Soil sensor device

Abstract

To provide a soil sensor device which allows sensing of the concentration of such specific ions as nitrate ions even in a dry soil with low moisture content.SOLUTION: A soil sensor device for detecting specific ions in water vapor in a soil includes: a housing of which opening part can be arranged so as to be in contact with or penetrated into a soil; a graphene field effect transistor arranged in the housing as a sensor element for specific ions; and a filter arranged closer to the opening than the graphene field effect transistor in the housing, the filter transmitting water vapor including specific ions.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a soil sensor device for detecting specific ions contained in soil.

Background Art

[0002] In recent years, due to the aging of farmers and the like, it has become increasingly difficult to ensure the sustainability of agricultural production and stably supply food in the future. Based on such a situation, the demonstration of the use of smart agricultural machines and the like is progressing, but the improvement of yield and profitability is insufficient, and many of the causes are due to soil management. Therefore, the realization of precision farming that can sense and control indicators related to soil health in real time is desired. For the purpose of realizing this, for example, the development of state-of-the-art sensors capable of sensing in real time the concentration and physical properties of substances in soil that respond immediately to the growth of crops is required.

[0003] Conventionally, as an example of sensors, an ion sensor that has high ion selectivity and can quantitatively measure the concentration of specific ions without the need for pretreatment in the fields of clinical analysis and environmental analysis is known. The ion sensor has a working electrode, a reference electrode, and a potentiometer, and the potentiometer measures the potential difference between the reference electrode generated by the working electrode capturing a specific substance. An ion sensor having this configuration can analyze various substances by changing the working electrode according to the substance contained in the solution (see, for example, Patent Document 1).

[0004] However, the above ion sensor has a configuration in which the potential is measured by the working electrode contacting the solution, and in soil with a low water content rate, it is impossible to sense the concentration of specific ions, and there is a possibility that the concentration cannot be measured.

[0005] Furthermore, an n-type transistor sensor is also known, comprising a source electrode, a drain electrode, an n-type channel formed of carbon nanotubes provided between the source electrode and the drain electrode, and a nitrogen compound film directly formed on the channel by thermal CVD, wherein the channel is converted from p-type to n-type during nitrogen compound film formation, and the detection target is detected as a change in the current flowing through the channel (see, for example, Patent Document 2). In addition, a system is also known that, in a method of estimating the concentration of volatile components in a liquid after measuring the concentration of volatile components in the gas phase using a gas sensor, allows for the measurement of the concentration of volatile components in the liquid without waiting for a gas-liquid equilibrium state to be reached (see, for example, Patent Document 3).

[0006] However, even with the n-type transistor sensors and gas sensors mentioned above, there was a risk that the concentration of specific ions could not be sensed in soils with low moisture content, making concentration measurement impossible. In other words, it is difficult to effectively utilize the technologies described in Patent Documents 1 to 3 for soil management in fields such as agriculture. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 4195938 [Patent Document 2] Patent No. 4891550 [Patent Document 3] Patent No. 4977087 [Overview of the project] [Problems that the invention aims to solve]

[0008] The technology disclosed herein was developed to solve the above-mentioned problem, and its purpose is to reduce the concentration of specific ions, such as nitrate ions, even in dry soil with low moisture content. The objective is to provide a soil sensor device that enables [specific action / scanning]. [Means for solving the problem]

[0009] To solve the above problems, this disclosure provides a soil sensor device for detecting specific substances contained in soil in the gas phase, A housing that can be positioned so that the portion with an opening is in contact with or penetrates the soil, A graphene field-effect transistor, which serves as a sensor element for the specific substance, is arranged inside the housing. The housing includes a filter positioned on the opening side of the graphene field-effect transistor, which allows the specific substance to pass through in the gas phase, This soil sensor device is characterized by having the following features.

[0010] The soil sensor device according to this disclosure is equipped with a graphene field-effect transistor as a sensor element. This graphene field-effect transistor is a sensor that detects a specific substance or measures the amount of a specific substance by utilizing the change in drain-source current caused by the adsorption or absorption of a specific substance into a graphene channel formed between the drain electrode and the source electrode. The specific substance is, for example, nitrate ions. The gas phase is a state in which water containing the specific substance (for example, nitrate ions) vaporizes into water vapor containing nitrate ions.

[0011] Furthermore, according to the soil sensor device of this disclosure, a portion of the housing having an opening is placed in contact with or penetrates the soil, and of the substances introduced into the inside of the housing through the opening, a specific substance passes through the filter in the gas phase, reaches a graphene field-effect transistor, and is adsorbed or absorbed by the graphene channel, thereby detecting the specific substance or measuring the amount (including concentration) of the specific substance.

[0012] According to this, by simply placing the soil sensor device with the opening of the housing in contact with or into the soil, specific substances from the soil can be adsorbed or absorbed into the graphene channel of the graphene field-effect transistor in the gas phase, making it easier to detect specific substances or measure the amount of specific substances even in soil with low moisture content.

[0013] Furthermore, the present disclosure may further include a measuring unit that outputs a signal corresponding to the amount of the specific substance based on the value of the drain-source current when a predetermined gate voltage is applied to the graphene field-effect transistor.

[0014] According to this, the soil sensor device described in this disclosure alone can detect a specific substance or measure the amount of a specific substance. The measurement unit may be located inside or outside the housing. The measurement unit may further include a storage unit for storing the output results, or a communication unit for transmitting the output results to an externally located device via communication.

[0015] Furthermore, in this disclosure, the graphene channel in the graphene field-effect transistor may consist of a single layer of graphene. This makes it possible to relatively increase the surface area per unit volume of the graphene channel to which a specific substance is adsorbed or absorbed in the gas phase, thereby further improving sensitivity to a specific substance.

[0016] Furthermore, in this disclosure, the housing may have a substantially cylindrical shape, with a maximum width of 1 cm or more and 10 cm or less, and a length of 3 cm or more and 20 cm or less. This makes it possible to make the soil sensor device easily portable and improve convenience.

[0017] Furthermore, in this disclosure, the filter may be attached to the housing in a replaceable manner. The aforementioned filter, which allows a specific substance to pass through in the gas phase, may become clogged or otherwise experience a decrease in function with use. Therefore, by attaching the filter to the housing in a replaceable manner, even when performing fixed-point measurements, it becomes possible to replace only the filter periodically or irregularly, eliminating the need to replace the entire soil sensor device and improving the efficiency of the measurement work.

[0018] Furthermore, in this disclosure, the housing may be further equipped with a temperature and humidity sensor for detecting temperature and humidity, and a pressure sensor for detecting pressure. This makes it possible to simultaneously acquire relevant environmental data such as temperature, humidity, and atmospheric pressure in addition to detecting a specific substance or measuring the amount of a substance, enabling more useful measurements. Also, if the measured amount of the detected substance is affected by temperature, humidity, or pressure, the measured amount of the substance can be corrected using the measurements from the temperature, humidity, and pressure sensors, enabling more accurate measurements.

[0019] Furthermore, in this disclosure, the housing may be further equipped with a self-contained power supply that supplies power to at least the graphene field-effect transistor. This would make it easier to perform fixed-point measurements and continuous measurements with the soil sensor device according to this disclosure.

[0020] Furthermore, the present disclosure may further include a suction device that guides the specific substance through the filter in the gas phase into the graphene channel of the graphene field-effect transistor. This makes it possible to forcibly draw in the specific substance in the gas phase through an opening in the housing by operating the suction device, guide it through the filter into the graphene channel of the graphene field-effect transistor, and as a result, to more efficiently detect the specific substance or measure the amount of the specific substance.

[0021] In addition, in the present disclosure, it may be further provided with a flow sensor inside the housing for measuring the flow rate of a fluid containing the specific substance that permeates the filter in the gas phase. According to this, when a flow of a specific substance is generated inside the housing using a suction machine, by measuring the flow rate, it becomes possible to more accurately obtain the amount of the specific substance guided in the gas phase to the graphene channel in the graphene field effect transistor. As a result, it is possible to measure the concentration of a specific substance with higher accuracy.

[0022] In addition, in the present disclosure, it may be further provided with a moisture sensor for measuring the amount of moisture in the soil. According to this, it is possible to simultaneously obtain the amount of moisture in the soil (including the volumetric water content) that is likely to affect the measured value of the amount of a specific substance, and it is possible to improve the accuracy of detecting a specific substance or measuring the amount of a specific substance.

[0023] In addition, in the present disclosure, the moisture sensor may be installed at a portion of the housing that contacts or penetrates the soil. According to this, it is possible to directly contact or penetrate the moisture sensor into the soil to obtain the amount of moisture. As a result, it is possible to improve the measurement accuracy of the amount of moisture. Here, the portion of the housing that contacts or penetrates the soil may be around or near an opening provided in the housing. Also, the moisture sensor may be in a form in which a single or a plurality of rod-shaped insertion sensor portions are inserted. According to this, by inserting the insertion sensor portion of the moisture sensor into the ground, it is possible to contact or penetrate the portion where the opening of the housing is provided with the soil, and it is possible to simultaneously measure the amount of moisture in the soil and prepare for detecting a specific substance or measuring the amount of a substance. Also, it is possible to more stably fix the soil sensor device to the soil.

[0024] In addition, in the present disclosure, the specific substance may be nitrate ions. According to this, it is possible to more easily and accurately detect nitrate ions or measure the amount of nitrate ions, which are important in growing crops, and it is possible to more efficiently obtain information necessary for increasing the yield of crops.

[0025] Note that the means for solving the above problems can be used in combination with each other as much as possible.

Advantages of the Invention

[0026] According to the technology disclosed in this case, it is possible to sense the concentration of specific ions such as nitrate ions even in dry soil with a low water content.

Brief Description of the Drawings

[0027] [Figure 1] FIG. 1A is a schematic diagram for explaining an example of the use of the soil ion detection device according to Example 1. FIGS. 1B and 1C are schematic diagrams for explaining FIG. 1A in more detail. [Figure 2] FIGS. 2A to 2C are schematic diagrams for explaining an example of the configuration of the soil ion detection device according to Example 1 in more detail. [Figure 3] FIG. 3 is a graph showing the relationship between the value of the current between the drain electrode and the source electrode and the value of the voltage of the gate electrode in the soil ion detection device according to Example 1. [Figure 4] FIG. 4 is a schematic diagram for explaining an example of the configuration of the soil ion detection device according to Example 2. [Figure 5] FIG. 5 is a schematic diagram for explaining an example of the configuration of the soil ion detection device according to Example 3. [Figure 6] FIG. 6 is a schematic diagram for explaining an example of the configuration of the soil ion detection device according to Example 4. [Figure 7] FIG. 7 is a schematic diagram for explaining an example of the configuration of the soil ion detection device according to Example 5.

Modes for Carrying Out the Invention

[0028] 〔Example 1〕 The embodiments of this disclosure will be described in detail below with reference to the drawings. Note that the embodiments described below are only one aspect of this disclosure and do not limit the technical scope of the present invention.

[0029] <Device configuration> Figure 1A is a schematic diagram illustrating an example of use of the soil ion detection device 1 according to Example 1. The soil ion detection device 1 according to Example 1 is used, for example, in fields such as agriculture, and is used by contacting the surface of field soil 2 or by partially penetrating into the field soil 2, as shown in Figure 1A. Moisture exists in the gaps between the soil particles 21 in the field soil 2, or inside the soil, and some of this moisture is in the form of water vapor 22. This water vapor 22 may contain highly water-soluble ions, such as nitrate ions. In the following, it will be assumed that the water vapor 22 contains a certain amount of nitrate ions, and nitrate ions correspond to a specific substance in this disclosure, but the specific substance may be something other than nitrate ions. The soil ion detection device 1 corresponds to a soil sensor device in this disclosure.

[0030] Nitrate ions contained in field soil 2 are synthesized into organic nitrogen-containing compounds through nitrogen assimilation. These organic nitrogen-containing compounds become fertilizer for plants 3 planted in field soil 2. In addition, nitrate ions are reduced to nitrogen gas by the reducing action of denitrifying bacteria and released into the atmosphere. This nitrogen gas is taken into field soil 2, and bacteria such as rhizobia that live symbiotically with leguminous plants perform nitrogen fixation, synthesizing nitrogen compounds that can be used by living organisms. The gas is absorbed into the field soil 2 and oxidized to nitrate ions via ammonium and nitrite. In other words, nitrate ions are important substances for plant growth 3 and nitrogen cycling, and sensing the concentration of nitrate ions contained in water vapor 22 leads to the analysis of big data of the field soil 2 and the management of the health of the field soil 2.

[0031] Figure 1B is a schematic diagram illustrating Figure 1A in more detail. The soil ion detector 1 includes, as part of its components, a housing 11 having a substantially cylindrical shape with a closed upper end, and a filter 12 located near the opening of the housing 11, and in Figure 1, on the surface in contact with the surface of the field soil 2. The filter 12 is permeable to moisture and allows water vapor 22 in the field soil 2 to pass through and be introduced into the housing 11. The filter 12 does not allow soil 21 or the liquid moisture contained in the soil 21 to pass through, so these are not introduced into the housing 11. The end face of the housing 11 opposite to the opening where the filter 12 is located may be opened depending on the usage conditions.

[0032] The housing 11 does not have to be approximately cylindrical in shape; it may have a cylindrical shape with a polygonal cross-section. Also, as shown in Figure 1C, the housing 11 may have, for example, a rectangular parallelepiped shape. Furthermore, filters 12 may be provided at multiple locations on the housing 11 (two locations in Figure 1C). In this case, it is preferable to provide openings and filters 12 on two opposing faces of the six faces of the rectangular parallelepiped, so that a flow path for water vapor containing nitrate ions is formed between the two filters 12. The entire soil ion detection device 1 may also be used by leaving it in the field soil 2.

[0033] Regarding the size of the housing 11, for example, the maximum diameter D of the top base may be 1 cm or more and 10 cm or less, and the total length L may be 3 cm or more and 20 cm or less. This makes the soil ion detector 1 portable and allows for easy use even in locations where it is difficult to transport equipment by car or other means. In addition, the filter 12 may be attached to the housing 11 in a replaceable manner. This eliminates the need to replace the entire soil ion detector 1 even if the filter 12 becomes clogged or otherwise degraded due to long-term use, allowing one soil ion detector 1 to be used repeatedly.

[0034] Figure 2A is a schematic diagram illustrating in more detail an example of the configuration of the soil ion detection device 1 according to Example 1. In addition to the housing 11 and filter 12 described above, the soil ion detection device 1 according to Example 1 has a graphene field-effect transistor 13 (hereinafter also referred to as GFET 13) inside the housing 11. As shown in Figure 2A, the GFET 13 has a drain electrode 131, a source electrode 132 and a gate electrode 133 formed on a substrate 15 via an insulating film 14, and a graphene channel 134 formed between the drain electrode 131 and the source electrode 132. An insulating layer 135 is also provided between the gate electrode 133 and the graphene channel 134. Figure 2A further shows a measurement unit 16 that measures the amount of nitrate ions based on the drain-source current Asd obtained from the drain electrode 131 and the source electrode 132, and the gate voltage Vg, which is the potential of the gate electrode 133, and a display unit 17 that displays the measured results. The measurement unit 16 and the display unit 17 may be integrally provided as part of the soil ion detection device 1, or they may be configured separately from the soil ion detection device 1 using an external device such as an external PC. In Figure 2, the GFET 13 is fixed to the inside side of the housing 11 using a mounting member (not shown).

[0035] The graphene channel 134 is a channel consisting of a single layer of graphene having a structure in which carbon atoms are bonded together by single or double bonds. This allows for a relative increase in the surface area per unit volume of the graphene channel 134 to which water vapor 22 is adsorbed or absorbed. As described above, after the water vapor 22 is absorbed by the filter 12 and introduced into the housing 11, nitrate ions contained in the water vapor 22 are adsorbed or absorbed with high sensitivity by the graphene channel 134. As a result, the drain electrode 131 and the source electrode A change occurs in the current between electrodes 132. Specifically, as shown in the graph in Figure 3, the relationship between the voltage of the gate electrode 133 (gate voltage) and the current between the drain electrode 131 and the source electrode 132 (drain-source current) changes. For example, with respect to the gate voltage shown by the auxiliary line in Figure 3, the value of the drain-source current decreases from position (1) to position (2).

[0036] The gate electrode 133 does not necessarily have to be located on top of the graphene channel 134. As shown in Figure 2B, the gate electrode 133 may be located on the back surface of the substrate 15 (the side opposite to the side on which the insulating film 14 is provided). Also, as shown in Figure 2C, the gate electrode 133 and the graphene channel 134 may be connected via a sensitive film 136.

[0037] Returning to the explanation of Figure 2A, as described above, the graphene channel 134 adsorbs or absorbs nitrate ions, causing a change in the drain-source current. Based on this change, the measurement unit 16 measures the amount of nitrate ions. It is also possible to calculate the concentration of nitrate ions from the amount of nitrate ions.

[0038] As described above, the graphene channel 134 adsorbs or absorbs nitrate ions with high sensitivity, making it possible to measure the amount of nitrate ions with high accuracy in the soil ion detection device 1. In other words, the soil ion detection device 1 according to Example 1 makes it possible to sense nitrate ions even in dry field soil 2 with a moisture content of, for example, 25% or less. As a result, it is possible to manage the health of the field soil 2 with higher accuracy, as described above.

[0039] [Example 2] Next, the soil ion detection device 1a according to Embodiment 2 of this disclosure will be described with reference to Figure 4. Since the soil ion detection device 1a shares many components with the soil ion detection device 1 shown in Figure 2A of Embodiment 1, the same components are denoted by the same reference numerals, and further explanation is omitted. In Embodiment 2 and subsequent embodiments, water vapor 22 is not shown. One difference between the soil ion detection device 1a shown in Figure 2A of Embodiment 1 and the soil ion detection device 1a shown in Figure 4 of Embodiment 2 is that the soil ion detection device 1a is equipped with a temperature and humidity sensor 4 and a pressure sensor 5.

[0040] <Device configuration> In Example 2, the temperature and humidity sensor 4 and the pressure sensor 5 are provided on a substrate 15a common to the GFET 13. The temperature and humidity sensor 4 can detect temperature and humidity, and the pressure sensor 5 can detect pressure. If the measured amount of nitrate ions is affected by temperature, humidity, or pressure, the measurement unit 16 corrects the measured value when measuring the amount of nitrate ions using the values ​​detected by the temperature and humidity sensor 4 and the pressure sensor 5, thereby obtaining a highly reliable measured value. Furthermore, for example, in fixed-point observations, obtaining incidental information such as temperature, humidity, and pressure makes it possible to gain more knowledge about the soil.

[0041] [Example 3] Next, the soil ion detection device 1b according to Embodiment 3 of this disclosure will be described with reference to Figure 5. Since the soil ion detection device 1b shares many components with the soil ion detection device 1 shown in Figure 2A of Embodiment 1, the same components are denoted by the same reference numerals, and further explanation is omitted. One difference between the soil ion detection device 1b shown in Figure 2A of Embodiment 1 and the soil ion detection device 1b shown in Figure 5 of Embodiment 3 is that the soil ion detection device 1b is equipped with a self-contained power supply 6.

[0042] <Device configuration> In Example 3, a self-contained power supply 6 is provided on the substrate 15a. The self-contained power supply 6 supplies power to at least the GFET 13. In this embodiment as well, the soil ion detector 1b can be used independently by the self-contained power supply 6. Since the soil ion detector 1b is portable, the self-contained power supply 6 provided by the soil ion detector 1b may be, for example, a small, lightweight lithium-ion battery capable of storing a large amount of electricity. The soil ion detector 1b shown in Figure 5 of Embodiment 3 and the soil ion detector 1a shown in Figure 4 of Embodiment 2 may be combined. That is, the soil ion detector 1b shown in Figure 5 may be equipped with a temperature and humidity sensor 4 and a pressure sensor 5 in addition to the self-contained power supply 6. In this case, power can also be supplied from the self-contained power supply 6 to the temperature and humidity sensor 4 and the pressure sensor 5, and the soil ion detector 1b can be installed in the field soil 2 for a long period of time without the need for an external power supply.

[0043] [Example 4] Next, the soil ion detection device 1c according to Embodiment 4 of this disclosure will be described with reference to Figure 6. Since the soil ion detection device 1c shares many components with the soil ion detection device 1 shown in Figure 2A of Embodiment 1, the same components are denoted by the same reference numerals, and further explanation is omitted. One difference between the soil ion detection device 1c shown in Figure 2A of Embodiment 1 and the soil ion detection device 1c shown in Figure 6 of Embodiment 4 is that the soil ion detection device 1c shown in Figure 6 of Embodiment 4 is equipped with a suction device 7 and a flow sensor 8.

[0044] <Device configuration> In Example 4, a suction device 7 equipped with a pump and fan is provided at one end of the housing 11 opposite to the opening where the filter 12 is located. The operation of the suction device 7 allows the filter 12 to forcibly pass water vapor 22 through and guide it to the graphene channel 134. As a result, water vapor 22 is more easily adsorbed or absorbed by the graphene channel 134, improving the accuracy of the measurement unit 16 in measuring the amount of nitrate ions. In addition, the flow sensor 8 can measure the flow rate of the fluid containing water vapor 22 passing through the filter 12. By using the measured flow rate, the amount of water vapor guided to the graphene channel 134 of the GFET 13 can be estimated with greater accuracy, improving the measurement accuracy of the amount of nitrate ions. Note that the soil ion detection device 1c shown in Figure 6 of Example 4 may be combined with the soil ion detection device 1a shown in Figure 4 of Example 2 or the soil ion detection device 1b shown in Figure 5 of Example 3.

[0045] As described in this embodiment, by using the suction device 7, the housing 11 can be separated into a first housing (not shown) having a filter 12 and a second housing (not shown) having a GFET 13, and the two can be connected by a tube. With this configuration, it is possible to bring the first housing, which has the filter 12 as a water vapor intake, into contact with or allow it to enter the soil, guide the water vapor to the second housing equipped on the agricultural machine, and measure the amount of nitrate ions.

[0046] [Example 5] Next, the soil ion detection device 1d according to Embodiment 5 of this disclosure will be described with reference to Figure 7. Since the soil ion detection device 1d shares many components with the soil ion detection device 1 shown in Figure 2A of Embodiment 1, the same components are denoted by the same reference numerals, and further explanation is omitted. One difference between the soil ion detection device 1d shown in Figure 2A of Embodiment 1 and the soil ion detection device 1d shown in Figure 7 of Embodiment 5 is that the soil ion detection device 1d is equipped with a moisture sensor 9.

[0047] <Device configuration> In Example 5, a rod-shaped moisture sensor 9 is provided so as to extend from near the opening of the housing 11, where the filter 12 is located, to the outside on the tip side (opposite side from the GFET 13). One or more moisture sensors 9 may be provided. The moisture sensor 9 makes it possible to simultaneously acquire the amount of moisture in the field soil 2, which tends to affect the measurement of the amount of nitrate ions. By acquiring the amount of moisture in the field soil 2, the measurement unit 1 When measuring the amount of nitrate ions, the measured value is corrected, allowing for the acquisition of more accurate measurements. Furthermore, the method of using the soil ion detector 1d is similar to the method shown in Figure 1, where the moisture sensor 9 is brought into contact with the surface of the field soil 2, or partially inserted into the field soil 2. This allows for more reliable acquisition of the amount of moisture. Note that the soil ion detector 1d shown in Figure 7 of Example 5 may be combined with the soil ion detector 1a shown in Figure 4 of Example 2, the soil ion detector 1b shown in Figure 5 of Example 3, or the soil ion detector 1c shown in Figure 6 of Example 4. [Explanation of Symbols]

[0048] 1, 1a, 1b, 1c, 1d... Soil ion detection device 11.. Cabinet 12...filter 13..GFET 131...Drain electrode 132...Source electrode 133... Gatekeeper 134...Graphene Channel 135...Insulating layer 136... Sensitive membrane 14. Insulating film 15, 15a... circuit board 16. Measurement section 17...Display section 2. Field soil 21...Sat 22...water vapor 3...plant 4. Temperature and humidity sensor 5. Pressure sensor 6... Independent power supply 7...Suction machine 8. Flow sensor 9. Moisture sensor

Claims

1. A soil sensor device that detects specific substances contained in soil in the gas phase, A housing that can be positioned so that the portion with an opening is in contact with or penetrates the soil, A graphene field-effect transistor, which serves as a sensor element for the specific substance, is arranged inside the housing. The housing includes a filter positioned on the opening side of the graphene field-effect transistor, which allows the specific substance to pass through in the gas phase, Equipped with, The housing has a cylindrical shape with at least one end face that comes into contact with or enters the soil being open. A soil sensor device characterized in that the filter is replaceably attached to an opening on the end face of the housing that contacts or enters the soil.

2. The soil sensor device according to claim 1, further comprising a measuring unit that outputs a signal corresponding to the amount of a specific substance based on the value of the drain-source current when a predetermined gate voltage is applied to the graphene field-effect transistor.

3. The soil sensor device according to claim 1, characterized in that the graphene channel in the graphene field-effect transistor consists of a single layer of graphene.

4. The soil sensor device according to claim 1, characterized in that the maximum width of the housing is 1 cm or more and 10 cm or less, and the length of the housing is 3 cm or more and 20 cm or less.

5. The soil sensor device according to claim 1, further comprising a temperature and humidity sensor for detecting temperature and humidity, and a pressure sensor for detecting pressure, inside the housing.

6. The soil sensor device according to claim 1, further comprising a self-contained power supply inside the housing for supplying power to at least the graphene field-effect transistor.

7. The soil sensor device according to claim 1, further comprising a suction device that causes the specific substance to pass through the filter in the gas phase and guide it to the graphene channel in the graphene field-effect transistor.

8. The soil sensor device according to claim 7, further comprising a flow sensor inside the housing for measuring the flow rate of a fluid containing the specific substance that passes through the filter in the gas phase.

9. The soil sensor device according to claim 1, further comprising a moisture sensor for measuring the amount of moisture in the soil.

10. The soil sensor device according to claim 9, characterized in that the moisture sensor is installed in a portion of the housing that comes into contact with or penetrates the soil.

11. The soil sensor device according to claim 1, characterized in that the aforementioned specific substance is a nitrate ion.

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