Farmland Pollution Monitoring System, Method for Monitoring Underground Leaching Water Volume, and Device for Monitoring Underground Leaching Water Volume

Abstract

The object of the present invention is to provide a farmland pollution monitoring system, a method for monitoring the underground leaching water volume and a device for monitoring the underground leaching water volume, which can achieve real-time in-situ monitoring of the nitrogen leaching water volume in farmland under the state of soil moisture content from unsaturated flow to supersaturated flow. The farmland pollution monitoring system includes: a soil moisture sensor, a soil pressure sensor, a rainfall sensor and a control box; the soil moisture sensor is arranged at different depths of the soil; the soil pressure sensor is arranged on the soil surface layer; the rainfall sensor is exposed and arranged above the soil; the soil moisture sensor, the soil pressure sensor and the rainfall sensor are electrically connected to the control box through sensor wires and transmit data.

Description

Technical Field

[0001] The present invention relates to the technical field of monitoring agricultural nitrogen leaching water volume, and specifically relates to a farmland pollution monitoring system, a leaching water volume monitoring method and an underground leaching water volume monitoring device. Background Art

[0002] In modern agriculture, nitrogen leaching in farmland refers to the process in which nitrogen in the soil penetrates downward with rainwater or irrigation water into the deep soil or even groundwater. By monitoring the nitrogen leaching situation, water source pollution, soil health and biogeochemical cycles can be effectively controlled. And the monitoring of the underground leaching water volume in farmland is crucial for the monitoring of farmland nitrogen. Therefore, by real-time monitoring the underground leaching water volume in farmland, the dynamic changes of nitrogen migration in the soil can be accurately reflected, helping farmers and farmland managers timely understand the soil moisture condition, which plays a crucial role in formulating irrigation plans, fertilization plans and adjusting crop management measures.

[0003] At present, the existing methods for monitoring the underground leaching water volume of farmland nitrogen mainly include the following several kinds:

[0004] (1) The tensiometer method with a ceramic head, combined with a solution extractor, and repeated sampling at the same position, is often used in the measurement of the leaching solution of the soil at a depth of 200 cm for field crops. This method is easy to install, but it is difficult to obtain enough extraction solution when the soil moisture content is low or the soil is very dry, with great uncertainty.

[0005] (2) The leaching pan or leaching bucket method, which is to extract the leaching solution that seeps into the leaching pan or leaching bucket at the same position by a vacuum pump. This method is simple and easy to operate, and is often used in the measurement of the leaching solution of the soil at a depth of 90 cm for vegetable planting, but it cannot measure unsaturated flow and has a large measurement error.

[0006] (3) The lysimeter method, which is a research device for collecting soil columns in a container or frame to collect the leaching water at different depths to measure the leaching loss of soluble substances, or a device for collecting the pore water from the soil and for measuring the soluble components in the field drainage. It can obtain the leaching solution volume and nitrogen and phosphorus concentrations at a certain depth simultaneously, but the construction cost is relatively high.

[0007] To sum up, the existing methods for monitoring the underground leaching water volume in farmland have defects such as requiring staff to regularly go to the site to collect leaching solutions, only single-point monitoring resulting in insufficient spatial representativeness, small measurement range, poor timeliness, high cost, and difficult error control. Summary of the Invention

[0008] The purpose of the present invention is to provide a farmland pollution monitoring system, an underground leaching water volume monitoring method and an underground leaching water volume monitoring device, which can monitor the underground leaching water volume in farmland in real time.

[0009] To solve the above problems, a first aspect of the present invention provides a method for monitoring the amount of underground leaching water, including:

[0010] Step S1000: Obtain a soil sample to be measured, and perform soil texture analysis to obtain the unsaturated hydraulic conductivity, saturated hydraulic conductivity, and fitting parameters of the soil water characteristic curve of the soil sample;

[0011] Step S2000: Obtain the soil water potential at the soil mass at the first soil depth in different time periods, as well as the soil water potential, volumetric water content, temperature, and electrical conductivity at the soil mass at the second soil depth;

[0012] Step S3000: Calculate the amount of leaching water in the first period at the soil mass at the second soil depth based on the soil water potential at the soil mass at the first soil depth, and the soil water potential, volumetric water content, temperature, and electrical conductivity at the soil mass at the second soil depth;

[0013] Step S4000: Select the leaching water amount data within the time range of the crop growth cycle, and accumulate the leaching water amounts in continuous different time periods through linear interpolation to obtain the leaching water amount at the soil mass at the second soil depth within the crop growth cycle;

[0014] Step S5000: Obtain the nitrogen concentration in the farmland, and calculate the nitrogen leaching amount in the farmland within the crop growth cycle based on the leaching water amount at the soil mass at the second soil depth within the crop growth cycle.

[0015] Further, in the above method for monitoring the amount of underground leaching water, the calculation formula for the amount of leaching water in the first period at the soil mass at the second soil depth in step S3000 is:

[0016] (1)

[0017] Where, is the amount of leaching water in the first period at the soil mass at the second soil depth, is the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil matrix potential, is the proportional coefficient between the soil electrical conductivity and the soil volumetric water content, is the temperature compensation coefficient under a specific soil type, is the soil water potential at the soil mass at the first soil depth, is the soil water potential at the soil mass at the second soil depth, is the soil thickness between the first soil depth and the second soil depth, is the saturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil volume water content, is the residual water content, Saturated water content.

[0018] Further, in the above-mentioned underground leaching water volume monitoring method, the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth The calculation formula is:

[0019] (2)

[0020] Where, and are respectively the fitting parameters of the soil water characteristic curve of the soil mass from the first soil depth to the second soil depth.

[0021] Further, in the above-mentioned underground leaching water volume monitoring method, in step S4000, the calculation formula for the leaching water volume at the soil mass at the second soil depth during the crop growth period is:

[0022] (3)

[0023] Where, is the leaching water volume at the soil mass at the second soil depth during the crop growth period, is the crop growth period.

[0024] Further, in the above-mentioned underground leaching water volume monitoring method, in step S5000, the calculation formula for the nitrogen leaching amount in the farmland during the crop growth period is:

[0025] (4)

[0026] Where, is the nitrogen leaching amount in the farmland during the crop growth period, is the nitrogen concentration.

[0027] In a second aspect, the present invention also provides a farmland pollution monitoring system for performing the underground leaching water volume monitoring method described in any one of the foregoing, including: a soil moisture sensor, a soil pressure sensor, a rain sensor, and a control box; the soil moisture sensor is arranged at different depths of the soil; the soil pressure sensor is arranged on the soil surface; the rain sensor is exposed above the soil; the soil moisture sensor, the soil pressure sensor, and the rain sensor are electrically connected to the control box through sensor wires and transmit data.

[0028] Further, the above-mentioned farmland pollution monitoring system further includes: a screw slide table connecting member and a multi-layer monitoring bracket; the multi-layer monitoring bracket has a slender rod; the soil moisture sensor is fixedly connected to the multi-layer monitoring bracket through the screw slide table connecting member, and the soil moisture sensors are arranged at intervals.

[0029] Further, the above-mentioned farmland pollution monitoring system further includes: an antenna and a solar panel; the antenna is arranged on the control box; the solar panel is fixedly connected to the control box through a bracket.

[0030] In a third aspect, the present invention also provides an underground leaching water volume monitoring device.

[0031] Soil sample acquisition module: used to acquire a soil sample to be measured, and perform soil texture analysis to obtain the unsaturated hydraulic conductivity, saturated hydraulic conductivity and fitting parameters of the soil water characteristic curve of the soil sample.

[0032] Soil water potential acquisition module: used to acquire the soil water potential at the soil body at the first soil depth at different time periods, as well as the soil water potential, volumetric water content, temperature, and electrical conductivity at the soil body at the second soil depth.

[0033] Leaching water volume calculation module: used to calculate the leaching water volume at the soil body at the second soil depth during the first period according to the soil water potential at the soil body at the first soil depth, and the soil water potential, volumetric water content, temperature, and electrical conductivity at the soil body at the second soil depth.

[0034] Specifically, the calculation formula for the leaching water volume passing through the soil body at the second soil depth during the first period is:

[0035] (1)

[0036] Where, is the leaching water volume passing through the soil body at the second soil depth during the first period, is the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil matrix potential, is the proportional coefficient between the soil electrical conductivity and the soil volumetric water content, is the temperature compensation coefficient under a specific soil type, is the soil water potential at the soil body at the first soil depth, is the soil water potential at the soil body at the second soil depth, is the soil thickness between the first soil depth and the second soil depth, is the saturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth. is the soil volume water content, is the residual water content, and is the saturated water content.

[0037] When the volume water content is within and , it is the unsaturated state of soil moisture; when the volume water content , it is the saturated and supersaturated state of soil moisture. According to the different soil moisture states, the corresponding calculation formula for the leaching water volume is selected.

[0038] Among them, the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth is calculated by the formula:

[0039] (2)

[0040] Among them, , are the fitting parameters of the soil water characteristic curve of the soil mass from the first soil depth to the second soil depth, respectively.

[0041] Accumulative leaching water volume module: used to select the leaching water volume data within the time range of the crop growth cycle, and accumulate the leaching water volume of continuous different time periods by linear interpolation method to obtain the leaching water volume at the soil mass at the second soil depth within the crop growth cycle.

[0042] Specifically, the calculation formula for the leaching water volume at the soil mass at the second soil depth within the crop growth cycle is:

[0043] (3)

[0044] Among them, is the leaching water volume at the soil mass at the second soil depth within the crop growth cycle, is the crop growth cycle.

[0045] Nitrogen concentration calculation module: used to obtain the nitrogen concentration in the farmland and calculate the nitrogen leaching amount in the farmland within the crop growth cycle according to the leaching water volume at the soil mass at the second soil depth within the crop growth cycle.

[0046] Specifically, the calculation formula for the nitrogen leaching amount in the farmland within the crop growth cycle is:

[0047] (4)

[0048] Among them, is the nitrogen leaching amount in the farmland within the crop growth cycle, is the nitrogen concentration.

[0049] By burying soil moisture sensors at different depths in the soil, collecting soil moisture data such as soil water potential at different soil depths at different time periods, the leaching water volume at different soil depths can be obtained. After accumulation, the leaching water volume at the soil body at the second soil depth within the first period can be obtained. By integrating over consecutive time periods during the crop growth cycle, the leaching water volume at the soil body at the second soil depth during the crop growth cycle can be obtained, thus completing the real-time monitoring of the leaching water volume. Then, by measuring the nitrogen concentration with a probe sensor or a spectral sensor, the measurement of the nitrogen leaching volume in the farmland during the crop growth cycle can be completed. The entire monitoring process requires no manual intervention, has a fast response speed, accurate data, and significantly reduces the operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic structural diagram of the farmland pollution monitoring system of the present invention;

[0051] Figure 2 is a flowchart of the steps of an embodiment of the method for monitoring underground leaching water volume of the present invention;

[0052] Figure 3 is a structural block diagram of the device for monitoring underground leaching water volume of the present invention.

[0053] REFERENCE SIGNS:

[0054] 1: Soil moisture sensor; 2: Soil pressure sensor; 3: Rainfall sensor; 4: Control box; 5: Sensor connection wire; 6: Screw table connecting part; 7: Multi-layer monitoring bracket; 8: Antenna, 9: Solar panel; 10: Bracket; 11: Monitoring well. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention. In the description of the present invention, it should be noted that the terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0056] The following will be combined with Figure 1 to describe the farmland pollution monitoring system shown in the present invention in detail.

[0057] Refer to Figure 1The farmland pollution monitoring system shown in this embodiment includes: several groups of soil moisture sensors 1, soil pressure sensors 2, rainfall sensors 3, a control box 4, and sensor cables 5. The soil moisture sensors 1 are installed at different depths in the soil, the soil pressure sensor 2 is installed on the soil surface, and the rainfall sensor 3 is installed exposed above the soil or on the control box 4. The soil moisture sensors 1, soil pressure sensors 2, and rainfall sensors 3 are each electrically connected to the control box 4 via the sensor cables 5 and transmit data. To facilitate the installation of the soil moisture sensors 1 at a predetermined depth, this embodiment also includes: a screw slide connector 6 and a multi-layer monitoring bracket 7. The multi-layer monitoring bracket 7 comprises a slender rod with its bottom fixed to the bottom of the monitoring well 11. The screw slide connector 6 is horizontally arranged on the slender rod to form a ladder-like structure. The soil moisture sensors 1 are fixedly connected to the multi-layer monitoring bracket 7 via the screw slide connector 6. By adjusting the spacing between the soil moisture sensors 1, the depth of the soil moisture sensors 1 buried in the soil after the multi-layer monitoring bracket 7 is buried can be adjusted, ensuring that the soil moisture sensors 1 will not be displaced by water erosion during long-term monitoring. In order to transmit data with the server, an antenna 8 is also provided on the control box 4. At the same time, the control box 4 has a built-in battery, and the battery power is supplemented by a solar panel 9, which is fixedly mounted on a bracket 10.

[0058] When placing the soil moisture sensor 1, drill a hole to form a monitoring well 11 with a hole diameter of 30 cm, then fix the soil moisture sensor 1 on the multi-layer monitoring bracket 7, adjust the position of the soil moisture sensor 1, and then place it into the monitoring well 11. Use an extended ratchet wrench to rotate the screw slide connector 6 to push the soil moisture sensor 1 into the soil.

[0059] During the excavation of monitoring well 11, soil texture parameters are obtained for each installation layer, and the collection frequency of soil moisture sensor 1 is pre-set based on the soil texture parameters. Once installed, soil moisture sensor 1 is responsible for collecting soil moisture data such as soil water potential, volumetric water content, temperature, and electrical conductivity. Soil texture analysis is used to obtain relevant parameters such as saturated hydraulic conductivity, residual water content, saturated water content, shape parameters of the soil moisture characteristic curve, and the empirical coefficient of hydraulic conductivity. Soil pressure sensor 2 and rainfall sensor 3 collect pressure data and rainfall data, respectively.

[0060] When the data monitored by the rainfall sensor 3 reaches the threshold, it enters the rainfall mode at this time, and the acquisition frequency of the soil moisture sensor 1 is increased to the first acquisition frequency, that is, data is acquired once every 1 minute. At the same time, the working duration and monitoring time interval can also be intelligently adjusted according to the amount of rainfall. When it drops below the threshold, the pre-set acquisition frequency is restored, that is, data is acquired once every 1 hour. When the pressure data monitored by the soil pressure sensor 2 also reaches the threshold, it enters the irrigation mode at this time, and the acquisition frequency of the soil moisture sensor 1 is increased to a second acquisition frequency higher than the first acquisition frequency, that is, data is acquired twice every 1 minute. At the same time, the working duration and monitoring time interval can also be intelligently adjusted according to the amount of rainfall. When it drops below the threshold, the pre-set acquisition frequency is restored, which can avoid the problem of data loss of leaching water volume easily when the soil water flow rate is fast.

[0061] The principle of this embodiment is as follows: The soil moisture sensor 1 collects soil moisture data at different soil depths in real time (such as soil water potential, volumetric water content, temperature, conductivity, etc. data). According to the soil moisture data, the leaching water volume passing through the soil moisture sensor 1 in a period of time (such as one hour) is obtained. Without pumping the leaching water to the ground, the leaching water volume is accumulated continuously in the time of the growth cycle, and the leaching water volume of the crops at the soil depth where the soil moisture sensor 1 is located in the growth cycle is obtained. When installing the soil moisture sensor 1, only a monitoring well 11 with a drilling diameter of 30 cm is required, which causes less damage to the original soil. The first soil depth and the second soil depth are determined according to the different crop varieties planted in the farmland. For example, the measurement of leaching water volume in the vegetable planting area is generally about 90 cm, and the measurement of leaching water volume in the farmland of crops such as wheat and corn in the field is generally 200 cm. At the same time, because the soil moisture sensor 1 is fixed on the multi-layer monitoring bracket 7, the relative position will not change during the whole monitoring process, which is applicable to the mixed planting area of multiple vegetation.

[0062] If there are large differences in the distribution of soil types in the farmland, the data measured by the soil moisture sensor 1 at this time will not be representative. At this time, multiple soil moisture sensors 1 can be arranged at different positions of the first soil depth and the second soil depth to establish a sensor data acquisition group, which greatly increases the farmland soil measurement area, so that the data of leaching water volume is more valuable. A probe sensor or a spectral sensor is also arranged in the farmland to measure the nitrogen concentration, and the nitrogen leaching volume in the farmland during the growth cycle of the crops can be obtained by combining the data of leaching water volume.

[0063] In the second aspect, the present invention also provides an embodiment of a method for monitoring underground leaching water volume.

[0064] Reference Figure 2 , shows the step flowchart of this embodiment, including:

[0065] Step S1000: obtaining a soil sample to be tested, performing soil texture analysis to obtain the unsaturated hydraulic conductivity, saturated hydraulic conductivity and fitting parameters of the soil moisture characteristic curve of the soil sample;

[0066] Step S2000: obtaining the soil water potential at a first soil depth and the soil water potential, volumetric water content, temperature, and electrical conductivity at a second soil depth in different time periods;

[0067] Step S3000: Calculating the amount of leached water in the soil at the second soil depth during a first period based on the soil water potential in the soil at the first soil depth, and the soil water potential, volumetric water content, temperature, and electrical conductivity in the soil at the second soil depth;

[0068] Specifically, the calculation formula for the amount of leached water passing through the soil at the second soil depth during the first period is:

[0069] (1)

[0070] in, is the amount of leached water passing through the soil at the second soil depth during the first period, is the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil matrix potential, is the proportional coefficient between soil electrical conductivity and soil volume water content, is the temperature compensation coefficient, is the soil water potential at the soil mass at the first soil depth, is the soil water potential at the soil mass at the second soil depth, is the soil thickness between the first soil depth and the second soil depth, is the saturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the volumetric water content of the soil, is the residual water content, Saturated water content.

[0071] When the volume water content exist and When the volumetric water content is between When the soil is saturated or oversaturated, the calculation formula for leaching water should be selected according to the different soil moisture states.

[0072] Among them, the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth is The calculation formula is:

[0073] (2)

[0074] Among them, and are respectively the fitting parameters of the soil water characteristic curve of the soil mass from the first soil depth to the second soil depth.

[0075] Step S4000: Select the leaching water volume data within the time range of the crop growth cycle, and accumulate the leaching water volume at continuously different time periods by linear interpolation to obtain the leaching water volume at the soil mass at the second soil depth within the crop growth cycle.

[0076] Specifically, the calculation formula for the leaching water volume at the soil mass at the second soil depth within the crop growth cycle is:

[0077] (3)

[0078] Among them, is the leaching water volume at the soil mass at the second soil depth within the crop growth cycle, is the crop growth cycle.

[0079] Step S5000: Obtain the nitrogen concentration in the farmland, and calculate the nitrogen leaching amount in the farmland within the crop growth cycle based on the leaching water volume at the soil mass at the second soil depth within the crop growth cycle.

[0080] Specifically, the calculation formula for the nitrogen leaching amount in the farmland within the crop growth cycle is:

[0081] (4)

[0082] Among them, is the nitrogen leaching amount in the farmland within the crop growth cycle, is the nitrogen concentration.

[0083] Thirdly, the present invention also provides an embodiment of an underground leaching water volume monitoring device.

[0084] Referring to Figure 3 , the underground leaching water volume monitoring device in this embodiment includes: <{

[0085] An acquisition module for a soil sample to be measured: used to acquire a soil sample to be measured, and analyze the soil texture to obtain the unsaturated hydraulic conductivity, saturated hydraulic conductivity and fitting parameters of the soil water characteristic curve of the soil sample;

[0086] An acquisition module for soil water potential: used to acquire the soil water potential at the soil mass at the first soil depth at different time periods, as well as the soil water potential, volumetric water content, temperature and conductivity at the soil mass at the second soil depth.

[0087] Leaching water volume calculation module: used to calculate the leaching water volume in the first period at the soil body at the second soil depth according to the soil water potential at the soil body at the first soil depth, and the soil water potential, volumetric water content, temperature, and conductivity at the soil body at the second soil depth;

[0088] Specifically, the calculation formula for the leaching water volume passing through the soil body at the second soil depth in the first period is:

[0089] (1)

[0090] Where, is the leaching water volume passing through the soil body at the second soil depth in the first period, is the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil matrix potential, is the proportionality coefficient between soil conductivity and soil volumetric water content, is the temperature compensation coefficient, is the soil water potential at the soil body at the first soil depth, is the soil water potential at the soil body at the second soil depth, is the soil thickness between the first soil depth and the second soil depth, is the saturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil volumetric water content, is the residual water content, Saturated water content.

[0091] When the volumetric water content is between and , it is the unsaturated state of soil moisture; when the volumetric water content , it is the saturated and supersaturated state of soil moisture. Select the corresponding calculation formula for leaching water volume according to different soil moisture states.

[0092] [[ID=5,0]]Where, the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth has the following calculation formula:

[0093] (2)

[0094] Where, and are respectively the fitting parameters of the soil water characteristic curve of the soil body from the first soil depth to the second soil depth.

[0095] Accumulated leaching water volume module: It is used to select the leaching water volume data within the time range of the crop growth cycle, and accumulate the leaching water volume at different continuous time periods by the linear interpolation method to obtain the leaching water volume at the soil body at the second soil depth within the crop growth cycle.

[0096] Specifically, the calculation formula for the leaching water volume at the soil body at the second soil depth within the crop growth cycle is:

[0097] (3)

[0098] Where, is the leaching water volume at the soil body at the second soil depth within the crop growth cycle, is the crop growth cycle.

[0099] Nitrogen concentration calculation module: It is used to obtain the nitrogen concentration in the farmland and calculate the nitrogen leaching amount in the farmland within the crop growth cycle according to the leaching water volume at the soil body at the second soil depth within the crop growth cycle.

[0100] Specifically, the calculation formula for the nitrogen leaching amount in the farmland within the crop growth cycle is:

[0101] (4)

[0102] Where, is the nitrogen leaching amount in the farmland within the crop growth cycle, [[ID={32]] is the nitrogen concentration.

[0103] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principles of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modification examples falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for monitoring underground leaching water volume, characterized in that: include: Step S1000: obtaining a soil sample to be tested, performing soil texture analysis to obtain the unsaturated hydraulic conductivity, saturated hydraulic conductivity and fitting parameters of the soil moisture characteristic curve of the soil sample; Step S2000: obtaining, by means of a soil moisture sensor, soil water potential at a first soil depth in different time periods, and soil water potential, volumetric water content, temperature, and electrical conductivity at a second soil depth; Step S3000: Calculating the amount of leached water in the soil at the second soil depth during a first period based on the soil water potential in the soil at the first soil depth, and the soil water potential, volumetric water content, temperature, and electrical conductivity in the soil at the second soil depth; The calculation formula for the amount of leached water passing through the soil at the second soil depth during the first period in step S3000 is: ， (1) in, is the amount of leached water passing through the soil at the second soil depth during the first period, is the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil matrix potential, is the proportional coefficient between soil electrical conductivity and soil volume water content, is the temperature compensation coefficient, is the soil water potential at the soil mass at the first soil depth, is the soil water potential at the soil mass at the second soil depth, is the soil thickness between the first soil depth and the second soil depth, is the saturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the volumetric water content of the soil, is the residual water content, Saturated water content; Step S4000: selecting leaching water volume data within a time range of a crop growth cycle, and accumulating the leaching water volumes of different consecutive time periods by linear interpolation to obtain the leaching water volume at the second soil depth within the crop growth cycle; Step S5000: Obtain the nitrogen concentration in the farmland, and calculate the nitrogen leaching amount of the farmland during the crop growth cycle based on the leaching water amount at the second soil depth during the crop growth cycle.

2. The underground leaching water monitoring method according to claim 1, characterized in that: The unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth The calculation formula is: （2） in, 、 are the fitting parameters of the soil moisture characteristic curve of the soil from the first soil depth to the second soil depth.

3. The underground leaching water monitoring method according to claim 2, characterized in that: In step S4000, the calculation formula for the leached water amount at the soil body at the second soil depth during the crop growth period is: （3） in, is the leached water volume at the soil body at the second soil depth during the crop growth period, is the crop growth cycle.

4. The underground leaching water monitoring method according to claim 3, characterized in that: In step S5000, the calculation formula for the amount of nitrogen leaching from farmland during the crop growth cycle is: ，(4) in, is the amount of nitrogen leaching from farmland during the crop growth cycle, is the nitrogen concentration.

5. A farmland pollution monitoring system for executing the underground leaching water monitoring method according to any one of claims 1 to 4, characterized in that: include: Soil moisture sensor (1), soil pressure sensor (2), rainfall sensor (3) and control box (4); The soil moisture sensor (1) is arranged at different depths in the soil; The soil pressure sensor (2) is arranged on the soil surface; The rain sensor (3) is exposed and arranged above the soil; The soil moisture sensor (1), the soil pressure sensor (2) and the rainfall sensor (3) are electrically connected to the control box (4) via a sensor connection line (5) and transmit data.

6. The farmland pollution monitoring system according to claim 5, characterized in that: Also includes: Screw slide connector (6) and multi-layer monitoring bracket (7); The multi-layer monitoring bracket (7) has a slender rod; The soil moisture sensor (1) is fixedly connected to the multi-layer monitoring bracket (7) via the screw rod slide connector (6), and the soil moisture sensors (1) are arranged at intervals.

7. The farmland pollution monitoring system according to claim 6, characterized in that: Also includes: Antenna (8), solar panel (9); The antenna (8) is arranged on the control box (4); The solar panel (9) is fixedly connected to the control box (4) via a bracket (10).

8. An underground leaching water monitoring device, characterized in that: include: Acquiring soil samples to be tested module: used to obtain soil samples to be tested, perform soil texture analysis to obtain the unsaturated hydraulic conductivity, saturated hydraulic conductivity and fitting parameters of the soil moisture characteristic curve of the soil sample; Soil water potential acquisition module: used to obtain the soil water potential of the soil at the first soil depth in different time periods, as well as the soil water potential, volumetric water content, temperature, and electrical conductivity of the soil at the second soil depth; a leaching water calculation module configured to calculate the leaching water amount of the soil at the second soil depth during a first period based on the soil water potential of the soil at the first soil depth and the soil water potential, volumetric water content, temperature, and electrical conductivity of the soil at the second soil depth; Specifically, the calculation formula for the amount of leached water passing through the soil at the second soil depth during the first period is: ， in, is the amount of leached water passing through the soil at the second soil depth during the first period, is the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the soil matrix potential, is the proportional coefficient between soil electrical conductivity and soil volume water content, is the temperature compensation coefficient, is the soil water potential at the soil mass at the first soil depth, is the soil water potential at the soil mass at the second soil depth, is the soil thickness between the first soil depth and the second soil depth, is the saturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth, is the volumetric water content of the soil, is the residual water content, Saturated water content; When the volume water content exist and When the volumetric water content is between When the soil is saturated or oversaturated, the calculation formula for leaching water should be selected according to the different soil moisture states. Among them, the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth is The calculation formula is: ，（4） in, 、 are the fitting parameters of the soil moisture characteristic curve of the soil from the first soil depth to the second soil depth; Cumulative leaching water volume module: used to select leaching water volume data within the time range of the crop growth cycle, and accumulate the leaching water volume of different consecutive time periods through linear interpolation to obtain the leaching water volume at the second soil depth within the crop growth cycle; Specifically, the calculation formula for the leached water volume at the second soil depth during the crop growth cycle is: ，（5） in, is the leached water volume at the second soil depth during the crop growth cycle, for the crop growth cycle; Nitrogen concentration calculation module: used to obtain the nitrogen concentration in the farmland and calculate the nitrogen leaching amount of the farmland during the crop growth cycle based on the leaching water amount at the second soil depth during the crop growth cycle; Specifically, the calculation formula for nitrogen leaching from farmland during the crop growth cycle is: ，(4) in, is the amount of nitrogen leaching from farmland during the crop growth cycle, is the nitrogen concentration.

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