Farmland nitrogen leaching multi-parameter sensor and detection method

Abstract

The invention relates to a farmland nitrogen leaching multi-parameter sensor and a detection method, the farmland nitrogen leaching multi-parameter sensor comprises a liquid circulation system, the liquid circulation system comprises a soil water taking probe for obtaining a solution in soil and a detection circulation device for receiving the solution for optical detection; the optical detection system comprises a light source and a spectrograph; the light source irradiates the detection circulation device, and the spectrograph receives light penetrating through the detection circulation device to obtain an absorption spectrum of liquid to be detected in the detection circulation device. Corresponding to-be-detected liquid is obtained from soil through the liquid circulation system, the optical detection system irradiates and obtains the absorption spectrum of the to-be-detected liquid so as to obtain corresponding component information, in-situ detection of the soil component information is achieved, and multiple times of continuous detection in a certain period is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental detection sensors, and particularly to a multi-parameter sensor for farmland nitrogen leaching. Background Art

[0002] For the determination of soil nitrate nitrogen and ammonium nitrogen, the national standard (GB / T32737-2016) and the industry standard method (HJ634-2012) are both the fresh soil sample potassium chloride solution extraction spectrophotometry method. In recent years, there are electrochemical methods, chromatography, capillary electrophoresis, etc. Traditional detection has deficiencies. One is that the sampling process is cumbersome and cannot meet the requirements of in-situ online and dynamic detection. The other is that the detection equipment is large in size and requires professional operation. Currently, the in-situ real-time sensing methods related to nitrogen detection are mainly divided into two categories: optical methods and electrochemical methods. Ben-Gurion University of the Negev in Israel developed a nitrogen monitoring sensor based on absorption spectroscopy, which can achieve real-time continuous nitrate nitrogen detection, but this sensor can only detect nitrate nitrogen. The University of Edward in the United States developed a soil nitrate nitrogen sensor based on the solid electrode method, and this sensor is not suitable for long-term field monitoring. Imperial College London in the UK detected volatile ammonia in the soil through a simple electrode ammonia sensor, and then combined with machine learning methods to invert the content of nitrate nitrogen in the soil. The detection accuracy of this method is relatively low. Currently, most of the underground leaching nitrogen monitoring sensors at home and abroad are in their infancy, and most nitrogen sensors are single-index detections. In addition, how to complete reliable and long-term effective soil water intake operations is also a problem that needs to be solved in the above measurement methods. Summary of the Invention

[0003] In order to overcome the deficiencies of the prior art and achieve the in-situ online detection of soil elements during agricultural irrigation, the present application provides a multi-parameter sensor for farmland nitrogen leaching.

[0004] The present application provides a multi-parameter sensor for farmland nitrogen leaching, including a liquid circulation system, which includes a soil water intake probe for obtaining the solution in the soil and a detection circulator for receiving the solution for optical detection; an optical detection system, which includes a light source and a spectrometer; the light source irradiates the detection circulator, and the spectrometer receives the light passing through the detection circulator to obtain the absorption spectrum of the liquid to be detected in the detection circulator.

[0005] Preferably, the soil water intake probe includes a permeable shell, and a water storage cavity is formed inside the permeable shell; It further includes a water suction pipe, the water suction pipe extends into the water storage cavity, and the water storage cavity is closed at the insertion part of the water suction pipe.

[0006] Preferably, the water suction pipe extends to the bottom of the water storage cavity, and the bottom is the other end of the water storage cavity corresponding to the end where the water suction pipe is inserted.

[0007] Preferably, at least part of the water-permeable shell is made of a rigid porous material, and the solution can enter the water storage cavity through the porous structure on the water-permeable shell.

[0008] Preferably, the water-permeable shell has a nested inner shell and an outer shell; both the inner shell and the outer shell are rigid porous materials through which the solution can pass; the pore size of the outer shell is larger than the pore size of the inner shell.

[0009] Preferably, there is an interlayer gap between the inner shell and the outer shell, and the interlayer gap is filled with a flexible water-permeable material; Or, a vibration assembly is arranged in the interlayer gap, and the vibration assembly drives the water-permeable shell to vibrate; Or, a hydroxyapatite material for adsorbing heavy metal ions is preset in the water storage cavity.

[0010] Preferably, the liquid circulation system further includes a negative pressure extraction device; the negative pressure extraction device generates negative pressure, and the negative pressure sucks the liquid in the soil into the cavity of the detection circulator at the soil water intake probe; the soil water intake probe is connected to the detection circulator, and the detection circulator is connected to the negative pressure extraction device.

[0011] Preferably, the negative pressure extraction device further includes a negative pressure generator and a liquid retention device. The liquid retention device is connected to the negative pressure generator, and the liquid retention device also has an interface communicating with the outside to communicate with the detection circulator.

[0012] Preferably, the liquid circulation system further includes a reference liquid supply system, which includes a reference liquid container connected to the detection circulator, and the reference liquid is supplied to the detection circulator through the reference liquid container.

[0013] Preferably, a first controllable on-off valve is provided on the pipeline between the detection circulator and the soil water intake probe, and a second controllable on-off valve is provided on the passage between the reference liquid container and the detection circulator; By selectively opening the first control valve and the second control valve, the liquid to be detected is controlled to enter the detection circulator or the reference liquid is enabled to enter the detection circulator.

[0014] This application also provides a detection method using a multi-parameter sensor for farmland nitrogen leaching. A nitrogen detection model is constructed and the nitrogen detection model is used to execute a detection task. The construction of the nitrogen detection model includes the following steps: Step1: Input the training set sample data set , the total number of data wavelengths is ones, and the number of samples is ones, , Determine the basic wavelength set as where , The remaining wavelength set is , So the sample of the basic band dataset at this time , The remaining set data

[0015] According to the set Build a model to obtain evaluation indicators , initialize the integer variable ; ; ; Step2: Select one wavelength from the wavelength set in turn and add it to . Assume is the first wavelength, and the data added to at this time is , According to the set Build a model to obtain evaluation indicators ; Select the second wavelength for the second time and add it to the set. Then build a model according to the set to obtain evaluation indicators ; Select in turn, and obtain the evaluation indicator set . Take the largest evaluation indicator in it. The corresponding wavelength at this time is ; If is greater than the previous , assign to , remove the wavelength in the set , , obtain the new . At the same time, add the wavelength to , , and continue to execute Step2. If is less than or equal to the previous , terminate the algorithm.

[0016] Preferably, in the steps of building the nitrogen detection model, model libraries are established for different application scenarios, and the application scenarios at least include three application scenarios: fields, vegetables, and orchards.

[0017] The present invention provides a detection system for measuring nitrogen in soil through spectral measurement. The system obtains the corresponding liquid to be detected from the soil through a liquid circulation system, irradiates the liquid to be detected through an optical detection system, and obtains the absorption spectrum of the liquid to be detected, thereby obtaining the corresponding component information. By the above method, the system can realize the in-situ detection of soil component information and can realize multiple consecutive detections within a certain period on this basis. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the soil water intake probe of the present application; Figure 2 It is a schematic diagram of the use of the soil water intake probe of the present application; Figure 3 It is a schematic structural diagram of another embodiment of the soil water intake probe of the present application; Figure 4 It is a schematic diagram of the system composition of the farmland nitrogen leaching multi-parameter sensor of the present invention; Figure 5 It is a schematic diagram of a specific embodiment of the farmland nitrogen leaching multi-parameter sensor of the present invention; Figure 6 It is an implementation flowchart of the detection method of the present invention; Figure 7 It is a specific flowchart of the detection method of the present invention.

[0019] In the figure: 1: Soil water intake probe; 11: Water suction pipe; 12: Permeable shell; 121: Inner shell; 122: Outer shell; 123: Vibration assembly; 12S: Water storage cavity; 2: Detection flow-through device; 3: Negative pressure extraction device; 31: Negative pressure generator; 32: Liquid retention device; 4: Light source; 5: Spectrometer; 6: Reference liquid container; 91: First control valve; 92: Second control valve; 93: Third control valve. Detailed Embodiments

[0020] The following combines the drawings and specific embodiments to describe the present invention in detail. In this specification, the drawing size ratio does not represent the actual size ratio. It is only used to reflect the relative positional relationship and connection relationship between components. Components with the same name or the same reference numeral represent similar or the same structures, and are for illustrative purposes only.

[0021] Figure 1This is a schematic structural diagram of the soil water intake probe of the present application. The soil water intake probe 1 includes a permeable shell 12, and a water storage cavity 12S with a relatively small water storage volume is formed inside the permeable shell 12. On this basis, a water suction pipe 11 is further included. The water suction pipe 11 extends into the water storage cavity 12S, and the water storage cavity 12S is closed at the insertion position of the water suction pipe 11, so that the water storage cavity 12S is only connected to the external pipeline through the water suction pipe 11. The soil water intake probe 1 plays a role when inserted into the soil at a certain depth. Specifically, as Figure 2 shown, the entire soil water intake probe 1 is buried at a certain depth under the soil. When a negative pressure is generated in the water suction pipe 11, under the action of the negative pressure, the water in the soil will penetrate the pores of the permeable shell 12 and enter the water storage cavity 12S, and then be pumped out of the water storage cavity 12S through the water suction pipe 11.

[0022] The permeable shell 12 is usually at least partially made of a hard porous material so that water can penetrate through the permeable shell 12 and enter the water storage cavity 12S. The permeable shell 12 can be made of a porous ceramic material, such as a porous ceramic cup, or a porous ceramic tube with one end closed. Preferably, the water suction pipe 11 should extend to the bottom of the water storage cavity 12S. Here, the bottom refers to the other end of the water storage cavity 12S corresponding to the end where the water suction pipe 11 is inserted. In the normal case when the soil water intake probe 1 is applied, as Figure 2 shown, it is placed in the soil with one end of the fixed water suction pipe 11 facing upward. At this time, after the water suction pipe 11 extends to the bottom of the water storage cavity 12S, at least it can be ensured that under the action of negative pressure, the already permeated solution in the water storage cavity 12S can be completely pumped out through the water suction pipe 11, that is, there is no residual solution in the water storage cavity 12S. This is obviously beneficial to ensuring the validity of the measurement results in multiple measurements because there is no remaining solution to interfere with subsequent measurements. Generally, due to the limited amount of water required for detection, the volume of the water storage cavity 12S is usually set relatively small, about 2 mL.

[0023] Furthermore, the permeable shell 12 can have a multi-layer nested structure to optimize the sampling effect and service life for long-term use. As Figure 3As shown, it provides an embodiment having an inner shell 121 and an outer shell 122. Both the inner shell 121 and the outer shell 122 are porous medium materials through which the solution can pass to ensure that the aqueous solution in the soil can enter the water storage cavity 12S. The pore size of the outer shell 122 is larger than that of the inner shell 121. The purpose is to achieve the function of gradient filtration, that is, to filter out large particulate matters in the soil through the outer shell 122 and filter out smaller colloidal particles and other substances in the solution through the inner shell 121. In fact, the pore size of the outer shell 122 is preferably controlled between 50 - 100 μm, while the pore size of the inner shell 121 is preferably controlled between 1 - 10 μm. In particular, in order to control the different porosities of the outer shell 122 and the inner shell 121, the materials used for the inner shell 121 and the outer shell 122 are usually slightly different. For example, for the outer shell 122, the material is usually alumina ceramic with high porosity, and the inner shell 121 preferably uses silicon carbide or nano-zirconia ceramic materials. To avoid the water-permeable shell 12 from cracking due to the inconsistent temperature shrinkage rates between the inner shell 121 and the outer shell 122 at different temperatures in different seasons during use. Preferably, an appropriate gap is reserved between the inner shell 121 and the outer shell 122 so that the inner shell 121 and the outer shell 122 do not contact each other. The gap between the two is at least 0.5 mm or more, which not only facilitates the combination of the inner shell 121 and the outer shell 122 but also avoids excessive stress and resulting rupture due to the inconsistent temperature shrinkage rates between the two. To avoid solution residue in the interlayer gap, preferably, a flexible water-permeable material, such as silica gel material or other optional materials, is filled in the interlayer gap. The purpose is to fill the interlayer gap and prevent excessive solution retention in the interlayer gap, which may affect the measurement and sampling accuracy of the solution during repeated measurements. Flexible water-permeable materials such as silica gel usually also have a porous structure to reduce the flow resistance generated when the solution enters the water storage cavity 12S during use.

[0024] Furthermore, a vibration assembly 123 can be installed in the interlayer gap between the inner shell 121 and the outer shell 122. Its primary function is to reduce the permeation resistance of the soil solution, thereby improving the efficiency of solution sampling under low negative pressure. The vibration assembly 123 drives the permeable shell 12 to generate high-frequency vibrations, breaking the hydrogen bonds between the water in the soil surrounding the permeable shell 12 and the soil medium, making it easier for the water to escape and flow, thereby reducing the flow resistance of the solution in the soil. Furthermore, the vibration effect of the vibration assembly 123 also breaks the adhesion of the water to the pore walls of the inner shell 121 and the outer shell 122. Therefore, the permeation resistance of the solution can be reduced. The vibration assembly 123 is generally an electrically driven piezoelectric vibration element, which is encapsulated in the interlayer gap between the inner shell 121 and the outer shell 122. To achieve the vibration-driven effect, the vibration frequency of the vibration assembly 123 in this application is controlled between 20-50 kHz, with an amplitude of approximately 1-5 μm. Furthermore, another secondary reason for using the vibration assembly 123 is to increase its reusable service life. That is, before reusing the soil water sampling probe 1, the contaminants in the pores of the permeable shell 12 can be removed by the vibration operation of the vibration component 123 when cleaning the soil water sampling probe 1, thereby helping to maintain the penetration effect of the soil water sampling probe 1 during repeated use. Furthermore, the subsequent application mainly needs to realize the detection of the nitrogen content of the solution in the soil. In order to prevent impurities such as heavy metal ions from affecting the detection effect of the obtained solution, preferably, a hydroxyapatite material that can adsorb heavy metal ions is pre-placed in the water storage chamber 12S. The hydroxyapatite material can be a particulate matter filling the water storage chamber 12S, or a coating attached to the inner surface of the water storage chamber 12S.

[0025] The soil water sampling probe 1 can be used as a multi-parameter sensor for nitrogen leaching in farmland. Figure 4 The diagram below is a system diagram of the multi-parameter sensor for nitrogen leaching in farmland. The system consists of a liquid circulation system and an optical detection system. The two parts are connected by a detection flow device 2 to realize the soil nitrogen detection function. Specifically, the liquid circulation system includes a soil water sampling probe 1, a detection flow device 2, and a negative pressure extraction device 3. The soil water sampling probe 1 is mainly used to extract water from the soil. The soil water sampling probe 1 can be a porous ceramic cup, as shown in the diagram below. Figure 3 As shown, it has a double-layer structure, with a porous cylindrical ceramic structure on the outside and a polytetrafluoroethylene cylinder on the inside. Its interface connects to the corresponding pipeline, and the internal volume is approximately 2ml. When used, the soil water sampling probe 1, such as a porous ceramic cup, is inserted into the soil. When negative pressure is generated in the pipeline, moisture in the soil can enter the porous ceramic cup through the porous cylindrical ceramic structure and enter the corresponding pipeline.

[0026] The detection flow cell 2 is a light-transmitting container with a fluid passage, usually a micro flow cell, which is connected to the soil water sampling probe 1 through a pipeline. Usually, the detection flow cell 2 has a small internal volume to reduce the volume of the detection liquid therein, so as to fill the detection flow cell 2 with the detection liquid to be detected under the condition of obtaining less liquid to be detected in the soil, so as to realize the detection of the liquid to be detected in the detection flow cell 2 by optical means. Usually, in order to reduce the volume of the detection flow cell 2, the cross-section of the liquid passage of the detection flow cell 2 is small, and the internal volume is 400 ul. The detection area of the detection flow cell 2 facing the optical path can be increased by setting a U-shaped or multi-path reciprocating liquid flow path to ensure the optical detection effect.

[0027] Usually, there is also a negative pressure extraction device 3, and the negative pressure extraction device 3 is connected to the detection flow cell 2. Therefore, in the liquid flow path, there is a liquid passage sequentially from the soil water sampling probe 1, the detection flow cell 2 to the negative pressure extraction device 3. Its working mode is that when the negative pressure extraction device 3 generates negative pressure, the negative pressure in the pipeline acts at the soil water sampling probe 1, sucking the liquid in the soil into the pipeline and filling the cavity of the detection flow cell 2.

[0028] As for the optical detection system, the detection flow cell 2 exists as a part of it at the same time. The optical detection system also includes a light source 4 and a spectrometer 5. The light source 4 irradiates the detection flow cell 2, and the spectrometer 5 receives the light transmitted through the detection flow cell 2 to obtain the absorption spectrum of the liquid to be detected in the detection flow cell 2.

[0029] As Figure 5 shown, in actual applications, the light source 4 can use a xenon lamp light source. Specifically, the light can also be incident into the detection flow cell 2 through an optical window through a collimating optical fiber. The wavelength range of the xenon lamp is 185 - 2000 nm, and the power is 2W. The light emitted from the micro flow cell passes through the detection flow cell 2 and then enters the spectrometer 5 through a collection optical fiber. The spectrometer collects the nitrogen absorption spectrum. The inside of the micro flow cell is U-shaped, and the internal volume is 400 ul. The light source 4, the detection flow cell 2 and the spectrometer 5 constitute an optical detection unit.

[0030] In other embodiments, the negative pressure extraction device 3 further includes a negative pressure generator 31 and a liquid retention device 32. The liquid retention device 32 is connected to the negative pressure generator 31, and at the same time, the liquid retention device 32 also has an interface communicating with the outside to communicate with the detection flow-through device 2. As the name implies, the negative pressure generator 31 is used to generate negative pressure in the fluid passage. The liquid retention device 32 has a relatively large volume to store the liquid to be detected that enters the pipeline during multiple detections, so as to prevent the liquid from filling the pipeline or entering the negative pressure generator 31. The liquid retention device 32 can be a liquid storage device with a relatively large capacity to collect or discharge the corresponding liquid. Or preferably, it has a selectively openable discharge port, and when needed, the discharge port can be opened to discharge the liquid in the pipeline.

[0031] In a further embodiment, the liquid circulation system further includes a reference liquid supply system, which includes a reference liquid container 6 connected to the detection flow-through device 2. In specific cases, the reference liquid is supplied to the detection flow-through device 2 through the reference liquid container 6. The reference liquid enters the detection flow-through device 2 at regular intervals, such as once a week, or according to actual working needs, to obtain a reference spectrum.

[0032] In order to enable the reference liquid and the liquid to be detected to enter the detection flow-through device 2 for detection without interfering with each other, a first control valve 91 with controllable opening and closing is usually provided on the pipeline between the detection flow-through device 2 and the soil water intake probe 1, and a second control valve 92 with controllable opening and closing is provided on the passage between the reference liquid container 6 and the detection flow-through device 2. By selectively opening the first control valve 91 and the second control valve 92 when the negative pressure extraction device 3 is working, the liquid to be detected is actually controlled to enter the detection flow-through device 2 or the reference liquid is made to enter the detection flow-through device 2.

[0033] The reference liquid container 6 is filled with a reference liquid, such as deionized water. The reference liquid container 6 is connected to the second control valve 92 through a silica gel tube or a tetrafluoro tube. The second control valve 92 is connected to one end of the detection flow-through device 2.

[0034] The liquid circulation system is connected by a silica gel tube or a tetrafluoro tube (inner diameter ≤ 2 mm). A third control valve 93 is provided between the liquid retention device 32 and the negative pressure generator 31. The third control valve 93 is preferably a one-way valve, which enables the pipeline to remain in a vacuum negative pressure state during the period when the negative pressure generator, such as a vacuum pump, stops working. The porous ceramic cup is inserted into the soil to a certain depth (such as 90 cm), and the micro vacuum pump is turned on, and the entire pipeline forms a vacuum negative pressure. The water in the soil pores enters the porous ceramic cup due to the negative pressure, and then enters the micro flow cell and the liquid collection bottle through the pipeline in sequence. The leaching solution entering the liquid collection bottle can be used as a sample for laboratory nitrogen analysis and compared with the on-line monitoring results.

[0035] The power supply is a rechargeable lithium battery. The battery power can ensure the normal operation of the sensor for 8 - 10 hours. The industrial control computer controls the data acquisition, processing and transmission of the sensor and the control of the vacuum pump, etc. The fixing unit has an upper and lower double-layer structure, including an upper fixing plate, a lower fixing plate and two struts. The optical detection unit is fixed to the lower fixing plate. The power supply, the industrial control computer and the vacuum pump are fixed on the upper fixing plate. The optical detection unit, the power supply, the vacuum pump, the fixing unit, the reference liquid bottle and the liquid collection bottle are all located inside the housing. There are interface windows and pipeline holes on the housing.

[0036] For the detection of nitrogen (nitrate nitrogen, ammonium nitrogen and total nitrogen) in various application scenarios such as fields, vegetables, orchards, etc., nitrogen detection models are respectively constructed for each application scenario, and a multi-scenario application model library is established. There may be multiple model libraries for one application scenario. When there are major changes in the soil environment, such as a large amount of fertilization, the models for the corresponding scenarios need to be reconstructed. The modeling methods can be partial least squares regression method, support vector machine method and deep neural network.

[0037] In the modeling process, the obtained spectra have hundreds or even thousands of wavelengths. Some wavelengths contain noise or other useless information that has nothing to do with the detection index. By a specific method, a useful wavelength set is selected and the irrelevant wavelength data is removed. In this way, not only can noise and redundant data be reduced, but also information is not lost, and a better regression model can be established.

[0038] Such as Figure 4 、 5 As shown, the present application also provides a detection method based on the above-mentioned multi-parameter sensor for farmland nitrogen leaching. The specific steps are as follows: Step1: Input the training set sample data set , the total number of data wavelengths is ones, the number of samples is ones, , the full-band set , Determine the basic wavelength set as

[0039] where , The remaining wavelength set is , So the basic band data set sample at this time is , The remaining set data

[0040] According to the set establish a model to obtain relevant indicators , here is used as the judgment standard to obtain the evaluation index , initialize an integer variable ; ; ; Step2: Select a wavelength from the wavelength set in sequence and add it to Assume is the first wavelength. At this time, the data added to the set is ,

[0041] Based on the set build a model to obtain the evaluation index ; Select the second wavelength for the second time . At this time the data in the set are respectively

[0042] Then, based on the set build a model to obtain the evaluation index ; Select in sequence to obtain a set of evaluation indexes, and take the largest evaluation index . At this time, the corresponding wavelength is . If is greater than the previous , assign to , remove the wavelength in the set , , to obtain a new , and at the same time add the wavelength to , . , and continue to execute Step2. If is less than or equal to the previous , terminate the algorithm.

[0043] Step3: Several situations for setting to end the algorithm in advance can be set, such as the number of points of added wavelengths , or the evaluation index reaches a preset certain value , and terminate the algorithm.

[0044] The above content is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A multi-parameter sensor for farmland nitrogen leaching, characterized in that, including a liquid circulation system, which includes a soil water intake probe (1) for obtaining the solution in the soil and a detection circulator (2) for receiving the solution for optical detection; an optical detection system, which includes a light source (4) and a spectrometer (5); the light source (4) irradiates the detection circulator (2), and the spectrometer (5) receives the light passing through the detection circulator (2) to obtain the absorption spectrum of the liquid to be detected in the detection circulator (2).

2. The multi-parameter sensor for farmland nitrogen leaching according to claim 1, characterized in that The soil water intake probe (1) includes a permeable shell (12), and a water storage cavity (12S) is formed inside the permeable shell (12); It further includes a water suction pipe (11), the water suction pipe (11) extends into the water storage cavity (12S), and the water storage cavity (12S) is closed at the insertion part of the water suction pipe (11).

3. The multi-parameter sensor for farmland nitrogen leaching according to claim 2, characterized in that, The water suction pipe (11) extends to the bottom of the water storage cavity (12S), and the bottom is the other end of the water storage cavity (12S) corresponding to the end where the water suction pipe (11) is inserted.

4. The multi-parameter sensor for farmland nitrogen leaching according to claim 2, wherein At least part of the permeable shell (12) is made of a hard porous material, and the solution can enter the water storage cavity (12S) through the porous structure on the permeable shell (12).

5. The multi-parameter sensor for farmland nitrogen leaching according to claim 2, characterized in that The permeable shell (12) has a sleeved inner shell (121) and an outer shell (122); both the inner shell (121) and the outer shell (122) are hard porous materials through which the solution can pass; the pore size of the outer shell (122) is larger than the pore size of the inner shell (121).

6. The multi-parameter sensor for farmland nitrogen leaching according to claim 5, characterized in that, There is an interlayer gap between the inner shell (121) and the outer shell (122), and the interlayer gap is filled with a flexible permeable material; or, a vibration component (123) is arranged in the interlayer gap, and the vibration component (123) drives the permeable shell (12) to vibrate; or, a hydroxyapatite material for adsorbing heavy metal ions is preset in the water storage cavity (12S).

7. The multi-parameter sensor for farmland nitrogen leaching according to claim 1, characterized in that, The liquid circulation system further includes a negative pressure suction device (3); the negative pressure suction device (3) generates negative pressure, and the negative pressure sucks the liquid in the soil into and fills the cavity of the detection circulator (2) at the soil water intake probe (1); the soil water intake probe (1) is connected to the detection circulator (2), and the detection circulator (2) is connected to the negative pressure suction device (3).

8. The multi-parameter sensor for farmland nitrogen leaching according to claim 7, wherein The negative pressure suction device (3) further includes a negative pressure generator (31) and a liquid retention device (32), the liquid retention device (32) is connected to the negative pressure generator (31), and the liquid retention device (32) also has an interface communicating with the outside to connect to the detection circulator (2), or, the liquid circulation system further includes a reference liquid supply system, which includes a reference liquid container (6) connected to the detection circulator (2), and the reference liquid is supplied to the detection circulator (2) through the reference liquid container (6).

9. A detection method for the multi-parameter sensor for farmland nitrogen leaching as described in any one of claims 1-8, characterized in that, Construct a nitrogen detection model and apply this nitrogen detection model to execute the detection task. The construction of the nitrogen detection model includes the following steps: Step1: Input the training set sample data set , the total number of data wavelengths is ones, and the number of samples is ones. ， Determine that the set of base wavelengths is , where , The remaining wavelength set is , So the basic band dataset sample at this time ， The remaining set of data According to the set Build a model to obtain evaluation indicators , initialize integer variables ; ; ; Step2: Select a wavelength from the wavelength set and add it to in sequence. Assume is the first wavelength. At this time, the data added to set is , Based on the set Build a model to obtain evaluation indicators ; Select the second wavelength for the second time Add it to the set, and then according to the set build a model to obtain the evaluation index ; Select successively again to obtain an evaluation index set and take the largest evaluation index among them At this time, the corresponding wavelength is ; If is greater than the previous , assign to , remove the in the set wavelength, , to obtain a new , and at the same time add the wavelength to , , and continue to execute Step2. If is less than or equal to the previous , terminate the algorithm.

10. A detection method as described in claim 9, characterized in that, In the steps of constructing the nitrogen detection model, model libraries are established respectively for different application scenarios, and the application scenarios at least include three application scenarios: fields, vegetables, and orchards.

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