Hydroponic method and hydroponic apparatus

Abstract

To provide a hydroponic method and a hydroponic apparatus capable of preventing the occurrence of oxygen deficiency in root parts in hydroponics mainly for root vegetables.SOLUTION: A hydroponic cultivation method for cultivating a plant includes arranging a plant part existing on the ground in soil cultivation in a ground part, arranging a plant part existing underground in soil cultivation in an underground part, providing a partition plate that partitions a boundary between the ground part and the underground part, setting the underground part to a gas-liquid mixed environment for 12 hours to 24 hours a day, and setting a carbon dioxide concentration of the ground part to be higher than a carbon dioxide concentration of the underground part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a hydroponic cultivation method and a hydroponic cultivation device. [Background technology]

[0002] Hydroponic cultivation has traditionally been used industrially to grow vegetables and other plants. Known methods for accelerating growth in this case include controlling the temperature, humidity, airflow, light intensity, and carbon dioxide concentration of the aboveground parts. For the underground parts, a method of managing nutrients in the water during hydroponic cultivation is also known. Factory-grown leafy vegetables, in particular, are already on the market, and the technology is well established. However, hydroponic cultivation of root vegetables, including potatoes, and plant factories are still in the research stage, with the exception of varieties with small roots, such as daikon radish, because special care is required to manage the roots.

[0003] Measures that need to be taken for the roots include oxygen deficiency and water pressure in the underwater portion of hydroponic cultivation. In plants, the above-ground parts, which perform photosynthesis, take in carbon dioxide and produce oxygen, but the underground parts do not perform photosynthesis and therefore consume oxygen like animals. As a result, oxygen deficiency can occur in the roots, which can be an inhibitory factor. Water pressure can also cause a blockage in the flow of various nutrients transported within the plant, including nutrients produced through photosynthesis.

[0004] Furthermore, even in plant factories, it is difficult to avoid hydroponic cultivation due to the impact on growth rate, and the same countermeasures are required. Oxygen deficiency during hydroponic cultivation is also an issue for crops other than root vegetables and potatoes, but it is a particularly important factor for root vegetables and potatoes, which have edible parts in the roots.

[0005] As for technologies related to root vegetable cultivation, a method for cultivating potatoes has been proposed in which the structure is divided into above-ground parts, edible parts, and roots (see, for example, Patent Document 1). Other proposed technologies include using a siphon to manage the water level in the roots to prevent the roots from submerging in water (see, for example, Patent Document 2), and controlling the water level according to the difference in the growth rate of the roots of individual crops (see, for example, Patent Document 3). Also proposed, although not for root vegetables, is a technology for blowing air into water as an underground innovation in hydroponic cultivation (see, for example, Patent Document 5), and a technology for using mist for above-ground parts (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6172647 [Patent Document 2] Patent No. 5535390 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-100573 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-73467 [Patent Document 5] Japanese Patent Application Publication No. 11-66 Summary of the Invention [Problem to be solved by the invention]

[0007] In soil cultivation, the roots are often not in contact with water, so oxygen deficiency is unlikely to occur. Root vegetables, which grow on their roots, are considered to be best grown in well-drained soil such as alluvial fans, which prevents oxygen deficiency. On the other hand, in hydroponic cultivation, where the roots are constantly submerged, oxygen deficiency is a major problem because it is difficult for the roots to absorb oxygen.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a hydroponic cultivation method and hydroponic cultivation device that can prevent oxygen deficiency in the roots of root vegetables during hydroponic cultivation. [Means for solving the problem]

[0009] The hydroponic cultivation method of the embodiment is a hydroponic cultivation method for cultivating plants, characterized in that plant parts that would be above ground in soil cultivation are arranged in the above-ground part, plant parts that would be underground in soil cultivation are arranged in the underground part, a partition plate is provided to separate the boundary between the above-ground part and the underground part, the underground part is in an air-liquid mixed environment for 12 to 24 hours a day, and the carbon dioxide concentration in the above-ground part is made higher than the carbon dioxide concentration in the underground part.

[0010] The hydroponic cultivation device of the embodiment is a hydroponic cultivation device for cultivating plants, and is equipped with an above-ground portion for arranging plant parts that would be above ground in soil cultivation, an underground portion for arranging plant parts that would be below ground in soil cultivation, a partition plate that separates the above-ground portion from the underground portion, and an air-liquid mixed environment forming mechanism that creates an air-liquid mixed environment in the underground portion for 12 to 24 hours a day, and is characterized in that the carbon dioxide concentration in the above-ground portion is higher than the carbon dioxide concentration in the underground portion. [Effects of the Invention]

[0011] According to the present invention, a hydroponic cultivation method and a hydroponic cultivation device can be provided that can prevent oxygen deficiency from occurring in the roots of root vegetables in hydroponic cultivation. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic configuration of a hydroponic cultivation method and a hydroponic cultivation device according to a first embodiment. [Figure 2] FIG. 10 is a diagram schematically illustrating the general configuration of a hydroponic cultivation method and a hydroponic cultivation device according to a second embodiment. [Figure 3] FIG. 10 is a diagram schematically illustrating the general configuration of a hydroponic cultivation method and a hydroponic cultivation device according to a third embodiment. [Figure 4] FIG. 10 is a diagram schematically illustrating the general configuration of a hydroponic cultivation method and a hydroponic cultivation device according to a fourth embodiment. [Figure 5]FIG. 10 is a diagram schematically illustrating the general configuration of a hydroponic cultivation method and a hydroponic cultivation device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, hydroponic cultivation methods and hydroponic cultivation devices according to several embodiments will be described with reference to the drawings. The hydroponic cultivation methods and hydroponic cultivation devices according to these embodiments are suitable for industrially cultivating plants, mainly root vegetables, by hydroponic cultivation.

[0014] (First embodiment) FIG. 1 is a diagram showing a schematic diagram of a hydroponic cultivation method and apparatus according to a first embodiment. Note that FIG. 1 shows the schematic diagram of one cultivated plant 1. In actual hydroponic cultivation on an industrial scale, a large number of these components are arranged side by side. As shown in FIG. 1, the cultivated plant 1 has an above-ground part 1a, which is a plant part that exists above ground in soil cultivation, such as the plant's leaves, and an underground part 1b, which is a plant part that exists below ground in soil cultivation, such as the plant's roots.

[0015] The hydroponic cultivation device 10 comprises an above-ground part 11 in which the above-ground part 1a of the plant 1 is placed, and an underground part 12 in which the underground part 1b of the plant 1 is placed, with a partition plate 13 provided to separate the above-ground part 11 from the underground part 12. This partition plate 13 separates the environment in which the above-ground part 1a of the plant 1 is placed from the environment in which the underground part 1b is placed. The underground part 12 comprises a cultivation container 14 for accommodating the underground part 1b.

[0016] The hydroponic cultivation device 10 also includes a water pump 15, which is connected to a water supply pipe 16. In the example shown in Fig. 1, the water supply pipe 16 is installed in the ceiling of the underground portion 12 along the partition plate 13, and is configured to allow the nutrient solution 17 to drip downward from the top of the underground portion 12 in a shower-like manner from multiple locations. This allows the water pump 15 and the water supply pipe 16 to supply the nutrient solution 17 to the underground portion 1b of the plant 1 placed in the underground portion 12.

[0017] In the underground portion 12, the portion other than that subjected to the shower-like water flow is in a gas-phase environment. The frequency of application of the nutrient solution 17 is preferably at least once every two to twenty-four hours, avoiding extreme conditions, in order to balance absorption of the nutrient solution 17 with avoiding oxygen deficiency. In this case, once the nutrient solution 17 is applied, the nutrient solution 17 adheres to the roots, which are the underground portion 1b of the plant 1, for a while, and also maintains contact with the gas, creating a gas-liquid mixed state. In other words, by applying the nutrient solution 17 using the shower-like water flow, the underground portion 1b of the plant 1 can be in contact with the nutrient solution 17 while still in the gas phase.

[0018] If the flow path of the shower-like water flow is too narrow, nutrients may react with carbon dioxide contained in the gas phase and precipitate as solids that cannot be absorbed by the plant. Calcium and magnesium, which are particularly lacking in plants, react with carbon dioxide and precipitate easily, so a larger cross-sectional area of ​​the flow path of the shower-like water flow is preferable to reduce contact with the gas phase. On the other hand, if the cross-sectional area of ​​the flow path of the shower-like water flow is too large, the force of the water flow may damage the underground part 1b of the cultivated plant 1. For this reason, it is preferable to set the diameter of the flow path of the shower-like water flow to about 1 mm. This prevents oxygen deficiency, supplies nutrients, and prevents damage to the cultivated plant 1.

[0019] As described above, in the hydroponic cultivation device 10 of the first embodiment, the underground portion 12 in which the underground portion 1b of the plant 1 is located can be placed in an air-liquid mixed state by the water pump 15 and water supply piping 16 as an air-liquid mixed environment forming mechanism. The underground portion 12 (underground portion 1b of the plant 1) is preferably placed in an air-liquid mixed state for 12 to 24 hours per day. Furthermore, by placing the underground portion 12 in an air-liquid mixed environment, preferably for 24 hours per day, the amount of nutrient absorption can be maximized.

[0020] Furthermore, with regard to the carbon dioxide concentration in the above-ground part 11 and the underground part 12, it is preferable that the carbon dioxide concentration in the above-ground part 11 is higher than the carbon dioxide concentration in the underground part 12. Specifically, the carbon dioxide concentration in the underground part 12 is preferably 450 ppm or less, and more preferably 100 ppm or less, to prevent loss of nutrients. Furthermore, the carbon dioxide concentration in the above-ground part 11 is higher than the carbon dioxide concentration in the underground part 12, preferably about 1200 to 1600 ppm, and more preferably 1500 ppm to 1600 ppm, to further accelerate growth.

[0021] Because the cultivated plant 1 takes in carbon dioxide in the above-ground part 1a and performs photosynthesis, a higher carbon dioxide concentration in the above-ground part 11 is advantageous for growth. However, when the carbon dioxide concentration exceeds 1600 ppm, the carbon dioxide concentration inside the plant rises too much, causing the plant to tend to close its stomata. When the stomata close, the flow of water within the cultivated plant 1 and the accompanying flow of minerals such as calcium decrease, resulting in a mineral deficiency in the above-ground part 1a, such as the leaves, and causing poor growth of the cultivated plant 1 itself. Therefore, the upper limit for carbon dioxide concentration is set at around 1600 ppm.

[0022] Furthermore, when the growing plant 1 takes in carbon dioxide, a low-concentration layer of carbon dioxide is generated near the leaf surface. Therefore, it is desirable for the aboveground part 11 to have a gas flow strong enough to prevent damage to the growing plant 1 itself, for example, a gas flow with a wind speed of approximately 0.2 to 0.8 m / s. Furthermore, a flow of 0.2 to 0.3 m / s is preferable to allow for proper growth at the lowest operating cost. The temperature of the aboveground part 11 is preferably approximately 17°C to 30°C, where enzymes are most effectively utilized during organic synthesis, a step in photosynthesis. A temperature of 21°C to 25°C is even more preferable for optimal growth. Chemical reactions, including organic synthesis, generally proceed more quickly at higher temperatures, and temperatures below 17°C slow the rate of photosynthesis. On the other hand, in organic synthesis, which involves a binding process with enzymes, excessively high temperatures inhibit the binding process. Therefore, organic synthesis is more efficiently carried out at temperatures below 30°C.

[0023] The growing plant 1 uses water evaporation from the leaves as a driving force to absorb water and the minerals that accompany the water from the roots, so a high humidity environment prevents the plant from absorbing water, which adversely affects growth. For this reason, it is preferable to set the upper limit of humidity in the above-ground part 11 at around 90%. On the other hand, in low humidity conditions, the plant closes its stomata to prevent drying, which inhibits the uptake of carbon dioxide, so it is preferable to set the lower limit of humidity at around 75%. For these reasons, it is preferable to set the humidity in the above-ground part 11 at around 75% to 90%.

[0024] Although not shown in Fig. 1, the hydroponic cultivation device 10 is provided with a lighting device such as a fluorescent lamp or an LED for irradiating light onto the cultivated plant 1 on the above-ground part 11. The amount of light irradiated onto the above-ground part 11 by this lighting device is set to 200 µmol / m, which is the amount of light that can induce growth by photosynthesis. 2 / s (Photosynthetic Photon Flux Density (PPFD)) or more, preferably 1000 to 2000 μmol / m 2 / s can achieve the optimal growth rate. While the longer the light exposure time, the greater the amount of photosynthesis, if water is used for photosynthesis, the water will not reach the tip of the plant, which will have a negative impact on mineral transport. Therefore, it is necessary to set a time during the day when photosynthesis does not occur. For this reason, it is preferable to limit the light exposure time to around 16 hours per day.

[0025] For the underground portion 12, there is no need to set an upper limit on humidity because there is no risk of stomatal blockage like in the above-ground portion 11, even at high humidity, but it is preferable to set the humidity at around 90% to prevent drying. Furthermore, since calcium absorbed by the cultivated plant 1 reacts with carbon dioxide and changes from an ionic state that can be absorbed by the plant to a solid state that cannot be absorbed by the plant, it is preferable that the carbon dioxide concentration in the underground portion 12 be 450 ppm or less, which is the same or lower than that in the atmosphere. Furthermore, since the roots of some plants turn green when exposed to light, the light intensity in the underground portion 12 should be 10 μmol / m 2 / s (Photosynthetic Photon Flux Density (PPFD)) or less, and more preferably 5 μmol / m 2 By keeping the density below / s, greening can be prevented reliably.

[0026] The gas and liquid in the underground portion 12 do not need to be constantly mixed, and may be in an environment where the gas and liquid phases alternate depending on the time of day, or where the gas and liquid phases alternate. Also, the gas-liquid mixture ratio does not necessarily need to be constant, and as long as the plant 1 can absorb the moisture and nutrients necessary for its growth, the frequency of contact with water may be low.

[0027] The moisture and nutrients such as nitrogen and phosphorus necessary for the growing plant 1 are absorbed along with moisture primarily from the roots, which are the underground part 1b, so contact of the nutrient solution with the roots is essential. On the other hand, contact with the gas phase is essential to prevent oxygen deficiency in the roots. By mixing the gas and liquid in time and space, oxygen deficiency can be prevented and sufficient moisture and nutrient absorption can be achieved. This allows the roots to absorb nutrients while preventing oxygen deficiency in the roots.

[0028] (Second embodiment) Next, a hydroponic cultivation method and a hydroponic cultivation device according to a second embodiment will be described with reference to Fig. 2. Note that parts corresponding to those of the first embodiment shown in Fig. 1 are given the same reference numerals and redundant description will be omitted.

[0029] The second embodiment is a modification of the first embodiment. In the first embodiment, the nutrient solution 17 is supplied from above in a shower-like manner. However, in the hydroponic cultivation device 10a of the second embodiment, as shown in FIG. 2, the nutrient solution 17 is applied from below to the upper partition plate 13, and the nutrient solution 17 that bounces off the partition plate 13 hits the underground portion 1b in the form of raindrops.

[0030] As in the second embodiment, the nutrient solution 17 may be indirectly supplied to the underground portion 1b of the plant 1. In this case, too, the flow path diameter of the nutrient solution 17 is preferably, for example, about 1 mm or less. In the second embodiment, the same actions and effects as in the first embodiment can be obtained.

[0031] (Third embodiment) Next, a hydroponic cultivation method and a hydroponic cultivation device according to a third embodiment will be described with reference to Fig. 3. Note that parts corresponding to those of the first embodiment shown in Fig. 1 are given the same reference numerals and redundant explanations will be omitted.

[0032] As shown in Figure 3, in a hydroponic cultivation device 10b of the third embodiment, the nutrient solution 17 is sprayed as a mist by a mist generator 18 into the gas phase space of the underground portion 12. The particle size of the mist is preferably, for example, about 120 µm or less. Methods for spraying the nutrient solution 17 in a mist state can include a method using a nozzle or a method using ultrasound. Although Figure 3 shows an example in which the mist is sprayed horizontally, the mist may also be sprayed vertically.

[0033] In an environment where the mist-like nutrient solution 17 and the gas phase exist, oxygen and nutrients can be supplied. In the third embodiment, the contact area between the nutrient solution 17 and the gas phase is larger than in the first and second embodiments described above, and calcium and carbon dioxide in the nutrient solution 17 are more likely to mix. Therefore, it is preferable that the carbon dioxide concentration in the underground part 12 is lower than the atmospheric concentration of about 450 ppm. As described above, it is preferable that the carbon dioxide concentration above ground be maintained at a high concentration of about 1200 ppm to 1600 ppm. In this way, it is preferable to change the gas phase circulation between the aboveground part and the underground part.

[0034] Furthermore, because it is predicted that calcium and magnesium will be consumed in greater quantities due to reactions with carbon dioxide than in conventional hydroponic cultivation, it is preferable to increase the calcium and magnesium concentrations. The required amounts of these nutrients vary depending on the plant species, but as an example, a calcium concentration of approximately 120 mg / L to 300 mg / L and a magnesium concentration of approximately 20 mg / L to 60 mg / L are considered. The upper limit of these concentrations is the concentration at which damage to the plant due to excessive administration does not occur, and the lower limit is the concentration at which poor growth does not occur. This prevents oxygen deficiency and ensures the supply of nutrients.

[0035] (Fourth embodiment) Next, a hydroponic cultivation method and a hydroponic cultivation device according to a fourth embodiment will be described with reference to Fig. 4. Note that parts corresponding to those of the first embodiment shown in Fig. 1 are given the same reference numerals and redundant description will be omitted.

[0036] As shown in FIG. 4, in the fourth embodiment, a water-absorbent material 19, such as a water-absorbent sponge, is installed in the underground portion 12 of a hydroponic cultivation device 10c, and a nutrient solution flow path 20 is installed below the water-absorbent material 19. A portion of the nutrient solution 17 is absorbed and drawn up by the water-absorbent material 19, such as a water-absorbent sponge. Furthermore, slits are made in the water-absorbent material 19 in the area where the underground portion 1b of the plant 1 will be located. The water-absorbent material 19 does not necessarily have to be spread over the entire surface; it can be applied with the minimum amount necessary for the plant 1 to obtain moisture. The presence of the water-absorbent material 19 allows the nutrient solution 17 and the gas phase to coexist. Furthermore, making slits in the water-absorbent material 19 prevents the growth of the underground portion 1b of the plant 1 from being hindered.

[0037] As a result, the cultivated plant 1 can grow in an air-phase environment while obtaining water and nutrients, and therefore the plant can be grown without being inhibited from growing.

[0038] (Fifth embodiment) Next, a hydroponic cultivation method and a hydroponic cultivation device according to a fifth embodiment will be described with reference to Fig. 5. Note that parts corresponding to those of the first embodiment shown in Fig. 1 are given the same reference numerals and redundant description will be omitted.

[0039] 5, in the fifth embodiment, the underground portion 12 of a hydroponic cultivation device 10d is filled with a nutrient solution 17, and a gas bubble 23 is introduced into the nutrient solution 17 by a pneumatic pump 21 and a pneumatic pipe 22. The gas 23 to be introduced contains oxygen, and is ideally air from which carbon dioxide has been removed, or oxygen, but air with atmospheric composition may also be used.

[0040] The gas 23 preferably has a flow rate of about 10 to 100 mL / min per liter of nutrient solution 17 and a bubble size of 1 to 10 mm. From the viewpoint of preventing oxygen deficiency, the oxygen concentration is preferably 20% or more, which is equal to or higher than atmospheric levels. From the viewpoint of the reaction between calcium and carbon dioxide in the nutrient solution, the carbon dioxide concentration is preferably 450 ppm or less, which is equal to or lower than atmospheric levels. To prevent the gas 23 from accumulating in the underground portion 12, it is preferable to provide an exhaust pipe or the like on the partition plate 13 or the like to serve as an exhaust path.

[0041] As described above, in the fifth embodiment, a gas 23 such as air is blown into the nutrient solution 17 to prevent oxygen deficiency. As in the third embodiment, because carbon dioxide reacts with the calcium and magnesium in the nutrient solution 17, a gas containing no carbon dioxide and 20% or more oxygen is preferable, if possible. When introducing air with atmospheric composition that includes carbon dioxide, a large amount of air is not necessarily healthy, so an upper limit is set for the amount of air introduced and a lower limit is set for the bubble size. This alleviates oxygen deficiency in the roots in the nutrient solution 17, solving the problem of oxygen deficiency. Furthermore, because the liquid phase does not contain any factors that particularly inhibit plant growth, healthy growth is also maintained.

[0042] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be combined without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0043] 1...cultivated plant, 1a...above-ground part, 1b...underground part, 10, 10a, 10b, 10c, 10d...hydroponic cultivation device, 11...above-ground part, 12...underground part, 13...partition plate, 14...cultivation container, 15...water supply pump, 16...water supply piping, 17...nutrient solution, 18...mist generator, 19...water-absorbing material, 20...nutrient solution flow path, 21...pneumatic pump, 22...pneumatic piping, 23...gas.

Claims

1. A hydroponic cultivation method for cultivating plants, comprising: In soil cultivation, plant parts present above ground are arranged above ground, In soil cultivation, plant parts that exist underground are placed underground, A partition plate is provided to separate the boundary between the above-ground part and the underground part, The underground portion is kept in a gas-liquid mixed environment for 12 to 24 hours a day, The carbon dioxide concentration in the above-ground portion is made higher than the carbon dioxide concentration in the underground portion. A hydroponic cultivation method characterized by:

2. The hydroponic cultivation method according to claim 1, The carbon dioxide concentration in the underground portion is 450 ppm or less, The carbon dioxide concentration in the above-ground part is set to 1200 ppm to 1600 ppm. A hydroponic cultivation method characterized by:

3. The hydroponic cultivation method according to claim 1 or 2, The airflow rate of the gas above ground is 0.2 to 0.8 m / s, the temperature is 17 to 30°C, the humidity is 75% to 90%, and the light intensity is 200 μmol / m ２ / s or more, and the light irradiation time is 12h to 16h, The humidity of the underground part is set to 90% or more, and the light intensity of the underground part is set to 10 μmol / m ２ / s or less A hydroponic cultivation method characterized by:

4. The hydroponic cultivation method according to claim 1 or 2, The underground portion is made into a gas phase, and the nutrient solution is dripped in a shower, or the nutrient solution is sprayed as a liquid by hitting the partition plate from below, creating a gas-liquid mixed environment. A hydroponic cultivation method characterized by:

5. The hydroponic cultivation method according to claim 1 or 2, The underground part is in a gas phase, and nutrient solution is supplied in mist form to create a gas-liquid mixed environment. A hydroponic cultivation method characterized by:

6. The hydroponic cultivation method according to claim 1 or 2, A water-absorbing material is placed in the underground portion, and the water-absorbing material is impregnated with nutrient solution to create an air-liquid mixed environment. A hydroponic cultivation method characterized by:

7. The hydroponic cultivation method according to claim 1 or 2, The underground part is made into a liquid phase by adding nutrient solution, and oxygen-containing gas is supplied as bubbles into the nutrient solution to create a gas-liquid mixed environment. A hydroponic cultivation method characterized by:

8. The hydroponic cultivation method according to claim 7, The oxygen-containing gas has a carbon dioxide concentration of 450 ppm or less. A hydroponic cultivation method characterized by:

9. A hydroponic cultivation device for cultivating plants, an above-ground part for arranging above-ground plant parts in soil cultivation; an underground portion for arranging plant parts present underground in soil cultivation; A partition plate that separates the boundary between the above-ground part and the underground part; a gas-liquid mixed environment forming mechanism that creates a gas-liquid mixed environment in the underground portion for 12 to 24 hours a day; Equipped with The carbon dioxide concentration in the above-ground portion is made higher than the carbon dioxide concentration in the underground portion. A hydroponic cultivation device characterized by:

10. The hydroponic cultivation device according to claim 9, The carbon dioxide concentration in the underground portion is 450 ppm or less, The carbon dioxide concentration in the above-ground part is set to 1200 ppm to 1600 ppm. A hydroponic cultivation device characterized by:

11. The hydroponic cultivation device according to claim 9 or 10, The gas-liquid mixed environment forming mechanism creates a gas phase in the underground portion and drips the nutrient solution in a shower, or sprays the nutrient solution from below onto the partition plate to create a liquid phase, creating a gas-liquid mixed environment. A hydroponic cultivation device characterized by:

12. The hydroponic cultivation device according to claim 9 or 10, The gas-liquid mixed environment forming mechanism makes the underground part a gas phase and supplies nutrient solution in the form of mist to create a gas-liquid mixed environment. A hydroponic cultivation device characterized by:

13. The hydroponic cultivation device according to claim 9 or 10, The gas-liquid mixed environment forming mechanism arranges a water-absorbing material in the underground portion, and impregnates the water-absorbing material with nutrient solution to form a gas-liquid mixed environment. A hydroponic cultivation device characterized by:

14. The hydroponic cultivation device according to claim 9 or 10, The gas-liquid mixed environment forming mechanism converts the underground portion into a liquid phase with the nutrient solution and supplies oxygen-containing gas as bubbles into the nutrient solution. A hydroponic cultivation device characterized by:

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