Plant Cultivation System

Abstract

To provide a plant growing system that can grow a plant under optimal conditions by directly measuring a moisture dynamic state in the body of the plant as electrostatic capacitance without damaging the plant and converting the measured electrostatic capacitance into relative stem capacitance, thereby linking the timing of watering with a moisture content.SOLUTION: A plant growing system includes: a moisture measuring device that outputs a signal on a moisture content in a stem; a data logger that records the moisture content in the stem; a watering device that supplies water to the plant; and a monitoring control device that controls a watering amount supplied to the plant by the watering device according to the moisture content in the stem. The moisture measuring device is set around the plant by sandwiching it in the stem of the plant, and measures the moisture content in the stem electrically in terms of capacity, and outputs an electrical signal according to the capacity. The monitoring control device converts the maximum and minimum values of the electrical signal measured by the moisture measuring device into a relative stem capacity, and controls the watering device based on the relative stem capacity to water the plant.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a plant cultivation system that measures the amount of water in the stems of plants to provide optimal irrigation. [Background technology]

[0002] The technology of acquiring biological information from plants and diagnosing their growth status to optimally control the cultivation environment based on the results is called SPA (Speaking Plant Approach) technology, and with the recent advancement of measuring equipment, SPA technology is being rapidly introduced into agricultural production sites.

[0003] In plant cultivation systems using SPA technology, the key element is how to obtain biological information about the plants, and various technologies have been made public.

[0004] For example, Patent Document 1 discloses a plant water dynamics sensor that can measure the dynamics of water flowing within plant parts such as the ends of new shoots and fruit stalks. The sensor includes a heater-equipped temperature probe equipped with a temperature sensor and a heater, a temperature probe equipped with a temperature sensor, an electrical resistance probe equipped with electrodes for measuring electrical resistance, and a support unit that supports each probe in a parallel arrangement. Since the position of the xylem can be detected from the electrical resistance measured by the electrical resistance probe, the temperature sensor can be accurately positioned at the position of the phloem or xylem. This allows for accurate measurement of the dynamics of water in plants.

[0005] Patent Document 2 discloses a moisture measuring device capable of non-contact measurement of the moisture content of a measurement object from outside the measurement object, and a soil irrigation system that accurately detects the moisture status of the soil using the moisture measuring device and controls the irrigation of the soil with an appropriate amount of water corresponding to the detected moisture status. An infusion solution transported through an irrigation tube is dripped onto a drop point. In a measurement area centered on the drop point, each moisture sensor detects the infrared intensity of each measurement point. The moisture sensor device calculates the soil surface temperature from the detected infrared intensity and determines the temperature difference with the outside air temperature. The temperature difference is then used to calculate the value and moisture content. A main control device controls the irrigation amount based on the calculated value and moisture content.

[0006] Patent document 3 discloses a plant cultivation system that allows people to communicate with the plant cultivation system in a fun way while also incorporating information from others, and that can provide plants with the elements necessary for plant cultivation as efficiently as possible.

[0007] This plant cultivation system is equipped with sensors that measure the environment related to people and plants, and is equipped with an illuminance measurement sensor that measures the illuminance of light necessary for plant cultivation, a moisture measurement sensor that measures the moisture necessary for plant cultivation, a temperature measurement sensor that measures the temperature of the environment in which the plant is placed, a human detection sensor that detects the presence of people, and a computer that acquires data by varying the acquisition period of measurement data for all sensors.

[0008] Patent Document 4 discloses a plant diagnostic method and device for diagnosing the health of vascular plants during cultivation. The device includes an AE data generator that detects acoustic emissions caused by cavitation in vascular plants based on the output signal of an AE sensor and generates AE data indicating the detection frequency per sampling time, a rhythm pattern memory that stores in advance rhythm patterns that indicate the periodic activity rhythm of vascular plants, and an activity calculator that calculates the activity level of vascular plants based on the AE data and rhythm patterns.

[0009] Patent Document 5 discloses an irrigation system that optimizes control during irrigation using soil condition detection sensors. The irrigation system includes a plurality of communicable soil condition detection sensors, a plurality of valves attached to irrigation pipes, and a control device that communicates with the plurality of soil condition detection sensors and controls the operation of the plurality of valves. The plurality of soil condition detection sensors communicate with the control device by making a communication request to the control device at a set communication interval. When the control device predicts that irrigation will be performed within a predetermined time, it sets the communication interval the first time it communicates with the plurality of soil condition detection sensors thereafter to be shorter than the communication interval before predicting that irrigation will be performed. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-145810 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-275615 [Patent Document 3] Japanese Patent Publication No. 2022-073419 [Patent Document 4] Japanese Patent Application Publication No. 2019-075995 [Patent Document 5] Japanese Patent Publication No. 2020-099217 Summary of the Invention [Problem to be solved by the invention]

[0011] In general, the life activities of living organisms follow a 24-hour rhythm known as the circadian rhythm. Most vascular plants transpire during the day, and transpiration fluctuates over a 24-hour period, reaching its peak during the day. By utilizing the relationship between transpiration and the normal biological rhythms of vascular plants, it is possible to promote the healthy growth of vascular plants.

[0012] To understand the state of plant growth, it is important to directly measure the sap flow rate of plants. This is because transpiration is directly related to the sap flow rate of plants. In particular, to improve the productivity and quality of crops and fruit trees, it is extremely important to measure the movement of water (i.e., water dynamics) in small plant parts only a few millimeters thick, such as the ends of new shoots and fruit stalks, which are located near the crop or fruit tree. It is also extremely important when measuring plant water dynamics that the sensor settings do not stress or damage the plant.

[0013] Furthermore, proper water supply through plant transpiration, i.e., optimizing the timing and amount of irrigation, is an essential element for plant growth.

[0014] However, the plant water dynamics sensor used in Patent Document 1 measures by inserting an electrode for measuring electrical resistance and a temperature sensor into the plant, which can damage the plant.

[0015] The water dynamics sensors in Patent Documents 2 and 3 measure the amount of water in the soil, but do not measure the water dynamics within the plant tissue.

[0016] Patent Document 4 utilizes cavitation (cavity formation) caused by tiny bubbles generated within the xylem. Cavitation is a phenomenon in which tiny bubbles are generated due to pressure changes in the xylem caused by transpiration in vascular plants, and the vibration waves generated by cavitation are acoustic emissions. This acoustic emission is difficult to detect and has a lot of noise. Furthermore, it does not directly detect the water dynamics within the plant body, but is an indirect signal transmitted via the cavitation phenomenon.

[0017] In Patent Document 5, the moisture status within the plant body is not detected, but the moisture status of the soil is detected, and therefore, it is not directly related to plant growth.

[0018] This invention directly measures the water dynamics within a plant as electrical capacitance without damaging the plant. death,To provide a plant growing system that grows plants under optimal conditions by linking the timing of irrigation with the amount of water by converting the measured capacitance into relative stem capacitance. the eyes The target. [Means for solving the problem]

[0019] In order to solve the above problems, the present invention proposes the following technical features.

[0020] (1) A plant cultivation system comprising a moisture measuring device that outputs a signal on the amount of water in the stem, a data logger that records the amount of water in the stem, an irrigation device that supplies water to the plant, and a monitoring and control device that controls the amount of water supplied to the plant by the irrigation device according to the amount of water in the stem, wherein the moisture measuring device is clamped to and set around the stem of the plant, measures the amount of water in the stem electrically in terms of capacitance, and outputs an electrical signal according to the capacitance, and the monitoring and control device converts the maximum and minimum values ​​of the electrical signal measured by the moisture measuring device into relative stem capacity, and controls the irrigation device based on the relative stem capacity to irrigate the plant.

[0021] (2) It is preferable that the moisture measuring device is composed of a moisture sensor unit and a moisture sensor control unit, and that the moisture sensor unit has electrodes sandwiched between two insulating plates arranged facing each other at a certain distance, with a grounded electrostatic shield plate provided on the outside of the electrodes, and that the moisture sensor control unit has a capacitance-digital converter provided on the back surface of the substrate, and that the pair of electrodes and the capacitance-digital converter, together with the substrate, are covered with a shielding material.

[0022] (3) It is preferable that electrode portions each formed integrally with an electrode sandwiched between insulating plates and a shield plate are disposed opposite each other on the substrate, and that at least one of the electrode portions is movable.

[0023] (4) It is preferable that the device further includes a solar radiation sensor that measures the amount of solar radiation, a soil sensor that measures the electrical conductivity, volumetric moisture content, and temperature of the soil, and a temperature and humidity sensor that measures the temperature and humidity of the atmosphere.

[0024] (5) It is preferable that the moisture measuring device is equipped with a data logger and that the signal of the moisture content in the stem is recorded in the data logger.

[0025] (6) The irrigation device preferably comprises a storage container in which a portion of the absorbent material is placed and which stores water for irrigation that is absorbed by the absorbent material, at least a pair of electrodes, a support member for supporting the electrodes, an insulating member arranged to cover the periphery of the electrodes, and a waterproof member arranged to cover the electrodes covered with the support member and insulating member, and is connected to the storage container and is preferably equipped with a water level sensor unit that measures the electrostatic capacitance between the electrodes to detect the water level in the storage container, and a valve member that opens and closes a conduit that supplies water to the storage container and the water level sensor unit.

[0026] (7) It is preferable that the bubble member be opened when the relative stem volume within the plant body detected by the moisture measuring device decreases, and be closed when the relative stem volume within the plant body detected by the moisture measuring device increases from a low state. [Effects of the Invention]

[0027] The present invention can provide a plant cultivation system that can grow plants under optimal conditions by directly measuring the water dynamics within the plant as electrical capacitance without damaging the plant and synchronizing the timing of irrigation. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is an explanatory diagram of a plant cultivation system A according to the present invention. [Figure 2] Plant cultivation system B is obtained by further providing a sunlight sensor 5, a soil sensor 6, and a temperature and humidity sensor 7 to plant cultivation system A according to the present invention. [Figure 3] FIG. 1 is a diagram showing the configuration of a moisture measuring device 10. [Figure 4] 1 shows the state in which the capacitance of a plant is measured using the moisture measuring device 10 of the present invention. [Figure 5] A moisture sensor model 70 and a moisture sensor equivalent circuit model 72 are shown. [Figure 6] This is an irrigation device 4 that waters the container from the bottom where the plants are grown. [Figure 7] FIG. 3 is a diagram illustrating plant photosynthesis and changes in water content 30. [Figure 8] 8 shows an XY cross section of the stem 34 of FIG. 7. [Figure 9] FIG. 1 is a conceptual diagram for explaining circadian rhythms. [Figure 10] An example of sunlight intensity over a 24-hour period is shown. [Figure 11] 10 is a graph for calculating the value of relative stem capacity. [Figure 12] 1 is a graph for converting measured capacitance values ​​into relative stem capacitance Cr. [Figure 13] 1 shows a prototype moisture measuring device 10. [Figure 14] The figure shows a state in which a plant 26 to be measured is set in the moisture measuring device 10. [Figure 15] The figure shows a state in which the moisture sensor unit 75 of the practical moisture measuring device 10 is attached to the stem of a tomato. [Figure 16] In the practical plant cultivation system B, the moisture measuring device 10 is actually attached to a tomato stem 82. [Figure 17] This is an example of measuring the relative stem capacity Cr (%) of a tomato stem on a sunny day. [Figure 18] This is an example of measuring the relative stem capacity Cr of a tomato stem on a cloudy day. [Figure 19] This is an example of measuring the relative stem capacity Cr of tomato stems on a rainy day. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention is a plant cultivation system that can cultivate plants under optimal conditions. The present invention will be described below with reference to the drawings. Note that the components in this embodiment can be appropriately replaced with existing components, and various variations are possible by combining them with other existing components. Therefore, the description of this embodiment does not limit the content of the invention described in the claims.

[0030] Figure 1 is an explanatory diagram of a plant cultivation system A1 according to the present invention. The plant cultivation system comprises a moisture measuring device 10 that outputs a signal indicating the amount of water in the stem, a data logger 3 that records the amount of water in the stem, an irrigation device 4 that supplies water to the plant, and a monitoring and control device 2 that controls the amount of water supplied to the plant by the irrigation device 4 according to the amount of water in the stem. The moisture measuring device 10 is composed of a moisture sensor unit 75 and a moisture sensor control unit 76. The moisture sensor unit 75 is set around the stem of the plant, sandwiching it between the stems, and measures the amount of water in the stem electrically by capacitance, outputting an electrical signal according to the capacitance.

[0031] The plant moisture measuring device 10 converts the change in moisture flowing through the plant's ducts into an electrical signal as capacitance. To set it on a plant, the stem is simply clamped between two electrodes of the moisture sensor unit 75 provided in the moisture measuring device 10, and there is absolutely no stress or damage to the plant. This is one of the features of this system. The capacitance that indicates the change in moisture is minute, on the order of femtofarads (10 -15 ) level of capacitance. Therefore, noise generation must be kept to a minimum.

[0032] The plant moisture measuring device 10 is equipped with a data logger 3. The data logger 3 is a recording device that stores the amount of water in the stem measured by the moisture measuring device 10 as an electrical signal. The amount of water in the stem is measured by sampling at regular intervals, but it is also possible to record a continuous signal. Details of the moisture measuring device 10 will be described later.

[0033] The irrigation device 4 irrigates by opening and closing the water supply valve provided in the irrigation device 4 in response to the output signal of the moisture measuring device 10. The output signal of the moisture measuring device 10 is the change in the moisture content in the stem over time, and when the moisture content in the stem is decreasing, the water supply valve of the irrigation device 4 is opened, and when the moisture content in the stem is increasing, the water supply valve of the irrigation device 4 is closed.

[0034] The monitoring and control device 2 calculates the amount of water in the stem as the relative stem volume, which will be described later, based on the data output from the moisture measuring device 10. The relative stem volume can also be considered as the water content. The irrigation device 4 is controlled in response to changes in this relative stem volume. That is, if the relative stem volume is decreasing, the water supply valve of the irrigation device 4 is opened, and if the relative stem volume is increasing, the water supply valve of the irrigation device 4 is closed.

[0035] 2 shows plant cultivation system B, which is plant cultivation system A according to the present invention, further equipped with a sunlight sensor 5, a soil sensor 6, and a temperature and humidity sensor 7. The sunlight sensor 5, soil sensor 6, and temperature and humidity sensor 7 can take environmental conditions into account to allow appropriate irrigation to be performed according to the plant being cultivated. For example, in cultivating tomatoes, when the fruit is growing, it is possible to adopt a cultivation method such as reducing the amount of irrigation to increase sweetness based on the information from the sunlight sensor 5, soil sensor 6, and temperature and humidity sensor 7.

[0036] Furthermore, by using information on the plants being grown as basic data and combining it with data from the moisture measuring device 10, the sunlight sensor 5, the soil sensor 6, and the temperature and humidity sensor 7, AI can be used to provide optimal irrigation, enabling optimal growth of the plants. These controls are performed by the monitoring and control device 2.

[0037] Next, the moisture measuring device 10 will be described.

[0038] 3 is a diagram showing the configuration of the moisture measuring device 10. The moisture measuring device 10 is made up of a moisture sensor unit 75 and a moisture sensor control unit 76. The area sandwiched between electrodes 16-1 and 16-2 of the moisture sensor unit 75 forms a capacitor, and the measurement principle is to apply a voltage to this capacitance and find the capacitance from the accumulated charge.

[0039] However, because plants have a low water content, noise generated in the electrodes must be minimized in order to measure minute capacitance. For this reason, in the present invention, conductive, flat-plate-shaped electrode 16-1 is sandwiched between insulating plate A 14-1 and insulating plate B 18-1. Electrode 16-2, which is positioned opposite it at a fixed distance, is also sandwiched between insulating plates A 14-2 and insulating plate B 18-2. This structure prevents noise from being generated in electrodes 16-1 and 16-2. Insulating plates B 18-1 and B 18-2 are positioned facing each other.

[0040] Shield plates 12-1 and 12-2 are provided on the outside of insulating plate A14-2 and insulating plate A14-2. Shield plate 12-1 is positioned with a certain space between it and insulating plate 14-1. Similarly, shield plate 12-2 is positioned with a certain space between it and insulating plate 14-2. Furthermore, shield plates 12-1 and 12-2 are grounded. Shield plates 12-1 and 12-2 are conductive metal plates that block external noise.

[0041] Electrode 16-1 sandwiched between shield plate 12-1, insulating plate A14-1, and insulating plate B18-1 (acrylic plate) is fixed to substrate 20. Electrode 16-2 sandwiched between shield plate 12-2, insulating plate A14-2, and insulating plate B18-22 is similarly fixed to substrate 20. Fixing these prevents noise from being generated due to minute vibrations.

[0042] The insulating plates B18-1 and B18-2 are made of acrylic insulators, and the electrodes 16-1 and 16-2 are made of metal plates.

[0043] A capacitance-digital converter 24 is provided on the back surface of the substrate 20. The capacitance-digital converter 24 has the function of converting the electrostatic capacitance between the electrodes 16-1 and 16-2 into a digital signal. The electrodes 16-1 and 16-2 are connected to the capacitance-digital converter 24 by vias 22 provided through the substrate 20. The vias 22 are formed by providing holes in the substrate 20 and filling them with a conductive material, connecting the electrodes 16-1 and 16-2 to the capacitance-digital converter 24 over the shortest distance. Of course, the connection may also be made by lead wires provided through holes provided in the substrate 20.

[0044] The capacitance-to-digital converter 24 measures the charge accumulated between the electrodes 16-1 and 16-2 to be measured. An excitation source using a square wave as the excitation signal and the input of the ΣΔ modulator are connected to electrodes 16-1 and 16-2. The charge accumulated by applying the square wave is sampled by the ΣΔ modulator to determine the capacitance and digitize it. This is because the applied voltage V, accumulated charge Q, and capacitance C have the relationship Q = C·V. The capacitance C can be calculated by C = Q / V. The obtained capacitance C is sent as a digitized signal to the control unit, where data processing is performed.

[0045] As explained above, the moisture measuring device of the present invention prevents noise from occurring at the electrodes, blocks external noise, and digitizes the measured capacitance and transmits it from the moisture measuring device, thereby minimizing the effects of noise. This allows capacitance to be measured with high accuracy, making it possible to measure even minute capacitance due to water in plants.

[0046] FIG. 4 shows the state in which the capacitance of a plant is measured using the moisture measuring device 10 of the present invention. FIG. 4(A) is a schematic cross-sectional view showing the side view, and FIG. 4(B) is a schematic plan view. A plant 26 to be measured is placed in the space between insulating plates B18-1 and B18-2. The moisture measuring device 10 of the present invention is intended to be installed on a plant stem to measure changes in the stem's water content. Therefore, the moisture measuring device 10 is set from the side of the plant stem so that the stem is sandwiched between insulating plates B18-1 and B18-2 of the moisture measuring device 10. As shown in FIG. 4(B), the moisture measuring device 10 of the present invention is set on a portion of the stem. The moisture measuring device 10 measures changes in the amount of water flowing through the xylem and phloem of a plant stem as capacitance. The amount of water flowing through the xylem and phloem changes depending on the plant's photosynthesis, respiration, etc.

[0047] The distance between the electrodes may be set arbitrarily according to the plant 26 to be measured. One of the electrodes may be movable and fixed at any position. When moving an electrode, for example, when moving electrode 16-2, insulating plate B 18-2, insulating plate A 14-2, and shield plate 12-2 are moved together to reduce the influence of noise.

[0048] FIG. 5 shows a moisture sensor model 70 and a moisture sensor equivalent circuit model 72. Measurements made by the measuring device 10 are measurements of the capacitance between the electrodes 16-1 and 16-2, and the parts directly related to this capacitance are the electrode 16-1, insulating plate B18-1, insulating plate B18-2, and electrode 16-2, and this part will be referred to as the moisture sensor. FIG. 5 shows a model in which a plant 26 to be measured is placed on the moisture sensor. If the thickness of the insulating plate B18-1 is d i1 , the distance between the insulating plate B18-1 and the plant 26 to be measured is d a1 , the distance between the plant 26 to be measured and the insulating plate B18-2 is d a2 , the thickness of the insulating board B18-1 is d i2 It was decided.

[0049] In this case, the moisture sensor equivalent circuit model 72 has an equivalent resistance R e1 and equivalent resistance R e2The area of ​​the opposing surfaces of insulating plate B18-1 and insulating plate B18-2 is S, the dielectric constant of vacuum is ε0, and the dielectric constant of insulating plate B18-1 and insulating plate B18-2 is ε i Then, the equivalent capacitance C of the insulating plate B18-1 is i1 is C i1 =ε0ε i S / d i1 , the equivalent capacitance C of insulating plate B18-2 i2 is C i2 =ε0ε i S / d i2 The distance between the insulating plate B18-1 and the plant 26 to be measured is d a1 Then, the equivalent capacitance C a1 is C a1 =ε0S / d a1 This becomes:

[0050] The distance between the insulating plate B18-2 and the plant 26 to be measured is d a2 Then, the equivalent capacitance C a2 is C a2 =ε0S / d a2 The measured plant 26 has a capacitance due to water passing through the vascular bundle 56, C W , the capacitance due to the basic tissue and epidermis other than water is C P The space between the electrodes that is not covered by the plant 26 under test is connected in parallel with the capacitance of the plant 26 under test, but this is not taken into consideration here.

[0051] As a result, the moisture sensor equivalent circuit model 72 is an equivalent circuit model 72 in which each equivalent resistance and each equivalent capacitance are connected in series, as shown in Figure 5. Since the electrodes 16-1 and 16-2 use conductive metal, the equivalent resistance R e1 and equivalent resistance R e2 is so small that it can be ignored, making it practically possible to measure the capacitance between the electrodes.

[0052] Capacitance C due to plant water WThe capacitance is fixed at a constant value except for the water content. Therefore, the change in measured capacitance is the change in water content. The relative dielectric constant of water is approximately 80, while the relative dielectric constant of plants is said to be around 5 to 10. It has also been reported that the relative dielectric constant of tomato leaves is 2 to 4. Because the relative dielectric constant of water is much larger than that of plants, it is possible to measure capacitance even with a small amount of water.

[0053] The irrigation device 4 described above irrigates the soil in which the plants are grown from above, but if the plants are grown in containers, it is possible to irrigate them from the bottom of the container through a liquid-absorbing material. Below, we will explain the irrigation device 4 from the bottom of the container.

[0054] 6 shows an irrigation device 4 for growing plants from the bottom of a container. The irrigation device 4 is composed of a storage container 110, inside which a portion of a liquid-absorbent material 112 is placed, for storing water for irrigation that is absorbed by the liquid-absorbent material 112, and a water level sensor unit 130 equipped with a pair of electrodes 122, 124 and a support member 120 that supports the pair of electrodes 122, 124. A cultivation area is provided above the storage container 110, where soil 114 is placed to grow plants. A conduit that supplies water to the storage container 110 and the water level sensor unit 130 is equipped with a valve member 126 that opens and closes.

[0055] The cultivation area is not particularly limited in shape, depth, size, etc., as long as it is capable of cultivating plants, and when using a storage container 110, a ceramic or resin pot or box may be used as appropriate.

[0056] Any suitable soil can be used as the soil 114 as long as it is suitable for growing plants. For example, it may be artificial soil made from crushed wood bark, natural soil, commercially available soil for planters, or any of these with fertilizers added.

[0057] The liquid-absorbent material 112 is used to irrigate plants by bottom watering, and can be made of any material that can absorb water 116. Suitable liquid-absorbent fabrics, such as woven and nonwoven fabrics, can be used, and commercially available products can be used. Woven and nonwoven fabrics made from various natural fibers, such as cotton, silk, and linen, or various synthetic fibers, such as polyester, can be used. Other suitable materials for the liquid-absorbent material 112 include urethane, paper, and ceramics.

[0058] In the storage container 110, a root-barrier and liquid-permeable sheet that prevents plant roots from reaching the liquid-absorbent material 112 may be laid on top of the liquid-absorbent material 112 within the cultivation area. By laying the root-barrier and liquid-permeable sheet, it is possible to prevent plant roots from extending below the liquid-absorbent material 112, while maintaining the diffusion of water 116 from the liquid-absorbent material 112 into the soil 114. Commercially available root-barrier and liquid-permeable fabrics can be used as the root-barrier and liquid-permeable sheet. For example, a spunbond nonwoven fabric can be used as the root-barrier and liquid-permeable sheet.

[0059] The water 116 may be an aqueous solution containing water. The water 116 is preferably a nutrient solution containing mineral components, such as liquid fertilizer. The water 116 is not particularly limited as long as it can be used for growing plants, such as tap water, rainwater, or well water.

[0060] The water level sensor unit 130 further includes a water level control unit 128. The storage container 110 is used to temporarily store water 116 for irrigation, and is configured so that a portion of the liquid-absorbent material 112 is disposed inside and can maintain a state in which at least a portion of the liquid-absorbent material 112 is immersed in the stored water 116. The storage container 110 is not limited in configuration as long as it can temporarily store the water 116 and can maintain a state in which a portion of the liquid-absorbent material 112 is immersed in the water 116. For example, the storage container 110 in this embodiment uses a container with an entirely open top surface, but the top surface may be partially open, or the container may be covered with a lid or the like as long as a portion of the liquid-absorbent material 112 can be disposed inside the container.

[0061] The water level sensor unit 130 is for measuring the water level of the water 116 stored in the storage container 110, and is installed above the storage container 110 and below the water level L of the water 116. When the valve 126 is opened, the water 116 flows from the conduit into the water level sensor unit 130 and the storage container 110.

[0062] The water level sensor unit 130 has a pair of electrodes 122, 124, measures the capacitance between the electrodes, and outputs a water level detection signal (analog signal) to a water level control unit 128 that has an A / D conversion unit. The water level control unit 128 is connected to the monitoring control unit 2 (not shown). As shown in FIG. 6, the pair of electrodes 122, 124 are made of conductive rod-shaped members, and are formed from, for example, metals such as copper and iron, or alloys such as stainless steel (SUS), but are not limited to these materials, and any conventionally known material having conductivity can be selected and used as appropriate.

[0063] Figure 7 is a diagram explaining plant photosynthesis and changes in water content 30. Plant photosynthesis is the process by which chlorophyll present in leaves 32 uses carbon dioxide CO2 from the air and water absorbed from roots 36 with the energy of light to produce oxygen O2 and sugars (carbohydrates). These sugars provide the energy for plant growth. Meanwhile, plants breathe, taking in oxygen from the air and burning the sugars while expelling carbon dioxide, thereby obtaining energy for growth. The water used for photosynthesis is transported from roots 36 to leaves through vessels in xylem 52 in the plant's stem 34. The aqueous solution containing sugars produced by photosynthesis moves through phloem 54.

[0064] Furthermore, transpiration occurs in the leaves 32, where water from the roots 36 is converted into water vapor and released from the leaves, and it is thought that 90% of the absorbed water is released through transpiration. The purposes of transpiration are to promote water absorption from the roots 36, regulate the amount of water, regulate the temperature of the leaves 32, deliver nutrients dissolved in water to the leaves, and discard unnecessary water.

[0065] Figure 8 shows an XY cross section of the stem 34 in Figure 7. Plant tissue consists of vascular bundles 56, ground tissue 60, and epidermis 62. The epidermis 62 is tissue that covers the surface of the plant, protecting the plant and regulating the entry and exit of substances. The vascular bundles 56 are located in the circular vascular cambium 58 and consist of xylem 52 and phloem 54. The xylem 52 consists of xylem and tracheids. Xylem is a cylindrical tube through which water absorbed from the soil rises and is formed when the cell walls that separate cells die. In tracheids, the cell walls that separate cells remain, and water moves through the cell walls.

[0066] Phloem 54 is a passageway through which the aqueous solution containing sugars produced by photosynthesis moves. The cells forming the rows become hollow, forming phloem. The cells do not disappear completely, but rather some cytoplasm remains and many small pores remain. The area where the phloem are gathered is the phloem 54.

[0067] Thus, the water content measured in the stem 34 is the amount of water passing through the xylem 52 and phloem 54. This water content depends on photosynthesis and respiration, and is affected by sunlight. For this reason, plants grow according to a circadian rhythm based on a 24-hour period.

[0068] Figure 9 is a conceptual diagram to explain circadian rhythms. It shows the strength of plant activity over time, and is dependent on the existence of an internal clock. In plants, not only flowering but also other phenomena such as the opening and closing of stomata, the elongation of leaves and stems, and photosynthetic activity are controlled by the internal clock. Plants can grow more efficiently if they actively carry out photosynthesis during the hours when the sun is out, so they prepare for this before sunrise. Some plants also increase their own resistance to low-temperature stress in preparation for the cold nights.

[0069] Furthermore, plants' internal clocks are involved not only in the flow of time throughout the day, but also in recognizing the seasons, and some flowers that bloom in spring or autumn are able to sense changes in the length of daylight. In order to recognize the temporal changes in the light stimuli they receive from the outside, plants must have their own clocks as a measuring stick, and by comparing the circadian rhythm of their internal clocks with changes in the external environment, plants are able to sense the change of seasons and grow accordingly.

[0070] Figure 10 shows an example of sunlight intensity over one day (24 hours). This shows the light intensity of sunlight on a sunny day (sunny) 66 and the light intensity of sunlight on a rainy day (rainy weather) 68. The light intensity is strong during sunny days, and weak during rainy days. These differences in light intensity affect photosynthesis, and it is thought that the amount of water in the stem also changes with light intensity.

[0071] Next, a method for calculating a relative stem capacity value corresponding to the moisture content of the capacity value measured by the moisture measuring device 10 will be described.

[0072] FIG. 11 is a graph for calculating the relative stem capacity value. The vertical axis represents the capacity value (fF) measured by the moisture measuring device 10, and the horizontal axis represents the time (h) in one day. Cmax: Maximum capacitance measured from 0 to 24 hours (The maximum capacitance value is always updated during measurement.) Cmin: Capacitance value when the measuring device is open (without clamping the plant stem) Cx: capacitance value at measurement time Cr(%): Relative stem capacity The relative stem capacity Cr (%) is Cr={(Cx-Cmin) / (Cmax-Cmin)}×100(%) Calculated as follows.

[0073] Figure 12 is a graph for converting measured capacitance values ​​into relative stem capacitance Cr. In Figure 12, the maximum capacitance value Cmax measured from midnight to midnight is 809 fF, and the capacitance value Cmin when the measuring device 4 is open (without clamping the plant stem) is 426 fF. Therefore, the relative stem capacitance Cr (%) at the time of measurement can be calculated as follows using the capacitance value Cx at the time of measurement: Cr(%)={(Cx-Cmin) / (Cmax-Cmin)}×100 ={(Cx-426×10 -12 ) / 383×10 -12}×100 (Example)

[0074] As an embodiment, a water content measuring device and a plant growing system using this water content measuring device will be described.

[0075] Figure 13 shows a prototype moisture measuring device 10. The moisture measuring device 10 is composed of a moisture sensor unit 76 and a moisture sensor control unit 76. The moisture sensor unit 76 uses a copper-plated epoxy resin printed circuit board, with the copper-plated portion serving as the electrode and the epoxy resin portion serving as the substrate serving as insulating plate B. The relative dielectric constant of epoxy resin is 2.5 to 6. An acrylic plate serving as insulating plate A was attached to the copper-plated surface to form an electrode sandwiched between the insulating plates. An aluminum plate was used as the shielding plate. The electrode surface was approximately 20 mm x 30 mm, and the thicknesses of insulating plates A and B were 2 to 3 mm. The measurement space (the distance between insulating plates B18-1 and B18-2) was 15 mm wide. The shielding plate was installed behind insulating plate A, leaving a space of approximately 7 mm. An aluminum-coated sheet was used as the shielding sheet 74 surrounding the moisture measuring device 10.

[0076] The output from the capacitance-digital converter provided in the moisture measuring device 10 is sent to the moisture sensor control unit 76 via a four-core cable. The moisture sensor control unit 76 converts the output from the capacitance-digital converter into capacitance in real time and displays it on the display unit. Furthermore, the sampling period for measuring capacitance can be set arbitrarily, and capacitance can also be measured at regular intervals. The measured capacitance is sent to a computer via an RS232C cable, where the data is saved and analyzed.

[0077] 14 shows the state in which a plant 26 to be measured is set in the moisture measuring device 10. The stem of the plant is fixed by tying it to the moisture sensor unit 75 of the moisture measuring device 10 with a fixing string 78. The moisture measuring device 10 and the plant 26 to be measured are surrounded by a shielding sheet 74 to suppress the influence of external noise.

[0078] Figure 15 shows the moisture sensor unit 75 of the practical moisture measuring device 10 attached to the stem of a tomato. The tomatoes are grown in pots. The potted tomatoes are placed on a plantain so that the roots receive a constant supply of moisture. The moisture sensor unit 75 has been improved to a practical level and is attached to the tomato stem.

[0079] Figure 16 shows a practical plant cultivation system B8 in which a moisture measuring device 10 is actually attached to a tomato stem 82. The tomatoes are grown in a greenhouse tomato cultivation facility. A moisture sensor unit 75 is attached to the tomato stem, and a moisture sensor control unit 76 is installed in front of the tomato to be measured. The moisture sensor control unit 76 is set in a waterproof case, and Figure 16 also shows the waterproof case with its cover open. In addition, although not visible in the external photograph of Figure 16, a solar radiation sensor 5, soil sensor 6, temperature sensor 7, and irrigation device 4 are also set. Data from the moisture measuring device 10 is sent to a data logger 3 and monitoring control device 2 via the moisture sensor control unit 76, and the data is stored in the data logger 3, where it is processed and analyzed by the monitoring control device 2.

[0080] Figure 17 shows an example of measuring the relative stem capacitance Cr (%) of a tomato stem during the day on a sunny day. The measurement was taken in early April on greenhouse-grown tomatoes. The temperature was around 20°C. The time period was 24 hours, from midnight to midnight. The sampling period was 300 ms.

[0081] In Figure 17, the relative stem capacity Cr on a sunny day gradually increases from approximately 80% in the nighttime time region (1), reaching a high relative stem capacity Cr of 100% at 8:03 AM. As the morning sunrise approaches, sunlight is irradiated onto the tomatoes, and the relative stem capacity Cr decreases in time region (2). The decreasing relative stem capacity Cr reaches a saturation point at approximately 10:31 AM, reaching a minimum of 45%. After that, the relative stem capacity Cr remains almost unchanged in time region (3), before rising again from approximately 4:49 PM. In time region (4), the influence of sunset increases the relative stem capacity Cr until approximately 6:33 PM, reaching approximately 75%. After that, a slow upward trend is observed.

[0082] It is thought that the water content of a tomato stem increases due to transpiration, causing the stem diameter to shrink and capacitance to decrease. This can be measured from changes in capacitance using the moisture sensor equivalent circuit model 72 shown in Figure 5. Therefore, sunlight exposure causes water to transpire from the tomato leaves, and photosynthesis in the leaves becomes active, consuming a lot of water. The amount of water absorbed by the roots and transported through the vascular bundles decreases, causing the stem diameter to shrink and the stem water content to decrease, resulting in a decrease in the measured capacitance. In the afternoon, the stem capacitance tends to increase, indicating an increase in water content. This is thought to be because photosynthesis is active in the morning, and in the afternoon, the sugars produced by photosynthesis are actively transported throughout the plant through the phloem, causing the stem diameter to expand and the water content to increase.

[0083] The monitoring and control device 2 controls the irrigation device 4 to irrigate in conjunction with this relative stem capacity Cr. The amount of water irrigated from the irrigation device 4 is determined in time region (1), which is a time period when there is no water transpiration from the tomato leaves and water is retained within the stems, and in this state, irrigation is not necessary. In time region (2), sunlight is irradiated by sunrise B, and in relation to the solar radiation, photosynthesis begins in the tomato leaves, and transpiration from the leaves also begins. In this time region (2), the amount of water irrigated is gradually increased.

[0084] In time domain (3), sunlight reaches the entire tomato leaf, photosynthesis reaches its maximum, and at the same time, transpiration from the leaves also reaches its maximum. Therefore, irrigation must be carried out thoroughly, and the amount of irrigation is maximized. In time domain (4), the sun sets, the sunlight's radiation weakens, and the sun sets. Therefore, the amount of irrigation is gradually reduced, and irrigation is stopped around 6:33 PM.

[0085] The amount of irrigation is controlled by the monitoring and control device 2 by comprehensively utilizing data from the solar radiation sensor 6, soil sensor 6, and temperature and humidity sensor 7. Furthermore, the amount of irrigation can also be controlled by applying AI that incorporates basic information about the tomatoes.

[0086] Figure 18 shows an example of measuring the relative stem capacity Cr of tomato stems on a cloudy day. In time domain (1), which is the nighttime time domain in Figure 18, the relative stem capacity Cr gradually increases from approximately 77%, reaching a high value of nearly 100% at around 8:00 AM. With the morning sunrise, sunlight is irradiated onto the tomatoes, and the relative stem capacity Cr decreases in time domain (2). However, because it was a cloudy day, the rate of decrease was small, and the relative stem capacity Cr saturated at approximately 77% at around 12:01 PM and then saturated again at a minimum of 70% at around 2:20 PM. Then, in time domain (4), the relative stem capacity Cr rapidly increased from 4:04 PM to 5:33 PM, reaching 92%. After that, the relative stem capacity Cr showed a slower increase, reaching 100% at around 11:29 PM.

[0087] The monitoring and control device 2 controls the irrigation device 4 to irrigate in conjunction with this relative stem capacity Cr. The amount of water irrigated from the irrigation device 4 is determined in time region (1), which is a time period when there is no water transpiration from the tomato leaves and water is retained within the stems, and in this state, irrigation is not necessary. In time region (2), sunlight is irradiated at sunrise, and in relation to the insolation, photosynthesis begins in the tomato leaves and transpiration from the leaves also begins. In time region (2), the amount of water irrigated is gradually increased, but the decrease in relative stem capacity Cr is gradual and the amount of water irrigated is small.

[0088] In the next time region (3), the amount of sunlight is low and the relative stem capacity Cr is high at 70-80%, so the amount of irrigation can be reduced. In time region (4), the sun sets, but the relative stem capacity Cr in time region (3) is high at 70-80%, so irrigation can be stopped at around 4:04 PM.

[0089] Figure 19 shows an example of measuring the relative stem capacity Cr of tomato stems on a rainy day. The relative stem capacity Cr on a rainy day is over 90% in the nighttime time region (1), the morning sunrise time regions (2) and (3), and even the sunset time region (4). Therefore, irrigation is not necessary.

[0090] The plant cultivation system of the present invention was explained using the cultivation of tomatoes as an example, and the moisture measuring device was able to measure minute changes in the amount of moisture in the tomato stems as capacitance. By converting this measured capacitance into relative stem capacitance, the timing and amount of irrigation could be quantitatively determined, and the system functioned as an optimal plant cultivation system. The plant cultivation system of the present invention is not limited to tomatoes and can be applied to other plants as well.

[0091] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and applications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0092] 1. Plant Cultivation System A 2. Monitoring and control equipment 3 Data Logger 4 Irrigation equipment 5. Sunlight sensor 6 Soil Sensor 7 Temperature and humidity sensor 8 Plant Cultivation System B 10 Moisture measuring device 12-1, 12-2 Shield plate 14-1, 14-2 Insulation plate A 16-1, 16-2 electrode 18-1, 18-2 Insulating plate B 20 Substrate 22 Beer 24 Capacitance Digital Converter 26 Plants to be measured 30 Plant photosynthesis and changes in water content 32 leaves 34 Stem 36 roots 50 Plant stem cross section 52 Wood 54 Phloem 56 Vascular bundle 58 Vascular cambium 60 Basic organization 62 Epidermis 64 Circadian Rhythm 66 Sunlight (sunny) 68 Sunlight (Rainy Weather) 70 Moisture Sensor Model 72 Moisture sensor equivalent circuit model 74 Shield Sheet 75 Moisture sensor part 76 Moisture sensor control unit 78 String 80 Measurement System 82 Tomato stem 110 Storage container 112 Liquid absorbing material 114 Soil 116 Water 120 Support member 122,124 Pair of electrodes 126 Valve 128 Water level control unit 130 Water level sensor unit

Claims

1. a moisture measuring device that outputs a signal of the moisture content in the stem; A data logger that records the water content in the stem; an irrigation device for supplying water to plants; a monitoring and control device that controls the amount of water supplied to the plants by the irrigation device according to the amount of water in the stems; Equipped with The moisture measuring device is set around the stem of a plant, measures the amount of moisture in the stem electrically by capacitance, and outputs an electrical signal according to the capacitance; The irrigation device is a storage container in which a portion of the liquid-absorbent material is disposed and which stores water for irrigation that is absorbed by the liquid-absorbent material; a water level sensor unit that includes at least a pair of electrodes, a support member that supports the electrodes, an insulating member that is provided so as to cover the periphery of the electrodes, and a waterproof member that is provided so as to cover the electrodes that are covered with the support member and the insulating member, and that is in communication with the storage container and that measures the electrostatic capacitance between the electrodes to detect the water level of the storage container; a valve member that opens and closes a conduit that supplies water to the reservoir and the water level sensor unit; Equipped with the valve member is opened when the relative stem volume in the plant body detected by the moisture measuring device decreases, and is closed when the relative stem volume in the plant body detected by the moisture measuring device increases from a low state; The monitoring and control device converts the maximum and minimum values ​​of the electrical signal measured by the moisture measuring device into the relative stem capacity, The relative stem capacity Cr (%) was calculated by the following formula: Cr = {(Cx - Cmin) / (Cmax - Cmin)} x 100 (%), where Cmax is the maximum capacity measured from 0 to 24:00, Cmin is the capacity when the measuring device is open (without clamping the plant stem), and Cx is the capacity at the time of measurement. Controlling the irrigation device in conjunction with the relative stem capacity to perform irrigation; A plant cultivation system characterized by:

2. The moisture measuring device comprises a moisture sensor unit and a moisture sensor control unit, the moisture sensor unit has electrodes sandwiched between two insulating plates, arranged facing each other at a certain distance, and a grounded shield plate provided on the outside of the electrodes; the moisture sensor control unit is provided with a capacitance-digital converter on the back surface of the substrate; the pair of electrodes and the capacitance-digital converter are covered with a shielding material together with the substrate; 2. The plant cultivation system according to claim 1.

3. Electrode sections formed integrally with the electrode sandwiched between the insulating plates and the shield plate are disposed opposite each other on a substrate, and at least one of the electrode sections is movable; 3. The plant cultivation system according to claim 2,

4. Furthermore, the device is provided with a solar radiation sensor that measures the amount of solar radiation, a soil sensor that measures the electrical conductivity, volumetric moisture content and temperature of the soil, and a temperature and humidity sensor that measures the temperature and humidity of the atmosphere.

2. The plant cultivation system according to claim 1,

5. The moisture measuring device is provided with a data logger, and the stem moisture content signal is recorded in the data logger.

2. The plant cultivation system according to claim 1,

6. A moisture measuring device that outputs a signal of moisture content in the stem; A data logger that records the water content in the stem; an irrigation device for supplying water to plants; a monitoring and control device that controls the amount of water supplied to the plants by the irrigation device according to the amount of water in the stems; Equipped with The moisture measuring device is set around the stem of a plant, measures the amount of moisture in the stem electrically by capacitance, and outputs an electrical signal corresponding to the capacitance. The irrigation device is a storage container in which a portion of the liquid-absorbent material is disposed and which stores water for irrigation that is absorbed by the liquid-absorbent material; a water level sensor unit that includes at least a pair of electrodes, a support member that supports the electrodes, an insulating member that is provided so as to cover the periphery of the electrodes, and a waterproof member that is provided so as to cover the electrodes that are covered with the support member and the insulating member, and that is in communication with the storage container and that measures the electrostatic capacitance between the electrodes to detect the water level of the storage container; a valve member that opens and closes a conduit that supplies water to the reservoir and the water level sensor unit; Equipped with the valve member is opened when the relative stem volume in the plant body detected by the moisture measuring device decreases, and is closed when the relative stem volume in the plant body detected by the moisture measuring device increases from a low state, The monitoring and control device converts the maximum and minimum values ​​of the electrical signal measured by the moisture measuring device into the relative stem capacity, The relative stem capacity Cr (%) was calculated by the following formula: Cr = {(Cx - Cmin) / (Cmax - Cmin)} x 100 (%), where Cmax is the maximum capacity measured from 0 to 24:00, Cmin is the capacity when the measuring device is open (without clamping the plant stem), and Cx is the capacity at the time of measurement. Controlling the irrigation device in conjunction with the relative stem capacity to perform irrigation; A plant cultivation method characterized by the above.

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