Culture solution, strawberry cultivation facility, and strawberry cultivation method

Abstract

A culture solution used for circulation-type hydroponic cultivation of strawberries contains nitrogen components and sulfate ions, contains ammonium ions and nitrate ions as nitrogen components, has a concentration of ammonium ions of 0.3 me / L or more, has a proportion of the concentration of ammonium ions to the concentration of nitrogen components in the culture solution of from 5% to 30%, and contains sulfate ions in a proportion such that the concentration of sulfate ions is from 0.5 me / L to 1.5 me / L when the concentration of the nitrogen component is 10 me / L.

Description

Culture medium, strawberry cultivation facility, and strawberry cultivation method

[0001] The present invention relates to a culture solution for use in cultivating strawberries and a strawberry cultivation facility. This application claims priority to Japanese Patent Application No. 2023-195465, filed November 16, 2023, the contents of which are incorporated herein by reference.

[0002] BACKGROUND ART Conventionally, a technique for cultivating strawberries indoors using a culture solution contained in a container has been known.

[0003] For example, Patent Document 1 discloses a cultivation facility in which a culture solution is circulated between a container for cultivating plants such as strawberries and a tank.

[0004] By circulating the culture solution, as in the cultivation equipment described in Patent Document 1, it is possible to prevent the culture solution from spoiling and the strawberry roots from rotting, and also to reduce the amount of culture solution used.

[0005] Japanese Patent Application Laid-Open No. 2021-061763

[0006] However, the concentration of components in the culture solution generally changes as cultivation continues, and the pH tends to increase due to these component changes. As a result, the culture solution becomes unsuitable for strawberry cultivation, necessitating the use of a pH adjuster to adjust the pH or replacing the culture solution, which increases the cost of cultivation.

[0007] The present invention has been made in consideration of the above circumstances, and provides a culture solution, a strawberry cultivation facility, and a strawberry cultivation method that can suppress changes in the concentration of components in the culture solution even when recirculating hydroponic culture of strawberries is continued for a long period of time.

[0008] In order to solve the above problems, one aspect of the present invention includes the following aspects.

[0009] [1] A culture solution used in recirculating hydroponic cultivation of strawberries, comprising a nitrogen component and sulfate ions, the nitrogen components being ammonium ions and nitrate ions, the concentration of the ammonium ions being 0.3 me / L or more, the proportion of the concentration of the ammonium ions in the concentration of the nitrogen components in the culture solution being 5% or more and 30% or less, and the culture solution containing the sulfate ions in a proportion such that when the concentration of the nitrogen components is 10 me / L, the concentration of the sulfate ions is 0.5 me / L or more and 1.5 me / L or less.

[0010] [2] The culture medium according to [1], wherein the culture medium contains sulfate ions in a ratio such that the concentration of the sulfate ions is 0.5 me / L or more and 1.2 me / L or less when the concentration of the nitrogen component is 10 me / L.

[0011] [3] The culture solution for recirculating hydroponics according to [1] or [2], wherein the concentration of the ammonium ions accounts for 8% or more and 20% or less of the concentration of nitrogen components in the culture solution.

[0012] [4] A closed strawberry cultivation facility comprising a light irradiation device that irradiates strawberries with light, a container for cultivating strawberries, a culture solution described in any one of [1] to [3], a storage tank that stores the culture solution, and a circulation pump that circulates the culture solution between the container and the storage tank.

[0013] [5] The strawberry cultivation facility described in [4], which is equipped with an EC measuring device that measures the EC value of the circulating culture solution.

[0014] [6] A strawberry cultivation method in a closed strawberry cultivation facility equipped with a light irradiation device that irradiates strawberries with light, in which the culture solution described in any one of [1] to [3] is circulated between a container for cultivating strawberries and a storage tank for storing the culture solution, the EC value of the culture solution is measured while the culture solution is circulating or when the circulation of the culture solution is temporarily stopped, and unused culture solution is added to the culture solution being circulated based on the measured EC value, thereby adjusting the EC value of the culture solution being circulated to be within a predetermined target EC value range.

[0015] [7] The strawberry cultivation method described in [6], wherein the target EC value range is 0.75 dS / m or more and 0.85 dS / m or less.

[0016] According to the present invention, it is possible to provide a culture solution, a strawberry cultivation facility, and a strawberry cultivation method that can suppress changes in the concentration of components in the culture solution even when strawberries are grown in a recirculating nutrient solution for a long period of time.

[0017] FIG. 1 is a schematic partial cross-sectional view of a strawberry cultivation facility according to a preferred embodiment of the present invention. FIG. 2 is a schematic diagram showing cultivation schedules for each of three test plots. FIG. 3 is a graph showing the change in culture solution composition in test plot 1, where a conventional culture solution was circulated. FIG. 4 is a graph showing the change in culture solution composition in test plot 2. FIG. 5 is a graph showing the change in culture solution composition in test plot 3. FIG. 6 is a graph showing the annual reduction in waste liquid when the culture solution in test plot 3 is used compared to when the culture solution in test plot 1 is used. FIG. 7 is a graph showing the annual reduction in waste nitrogen when the culture solution in test plot 3 is used compared to when the culture solution in test plot 1 is used.

[0018] Hereinafter, preferred embodiments of the present invention will be described in detail, with reference to the drawings as needed.

[0019] FIG. 1 is a schematic partial cross-sectional view of a strawberry cultivation facility 1 according to a preferred embodiment of the present invention.

[0020] The strawberry cultivation facility 1 is a closed cultivation facility for performing circulating hydroponic cultivation, and includes a light irradiation device 2 that irradiates strawberries 8 with light, a cultivation container 6 for cultivating the strawberries 8, a culture solution 3 for cultivating the strawberries 8, a storage tank 9 for storing the culture solution 3, and a circulation pump 4. The cultivation container 6 is an example of the "container" of the present invention.

[0021] In this specification, unless otherwise specified, "strawberry" refers to a plant belonging to the genus Fragaria in the family Rosaceae. Strawberry also includes hybrids such as Fragaria x ananassa.

[0022] "Closed type" refers to a cultivation facility that has a closed cultivation space separated from the outside, is fully air-conditioned, uses artificial light, and is less susceptible to the effects of outside temperature and humidity, and refers to a so-called plant factory. Note that glasshouses and vinyl greenhouses are not included in the closed type cultivation facility because they are strongly affected by outside air.

[0023] (Light Irradiation Device) In this embodiment, the light irradiation device 2 is configured by an LED light, but it may be any other lighting device such as a fluorescent lamp as long as it can irradiate light necessary for photosynthesis of the strawberries 8.

[0024] (Cultivation Container) A polystyrene foam plate member 6a is disposed inside the cultivation container 6 to support the strawberries 8. A through-hole 6a1 is formed in the plate member 6a, penetrating in the vertical direction.

[0025] The roots of the strawberries 8 extend downward through the through-holes 6a1 of the plate member 6a and are immersed in the culture solution 3 stored in the lower part of the cultivation container 6. The stems and leaves of the strawberries 8 extend upward of the plate member 6a.

[0026] The cultivation containers 6 are arranged in multiple stages (three stages in FIG. 1) in the vertical direction, and are connected to a pipe 6b that transfers the culture solution 3 stored inside downward.

[0027] (Circulation Pump) The circulation pump 4 circulates the culture solution 3 between the cultivation containers 6 and the storage tank 9. More specifically, the circulation pump 4 transfers the culture solution 3 stored in the storage tank 9 to the uppermost cultivation container 6. The culture solution 3 transferred to the uppermost cultivation container 6 flows into the pipe 6b when the water level in the cultivation container 6 reaches a predetermined level that exceeds the height of the upper end 6b1 of the pipe 6b, and is transferred through the pipe 6b to the cultivation container 6 immediately below.

[0028] Thereafter, the culture solution 3 is repeatedly transferred through the pipe 6b to the lower cultivation vessels 6 in the same manner. When the culture solution 3 reaches the lowest cultivation vessel 6, it is transferred through the pipe 6b to the storage tank 9. The culture solution 3 thus returned to the storage tank 9 is transferred again by the circulation pump 4 to the uppermost cultivation vessel 6.

[0029] In addition, the strawberry cultivation facility only needs to be able to circulate the culture solution 3 in each cultivation container 6 between the storage tank and the facility, and there are no particular limitations on the presence or absence of piping 6b, its placement, the route of the culture solution, etc.

[0030] For example, it is not necessarily necessary to transfer the culture solution 3 between the cultivation containers 6, and the culture solution 3 in the storage tank 9 may be configured to be supplied directly to each cultivation container 6 using a circulation pump 4.

[0031] (Storage Tank) The storage tank 9 in Fig. 1 is connected to the cultivation containers 6 via the circulation pump 4 and the piping 6b. In the strawberry cultivation facility 1, the storage tank 9 is located below the multi-tiered cultivation containers 6. The storage tank 9 may have any configuration as long as it is capable of storing the culture solution.

[0032] (EC Measuring Device) Inside the storage tank 9, there are arranged an EC measuring device 9a that measures the EC (Electrical Conductivity) value of the circulating culture solution 3, and a pH measuring device 9b that measures the pH of the circulating culture solution 3.

[0033] By providing the storage tank 9 with an EC meter 9a and a pH meter 9b, the state of the culture solution 3 can be easily confirmed. However, it is not necessarily required to provide the storage tank 9 with an EC meter 9a and a pH meter 9b. Measuring devices capable of measuring both the EC value and the pH value may be used. Furthermore, the EC meter 9a and the pH meter 9b to be placed inside the storage tank 9 are preferably of a type that does not require calibration.

[0034] (Nutrient Solution) In general, in plant factories, elements absorbed by strawberries during their growth are dissolved in water and supplied to the strawberries as a nutrient solution. Nine essential macroelements (carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S)) are known to be essential for plant growth. Of these, carbon is supplied from carbon dioxide in the air, while hydrogen and oxygen are supplied from water. Therefore, the primary purpose of the nutrient solution is to supply the other six elements as nutrients.

[0035] These six elements (nutrients) are dissolved in the culture solution in the form of ions (cations and anions) of each element or chemical species containing each element. The composition of the culture solution 3 is adjusted by adjusting the concentration of each ion.

[0036] As the cultivation progresses, the ions contained in the culture solution 3 are absorbed by the strawberries, resulting in a change in the composition of the culture solution 3. Therefore, as the cultivation of the strawberries progresses, it becomes necessary to adjust the amount of ions in the culture solution 3 to make up for elements that are deficient in the culture solution 3.

[0037] Here, because strawberries absorb each element (each ion) at different rates, the ratio of each component differs between the culture solution 3 at the beginning of cultivation and the culture solution 3 after the nutrients have been absorbed as cultivation progresses. Ideally, the content of each element would be measured in detail and the deficiency added for each element. However, from the perspective of managing a plant factory, such operations (measurement and individual component adjustment) are cumbersome and unrealistic. Therefore, the content of each element is managed collectively using the EC value, and the concentration of each ion in the culture solution 3 is adjusted by adding a stock solution of the culture solution at a predetermined concentration to the culture solution 3 used for cultivation.

[0038] When the composition of the culture solution is controlled by the above-described procedure, ions that are consumed in large quantities tend to decrease, while ions that are consumed less tend to accumulate in the culture solution 3. As a result, the composition of the culture solution 3 used for cultivation will eventually deviate significantly from the initially set composition. In this case, the entire volume of the culture solution 3 must be replaced.

[0039] In contrast, the culture medium of this embodiment is capable of suppressing the above-mentioned changes in the concentrations of the components of the culture medium, compared to conventional culture mediums.

[0040] The culture solution 3 of this embodiment contains nitrogen components and sulfate ions. The nitrogen components include ammonium ions and nitrate ions.

[0041] The composition of the culture solution 3 will be explained in detail below. This composition is the one at the start of cultivation of strawberries 8 (when the culture solution 3 is first supplied to each cultivation container 6), and as mentioned above, the composition of the culture solution 3 changes as cultivation progresses.

[0042] The concentration of ammonium ions in the culture solution 3 is 0.3 me / L or more and 2.0 me / L or less, preferably 0.3 me / L or more and 1.0 me / L or less, and more preferably 0.3 me / L or more and 0.7 me / L or less.

[0043] The proportion of the ammonium ion concentration in the nitrogen component concentration (the sum of the ammonium ion concentration and the nitrate ion concentration) in the culture solution 3 is 5% or more and 30% or less. The ammonium ion concentration is preferably 7% or more, more preferably 8% or more, and even more preferably 9% or more. The ammonium ion concentration is preferably 25% or less, more preferably 20% or less, even more preferably 15% or less, and most preferably 12% or less. The upper and lower limits of the ammonium ion concentration can be combined in any desired manner.

[0044] The ratio of the concentration of ammonium ions to the concentration of nitrogen components in the culture solution 3 is preferably 7% or more and 25% or less, more preferably 8% or more and 20% or less, even more preferably 9% or more and 15% or less, and most preferably 9% or more and 12% or less.

[0045] In general, the pH of the nutrient solution tends to rise in recirculating hydroponic culture systems, and down agents containing phosphate are often used. As a result, the concentration of phosphate ions in the nutrient solution rises excessively, necessitating frequent replacement of the nutrient solution in the storage tank and the cultivation container.

[0046] In contrast, according to the present embodiment, by using a culture solution in which the concentration of weakly basic ammonium ions with buffering properties and the ratio of these ions to the nitrogen component are within the above ranges, it is possible to suppress an increase in pH and reduce the amount of down agent used, thereby reducing the frequency of changing the culture solution during cultivation.

[0047] It is well known that high concentrations of ammonium ions in a culture solution can cause excessive damage to plants. However, as will be described in detail in the Examples below, the present inventors have discovered that excessive damage to strawberries does not occur even when the ammonium ion concentration is set to 0.3 me / L or higher and the proportion of ammonium ions in the nitrogen components is set to 7% or higher in strawberry cultivation. Ammonium ions are consumed as a nitrogen source by strawberries 8.

[0048] The nitrate ion concentration in the culture solution 3 is preferably in the range of 4.0 me / L to 6.0 me / L, more preferably in the range of 4.7 me / L to 6.0 me / L, and most preferably in the range of 5.0 me / L to 5.5 me / L, and may be in the range of 5.0 me / L to 5.3 me / L. However, the nitrate ion concentration is not limited to these ranges. The upper and lower limits of the nitrate ion concentration can be combined arbitrarily.

[0049] The concentration of nitrogen components in the culture solution 3, in other words, the total concentration of ammonium ions and nitrate ions, is preferably 5.0 me / L to 6.5 me / L, more preferably 5.3 me / L to 6.0 me / L, and most preferably 5.6 me / L to 6.0 me / L. By setting the concentration of nitrogen components within this range, changes in the nitrate ion concentration during cultivation can be suppressed.

[0050] The sulfate ion concentration in the culture solution 3 is preferably in the range of 0.2 me / L to 0.5 me / L, and more preferably in the range of 0.2 me / L to 0.4 me / L. Sulfur components such as sulfate ions are essential for plant growth but are consumed in small amounts. Furthermore, sulfate ions are mixed into the culture solution during preparation as counterions to the Mg ions contained in the culture solution. Therefore, the sulfate ion concentration in the culture solution generally tends to continue to increase. In contrast, by setting the sulfate ion concentration within the above numerical range, sulfur can be sufficiently supplied to the strawberries 8, and the increase in sulfate ion concentration during cultivation can be suppressed, reducing the frequency of changing the culture solution 3.

[0051] If the concentration of sulfate ions in the culture solution falls below 0.2 me / L, the supply of sulfur will be insufficient, which may adversely affect the growth of the strawberries. If the concentration of sulfate ions in the culture solution exceeds 0.5 me / L, the amount consumed by the strawberries 8 will be exceeded, which may lead to an increase in the concentration of sulfate ions during cultivation and may require more frequent replacement of the culture solution.

[0052] Furthermore, when the concentration of the culture solution 3 is adjusted (diluted or concentrated) to a nitrogen component concentration (the sum of the ammonium ion concentration and the nitrate ion concentration) of 10 me / L, the sulfate ion concentration is preferably 0.5 me / L to 1.5 me / L, more preferably 0.5 me / L to 1.2 me / L. By setting the ratio of sulfate ions to nitrogen components within the above range, the ratio of nitrogen components to sulfate ions in the culture solution can be adjusted to match the consumption rates of nitrogen components and sulfur components by strawberries 8. Therefore, excessive increases and decreases in nitrogen components and sulfate ions in the culture solution during cultivation can be suppressed.

[0053] In one embodiment, the present invention provides a culture solution for use in recirculating hydroponic cultivation of strawberries. This culture solution is the culture solution 3 described in detail in the embodiment of the strawberry cultivation facility 1, or a concentrated version of the culture solution 3 (hereinafter referred to as the concentrated solution).

[0054] The ammonium ion concentration in the concentrate of culture solution 3 is also 0.3 me / L or more, and the ammonium ion concentration in the nitrogen component concentration in the concentrate of culture solution 3 is in the range of 2% to 30%. Furthermore, when the nitrogen component concentration in the concentrate of culture solution 3 is adjusted to 10 me / L, the concentrate of culture solution 3 contains sulfate ions in a ratio of 0.5 me / L to 1.5 me / L (preferably 1.2 me / L or less).

[0055] The concentration rate of the culture solution 3 is not particularly limited, but may be set to, for example, 100 times, 200 times, or 300 times the concentration of the above-mentioned components in the culture solution 3. For example, in the case of a concentrate concentrated to a concentration 100 times that of the culture solution 3, the concentration of ammonium ions is 30 me / L or more. When used, the concentrate of the culture solution 3 is diluted to an appropriate concentration.

[0056] In one embodiment, the present invention provides a strawberry cultivation method in which the culture solution 3 used in the recirculating hydroponic cultivation of strawberries is circulated between a container 6 for cultivating strawberries 8 and a storage tank 9 for storing the culture solution 3 in a closed strawberry cultivation facility 1 equipped with a light irradiation device 2 that irradiates light onto strawberries 8.

[0057] In this strawberry cultivation method, the EC value of the culture solution 3 is measured while the culture solution 3 is circulating or when the circulation of the culture solution 3 is temporarily stopped, and based on the measured EC value, fresh unused culture solution 3 is added to the circulating culture solution 3, thereby adjusting the EC value of the circulating culture solution 3 to be within a predetermined target EC value range.

[0058] The range of the target EC value may be, for example, 0.75 dS / m or more and 0.88 dS / m or less, 0.75 dS / m or more and 0.85 dS / m or less, 0.78 dS / m or more and 0.88 dS / m or less, or 0.78 dS / m or more and 0.85 dS / m or less. The EC value of the culture solution 3 may be measured using the EC measuring device 9a.

[0059] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these modifications are also included within the scope of the present invention.

[0060] Hereinafter, the strawberry cultivation method will be described with reference to examples, but the present invention is not limited to the following examples.

[0061] (Experimental Conditions) In this example, Yotsuboshi (Japanese variety registration number: 25605), a type of everbearing strawberry, was cultivated in a plant factory within the Tokushima Plant of Nisshinbo Holdings Inc. Environmental conditions such as temperature and humidity are controlled within the plant factory, so it is assumed that the results shown below are not affected by seasonal changes.

[0062] The strawberry cultivation containers were multi-tiered, and a total of 1,800 L of nutrient solution was circulated between the cultivation containers and the storage tank in each of the three test plots described in detail below, cultivating 1,600 plants. The spacing between plants was set to between 15 cm and 30 cm, and the row spacing was set to between 10 cm and 20 cm. As shown in Figure 1, three containers arranged vertically were supported by one shelf, and the total length was 1,000 m. ２ Sixteen such shelves were provided per room.

[0063] In this example, the optimum range for the composition of the culture solution is determined to be a range where the concentrations of sulfate ions, phosphate ions, and nitrate ions are doubled or halved from the concentration at the start of cultivation. When at least one of sulfate ions, phosphate ions, and nitrate ions is doubled or more or halved from the concentration at the start of cultivation, the culture solution is determined to be in a state where it should be replaced (a state that meets the replacement criteria).

[0064] Figure 2 is a schematic diagram showing the cultivation schedule for each of the three test plots. As shown in Figure 2, the experimental period differed depending on the three test plots. The experimental period for test plot 1 was from June 30, 2022 to January 24, 2023. The experimental period for test plot 2 was from June 30, 2022 to December 14, 2022. The experimental period for test plot 3 was from September 1, 2022 to January 24, 2023. Note that the "full exchange" shown in Figure 2 refers to the complete exchange of the culture solution.

[0065] White LED lighting was placed above the strawberries. The photosynthetic photon flux density was 300 μmol / m ２ ・It was s.

[0066] In this experiment, three test plots (test plots 1 to 3) were prepared for cultivating strawberries, each using a nutrient solution with a different composition. In each test plot, changes in the composition of the nutrient solution when cultivated in each nutrient solution, the yield of false fruit, and the effect of the nutrient solution on the quality of the false fruit were investigated. For the sake of convenience, false fruit will be referred to as "fruit" below.

[0067] Table 1 below shows the main recipe for preparing the culture solution for Test Plot 1. In addition to the fertilizer and raw water shown in Table 1, the culture solution for Test Plot 1 also contained the trace elements shown in Table 4.

[0068] Table 2 below shows the main formulation for preparing the culture solution for Test Plot 2. In Test Plot 2, in addition to the fertilizer and raw water shown in Table 2, trace elements shown in Table 5 were also added.

[0069] Table 3 below shows the main recipe for preparing the culture solution for Test Group 3. The culture solution for Test Group 3 additionally contained the trace elements shown in Table 5.

[0070] Of the three test plots, test plot 1 is a comparative example in which OAT Agrio's "SA formulation" was used as the culture solution. The other two test plots 2 and 3 were OR (original) formulations and are examples of the present invention.

[0071] The culture solution is composed of water and various ions dissolved in the water. The water (raw water) is usually agricultural water available in the region where the present invention is implemented, and the ion concentration varies depending on the region. Furthermore, the concentration of each ion is set as a target value in the culture solution. Therefore, the culture solution is prepared by adding an amount of ions to the raw water that corresponds to the difference between the "ion concentration carried by the raw water" and the "target ion concentration."

[0072] In Tables 1 to 3 above, the "raw water" row shows the ion concentration of the water used to prepare the culture solution.

[0073] The "Set concentration" row shows the concentration of each cationic component (NH ４ ＋ , K.​​​＋ , Ca ２＋ , Mg ２＋ , Na ＋ , H ＋ ) and each anion component (NO ３ － , P.O. ４ ３－ , S.O. ４ ２－ , Cl － ) target concentrations are shown.

[0074] The "concentration of additional components" indicates the amount (concentration) of each cationic component and each anionic component to be added to the raw water, taking into account the concentrations of the cationic and anionic components in the raw water used for the culture medium and the above-mentioned "set concentration."

[0075] Also, "Ca(NO ３ ) ２ ・4H ２ From the "Mg(NO ３ ) ２ ・6H ２ Each of the five or six lines up to the line "0" shows the amount (concentration) of each cationic component and each anionic component to be added to the raw water so that the amount (concentration) of each component is the value shown in the "Concentration of added component" line.

[0076] Each cationic component and each anionic component was added to a storage tank to give the concentration shown in each of the five or six rows above.

[0077] To the storage tank of test area 1, in addition to the formulation in Table 1 above, fertilizer ME for hydroponic cultivation manufactured by OAT Agrio containing trace elements in the amounts shown in Table 4 below was added.

[0078]

[0079] In addition, the storage tanks of test plots 2 and 3 were each supplied with a hydroponic fertilizer ME manufactured by OAT Agrio, containing trace elements in the amounts shown in Table 5 below.

[0080]

[0081] ​​Meanwhile, Table 6 below shows the actual concentrations of components in the culture solutions prepared according to the formulations shown in Tables 1 to 5 in the storage tanks in each of the test plots 1 to 3, which were measured when the circulation between the storage tanks and the cultivation space was started (when cultivation was started).

[0082]

[0083] The culture solution for each of the test plots 1 to 3 was supplied to the cultivation vessel with the composition shown in Table 6. The amount of culture solution circulating in each test plot was approximately 1,800 L, including the capacity of the storage tank.

[0084] The ratio of the ammonium ion concentration to the nitrogen component (nitrate ion and ammonium ion) concentration in the culture solution for each test group is shown in Table 7 below.

[0085]

[0086] As shown in Table 7, the ratio of ammonium ion concentration to the nitrogen component concentration was 0.0% in the culture solution of Test Area 1 (comparison example), in the 7% range in the culture solution of Test Area 2, and in the 10% range in the culture solution of Test Area 3.

[0087] The EC and pH values ​​of the circulating culture solution in each test plot 1 to 3 were measured daily in the storage tank. Based on the measured EC values, a calculated amount of unused culture solution was added to the storage tank to achieve an EC value of 0.8 dS / m for the approximately 1,800 L of culture solution circulating between the cultivation containers and the storage tank. A HORIBA D-54 (manufactured by HORIBA, Ltd.) was used to measure the EC and pH values. During the cultivation period, the EC value fluctuated between 0.78 and 0.88 dS / m. When the EC value exceeded 0.78 dS / m, no culture solution was added. Even when the EC value exceeded 0.8 dS / m, dilution with raw water was not performed.

[0088] Furthermore, when the pH of the circulating culture medium was measured and found to be above 6.5, a Down agent was added to the storage tank. The Down agent used was OAT Agrio's pH adjuster Down (for descending).

[0089] ​​During the cultivation period, the leaves were removed so that each plant had 5 or 6 leaves. Mature fruits were harvested daily.

[0090] (Investigation items) During the cultivation period, the composition of the circulating nutrient solution, growth status, fruit yield, fruit weight, amount discarded, and fruit quality were investigated every two weeks.

[0091] The composition of the circulating culture medium was investigated by high performance liquid chromatography.

[0092] In the survey of growth status (growth survey), leaf area, fruit number, plant height, and leaf-to-fruit ratio were investigated. In the survey of leaf area, leaves were randomly selected from strawberries in each test plot after defoliation, and the leaf area was measured using image analysis software called Lia32.

[0093] (Experimental Results) Figure 3 is a graph showing the change in the composition of the culture solution over time as a function of the number of days of cultivation until the first complete exchange in each of the three test plots. Figure 3A shows the change in the composition of the culture solution in test plot 1, where a conventional culture solution was circulated, Figure 3B shows the change in the composition of the culture solution in test plot 2, and Figure 3C shows the change in the composition of the culture solution in test plot 3.

[0094] Table 8 below shows the number of days of cultivation until the first full replacement in each of the three test plots 1 to 3, the total amount of down agent containing phosphoric acid used during the cultivation period, and the amount of down agent used per day, calculated by dividing the total amount used by the number of days of cultivation.

[0095]

[0096] As shown in Figures 3A, 3B, and 3C, the concentrations of phosphate and sulfate ions tended to increase, while the concentration of nitrate ions tended to decrease in all test plots. The arrows in Figures 3A, 3B, and 3C indicate the changes in phosphate ion concentration.

[0097] As shown in Figure 3A, in the comparative example, experimental plot 1, the phosphate ion concentration was more than twice the 1.5 me / L at the start of cultivation 20 days after the start of cultivation, satisfying the criteria for replacing the culture solution. Even after the SA formulation culture solution satisfied the criteria for replacement, cultivation was continued until the 62nd day.

[0098] In contrast, in Test Area 2, where a culture solution containing a 7% OR formulation with an ammonium ion concentration in the 7% range was circulated, the ammonium ion concentration was set higher than in Test Area 1, so the increase in pH was suppressed. As a result, the amount of Down agent used was reduced and the phosphate ion concentration was suppressed. Therefore, compared to Test Area 1, the period until the culture solution replacement criteria were met could be extended.

[0099] In test area 2, the sulfate ion concentration increased, and the replacement standard was met approximately 5 weeks (34 days) after the start of cultivation. Even after the replacement standard was met, cultivation was continued until 62 days later.

[0100] On the other hand, in test area 3, where a 10% OR formulation with an ammonium ion concentration in the 10% range was circulated, the phosphate ion concentration was maintained within the appropriate range until it exceeded twice the concentration at the start of cultivation, approximately 13 weeks after the start of cultivation (day 91).

[0101] This result is thought to be due to the fact that the ammonium ion concentration in the culture solution of test area 3 was higher than that in the culture solutions of test areas 1 and 2, and that the sulfate ion concentration was set lower than that in the culture solutions of test areas 1 and 2.

[0102] In this way, the amount of Down Agent used could be reduced by using the culture solution with 7% OR formulation in Test Area 2 or the culture solution with 10% OR formulation in Test Area 3. In the three test areas, the amount of Down Agent used could be reduced more as the proportion of ammonium ions in the nitrogen components increased (see Table 8).

[0103] For example, if the culture medium containing 10% OR in test area 3 is used and the entire culture medium is replaced once every three months, the amount of down agent used per year can be reduced by approximately 68% compared to when the culture medium in test area 1 is used.

[0104] In addition, the culture solutions of Test Areas 2 and 3 can extend the period until the culture solution replacement criteria are met compared to conventional culture solutions. Therefore, as will be explained further below, the amount of culture solution wasted, and therefore the amount of nitrogen wasted, can be reduced, which is very useful from the perspective of the SDGs.

[0105] Table 9 below shows the amount of culture solution per shelf, the culture solution replacement cycle, the number of times per year that the culture solution was replaced, and the annual amount of drainage for each of the test plots 1 to 3.

[0106]

[0107] As shown in Table 9, if the culture medium replacement frequency in test area 1 is 18 days, the culture medium replacement frequency in test area 2 is 35 days, and the culture medium replacement frequency in test area 3 is 91 days, the annual amount of waste liquid per shelf will be 36.5 tons in test area 1, 18.8 tons in test area 2, and 7.2 tons in test area 3.

[0108] Table 10 below shows the results per shelf and per 1000m in each test area 1 to 3. ２ Annual wastewater volume per 1000m ２ The annual nitrogen waste per unit area is shown.

[0109]

[0110] Furthermore, Figure 4A shows the annual reduction in wastewater when the culture medium from test area 3 is used compared to when the culture medium from test area 1 is used, and Figure 4B shows the annual reduction in waste nitrogen when the culture medium from test area 3 is used compared to when the culture medium from test area 1 is used.

[0111] 1000ml when using the culture solution of test area 1 ２ The annual amount of waste liquid per (16 shelves) is (36.5 x 16 =) 584 tons.

[0112] In contrast, when the culture solution of Test Area 2 was used, 1000 ml ２ The annual amount of wastewater per unit is (18.8 x 16 =) approximately 300 tons.

[0113] ​​Therefore, when the culture medium containing 7% OR in Test Area 2 was used, the amount of waste liquid could be reduced by approximately 49% compared to when the culture medium containing SA in Test Area 1 was used.

[0114] In addition, when the culture solution of test area 3 was used, 1000 ml ２ The annual amount of wastewater per unit is (7.2 x 16 =) approximately 116 tons.

[0115] Therefore, when the culture medium containing 10% OR in Test Area 3 was used, the amount of wastewater could be reduced by approximately 80% compared to when the culture medium containing SA in Test Area 1 was used, as shown in Figure 4A.

[0116] On the other hand, the 1000m of test area 1 ２ The annual amount of nitrogen waste in test area 1 was calculated by multiplying the annual amount of wastewater per year by the nitrogen concentration in the wastewater and the atomic weight of nitrogen, 14, to be approximately 31.5 kg.

[0117] In contrast, the 1000m test area ２ The annual amount of nitrogen waste in test area 2 was calculated by multiplying the annual amount of wastewater per year by the nitrogen concentration in the wastewater and the atomic weight of nitrogen, 14, to be approximately 12.2 kg.

[0118] Therefore, when using the 7% OR formulation culture solution in test area 2, the annual amount of nitrogen waste can be reduced by approximately 61% compared to when using the SA formulation culture solution in test area 1.

[0119] In addition, the 1000m of test area 3 ２ The annual amount of nitrogen waste in test area 3 was calculated by multiplying the annual amount of wastewater per year by the nitrogen concentration in the wastewater and the atomic weight of nitrogen, 14, to be approximately 6.8 kg.

[0120] Therefore, when using the 10% OR formulation culture solution in test area 3, the annual amount of nitrogen waste can be reduced by approximately 78% compared to when using the SA formulation culture solution in test area 1.

[0121] In addition, the 10% OR formulation culture solution in Test Plot 3, in which the nitrogen concentration (total concentration of ammonium ion and nitrate ion) at the start of cultivation was in the range of 5.0 me / L to 6.5 me / L and the nitrate ion concentration was in the range of 5.0 me / L to 5.5 me / L, effectively suppressed changes in the nitrate ion concentration during cultivation (see Figure 3C).

[0122] Table 11 below shows the results of the survey on the growth status in each of the three test plots.

[0123] *In Table 11, the number of fruits includes flowers. *In Table 11, there is a significant difference at the 5% level between different alphabets (a, b) in the same column by Tukey's multiple test (n≧10).

[0124] As shown in Table 11, the strawberry plant height increased with increasing proportion of ammonium ions in the nitrogen component. No significant differences were observed between the test plots in leaf area, fruit number, and leaf-to-fruit ratio.

[0125] Table 12 below shows the results of the survey on the growth status in each of the three test plots.

[0126]

[0127] *The total yield and discarded amount in Table 12 is the total for 1,600 plants, and the discarded amount includes small fruits, deformed fruits, poor coloring, and overripe fruits. *In Table 12, there was a significant difference at the 5% level between different letters (a, b) in the same column by Tukey's multiple test (n = 52).

[0128] Table 13 below shows the amount of small and deformed fruit in each of the three test plots.

[0129] *In Table 13, small fruits refer to fruits weighing 6g or less. *In Table 13, the number of deformed fruits is the total for 1,600 plants. *In Table 13, there was a significant difference at the 1% level between different letters in the same column using Tukey's multiple test (n=52).

[0130] No significant difference in total yield was confirmed among the three test sections, but the amount discarded was the lowest in test section 3, which used a 10% OR formulation (see Table 12). This result is thought to be due to the low incidence of small fruits and deformed fruits in test section 3 (see Table 13). This suggests that the occurrence of small fruits and deformed fruits can be suppressed by using a nutrient solution with a 10% OR formulation, in which the ammonium ion concentration in the nitrogen component concentration is in the 10% range.

[0131] Table 14 below shows the fruit quality survey results for each of the three test plots.

[0132]

[0133] In Table 14, "ns" in the t-test column indicates that there is no significant difference at the 5% level (n = 5). A digital refractometer HI96811 (manufactured by Hanna Instruments Japan) was used to measure the sugar content of the fruit.

[0134] As shown in Table 14, no significant difference in fruit quality was observed between test group 3, which used a culture solution containing 10% OR formulation, and test group 1, which used a culture solution containing the SA formulation (comparison example). This result suggests that increasing the ammonium ion concentration compared to conventional culture solutions does not affect fruit quality.

[0135] According to the present invention, the ammonium ion concentration in the culture solution used in recirculating hydroponic cultivation of strawberries is set to 0.3 me / L or more, the proportion of the ammonium ion concentration in the nitrogen component concentration in the culture solution is set to 5% or more and 30% or less, and sulfate ions are added in a proportion such that the sulfate ion concentration is 0.5 me / L or more and 1.5 me / L or less when the nitrogen component concentration is 10 me / L.This makes it possible to suppress changes in the component concentrations of the culture solution even when recirculating hydroponic cultivation of strawberries is continued for a long period of time, and therefore the present invention is industrially applicable.

[0136] DESCRIPTION OF SYMBOLS 1... strawberry cultivation facility, 2... light irradiation device, 3... culture solution, 4... circulation pump, 6... cultivation container, 6a... plate member, 6a1... through hole, 6b... piping, 6b1... upper end portion, 8... strawberries, 9... storage tank, 9a... EC meter, 9b... pH meter

Claims

1. A culture solution used in a recirculating nutrient solution culture for strawberries, comprising a nitrogen component and sulfate ions, the nitrogen components being ammonium ions and nitrate ions, the concentration of the ammonium ions being 0.3 me / L or more, the proportion of the concentration of the ammonium ions in the concentration of the nitrogen components in the culture solution being 5% or more and 30% or less, and the culture solution containing the sulfate ions in a ratio such that when the concentration of the nitrogen component is 10 me / L, the concentration of the sulfate ions is 0.5 me / L or more and 1.5 me / L or less.

2. The culture medium according to claim 1, wherein the concentration of the sulfate ions is 0.5 me / L or more and 1.2 me / L or less when the concentration of the nitrogen component is 10 me / L.

3. The culture medium according to claim 1 or 2, wherein the concentration of said ammonium ions in the concentration of nitrogen components in said culture medium is 8% or more and 20% or less.

4. A closed strawberry cultivation facility comprising: a light irradiation device that irradiates strawberries with light; a container for cultivating strawberries; the culture solution according to claim 1 or 2; a storage tank for storing the culture solution; and a circulation pump that circulates the culture solution between the container and the storage tank.

5. The strawberry cultivation facility according to claim 4, further comprising an EC measuring device for measuring the EC value of the circulating culture solution.

6. A method for cultivating strawberries, comprising: in a closed strawberry cultivation facility equipped with a light irradiation device that irradiates light onto strawberries, circulating the culture solution according to claim 1 or 2 between a container for cultivating strawberries and a storage tank for storing the culture solution; measuring the EC value of the culture solution while the culture solution is circulating or when the circulation of the culture solution is temporarily stopped; and adding unused culture solution to the culture solution being circulated based on the measured EC value, thereby adjusting the EC value of the culture solution being circulated to be within a predetermined target EC value range.

7. The strawberry cultivation method according to claim 6, wherein the target EC value ranges from 0.75 dS / m to 0.85 dS / m.

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