Plant moisture content sensor and method for measuring plant moisture content

Abstract

Provided are a plant water content sensor and a plant water content measurement method whereby the water content of a plant can be measured in a non-destructive manner.　The plant water content sensor (1) comprises: a water content probe (20) that has provided therein a read electrode pair (21) comprising a pair of electrodes (22, 22) that are arranged having a prescribed interval therebetween, said water content probe also comprising a water-sensitive film (23) bridging the pair of electrodes (22, 22); and a support (10) that supports the water content probe (20). The water content probe (20) is inserted into the plant and the water content of the plant can be measured by reading the impedance or capacitance from the read electrode pair (21).

Description

[Technical field]

[0001] The present invention relates to a plant water content sensor and a method for measuring plant water content, and more particularly to a sensor and method used to measure the water content of plants. [Background technology]

[0002] In crop and fruit production, it is desirable to irrigate and replenish nutrients at appropriate times according to the growth state of the plants from the viewpoint of productivity. However, in many agricultural fields, irrigation and nutrient supply are currently performed based on experience and intuition, such as the number of days without rain. Such a method that relies on experience requires skill, and is time-consuming and laborious. In addition, since the benchmark indicators are based on personal experience, it is difficult for anyone to carry out the method easily.

[0003] In recent years, there has been a growing movement to introduce information technology into agriculture, such as smart agriculture. It is expected that information technology will enable optimal production based on physiological information of plants, without relying on humans.

[0004] Examples of physiological information of plants that are necessary for irrigation management include vascular sap flow rate and water content. In particular, in order to improve the productivity and quality of crops and fruit trees, it is important to measure the vascular sap flow rate and water content in the details of the plant, such as the shoot ends and fruit stalks. Of these, the inventor of this application has already proposed a sensor for measuring the vascular sap flow rate in the details of the plant (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-145810 A Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, the only method currently known for measuring the water content of herbaceous plants is the destructive method, in which the plant is crushed and the water content is measured from the weight change before and after heat drying. Therefore, it is not possible to measure the water content of a plant while it is growing.

[0007] In view of the above circumstances, an object of the present invention is to provide a plant moisture content sensor and a plant moisture content measurement method that can measure the moisture content of a plant non-destructively. [Means for solving the problem]

[0008] The plant moisture content sensor of the first embodiment is characterized in that it comprises a moisture content probe having a readout electrode pair consisting of a pair of electrodes arranged at a predetermined distance and a water-sensitive membrane spanning the pair of electrodes, an electrical conductivity probe having an electrical conductivity electrode pair consisting of a pair of electrodes arranged at a predetermined distance, and a support portion that supports the moisture content probe and the conductivity probe in a parallel arrangement. The plant moisture content sensor of the second aspect is characterized in that, in the first aspect, it comprises a temperature probe having a temperature sensor, and the temperature probe is supported on the support part in a state aligned parallel to the moisture content probe. The plant water content sensor of a third aspect is the first or second aspect, characterized in that the water-sensitive film is formed of polyimide. The plant water content sensor of a fourth aspect is characterized in that in any one of the first to third aspects, the surface of the water-sensitive film is subjected to a hydrophilization treatment. The plant water content sensor of a fifth aspect is characterized in that, in any of the first to fourth aspects, the water-sensitive film is provided from the position where the readout electrode pair is arranged to the base end of the water content probe. The plant water content sensor of a sixth aspect is characterized in that in any one of the first to fifth aspects, the water content probe has a tip angle of 40 to 60°. The plant water content sensor of the seventh aspect is characterized in that, in the first aspect, the electrical conductivity probe has a plurality of the electrical conductivity electrode pairs, and the plurality of the electrical conductivity electrode pairs are arranged in line in the axial direction of the electrical conductivity probe. The plant moisture content sensor of the eighth aspect is characterized in that in the second aspect, it comprises a heater-equipped temperature probe having a temperature sensor and a heater, and the heater-equipped temperature probe is supported on the support part in a state aligned parallel to the temperature probe. A ninth aspect of the method for measuring water content in plants includes inserting a water content probe into a plant, the water content probe having a readout electrode pair consisting of a pair of electrodes arranged at a predetermined distance and a water-sensitive membrane spanning the pair of electrodes, inserting an electrical conductivity probe into the plant, the electrical conductivity probe having an electrical conductivity electrode pair consisting of a pair of electrodes arranged at a predetermined distance, determining electrical conductivity from the electrical resistance between the pair of electrodes that constitute the electrical conductivity electrode pair, determining the sensor sensitivity coefficient B in equation (1) from the measured electrical conductivity, measuring the impedance between the pair of electrodes that constitute the readout electrode pair, and determining the water content of the plant from the measured impedance based on equation (1). TIFF0007669049000001.tif14149Here, Z is the measured impedance value, Z0 is the impedance when the water-sensitive film has not absorbed water, B is the sensor sensitivity coefficient, and WC is the water content. The method for measuring water content in a plant of a tenth aspect is the ninth aspect, characterized in that the sensor sensitivity coefficient B is calculated from the measured electrical conductivity based on formula (2). TIFF0007669049000002.tif8149Here, B is the sensor sensitivity coefficient, σ is the electrical conductivity, and a and b are predetermined coefficients. Effect of the Invention

[0009] According to the first aspect, the water content of a plant can be measured by inserting the water content probe into the plant and reading out the impedance or capacitance from the readout electrode pair. Also, the water content of a plant can be measured with high accuracy by compensating the measured water content value based on the electrical conductivity of the water in the plant measured by the electrical conductivity probe. According to the second aspect, the water content of the plant can be measured with high accuracy by compensating the measured water content electric potential or electrical conductivity value based on the temperature of the water in the plant measured by the temperature probe. According to the third aspect, since the water-sensitive film is made of polyimide, the water-sensitive film is less likely to dissolve in the water in the plant, and therefore long-term measurement is possible. According to the fourth aspect, since the surface of the water-sensitive film is hydrophilized, the response speed of the water content measurement is increased. According to the fifth aspect, a part of the water-sensing film is disposed outside the plant, so that dehydration from the water-sensing film is smoothly carried out, and the response speed when the water content decreases is increased. According to the sixth aspect, the tip of the moisture content probe is sharp, so that when the probe is pierced into a plant, the water content in the plant is prevented from flowing out, and therefore the water content of the plant can be measured with high accuracy. According to the seventh aspect, since the electrical conductivity electrode pair is arranged side by side in the axial direction of the electrical conductivity probe, the electrical conductivity distribution inside the plant can be determined and the position of the xylem can be accurately determined. According to the eighth aspect, since the vascular sap flow rate can be measured in addition to the water content of the plant, the water dynamics of the plant can be understood from multiple angles. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a plan view of a plant water content sensor according to a first embodiment. [Diagram 2] FIG. 2 is a side view of the plant water content sensor according to the first embodiment. [Diagram 3] 3 is a cross-sectional view taken along line III-III in FIG. 1. [Figure 4] FIG. 2 is an explanatory diagram of a usage state of the plant water content sensor according to the first embodiment. [Diagram 5] FIG. 11 is a plan view of a plant water content sensor according to a second embodiment. [Figure 6] FIG. 11 is a plan view of a plant water content sensor according to a third embodiment. [Figure 7] 1 is an explanatory diagram of the tip angle θ, width W, and thickness T of a probe. [Figure 8] 13 is a graph showing test results of response characteristics. [Figure 9] 1 is a graph showing the relationship between moisture content and impedance. [Figure 10] 1 is a graph showing the change over time in water content (impedance) of tomatoes under different growing conditions. [Figure 11] 1 is a graph showing the relationship between moisture content and impedance. [Figure 12] 1 is a graph showing the relationship between electrical conductivity and sensor sensitivity coefficient. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Next, an embodiment of the present invention will be described with reference to the drawings. [First embodiment] The plant moisture content sensor 1 according to the first embodiment of the present invention can be attached to the details of a plant, such as the shoot end, fruit stalk, etc. The plant moisture content sensor 1 has a function of measuring the moisture content in the details of a plant.

[0012] (Plant water content sensor) First, the configuration of the plant water content sensor 1 will be described. 1, the plant moisture content sensor 1 includes a support 10. The support 10 is provided with a moisture content probe 20, an electrical conductivity probe 30, and a temperature probe 40. The plant moisture content sensor 1 is attached to the plant by inserting these probes 20, 30, and 40 into the plant.

[0013] The moisture content probe 20 is used to measure the moisture content of the plant. The electrical conductivity probe 30 is used to measure the electrical conductivity of the moisture in the plant. The measured electrical conductivity is used to compensate the moisture content measurement value. Therefore, in cases where there is no need for compensation based on electrical conductivity, the plant moisture content sensor 1 does not need to be provided with the electrical conductivity probe 30. The temperature probe 40 is used to measure the temperature of the moisture in the plant. The measured temperature is used to compensate for either or both of the moisture content measurement value and the electrical conductivity measurement value. Therefore, in cases where there is no need for compensation based on temperature, the plant moisture content sensor 1 does not need to be provided with the temperature probe 40.

[0014] The probes 20, 30, 40 are arranged in parallel on the same plane, with their base ends supported by the support 10. The order in which the probes 20, 30, 40 are arranged is not particularly limited. However, when both the moisture content measurement value and the electrical conductivity measurement value are temperature compensated, it is preferable to place the temperature probe 40 near both the moisture content probe 20 and the electrical conductivity probe 30. In other words, it is preferable to place the temperature probe 40 between the moisture content probe 20 and the electrical conductivity probe 30.

[0015] The support 10 and the probes 20, 30, 40 are formed by processing a semiconductor substrate. Examples of the semiconductor substrate include a silicon substrate and an SOI (Silicon on Insulator) substrate. The semiconductor substrate is processed using MEMS techniques such as photolithography, etching, and thin film formation such as sputtering and vapor deposition.

[0016] ·Support part The support part 10 is a member that supports the probes 20, 30, and 40. The support part 10 is a plate material that is rectangular in plan view, and all of the probes 20, 30, and 40 are supported on one long side. The length of the support part 10 in the longitudinal direction may be long enough to arrange all of the probes 20, 30, and 40 at a predetermined interval. The length of the short side of the support part 10 is not particularly limited.

[0017] ·probe Each of the probes 20, 30, 40 is a rod-shaped member and is provided in a cantilever shape on the edge (long side) of the support part 10. The tip of each of the probes 20, 30, 40 is preferably formed into a pointed shape such as a triangle. If the tip of the probes 20, 30, 40 is sharp, the insertion resistance when the probes 20, 30, 40 are inserted into the fine parts of a plant can be reduced.

[0018] Specifically, the tip angle of each of the probes 20, 30, 40 is preferably 40 to 60°. When the probes 20, 30, 40 are pierced into a plant, the pierced part and the cells around it may be destroyed, causing water in the plant to flow out. The measured water content becomes smaller than the actual value due to the amount of water that flows out. The sharper the tip of the probes 20, 30, 40, the more water can be suppressed from flowing out of the plant. If the tip angle of the probes 20, 30, 40 is 60° or less, the tip is sufficiently sharp, so that the water in the plant can be suppressed from flowing out when the probes are pierced into the plant. Therefore, the water content of the plant can be measured with high accuracy. On the other hand, if the tip angle of the probes 20, 30, 40 is made too small, the width of the probes 20, 30, 40 becomes too thin, making it impossible to secure an area for mounting the element described later, or the axial length becomes too long. If the tip angle of the probes 20, 30, 40 is set to 40° or more, the width and length of the probes 20, 30, 40 can be made to be of appropriate dimensions.

[0019] Each of the probes 20, 30, 40 is formed to a size that allows it to be inserted into the small part of the plant having a stem or axial diameter of about several mm, such as the shoot end or fruit stalk. The length of each of the probes 20, 30, 40 (length from the base end to the tip in the axial direction) is formed to a size that allows the tip of the probe to be placed in the xylem or phloem of the plant when it is inserted into the small part of the plant. For example, the length of each of the probes 20, 30, 40 is 50 to 1,500 μm.

[0020] The width of each of the probes 20, 30, 40 is not particularly limited, but is, for example, 50 to 500 μm. The narrower the width of the probes 20, 30, 40, the less damage can be caused to the plant.

[0021] As shown in FIG. 2, each of the probes 20, 30, 40 is formed thinner than the thickness of the support 10 by removing the lower part of the semiconductor substrate SS. The thickness of each of the probes 20, 30, 40 is set thinner than the width of the phloem and xylem of the plant. The thickness of each of the probes 20, 30, 40 depends on the type of plant and the thickness of the stem to be measured, but is, for example, 50 to 300 μm. If the thickness is 50 μm or more, the strength is sufficient and there is no risk of the probes 20, 30, 40 breaking when inserted into or removed from the stem of the plant. In addition, since the thickness of the xylem and xylem is about 100 to 400 μm depending on the type of plant, if the thickness is 300 μm or less, the probes 20, 30, 40 can be prevented from blocking the xylem or xylem even if they are inserted into the xylem or xylem.

[0022] It is more preferable that the thickness of each of the probes 20, 30, 40 is 50 to 100 μm. The thinner the probes 20, 30, 40, the less damage they cause to the plant. If the thickness of each of the probes 20, 30, 40 is 100 μm or less, the outflow of water from within the plant can be suppressed, and the water content of the plant can be measured with high accuracy.

[0023] The probes 20, 30, 40 having such shapes are formed, for example, by the following procedure. Photolithography of the probe shape is performed on the semiconductor substrate SS, and unnecessary parts are removed by dry etching such as ICP-RIE to form the original probe shape. Next, the semiconductor substrate SS is etched from the back surface so that the probes 20, 30, 40 have a cantilever shape. In this process, dry etching such as ICP-RIE is used. The semiconductor substrate SS is etched from the back surface, and the etching is stopped when the probes 20, 30, 40 are separated. In this way, the cantilever-shaped probes 20, 30, 40 can be formed.

[0024] Moisture content probe As shown in Fig. 1, the moisture content probe 20 is provided at its tip with a readout electrode pair 21. The readout electrode pair 21 is made up of a pair of electrodes 22, 22 arranged at a predetermined distance. Two electrode pads 22e, 22e connected to the two electrodes 22 via wiring are provided on the upper surface of the support 10. In addition, the moisture content probe 20 is provided with a water-sensitive film 23.

[0025] When the water content probe 20 is inserted into a plant, the water in the plant is absorbed into the water-sensitive film 23. The amount of water absorbed into the water-sensitive film 23 is read out as the impedance or capacitance between the electrodes 22, 22. This allows the water content of the plant to be measured.

[0026] 3, a pair of electrodes 22, 22 are formed on the surface of a semiconductor substrate SS constituting the moisture content probe 20. There are no particular limitations on the size of the electrode 22 as long as it can be disposed at the tip of the moisture content probe 20. The electrode 22 is formed, for example, by depositing a thin metal film of Au, Al, etc., on the semiconductor substrate SS by a sputtering method, a vapor deposition method, or the like.

[0027] The water-sensitive film 23 is formed on the pair of electrodes 22, 22 so as to span them. The water-sensitive film 23 has a function of absorbing moisture and is formed of a material having a lower relative dielectric constant than water. In this specification, the term "water-sensitive film" means a film having a function of absorbing moisture and formed of a material having a lower relative dielectric constant than water. Since the relative dielectric constant of water at a temperature of 20°C is about 80, it is sufficient that the relative dielectric constant of the water-sensitive film 23 is smaller than 80. However, since the greater the difference between the relative dielectric constant of the water-sensitive film 23 and the relative dielectric constant of water, the higher the measurement accuracy of the moisture content, the relative dielectric constant of the water-sensitive film 23 is preferably 1 to 3.

[0028] The material of the water-sensitive film 23 is preferably insoluble in water and thermally and chemically stable. Lithium chloride, metal oxides, ceramics, polymeric materials, etc. can be used as the material of the water-sensitive film 23. However, lithium chloride is toxic to plants, and therefore cannot be said to be excellent in applicability to plants. Examples of metal oxides and ceramics include aluminum oxide (Al2O3) and silicon dioxide (SiO2). Metal oxides and ceramics are insoluble in water. However, metal oxides and ceramics are hard materials and require high-temperature heat treatment during the manufacturing process. In contrast, polymeric materials are excellent in applicability to plants and are soft materials. Examples of polymeric materials include polyimide and polyvinyl alcohol. Among these, polyimide is preferable from the viewpoint of ease of mounting on a semiconductor Si substrate. In addition, polyimide is difficult to dissolve in water, so it is suitable for long-term measurement of moisture in plants. Therefore, if the water-sensitive film 23 is formed of polyimide, the water-sensitive film 23 is difficult to dissolve in moisture in plants, and long-term measurement is possible.

[0029] When the water-sensitive film 23 is made of a polymeric material, the surface of the water-sensitive film 23 may be hydrophilized. This makes it easier for the water-sensitive film 23 to absorb moisture from within the plant, and the response speed of the moisture content measurement becomes faster. For example, when the water-sensitive film 23 is made of polyimide, the surface of the water-sensitive film 23 may be oxygen plasma treated. When the surface of the polyimide is oxygen plasma treated, carbonyl groups are introduced and the surface of the polyimide is made hydrophilic. This also has the effect of increasing the surface area of ​​the polyimide. As the water-sensitive film 23 is hydrophilized and its surface area increases, the water-sensitive film 23 is easier to absorb moisture from within the plant, and the response speed of the moisture content measurement becomes faster.

[0030] Electrical Conductivity Probe As shown in Fig. 1, an electrical conductivity electrode pair 31 is provided at the tip of an electrical conductivity probe 30. The electrical conductivity electrode pair 31 is composed of a pair of electrodes 32, 32 arranged at a predetermined interval. The electrical conductivity electrode pair 31 is for measuring the electrical conductivity of water (such as vascular bundle sap) present between the electrodes 32, 32. The electrode 32 is not particularly limited as long as it has a size that can be arranged at the tip of the electrical conductivity probe 30. The electrode 32 is formed by depositing a thin metal film such as Au or Al on a semiconductor substrate SS by, for example, a sputtering method, a vapor deposition method, or the like.

[0031] Two electrode pads 32e, 32e connected to the two electrodes 32, 32 via wiring are disposed on the upper surface of the support 10. The electrical conductivity can be measured by an AC two-electrode method. That is, an AC power source and an ammeter are connected in series between a pair of electrode pads 32e, 32e corresponding to a pair of electrodes 32, 32. A current is supplied between the electrodes 32, 32 by the AC power source, and the current flowing between the electrodes 32, 32 is measured by the ammeter. Based on Ohm's law, the electrical resistance between the electrodes 32, 32 is calculated from the current measured by the ammeter, and the electrical conductivity is obtained from the electrical resistance.

[0032] To measure the electrical conductivity of water in a plant, it is preferable that the measurement range of electrical conductivity is at least 0 to 10 mS / cm. The measurement range of electrical conductivity by the AC two-electrode method depends on the cell constant K of the electrode pair. Here, the cell constant K is calculated by dividing the inter-electrode distance L by the electrode surface area S. In other words, the measurement range of electrical conductivity depends on the shape of the electrode 32. The shape of the electrode 32 can be selected from various shapes such as a three-dimensional electrode, a comb-shaped electrode, and a flat electrode.

[0033] Temperature probe A temperature sensor 41 is provided at the tip of the temperature probe 40. The temperature sensor 41 has a function of sensing temperature, and is not particularly limited as long as it is of a size that can be arranged at the tip of the temperature probe 40. The temperature sensor 41 may be a resistance temperature detector, a pn junction diode, a thermocouple, or the like. Since the plant water content sensor 1 is expected to be used outdoors, it is preferable to use a resistance temperature detector that is not light-dependent as the temperature sensor 41. In addition, two electrode pads 41e, 41e connected to the temperature sensor 41 via wiring are provided on the upper surface of the support 10.

[0034] The resistance temperature sensor is formed by depositing a thin film of a metal suitable for a resistance temperature sensor, such as Au, on the semiconductor substrate SS by, for example, sputtering or vapor deposition. The electrical resistance of the resistance temperature sensor increases with increasing temperature. A constant current source is connected between the two electrode pads 41e, 41e. The constant current source supplies a constant current to the resistance temperature sensor, and the voltage is measured by a voltmeter. The temperature can be calculated from the voltage measured by the voltmeter.

[0035] The moisture content probe 20, the electrical conductivity probe 30, and the temperature probe 40 may each be configured as separate probes, or some or all of them may be configured as a single probe. In other words, the read electrode pair 21, the water-sensitive membrane 23, the electrical conductivity electrode pair 31, and the temperature sensor 41 may all be mounted on a single probe.

[0036] (Manufacturing method) Next, an example of a method for manufacturing the plant water content sensor 1 will be described. First, the surface of the silicon substrate is wet oxidized to form an oxide film. Next, Cr is sputtered onto the oxide film as an adhesive layer, and Au is sputtered onto the adhesive layer to form various electrodes, resistance temperature detectors, and wiring. Next, a resist is applied to form a wiring protection film. Next, polyimide is applied to form the water-sensitive film 23. Finally, unnecessary parts of the silicon substrate are removed by dry etching to form the probes 20, 30, and 40.

[0037] It should be noted that the plant water content sensor 1 may be formed by a method other than the MEMS technology as long as it can be formed to have the above-mentioned dimensions and functions, and the material is not limited to a silicon substrate.

[0038] (Plant water content measurement method) Next, a method for measuring the water content using the plant water content sensor 1 will be described.

[0039] ·attachment First, the plant water content sensor 1 is attached to the shoot end, fruit stalk, etc. of the plant to be measured. Specifically, as shown in Fig. 4, all the probes 20, 30, 40 of the plant water content sensor 1 are pierced and attached to the plant. At this time, the probes 20, 30, 40 are arranged along the xylem XY and phloem PH of the plant.

[0040] When the probes 20, 30, 40 are inserted into the plant, the tips of the probes 20, 30, 40 pass through the cortex CO of the plant and reach the phloem PH. When the probes are inserted deeper, the tips of the probes 20, 30, 40 reach the xylem XY and then the pith PI. The electrical conductivity of water in the plant depends heavily on the water absorbed from the soil, i.e., the xylem sap. For this reason, it is preferable to place the electrical conductivity probe 30 and the temperature probe 40 in the xylem XY.

[0041] Incidentally, it is sufficient that the water-sensitive film 23 is formed in an area that at least covers the readout electrode pair 21. However, it is preferable that the water-sensitive film 23 is provided from the arrangement part of the readout electrode pair 21 to the base end of the moisture content probe 20. It is more preferable that the water-sensitive film 23 is provided so as to cover a part of the upper surface of the support part 10 from the base end of the moisture content probe 20. In this way, a part of the water-sensitive film 23 is provided outside the plant.

[0042] The water-sensing membrane 23 absorbs water according to the amount of water in the plant. To detect a decrease in water content in the plant, it is necessary to dehydrate the water absorbed by the water-sensing membrane 23. If a part of the water-sensing membrane 23 is placed outside the plant, dehydration is promoted from this part exposed to the outside air. As dehydration from the water-sensing membrane 23 is performed smoothly, the response speed when the water content decreases becomes faster.

[0043] Moisture content measurement (impedance method) When the water content probe 20 is inserted into a plant, the water in the plant is absorbed by the water-sensitive film 23. The amount of water absorbed by the water-sensitive film 23 changes according to the amount of water in the plant. Also, the impedance between the electrodes 22, 22 constituting the read electrode pair 21 changes according to the amount of water absorbed by the water-sensitive film 23.

[0044] The relationship between the impedance Z [kΩ] between the electrodes 22, 22 and the water content WC [%] of the plant is expressed by equation (1).

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[0045] Z0 and B are determined in advance by testing. When measuring the water content of a plant, the impedance Z between the electrodes 22, 22 is measured. Then, the water content WC of the plant is calculated from the impedance measurement Z based on equation (1).

[0046] Moisture content measurement (capacitive method) There is a relationship in which an increase in the amount of water absorbed by the water-sensitive film 23 increases the capacitance between the electrodes 22, 22 that make up the readout electrode pair 21. In particular, if the material of the water-sensitive film 23 is appropriately selected, a linear relationship will be established between the amount of water absorbed by the water-sensitive film 23 and the capacitance between the electrodes 22, 22. This relationship is determined in advance by testing. When measuring the water content of a plant, the capacitance C between the electrodes 22, 22 is measured. Then, based on the relationship between the capacitance and the water content, the water content WC of the plant is determined from the measured capacitance C.

[0047] As described above, by inserting the water content probe 20 into a plant and reading out the impedance or capacitance from the read electrode pair 21, the water content of the plant can be measured.

[0048] Electrical conductivity compensation The moisture content measurement value obtained by the moisture content probe 20 depends on the electrical conductivity of the water in the plant. Therefore, it is preferable to compensate the moisture content measurement value with the electrical conductivity. The electrical conductivity of the water (mainly xylem sap) in the plant can be measured by the electrical conductivity electrode pair 31 of the electrical conductivity probe 30. The moisture content measurement value is compensated based on the electrical conductivity measured by the electrical conductivity probe 30. This allows the moisture content of the plant to be measured with high accuracy.

[0049] For example, when the water content is determined from the impedance between electrodes 22, 22, the sensor sensitivity coefficient B in formula (1) is determined in advance using solutions with various electrical conductivities. When measuring the water content of a plant, the electrical conductivity of the water inside the plant is measured at the same time. The water content WC of the plant is determined from the impedance Z based on formula (1) to which the sensor sensitivity coefficient B corresponding to the measured electrical conductivity is applied. In this way, the measured water content value can be compensated by determining the sensor sensitivity coefficient B from the measured electrical conductivity.

[0050] The inventors of the present application have also found that the sensor sensitivity coefficient B is linearly dependent on the electrical conductivity σ. Therefore, the impedance Z is measured in advance by the moisture content probe 20 using solutions with various electrical conductivities σ, the sensor sensitivity coefficient B in formula (1) is determined, and the relationship between the electrical conductivity σ and the sensor sensitivity coefficient B is fitted with a linear function. In other words, the coefficients a and b are determined in the relationship between the electrical conductivity σ and the sensor sensitivity coefficient B expressed by the following formula (2).

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[0051] When measuring the water content of a plant, the impedance Z is measured by the water content probe 20, and the electrical conductivity σ is measured by the electrical conductivity probe 30. A sensor sensitivity coefficient B is calculated from the measured electrical conductivity value σ based on equation (2). The water content WC of the plant is calculated from the impedance Z based on equation (1) to which the calculated sensor sensitivity coefficient B is applied.

[0052] Similarly, when determining the water content from the capacitance between the electrodes 22, 22, solutions of various electrical conductivities are used to determine in advance the relationship between the amount of water absorbed by the water-sensitive film 23 and the capacitance between the electrodes 22, 22. When measuring the water content of the plant, the electrical conductivity of the water in the plant is measured at the same time. Based on the water amount-capacity relationship corresponding to the measured electrical conductivity, the water content WC of the plant is determined from the capacitance C.

[0053] The electrical conductivity of water within a plant is itself physiological information useful for plant production. By placing the tip of the electrical conductivity probe 30 in the xylem XY, the electrical conductivity of the xylem sap can be measured. Fertilizer spread on the soil is decomposed into salts such as nitrate nitrogen by microorganisms. There is also a positive correlation between the salt concentration and electrical conductivity. Therefore, by measuring the electrical conductivity of the xylem sap, it is possible to quantify the nutrients taken up by the plant.

[0054] ·Temperature compensation The electrical conductivity measurements obtained by the electrical conductivity probe 30 depend on temperature. In general, the electrical conductivity measurements change by 1 to 3% per 1°C. Therefore, it is preferable to temperature compensate the electrical conductivity measurements. The temperature of the water (mainly xylem sap) in the plant can be measured by the temperature sensor 41 of the temperature probe 40. The electrical conductivity measurements are compensated based on the temperature measured by the temperature probe 40. This allows the electrical conductivity of the water in the plant to be determined with high accuracy. The water content can be determined with high accuracy by further compensating the water content measurement using the electrical conductivity after temperature compensation.

[0055] Temperature compensation of the measured electrical conductivity is performed, for example, by the following procedure. That is, the measured electrical conductivity is converted into electrical conductivity σ at a reference temperature of 25° C. based on the formula (3). 25 [S / m], where α is the temperature coefficient, T is the temperature of the liquid being measured [℃], and σ is the measured electrical conductivity [S / m].

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[0056] The temperature coefficient α is calculated from formula (4), where T1 is a temperature [°C] other than 25°C and T2, T2 is a temperature [°C] other than 25°C and T1, σ1 is the measured electrical conductivity [S / m] at T1, and σ2 is the measured electrical conductivity [S / m] at T2.

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[0057] When the water-sensitive film 23 is made of polyimide, the measured water content value measured by the water content probe 20 does not depend on temperature. However, when the water-sensitive film 23 is made of another material, the measured water content value may depend on temperature. In such a case, the measured water content value may be temperature compensated. That is, the measured water content value is directly compensated based on the temperature measured by the temperature probe 40. This allows the water content to be measured with high accuracy.

[0058] The plant moisture content sensor 1 can be used to non-destructively measure the moisture content of plants, particularly in the fine details of the plant, such as the shoot tips and fruit stalks. For example, it is known that tomatoes have a higher sugar content when grown under moisture stress. The plant moisture content sensor 1 can provide an indicator to avoid extreme moisture deficiency and fruit cracking caused by a sudden flow of vascular sap into the fruit, making it possible to apply appropriate moisture stress. In this way, it can be used for the stable production of high quality crops and fruit trees.

[0059] Second Embodiment Next, a plant water content sensor 2 according to a second embodiment of the present invention will be described. 5, in the plant water content sensor 2 of this embodiment, the electrical conductivity probe 30 is formed to be longer than the other probes 20 and 40. In addition, the electrical conductivity probe 30 has a plurality of electrical conductivity electrode pairs 31 arranged side by side in the axial direction.

[0060] 5, the electrical conductivity probe 30 is provided with two electrical conductivity electrode pairs 31. The electrical conductivity electrode pair 31 on the base end side is disposed at approximately the same position as the temperature sensor 41 of the temperature probe 40 in the direction of piercing the plant. The electrical conductivity electrode pair 31 on the tip end side is disposed at a deeper position than the temperature sensor 41 when pierced into the plant.

[0061] Since xylem sap contains salts such as nitrate nitrogen, it has the property of having a higher electrical conductivity than the water contained in other parts (cortex CO, phloem PH, pith PI, etc.). By inserting the electrical conductivity probe 30, the electrical conductivity distribution inside the plant can be seen and the position of xylem XY can be accurately determined. By positioning the electrical conductivity electrode pair 31 on the base end side at xylem XY, the probes 20, 30, 40 can be inserted to an appropriate depth.

[0062] Third Embodiment Next, a plant water content sensor 3 according to a third embodiment of the present invention will be described. The plant water content sensor 3 has a function of measuring the vascular sap flow rate in addition to the water content of a plant.

[0063] (Plant water content sensor) 6, the plant moisture content sensor 3 of this embodiment is the same as the plant moisture content sensor 1 of the first embodiment except that the temperature probes 40 are replaced by two, a first temperature probe 40A and a second temperature probe 40B, and a heater-equipped temperature probe 50 is added. Since the rest of the configuration is the same as in the first embodiment, the same members are denoted by the same reference numerals and the description thereof will be omitted.

[0064] The first and second temperature probes 40A, 40B are used in combination with the heater-equipped temperature probe 50 to measure the vascular bundle sap flow rate. The temperature measured by the first temperature probe 40A is also used for temperature compensation of the moisture content measurements and electrical conductivity measurements.

[0065] The first and second temperature probes 40A, 40B and the heater-equipped temperature probe 50 are arranged in parallel with the other probes 20, 30 in the same plane, with their base ends supported by the support part 10. The first and second temperature probes 40A, 40B are provided in positions sandwiching the heater-equipped temperature probe 50. The first and second temperature probes 40A, 40B and the heater-equipped temperature probe 50 have the same shape and dimensions as the other probes 20, 30.

[0066] Temperature probe The first and second temperature probes 40A and 40B each have a configuration similar to that of the temperature probe 40 of the first embodiment. That is, the first and second temperature probes 40A and 40B each have a temperature sensor 41 at the tip. The temperature sensor 41 can measure the temperature of the vascular bundle sap.

[0067] -Heated temperature probe A temperature sensor 51 is provided at the tip of the heater-equipped temperature probe 50. The same temperature sensor 51 as the temperature sensor 41 of the temperature probe 40 can be used as the temperature sensor 51. Two electrode pads 51e connected to the temperature sensor 51 via wiring are provided on the upper surface of the support part 10. The temperature sensor 51 can measure the temperature in a similar manner to the temperature sensor 41 of the temperature probe 40.

[0068] The heater-equipped temperature probe 50 is provided with a heater 52. The heater 52 may be located at any position other than the tip as long as it can supply heat to the heater-equipped temperature probe 50. The heater 52 is not particularly limited as long as it is of a size that can be disposed in the heater-equipped temperature probe 50. For example, a pn junction diode formed using an oxidation diffusion furnace can be used as the heater 52. The heater 52 may also be formed by forming a thin film of Pt (platinum), NiCr (nichrome), or ITO (indium tin oxide material) by a sputtering method, a vapor deposition method, or the like, and processing it into a predetermined shape.

[0069] Two electrode pads 52e connected to the heater 52 via wiring are disposed on the upper surface of the support 10. A DC constant voltage source is connected between the two electrode pads 52e, 52e. The DC constant voltage source supplies a constant voltage in the forward direction to the heater 52, which is a pn junction diode. Heat can be generated by passing a current through the heater 52.

[0070] (Measurement method) Next, a method for measuring the vascular sap flow rate using the plant water content sensor 3 will be described.

[0071] As shown in Figure 6, the plant water content sensor 3 is attached by inserting all of the probes 20, 30, 40A, 40B, 50 into the plant. When measuring the flow rate of phloem sap, the tips of the first and second temperature probes 40A, 40B and the heater-equipped temperature probe 50 are placed in the phloem PH. When measuring the flow rate of xylem sap, the tips of the first and second temperature probes 40A, 40B and the heater-equipped temperature probe 50 are placed in the xylem XY. Below, an example of measuring the flow rate of xylem sap will be explained.

[0072] First, the heater 52 provided in the heater-equipped temperature probe 50 is operated. When the heater 52 is operated, thermal energy is supplied from the heater 52 to the heater-equipped temperature probe 50. The thermal energy supplied to the heater-equipped temperature probe 50 is released from the surface of the heater-equipped temperature probe 50 to the vessel liquid flowing inside the vessel XY.

[0073] At this time, the temperatures of the first and second temperature probes 40A, 40B and the heater-equipped temperature probe 50 are measured by the temperature sensors 41, 41, 51. Then, the temperatures of the first temperature probe 40A and the second temperature probe 40B are compared to identify the direction of the vessel flow.

[0074] Assume that the direction of xylem flow is upward in Fig. 6. The first and second temperature probes 40A, 40B are positioned on either side of the heater-equipped temperature probe 50. The temperature of the xylem liquid is raised by the heater-equipped temperature probe 50. Therefore, the temperature measured by the first temperature probe 40A located downstream of the heater-equipped temperature probe 50 is higher than the temperature measured by the second temperature probe 40B located upstream. Using this, the direction of xylem flow can be identified as the direction from the second temperature probe 40B, which has a lower temperature, to the first temperature probe 40A, which has a higher temperature.

[0075] Next, the flow rate of xylem liquid is measured based on the Granier method from the temperatures measured by the first and second temperature probes 40A, 40B and the heater-equipped temperature probe 50. Here, calculations are made based on the temperature difference between the second temperature probe 40B, which has the lower temperature of the first and second temperature probes 40A, 40B, and the heater-equipped temperature probe 50. The second temperature probe 40B, which has the lower temperature, is positioned upstream of the heater-equipped temperature probe 50 in the xylem flow.

[0076] For example, when the flow rate of xylem liquid is high (flow velocity is fast), the xylem liquid near the heater-equipped temperature probe 50 is constantly being replaced with new xylem liquid. Therefore, if the thermal energy supplied to the heater-equipped temperature probe 50 is constant, the temperature of the heater-equipped temperature probe 50 will be low. On the other hand, when the flow rate of xylem liquid is low (flow velocity is slow), the xylem liquid near the heater-equipped temperature probe 50 will be in a stagnant state. Therefore, if the thermal energy supplied to the heater-equipped temperature probe 50 is constant, the temperature of the heater-equipped temperature probe 50 will be high.

[0077] Therefore, the flow velocity of the vessel liquid can be obtained from the temperature difference ΔT between the second temperature probe 40B and the heater-equipped temperature probe 50. Specifically, as shown in equation (5), the temperature difference ΔT is a function of the flow velocity u. Based on this function, the flow velocity u can be calculated from the temperature difference ΔT.

number

[0078] In addition, the flow rate F can be calculated from the flow velocity u based on equation (6).

number

[0079] If the tips of the first and second temperature probes 40A, 40B and the heater-equipped temperature probe 50 are placed in the phloem PH of the plant, the flow velocity and flow rate of the phloem sap can be determined as well as the phloem flow direction. The plant water content sensor 3 can also measure the flow rate of the vascular sap by a heat pulse method. The plant water content sensor 3 may be provided with only one temperature probe 40. The flow rate of the vascular sap can also be measured with this configuration.

[0080] In this way, the plant water content sensor 3 can measure the vascular sap flow rate in addition to the water content of the plant. This allows the water dynamics of the plant to be understood from multiple angles, providing a more detailed understanding of the plant's condition. EXAMPLES

[0081] (Tip angle) First, a test was performed on the tip angle of the probe. As shown in Figure 7, a flat probe was fabricated using a silicon substrate. The tip angle θ, width W, and thickness T of the probe are defined as shown in Figure 7. Four probes were fabricated with tip angles θ of 136°, 120°, 90°, and 60°. All of the probes have a width W of 480 μm and a thickness T of 300 μm.

[0082] A sample (PDMS: Polydimethylsiloxane, DuPont Toray Specialty Materials Co., Ltd.) with a Young's modulus (2.2 MPa) similar to that of plants was prepared. The resistance when each probe was inserted into the sample was measured using a force sensor (DynPick WEF-6A, Wacotec Co., Ltd.). The results showed that the resistance when the probe penetrated the sample was as shown in Table 1. Table 1 shows that the smaller the tip angle θ of the probe, the smaller the resistance to penetration. [Table 1]

[0083] Next, the state of each probe when it was inserted into a cucumber stem was observed under a microscope. When the probes had tip angles θ of 136°, 120°, and 90°, deformation of the stem and outflow of water from the stem were confirmed. On the other hand, when the probe had a tip angle θ of 60°, neither deformation of the stem nor outflow of water from the stem was confirmed. This confirmed that if the tip angle θ of the probe is 60° or less, it is possible to suppress the outflow of water from within the plant when it is inserted into the plant.

[0084] (Sensor manufacturing) Next, a plant water content sensor with the configuration shown in Figure 1 was fabricated using a silicon substrate. The tip angle θ of each probe is 60°, the width W is 480 μm, the thickness T is 300 μm, and the length (length from the base end to the tip in the axial direction) is 1,200 μm. Various electrodes, resistance temperature detectors, and wiring are made of Au. The water-sensitive film is made of polyimide.

[0085] (Response characteristics) Next, the response characteristics of the fabricated plant water content sensor were evaluated. Absorbent cotton was soaked in 0.05 mol / L KCl solution, and two types of absorbent cotton were prepared by adjusting the moisture content to 90% or 60% using an electronic balance (AUW220D, Shimadzu Corporation, the same applies below).

[0086] Each cotton wool was placed in contact with the water-sensitive film of the moisture content probe and then removed after a certain period of time. The change in impedance measured by the moisture content probe over time during this period is shown in the graph of Figure 8.

[0087] From the graph in Figure 8, the impedance measurement value stabilizes about 20 seconds after the absorbent cotton is brought into contact with the water-sensitive film. Also, the impedance measurement value stabilizes about 30 seconds after the absorbent cotton is removed from the water-sensitive film. This shows that the response speed of the moisture content probe is about 30 seconds. Compared to the time scale of plant irrigation (several hours), this response speed is sufficiently fast.

[0088] In addition, after the absorbent cotton is brought into contact with the water-sensitive film and the impedance measurement value stabilizes, the impedance measurement value remains almost constant until the absorbent cotton is removed. This confirms the stability of the moisture content measurement. Furthermore, after the absorbent cotton is removed from the water-sensitive film, the impedance returns to the value before the absorbent cotton was brought into contact with the water-sensitive film. This confirms that the moisture content has sufficient reproducibility. From the above, it is confirmed that the moisture content probe has good response characteristics.

[0089] (calibration) Next, the moisture content measurement was calibrated. A plant moisture content sensor was attached to a cutting of a tomato (Solanum Lycopersicum L., the same applies below) placed on an electronic balance. The electronic balance measured the change in moisture content of the cutting as it dried. The moisture content probe also measured the change in impedance over time. The results are shown in Figure 9. The electrical conductivity of the moisture in the cutting was measured with an electrical conductivity probe, which was 4.8 mS / cm. The temperature of the moisture in the cutting was measured with a temperature probe, which was 26°C.

[0090] As can be seen from the graph in Figure 9, the impedance changes exponentially with the change in moisture content. When the measurement points were fitted with equation (1), Z0 = 1.27 × 10 3 , B=0.0165. Furthermore, the moisture content of a typical plant is 98-60%. From the graph in FIG. 9, it was confirmed that the plant moisture content sensor can measure moisture content in the range of 100-40%, which covers the range of moisture content of a typical plant.

[0091] (Measurements under growing conditions) Next, the water content of tomatoes was measured under natural conditions. A plant moisture sensor was attached to the stem of a tomato plant that was sown in culture soil (420036, DCM Holdings Co., Ltd.) and grown in an artificial weather chamber (NC-HC, Nippon Medical and Chemical Equipment Co., Ltd.). The plant moisture sensor was attached 150 mm from the soil surface. The environment inside the artificial weather chamber was set to a temperature of 25°C, humidity of 70%, and carbon dioxide concentration of 500 ppm. The amount of light inside the artificial weather chamber was changed to match the actual time. Water-stress cultivation was performed by providing 500 mL of water only twice, at the start of measurement and after five days had passed. Figure 10 shows the change in moisture content over time measured by the plant moisture sensor during this period.

[0092] As shown in Figure 10, the water content changes depending on the time of day and night, and decreases with each passing day. Furthermore, the water content after watering at the start of the measurement is about the same as the water content after watering five days later. This change in water content can be said to reproduce the change in plant water content caused by rainfall. This confirmed that the plant water content sensor can measure plant water content non-destructively in real time.

[0093] (Electrical conductivity compensation) Next, the relationship between the sensor sensitivity coefficient B in formula (1) and the electrical conductivity σ was confirmed. Three types of KCl solutions with adjusted electrical conductivity σ of 1.9, 5.4, and 9.7 mS / cm were prepared. Absorbent cotton was soaked in the KCl solution, and the moisture content was measured using an electronic balance. The absorbent cotton was also brought into contact with the water-sensitive film of the moisture content probe, and the impedance was measured. This procedure was performed for each of the three types of KCl solutions, while changing the moisture content of the absorbent cotton. The relationship between the moisture content and the impedance obtained as a result is shown in Figure 11.

[0094] The measurement points shown in Figure 11 were fitted with equation (1) to determine the sensor sensitivity coefficient B. Figure 12 shows the relationship between the electrical conductivity σ of the KCl solution and the sensor sensitivity coefficient B. Figure 12 shows that there is a linear relationship between the electrical conductivity σ and the sensor sensitivity coefficient B. When the measurement points shown in Figure 12 were fitted with a linear function, the coefficients in equation (2) for the fabricated moisture content probe were determined to be a = 0.0006 and b = 0.0064.

[0095] From the above, it was confirmed that if the relationship between the sensor sensitivity coefficient B and the electrical conductivity σ is determined in advance through testing or other means, the moisture content measurement value obtained with the moisture content probe can be compensated for by the electrical conductivity. [Explanation of symbols]

[0096] 1, 2, 3 Plant Water Content Sensor 10 Support part 20 Moisture Probe 21 Readout electrode pair 22 electrodes 23 Water sensitive membrane 30 Electrical Conductivity Probe 31 Electrical Conductivity Electrode Pair 32 electrodes 40 Temperature Probe 41 Temperature Sensor

Claims

1. a moisture content probe including a readout electrode pair consisting of a pair of electrodes arranged at a predetermined interval and a water-sensitive membrane spanning the pair of electrodes; an electrical conductivity probe provided with an electrical conductivity electrode pair consisting of a pair of electrodes arranged at a predetermined interval; a support portion for supporting the moisture content probe and the conductivity probe in a parallel arrangement. A plant moisture content sensor comprising:

2. A temperature probe having a temperature sensor provided thereon; The temperature probe is supported on the support in a state parallel to the moisture content probe.

2. The plant water content sensor according to claim 1.

3. The water-sensitive film is made of polyimide.

3. The plant water content sensor according to claim 1 or 2.

4. The surface of the water-sensitive film is hydrophilized.

4. The plant water content sensor according to claim 1,

5. The water-sensitive film is provided from the portion where the read electrode pair is disposed to the base end of the water content probe.

5. The plant water content sensor according to claim 1,

6. The tip angle of the moisture content probe is 40-60° 6. The plant water content sensor according to claim 1,

7. the electrical conductivity probe has a plurality of the electrical conductivity electrode pairs; The plurality of electrical conductivity electrode pairs are arranged side by side in the axial direction of the electrical conductivity probe.

2. The plant water content sensor according to claim 1.

8. A heater-equipped temperature probe is provided with a temperature sensor and a heater, The heater-equipped temperature probe is supported on the support part in a state where it is arranged in parallel with the temperature probe.

3. The plant water content sensor according to claim 2.

9. A water content probe having a readout electrode pair consisting of a pair of electrodes arranged at a predetermined interval and a water-sensitive membrane spanning the pair of electrodes is inserted into the plant; An electrical conductivity probe having an electrical conductivity electrode pair consisting of a pair of electrodes arranged at a predetermined interval is inserted into the plant; determining electrical conductivity from the electrical resistance between the pair of electrodes constituting the electrical conductivity electrode pair; The sensor sensitivity coefficient B in formula (1) is calculated from the measured electrical conductivity. measuring an impedance between the pair of electrodes constituting the read electrode pair; Determine the water content of the plant from the impedance measurements based on equation (1) A method for measuring the water content of a plant. Z=Z ０ ×10 －Ｂ・ＷＣ (1) where Z is the impedance measurement, Z ０ is the impedance when the water-sensitive film does not absorb water, B is the sensor sensitivity coefficient, and WC is the water content.

10. The sensor sensitivity coefficient B is calculated from the measured electrical conductivity based on the formula (2).

10. The method for measuring water content in a plant according to claim 9. B = aσ + b (2) Here, B is the sensor sensitivity coefficient, σ is the electrical conductivity, and a and b are predetermined coefficients.

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