Farmland pollution monitoring system, underground leaching water amount monitoring method and underground leaching water amount monitoring device

Abstract

The invention aims to provide a farmland pollution monitoring system, an underground leaching water quantity monitoring method and an underground leaching water quantity monitoring device, which can realize the real-time in-situ monitoring of the farmland nitrogen leaching water quantity under the condition that the soil moisture content is changed from an unsaturated flow state to a supersaturated flow state, comprising a soil moisture sensor, a soil pressure sensor, a rainfall sensor and a control box, the soil moisture sensors are arranged at different depths of soil; the soil pressure sensor is arranged on the surface layer of the soil; the rainfall sensor is arranged above the soil in an exposed manner; the soil moisture sensor, the soil pressure sensor and the rainfall sensor are electrically connected with the control box through sensor connecting lines and transmit data.

Description

Technical Field

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

[0002] In modern agriculture, nitrogen leaching from farmland refers to the process in which nitrogen in the soil penetrates into the deep soil layer or even groundwater along with rainwater or irrigation water. Water pollution, soil health and biogeochemical cycles can be effectively controlled through nitrogen leaching. The monitoring of underground leaching water in farmland is crucial to the monitoring of nitrogen in farmland. Therefore, real-time monitoring of underground leaching water in farmland can accurately reflect the dynamic changes of nitrogen migration in the soil, help farmers and farmland managers understand the moisture status of the soil in a timely manner, and play a vital role in formulating irrigation plans, fertilization plans, and adjusting crop management measures.

[0003] At present, the existing methods for monitoring the amount of nitrogen underground leaching water in farmland are mainly as follows: (1) The clay head tensiometer method, combined with a solution extractor, repeatedly samples at the same location. It is often used to measure soil leaching solutions at a depth of 200 cm for field crops. This method is easy to install, but it is difficult to obtain sufficient extract when the soil moisture content is low or the soil is very dry, and it has great uncertainty.

[0004] (2) Leaching tray or leaching bucket method: This method uses a vacuum pump to extract the leachate that seeps into the leaching tray or leaching bucket at the same location. This method is simple and easy to use and is often used to measure the leachate in the soil at a depth of 90 cm for vegetable planting. However, it cannot measure unsaturated flow and has a large measurement error.

[0005] (3) Lysimeter method: a research device that collects seepage water at different depths in a container or frame to measure the leaching loss of soluble substances or a device that collects water from soil pores and is used to measure the soluble components in field drainage. It can simultaneously obtain the volume of the elution liquid and the nitrogen and phosphorus concentration at a certain depth, but the construction cost is relatively high.

[0006] In summary, the existing methods for monitoring underground leaching water in farmland have the following defects: the staff are required to go to the site regularly to collect leaching solution, and only single-point monitoring can be performed, resulting in insufficient spatial representativeness, small measurement range, poor timeliness, high cost, and difficult error control. Summary of the invention

[0007] 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 of farmland in real time.

[0008] In order to solve the above problems, the first aspect of the present invention provides a method for monitoring underground leaching water volume, comprising: 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 the soil water potential at a first soil depth in different time periods, and the soil water potential, volumetric water content, temperature, and electrical conductivity at a second soil depth; Step S3000: Calculate the leached water volume of the soil at the second soil depth in a first period according to 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; Step S4000: selecting leaching water volume data within the time range of the crop growth cycle, and accumulating the leaching water volume of different consecutive time periods by linear interpolation to obtain the leaching water volume at the soil body 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 soil body at the second soil depth during the crop growth cycle.

[0009] Furthermore, the calculation formula for the leached water volume passing through the soil at the second soil depth during the first period in step S3000 in the above-mentioned underground leached water volume monitoring method 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 proportionality coefficient between soil electrical conductivity and soil volume water content, is the temperature compensation coefficient for 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 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 soil, is the residual water content, Saturated water content.

[0010] Furthermore, in the above-mentioned underground leaching water monitoring method, the unsaturated hydraulic conductivity of the soil layer between the first soil depth and the second soil depth is 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.

[0011] Furthermore, in step S4000 of the above-mentioned underground leaching water monitoring method, the calculation formula of the leaching 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.

[0012] Furthermore, in step S5000 of the above-mentioned underground leaching water monitoring method, the calculation formula for the nitrogen leaching amount of 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.

[0013] In the second aspect, the present invention also provides a farmland pollution monitoring system for executing any of the aforementioned underground leaching water monitoring methods, comprising: 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; the rainfall sensor is exposed above the soil; the soil moisture sensor, the soil pressure sensor and the rainfall sensor are electrically connected to the control box through sensor lines and transmit data.

[0014] Furthermore, the above-mentioned farmland pollution monitoring system also includes: a screw slide connector 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 connector, and the soil moisture sensors are arranged at intervals.

[0015] Furthermore, the above-mentioned farmland pollution monitoring system also includes: an antenna and a solar panel; the antenna is arranged on the control box; and the solar panel is fixedly connected to the control box via a bracket.

[0016] In a third aspect, the present invention also provides an underground leaching water monitoring device, A module for obtaining soil samples to be tested: 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 acquire soil water potential at the first soil depth in different time periods, as well as soil water potential, volumetric water content, temperature, and electrical conductivity at the second soil depth; Leaching water calculation module: used to calculate the leaching water volume of the soil at the second soil depth in a first period according to 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: (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 proportionality coefficient between soil electrical conductivity and soil volume water content, is the temperature compensation coefficient for 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 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 soil, is the residual water content, Saturated water content.

[0017] 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 volume should be selected according to the different soil moisture states.

[0018] 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: (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.

[0019] 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 in the crop growth cycle.

[0020] Specifically, the calculation formula for the leached water volume at the second soil depth during the crop growth cycle is: (3) in, is the leaching water volume at the second soil depth during the crop growth cycle, The crop growth cycle.

[0021] Module for calculating nitrogen concentration: 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.

[0022] 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.

[0023] By burying soil moisture sensors at different soil depths, soil moisture data such as soil water potential at different soil depths in different time periods are collected, so as to obtain the leached water volume at different soil depths. The leached water volume passing through the soil body at the second soil depth in the first period is accumulated, and the leached water volume at the soil body at the second soil depth in the crop growth cycle can be obtained after integration of continuous time periods during the crop growth cycle, thereby completing real-time monitoring of the leached water volume. The nitrogen concentration is then measured by a probe sensor or a spectral sensor, and the measurement of nitrogen leaching volume in the farmland during the crop growth cycle can be completed. The entire monitoring process does not require human intervention, has a fast response speed, accurate data, and greatly reduced operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the farmland pollution monitoring system of the present invention; Figure 2 is a flowchart of the steps of an embodiment of a method for monitoring underground leaching water volume of the present invention; Figure 3 It is a structural block diagram of the underground leaching water monitoring device of the present invention.

[0025] Reference numerals: 1: Soil moisture sensor; 2: Soil pressure sensor; 3: Rainfall sensor; 4: Control box; 5: Sensor connection; 6: Screw slide connector; 7: Multi-layer monitoring bracket; 8: Antenna, 9: Solar panel; 10: Bracket; 11: Monitoring well. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept 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 understood as indicating or implying relative importance.

[0027] Combine the following Figure 1 The farmland pollution monitoring system shown in the present invention is described in detail.

[0028] refer to Figure 1 The farmland pollution monitoring system shown in this embodiment includes: several groups of soil moisture sensors 1, soil pressure sensors 2, rainfall sensors 3, control boxes 4, and sensor connections 5. The soil moisture sensors 1 are set at different depths in the soil, the soil pressure sensors 2 are set on the soil surface, and the rainfall sensors 3 are exposed and set above the soil, or can be set on the control box 4. The soil moisture sensors 1, soil pressure sensors 2, and rainfall sensors 3 are respectively electrically connected to the control box 4 through the sensor connection 5 and transmit data. In order to facilitate the installation of the soil moisture sensor 1 to 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 has a slender rod, the bottom of which is 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 sensor 1 is fixedly connected to the multi-layer monitoring bracket 7 through the screw slide connector 6. By adjusting the interval between the soil moisture sensors 1, the depth of the soil moisture sensor 1 immersed in the soil after the multi-layer monitoring bracket 7 is buried in the soil can be adjusted, so that the soil moisture sensor 1 will not change its position due to 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, and the solar panel 9 is fixedly mounted on the bracket 10.

[0029] When placing the soil moisture sensor 1, a monitoring well 11 is formed by drilling with a hole diameter of 30 cm, and then the soil moisture sensor 1 is fixed on the multi-layer monitoring bracket 7, and the position of the soil moisture sensor 1 is adjusted, and then placed in the monitoring well 11. An extended ratchet wrench can be used to rotate the screw slide connector 6 to push the soil moisture sensor 1 into the soil.

[0030] During the excavation of the monitoring well 11, the soil texture parameters of each installation layer are obtained, and the collection frequency of the soil moisture sensor 1 is pre-set according to the soil texture parameters. After the soil moisture sensor 1 is installed, it is responsible for collecting soil moisture data such as soil water potential, volumetric water content, temperature, and electrical conductivity. Through soil texture analysis, relevant parameters such as saturated hydraulic conductivity, residual water content, saturated water content, shape parameters of soil moisture characteristic curves, and empirical coefficients of hydraulic conductivity are obtained, while the soil pressure sensor 2 and rainfall sensor 3 collect pressure data and rainfall data respectively.

[0031] When the data monitored by the rainfall sensor 3 reaches the threshold, the system enters the rainfall mode, and increases the collection frequency of the soil moisture sensor 1 to the first collection frequency, that is, collects data once every 1 minute. At the same time, the working time and monitoring time interval can be intelligently adjusted according to the amount of rainfall. When it drops below the threshold, the preset collection frequency is restored, that is, data is collected once every 1 hour. When the pressure data monitored by the soil pressure sensor 2 also reaches the threshold, the system enters the irrigation mode, and increases the collection frequency of the soil moisture sensor 1 to the second collection frequency higher than the first collection frequency, that is, collects data twice every 1 minute. At the same time, the working time and monitoring time interval can be intelligently adjusted according to the amount of rainfall. When it drops below the threshold, the preset collection frequency is restored, which can avoid the problem of easy loss of data when collecting leaching water when the soil water flow rate is fast.

[0032] The principle of this embodiment is: soil moisture data (such as soil water potential, volumetric water content, temperature, conductivity, etc.) at different soil depths are collected in real time through the soil moisture sensor 1, and the amount of leached water passing through the soil moisture sensor 1 in a time period (such as one hour) is obtained based on the soil moisture data. There is no need to extract the leached water to the ground. The amount of leached water at the soil depth where the soil moisture sensor 1 is located during the growth cycle of the crop is accumulated according to the continuous and uninterrupted leached water amount over the time of the growth cycle. When installing the soil moisture sensor 1, only a monitoring well 11 with a diameter of 30 cm needs to be drilled, which causes less damage to the original soil. The first soil depth and the second soil depth are determined according to the different varieties of crops planted in the farmland. For example, the leached water measurement in the vegetable planting area is generally around 90 cm, and the leached water measurement in the field wheat, corn and other crop planting areas is generally 200 cm. At the same time, since the soil moisture sensor 1 is fixed on the multi-layer monitoring bracket 7, the relative position will not change during the entire monitoring process, which is suitable for mixed planting areas of multiple vegetation.

[0033] If the soil type distribution of the farmland is greatly different, the data measured by the soil moisture sensor 1 will be unrepresentative. In this case, 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 collection group, thereby greatly increasing the farmland soil measurement area, thereby making the leaching water data more valuable for reference. Probe sensors or spectral sensors are also arranged in the farmland to measure the nitrogen concentration. Combined with the leaching water data, the nitrogen leaching amount of the farmland during the crop growth cycle can be obtained.

[0034] In a second aspect, the present invention also provides an embodiment of a method for monitoring underground leaching water volume.

[0035] refer to Figure 2 , shows a flow chart of the steps of this embodiment, including: 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 the soil water potential at the first soil depth in different time periods, and the soil water potential, volumetric water content, temperature, and electrical conductivity at the second soil depth; Step S3000: Calculate the leached water volume of the soil at the second soil depth in a first period according to 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: (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 proportionality coefficient between soil electrical conductivity and soil volume 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 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 soil, is the residual water content, Saturated water content.

[0036] 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 volume should be selected according to the different soil moisture states.

[0037] 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: (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.

[0038] Step S4000: Select leaching water volume data within the time range of the crop growth cycle, and accumulate the leaching water volumes of different consecutive time periods by linear interpolation to obtain the leaching water volume at the soil body at the second soil depth within the crop growth cycle.

[0039] Specifically, the calculation formula for the leached water volume at the second soil depth during the crop growth cycle is: (3) in, is the leaching water volume at the second soil depth during the crop growth cycle, The crop growth cycle.

[0040] 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.

[0041] 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.

[0042] In a third aspect, the present invention also provides an embodiment of an underground leaching water volume monitoring device.

[0043] refer to Figure 3 The underground leaching water monitoring device of this embodiment includes: A module for obtaining soil samples to be tested: 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 acquire soil water potential at the first soil depth in different time periods, as well as soil water potential, volumetric water content, temperature, and electrical conductivity at the second soil depth; Leaching water calculation module: used to calculate the leaching water volume of the soil at the second soil depth in a first period according to 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: (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 proportionality coefficient between soil electrical conductivity and soil volume 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 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 soil, is the residual water content, Saturated water content.

[0044] 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 volume should be selected according to the different soil moisture states.

[0045] 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: (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.

[0046] 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 in the crop growth cycle.

[0047] Specifically, the calculation formula for the leached water volume at the second soil depth during the crop growth cycle is: (3) in, is the leaching water volume at the second soil depth during the crop growth cycle, The crop growth cycle.

[0048] Module for calculating nitrogen concentration: 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.

[0049] 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.

[0050] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the 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 the soil water potential at a first soil depth in different time periods, and the soil water potential, volumetric water content, temperature, and electrical conductivity at a second soil depth; Step S3000: Calculate the leached water volume of the soil at the second soil depth in a first period according to 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; Step S4000: selecting leaching water volume data within the time range of the 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 calculation formula of the leached water volume at the soil body passing through 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 proportionality coefficient between soil electrical conductivity and soil volume 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 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 soil, is the residual water content, Saturated water content.

3. The underground leaching water monitoring method according to claim 2 is 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.

4. The underground leaching water monitoring method according to claim 3 is characterized in that: In step S4000, the calculation formula for the leached water volume 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.

5. The underground leaching water monitoring method according to claim 4 is 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.

6. A farmland pollution monitoring system, used to implement the underground leaching water monitoring method according to any one of claims 1 to 5, characterized in that: include: A soil moisture sensor (1), a soil pressure sensor (2), a rainfall sensor (3) and a control box (4); The soil moisture sensor (1) is arranged at different depths of the soil; The soil pressure sensor (2) is arranged on the soil surface; The rain sensor (3) is arranged exposed 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.

7. The farmland pollution monitoring system according to claim 6, characterized in that: Also includes: A screw slide connecting piece (6) and a 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 connection piece (6), and the soil moisture sensors (1) are arranged at intervals.

8. The farmland pollution monitoring system according to claim 7, 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).

9. An underground leaching water monitoring device, characterized in that: include: A module for obtaining soil samples to be tested: 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 acquire soil water potential at the first soil depth in different time periods, as well as soil water potential, volumetric water content, temperature, and electrical conductivity at the second soil depth; Leaching water calculation module: used to calculate the leaching water volume of the soil at the second soil depth in a first period according to 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: （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 proportionality coefficient between soil electrical conductivity and soil volume 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 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 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 volume is 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: （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; 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 by linear interpolation to obtain the leaching water volume at the second soil depth in the crop growth cycle. Specifically, the calculation formula for the leached water volume at the second soil depth during the crop growth cycle 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; Calculation of nitrogen concentration module: used to obtain the nitrogen concentration in the farmland, and calculate the nitrogen leaching amount of the farmland during the crop growth cycle according to the leaching water volume 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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