A rapid soil nitrogen detection device and its rapid detection method

Abstract

The present invention relates to a rapid soil nitrogen detection device and method, which, compared with the prior art, solves the problem of difficulty in rapid soil nitrogen detection. The high-frequency differential conductivity detector of the present invention includes a measuring capillary, a reference capillary, a signal generating circuit, and a current acquisition and analysis circuit, which are installed in a shielded housing. An annular electrode A is mounted on the measuring capillary, and an annular electrode C is mounted on the reference capillary. Both annular electrodes A and C are connected to the signal output terminal of the signal generating circuit. Annular electrode B is mounted on the measuring capillary, and annular electrode D is mounted on the reference capillary. Annular electrodes B and D are connected in series to the input terminal of the current acquisition and analysis circuit. The present invention can perform rapid soil nitrogen detection directly on site. After the soil is directly extracted with ultrapure water, the soil water extract obtained can be used for rapid soil nitrogen detection.

Description

Technical Field

[0001] The present invention relates to the technical field of soil trace element detection, in particular to a soil nitrogen rapid detection device and a rapid detection method thereof. Background Art

[0002] Traditional soil nitrogen testing requires collecting soil samples on-site and then sending them to a specialized laboratory. The samples go through a complex pre-treatment process such as air drying and grinding, and are then tested using equipment such as automatic nitrogen analyzers. The entire testing process is long and costly.

[0003] Some existing soil testing methods utilize conductivity. These conductivity detectors only measure changes in conductivity between two electrodes. Because the buffer solution in the channel itself has a background conductivity, these methods produce a non-zero background signal even when no ions are passing through the detector. This reduces the detection device's nitrogen concentration measurement range.

[0004] Especially in situations where soil nitrogen content is relatively low, the actual ion detection signal can even be smaller than the background signal, resulting in significant measurement errors. Furthermore, as the external environment, such as temperature, humidity, and air pressure, changes, the background conductivity also changes, rendering traditional fixed-value compensation methods ineffective.

[0005] Therefore, a new method is needed to dynamically offset the background conductivity so that the detection device can obtain a larger soil nitrogen measurement range and detection accuracy. Summary of the Invention

[0006] The purpose of the present invention is to solve the defect in the prior art that it is difficult to quickly detect soil nitrogen, and to provide a soil nitrogen rapid detection device and a rapid detection method thereof to solve the above problem.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] A soil nitrogen rapid detection device includes a high-voltage electrode A, a high-voltage electrode B, an ampere bottle A, an ampere bottle B and an ampere bottle C. The ampere bottle A is filled with a soil water extract, and the ampere bottles B and C are both filled with a buffer solution.

[0009] The device also includes a high-frequency differential conductivity detector, which includes a measuring capillary, a reference capillary, a signal generating circuit, and a current acquisition and analysis circuit installed in a shielded shell. An annular electrode A is sleeved on the measuring capillary, and an annular electrode C is sleeved on the reference capillary. Annular electrodes A and C are both connected to the signal output end of the signal generating circuit. Annular electrode B is sleeved on the measuring capillary, and annular electrode D is sleeved on the reference capillary. Annular electrodes B and D are connected in series to the input end of the current acquisition and analysis circuit. The two ends of the reference capillary are respectively inserted into ampoule bottle B and ampoule bottle C, and one end of the measuring capillary is inserted into ampoule bottle C. When the sample is injected, the other end of the measuring capillary is inserted into ampoule bottle A. When the sample is measured, the other end of the measuring capillary is inserted into ampoule bottle B.

[0010] The annular electrodes A, B, C and D are arranged in a rectangular shape and are located at the four vertices of the rectangle respectively. The distance between the annular electrodes A and B is 1.5 mm, and the distance between the annular electrodes C and D is 1.5 mm.

[0011] The measuring capillary and the reference capillary have the same dimensions, with an outer diameter of 365 μm, an inner diameter of 70 μm, and a length of 45 mm.

[0012] The annular electrode A, annular electrode B, annular electrode C and annular electrode D are all made of 0.1 mm copper foil and are 8 mm in length.

[0013] The soil water extract is prepared by adding 10 g of soil sample and 50 ml of ultrapure water to a 100 ml conical flask, shaking at a frequency of 180 r / min for half an hour, standing for 10 minutes, and filtering the upper clear liquid. The buffer is 10 mmol / L MES / His, wherein His is L-histidine His and MES is 2-(N-morpholino)ethanesulfonic acid.

[0014] A rapid detection method for a soil nitrogen rapid detection device comprises the following steps:

[0015] Calibration of the high-frequency differential conductivity detector: Prepare nine standard solutions with the following ion concentrations D: 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, 500 μg / L, and 1000 μg / L. Use the high-frequency differential conductivity detector to measure and obtain the area S of the current peak at the corresponding concentration. Then use the least squares method to calculate the slope a and intercept b of the fitting curve to complete the calibration of the high-frequency differential conductivity detector.

[0016] Collecting a soil nitrogen sample to be tested and generating a soil water extract to be tested;

[0017] The sampling process and the measurement and detection process are processed, and the soil nitrogen detection calculation is performed; the signal generating circuit outputs the same voltage on the measuring capillary and the reference capillary, that is, the output voltage U a and U b The amplitude and frequency are the same, the phase difference is 180 degrees, and the output current is 0;

[0018] The current acquisition and analysis circuit records the test current I generated by the soil water extract to be tested, generates a curve of the test current I and its corresponding peak area S, and calculates the nitrogen ion concentration D. The calculation formula is as follows:

[0019] D=a×S+b,

[0020] Where: a is the slope of the fitting curve, and b is the intercept of the fitting curve.

[0021] The calibration of the high-frequency differential conductivity detector comprises the following steps:

[0022] Nine standard solutions were prepared as calibrated soil water extracts, with the concentrations of the ions to be measured being: 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, 500 μg / L, and 1000 μg / L.

[0023] Carry out standard solution injection process;

[0024] Carry out standard solution measurement and detection process processing;

[0025] The signal generating circuit outputs the same voltage on the measuring capillary and the reference capillary, that is, the output voltage U a and U b The amplitude and frequency are the same, the phase difference is 180 degrees, and the output current is 0;

[0026] The current acquisition and analysis circuit obtains the change curves of the current I of the nine standard solutions and calculates the area S of their current peaks;

[0027] According to the linear relationship between ion concentration and current peak area, the slope a and intercept b of the linear relationship are solved using the current peak area S of 9 standard solutions. The calculation formula is as follows:

[0028]

[0029]

[0030] Where a is the slope of the fitting curve; b is the intercept of the fitting curve; S iis the area of the current peak corresponding to the 9 standard solutions, the subscript i represents different standard solutions; S is the average of the current peak areas of the 9 standard solutions; D i is the ion concentration of 9 standard solutions, subscript i represents different standard solutions; D is the average ion concentration of the 9 standard solutions.

[0031] The injection process comprises the following steps:

[0032] Inject buffer into the measuring capillary and the reference capillary, then insert one end of the measuring capillary into ampoule bottle A, one end of the reference capillary into ampoule bottle B, and the other ends of the measuring capillary and the reference capillary into ampoule bottle C;

[0033] Apply 10kV DC high voltage to both high voltage electrode A and high voltage electrode B for n seconds, where n<15;

[0034] The ammonium ions and nitrate ions in the soil water extract in the ampoule bottle A enter the measuring capillary, completing the sample injection process.

[0035] The measurement and detection process includes the following steps:

[0036] Place the high voltage electrode A, one end of the measuring capillary and the reference capillary into the ampoule bottle B containing the buffer solution, and the other ends of the measuring capillary and the reference capillary into the ampoule bottle C containing the buffer solution;

[0037] A DC high voltage of 20 kV is applied to both high voltage electrode A and high voltage electrode B for n minutes, where n<15. Under the action of the high voltage, the ammonium ions and nitrate ions in the measuring capillary are separated into ammonium ion groups and nitrate ion groups, which are respectively detected by high frequency differential conductivity detectors to complete the measurement and detection process.

[0038] Beneficial effects

[0039] Compared with the prior art, the soil nitrogen rapid detection device and rapid detection method of the present invention can directly perform rapid soil nitrogen detection on site. After the soil is directly extracted with ultrapure water, the soil water extract obtained is used to perform rapid soil nitrogen detection.

[0040] The high-frequency differential conductivity detector proposed in this invention adds a reference capillary with the same mechanical dimensions and internal filling as the traditional measuring capillary, forming a four-electrode high-frequency differential conductivity detector. This detector uses the principle of an unbalanced bridge to measure the conductivity difference between the two capillaries, making it more sensitive to conductivity changes in the measuring capillaries. Furthermore, the presence of the reference channel allows the detector to offset errors caused by environmental changes such as temperature, humidity, and air pressure, resulting in extremely high anti-interference capabilities.

[0041] The present invention applies high-voltage electrophoresis to the detection of soil nitrogen, achieving rapid separation of ammonium ions and nitrate ions in soil water extracts in capillary channels. Combined with the designed high-frequency differential conductivity detector, soil nitrogen measurement can be completed within ten minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the structure of the present invention during the sample injection process;

[0043] Figure 2 This is a schematic diagram of the structure of the present invention during the sample measurement process;

[0044] Figure 3 This is a structural principle diagram of the high-frequency differential conductivity detector of the present invention;

[0045] Figure 4 This is a schematic diagram of the present invention in use;

[0046] Figure 5 Schematic diagram of the equivalent circuit of the high-frequency differential conductivity detector of the present invention;

[0047] Figure 6 This is a curve diagram of the collected current variation in the high-frequency differential conductivity detector calibration link of the present invention;

[0048] Figure 7 This is a curve diagram of the current collection change in the soil nitrogen detection and calculation link of the present invention;

[0049] Among them, 1-high-frequency differential conductivity detector, 2-amphetometer bottle A, 3-amphetometer bottle B, 4-amphetometer bottle C, 5-high-voltage electrode A, 6-high-voltage electrode B, 7-measuring capillary, 8-reference capillary, 9-soil water extract, 10-buffer, 11-signal generating circuit, 12-current acquisition and analysis circuit, 13-ring electrode A, 14-ring electrode B, 15-ring electrode C, 16-ring electrode D, 17-shielding shell. DETAILED DESCRIPTION

[0050] In order to provide a further understanding and appreciation of the structural features and effects achieved by the present invention, a detailed description is provided with reference to preferred embodiments and accompanying drawings as follows:

[0051] like Figure 1 and Figure 2As shown, the rapid soil nitrogen detection device of the present invention includes a high-voltage electrode A5, a high-voltage electrode B6, an ampoule A2, an ampoule B3, and an ampoule C4. Ampoule A2 contains a soil water extract 9, and ampoules B3 and C4 each contain a buffer solution 10. Here, the soil water extract 9 is prepared by adding 10g of soil sample and 50ml of ultrapure water to a 100ml conical flask, shaking at 180 rpm for half an hour, and then filtering the supernatant after 10 minutes. Buffer solution 10 is 10 mmol / L MES / His, where His is L-histidine and MES is 2-(N-morpholino)ethanesulfonic acid.

[0052] like Figure 3 As shown, the high-frequency differential conductivity detector 1 includes a measuring capillary 7, a reference capillary 8, a signal generating circuit 11, and a current acquisition and analysis circuit 12, housed within a shielded housing 17. The measuring capillary 7 and the reference capillary 8 have identical dimensions and specifications. Both have an outer diameter of 365 μm, an inner diameter of 70 μm, and a length of 45 mm. The signal generating circuit 11 generates signals, and the current acquisition and analysis circuit 12 collects current signals. The shielded housing 17 is an aluminum metal enclosure that provides shielding from external interference.

[0053] Ring electrode A13 is placed over the measuring capillary 7, and ring electrode C15 is placed over the reference capillary 8. Both ring electrodes A13 and C15 are connected to the signal output of the signal generating circuit 11. Ring electrode B14 is placed over the measuring capillary 7, and ring electrode D16 is placed over the reference capillary 8. Ring electrodes B14 and D16 are connected in series to the input of the current acquisition and analysis circuit 12. Ring electrodes A13, B14, C15, and D16 are arranged in a rectangular shape, located at the four vertices of the rectangle, ensuring uniform spacing between the electrodes. The spacing between ring electrodes A13 and B14 is 1.5 mm, and the spacing between ring electrodes C15 and D16 is 1.5 mm. Ring electrodes A13, B14, C15, and D16 are all made of 0.1 mm copper foil and are 8 mm long.

[0054] The two ends of the reference capillary 8 are respectively inserted into the ampoule bottle B3 and the ampoule bottle C4, and one end of the measuring capillary 7 is inserted into the ampoule bottle C4. Figure 1 As shown, when the sample injection process is performed, the other end of the measuring capillary 7 is inserted into the ampoule bottle A2; Figure 2 As shown, when the sample measurement process is performed, the other end of the measuring capillary 7 is inserted into the ampoule bottle B3.

[0055] Here, since nitrogen in the soil exists mainly in the form of nitrate ions and ammonium ions in its water extract, the nitrogen content in the soil can be reflected by measuring the content of nitrate ions and ammonium ions in the soil water extract. (Because nitrate ions and ammonium ions contain nitrogen)

[0056] The high-frequency differential conductivity detector consists of four annular electrodes surrounding the capillary tube, a signal generating circuit connected to the electrodes, and a current acquisition and analysis circuit. Figure 5 The internal equivalent circuit is shown.

[0057] Among them, capacitors C1, C2, C3, and C4 are the wall capacitances generated by the outer wall of the capillary, and C1 = C2 = C3 = C4. G1 is the conductivity of the solution between annular electrode A13 and annular electrode C15. G2 is the conductivity of the solution between annular electrode B14 and annular electrode D16. A bridge circuit is formed between the four electrodes. When no ions pass through the detector, G1 = G2. At the same time, since the output voltages Ua and Ub of the signal generating circuit have the same amplitude and frequency, and a phase difference of 180 degrees, the output current I is 0. When ions with a concentration of D pass through the detector, G1 ≠ G2. At this time, due to the imbalance between the upper and lower parts of the circuit, the value of the output current I is not 0. Here, since the output voltage frequency of the signal generating circuit 11 is relatively high (here 1 MHz), the influence of the wall capacitance can be ignored, so the current I is proportional to the change in conductivity G3, G3 = G1-G2, and the ion concentration D is proportional to G3.

[0058] In summary:

[0059] (1) When no ions pass through the detector, there is no current output, that is, I = 0;

[0060] (2) When ions with a concentration of D pass through the detector, a current I is generated, and the magnitude of the current I is proportional to D. In the process of ions with a concentration of D passing through the detector, the current I changes over time, from zero to a maximum value, and then returns to zero, forming a current peak, such as Figure 6 shown.

[0061] Here, the current acquisition and analysis circuit can collect the change curve of the current I and calculate the area S of the current peak. Since the ion concentration D and the area S of the current peak are linearly correlated, D = a*S+b, where a and b are linear correlation coefficients.

[0062] The linear correlation coefficients a and b here are determined during the calibration of the detector. First, prepare 9 standard solutions with the concentrations D of the ions to be measured, namely 1μg / L, 5μg / L, 10μg / L, 20μg / L, 50μg / L, 100μg / L, 200μg / L, 500μg / L, and 1000ug / L. Use the device to measure them respectively to obtain the area S of the current peak at different concentrations. Then use the least squares method to calculate the values of a and b. The calculation formula is as follows:

[0063]

[0064]

[0065] To sum up, the core principle of the high-frequency differential conductivity detector is to detect the current I. When no ions pass through, I is 0. When ions with a concentration of D pass through, I is not zero. By recording the changes in I, there will be an I curve. By calculating the peak area S on the curve, the concentration of the ions can be calculated using the formula D = a*S+b.

[0066] According to the above principle, the detection process for nitrate ions and ammonium ions is as follows: Figure 4 As shown, after the injection is completed, the soil water extract 9 enters the capillary. A high voltage of 20KV is applied to the two poles of the capillary by a high-voltage power supply. The ammonium ions, nitrate ions and other ions (ions unrelated to soil nitrogen) in the soil water extract will move along the direction of the arrow toward the high-frequency differential conductivity detector 1 under the action of the electric field. Due to different charge-to-mass ratios, different ions have different migration speeds. In this way, different ion groups will be formed in the capillary, which completes the separation of different ions (this high-voltage separation method is fast and efficient). As the ion groups continue to migrate in the capillary, they will pass through the high-frequency differential conductivity detector 1 in turn at different times. The detector will record the curve of the change of current I over time, as shown Figure 7 As shown in the figure, different ions will form ion peaks with different areas on the curve.

[0067] Before actual soil testing, the device is calibrated with standard ammonium and nitrate solutions of varying concentration gradients. The corresponding nitrate and ammonium ion peak times and peak areas at different concentrations are recorded to obtain the peak times and corresponding linear correlation coefficients a and b. During the actual measurement, the current acquisition and analysis circuit within the high-frequency differential conductivity detector 1 analyzes the collected current waveform and calculates the nitrate and ammonium ion concentrations in the soil extract based on the peak times and peak areas, representing the nitrogen content in the soil.

[0068] Therefore, a rapid detection method of a soil nitrogen rapid detection device is also provided, comprising the following steps:

[0069] The first step is to calibrate the high-frequency differential conductivity detector 1.

[0070] Nine standard solutions with the concentrations D of the ions to be measured being 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, 500 μg / L, and 1000 μg / L were prepared, and the high-frequency differential conductivity detector (1) was used for measurement to obtain the area S of the current peak corresponding to the concentration. The slope a and intercept b of the fitting curve were calculated using the least squares method to complete the calibration of the high-frequency differential conductivity detector 1.

[0071] The specific steps for calibrating the high-frequency differential conductivity detector 1 are as follows:

[0072] (1) Prepare nine standard solutions as calibrated soil water extract 9, whose ion concentrations to be measured are: 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, 500 μg / L, and 1000 μg / L.

[0073] (2) Carry out the standard solution injection process.

[0074] The standard solution injection process is as follows:

[0075] First, inject buffer 10 into the measuring capillary 7 and the reference capillary 8, then insert one end of the measuring capillary 7 into the ampoule bottle A2, one end of the reference capillary 8 into the ampoule bottle B3, and the other ends of the measuring capillary 7 and the reference capillary 8 into the ampoule bottle C4;

[0076] Secondly, a DC high voltage of 10 kV is applied to both the high voltage electrode A5 and the high voltage electrode B6 for n seconds, where n<15;

[0077] Finally, the ammonium ions and nitrate ions in the soil water extract 9 in the ampoule bottle A2 enter the measuring capillary 7, completing the sample injection process.

[0078] (3) Carry out standard solution measurement and detection process processing.

[0079] The measurement and detection process includes the following steps:

[0080] First, place one end of the high voltage electrode A5, the measuring capillary 7, and the reference capillary 8 into the ampoule bottle B3 containing the buffer solution 10;

[0081] Finally, a DC high voltage of 20 kV is applied to both the high voltage electrode A5 and the high voltage electrode B6 for n minutes, where n<15, usually within 10 minutes. Under the action of the high voltage, the ammonium ions and nitrate ions in the measuring capillary 7 are separated into ammonium ion groups and nitrate ion groups, respectively, and pass through the high frequency differential conductivity detector 1 to complete the measurement and detection process.

[0082] (4) The signal generating circuit 11 outputs the same voltage on the measuring capillary and the reference capillary 8, that is, the output voltage U a and U b The amplitude and frequency are the same, the phase difference is 180 degrees, and the output current is 0.

[0083] (5) The current acquisition and analysis circuit obtains the change curves of the current I of the nine standard solutions and calculates the area S of their current peaks.

[0084] (6) According to the linear relationship between ion concentration and current peak area, the slope a and intercept b of the linear relationship are solved using the current peak area S of the 9 standard solutions. The calculation formula is as follows:

[0085]

[0086]

[0087] Where a is the slope of the fitting curve; b is the intercept of the fitting curve; S i is the area of the current peak corresponding to the 9 standard solutions, the subscript i represents different standard solutions; S is the average of the current peak areas of the 9 standard solutions; D i is the ion concentration of 9 standard solutions, subscript i represents different standard solutions; D is the average ion concentration of the 9 standard solutions.

[0088] The second step is to collect the soil nitrogen sample to be tested and generate the soil water extract 9 to be tested.

[0089] The third step is to carry out the sampling process processing and the measurement and detection process processing. Here, the sampling process processing and the measurement and detection process processing are carried out for the soil nitrogen sample to be tested, and the process content is the same as before.

[0090] Step 4: Detection and calculation of soil nitrogen: The signal generating circuit 11 outputs the same voltage on the measuring capillary and the reference capillary 8, that is, the output voltage U a and U b The amplitude and frequency are the same, the phase difference is 180 degrees, and the output current is 0.

[0091] The current acquisition and analysis circuit records the test current I generated by the soil water extract 9 to be tested, and generates a curve of the test current I and its corresponding peak area S, and calculates the nitrogen ion concentration D, which is calculated as follows:

[0092] D=a×S+b,

[0093] Where: a is the slope of the fitting curve, and b is the intercept of the fitting curve.

[0094] The nitrogen ion concentration D in the soil can be quickly calculated.

[0095] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A soil nitrogen rapid detection device, comprising a high-voltage electrode A (5), a high-voltage electrode B (6), an ampere bottle A (2), an ampere bottle B (3) and an ampere bottle C (4), wherein the ampere bottle A (2) is filled with a soil water extract (9), and the ampere bottles B (3) and the ampere bottle C (4) are both filled with a buffer solution (10), characterized in that: The high-frequency differential conductivity detector (1) includes a measuring capillary (7), a reference capillary (8), a signal generating circuit (11), and a current acquisition and analysis circuit (12) installed in a shielding shell (17); a ring electrode A (13) is sleeved on the measuring capillary (7); a ring electrode C (15) is sleeved on the reference capillary (8); the ring electrode A (13) and the ring electrode C (15) are both connected to the signal output end of the signal generating circuit (11); and a ring electrode B (14) is sleeved on the measuring capillary. (7), the annular electrode D (16) is sleeved on the reference capillary (8), the annular electrode B (14) and the annular electrode D (16) are connected in series to the input end of the current acquisition and analysis circuit (12), the two ends of the reference capillary (8) are respectively inserted into the ampere bottle B (3) and the ampere bottle C (4), one end of the measuring capillary (7) is inserted into the ampere bottle C (4), when the sample is injected, the other end of the measuring capillary (7) is inserted into the ampere bottle A (2), and when the sample is measured, the other end of the measuring capillary (7) is inserted into the ampere bottle B (3); The annular electrode A (13), annular electrode B (14), annular electrode C (15) and annular electrode D (16) are arranged in a rectangular shape and are respectively located at the four vertices of the rectangle. The spacing between the annular electrode A (13) and the annular electrode B (14) is 1.5 mm, and the spacing between the annular electrode C (15) and the annular electrode D (16) is 1.5 mm. The measuring capillary (7) and the reference capillary (8) have the same size, with an outer diameter of 365 μm, an inner diameter of 70 μm and a length of 45 mm. The annular electrode A (13), annular electrode B (14) and annular electrode C (15) are arranged in a rectangular shape and are respectively located at the four vertices of the rectangle. The spacing between the annular electrode A (13) and the annular electrode B (14) is 1.5 mm, and the spacing between the annular electrode C (15) and the annular electrode D (16) is 1.5 mm. Electrode B (14), annular electrode C (15) and annular electrode D (16) are all made of 0.1mm copper foil and are 8mm in length; the soil water extract (9) is prepared by adding 10g soil sample and 50ml ultrapure water into a 100ml conical flask, oscillating at a frequency of 180r / min for half an hour, leaving it for 10 minutes, and filtering the upper clear liquid; the buffer (10) is 10mmol / L MES / His, wherein His is L-histidine His and MES is 2-(N-morpholino)ethanesulfonic acid.

2. The rapid detection method of a soil nitrogen rapid detection device according to claim 1, characterized in that: The following steps are involved: 21) Calibration of high-frequency differential conductivity detector: Prepare nine standard solutions with the concentrations D of the ions to be measured being 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, 500 μg / L, and 1000 μg / L, respectively. Use high-frequency differential conductivity detector (1) to measure and obtain the area S of the current peak corresponding to the concentration. Then use the least squares method to calculate the slope a and intercept b of the fitting curve to complete the calibration of high-frequency differential conductivity detector (1). 22) collecting a soil nitrogen sample to be tested and generating a soil water extract to be tested (9); 23) performs sampling process processing and measurement detection process processing, and performs soil nitrogen detection calculation; the signal generating circuit (11) outputs the same voltage on the measuring capillary (7) and the reference capillary (8), that is, the output voltage U a and U b The amplitude and frequency are the same, the phase difference is 180 degrees, and the output current is 0; The current acquisition and analysis circuit (12) records the test current I generated by the soil water extract (9) to be tested, and generates a curve of the test current I and its corresponding peak area S, and calculates the nitrogen ion concentration D, which is calculated as follows: D=a×S+b, Where: a is the slope of the fitting curve, and b is the intercept of the fitting curve.

3. The rapid detection method of a soil nitrogen rapid detection device according to claim 2, characterized in that: The calibration of the high-frequency differential conductivity detector comprises the following steps: 31) Prepare nine standard solutions as calibrated soil water extracts (9), with the concentrations of the ions to be measured being: 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, 500 μg / L, and 1000 μg / L; 32) Perform standard solution injection process; 33) Perform standard solution measurement and detection process; 34) The signal generating circuit (11) outputs the same voltage on the measuring capillary and the reference capillary (8), namely the output voltage U a and U b The amplitude and frequency are the same, the phase difference is 180 degrees, and the output current is 0; 35) The current acquisition and analysis circuit obtains the change curves of the current I of the 9 standard solutions and calculates the area S of their current peaks; 36) According to the linear relationship between ion concentration and current peak area, the slope a and intercept b of the linear relationship are solved using the current peak area S of the 9 standard solutions. The calculation formula is as follows: Where a is the slope of the fitting curve; b is the intercept of the fitting curve; S i is the area of the current peak corresponding to the nine standard solutions, and the subscript i represents different standard solutions; is the average current peak area of 9 standard solutions; D i is the ion concentration of 9 standard solutions, and the subscript i represents different standard solutions; It is the average value of the ion concentration of 9 standard solutions.

4. The rapid detection method of a soil nitrogen rapid detection device according to claim 2, characterized in that: The injection process comprises the following steps: 41) Injecting buffer solution (10) into the measuring capillary (7) and the reference capillary (8), then inserting one end of the measuring capillary (7) into the ampoule bottle A (2), one end of the reference capillary (8) into the ampoule bottle B (3), and the other ends of the measuring capillary (7) and the reference capillary (8) into the ampoule bottle C (4); 42) Apply a 10 kV DC high voltage to both high voltage electrode A (5) and high voltage electrode B (6) for n seconds, where n < 15; 43) The ammonium ions and nitrate ions in the soil water extract (9) in the ampoule bottle A (2) enter the measuring capillary (7), completing the sample injection process.

5. The rapid detection method of a soil nitrogen rapid detection device according to claim 2, characterized in that: The measurement and detection process includes the following steps: 51) placing one end of the high-voltage electrode A (5), the measuring capillary (7) and the reference capillary (8) into an ampoule bottle B (3) containing a buffer solution (10), and placing the other ends of the measuring capillary (7) and the reference capillary (8) into an ampoule bottle C (4) containing a buffer solution (10); 52) A DC high voltage of 20 kV is applied to both the high voltage electrode A (5) and the high voltage electrode B (6) for n minutes, where n < 15. Under the action of the high voltage, the ammonium ions and nitrate ions in the measuring capillary (7) are separated into ammonium ion groups and nitrate ion groups, respectively, and the measurement and detection process is completed by passing through a high frequency differential conductivity detector (1).

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