simulate the calibration of the total water potential and capacitance value in the soil model. The number of calibration points is 6 - 7, and the calibrated capacitance value C is expressed as K1C; among them, the suction model is a relationship curve graph between suction and capacitance value C under general circumstances; the suction value can be simulated by adjusting the vacuum container. Put the porous medium material in a saturated state into the vacuum container, set 6 - 7 different suction values, and keep the porous medium material in the same state for half an hour for each group. Read the capacitance value C calculated by the sensor; thus, 6 - 7 groups of data points are obtained, and the suction-capacitance curve graph is drawn. In this way, during measurement, the suction, that is, the total water potential value, can be obtained by referring to the curve of the calibration experiment according to the read capacitance value.

[0043] In a further implementation, the calibration of the resistance value R is as follows: Place the porous medium material in KCl solutions of different standards such as 0.001 mol / L, 0.01 mol / L, 0.1 mol / L, and 1 mol / L to establish a multi-point conductance model, and simulate the calibration of the solute potential and resistance value in the soil model. The number of calibration points is 4, and the calibrated resistance value R is expressed as K2R; under the conditions of different standard KCL solutions at the experimental temperature, taking 4 calibration points as the basis of 4 groups of data, the osmotic potential of the solution, that is, the solute potential b, can be obtained according to the following formula, and then the solute potential-conductance (resistance) curve graph can be drawn. In this way, during measurement, the solute potential can be obtained by referring to the curve of the calibration experiment according to the read resistance value.

[0044] =-icR’T;

[0045] Among them, is the osmotic potential of the solution;

[0046] R’ is the gas constant (0.0083 L / mol K);

[0047] c is the molar concentration of the solution (mol / L);

[0048] i is the osmotic coefficient of the solute.

[0049] The capacitance value C and resistance value R obtained through the equivalent circuit are compared with the capacitance calibration value K1C obtained in the suction model and the resistance calibration value K2R obtained in the conductance model to verify the accuracy and reliability of the entire equivalent circuit; based on the above calibration work and the mapping relationship, the matrix potential a = C - R = K1C - K2R, and the solute potential b = R = K2R.

[0050] Example 2

[0051] Based on the fact that there is a mapping relationship between the capacitance and resistance of the porous medium material in Example 1 and the total water potential and solute potential in the soil to be measured, the present invention designs an equivalent circuit for actually measuring the capacitance and resistance of the porous medium material after reaching water balance in the soil. Therefore, as shown in the appendix Figure 1 shown, the equivalent circuit includes: an AC signal source U1, a first amplifier U2, a second amplifier U3, a resistor R1, a variable resistor R2, a resistor Rf, an equivalent circuit Rx, a capacitor C1, and a capacitor C2; their connection relationship is: one end of the AC signal source is connected to one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the resistor R1, the other end of the resistor R1 is connected to the pin 2 of the variable resistor R2, the pin 3 of the variable resistor R2 is connected to the other end of the AC signal source, the pin 1 of the variable resistor R2 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to one end of the equivalent circuit Rx, and is also connected to the pin 3 of the amplifier U2, and the pin 2 of the amplifier U2 is connected to the pin 1 of the amplifier U2; the other end of the equivalent circuit Rx is connected to the pin 2 of the amplifier U3, and the pin 1 and pin 3 of the amplifier U3 are both connected to the other end of the AC signal source; one end of the resistor Rf is connected to the pin 2 of the amplifier U3, and the other end is connected to the pin 2 of the amplifier U3;

[0052] Among them, the equivalent circuit Rx can be equivalent to the state of the porous medium material after the moisture reaches equilibrium. The equivalent circuit Rx includes: a DC component U, a capacitor C A and a resistor R A ; among them, the positive pole of the DC component U is connected to the pin 3 of the amplifier U2, the capacitor C A and the resistor RA They are connected in parallel, with one end connected to the negative pole of the DC component U and the other end connected to pin 2 of U3.

[0053] In the equivalent circuit, capacitor C A and resistor R A are the objects to be measured, and the porous medium material generates a DC component U after the moisture reaches equilibrium. To prevent the DC component U from affecting the detection result, a capacitor C2 is designed to cancel this DC component U. The capacitor in the ED21 material after the moisture reaches equilibrium can be regarded as being connected in parallel with the resistor. When an alternating current flows through the two ends, it will flow through capacitor C A and resistor R A respectively. Among them, the capacitive reactance of capacitor C A will change due to different frequencies, while the impedance of resistor R A will not change due to different frequencies. According to this characteristic, by inputting alternating currents with two different frequencies, the capacitance value C of capacitor C A and the resistance value R of resistor R A can be detected from it.

[0054] In other words, the capacitance value C and the resistance value R of the porous medium material in the corresponding soil after reaching water equilibrium are measured in the equivalent circuit, and there is the following mapping relationship with the matrix potential a and the solute potential b in the actual soil; based on the mapping relationship, the matrix potential a = C - b = C - R and the solute potential b = R are obtained.

[0055] Example 3

[0056] In Example 2, taking the porous medium material as the transition medium, taking the porous medium material reaching water equilibrium as the measurement condition, and using the equivalent circuit as the measurement tool to obtain the equivalent parameters, and obtaining the parameter values in the actual soil through the preset mapping relationship. However, there is often a certain deviation value in the equivalence. At this time, it is necessary to correct the measured value. In a further example, the capacitance value C of capacitor C A and the resistance value R of resistor R A The calculation and correction process includes:

[0057] Step 1. Parameter setting: The AC voltage between pin 1 and pin 2 of amplifier U2 is U f , the AC voltage between pin 1 and pin 3 of amplifier U3 is U0; input a sinusoidal alternating current with a lower frequency, and measure U f as U fl ; measure U0 as U 0l ; input a sinusoidal alternating current with a higher frequency, and measure U f as U fh ; measure U0 as U 0h ;

[0058] Step 2: When the AC voltage value U fl is not equal to the U fh value, the capacitance value C and the resistance value R should be corrected. Set the voltage correction coefficient as , and the frequency correction coefficient ; = = , = ;

[0059] Step 3: Calculate the corrected capacitance value C and resistance value R. Since there is a 90° phase difference in the currents flowing through the capacitor C A and the resistor R A , complex numbers need to be used for calculation. Taking the current as the basic calculation formula, the correction process of the resistance value R is as follows:

[0060]

[0061] Also, there is the capacitive reactance formula: ; ; Therefore ;

[0062] ;

[0063] Then the correction process of the capacitance value C is as follows: ;

[0064] At the same time

[0065] Because of the capacitive reactance formula: ,

[0066] So:

[0067] = .

Claims

1. A soil water potential equivalent measurement system, characterized in that, The described soil water potential equivalent measurement system includes: A measurement soil model, which is set to select a corresponding water potential equilibrium material according to the properties of the soil to be measured; A soil water potential equivalent circuit, which is set to measure the equivalent parameters of the water potential equilibrium material; The soil water potential equivalent circuit includes: an AC signal source U1, a first amplifier U2, a second amplifier U3, a resistor R1, a variable resistor R2, a resistor Rf, an equivalent circuit Rx, a capacitor C1, and a capacitor C2; the connection relationship is as follows: one end of the AC signal source is connected to one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the resistor R1, the other end of the resistor R1 is connected to pin 2 of the variable resistor R2, pin 3 of the variable resistor R2 is connected to the other end of the AC signal source, pin 1 of the variable resistor R2 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to one end of the equivalent circuit Rx and is also connected to pin 3 of the amplifier U2, pin 2 of the amplifier U2 is connected to pin 1 of the amplifier U2; the other end of the equivalent circuit Rx is connected to pin 2 of the amplifier U3, and both pin 1 and pin 3 of the amplifier U3 are connected to the other end of the AC signal source; one end of the resistor Rf is connected to pin 2 of the amplifier U3 and the other end is connected to pin 2 of the amplifier U3; Wherein, the water potential equilibrium material is a porous medium material; Among them, the equivalent circuit Rx can be equivalent to the state after the moisture in the porous medium material reaches equilibrium. The equivalent circuit Rx includes: a DC component U, a capacitor C A and a resistor R A ; among them, the positive pole of the DC component U is connected to pin 3 of the amplifier U2, and the capacitor C A and the resistor R A are connected in parallel, one end is connected to the negative pole of the DC component U, and the other end is connected to pin 2 of U3; A pre-created mapping relationship, which is set to calculate the actual water potential parameters of the soil to be measured based on the equivalent parameters of the water potential equilibrium material; The calibration and correction method implemented by the system includes: Step 1. Parameter setting: The AC voltage between pin 1 and pin 2 of the amplifier U2 is U f , and the AC voltage between pin 1 and pin 3 of the amplifier U3 is U0; when measuring the equivalent circuit, data at least at two different frequency moments are recorded to calculate the capacitance value C and the resistance value R; among them, a sinusoidal AC current with a lower frequency is input, and U f is measured as U fl ; U0 is measured as U 0l ; a sinusoidal AC current with a higher frequency is input, and U f is measured as U fh ; U0 is measured as U 0h ; Step 2. When the AC voltage value U fl is not equal to the value of U fh , the capacitance value C and the resistance value R should be corrected. Set the voltage correction coefficient as , and the frequency correction coefficient ; = = , = ; Step 3. Calculate the corrected capacitance value C and resistance value R. Since there is a 90° phase difference in the current flowing through the capacitor C A and the resistor R A , complex numbers need to be used for calculation. Taking the current as the basic calculation formula, the correction process for the resistance value R is as follows: There is also the capacitive reactance formula: ; ; Therefore: ; ； Then the correction process of the capacitance value C is as follows: ; , while ; Due to the capacitive reactance formula: , so: = 。 2. The soil water potential equivalent measurement system according to claim 1, characterized in that, The measurement soil model includes: a non-salinized soil measurement model and a saline-alkali soil measurement model; The actual soil water potential parameters of the non-salinized soil measurement model at least include: matrix potential a; The actual soil water potential parameters of the saline-alkali soil measurement model at least include: matrix potential a and solute potential b.

3. The soil water potential equivalent measurement system according to claim 1, characterized in that, The bubble pressure value of the porous medium material is at least 1000 hPa, and its pore size is: 0.45 μm - 1 μm; 2 to 4 needles of electrodes are embedded inside the porous medium material.

4. The soil water potential equivalent measurement system according to claim 1, characterized in that, Calibration work of the porous medium material before use; The capacitor C A has a capacitance value representing the total water potential as C, and the resistor R A has a resistance value representing the solute potential as R.

5. The soil water potential equivalent measurement system according to claim 4, characterized in that, The calibration work specifically includes the following processes: Calibration of capacitance value C: Use the porous medium material to establish a suction model of 0 - 10000 kPa, simulate the calibration of the total water potential and capacitance value in the soil model, and there are 6 - 7 calibration points. The calibrated capacitance value C is expressed as K1C.

6. The soil water potential equivalent measurement system according to claim 5, wherein The calibration work also includes: Calibration of resistance value R: Place the porous medium material sensor in KCl solutions of different standards of 0.001 mol / L, 0.01 mol / L, 0.1 mol / L, and 1 mol / L to establish a multi-point conductance model, simulate the calibration of the solute potential and resistance value in the soil model, and there are 4 calibration points. The calibrated resistance value R is expressed as K2R.

7. The soil water potential equivalent measurement system according to claim 6, characterized in that, Based on the mapping relationship, matrix potential a = K1C - K2R and solute potential b = K2R are obtained.

8. The soil water potential equivalent measurement system according to claim 1, characterized in that It also includes: A resistance temperature detector (RTD) measurement circuit, which is used to synchronously measure the temperature of a corresponding soil model.

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