Cultivation method and cultivation device

Abstract

Provided are a cultivation method and a cultivation device capable of maintaining a culture solution in a well-foamed state within a cultivation tank. This plant cultivation method comprises a step for circulating a culture solution by supplying the culture solution to a cultivation tank in which the rhizosphere of a plant is accommodated, discharging the culture solution from the cultivation tank, and re-supplying the discharged culture solution to the cultivation tank. In the method, the culture solution exists in a foamed state in the cultivation tank. At least one of the supplying and the discharging of the culture solution is performed so as to prevent foam of the culture solution existing in the cultivation tank from becoming bulky.

Description

Cultivation method and cultivation device

[0001] The present invention relates to a cultivation method and a cultivation device.

[0002] In recent years, attempts have been made to cultivate various plants, such as leafy vegetables and fruit vegetables, using hydroponic cultivation (also known as nutrient solution cultivation, etc.), which uses a culture solution. Hydroponic cultivation has advantages such as eliminating the risk of soil-borne diseases and making it easy to manage the nutritional status of crops. However, because hydroponic cultivation is prone to root rot, it is necessary to supply sufficient air to the culture solution in the cultivation tank by bubbling or other methods.

[0003] One hydroponic cultivation method that has been studied is to cultivate plants by keeping a culture solution in a foam state in a cultivation tank. This type of hydroponic cultivation is also called foam culture. Patent Document 1 describes a cultivation method for cultivating plants using a culture solution, characterized by forming bubbles in the culture solution and bringing the bubbles into contact with the roots of the cultivated plants. Patent Document 2 also describes a hydroponic cultivation method for plants, characterized by using a water-soluble polymer aqueous solution containing bubbles as a culture medium.

[0004] JP-A-6-153720 JP-A-7-213182

[0005] In hydroponic cultivation, it is common for the culture solution to be circulated and reused repeatedly. However, in foam culture, in which the culture solution is used in a foamy state, if the culture solution is circulated for a long period of time, the foaming of the culture solution may deteriorate over time, and it may become impossible to supply the culture solution in a good foamy state to the cultivation tank. Specifically, it is desirable for the culture solution to exist in the cultivation tank in a fine foamy state, but if the culture solution is circulated for a long period of time, it becomes difficult to form fine foam, and the foaming becomes poor. Culture solution that foams poorly and is in a poor foamy state may reduce plant growth. In addition, coarse foam easily dries and precipitates on plant roots, etc., which may reduce plant growth.

[0006] The present invention was made based on the above circumstances, and its purpose is to provide a cultivation method and cultivation device that can keep a culture solution in a good foam state in a cultivation tank.

[0007] The above objectives are as follows: [1] A method for cultivating plants, comprising a step of supplying a culture solution to a cultivation tank containing the rhizosphere of a plant, discharging the culture solution from the cultivation tank, and re-supplying the discharged culture solution to the cultivation tank, thereby circulating the culture solution, wherein the culture solution exists in the cultivation tank in a foamy state, and at least one of supplying and discharging the culture solution is performed so as to prevent the bubbles of the culture solution existing in the cultivation tank from becoming coarse; [2] The cultivation method of [1], wherein, in the circulating step, the culture solution is supplied in a foamy state to the cultivation tank, and the culture solution is discharged in a foamy state from a position lower than or at the same height as the position where the culture solution is supplied in the cultivation tank; [3] The cultivation method of [1], wherein, in the circulating step, the culture solution is supplied in a foamy state from the top of the cultivation tank, and the culture solution is discharged in a foamy state from the lowest position of the cultivation tank; [4] The cultivation method of [1], wherein in the circulating step, droplets of the culture solution are dropped from the top of the cultivation tank onto the foam of the culture solution present in the cultivation tank; [5] Any of the cultivation methods of [1] to [4], wherein the culture solution contains a fertilizer and a water-soluble polymer; [6] Any of the cultivation methods of [1] to [5], wherein the foam of the culture solution present in the cultivation tank has a Sauter mean particle size of 400 μm or less; [7] Any of the cultivation methods of [1] to [6], wherein the bottom of the cultivation tank is inclined; [8] Any of the cultivation methods of [1] to [7], wherein the cultivation tank is a cylindrical body with a central axis disposed in a vertical or inclined direction; [9] Any of the cultivation methods of [1] to [8], wherein an outlet for the culture solution is provided at the lowest position of the cultivation tank, and the outlet is configured to allow spherical particles with a diameter of 1 cm to pass through;

[10] A cultivation device comprising a cultivation tank for containing the rhizosphere of plants, a foaming device for foaming the culture solution, and a culture solution circulation device for supplying the culture solution to the cultivation tank and re-supplying the culture solution discharged from the cultivation tank to the cultivation tank, wherein the culture solution is supplied to the cultivation tank in a foamed state and is discharged in a foamed state from a position lower than or at the same height as the position where the culture solution is supplied to the cultivation tank;

[11] The cultivation device of

[10] , which does not have a pump for discharging the culture solution from the cultivation tank;

[12] The cultivation device of

[10] or

[11] , in which the culture solution is discharged from the cultivation tank by its own weight;

[13] The cultivation device of any of

[10] to

[12] , in which the cultivation tank has a structure in which two container-like bodies, each opening downward, are stacked with a gap between them, and the space between the two container-like bodies is a space in which the rhizosphere of the plant is contained;

[14] A cultivation device comprising: a cultivation tank for containing the rhizosphere of the plant; and a culture solution circulating device that supplies the culture solution to the cultivation tank and supplies the culture solution discharged from the cultivation tank again to the cultivation tank, the culture solution circulating device being configured to drip the culture solution from the top of the cultivation tank onto the foam of the culture solution present in the cultivation tank;

[15] The cultivation device of

[14] , in which the cultivation tank is a cylindrical body with a central axis arranged in the vertical direction;

[0008] According to the present invention, a cultivation method and a cultivation device can be provided that can keep a culture solution in a good foam state in a cultivation tank.

[0009] Fig. 1 is a schematic diagram of a cultivation device according to a first embodiment of the present invention. Fig. 2 is a schematic diagram of a cultivation device according to a second embodiment of the present invention. Fig. 3 is a graph showing the measurement results of the change in Sauter mean particle size of foam over time in Experimental Example and Comparative Experimental Examples 1 and 2. Fig. 4 is a graph showing the measurement results of the change in dryness of foam over time in Experimental Example and Comparative Experimental Examples 1 and 2.

[0010] A cultivation method according to one embodiment of the present invention comprises a step of supplying a culture solution to a cultivation tank containing the rhizosphere of a plant, discharging the culture solution from the cultivation tank, and circulating the culture solution by supplying the discharged culture solution again to the cultivation tank, in which the culture solution exists in a foamy state, and at least one of the supply and discharge of the culture solution is carried out so as to prevent the foam of the culture solution existing in the cultivation tank from becoming coarse.

[0011] This cultivation method allows the culture solution to remain in a good foam state in the cultivation tank. While the reason for this is unclear, the following is thought to be the cause. According to the inventors' findings, the cause of the deterioration of the foamability of the culture solution over time when cultivation is performed for a long period of time while the culture solution is circulated is the coarsening and drying (decrease in moisture content) of the culture solution bubbles present in the cultivation tank. That is, when the culture solution bubbles remain in the cultivation tank, the bubbles grow and coarse. Coarsened bubbles that remain in the cultivation tank for a long period of time are prone to drying. Here, the culture solution used in a foam state typically contains, along with fertilizer, a water-soluble polymer to improve foamability. When the culture solution bubbles dry, the water-soluble polymer contained in the culture solution that forms the foam deteriorates, and repeated use of the culture solution is thought to gradually deteriorate the foamability. Furthermore, when the culture solution bubbles dry, the water-soluble polymer is more likely to precipitate, which is thought to gradually reduce the concentration of the water-soluble polymer in the recycled culture solution. This is also thought to be one of the causes of the deterioration of foamability. Furthermore, the fact that the foam of the culture solution dries and the water-soluble polymer precipitates on the roots of the plants in the cultivation tank is itself undesirable from the viewpoint of plant growth.

[0012] In contrast, in a cultivation method according to one embodiment of the present invention, at least one of supplying and discharging the culture solution is performed so as to prevent the foam of the culture solution present in the cultivation tank from becoming coarse. This prevents the foam of the culture solution in the cultivation tank from drying out, and even when the culture solution is used repeatedly over a long period of time, it is thought that a decrease in the foamability of the culture solution is prevented, and the culture solution in a good foam state can be maintained in the cultivation tank. In other words, the cultivation method according to one embodiment of the present invention may be a method in which at least one of supplying and discharging the culture solution is performed so as to prevent the foam of the culture solution present in the cultivation tank from drying out. According to the cultivation method according to one embodiment of the present invention, a decrease in the foamability of the culture solution is prevented, and the culture solution in a good foam state can be maintained in the cultivation tank, which is expected to improve cultivation efficiency.

[0013] Specific methods for supplying and / or discharging the culture solution so as to prevent the culture solution bubbles present in the cultivation tank from becoming coarse, as described in detail below, include a method of discharging the culture solution in a foamy state to the outside of the cultivation tank so that the culture solution bubbles do not remain in the cultivation tank, and a method of dripping droplets of the culture solution onto the culture solution bubbles in the cultivation tank. Below, a cultivation method and a cultivation device according to one embodiment of the present invention will be described in detail along with a specific embodiment of the cultivation device.

[0014] 1 includes a cultivation tank 11, a foaming device 12, a first storage tank 14, a pump 15, a second storage tank 16, and a pipe 17. The first storage tank 14, the pump 15, the second storage tank 16, and the pipe 17 constitute a culture solution circulation device 13.

[0015] The cultivation tank 11 contains the rhizosphere of the plant A to be cultivated. The rhizosphere is the space where the roots of the plant and the surrounding environment interact with each other. In other words, the cultivation tank 11 contains the roots of the plant A and the culture solution B in a foamy state.

[0016] The cultivation tank 11 shown in Figure 1 has a cross section cut in the vertical direction that is approximately arc-shaped. The cultivation tank 11 is equipped with a supply port 18 through which the culture solution B is supplied in a foam state, and a discharge port 19 through which the culture solution B is discharged in a foam state. In the cultivation tank 11, the discharge port 19 for the culture solution B is provided at the lowest position of the cultivation tank 11.

[0017] The cultivation tank 11 may be, for example, a curved pipe having a supply port 18 and a discharge port 19. The upper opening of the curved pipe-shaped cultivation tank 11 is the supply port 18, and the lower opening is the discharge port 19.

[0018] The cultivation tank 11 may have a structure in which two container-shaped bodies, each opening downward, are stacked with a gap between them. In this case, the space between the two container-shaped bodies is the space for containing the root zone of plant A. The two container-shaped bodies may have a shape in which the diameter gradually increases downward. Each container-shaped body may be circular in plan view or polygonal, etc. Each container-shaped body may be, for example, hemispherical, semi-elliptical, conical, pyramidal, etc. These two container-shaped bodies may have the same central axis and be arranged so that this central axis is vertical. Furthermore, the inner container-shaped body may be arranged so that it is covered by the outer container-shaped body. In this case, the diameter or size of the inner container-shaped body is larger than that of the outer container-shaped body. The tops of the containers may be open. The outer container-shaped body has multiple holes 21 for planting plant A. Furthermore, a second storage tank 16 may be provided at the top of the inner container-shaped body.

[0019] Culture solution B is supplied from above to the space between the two container-like bodies. That is, the upper side between the two container-like bodies is a supply port 18. Culture solution B is discharged from the lower side between the two container-like bodies. That is, the lower side between the two container-like bodies is a discharge port 19.

[0020] The appearance of the cultivation tank 11 may be a roughly hemispherical shape that is circular in a plan view. The appearance of the cultivation tank 11 may also be dome-shaped. The roughly hemispherical cultivation tank 11 may have a structure, for example, in which two hemispherical containers (bowls) with an opening in the center are stacked on top of each other. That is, the container-like body may be a hemispherical container. A second hemispherical container with a smaller diameter is placed inside a first hemispherical container with a larger diameter. The space between the two hemispherical containers is the space in which the roots of the plant A and the culture solution B in a foamy state are present. The upper side (top side) of the roughly hemispherical cultivation tank 11 is a supply port 18, and the lower side is a discharge port 19.

[0021] The supply port 18 and the discharge port 19 of the cultivation tank 11 are shaped so that the culture solution B is supplied in a foamy state and discharged in that foamy state. That is, the supply port 18 and the discharge port 19 are not covered with, for example, a mesh or the like. For example, the discharge port 19 is preferably configured to allow spherical particles with a diameter of 1 cm to pass through, and more preferably configured to allow spherical particles with a diameter of 2 cm or 3 cm to pass through. Similarly, the supply port 18 is preferably configured to allow spherical particles with a diameter of 1 cm to pass through, and more preferably configured to allow spherical particles with a diameter of 2 cm or 3 cm to pass through.

[0022] In the cultivation tank 11, the position of the discharge port 19 is lower than the position of the supply port 18, and the bottom surface 20 of the cultivation tank 11 is structured to be inclined. The bottom surface 20 of the cultivation tank 11 has a curved shape. In addition, as a form different from the cultivation tank 11 of FIG. 1, a box-shaped aquarium or the like may be used as the cultivation tank. For example, the cultivation tank can be configured by placing a box-shaped aquarium at an angle and providing a discharge port at the lowest position of the aquarium. The cultivation tank 11 may be made of resin, metal, or the like.

[0023] A plurality of holes 21 are provided on the outer surface (top surface) of the cultivation tank 11. Plants A are planted in the cultivation tank 11 so that parts of the plants A other than the roots protrude from the holes 21. The plants A to be cultivated are not particularly limited, but examples include vegetables such as tomatoes, cucumbers, melons, strawberries, mitsuba, leeks, shiso, lettuce, and radishes, and flowers such as tulips, roses, gerberas, and carnations. They may also include cut flowers such as lilies, bouvardia, roses, and carnations, and shrubs for rooftop greening such as umbellata, camellias, and sasanquas.

[0024] The foaming device 12 is a device that foams the culture solution B. The foaming device 12 in Fig. 1 is provided so as to foam the culture solution B in the second storage tank 16. The foaming device 12 is not particularly limited, and a known device can be used.

[0025] For example, the foaming device 12 may be an agitation device. That is, the culture solution B in the second storage tank 16 may be foamed by being agitated by the agitation device 12. The foaming device 12 may also be an aeration device. The culture solution B can be foamed by sending air into the second storage tank 16 in which the culture solution B is stored. Alternatively, the foaming device 12 may be a device that foams the culture solution B by using a spray method, a circulation method, a shaking method, or the like.

[0026] The culture solution circulation device 13 is a device that supplies the culture solution B to the cultivation tank 11 and supplies the culture solution B discharged from the cultivation tank 11 back to the cultivation tank 11. As described above, the culture solution circulation device 13 is composed of the first storage tank 14, the pump 15, the second storage tank 16, and the piping 17.

[0027] The first storage tank 14 stores the culture solution B. The first storage tank 14 is disposed below the outlet 19 of the cultivation tank 11. That is, the first storage tank 14 stores the culture solution B discharged from the cultivation tank 11. In other words, the first storage tank 14 is a tray for the culture solution B discharged from the cultivation tank 11. In this way, the cultivation device 1 may be provided with a tray (first storage tank 14) disposed below the cultivation tank 11. When starting cultivation using the cultivation device 1, the prepared culture solution B may be stored in the first storage tank 14 at first, or the culture solution B may be prepared in the first storage tank 14.

[0028] The first storage tank 14 may be provided with an analyzer that analyzes the type, concentration, etc. of each component of the culture solution B. When such an analyzer is provided, for example, if the concentration of a specific component in the culture solution B decreases, that component can be added, etc.

[0029] The pump 15 is a device that supplies the culture solution B in the first storage tank 14 to a second storage tank 16 that is provided at a higher position than the first storage tank 14. The culture solution B in the first storage tank 14 is sent by the pump 15 to the second storage tank 16 via a pipe 17.

[0030] The culture solution B sent to the second storage tank 16 is foamed by the foaming device 12 as described above. In the cultivation apparatus 1 of Fig. 1, the second storage tank 16 and the cultivation tank 11 are arranged so that the position of the upper end 22 of the second storage tank 16 coincides with the position of the lower end of the supply port 18 of the cultivation tank 11 (the height of the lower end of the supply port 18). Therefore, the culture solution B in a foamy state that overflows from the second storage tank 16 is supplied to the cultivation tank 11 from the supply port 18.

[0031] (Cultivation method using the cultivation device 1, advantages, etc.) The cultivation device 1 is configured to supply the culture solution B in a foam state to the cultivation tank 11 and discharge the culture solution B in a foam state from a position (discharge outlet 19) lower than the position (supply inlet 18) where the culture solution B is supplied to the cultivation tank 11. More specifically, the cultivation device 1 is configured to supply the culture solution B in a foam state from the supply inlet 18 provided at the top of the cultivation tank 11 and discharge the culture solution B in a foam state from the discharge outlet 19 provided at the lowest position of the cultivation tank 11.

[0032] By using the cultivation apparatus 1, a plant cultivation method can be performed, which includes a step of supplying culture solution B to a cultivation tank 11 containing the rhizosphere of a plant A, discharging the culture solution B from the cultivation tank 11, and resupplying the discharged culture solution B to the cultivation tank 11 to circulate the culture solution B, whereby the culture solution B exists in a foamy state in the cultivation tank 11. By using the cultivation apparatus 1, in the circulating step, the culture solution B can be supplied in a foamy state to the cultivation tank 11 and discharged in a foamy state from a position (discharge port 19) lower than the position (supply port 18) where the culture solution B is supplied in the cultivation tank 11. Furthermore, by using the cultivation apparatus 1, in the circulating step, the culture solution B can be supplied in a foamy state from the upper part (supply port 18) of the cultivation tank 11 and discharged in a foamy state from the lowest position (discharge port 19) of the cultivation tank 11.

[0033] Therefore, according to the cultivation apparatus 1 and the cultivation method using the cultivation apparatus 1, retention of foam of the culture solution B in the cultivation tank 11 is suppressed, and coarsening of the foam of the culture solution B present in the cultivation tank 11 is suppressed. As a result, according to the cultivation apparatus 1 and the cultivation method using the cultivation apparatus 1, drying of the foam of the culture solution B present in the cultivation tank 11 is suppressed, and the culture solution in a good foam state can be kept present in the cultivation tank. Note that the culture solution B discharged from the outlet 19 may contain liquid culture solution B.

[0034] Furthermore, in the cultivation apparatus 1, the bottom surface 20 of the cultivation tank 11 is inclined, and the discharge port 19 is provided at a position lower than the supply port 18 of the cultivation tank 11. Therefore, in the cultivation apparatus 1 and the cultivation method using the same, the culture solution B is discharged from the cultivation tank 11 by its own weight, and foam of the culture solution B is unlikely to remain in the cultivation tank 11. Furthermore, the cultivation apparatus 1 does not need to have a pump for discharging the culture solution B from the cultivation tank 11. A configuration in which the culture solution B is discharged from the cultivation tank 11 by its own weight in this way and no discharge pump is required is useful from an economical standpoint, etc.

[0035] Unlike the cultivation device 1 of FIG. 1 , the position where the culture solution is supplied (supply port) and the position where the culture solution is discharged (discharge port) in the cultivation tank may be at the same height. Even in such a case, the culture solution can be discharged from the cultivation tank in a foamy state. A discharge pump or the like may be provided so that the culture solution is efficiently discharged in a foamy state. Furthermore, the cultivation tank may be provided with multiple discharge ports. For example, some of the discharge ports may be provided at a lower position than the supply port, and other discharge ports may be provided at a higher position than the supply port.

[0036] In the cultivation apparatus 1 of Fig. 1, the bubbler 12 may be provided in the first storage tank 14 instead of the second storage tank 16. In this case, the culture solution B in a foamed state foamed in the first storage tank 14 is supplied by the pump 15 through the piping 17 to the second storage tank 16, and then supplied from the supply port 18 to the cultivation tank 11. Alternatively, the second storage tank 16 may be omitted, and the piping 17 and the supply port 18 may be directly connected. In this case, the culture solution B in a foamed state foamed in the first storage tank 14 is supplied by the pump 15 through the piping 17 to the cultivation tank 11 from the supply port 18.

[0037] 2 includes a cultivation tank 31, a storage tank 32, a pump 33, and a pipe 34. The cultivation tank 31 has a supply port 35 and a discharge port 36. A valve 37 may be provided at the discharge port 36 of the cultivation tank 31. The storage tank 32, the pump 33, and the pipe 34 constitute a culture solution circulation device 39.

[0038] The cultivation tank 31 contains the rhizosphere of a plant A to be cultivated. The cultivation tank 31 contains the roots of the plant A and a culture solution B in a foamy state.

[0039] The cultivation tank 31 shown in Figure 2 is a tubular body with a central axis extending vertically. The cultivation tank 31 may have, for example, a cylindrical shape. The upper opening of the cultivation tank 31 is a supply port 35 for the culture solution B, and the lower opening is a discharge port 36 for the culture solution B. The cultivation tank 31 may be a pipe made of resin, metal, or the like.

[0040] A plurality of holes 38 are provided on the side of the cultivation tank 31. The plant A is planted in the cultivation tank 31 so that parts of the plant A other than the roots protrude from the holes 38.

[0041] The storage tank 32 stores the culture solution B. The storage tank 32 is disposed below the cultivation tank 31. That is, the storage tank 32 stores the culture solution B discharged from the cultivation tank 31. In other words, the storage tank 32 is a tray for the culture solution B discharged from the cultivation tank 31. In this way, the cultivation device 2 may include a tray (storage tank 32) disposed below the cultivation tank 31. A valve 37 is provided at the discharge port 36 of the cultivation tank 31.

[0042] The pump 33 is a device that supplies the culture solution B in the storage tank 32 to the cultivation tank 31. The culture solution B in the storage tank 32 is supplied to the cultivation tank 31 by the pump 33 via a pipe 34. The culture solution B is configured to drip into the cultivation tank 31 in the form of droplets from a supply port 35 located at the top of the cultivation tank 31.

[0043] In this way, in the cultivation device 2, the storage tank 32, the pump 33 and the piping 34 constitute a culture solution circulation device that supplies culture solution B to the cultivation tank 31 and supplies culture solution B discharged from the cultivation tank 31 back to the cultivation tank 31.

[0044] In the cultivation apparatus 2, the culture solution circulation device may be configured to drip droplets of culture solution B into the cultivation tank 31 from the top of the cultivation tank 31. When culture solution B is dripped into the cultivation tank 31 in the form of droplets from the supply port 35 located at the top of the cultivation tank 31, the culture solution B bubbles due to the impact of the droplets colliding with the liquid surface of the culture solution B or with the culture solution B in a foamy state in the cultivation tank 31. Furthermore, if the valve 37 is closed and a certain amount of culture solution B is stored in the cultivation tank 31, the droplets will more easily collide with the liquid surface of the stored culture solution B, allowing for more efficient foaming.

[0045] During cultivation, valve 37 may be left open to allow the culture solution B to circulate. The culture solution B discharged from outlet 36 of cultivation tank 31 may be in the form of foam or droplets. As plant A grows, the amount of culture solution B absorbed by plant A increases, reducing the amount of culture solution B in cultivation tank 31, which may result in a decrease in the foaming of culture solution B in cultivation tank 31. In such a case, if it is desired to foam the culture solution B in cultivation tank 31 sufficiently again, valve 37 can be closed temporarily, and then the culture solution B can be filled in cultivation tank 31 and then the valve 37 can be opened, thereby foaming the culture solution B in cultivation tank 31.

[0046] (Cultivation method, advantages, etc. using the cultivation device 2) The cultivation device 2 is configured to drip droplets of culture solution B from the top of the cultivation tank 31 (supply port 35) onto the foam of culture solution B present in the cultivation tank 31.

[0047] By using the cultivation apparatus 2, a plant cultivation method can be carried out, which includes a step of supplying the culture solution B to a cultivation tank 31 containing the rhizosphere of a plant A, discharging the culture solution B from the cultivation tank 31, and circulating the culture solution B by supplying the discharged culture solution B again to the cultivation tank 31, in which the culture solution B exists in a foamy state in the cultivation tank 31. By using the cultivation apparatus 2, droplets of the culture solution B can be dripped from the top (supply port 35) of the cultivation tank 31 onto the foam of the culture solution B existing in the cultivation tank 31 in the circulating step.

[0048] In this way, by dripping droplets of culture solution B onto the foam of culture solution B, the grown foam breaks up and becomes smaller. Therefore, according to the culture device 2 and the cultivation method using the culture device 2, the foam of culture solution B in the cultivation tank 31 is prevented from becoming coarse. Furthermore, according to the culture device 2 and the cultivation method using the culture device 2, the act of dripping droplets of culture solution B itself prevents the culture solution B from drying out. Therefore, according to the culture device 2 and the cultivation method using the culture device 2, the foam of culture solution B present in the cultivation tank 31 is prevented from drying out, and the culture solution in a good foam state can be maintained in the cultivation tank.

[0049] Unlike the cultivation device 2 in Fig. 2, the cultivation tank may be a cylindrical body with a central axis disposed in an inclined direction. Even if the cultivation tank is inclined in this manner, the same effect can be achieved.

[0050] (Culture Solution) The culture solution used in the cultivation method and cultivation device according to one embodiment of the present invention will be described below. The culture solution may be any known one used in conventional foam culture.

[0051] The culture solution preferably contains a fertilizer and further contains a water-soluble polymer. The culture solution may be an aqueous solution.

[0052] The type of fertilizer is appropriately selected depending on the type of plant to be cultivated, and generally, known fertilizers can be used. Examples of fertilizers include Ca(NO ３ ) ２ ・4H ２ O, KNO ３ , N.H. ４ H２ P.O. ４ , MgSO ４ ・7H ２ O, N.H. ４ NO ３ , Fe-EDTA, H ３ BO ３ , MnCl ２ ・4H ２ The concentration of the fertilizer in the culture solution is not particularly limited, and may be the same as the concentration in a conventionally known culture solution for foam culture.

[0053] The water-soluble polymer refers to a polymer that can be dissolved in water. For example, the water-soluble polymer refers to a polymer that can be made into an aqueous solution at a concentration of 0.1% by mass or more at 20° C., and preferably a polymer that can be made into an aqueous solution at a concentration of 1% by mass or more at 20° C. When the culture solution contains a water-soluble polymer, the foaming is improved, and the culture solution can be kept in a better foam state in the cultivation tank.

[0054] Examples of water-soluble polymers contained in the culture medium include polyvinyl alcohol (PVA), polyethylene glycol (PEG), polypropylene glycol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl ether, isobutylene-maleic anhydride copolymer, polyallylamine, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, starch, sodium alginate, propylene glycol alginate, sodium starch glycolate, sodium starch phosphate, and modified versions thereof. Among these, PVA and PEG are preferred, and PVA is more preferred. The PVA may be unmodified or modified. The water-soluble polymer can be produced by a conventionally known method, or a commercially available product can be used. One or more water-soluble polymers can be used.

[0055] The lower limit of the concentration of the water-soluble polymer contained in the culture solution is preferably 0.001% by mass, more preferably 0.005% by mass, even more preferably 0.01% by mass, even more preferably 0.02% by mass, and in some cases 0.1% by mass is preferred. On the other hand, the upper limit of the concentration of the water-soluble polymer is preferably 10% by mass, more preferably 5% by mass, even more preferably 3% by mass, and in some cases 2% by mass, 1% by mass, 0.5% by mass, or 0.3% by mass is preferred. By setting the concentration of the water-soluble polymer within the above range, the foaming of the culture solution can be made better.

[0056] The culture solution may further contain other components in addition to water, fertilizer, and water-soluble polymer.

[0057] In the cultivation method according to one embodiment of the present invention and the cultivation method using the cultivation apparatus according to one embodiment of the present invention, the Sauter mean particle size of the culture solution foam present in the cultivation tank is preferably 400 μm or less. The upper limit of the Sauter mean particle size is more preferably 300 μm, and in some cases even more preferably 200 μm. By having such small particle size foam present in the cultivation tank, drying of the culture solution foam present in the cultivation tank is further suppressed, enabling better foam culture. The lower limit of the Sauter mean particle size is not particularly limited and may be 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 70 μm, or 100 μm.

[0058] <Other Embodiments> The present invention is not limited to the above-described embodiments, and the configuration may be modified without departing from the spirit and scope of the present invention. For example, the culture solution B may be supplied in a foamed state from the supply port 35 at the top of the cylindrical culture tank 31 of the culture device 2 shown in Figure 2. In this embodiment, the culture solution B may be discharged in a foamed state from the discharge port 36 of the culture tank 31, or in other states. To enable such an embodiment, for example, in the culture device 2 shown in Figure 2, a foaming device may be provided between the pump 33 and the culture tank 31, via the piping 34.

[0059] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples in any way.

[0060] Below are experimental results showing that shortening the residence time of the culture solution in a foamy state in the cultivation tank and circulating the culture solution suppressed the coarsening of the foam and drying (decrease in moisture content) of the culture solution present in the cultivation tank.

[0061] [Measurement method] Using a foam analyzer ("Dynamic Foam Analyzer DFA100" manufactured by KRUSS), the changes over time in the Sauter mean particle size and dryness of foam formed using a solution adjusted to 20°C were examined. The Sauter mean particle size of foam was calculated from the ratio of the sum of the foam volumes to the sum of the surface areas by processing images of the foam taken at arbitrary intervals. A power mean approximation curve was created from the acquired data, and the Sauter mean particle size at each time point was calculated. Since the dryness (moisture content) of foam is thought to be related to foam density, the dryness of foam was determined from the measured foam density. The foam density at each residence time was divided by the maximum foam density during the measurement period, and the resulting value was subtracted from 1 to obtain the absolute value, which was expressed as a percentage.

[0062] [Experimental Example] A PVA aqueous solution with a concentration of 0.1% by mass was prepared to simulate a culture solution. Foam from the PVA aqueous solution was formed using the foam analyzer described above. The foam from the PVA aqueous solution formed in the foam analyzer was discharged from the top of the device using a suction pump. The discharged PVA aqueous solution was recovered and resupplied to the foam analyzer using a supply pump. The PVA aqueous solution was recycled in this way, and the changes in the Sauter mean particle size and dryness of the foam over a 60-minute period were investigated.

[0063] Comparative Experiment 1: Foam was formed from an aqueous PVA solution using a foam analyzer. The foam formed in the foam analyzer was discharged from the top of the device using a suction pump. The discharged aqueous PVA solution was recovered and resupplied to the foam separator at 1 / 10 the speed of the experimental example, thereby reproducing the difference in foam circulation speed. The aqueous PVA solution was recycled in this manner, and the changes in the Sauter mean particle size and dryness of the foam over a 60-minute period were examined.

[0064] Comparative Experimental Example 2 The same procedure as in the experimental example was repeated except that a mesh (made of stainless steel, mesh size 200 μm) was attached to the suction pump when the foam of the PVA aqueous solution formed in the foam analyzer was discharged from the top of the apparatus using the suction pump, and the changes in the Sauter mean particle size and dryness of the foam over a period of 60 minutes were investigated.

[0065] The results of the above Experimental Example and Comparative Experimental Examples 1 and 2 are shown in Figures 3 and 4. As the foam residence time increased, as in Comparative Experimental Example 1, the foam coarsened and dried. Furthermore, when a mesh was attached to the suction pump, as in Comparative Experimental Example 2, the foam of the PVA aqueous solution temporarily remained, and the foam coarsened and dried. In contrast, it was confirmed that the foam coarsening and drying were suppressed by circulating the PVA aqueous solution (culture medium) so as to suppress the retention of the foam, as in the Experimental Examples.

[0066] The cultivation method and cultivation apparatus of the present invention can be suitably used for foam culture cultivation.

[0067] 1, 2 Cultivation device 11, 31 Cultivation tank 12 Foaming device 13, 39 Nutrient solution circulation device 14 First storage tank 15, 33 Pump 16 Second storage tank 17, 34 Piping 18, 35 Supply port 19, 36 Discharge port 20 Bottom surface 21, 38 Hole 22 Top end of second storage tank 32 Storage tank 37 Valve A Plant B Nutrient solution

Claims

1. A method for cultivating plants, comprising a step of supplying a culture solution to a cultivation tank containing the rhizosphere of a plant, discharging the culture solution from the cultivation tank, and circulating the culture solution by resupplying the discharged culture solution to the cultivation tank, wherein the culture solution exists in a foamy state within the cultivation tank, and at least one of the supply and discharge of the culture solution is carried out so as to prevent the foam of the culture solution existing within the cultivation tank from becoming coarse.

2. A cultivation method as described in claim 1, wherein in the circulating step, the culture solution is supplied to the cultivation tank in a foam state, and the culture solution is discharged in a foam state from a position lower than or at the same height as the position where the culture solution is supplied to the cultivation tank.

3. A cultivation method as described in claim 1, wherein in the circulating step, the culture medium is supplied in a foam state from the top of the cultivation tank and discharged in a foam state from the lowest position of the cultivation tank.

4. A cultivation method as described in claim 1, wherein in the circulating step, droplets of the culture solution are dripped from the top of the cultivation tank onto the foam of the culture solution present in the cultivation tank.

5. The cultivation method according to any one of claims 1 to 4, wherein the culture solution contains a fertilizer and a water-soluble polymer.

6. A cultivation method according to any one of claims 1 to 4, wherein the Sauter mean particle size of the culture solution foam present in the cultivation tank is 400 μm or less.

7. A cultivation method according to any one of claims 1 to 4, wherein the bottom of the cultivation tank is inclined.

8. A cultivation method according to any one of claims 1 to 4, wherein the cultivation tank is a cylindrical body with a central axis extending vertically or in an inclined direction.

9. A cultivation method according to any one of claims 1 to 4, wherein an outlet for the culture solution is provided at the lowest position of the cultivation tank, and the outlet is configured to allow spherical particles with a diameter of 1 cm to pass through.

10. A cultivation device comprising: a cultivation tank for containing the root zone of a plant; a foaming device for foaming the culture solution; and a culture solution circulation device for supplying the culture solution to the cultivation tank and re-supplying the culture solution discharged from the cultivation tank to the cultivation tank, wherein the cultivation device is configured to supply the culture solution in a foamy state to the cultivation tank and discharge the culture solution in a foamy state from a position lower than or at the same height as the position where the culture solution is supplied to the cultivation tank.

11. The cultivation device according to claim 10, which does not have a pump for discharging the culture solution from the cultivation tank.

12. A cultivation device according to claim 10 or 11, wherein the culture solution is discharged from the cultivation tank by its own weight.

13. A cultivation device as described in claim 10 or 11, wherein the cultivation tank has a structure in which two container-like bodies, each opening downward, are stacked with a gap between them, and the space between the two container-like bodies forms a space in which the root zone of the plant is contained.

14. A cultivation device comprising: a cultivation tank that contains the rhizosphere of a plant; and a culture solution circulation device that supplies culture solution to the cultivation tank and supplies the culture solution discharged from the cultivation tank back to the cultivation tank, wherein the culture solution circulation device is configured to drip droplets of the culture solution from the top of the cultivation tank onto the foam of the culture solution present in the cultivation tank.

15. The cultivation device according to claim 14, wherein the cultivation tank is a cylindrical body with a central axis extending vertically.

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