Nutrient solution for growing vegetables

Abstract

It reduces the concentration of nitrates in vegetables at harvest time and promotes vegetable growth by accelerating photosynthesis. [Solution] The nutrient solution for growing vegetables is a nutrient solution used when growing vegetables hydroponically by irradiating them with light from a lighting device. This nutrient solution contains 0.06 mg to 0.14 mg of nitrogen per liter and 0.1 mg to 0.25 mg of calcium oxide per liter.

Description

[Technical Field]

[0001] This disclosure relates to a method for producing vegetables and to lettuce. [Background technology]

[0002] Hydroponics is known as an alternative method of producing plants to conventional soil cultivation (see, for example, the descriptions in Patent Documents 1 to 5). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-7047 [Patent Document 2] Patent No. 5300993 [Patent Document 3] International Publication No. 2015 / 155914 [Patent Document 4] Japanese Patent Publication No. 2017-221177 [Patent Document 5] International Publication No. 2019 / 139031 [Overview of the project] [Problems that the invention aims to solve]

[0004] Regarding vegetable production using hydroponics, there is room for improvement in reducing the concentration of nitrates in vegetables at harvest time and promoting vegetable growth by accelerating photosynthesis. [Means for solving the problem]

[0005] The nutrient solution used to grow vegetables will be disclosed.

[0006] One form of nutrient solution for growing vegetables is a nutrient solution used when hydroponically cultivating vegetables by irradiating them with light from a lighting device, wherein the nitrogen content per liter is 0.06 mg to 0.14 mg and the calcium oxide content per liter is 0.1 mg to 0.25 mg. [Effects of the Invention]

[0007] For example, it can reduce the concentration of nitrates in vegetables at harvest time, and promote vegetable growth by accelerating photosynthesis. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows an example of the hydroponic cultivation period in the vegetable production method according to the first embodiment. [Figure 2] Figure 2(a) is a schematic perspective view showing an example of a cultivation site after sowing. Figure 2(b) is a schematic diagram showing an example of the cultivation site in Figure 2(a) after sowing, viewed from the left. [Figure 3] Figure 3(a) is a schematic perspective view showing an example of a cultivation site in the budding stage. Figure 3(b) is a schematic diagram showing an example of the cultivation site in the budding stage shown in Figure 3(a) viewed from the left. [Figure 4] Figure 4(a) is a schematic perspective view showing an example of a cultivation site during the seedling stage. Figure 4(b) is a schematic diagram showing an example of the cultivation site during the seedling stage shown in Figure 4(a) viewed from the left. [Figure 5] Figure 5(a) is a schematic perspective view showing an example of a cultivation site at the time of planting. Figure 5(b) is a schematic diagram showing an example of the cultivation site at the time of planting as shown in Figure 5(a), viewed from the left. [Figure 6] Figure 6(a) is a schematic perspective view showing an example of a cultivation site during the growing period. Figure 6(b) is a schematic diagram showing an example of the cultivation site in Figure 6(a) viewed from the left during the growing period. [Figure 7]FIG. 7(a) is a perspective view showing an example of the appearance of a lighting device. FIG. 7(b) is a perspective view showing an example of a state in which a translucent substrate is removed from the housing of the lighting device. [Figure 8] FIG. 8 is an exploded perspective view of an example of the lighting device. [Figure 9] FIG. 9(a) is a perspective view showing an example of the appearance of a light source. FIG. 9(b) is a view showing an example of a virtual cut surface along a plane drawn by a two-dot chain line in the light source of FIG. 9(a). [Figure 10] FIG. 10 is a diagram in which a spectrum related to the first light emitted by the light source is drawn as a thick solid line. [Figure 11] FIG. 11 is a diagram in which a photosynthetic action curve showing the degree to which light acts on photosynthesis for each wavelength is drawn as a thick solid line. [Figure 12] FIG. 12 is a diagram in which a spectrum related to the second light emitted by the light source is drawn as a thick solid line. [Figure 13] FIG. 13 is a diagram showing the main composition of each of the first nutrient solution, the second nutrient solution, the third nutrient solution, the fourth nutrient solution, the first reference nutrient solution, and the second reference nutrient solution.

BEST MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, the first embodiment will be described with reference to the drawings. In the drawings, parts having the same configuration and function are denoted by the same reference numerals, and duplicate descriptions will be omitted in the following description. The drawings are schematically shown. From FIGS. 2(a) to 9(b), a right-handed XYZ coordinate system is attached. In this XYZ coordinate system, the longitudinal direction along the horizontal direction of the lighting device 10 is taken as the +X direction, the short-side direction along the horizontal direction of the lighting device 10 is taken as the +Y direction, and the upward direction as the direction orthogonal to both the +X direction and the +Y direction is taken as the +Z direction.

[0010] <1. First Embodiment> <1-1. Outline of Hydroponic Cultivation of Vegetables> As shown in Figure 1, the hydroponic cultivation period for vegetables includes, for example, a first period P1, a second period P2, and a third period P3. The vegetables grown hydroponically (also called cultivated vegetables) include, for example, leafy vegetables such as lettuce.

[0011] The first period P1 is the period from the timing of sowing (time T0) to the timing of the start of seedling cultivation, including germination (time T1) (also called the germination period). The timing of sowing is the timing of sowing seeds in the seedbed. For example, sponge, polyurethane, or nonwoven fabric can be used for the seedbed. The timing of germination is the timing when cotyledons emerge from the seed in the seedbed. For example, if the target vegetable is lettuce, the cotyledons are two leaves. For lettuce, the length L1 of the period from sowing to seedling cultivation, including germination, is said to be, for example, around 7 days.

[0012] The second period P2 is the period from the time of seedling growth, including germination (time T1), to the time a predetermined number of days before the harvest time (time T4) (time T3). This second period P2 is the period during which vegetables mainly grow (also called the main growth period). The second period P2 can be divided into, for example, the early stage (also called the second A period) P2a and the later stage (also called the second B period) P2b.

[0013] Period 2A P2a corresponds to the period for growing seedlings (also called the seedling rearing period). For example, if the target vegetable is lettuce, the length of the seedling rearing period L2a is approximately 7 to 14 days. At the end of Period 2A P2a (time T2), the process of widening the spacing between seedlings after rearing (also called the spacing widening process) is carried out. The purpose of the spacing widening process is to reduce the inhibition of photosynthesis caused by overlapping leaves between adjacent vegetables as they grow, and to increase the room for growth. The spacing widening process may involve, for example, transplanting seedlings from the seedbed to a growing medium appropriate for their growth (also called planting). The growing medium may be, for example, sponge, polyurethane, or nonwoven fabric. During planting, the spacing between seedlings, such as between plants and between rows, is adjusted. The spacing widening process can also be achieved by dividing the seedbed and widening the spacing between seedlings, or by thinning out seedlings, without performing planting by transplanting seedlings from the seedbed to the growing medium.

[0014] Period 2B, P2b, is the period during which vegetables are grown from seedlings after the spacing has been widened (also called the cultivation growth period). For example, if the vegetable being cultivated is lettuce, the length of the cultivation growth period, L2b, is said to be about 10 to 16 days.

[0015] The third period, P3, is the period for further growing the vegetables before harvest (also called the pre-harvest period). The pre-harvest period is a predetermined number of days before the vegetables are harvested. The length of the pre-harvest period, L3, is typically between 1 and 7 days. For example, if the vegetable being cultivated is lettuce, the length of L3 is typically between 4 and 7 days.

[0016] From the above, a hydroponic vegetable production method has, for example, five steps S1 to S5 that are performed in order. Step S1 is the sowing of seeds. Step S2 is the process of allowing cotyledons to emerge from the seeds in the first period P1. Step S3 is the process of growing the vegetables in the second period P2 following the first period P1. Step S4 is the process of further growing the vegetables in the third period P3 following the second period P2. Step S5 is the process of harvesting the vegetables. When performing such hydroponic cultivation, the seedbed and growing medium are located in containers such as cultivation trays that store a culture solution (also called nutrient solution) for growing vegetables. The nutrient solution is a solution in which fertilizer components appropriate to the situation are dissolved. Also, during the germination period, for example, water is supplied from above the seeds sown in the seedbed to promote germination and the emergence of cotyledons from the seeds.

[0017] <1-2. Structure of the cultivation site in hydroponics> At the time of sowing, for example, as shown in Figures 2(a) and 2(b), multiple seeds 32a are arranged at appropriate intervals on a seedbed 31a located in the upper recess of the cultivation container 30a. The container 30a is, for example, a cultivation tray. This cultivation tray has a rectangular shape when viewed in plan from above in the direction of -Z. The container 30a contains a nutrient solution for growing vegetables. Therefore, the seedbed 31a is immersed in the nutrient solution. Also, for example, multiple lighting devices 10 are arranged on a support 34 located above the container 30a. The multiple lighting devices 10 are, for example, arranged parallel to each other at appropriate intervals. Power is supplied to each lighting device 10, for example, via a power supply 33.

[0018] During the first period P1, which is the germination period, for example, as shown in Figure 2(b), the light sources of each lighting device 10 are made to emit light for about 12 to 16 hours per day without using sunlight, and the light emitted from each lighting device 10 is irradiated onto multiple seeds 32a. In addition, water is supplied to the multiple seeds 32a. This promotes germination from each type of seed 32a. As a result, for example, as shown in Figures 3(a) and 3(b), cotyledons emerge from each of the multiple seeds 32a, and multiple vegetable seedlings 32b can be obtained. In Figures 2(b), 3(b), 4(b), 5(b), and 6(b), the direction of light propagation is indicated by a dashed-dot arrow for the light emitted from each lighting device 10, and the outer edge of the light is also drawn with a dashed-dot line.

[0019] During the 2A period P2a, which is the seedling stage, for example, as shown in Figures 4(a) and 4(b), the light sources of each lighting device 10 are made to emit light for about 12 to 16 hours per day without using sunlight, and the light emitted from each lighting device 10 is irradiated onto multiple vegetable seedlings 32b. This promotes the growth of multiple vegetable seedlings 32b, for example.

[0020] When the seedling stage is over, multiple vegetable seedlings 32b are transplanted, for example, by planting. Here, as shown in Figures 5(a) and 5(b), multiple vegetable seedlings 32b, which will become multiple target vegetables 32c, are arranged at appropriate intervals in the growing medium 31b located in the upper recess of the cultivation container 30b. Hereafter, the vegetable seedlings 32b and the target vegetables 32c will be collectively referred to as "vegetables" as appropriate. For example, a cultivation tray can be used for the container 30b. This cultivation tray has a long rectangular shape when viewed in plan from above in the downward direction (-Z direction). In the example of Figures 5(a) and 5(b), four long containers 30b are arranged in a nearly parallel manner. Each container 30b contains a nutrient solution for growing vegetables. Therefore, the growing medium 31b is immersed in the nutrient solution. Furthermore, for example, multiple lighting devices 10 are arranged on a support 34 located above the container 30a. The multiple lighting devices 10 are arranged parallel to each other with appropriate spacing between them. In the examples of Figures 5(a) and 5(b), the longitudinal direction of each lighting device 10 is, for example, perpendicular to the longitudinal direction of the container 30b. Power is supplied to each lighting device 10 via a power supply 33.

[0021] During the second B period P2b, which is the cultivation growth period, for example, as shown in Figure 5(b), the light sources of each lighting device 10 are made to emit light for about 12 to 16 hours per day without using sunlight, and the light emitted from each lighting device 10 is irradiated onto multiple target vegetables 32c. This promotes the growth of multiple target vegetables 32c.

[0022] In the third period P3, which is the period immediately preceding harvest, as shown in Figure 6(b), for example, the light sources of each lighting device 10 are made to emit light for about 12 to 16 hours per day without using sunlight, and the light emitted from each lighting device 10 is irradiated onto multiple target vegetables 32c. This promotes the growth of multiple target vegetables 32c, as shown in Figures 6(a) and 6(b).

[0023] Here, for example, the distance between the multiple lighting devices 10 and the seeds 32a, vegetable seedlings 32b, or vegetables to be cultivated 32c may be changed to an appropriate distance.

[0024] Furthermore, the multiple lighting devices 10 may be fitted with light sources that emit light having different spectra from each other, for example, between the first period P1, the second A period P2a, the second B period P2b, and the third period P3.

[0025] As described above, the hydroponic cultivation method for growing vegetables allows for the cultivation of target vegetables 32c without the use of sunlight.

[0026] <1-3. Configuration of the lighting system> As shown in Figures 7(a), 7(b), and 8, the lighting device 10 includes, for example, a housing 11, a wiring board 12, a plurality of light sources 1, and a light-transmitting substrate 13.

[0027] <1-3-1. Enclosure> The housing 11 has, for example, a long rectangular parallelepiped shape with a longitudinal direction along the +X direction, and an opening facing the -Z direction. The housing 11 has, for example, the function of holding the translucent substrate 13 and the function of dissipating the heat emitted by the light source 1 to the outside. The material of the housing 11 may be, for example, a metal such as aluminum, copper, or stainless steel, or plastic or resin. The housing 11 has, for example, a long main body 21 having a bottom 21a and a pair of holding parts 21b, and two lid parts 22. The bottom 21a has, for example, a longitudinal direction along the +X direction. The pair of holding parts 21b have, for example, a longitudinal direction along the +X direction while hanging down in the -Z direction from both ends of the bottom 21a in the width direction (+Y direction). Therefore, the main body 21 has an opening facing the -Z direction (downward) and openings located at both ends in the +X direction (longitudinal direction). The two lid portions 22 are in a state where, for example, the openings located at both ends of the main body portion 21 in the +X direction (longitudinal direction) are closed. In addition, each retaining portion 21b has a groove extending along the +X direction for holding the translucent substrate 13, for example, near the end in the -Z direction. In other words, a pair of grooves are positioned to face each other. The length of the housing 11 in the longitudinal direction (+X direction) is, for example, about 100 millimeters (mm) to 2000 mm.

[0028] <1-3-2. Wiring board> The wiring board 12 is located, for example, within the housing 11 and fixed to the housing 11. The wiring board 12 is fixed to a surface facing the -Z direction within the housing 11. A printed circuit board such as a rigid board, a flexible board, or a rigid-flexible board may be applied to the wiring board 12.

[0029] <1-3-3.Light source> Multiple light sources 1 are mounted on a wiring board 12 within the housing 11, for example, and are positioned in a straight line along the longitudinal direction of the housing 11. As shown in Figures 9(a) and 9(b), the light source 1 includes, for example, a substrate 2, a light-emitting element 3, a frame 4, a sealing member 5, and a wavelength conversion member 6.

[0030] <<Board 2>> The substrate 2 is, for example, an insulating substrate. The material of the substrate 2 may be, for example, a ceramic such as alumina or mullite, or a glass ceramic. The material of the substrate 2 may also be a composite material such as a material mixed with multiple types of ceramics, or a material mixed with ceramic and glass ceramic. Here, for example, if a polymer resin in which metal oxide fine particles are dispersed is used as the material of the substrate 2, the thermal expansion coefficient of the substrate 2 can be adjusted as appropriate. The substrate 2 also has, for example, a conductor (also called a wiring conductor) that electrically connects the inside and outside of the substrate 2. The material of the wiring conductor may be a conductive material such as tungsten, molybdenum, manganese, or copper. The wiring conductor can be manufactured, for example, by applying a metal paste obtained by adding an organic solvent to powder such as tungsten to a ceramic green sheet which will be the substrate 2 in a predetermined pattern, and then stacking and firing multiple ceramic green sheets. For example, if a plating layer of nickel or gold is attached to the surface of the wiring conductor, oxidation of the wiring conductor can be reduced. Furthermore, if a metallic reflective layer is positioned on the -Z-facing surface of substrate 2, spaced apart from the wiring conductors and the plating layer, the reflective layer can efficiently reflect light in the -Z direction. Examples of materials for the reflective layer include aluminum, silver, gold, copper, or platinum. The wiring pattern on substrate 2 is electrically connected to the wiring pattern on wiring board 12, for example, via solder or conductive adhesive. This allows, for example, a signal from wiring board 12 to be transmitted to the light-emitting element 3 via substrate 2, causing the light-emitting element 3 to emit light. Electricity is supplied to wiring board 12 via wiring from an externally provided power source.

[0031] <<hibi3>> The light-emitting element 3 is, for example, mounted on a substrate 2. The light-emitting element 3 is electrically connected, for example, to a plating layer attached to the surface of a wiring conductor on the substrate 2 via a brazing material or solder. The light-emitting element 3 is, for example, a light-emitting diode (LED) that can emit light outward in response to the recombination of electrons and holes in a pn junction region using a semiconductor. The light-emitting element 3 has a translucent substrate and an optoelectronic semiconductor layer located on the translucent substrate. The translucent substrate is, for example, a substrate on which the optoelectronic semiconductor layer can be grown using a chemical vapor deposition method such as metal-organic vapor deposition or molecular beam epitaxial deposition. The material of the translucent substrate is, for example, sapphire, gallium nitride, aluminum nitride, zinc oxide, zinc selenide, silicon carbide, silicon, or zirconium diboride. The thickness of the translucent substrate is, for example, about 50 micrometers (μm) to 1000 μm. The optical semiconductor layer includes, for example, a first semiconductor layer, an emissive layer, and a second semiconductor layer. The first semiconductor layer is located on, for example, a translucent substrate. The emissive layer is located on, for example, the first semiconductor layer. The second semiconductor layer is located on, for example, the emissive layer. The materials for the first semiconductor layer, the emissive layer, and the second semiconductor layer include, for example, nitride semiconductors, gallium phosphorus, or gallium arsenide as III-V semiconductors. Nitride semiconductors include, for example, gallium nitride, aluminum nitride, or indium nitride. The thickness of the first semiconductor layer is, for example, about 1 μm to 5 μm. The thickness of the emissive layer is, for example, about 25 nanometers (nm) to 150 nm. The thickness of the second semiconductor layer is, for example, about 50 nm to 600 nm. A light-emitting element 3 having such a configuration can emit excitation light in the wavelength range of, for example, about 370 nm to 420 nm.

[0032] <<Frame 4>> The frame 4 is positioned, for example, on the substrate 2 so as to surround the light-emitting element 3. The material of the frame 4 is, for example, a resin material mixed with powder. The powder material is, for example, a ceramic material or porous material such as aluminum oxide, titanium oxide, zirconium oxide, or yttrium oxide, or a metal oxide such as aluminum oxide, titanium oxide, zirconium oxide, or yttrium oxide. The frame 4 is, for example, stacked on the substrate 2 and connected to the substrate 2 via resin or the like. The frame 4 is positioned so as to surround the light-emitting element 3, for example, without being in contact with the light-emitting element 3. The inner wall surface of the frame 4 is positioned so as to expand outward from the end in the +Z direction to the end in the -Z direction. In other words, the inner wall surface of the frame 4 is inclined with respect to the Z axis such that, for example, the cross-section of the space inside the frame 4 along the XY plane expands as it proceeds toward the -Z direction. In this case, for example, the inner wall surface of the frame 4 functions as a surface (also called a reflective surface) that reflects the excitation light emitted from the light-emitting element 3. Here, for example, if the inner wall surface of the frame 4 is circular when viewed in a plan view in the +Z direction, the reflective surface can reflect the light emitted by the light-emitting element 3 in all directions. Furthermore, the inner wall surface of the frame 4 has, for example, a metal layer and a metallic plating layer (also called a plated metal layer) covering this metal layer on the inner circumferential surface of the frame 4, which is a sintered body. Here, the material of the metal layer can be, for example, tungsten, molybdenum, copper, or silver. The plated metal layer can be, for example, nickel or gold. Such a plated metal layer can reflect the light emitted by the light-emitting element 3. In other words, in this case, the inner wall surface of the frame 4 can play the role of a reflective surface that reflects the light emitted by the light-emitting element 3. The angle at which the inner wall surface of frame 4 is inclined with respect to the XY plane is, for example, an angle of about 55 to 70 degrees.

[0033] <<Sealing member 5>> The sealing member 5 is positioned, for example, filling the area inside the frame 4, excluding the portion along the -Z end of the enclosed space. This allows the sealing member 5 to seal, for example, the light-emitting element 3. The sealing member 5 is, for example, translucent. This allows the sealing member 5 to transmit light emitted from, for example, the light-emitting element 3. The material of the sealing member 5 is, for example, a translucent and insulating resin such as silicone resin, acrylic resin, or epoxy resin. The refractive index of the sealing member 5 is, for example, about 1.4 to 1.6.

[0034] <<Wavelength conversion component 6>> The wavelength conversion member 6 is located, for example, in a region along the -Z-direction end of the space inside the frame 4, which is enclosed by the frame 4. Here, for example, the wavelength conversion member 6 is located along the -Z-direction-facing surface of the sealing member 5. The wavelength conversion member 6 is located, for example, so as to fit within the space inside the frame 4. The wavelength conversion member 6 can, for example, convert the wavelength of light emitted by the light-emitting element 3. The wavelength conversion member 6 has, for example, a phosphor 7. More specifically, for example, the wavelength conversion member 6 has a form in which the phosphor 7 is contained in a light-transmitting and insulating resin (also called an insulating resin) or glass. The insulating resin material can be, for example, a light-transmitting insulating resin such as fluororesin, silicone resin, acrylic resin, or epoxy resin. Here, for example, a large number of phosphors 7 are located in a state in which they are dispersed substantially uniformly in the wavelength conversion member 6. The phosphors 7 can be excited by the light emitted from the light-emitting element 3 when the light enters the interior of the wavelength conversion member 6, and emit light. Here, for example, by appropriately setting the phosphor applied to phosphor 7, the spectrum of light emitted from light source 1 can be changed.

[0035] <1-3-4. Transparent substrate> The translucent substrate 13 is positioned, for example, to close an opening in the housing 11 facing the -Z direction. The material of the translucent substrate 13 is a material that allows light emitted from the light source 1 to pass through. For example, acrylic resin or glass can be used as the material of the translucent substrate 13. For example, a plate-like body having a rectangular front and back surface can be used for the translucent substrate 13. The length of the translucent substrate 13 along its longitudinal direction (+X direction) is, for example, about 98 mm to 1998 mm. The translucent substrate 13 is inserted into a pair of grooves in a pair of holding parts 21b from an opening located at the +X or -X end in the longitudinal direction (+X direction) of the main body 21, and slid along the +X direction, so that it is held by the pair of holding parts 21b at a position spaced apart from the multiple light sources 1 in the -Z direction. In the lighting device 10, the cover portion 22 is in a state where it is closing the openings located at the ends of the main body portion 21 in the +X and -X directions in the longitudinal direction (+X direction).

[0036] <1-4. Lighting conditions in hydroponics> In the hydroponic cultivation described above, for example, the lighting conditions for growing vegetables can be changed by appropriately changing the lighting device 10 that irradiates the vegetables with light.

[0037] <1-4-1. First light irradiation> In the first embodiment, for example, in the third step S3 of hydroponic vegetable cultivation, vegetables are grown by irradiating them with light having a maximum light intensity (also called the first maximum value) in the visible light wavelength range of 500 nm or less, specifically 420 nm to 490 nm (also called the first light) for at least a portion of the second period P2. This makes it possible to increase, for example, the glutamine content and sugar content of the vegetables. Therefore, for example, the taste of the vegetables after harvest can be improved. Note that the light intensity (W / m 2The value ( / nm) represents the irradiance of light per unit area and per unit wavelength. Furthermore, for example, the relative magnitudes of light intensities in the light spectrum will be explained as appropriate using the relative value of the light intensity (also called relative light intensity) when the maximum light intensity is set as a reference value (e.g., 1).

[0038] Here, for example, if vegetables are grown under the first light for at least a portion of the second period P2, it is thought that the glutamine content and sugar content of the harvested vegetables will increase through the following mechanism.

[0039] In the second period P2, when the vegetable seedlings 32b and the target vegetables 32c are irradiated with the first light, the vegetables are subjected to stress, and reactive oxygen species are generated within the vegetable cells. In response, the vegetables activate the citric acid cycle and other mechanisms to protect their tissues from reactive oxygen species, producing large amounts of antioxidants such as citric acid. Here, for example, α-ketoglutaric acid (2-oxoglutaric acid) and glutamic acid are produced in increased quantities. At this time, for example, reactions in the reaction cycle catalyzed by glutamine synthase (GS) and glutamate synthase (GOGAT) (also called the GS / GOGAT cycle) are promoted within the vegetables. In this GS / GOGAT cycle, for example, ammonium absorbed from the plant roots combines with glutamic acid using glutamine synthase (GS) as a catalyst to produce glutamine. The glutamine produced in this reaction reacts with 2-oxoglutaric acid to produce two molecules of glutamate, catalyzed by glutamate synthase (GOGAT). Of these two molecules, one is used in a reaction catalyzed by glutamine synthase (GS) to combine with ammonium absorbed from the plant roots. The remaining molecule is used in the synthesis of other amino acids. If the reactions in this GS / GOGAT cycle are accelerated, for example, the amount of glutamine as a precursor to glutamate increases. The ammonium used in the GS / GOGAT cycle is supplied, for example, from ammoniacal nitrogen and nitrate nitrogen contained in the nutrient solution. Nitrate nitrogen is converted to ammoniacal nitrogen by reduction in the roots and leaves, for example, and thus becomes a precursor to ammonium. Glutamine synthase (GS) is an enzyme contained in chloroplasts of vegetables, for example. Glutamate synthase (GOGAT) is an enzyme contained in vegetables, for example.

[0040] Furthermore, vegetables, for example, produce antioxidants such as ascorbic acid and polyphenols to protect their tissues from reactive oxygen species. These ascorbic acids and polyphenols are synthesized using sugars such as glucose and galactose. Therefore, in vegetables, for example, antioxidants accumulate to an appropriate level necessary for protecting their tissues, and sugars, which are precursors of antioxidants, also increase.

[0041] Here, by applying, for example, a blue phosphor that emits fluorescence at approximately 420 nm to 490 nm to the phosphor 7 contained in the wavelength conversion member 6 of the light source 1, the first light can be irradiated onto the vegetables. Examples of such blue phosphors include (Sr,Ca,Ba) 10 (PO4)6Cl2:Eu can be used. In this case, the light source 1 can emit light with a spectrum as shown by the thick solid line in Figure 10. The first light may contain, for example, a red light component. However, for example, the lower the proportion of the red light component in the first light, the lower the energy consumption of the light source 1 can be. Also, the photon flux density of the first light irradiated onto the vegetables may be, for example, 80 micromoles per square meter (80 μmol / m²). 2 ) or more. The photon flux density of the first light irradiated onto the vegetables is, for example, 100 μmol / m³. 2 From 250 μmol / m³ 2 It may be considered to be of a certain degree.

[0042] Here, for example, by appropriately setting a portion of the period in the hydroponic cultivation of vegetables during the third step S3 in which the first light is irradiated to grow the vegetables (also called the first light irradiation period), the glutamine content and sugar content of the vegetables can be moderately increased. For example, one could set the first light irradiation period to include the later part of the second period P2 (second B period) P2b. Alternatively, one could set the length of the first light irradiation period to be 1 / 4 to 1 / 2 of the total period of the first period P1, the second period P2, and the third period P3 (also called the total period). More specifically, one could set the first light irradiation period to be the second B period P2b. In this way, by appropriately setting the first light irradiation period, it is possible to achieve a good balance between vegetable growth and an increase in the glutamine content and sugar content of the vegetables. This makes it possible to efficiently produce vegetables with high flavor, for example. Furthermore, if, for example, the photon flux density (light intensity) of the first light irradiated onto the cultivated vegetables 32c during period P2b of the third step is increased, the glutamine content in the harvested vegetables may increase.

[0043] <1-4-2. Second light irradiation> In the first embodiment, for example, in the second step S2 to the fourth step S4 of hydroponic vegetable cultivation, vegetables may be grown by irradiating them with light having a maximum light intensity (also called the second maximum value) in the visible light wavelength range exceeding 500 nm (also called the second light) for a period different from the first light irradiation period. In this case, for example, the excessive production of antioxidants in the vegetables can be reduced, the bitterness caused by the presence of excess antioxidants in the vegetables after harvest can be reduced, and the sugar content of the vegetables after harvest can be increased. Therefore, for example, the taste of the vegetables can be improved.

[0044] Here, for example, if vegetables are grown with a second light irradiation period at a different time than the first light irradiation period, it is thought that the excessive increase in antioxidants in the harvested vegetables will be reduced and the sugar content will increase through the following mechanism. The following mechanism is described based on the photosynthetic action curves shown in Figure 11, which represent the average values ​​of photosynthetic action curves for 61 types of plants shown by McCree (1972) and Inada (1976).

[0045] For example, by irradiating vegetables with a second light source after the first light source, which promotes photosynthesis more effectively than the first light source, stress on the vegetables is reduced. This reduces, for example, the increased production of reactive oxygen species and the excessive generation of antioxidants within the vegetables. Also, for example, the second light source promotes normal photosynthesis more than the production of reactive oxygen species within the vegetables. As a result, for example, the production of amino acids necessary for vegetable growth is promoted through the reduction of organic acids. Furthermore, for example, the activation of the citric acid cycle caused by the first light source is stopped, and the production of sugars is promoted through the reduction action using organic acids produced in the citric acid cycle as raw materials.

[0046] Here, the second light is, for example, light that contains a large component of light in the red wavelength range. Specifically, as the second light, for example, it is conceivable to use light that has a maximum light intensity (also called the maximum light intensity) in the wavelength range of 590 nm to 650 nm, and whose light intensity value at a wavelength of 700 nm (also called the first value) is 20% or more of the maximum light intensity, and whose light intensity value at a wavelength of 800 nm (also called the second value) is 10% or less of the maximum light intensity. In this case, for example, by irradiating with a second light that can promote photosynthesis in vegetables more than the first light, it is possible to promote normal photosynthesis in vegetables rather than generating reactive oxygen species. Furthermore, for example, the second light contains a wide range of light components of wavelengths that contribute greatly to promoting photosynthesis, and the proportion of light components of wavelengths that contribute less to promoting photosynthesis is low in the second light. This makes it possible to promote the growth of vegetables and reduce the amount of energy consumed for light irradiation. As a result, for example, it becomes possible to efficiently produce vegetables with superior flavor.

[0047] Furthermore, for the spectrum of the second light, the wavelength that exhibits the maximum peak (maximum light intensity) (also called the first wavelength) is defined as λ1 [nm]. For the spectrum of the second light, the wavelength closest to the first wavelength λ1 that is shorter than the first wavelength λ1 and has a light intensity of 50 percent (also called the second wavelength) is defined as λ2 [nm]. For the spectrum of the second light, the wavelength closest to the first wavelength λ1 that is longer than the first wavelength λ1 and has a light intensity of 50 percent (also called the third wavelength) is defined as λ3 [nm]. In this case, as the spectrum of the second light, for example, a spectrum that has a maximum light intensity in the wavelength range of 610 nm to 630 nm and satisfies the requirements of equations (1) and (2) can be adopted.

[0048] λ1-70≦λ2≦λ1-30 (1) λ1+30≦λ3≦λ1+70 (2)

[0049] Here, for example, if the first wavelength λ1 is within the range of 615 nm to 625 nm, the second light may have fewer components of light in the wavelength range of 750 nm or higher, which contribute less to promoting photosynthesis. Also, in the second light, for example, in the light from a red phosphor, the ratio of the photon flux in the wavelength range of 610 nm to 630 nm to the photon flux in the wavelength range of 540 nm to 700 nm may be 15% to 25%. As a result, the second light emitted from light source 1 does not contain an excessive amount of light of a specific wavelength in the red light wavelength range of 540 nm to 700 nm, which contributes more to promoting photosynthesis, and the proportion of near-infrared light, which contributes less to promoting photosynthesis and can cause a decrease in the rate of photosynthesis, is reduced. Furthermore, if, for example, the absolute value of the difference between the first wavelength λ1 and the second wavelength λ2 is greater than the absolute value of the difference between the first wavelength λ1 and the second wavelength λ3, then the proportion of light components near 670 nm, which is the peak wavelength in the red light wavelength range in the photosynthetic action curve shown in Figure 11, will increase in the second light.

[0050] Here, the second light may include, for example, light components in the blue to violet wavelength range. For example, as the second light, light having a peak in light intensity smaller than the maximum light intensity (also called peak light intensity) in the visible light wavelength range of 500 nm or less may be used. This makes it possible to improve the glutamine content and sugar content of vegetables even during the period of irradiation with the second light. For example, according to the photosynthetic action curve shown in Figure 11, light in the blue light wavelength range of 420 nm to 490 nm also contributes to photosynthesis. Therefore, the spectrum of the second light may have a peak in the light component emitted from a blue phosphor in the wavelength range of 420 nm to 490 nm. Here, for example, the wavelength showing the peak in light intensity in the wavelength range of 420 nm to 490 nm in the spectrum of the second light (also called the fourth wavelength) is λ4 [nm], and the light intensity at the first wavelength λ1 (relative light intensity) is 1. In this case, for example, if the spectrum of the second light is adopted such that the light intensity (relative light intensity) at the fourth wavelength λ4 is 0.3 to 0.5, and the ratio of the photon flux from the blue phosphor in the 420 nm to 490 nm wavelength range to the photon flux from the red phosphor in the 540 nm to 700 nm wavelength range is 10% to 20%, then the second light will have a good balance of red and blue light necessary for photosynthesis.

[0051] Furthermore, the second light may include, for example, a component of light in the green wavelength range. Here, for example, according to the photosynthetic action curve shown in Figure 11, light in the green wavelength range of 490 nm to 540 nm also contributes to photosynthesis to some extent. For this reason, the spectrum of the second light may contain an appropriate amount of light emitted from the green phosphor in the wavelength range of 490 nm to 540 nm. Specifically, for example, when the light intensity (relative light intensity) at the first wavelength λ1 is set to 1, the spectrum of the second light is adopted in which the average value of the light intensity (relative light intensity) in the wavelength range of 490 nm to 540 nm is 0.1 or higher or 0.3 or higher. Also, in the spectrum of the second light, for example, the ratio of the photon flux from the green phosphor in the wavelength range of 490 nm to 540 nm to the photon flux from the red phosphor in the wavelength range of 540 nm to 700 nm may be 5% to 15%. Furthermore, in the spectrum of the second light, for example, the ratio of the photosynthetic photon flux from the green phosphor in the 490 nm to 540 nm wavelength range to the photosynthetic photon flux from the blue phosphor in the 420 nm to 490 nm wavelength range may be 45% to 65%. In this case, the second light has a good balance of red, blue, and green light necessary for photosynthesis. Here, the photosynthetic tissue of the leaf is differentiated into, for example, palisade tissue on the upper side of the leaf and spongy tissue on the lower side of the leaf. Red and blue light are absorbed by chloroplasts in the palisade tissue on the upper side of the leaf and contribute to photosynthesis. On the other hand, green light is not easily absorbed by chloroplasts, for example, but green light that passes through the palisade tissue on the upper side of the leaf and reaches the spongy tissue on the lower side of the leaf is absorbed by chloroplasts after repeated scattering in the spongy tissue and contributes to photosynthesis. Therefore, for example, if the second light also contains an appropriate amount of green light, photosynthesis can be promoted.

[0052] Incidentally, since the light emitted from light source 1 also includes excitation light in the near-ultraviolet region emitted by light-emitting element 3, the spectrum of the second light may have a peak in the wavelength range of 380 nm to 420 nm, for example. Here, for example, let λ5 [nm] be the wavelength (also called the fifth wavelength) that shows the peak of light intensity in the wavelength range of 380 nm to 420 nm in the spectrum of the second light, and let the light intensity (relative light intensity) at the first wavelength λ1 be 1. In this case, for example, in the spectrum of the second light, the light intensity (relative light intensity) at the fifth wavelength λ5 is 0.2 to 0.4, and the ratio of the photon flux in the wavelength range of 380 nm to 420 nm to the photon flux in the wavelength range of 540 nm to 700 nm from the red phosphor may be 1% to 10%.

[0053] Furthermore, regarding the second light emitted from light source 1, for example, it is conceivable that the color temperature is in the range of 1900K to 2100K, the average color rendering index (Ra) is in the range of 70 to 75, and the CIE chromaticity coordinate xy values ​​satisfy the relationships 0.4≦x≦0.5 and 0.3≦y≦0.4.

[0054] Here, the phosphor 7 contained in the wavelength conversion member 6 of the light source 1 is, for example, (Sr, Ca, Ba) 10 (PO4)6Cl2:Eu is used as a blue phosphor, and (Sr,Ba,Mg)2SiO4:Eu 2+ By applying a green phosphor using (Sr,Ca)AlSiN3:Eu and a red phosphor using (Sr,Ca)AlSiN3:Eu in a mixing ratio of 3:1:46, a second light irradiation that satisfies the above requirements can be achieved. In this case, the light source 1 can emit light with a spectrum as shown by the thick solid line in Figure 12.

[0055] The spectrum shown in FIG. 12 has the following characteristics. A first wavelength λ1 showing the maximum light intensity in the wavelength range of light from the red phosphor is about 616 nm, a second wavelength λ2 is about 578 nm, a third wavelength λ3 is about 677 nm, and the full width at half maximum with respect to the maximum light intensity is about 100 nm. The absolute value of the difference between the first wavelength λ1 and the third wavelength λ3, which is about 61 nm, is larger than the absolute value of the difference between the first wavelength λ1 and the second wavelength λ2, which is about 38 nm. The ratio of the photon flux in the wavelength range of 610 nm to 630 nm to the photon flux in the wavelength range of 540 nm to 700 nm of the light from the red phosphor is about 20%. Also, a fourth wavelength λ4 showing a peak in the wavelength range of light from the blue phosphor is about 453 nm, and when the light intensity (relative light intensity) at the first wavelength λ1 is 1, the light intensity (relative light intensity) at the fourth wavelength λ4 is about 0.41. The ratio of the photon flux in the wavelength range of 420 nm to 490 nm of the light from the blue phosphor to the photon flux in the wavelength range of 540 nm to 700 nm of the light from the red phosphor is about 15%. Also, when the light intensity (relative light intensity) at the first wavelength λ1 is 1, the average value of the light intensity (relative light intensity) in the wavelength range of 490 nm to 540 nm of the light from the green phosphor is about 0.21. The ratio of the photon flux in the wavelength range of 490 nm to 540 nm of the light from the green phosphor to the photon flux in the wavelength range of 540 nm to 700 nm of the light from the red phosphor is about 8.5%, and the ratio of the photon flux in the wavelength range of 490 nm to 540 nm of the light from the green phosphor to the photon flux in the wavelength range of 420 nm to 490 nm of the light from the blue phosphor is about 56%. Further, a fifth wavelength λ5 is about 406 nm, and when the light intensity (relative light intensity) at the first wavelength λ1 is 1, the light intensity (relative light intensity) at the fifth wavelength λ5 is about 0.36.

[0056] Also, the photon flux density of the second light irradiated to the vegetables is, for example, 80 micromoles per square meter (80 μmol / m 2 ) or more. The photon flux density of the second light irradiated to the vegetables may be, for example, on the order of 100 μmol / m 2 to 250 μmol / m 2 .

[0057] <1-5. Conditions for nutrient solution in hydroponics> In the hydroponic cultivation described above, for example, the nutrients supplied to the vegetables during cultivation can be changed by appropriately changing the nutrient solution stored in the cultivation containers 30a and 30b.

[0058] <1-5-1. Use of Nutrient Solution 1> In the first embodiment, for example, in the third step S3 of hydroponic vegetable cultivation, vegetables may be grown using a first nutrient solution during the first light irradiation period in which vegetables are grown by irradiating them with a first light. The first nutrient solution is, for example, a culture solution in which the nitrogen (N) content is 0.2 mg to 0.47 mg per liter and the calcium oxide (CaO) content is 0.33 mg to 0.83 mg per liter. This makes it possible to increase the sugar content of vegetables and to decrease the nitrate concentration in vegetables at harvest.

[0059] Here, the amounts of nitrogen (N), phosphorus pentoxide (P2O5), potassium oxide (K2O), magnesium oxide (MgO), calcium oxide (CaO), and iron (Fe) per liter in the first nutrient solution are set to, for example, the ranges shown in Figure 13. Specifically, the amount of nitrogen (N) per liter in the first nutrient solution is set to, for example, 0.2 mg to 0.47 mg. The amount of phosphorus pentoxide (P2O5) per liter in the first nutrient solution is set to, for example, 0.13 mg to 0.33 mg. The amount of potassium oxide (K2O) per liter in the first nutrient solution is set to, for example, 0.4 mg to 1 mg. The amount of magnesium oxide (MgO) per liter in the first nutrient solution is set to, for example, 0.12 mg to 0.27 mg. The calcium oxide (CaO) content per liter in the first nutrient solution is set to, for example, 0.33 mg to 0.83 mg. The iron (Fe) content per liter in the first nutrient solution is set to, for example, 0.003 mg to 0.01 mg.

[0060] Incidentally, in general hydroponic cultivation, for example, in the third step S3, vegetables are grown using the first reference nutrient solution during the second B period P2b, and vegetables are grown using the second reference nutrient solution during the second A period P2a. The first and second reference nutrient solutions are general-purpose culture solutions widely used for fruit vegetables, leafy vegetables, and flowers. The nitrogen (N), phosphorus pentoxide (P2O5), potassium oxide (K2O), magnesium oxide (MgO), calcium oxide (CaO), and iron (Fe) content per liter in the first and second reference nutrient solutions are set to the values ​​shown in Figure 13, for example. Specifically, the nitrogen (N) content per liter in the first reference nutrient solution is set to approximately 1.3 mg, for example. The phosphorus pentoxide (P2O5) content per liter in the first reference nutrient solution is set to approximately 0.6 mg, for example. The potassium oxide (K2O) content per liter of the first reference nutrient solution is set to approximately 2.03 mg. The magnesium oxide (MgO) content per liter of the first reference nutrient solution is set to approximately 1.15 mg. The calcium oxide (CaO) content per liter of the first reference nutrient solution is set to approximately 0.0075 mg. The iron (Fe) content per liter of the first reference nutrient solution is set to approximately 0.0135 mg. The nitrogen (N) content per liter of the second reference nutrient solution is set to approximately 0.52 mg. The phosphorus pentoxide (P2O5) content per liter of the second reference nutrient solution is set to approximately 0.24 mg. The potassium oxide (K2O) content per liter of the second reference nutrient solution is set to approximately 0.81 mg. The magnesium oxide (MgO) content per liter of the second reference nutrient solution is set to approximately 0.46 mg, for example. The calcium oxide (CaO) content per liter of the second reference nutrient solution is set to approximately 0.003 mg, for example. The iron (Fe) content per liter of the second reference nutrient solution is set to approximately 0.0054 mg, for example.

[0061] For example, if vegetables are grown using a first nutrient solution that has a lower nitrogen content and a higher calcium oxide content than the first and second reference nutrient solutions during the first light irradiation period, it is thought that the sugar content will increase and the nitrate concentration will decrease in the harvested vegetables through the following mechanism.

[0062] During the first light irradiation period, growing vegetables using the first nutrient solution reduces the nitrogen content in the nutrient solution, leading to a decrease in nitrate nitrogen. This, for example, reduces the concentration of nitrates in the vegetables at harvest. Also, for example, the reduced supply of nitrogen, which is a precursor to amino acids, moderately reduces amino acid synthesis through processes such as the synthesis of nitrogen and carbon (C). In contrast, for example, in response to the first light irradiation, vegetables produce antioxidants such as ascorbic acid and polyphenols to protect their tissues from reactive oxygen species. These ascorbic acid and polyphenols are synthesized using sugars such as glucose and galactose. Therefore, for example, in vegetables, antioxidants accumulate to an appropriate amount necessary for protecting their tissues, and the amount of sugars that serve as precursors to antioxidants increases. Also, for example, an increase in the concentration of calcium oxide in the nutrient solution promotes the production of antioxidants through adaptation to strong light, thus increasing the amount of sugars that serve as precursors to antioxidants.

[0063] <1-5-2. Use of the second nutrient solution> In the first embodiment, for example, in the second step S2 and third step S3 of hydroponic vegetable cultivation, vegetables may be grown using a second nutrient solution during a period prior to the first light irradiation period in which vegetables are grown by irradiating them with the first light. The second nutrient solution is, for example, a culture solution having a nitrogen content of 0.06 mg to 0.14 mg per liter and a calcium oxide content of 0.1 mg to 0.25 mg per liter. This makes it possible to reduce the nitrate concentration in the vegetables at harvest time and to promote vegetable growth by promoting photosynthesis.

[0064] Here, the amounts of nitrogen (N), phosphorus pentoxide (P2O5), potassium oxide (K2O), magnesium oxide (MgO), calcium oxide (CaO), and iron (Fe) per liter in the second nutrient solution are set to, for example, the ranges shown in Figure 13. Specifically, the amount of nitrogen (N) per liter in the second nutrient solution is set to, for example, 0.06 mg to 0.14 mg. The amount of phosphorus pentoxide (P2O5) per liter in the second nutrient solution is set to, for example, 0.04 mg to 0.1 mg. The amount of potassium oxide (K2O) per liter in the second nutrient solution is set to, for example, 0.12 mg to 0.3 mg. The amount of magnesium oxide (MgO) per liter in the second nutrient solution is set to, for example, 0.04 mg to 0.08 mg. The calcium oxide (CaO) content per liter in the second nutrient solution is set to, for example, 0.1 mg to 0.25 mg. The iron (Fe) content per liter in the second nutrient solution is set to, for example, 0.001 mg to 0.003 mg.

[0065] By the way, in typical hydroponic cultivation, for example, in the second step S2, vegetables are grown using the second reference nutrient solution mentioned above, and in the third step S3, vegetables are grown using the first reference nutrient solution during the second B period P2b, and vegetables are grown using the second reference nutrient solution during the second A period P2a.

[0066] Here, for example, if vegetables are grown using a second nutrient solution that has a lower nitrogen content and a higher calcium oxide content than the first and second reference nutrient solutions during the period prior to the first light irradiation period in the second step S2 and the third step S3, it is thought that the nitrate concentration in the vegetables after harvest will decrease and vegetable growth will be promoted by the following mechanism, through the promotion of photosynthesis.

[0067] If vegetables are grown using the second nutrient solution during the period prior to the first light irradiation period in the second step S2 and the third step S3, the nitrogen content in the nutrient solution decreases, leading to a decrease in nitrate nitrogen. This, for example, reduces the concentration of nitrates in the vegetables at harvest. Additionally, for example, an increase in the concentration of calcium oxide in the nutrient solution promotes photosynthesis in the plants.

[0068] <1-5-3. Use of the third nutrient solution> In the first embodiment, for example, in the third period P3 of the fourth step S4 in hydroponic vegetable cultivation, vegetables may be grown using a third nutrient solution. The third nutrient solution is, for example, a nutrient solution containing nitrogen in the form of ammonia nitrogen, with a nitrogen content of 0.21 mg to 0.42 mg per liter. This makes it possible to improve the taste of vegetables while reducing the concentration of nitrates in the vegetables at harvest time.

[0069] Here, the third nutrient solution may contain nitrogen (N) in the form of ammonium sulfate ((NH4)2SO4) as ammoniacal nitrogen. The nitrogen (N) content per liter of the third nutrient solution is set to, for example, the range shown in Figure 13.

[0070] By the way, in typical hydroponic cultivation, for example, in step 4, S4, it is conceivable to grow vegetables using the second reference nutrient solution mentioned above.

[0071] Here, for example, in step 4 S4, if vegetables are grown using a third nutrient solution that has a lower nitrogen content than the second reference nutrient solution and contains nitrogen in the form of ammonia nitrogen, it is thought that the concentration of nitrates in the harvested vegetables will decrease and the taste of the vegetables will improve through the following mechanism.

[0072] In step 4, S4, growing vegetables using the third nutrient solution reduces the concentration of nitrates in the vegetables at harvest time, for example, due to a decrease in nitrate nitrogen in the nutrient solution. Also, for example, supplying ammonia nitrogen while irradiating with the second light reduces the excessive production of antioxidants and moderately promotes amino acid synthesis, adding richness to the flavor and improving the taste of the vegetables.

[0073] <1-5-4. Use of Nutrient Solution 4> In the first embodiment, for example, in the third period P3 of the fourth step S4 in hydroponic cultivation of vegetables, the fourth nutrient solution may be used instead of the third nutrient solution to grow the vegetables. The fourth nutrient solution is, for example, a nutrient solution in which the nitrogen content is 0.01 mg or less per liter, the magnesium oxide content is 0.12 mg to 0.24 mg per liter, and the calcium oxide content is 0.54 mg to 0.8 mg per liter. This makes it possible to improve the taste of vegetables while reducing the nitrate concentration in the vegetables at harvest, and to promote the growth of vegetables by promoting photosynthesis.

[0074] Here, the amounts of nitrogen (N), phosphorus pentoxide (P2O5), potassium oxide (K2O), magnesium oxide (MgO), calcium oxide (CaO), and iron (Fe) per liter in the fourth nutrient solution are set to, for example, the ranges shown in Figure 13. Specifically, the amount of nitrogen (N) per liter in the fourth nutrient solution is set to, for example, 0.01 mg or less. The amount of phosphorus pentoxide (P2O5) per liter in the fourth nutrient solution is set to, for example, 0.2 mg to 0.4 mg. The amount of potassium oxide (K2O) per liter in the fourth nutrient solution is set to, for example, 0.72 mg to 1.2 mg. The amount of magnesium oxide (MgO) per liter in the fourth nutrient solution is set to, for example, 0.12 mg to 0.24 mg. The amount of calcium oxide (CaO) per liter in the fourth nutrient solution is set to, for example, 0.54 mg to 0.8 mg. The iron (Fe) content per liter in the fourth nutrient solution is set to, for example, 0.007 mg to 0.024 mg.

[0075] Here, for example, in step 4 S4, if vegetables are grown using a fourth nutrient solution that has a significantly lower nitrogen content, a similar magnesium oxide content, and a significantly higher calcium oxide content compared to the second reference nutrient solution, it is thought that the nitrate concentration in the harvested vegetables will decrease, the taste of the vegetables will improve, and the growth of the vegetables will be promoted by the following mechanism.

[0076] In step 4, S4, when vegetables are grown using the fourth nutrient solution, for example, a significant decrease in nitrogen concentration in the nutrient solution leads to a decrease in nitrate nitrogen, and thus a decrease in the concentration of nitrates in the vegetables at harvest. Also, for example, a significant decrease in nitrogen concentration in the nutrient solution reduces the supply of nitrogen, such as ammonia nitrogen and nitrate nitrogen, which are precursors to amino acids in photosynthesis, thus reducing the synthesis of amino acids through the synthesis of nitrogen and carbon (C). As a result, for example, in photosynthesis, the synthesis of organic acids as precursors to sugars becomes more active than the synthesis of amino acids, and the production of sugars through reduction using organic acids as raw materials is promoted. Consequently, for example, in photosynthesis, sugars increase preferentially over amino acids. Also, for example, an increase in calcium oxide concentration in the nutrient solution promotes photosynthesis in plants and promotes vegetable growth. Also, for example, maintaining an appropriate concentration of magnesium oxide in the nutrient solution ensures an appropriate supply of magnesium, a constituent element of chlorophyll, and maintains and promotes the reduction of carbon absorbed from carbon dioxide in the air. This, for example, promotes sugar production.

[0077] Furthermore, for example, if the fourth nutrient solution is used instead of the third nutrient solution in the fourth step, the vegetables may have a richer flavor because the fourth nutrient solution contains various nutrients other than nitrogen compared to the third nutrient solution. Therefore, depending on the purpose, the third and fourth nutrient solutions may be used differently. For example, the fourth nutrient solution may be used in the fourth step if a rich flavor is desired for the vegetables, while the third nutrient solution may be used in the fourth step if a light, mild flavor is desired for the vegetables.

[0078] <1-6. Specific Examples> In hydroponic cultivation, lettuce grown under the second light source during the first period (germination period) P1, the early stage (second A period) P2a of the second period (main growth period) P2, and the third period (pre-harvest period) P3, and under the first light source during the later stage (second B period) P2b of the second period P2, was obtained as the first specific example vegetable. In addition, lettuce grown under the second light source during all periods of the first period P1, the second period P2, and the third period P3 was obtained as the first reference example vegetable. Here, the first specific example vegetable and the first reference example vegetable were obtained under identical conditions except for the lighting conditions. Specifically, the second nutrient solution described above was used in the first period P1 and the second A period P2a. The first nutrient solution described above was used in the second B period P2b. The third nutrient solution described above was used in the third period P3. Furthermore, based on the conditions under which the vegetables of the first specific example were obtained, lettuce grown under conditions in which the nutrient solution used in the third period P3 was changed from the third nutrient solution to the fourth nutrient solution was obtained as the vegetables of the second specific example. In addition, lettuce extracted from commercially available open-field grown mixed salad was obtained as the vegetables of the second reference example. Furthermore, commercially available open-field grown head lettuce was obtained as the vegetables of the third reference example.

[0079] The glutamine content was then measured for the vegetables of the first specific example, the first reference example, the second reference example, and the third reference example. A liquid chromatograph-mass spectrometer (LC-MS) was used to measure the glutamine content. More specifically, a liquid chromatograph (LC-20AC) manufactured by Shimadzu Corporation and a mass spectrometer (compact) manufactured by Bruker were used. For the liquid chromatograph, a UHPLC PEEK Column InterSustain Amide 3μm 2.1×50mm was used as the column. In the cladient elution, the proportion of solution B in the free solution obtained by mixing solution A, which is a 0.1% aqueous acetic acid solution, and solution B, which is acetonitrile containing 0.1% acetic acid, was set to 99% after 1 minute from the start of measurement, to 80% after 2 minutes, and to 50% between 10 and 15 minutes. The flow rate of the free solution was set to 0.4 ml / min. The column temperature was set to 40 degrees Celsius. In addition, electrospray ionization (ESI) was used as the ionization method for the various components separated by liquid chromatography in the mass spectrometer. The measurement time was set to 0.5 to 15 minutes.

[0080] Here, the glutamine content in the first reference example vegetable was 27 ppm (parts per million). The glutamine content in the second reference example vegetable was 38 ppm. The glutamine content in the third reference example vegetable was 61 ppm. In contrast, the glutamine content in the first specific example vegetable was 220 ppm. In other words, lettuce with a glutamine content of 220 ppm was obtained. From these measurement results, it was inferred that, for example, in the third step S3 of hydroponic vegetable cultivation, if the vegetables are grown under the first light for at least a portion of the second period P2, the glutamine content in the vegetables will increase.

[0081] Furthermore, Brix values ​​were measured for the vegetables in the first specific example, the second specific example, and the second reference example. Brix value is a physical quantity used as a measure of sugar content, and was measured using a refractometer.

[0082] Here, the Brix value of the vegetables in the second reference example was 0.9. In contrast, the Brix values ​​of the vegetables in the first specific example ranged from 3 to 5.2. In other words, lettuce with a Brix value of 3 to 5.2 was obtained. From these measurement results, it was inferred that, for example, in the third step S3 of hydroponic vegetable cultivation, if the vegetables are grown with the first light for at least a portion of the second period P2, the Brix value of the vegetables will increase. Also, the Brix value of the vegetables in the second specific example ranged from 5 to 6.4. In other words, lettuce with a Brix value of 5 to 6.4 was obtained. From these measurement results, it was inferred that, for example, in the third period P3 of the fourth step S4 of hydroponic vegetable cultivation, if the vegetables are grown using the fourth nutrient solution instead of the third nutrient solution, the Brix value of the vegetables will likely improve even further.

[0083] From another perspective, for example, in the third step S3 of hydroponic vegetable cultivation, it was confirmed that growing lettuce with a Brix value of 3 or higher can be obtained by irradiating it with the first light for at least a portion of the second period P2. Also, for example, in the third step S3 of hydroponic vegetable cultivation, it was confirmed that growing lettuce with a glutamine content of 220 ppm or higher can be obtained by irradiating it with the first light for at least a portion of the second period P2. Therefore, for example, it was found that the taste of the vegetables improves.

[0084] Furthermore, the nitrate concentration was measured for the vegetables in the first specific example, the second specific example, and the second reference example. To measure the nitrate concentration, the ion electrode method was employed, which involves dropping a predetermined amount (0.3 ml (mL) or more) of sample juice and measuring the concentration of nitrate ions. A compact nitrate ion meter (LAQUAtwin) was used for this measurement. <no3-11c no3-11s no3-11>) was used.

[0085] Here, the nitrate concentration in the vegetables of the second reference example was 1860 ppm. In contrast, the nitrate concentration in the vegetables of the first specific example ranged from 760 ppm to 1300 ppm. From these measurement results, it was confirmed that, for example, hydroponic cultivation of vegetables using the first and second nutrient solutions, which have a lower nitrogen (N) content per liter than the first and second reference nutrient solutions used in general vegetable hydroponics, reduces the nitrate concentration in vegetables. From another perspective, for example, it was confirmed that growing lettuce using the first and second nutrient solutions hydroponically yields lettuce with a nitrate concentration of 1300 ppm or less. Therefore, it was found that, for example, healthier vegetables can be obtained. The nitrate concentration in the vegetables of the second specific example ranged from 180 ppm to 1100 ppm. These measurement results confirmed that, for example, in the third period P3 of step S4, hydroponic cultivation of vegetables using the fourth nutrient solution, which has an even lower nitrogen (N) content per liter than the third nutrient solution, makes it easier to reduce the nitrate concentration in the vegetables. From another perspective, for example, it was confirmed that growing lettuce using the fourth nutrient solution hydroponically yields lettuce with a nitrate concentration of 1100 ppm or less.

[0086] <1-7. Summary of the First Embodiment> In the hydroponic vegetable production method according to the first embodiment, for example, in the third step S3 of the hydroponic vegetable cultivation period, the vegetables are grown by irradiating them with first light having a maximum light intensity (first maximum value) in the visible light wavelength range of 500 nm or less for at least a portion of the second period P2. This makes it possible to increase, for example, the glutamine content and sugar content of the vegetables. Therefore, for example, the taste of the vegetables can be improved.

[0087] <2. Other Embodiments> This disclosure is not limited to the first embodiment described above, and various modifications and improvements are possible without departing from the gist of this disclosure. [Explanation of symbols]

[0088] 1 light source 3 Light-emitting elements 6 Wavelength conversion component 7. Phosphors 10 Lighting devices 30a,30b container 31a Nursery 31b culture medium 32a seeds 32b Seedling 32c Target vegetables for cultivation 33 Power supply 34 Support P1 Period 1 P2 Second Period P2a 2nd A period P2b 2nd B period P3 Third Period S1 Step 1 S2 Step 2 S3 Step 3 S4 Step 4 S5 Step 5

Claims

1. A nutrient solution for growing vegetables, used when hydroponically cultivating vegetables by irradiating them with light from a lighting device. A nutrient solution for growing vegetables, containing 0.06 mg to 0.14 mg of nitrogen per liter and 0.1 mg to 0.25 mg of calcium oxide per liter.

2. A nutrient solution for growing vegetables according to claim 1, A nutrient solution for growing vegetables, containing 0.04 mg to 0.1 mg of phosphorus pentoxide per liter.

3. A nutrient solution for growing vegetables according to claim 1 or claim 2, A nutrient solution for growing vegetables, containing 0.12 mg to 0.3 mg of potassium oxide per liter.

4. A nutrient solution for growing vegetables according to any one of claims 1 to 3, A nutrient solution for growing vegetables, containing 0.04 mg to 0.08 mg of magnesium oxide per liter.

5. A nutrient solution for growing vegetables according to any one of claims 1 to 4, A nutrient solution for growing vegetables, containing 0.001 mg to 0.003 mg of iron per liter.

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