Agricultural non-point source polluted soil nitrate nitrogen in-situ monitoring system and method

Abstract

The invention relates to an agricultural non-point source polluted soil nitrate nitrogen in-situ monitoring system and method, and aims to solve the technical problem that accurate in-situ monitoring of soil leaching nitrate nitrogen and a migration rule is difficult to realize. Wherein the soil leaching solution extraction device comprises moisture sensors buried in different soil depths, a leaching solution extraction probe, a solution storage container and a negative pressure source, and the detection device comprises at least two groups of micro-flow pool channels connected in parallel and a photoelectric detection path corresponding to nitrate nitrogen ultraviolet light absorption and non-absorption wavebands; the liquid pumping pipeline is respectively communicated with the liquid storage container and the micro-flow pool channel; the control module receives information collected by the moisture sensor and determines whether to send a negative pressure source starting instruction or not after comparing the information with a set value, a negative pressure cavity is formed in the leaching solution extraction probe, and soil leaching solution collection is achieved. The in-situ monitoring of the leaching nitrate nitrogen can be realized without disturbing the soil structure; the result is continuous, accurate and reliable, and a reliable way is provided for obtaining accurate data information related to agricultural non-point source pollution distribution, migration, development trend and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection monitoring, and particularly to an in-situ monitoring system and method for soil nitrate nitrogen in agricultural non-point source pollution. Background Art

[0002] Nitrate nitrogen (NO3⁻-N) is one of the typical agricultural non-point source pollutants. Due to its high solubility and mobility, nitrate nitrogen is extremely easy to leach in the soil. The negative impacts of soil nitrate nitrogen leaching on the environmental ecology are multi-faceted, including water pollution, soil degradation, ecosystem damage, greenhouse gas emissions, and human health risks, etc. Specifically, nitrate nitrogen is easily soluble in water and seeps into groundwater with water, resulting in an increase in the concentration of nitrate nitrogen in groundwater. Groundwater is an important drinking water source, and exceeding the standard of nitrate nitrogen (exceeding 10 mg / L) will endanger human health, such as causing methemoglobinemia. Nitrate nitrogen enters water bodies such as rivers and lakes with runoff, becoming one of the main inducements for eutrophication. Nitrate nitrogen leaching will also lead to soil nutrient loss, resulting in a decline in soil fertility or soil acidification, and further affecting soil quality and agricultural production. Nitrate nitrogen leaching has a negative impact on the farmland and surrounding ecosystems, such as a decline in biodiversity (destroying the aquatic ecosystem, causing sensitive species to disappear, and changing the plant community structure), harm to non-target organisms (after nitrate nitrogen leaching enters the water body, it may be converted into nitrite, which is toxic to aquatic organisms), etc.

[0003] The nitrate nitrogen in the soil mainly comes from chemical fertilizer application, organic fertilizer and livestock manure, biological nitrogen fixation, atmospheric deposition, soil organic matter decomposition, sewage irrigation, plant residue decomposition, and industrial activities, etc. Among these sources, agricultural production activities (such as fertilization and irrigation) are the main anthropogenic sources of nitrate nitrogen. Currently, in order to increase biological yields, farmers often overapply nitrogen fertilizers, resulting in the accumulation of nitrate nitrogen in the soil and further increasing the leaching risk.

[0004] Therefore, timely and effectively monitoring and detecting the distribution and migration status of nitrate nitrogen in the soil is an important prerequisite for preventing or controlling nitrate nitrogen leaching pollution. Traditionally, the determination of nitrate nitrogen in agricultural non-point source pollution relies on the method of sending samples taken on-site to the laboratory for routine analysis. However, this method not only has complex pre-treatment, is time-consuming and laborious, but also significantly reduces the measurement frequency. More importantly, after the soil leachate leaves the soil mass and undergoes long-term transportation, its nitrate nitrogen concentration may have a large error due to the changes of the sample over time and space. There is an urgent need for equipment and methods for in-situ monitoring of the separate conditions of nitrate nitrogen in each layer of the soil.

[0005] The information disclosed in this background art section is only used to deepen the understanding of the background art of the present disclosure, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] In long-term practical research, the inventors found that when using existing soil nitrate nitrogen monitoring equipment and methods for monitoring, some analyze and measure after destroying the soil structure and taking soil samples in layers (drilling with a soil drill or excavating a soil profile), and some rely on extracting leaching solution after rainfall or irrigation (which is difficult to monitor in a timely manner and disturbs the transport and distribution of nitrate nitrogen with water) for analysis and measurement; it is difficult to achieve low-cost long-term in-situ monitoring of nitrate nitrogen without destroying the soil structure or affecting the transport law of nitrate nitrogen, so as to obtain the distribution state and transport law of nitrate nitrogen in the actual field soil, and further provide a true and reliable basis for the treatment of nitrate nitrogen pollution. Therefore, in the present invention, a "water sensor + soil leaching solution extraction probe" is arranged in layers in the soil body. When the soil water content reaches a certain content, the leaching solution is extracted in a timely and effective manner for online non-polluting ultraviolet absorption spectroscopy measurement, and after the measurement, the soil leaching solution is reinjected into the corresponding soil area to avoid or reduce the disturbance to the soil structure and the distribution and transport of nitrate nitrogen.

[0007] According to one aspect of the present disclosure, an in-situ monitoring system for nitrate nitrogen in agricultural non-point source pollution soil is provided, including a soil leaching solution extraction device, a nitrate nitrogen detection device, a liquid extraction pipeline, and a control module; the soil leaching solution extraction device includes a certain number of soil water sensors, soil leaching solution extraction probes for being buried in different soil depths or layers, a liquid storage container corresponding to and communicating with the soil leaching solution extraction probes, and a negative pressure source for communicating with the soil leaching solution extraction probes when necessary; the nitrate nitrogen detection device includes at least two groups of parallel microfluidic cell channels and corresponding deep ultraviolet dual-wavelength photoelectric detection paths, and the deep ultraviolet dual-wavelength photoelectric detection paths respectively correspond to the ultraviolet light absorption band and non-absorption band of nitrate nitrogen; both ends of the liquid extraction pipeline are respectively connected to the liquid storage container and the microfluidic cell channel; the control module is used to receive and process the soil water information collected by the soil water sensors, and after comparing with the set soil water information, decide whether to issue an instruction to start connecting the negative pressure source to the soil leaching solution extraction probe to realize the collection of soil leaching solution.

[0008] In some embodiments of the present disclosure, the soil leaching solution extraction probe is in the shape of a tube with one end closed, and has micropores with a pore diameter of 45-55 µm on the tube wall. The material can be clay or similar porous materials, and it is preferably 20-50 cm in overall length and 20-100 mm in diameter; this kind of extraction probe can maintain the soil water potential balance, match the soil water potential through micropores or capillaries to achieve undisturbed water exchange; secondly, it is designed to prevent blockage, and the outer pore diameter is smaller than the soil particles to avoid the entry of suspended substances.

[0009] In some embodiments of the present disclosure, the ultraviolet light absorption band and non-absorption band are respectively wavelengths of 220-240 nm and 270-280 nm.

[0010] In some embodiments of the present disclosure, a liquid level sensor is disposed at a position corresponding to the liquid storage container, and the control module is configured to receive and process the liquid level information collected by the liquid level sensor, and determine whether to issue an instruction to start the liquid extraction pipeline to suck the leaching solution in the liquid storage container into the microfluidic channel for detection after comparing with the set information.

[0011] In some embodiments of the present disclosure, a peristaltic pump for generating a suction force is provided in the liquid extraction pipeline.

[0012] In some embodiments of the present disclosure, it further includes a reinjection pipeline with two ends respectively communicating with the outlet end of the microfluidic channel and the corresponding soil area, for realizing in-situ reinjection of the leaching solution.

[0013] In some embodiments of the present disclosure, the soil moisture sensor is a frequency domain reflectometry soil moisture sensor with RS485 bus data signal output.

[0014] In some embodiments of the present disclosure, the monitoring system further includes a wireless transceiver module for communicating with a host computer or a cloud platform.

[0015] According to a second aspect of the present disclosure, a method for in-situ monitoring of soil nitrate nitrogen is provided, which is implemented based on the above-mentioned in-situ monitoring system for soil nitrate nitrogen. The soil moisture sensor and the soil leaching solution extraction probe are respectively disposed at soil depths of 30-40 cm, 45-55 cm, and 85-95 cm in the soil area to be monitored. The implementation steps include: (1) Each of the soil moisture sensors detects and collects the soil moisture information at its corresponding depth position in real time or at intervals, and transmits it to the control module. After processing and comparing with the set information, it determines whether to issue an instruction to start the negative pressure source, so as to form a negative pressure cavity in the soil leaching solution extraction probe, and realize the convergence of the soil leaching solution in the corresponding soil leaching solution extraction probe; (2) The leaching solution filtered and accumulated in the soil leaching solution extraction probe flows into the corresponding liquid storage container. When the liquid level sensor corresponding to the liquid storage container detects that the liquid level of the soil leaching solution reaches the set value, the control module controls the liquid extraction pipeline to extract the accumulated leaching solution into the microfluidic channel of the nitrate nitrogen detection device, and measures the absorbance values of the leaching solution in the ultraviolet light absorption band and non-absorption band of nitrate nitrogen respectively; (3) Based on the absorbance values measured in the two ultraviolet light bands, calculate the nitrate nitrogen concentration at each corresponding soil depth position by the following formula: , wherein, is the nitrate nitrogen concentration in the soil leaching solution; k is the slope of the standard curve; fis the calibration coefficient related to the soil type; A 吸收波段 is the absorbance value of the leaching solution in the ultraviolet absorption peak band of nitrate nitrogen; A 非吸收波段 is the absorbance value of the soil leaching solution in the ultraviolet non-absorption band of nitrate nitrogen; b is the constant term of the standard curve equation; (4) Via the corresponding host computer or wireless transceiver module, upload the result obtained in the step (3) to the corresponding cloud platform or server to achieve authorized viewing on the corresponding monitoring platform, web page or mobile APP.

[0016] In some embodiments of the present disclosure, the calibration coefficient related to the soil type f is obtained by the following method: Measure the absorbance in the ultraviolet absorption band and the absorbance in the ultraviolet non-absorption band of the sample and the blank test solution respectively. Subtract the absorbance of the corresponding blank test solution from the absorbance of the sample test solution in the ultraviolet absorption band and the ultraviolet non-absorption band respectively, and calculate the ratio of the two to obtain it.

[0017] One or more technical solutions provided in the embodiments of the present application have at least any one of the following technical effects or advantages: 1. Realize long-term in-situ monitoring of the distribution and movement law of nitrate nitrogen in the soil body without disturbing or destroying the soil structure.

[0018] 2. Rely on deep ultraviolet dual-wavelength light source and high-sensitivity photodiode for on-line determination of nitrate nitrogen, without introducing external chemical substances, and avoid causing secondary pollution.

[0019] 3. The monitoring results are continuous, accurate and reliable, which is conducive to accurately identifying the long-term development trend, and the long-term monitoring cost is low and it is easy to popularize.

[0020] 4. Install multiple monitoring systems of the present invention in different areas of the farmland to realize on-line network monitoring of nitrate nitrogen in soil leaching solution, which can provide a reliable way to accurately obtain data information about the distribution, migration and development trend of agricultural non-point source pollution, and also provide accurate and reliable reference data for the prevention and control of agricultural non-point source pollution, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the layout principle schematic diagram of the in-situ monitoring system for soil nitrate nitrogen in an embodiment of the present application.

[0022] Figure 2 is the control principle schematic diagram of the in-situ monitoring system for soil nitrate nitrogen in an embodiment of the present application.

[0023] Figure 3Schematic diagram of the working principle of the nitrate nitrogen detection device in an embodiment of the present application.

[0024] Figure 4 For the in-situ monitoring system of farmland soil nitrate nitrogen in an embodiment of the present application, it includes the construction of sampling wells and the installation effect diagram of soil leachate extraction probes.

[0025] Figure 5 Results of soil nitrate nitrogen determination and comparative analysis in an embodiment of the present application. Detailed implementation manners

[0026] To better understand the technical solution of the present application, the above technical solution will be described in detail below in conjunction with the specification drawings and specific implementation manners.

[0027] Embodiment 1 This example discloses an in-situ monitoring system for nitrate nitrogen in agricultural non-point source polluted soil, as Figure 1 and Figure 2 shown, including a soil leachate extraction device, a nitrate nitrogen detection device, a liquid extraction pipeline, a control module, a reinjection pipeline and a wireless transceiver module; the soil leachate extraction device includes a certain number of soil moisture sensors (frequency domain reflectance soil moisture sensors with RS485 bus data signal output) for being buried in different soil depths or layers, soil leachate extraction probes (cylindrical clay pipes, 35 cm in length, 30 mm in diameter, with tiny pores of 45 - 55 µm in diameter on the pipe wall), a liquid storage container (liquid storage bottle) corresponding to and communicating with the soil leachate extraction probes, and a negative pressure source (such as a negative pressure pump) for communicating with the soil leachate extraction probes when necessary. A liquid level sensor is also provided at a position corresponding to the liquid storage container; the nitrate nitrogen detection device includes two groups of parallel microfluidic cell channels and corresponding deep ultraviolet dual-wavelength photoelectric detection paths, and wavelength light sources corresponding to the absorption band and non-absorption band are respectively provided in the deep ultraviolet dual-wavelength photoelectric detection paths (deep ultraviolet LED light sources encapsulated by two TO39 and 30D, and with peak wavelengths of 235 nm and 275 nm respectively), and the light hole diameters are 5.3 mm and 3.5 mm respectively; both ends of the liquid extraction pipeline are respectively communicated with the liquid storage container and the microfluidic cell channels, and a peristaltic pump for generating suction force is provided in the liquid extraction pipeline; the control module is used to receive and process the soil moisture content information collected by the soil moisture sensors, and decide whether to issue a command to start the negative pressure source after comparing with the set value, so as to form a negative pressure cavity in the soil leachate extraction probe to realize the collection of soil leachate; the in-situ monitoring system for soil nitrate nitrogen further includes a reinjection pipeline with both ends respectively communicated with the outlet end of the microfluidic cell channel and the corresponding soil area for realizing in-situ reinjection after the leachate is measured; the wireless transceiver module is used for communication connection with the upper computer or the cloud platform.

[0028] When the in-situ soil nitrate nitrogen monitoring system is operating, the soil moisture sensor obtains the soil moisture content in real-time or at intervals. When the soil moisture content reaches the set value, it triggers the start of the negative pressure source to generate negative pressure, forming a negative pressure cavity inside the soil leachate extraction probe. Under the action of negative pressure, the infiltration and collection of soil leachate are carried out. At the same time, under the action of negative pressure suction, the collected leachate is transported to the liquid storage container for temporary storage. The liquid volume in the liquid storage container is monitored in real-time by the corresponding installed ultrasonic liquid level sensor. The control module receives and processes the liquid level information collected by the ultrasonic liquid level sensor, and decides whether to issue an instruction after comparing it with the set information to start the liquid extraction pipeline to suck the leachate in the liquid storage container into the microfluidic channel for detection. For example, when the accumulated amount of leachate in the liquid storage container exceeds 30 ml, the negative pressure pump and the soil leachate extraction probe pause working, and a peristaltic pump is used to pump a certain amount of soil leachate from the liquid storage container and transport it to the two microfluidic channels of the nitrate nitrogen determination device for absorbance measurement. After the measurement is completed, the soil leachate is re-injected into the corresponding soil area through the re-injection pipeline (to reduce or avoid the disturbance or damage to the distribution of nitrate nitrogen in the soil caused by positioning monitoring). Finally, the nitrate nitrogen concentration in the soil leachate is transmitted to the designated location in real-time or at regular intervals through the wireless transceiver module (data processing and signal acquisition), including the data terminal, cloud platform or mobile APP, realizing remote transmission of the results, and can be viewed on the monitoring platform, web page or mobile APP.

[0029] The circuit part of the nitrate nitrogen detection device mainly includes an ultraviolet photoelectric detection module, a constant current drive and light source module, and a signal control and processing module. Its working principle is as Figure 3 shown. By activating the UV-LED light source module, the signal is received through the PWM module under the control of the microprocessor, and then ultraviolet light is emitted. The ultraviolet light irradiates the sample through the sample microfluidic channel. The ultraviolet photodetector diode captures these transmitted spectral signals and converts them into electrical signals. These electrical signals are then amplified, denoised and filtered to enhance the signal quality and remove unnecessary noise and interference. The preprocessed analog signal is sent to the A / D converter to be converted into a digital signal so that the microprocessor can perform more complex digital processing. The microprocessor calculates and analyzes the digital signal. The processed data can be transmitted to external devices through the host computer communication interface or stored in the memory for subsequent use. At the same time, the microprocessor sends the analysis result to the display, enabling the user to intuitively view the detection data. If necessary, the microprocessor can also adjust the LED drive circuit through the PWM module to change the brightness or switch state of the UV-LED light source to meet the detection requirements of different samples. The entire system is provided with stable power by the power supply module to ensure the normal operation of each component.

[0030] Example Two Select the agricultural non-point source pollution soil nitrate nitrogen in-situ monitoring system described in Embodiment 1 of the farmland test site layout of Henan Agricultural University for actual nitrate nitrogen monitoring verification and application (see Figure 1 and Figure 4 ). Design and construct a sampling well for farmland soil leachate ( Figure 4 a). Excavate a pit with a length of 130 cm, a width of 130 cm, and a depth of 200 cm at the intersection of farmland crops in the test site. The overall size of the sampling well for farmland soil leachate is 120 cm (length) × 120 cm (width) × 200 cm (height), which is welded with galvanized square steel, and the outside of the frame is integrally coated with a 6-mm-thick transparent PC endurance plate. Vertically place the coated sampling well into the pit, connect the pre-buried PVC pipe to the sampling well, and lay cables, optical cables, and leachate delivery pipelines through the PVC pipe, as shown in Figure 4 b.

[0031] It also includes the following steps: (1) Take a soil leachate extraction probe and a soil moisture sensor as a group, and bury them sequentially at the soil depths of 35 cm, 50 cm, and 90 cm in the soil of the area to be monitored, with a total of three groups, as shown in Figure 4 c; (2) Each of the soil moisture sensors detects and collects the soil moisture information at its corresponding depth position in real time or at intervals, and transmits it to the control module. After comparing with the set information processing, it decides whether to issue an instruction to start the negative pressure source, forming a negative pressure cavity in the soil leachate extraction probe, so as to realize the convergence of soil leachate in the corresponding soil leachate extraction probe; (3) The leachate filtered and accumulated in the soil leachate extraction probe flows into the corresponding liquid storage container. When the liquid level sensor corresponding to the liquid storage container detects that the liquid level of the leachate reaches the set value (volume water content of 19%), the control module controls the liquid extraction pipeline to extract the accumulated leachate into the microfluidic channel of the nitrate nitrogen detection device, and measures the absorbance values of the leachate in the ultraviolet light absorption band and non-absorption band of nitrate nitrogen respectively; (4) Based on the absorbance values measured in the two ultraviolet light bands, calculate the nitrate nitrogen concentration at each corresponding soil depth position by the following formula: , where C NO3 - -N is the nitrate nitrogen concentration in the leachate; k is the slope of the standard curve; fis the empirical calibration coefficient (the absorbance of the measured sample and the blank test solution in the ultraviolet light absorption band and the absorbance in the non-ultraviolet light absorption band are measured. The absorbance of the sample test solution in the ultraviolet light absorption band and the absorbance in the non-ultraviolet light absorption band are respectively subtracted from the absorbance of the corresponding blank test solution, and the ratio of the two is calculated to be the f value corresponding to the sample); A 吸收波段 is the absorbance value of the leaching solution in the ultraviolet light absorption peak band of nitrate nitrogen; A 非吸收波段 is the absorbance value of the leaching solution in the non-ultraviolet light absorption band of nitrate nitrogen; b is the constant term of the standard curve equation; (5) Via the corresponding host computer or wireless transceiver module, upload the result obtained in the step (4) to the corresponding cloud platform or server to achieve authorized viewing on the corresponding monitoring platform, web page or mobile APP.

[0032] At the first measurement, it is necessary to use analytical pure potassium chloride for zero calibration, and then use nitrate nitrogen standard samples with different concentration gradients for concentration calibration. When the soil leaching solution is transported to the microfluidic channel, the host computer sends calibration signals and measurement signals through the RS485 bus protocol, starts the 235nm and 275nm light sources to work, and according to the Lambert-Beer law ( A is the absorbance, T is the transmittance (transparency), which is the ratio of the intensity of the outgoing light ( I ) to the intensity of the incident light ( I 0 ); ɛ is the molar absorption coefficient, which is related to the properties of the absorbing substance and the wavelength of the incident light λ ; C is the concentration of the absorbing substance; L is the optical path length), and calculate A 235 and A 275 absorbances respectively, and upload them to the host computer for data processing. By measuring the A 235 and A 275 absorbance values of the nitrate nitrogen standard solution, the corrected absorbance A can be calculated according to the ultraviolet corrected absorbance formula: A = A 235 -f × A 275 , f The value is the calibration coefficient obtained from the experimental determination of the measured soil ( A 235 / A 275(ratio). Take the corrected absorbance as the ordinate and the nitrate nitrogen concentration as the abscissa to plot a standard curve. Measure the absorbance of the actual soil leachate and calculate the nitrate nitrogen concentration in the actual soil leachate using the standard curve.

[0033] Based on the above method, field measurements were carried out on the crop planting area of the experimental site. The nitrate nitrogen in the soil leachate was removed through step (3), and the absorbance values A of the treated solution at wavelengths of 235 nm and 275 nm were measured. 235 and A 275 , and the calibration coefficient can be determined. f， Furthermore, through step (4), the absorbance values A of the nitrate nitrogen standard solution were measured. 235 and A 275 , and a standard curve was established. As shown in Figure 5 a, the k value in the calculation formula of its nitrate nitrogen concentration can be determined. Further, by measuring the absorbance A of the soil leachate. 235 and A 275 , and inputting the k value and the f value into the upper computer, the nitrate nitrogen concentration of the actual soil sample was calculated. Comparing with the nitrate nitrogen concentration measured by the national standard ultraviolet double-wavelength method, the root mean square error was 0.335 mg / L and the average relative error was 17.31%, as shown in Figure 5 b.

[0034] According to the above system and monitoring method, the nitrate nitrogen concentration of the soil leachate extracted from a certain batch was tested, and the results are shown in Table 1.

[0035] Table 1 Test results of nitrate nitrogen concentration in soil leachate .

[0036] Although some preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted to include the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0037] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of its inventive concept. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. An in-situ monitoring system for nitrate nitrogen in agricultural non-point source pollution soil, comprising a soil leaching solution extraction device and a nitrate nitrogen detection device, characterized in that: It also includes a liquid extraction pipeline and a control module; the soil leaching solution extraction device includes a certain number of soil moisture sensors buried in different soil depths or layers, soil leaching solution extraction probes, liquid storage containers correspondingly connected to the soil leaching solution extraction probes, and a negative pressure source connected to the soil leaching solution extraction probes when necessary; the nitrate nitrogen detection device includes at least two groups of parallel micro-flow cell channels and corresponding deep ultraviolet dual-wavelength photoelectric detection pathways, and the deep ultraviolet dual-wavelength photoelectric detection pathways correspond to the ultraviolet light absorption band and non-absorption band of nitrate nitrogen respectively; the two ends of the liquid extraction pipeline are respectively connected to the liquid storage container and the micro-flow cell channel; the control module is used to receive and process the soil moisture information collected by the soil moisture sensor, and after comparing with the set soil moisture information, decide whether to issue an instruction to start the connection between the negative pressure source and the soil leaching solution extraction probe to realize soil leaching solution extraction.

2. The in-situ monitoring system for nitrate nitrogen in agricultural non-point source contaminated soil according to claim 1, characterized in that: The soil leaching solution extraction probe is in the shape of a tube with one end closed, and has micropores with a pore size of 45-55 μm on the tube wall.

3. The in-situ monitoring system for nitrate nitrogen in agricultural non-point source contaminated soil according to claim 1, characterized in that: The ultraviolet light absorption band and non-absorption band correspond to wavelengths of 220-240 nm and 270-280 nm, respectively.

4. The in-situ monitoring system for nitrate nitrogen in agricultural non-point source contaminated soil according to claim 1, characterized in that: A liquid level sensor is arranged at a position corresponding to the liquid storage container, and the control module is used to receive and process the liquid level information collected by the liquid level sensor, and decide whether to issue an instruction after comparing it with the set information, so as to start the liquid extraction pipeline to suck the elution solution in the liquid storage container into the microfluidic cell channel for detection.

5. The in-situ monitoring system for nitrate nitrogen in agricultural non-point source contaminated soil according to claim 1, characterized in that: A peristaltic pump for generating suction force is arranged in the liquid extraction pipeline.

6. The in-situ monitoring system for nitrate nitrogen in agricultural non-point source contaminated soil according to claim 1, characterized in that: It also includes a reinjection pipeline with two ends respectively connected to the outlet end of the micro-flow cell channel and the corresponding soil area, so as to realize the reinjection of soil leaching solution.

7. The in-situ monitoring system for nitrate nitrogen in agricultural non-point source contaminated soil according to claim 1, characterized in that: The soil moisture sensor is a frequency domain reflection soil moisture sensor with RS485 bus data signal output.

8. The in-situ monitoring system for nitrate nitrogen in agricultural non-point source soil pollution according to claim 1, characterized in that: It also includes a wireless transceiver module for communicating with a host computer or a cloud platform.

9. A method for in-situ monitoring of soil nitrate nitrogen, characterized in that: The in-situ monitoring system for soil nitrate nitrogen according to claim 1 is implemented, wherein the soil moisture sensor and the soil leaching solution extraction probe are respectively arranged at the soil depths of 30-40 cm, 45-55 cm, and 85-95 cm in the area to be monitored, and the implementation steps include: (1) Each of the soil moisture sensors detects and collects soil moisture information at its depth in real time or at intervals, and transmits it to the control module. After comparison with the set information processing, it decides whether to issue a command to start the negative pressure source, so as to form a negative pressure chamber in the soil leaching solution extraction probe, so that the soil leaching solution is gathered in the corresponding soil leaching solution extraction probe; (2) The leachate solution accumulated in the soil leachate extraction probe is stored in a corresponding liquid storage container. When the liquid level sensor corresponding to the liquid storage container detects that the soil leachate solution level reaches a set value, the control module controls the liquid extraction pipeline to extract the accumulated leachate solution into the micro-flow cell channel of the nitrate nitrogen detection device, and respectively measures the absorbance value of the leachate solution in the ultraviolet absorption band and non-absorption band of nitrate nitrogen; (3) Based on the absorbance values ​​measured in the two ultraviolet light bands, the nitrate nitrogen concentration at each corresponding soil depth is calculated by the following formula: ， In the formula, is the concentration of nitrate nitrogen in the soil leaching solution; k is the slope of the standard curve; f is the calibration factor related to soil type; A 吸收波段 It is the absorbance value of soil leaching solution in the ultraviolet absorption band of nitrate nitrogen; A 非吸收波段 It is the absorbance value of soil leaching solution in the non-absorption band of nitrate nitrogen ultraviolet light; b is the constant term of the standard curve equation; (4) Upload the result obtained in step (3) to the corresponding cloud platform or server via the corresponding host computer or wireless transceiver module to enable authorized viewing on the corresponding monitoring platform, web page or mobile phone APP.

10. The method for in-situ monitoring of soil nitrate nitrogen according to claim 9, characterized in that: The calibration coefficient f It is obtained by the following method: respectively determine the absorbance of the sample and blank test solution in the ultraviolet absorption band and the absorbance of the ultraviolet non-absorption band, deduct the corresponding blank test solution absorbance from the absorbance of the sample test solution in the ultraviolet absorption band and the absorbance of the ultraviolet non-absorption band, and calculate the ratio of the two.

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