Method for preparing nutrient solution for hydroponics

Abstract

This invention provides a method for preparing nutrient solutions in hydroponics that improves the productivity of hydroponic systems using raw material digestate. [Solution] The method for preparing the nutrient solution for hydroponics is a method for preparing the nutrient solution 111 using digestate, characterized by mixing an alkaline agent 131 with the nutrient solution 111 supplied to plant A to adjust the pH of the nutrient solution 111 to 6.0 or higher and 6.9 or lower (generating a prepared nutrient solution 121). Alternatively, the method for preparing the nutrient solution for hydroponics may involve mixing a prepared digestate with the nutrient solution 111 supplied to plant A to adjust the pH of the nutrient solution 111 to 6.0 or higher and 6.3 or lower.

Description

[Technical Field]

[0001] This invention relates to a method for preparing nutrient solutions for hydroponic cultivation. [Background technology]

[0002] Currently, research is being conducted on using digestate as a nutrient solution for hydroponics. Digestive solution contains nutrients such as nitrogen and potassium, which are necessary for plant growth. However, the nitrogen in digestate mainly exists in the form of ammoniacal nitrogen, and above a certain concentration, it can cause ammonia toxicity in plants. In other words, when using digestate in hydroponics, there is a problem in that the ammonia toxicity to plants cannot be reduced, making it impossible to directly utilize the nitrogen in digestate.

[0003] Patent Document 1 discloses a configuration for adjusting the pH of ammonia-containing wastewater (digestate), which is the liquid to be treated, to 7-12 by adding an alkaline agent such as sodium hydroxide, and a configuration for reducing the ammonia component concentration (paragraphs 0013-0015, etc.). Patent Document 2 discloses a solution supply method for supplying digestate, whose pH has been adjusted to 6.5-9.5, as a nutrient solution to a plant cultivation bed (paragraph 0033, etc.). Furthermore, Patent Document 3 discloses a nitrogen removal method for adjusting the pH of wastewater to 7-8 in an aerobic tank and then adjusting the pH to 6-8.5 (paragraphs 0062, 0071, etc.).

[0004] However, the digestate and wastewater disclosed in Patent Documents 1 to 3 have room for improvement in terms of improving the weight and quality of hydroponically grown plants, and there are challenges in improving the productivity of hydroponics using digestate (raw material digestate). In particular, according to Patent Document 3, dissolved oxygen and nitrogen are removed from the wastewater, and it is thought that it was not intended for use as a nutrient solution for hydroponics. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-444 [Patent Document 2] Japanese Patent Publication No. 2013-226089 [Patent Document 3] Japanese Patent Publication No. 2001-212591 [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the present invention was devised in view of the above-mentioned problems, and its objective is to provide a method for preparing nutrient solution for hydroponics that improves the productivity of a hydroponic cultivation system using raw material digestate. [Means for solving the problem]

[0007] The first invention is a method for preparing a nutrient solution for hydroponics, which prepares a nutrient solution using digested liquid, Includes at least one of the following: Asteraceae, Amaranthaceae, Amaryllidaceae, Apiaceae, or Brassicaceae plants. An alkaline agent is mixed into the nutrient solution supplied to the plants to adjust the pH of the nutrient solution to between 6.0 and 6.9. While doing so, it is circulated and repeatedly supplied to the plants. It is characterized by doing so.

[0008] The second invention relates to a method for preparing a nutrient solution for hydroponics, which involves preparing a nutrient solution using digested liquid. Includes at least one of the following: Asteraceae, Amaranthaceae, Amaryllidaceae, Apiaceae, or Brassicaceae plants. The nutrient solution supplied to the plants is mixed with a prepared digestate to adjust the pH of the nutrient solution to between 6.0 and 6.3. While doing so, it is circulated and repeatedly supplied to the plants. It is characterized by doing so. [Effects of the Invention]

[0009] According to the first invention, an alkaline agent is mixed into the nutrient solution supplied to the hydroponic cultivation tank to adjust the pH of the nutrient solution to between 6.0 and 6.9. As a result, the weight and quality of the hydroponically grown plants can be improved compared to cases where the pH is adjusted to below 6.0 or above 6.9 with an alkaline agent. This makes it possible to improve the productivity of a hydroponic cultivation system that utilizes raw material digestate.

[0010] According to the second invention, the adjusted digestive juice is mixed into the nutrient solution supplied to the hydroponic cultivation tank to adjust the pH of the nutrient solution to 6.0 or more and 6.3 or less. Therefore, compared with the case where the pH is adjusted to less than 6.0 or more than 6.3 with the adjusted digestive juice, the weight and quality of hydroponically cultivated plants can be improved. Thereby, the productivity of the hydroponic cultivation system using raw material digestive juice can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of the hydroponic cultivation system of the present embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a modification of the hydroponic cultivation system of the present embodiment. MODE FOR CARRYING OUT THE INVENTION

[0012] Hereinafter, an example of a method for adjusting a nutrient solution for hydroponic cultivation as an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the configurations in each drawing are schematically described for the sake of explanation, and for example, the size of each configuration and the size contrast among the configurations may be different from those shown in the drawings.

[0013] (Method for Adjusting Nutrient Solution for Hydroponic Cultivation) An example of the method for adjusting a nutrient solution for hydroponic cultivation in the present embodiment will be described with reference to the drawings. First, the hydroponic cultivation system 1 used in the method for adjusting a nutrient solution for hydroponic cultivation will be described.

[0014] <Hydroponic Cultivation System 1> The hydroponic cultivation system 1 is a system for adjusting the pH of a nutrient solution 111 using raw material digestive juice for hydroponically cultivating a plant A. While the raw material digestive juice is rich in nutrients such as nitrogen and potassium necessary for the growth of the plant A, it contains ammonia nitrogen (NH4 + ) is absorbed by the plant A, hydrogen ions (H + ) are released, causing the pH of the nutrient solution 111 to decrease sharply, which may significantly inhibit the growth of the plant A.

[0015] The nutrient solution 111 using raw material digested juice contains hydrogen carbonate ions (HCO3 - ) and organic substances compared with the case where an inorganic culture solution is used. Therefore, it has a high buffering capacity against pH decrease, and may mitigate the influence of ammonia toxicity on Plant A even under the condition of the same concentration of ammonia nitrogen. However, during the rapid growth period of Plant A, there is a concern that the pH will decrease and growth will be inhibited. In this regard, the hydroponic cultivation system 1 adjusts the pH of the nutrient solution 111 to prevent growth inhibition even during the growth period of Plant A, and improves the weight and quality of Plant A, thereby improving the productivity of hydroponic cultivation using raw material digested juice.

[0016] The hydroponic cultivation system 1 includes, for example, as shown in FIG. 1, a hydroponic cultivation tank 11 that accommodates the nutrient solution 111, an adjustment tank 12 that accommodates the adjusted nutrient solution 121, and an alkaline agent supply unit 13 that accommodates the alkaline agent 131.

[0017] Note that, as shown in FIG. 2 for example, the hydroponic cultivation system 1 may include a conditioned digested juice supply unit 14 that accommodates a pH adjustment digested juice (conditioned digested juice 141) different from the raw material digested juice, instead of the alkaline agent supply unit 13.

[0018] Each component included in the hydroponic cultivation system 1 is connected to each other via a water supply pipe indicated by an arrow in the drawings. For example, a polyethylene pipe or the like may be used as the water supply pipe.

[0019] <Plant A> Plant A is accommodated in the hydroponic cultivation tank 11. Plant A is fixed to the hydroponic cultivation tank 11 via a base such as a sponge, for example. As Plant A, those compatible with hydroponic cultivation are selected, and specifically include Asteraceae plants (such as leaf lettuce), Amaranthaceae plants (such as spinach, Swiss chard), Amaryllidaceae plants (such as Chinese chives), Apiaceae plants (such as parsley), and Brassicaceae plants (such as watercress, wasabi greens).

[0020] <Hydroponic Cultivation Tank 11> The hydroponic cultivation tank 11 accommodates the nutrient solution 111 and Plant A.

[0021] The hydroponic cultivation tank 11 supplies nutrient solution 111 to the adjustment tank 12, for example, via a water supply pipe. The hydroponic cultivation tank 11 also receives adjusted nutrient solution 121 from the adjustment tank 12, for example, via a water supply pipe.

[0022] For example, raw material digestate can be used directly as the nutrient solution 111. As the raw material digestate, a known digestate obtained by methane fermentation using biomass resources as raw material may be used. The pH of the nutrient solution 111 at the start of hydroponic cultivation is, for example, 6.0 to 6.9.

[0023] <Adjustment tank 12> The adjustment tank 12 contains the adjusted nutrient solution 121.

[0024] The adjustment tank 12 supplies the adjusted nutrient solution 121 to the hydroponic cultivation tank 11, for example, via a water supply pipe. The adjustment tank 12 receives the nutrient solution 111 from the hydroponic cultivation tank 11, for example, via a water supply pipe. The adjustment tank 12 receives the alkaline agent 131 from the alkaline agent supply unit 13, for example, via a water supply pipe, and mixes the nutrient solution 111 and the alkaline agent 131 to produce the adjusted nutrient solution 121.

[0025] The adjusted nutrient solution 121 is, for example, a liquid in which the pH of the nutrient solution 111 has been adjusted. The adjusted nutrient solution 121 may be produced by mixing the nutrient solution 111 with any liquid used to adjust the pH of the nutrient solution 111.

[0026] <Alkaline agent supply unit 13> The alkaline agent supply unit 13 contains the alkaline agent 131.

[0027] The alkaline agent supply unit 13 supplies alkaline agent 131 to the adjustment tank 12, for example, via a water supply pipe. The alkaline agent supply unit 13 may also supply alkaline agent 131 to the hydroponic cultivation tank 11, for example, via a water supply pipe, or it may supply alkaline agent 131 to both the hydroponic cultivation tank 11 and the adjustment tank 12.

[0028] As the alkaline agent 131, a known alkaline solution containing, for example, sodium hydroxide, may be used. The pH of the alkaline agent 131 is, for example, 8.0 to 12.0.

[0029] <Adjusted digestive fluid supply section 14> The prepared digested fluid supply unit 14 contains the prepared digested fluid 141.

[0030] The digested liquid supply unit 14 supplies the digested liquid 141 to the adjustment tank 12, for example, via a water supply pipe. The digested liquid supply unit 14 may supply the digested liquid 141 only to the hydroponic cultivation tank 11 via a water supply pipe, or it may supply the digested liquid 141 to both the hydroponic cultivation tank 11 and the adjustment tank 12.

[0031] The prepared digestate 141 may be the same as the raw material digestate already contained in the nutrient solution 111, or it may be a digestate with different components. The pH of the prepared digestate 141 is, for example, 7.0 to 9.0.

[0032] Next, the specific details of the method for preparing the nutrient solution for hydroponics in this embodiment will be explained.

[0033] In the example shown in Figure 1, the operator first places plant A and nutrient solution 111 into the hydroponic cultivation tank 11, and then places alkaline agent 131 into the alkaline agent supply unit 13. Here, the nutrient solution 111 is adjusted, for example, to a pH of 6.0 to 6.5 before being placed in the hydroponic cultivation tank 11. Subsequently, the nutrient solution 111 is circulated by repeatedly supplying it from the hydroponic cultivation tank 11 to the adjustment tank 12 and from the adjustment tank 12 to the hydroponic cultivation tank 11. At this time, as the pH of the nutrient solution 111 decreases over time, alkaline agent 131 is supplied from the alkaline agent supply unit 13 and mixed with the nutrient solution 111 in the adjustment tank 12 to produce an adjusted nutrient solution 121 with a pH of 6.0 to 6.9. Note that the adjusted nutrient solution 121 may be produced when the pH of the nutrient solution 111 in the adjustment tank 12 becomes 6.0 or lower, or when the pH of the nutrient solution 111 is greater than 6.0 but less than 6.9.

[0034] In other words, in the nutrient solution preparation method of this embodiment, an alkaline agent 131 is mixed into the nutrient solution 111 supplied to the hydroponic cultivation tank 11 to adjust the pH of the nutrient solution 111 to 6.0 or higher and 6.9 or lower. In this case, compared to adjusting the pH to less than 6.0 or greater than 6.9 with the alkaline agent 131, the weight and quality of the hydroponically cultivated plant A can be improved. This makes it possible to improve the productivity of the hydroponic cultivation system 1 using raw material digestate. The specific benefits of improving the weight and quality of plant A will be explained later.

[0035] In the example shown in Figure 2, the operator first places plant A and nutrient solution 111 into the hydroponic cultivation tank 11, and then places the prepared digestate 141 into the prepared digestate supply unit 14. Subsequently, the nutrient solution 111 is circulated by repeatedly supplying it from the hydroponic cultivation tank 11 to the preparation tank 12 and from the preparation tank 12 to the hydroponic cultivation tank 11. At this time, as the pH of the nutrient solution 111 decreases over time, the prepared digestate 141 is supplied from the prepared digestate supply unit 14 and mixed with the nutrient solution 111 in the preparation tank 12 to produce a prepared nutrient solution 121 with a pH of 6.0 or higher and 6.3 or lower. Note that the prepared nutrient solution 121 may be produced when the pH of the nutrient solution 111 in the preparation tank 12 falls below 6.0, or when the pH of the nutrient solution 111 is greater than 6.0 but less than 6.3.

[0036] In other words, in the nutrient solution preparation method of this embodiment, the prepared digestate 141 is mixed with the nutrient solution 111 supplied to the hydroponic cultivation tank 11 to adjust the pH of the nutrient solution 111 to 6.0 or higher and 6.3 or lower. In this case, compared to adjusting the pH to less than 6.0 or greater than 6.3 with the prepared digestate 141, the weight and quality of the hydroponically grown plant A can be improved. This makes it possible to improve the productivity of the hydroponic cultivation system 1 using raw material digestate.

[0037] This completes the process for preparing the nutrient solution for hydroponics.

[0038] According to this embodiment, an alkaline agent 131 is mixed into the nutrient solution 111 supplied to the hydroponic cultivation tank 11 to adjust the pH of the nutrient solution 111 to between 6.0 and 6.9. Therefore, compared to the case where the pH is adjusted to less than 6.0 or greater than 6.9 with the alkaline agent 131, the weight and quality of the hydroponically cultivated plant A can be improved. This makes it possible to improve the productivity of the hydroponic cultivation system 1 using raw material digestate.

[0039] Furthermore, according to this embodiment, the nutrient solution 111 supplied to the hydroponic cultivation tank 11 is mixed with the adjusted digestate 141 to adjust the pH of the nutrient solution 111 to between 6.0 and 6.3. Therefore, compared to the case where the pH is adjusted to less than 6.0 or greater than 6.3 with the adjusted digestate 141, the weight and quality of the hydroponically cultivated plant A can be improved. This makes it possible to improve the productivity of the hydroponic cultivation system 1 using raw material digestate. [Examples]

[0040] The present invention will be specifically described below with reference to examples and comparative examples using the embodiments described above.

[0041] In this experiment, lettuce was used as plant A. Improvements in the weight and quality of plant A were confirmed by comparing the fresh weight (g / piece), chlorophyll content (mg / g), carotenoid content (mg / g), soluble sugar content (mg / g), and total soluble sugar content (mg / piece) of lettuce for each preparation method of nutrient solution 111 using raw material digestate. The sample sizes were N=4 for fresh weight, and N=3 for chlorophyll content, carotenoid content, soluble sugar content, and total soluble sugar content.

[0042] The measurement methods were as follows: Fresh weight was measured using a precision balance after washing the harvested lettuce. Chlorophyll content was calculated using the Lichtenthaler method after measuring the acetone extract with a spectrophotometer. Carotenoid content was calculated using the Lichtenthaler method after measuring the same acetone extract with a spectrophotometer. Soluble sugar content and total soluble sugar content were measured and calculated using the anthrone sulfuric acid method.

[0043] Examples of the present invention and comparative examples are as follows. For Examples 1 to 5 and Comparative Examples 1 to 2, the pH was adjusted by mixing an alkaline agent 131 with a nutrient solution 111 obtained by diluting the raw material digestate. Specifically, the pH of the nutrient solution 111 was adjusted to 6.0 to 6.9 in Example 1, 6.0 to 6.7 in Example 2, 6.0 to 6.5 in Example 3, 6.0 to 6.3 in Example 4, and 6.0 to 6.1 in Example 5. In addition, in Comparative Example 1, the upper limit of the pH adjustment range was set to greater than 6.9 (6.0 to 7.0), and in Comparative Example 2, the lower limit of the pH adjustment range was set to less than 6.0 (5.9 to 6.9).

[0044] Furthermore, for Invention Examples 6 to 8 and Comparative Examples 3 to 4, the pH was adjusted by mixing the prepared digestate 141 with the nutrient solution 111, which was obtained by diluting the raw material digestate approximately 80 times. Specifically, the pH of the nutrient solution 111 was adjusted to 6.0 to 6.3 in Invention Example 6, 6.0 to 6.2 in Invention Example 7, and 6.0 to 6.1 in Invention Example 8. In addition, in Comparative Example 3, the upper limit of the pH adjustment range was set to greater than 6.3 (6.0 to 6.4), and in Comparative Example 4, the lower limit of the pH adjustment range was set to less than 6.0 (5.9 to 6.4).

[0045] Furthermore, in Comparative Example 5, the pH of nutrient solution 111, which was obtained by diluting the raw material digestate, was not adjusted. Also, in Comparative Example 6, the pH of the Hoagland solution in which nitrate nitrogen was replaced with ammonia nitrogen was not adjusted.

[0046] The components of the nutrient solution 111 used in this experiment are as follows. As the components per 1 L of the nutrient solution 111 prepared by diluting the raw material digested liquid, which was used in Invention Examples 1 to 8 and Comparative Examples 1 to 5, the NH4 + -N (ammonia nitrogen) was about 90 mg / L, NO3 - -N (nitrate nitrogen) was about 5 mg / L, PO4 3- -P (orthophosphate phosphorus) was about 25 mg / L, K (potassium) was about 80 mg / L, and Ca (calcium) was about 0 mg / L. Note that the pH of the nutrient solution 111 prepared by diluting the raw material digested liquid (pH 8.58) used in this experiment at the start of cultivation was 6.0 to 6.5.

[0047] In addition, as the components per 1 L of the Hoagland solution containing ammonia nitrogen used in Comparative Example 6, the NH4 + -N (ammonia nitrogen) was about 95 mg / L, NO3 - -N (nitrate nitrogen) was about 0 mg / L, PO4 3- -P (orthophosphate phosphorus) was about 25 mg / L, K (potassium) was about 160 mg / L, and Ca (calcium) was about 100 mg / L. In addition, the pH at the start of cultivation was 6.97.

[0048] As the raw material digested liquid for the nutrient solution 111, the digested liquid produced when methane fermentation is performed using chicken manure and rice husks as raw materials was used as it is. As the components per 1 L of the raw material digested liquid, the NH4 + -N (ammonia nitrogen) was about 6900 mg / L, NO2 - -N (nitrite nitrogen) was about 20 mg / L, NO3 --N (nitrate nitrogen) was approximately 419 mg / L, TON (total organic nitrogen) was approximately 1000 mg / L, TOP (total organic phosphorus) was approximately 120 mg / L, TIP (total inorganic phosphorus) was approximately 290 mg / L, TOC (total organic carbon) was approximately 10300 mg / L, TIC (inorganic carbon) was approximately 8900 mg / L, K (potassium) was approximately 3600 mg / L, protein was approximately 11200 mg / L, polysaccharides were approximately 1400 mg / L, HAc (acetic acid) was approximately 59.69 mg / L, and IHBu (isobutyric acid) was approximately 18.1 mg / L.

[0049] As the alkaline agent 131, commercially available sodium hydroxide was used by dissolving 0.1 g / L of water per liter. As the prepared digestate 141, the raw digestate was diluted in the same ratio as the nutrient solution 111, and NH4 + A solution containing approximately 90 mg / L of -N (ammonia nitrogen) was used.

[0050] The cultivation conditions for plant A were as follows. In the example of pH adjustment, when the pH of nutrient solution 111 reached the lower limit of adjustment, alkaline agent 131 or adjusted digestate 141 was continuously supplied to produce adjusted nutrient solution 121 with a pH at the upper limit of adjustment. The water temperature of nutrient solution 111 and adjusted nutrient solution 121 was set to 20±1℃, and the cultivation period was 36 days.

[0051] The results of this experiment are shown in Table 1. The values ​​in the table represent the average values ​​of the data obtained for each sample.

[0052] [Table 1]

[0053] According to the results of Example 1 of the present invention, the fresh weight was 64.6 [g / piece], the chlorophyll content was 7.4 [mg / g], the carotenoid content was 3.0 [mg / g], the soluble sugar content was 134.1 [mg / g], and the total soluble sugar content was 451.3 [mg / piece].

[0054] According to the results of Example 2 of the present invention, the fresh weight was 71.5 [g / piece], the chlorophyll content was 8.0 [mg / g], the carotenoid content was 3.4 [mg / g], the soluble sugar content was 145.8 [mg / g], and the total soluble sugar content was 542.3 [mg / piece].

[0055] According to the results of Example 3 of the present invention, the fresh weight was 77.5 [g / piece], the chlorophyll content was 8.6 [mg / g], the carotenoid content was 3.8 [mg / g], the soluble sugar content was 157.6 [mg / g], and the total soluble sugar content was 635.3 [mg / piece].

[0056] According to the results of Example 4 of the present invention, the fresh weight was 87.8 [g / piece], the chlorophyll content was 9.8 [mg / g], the carotenoid content was 4.1 [mg / g], the soluble sugar content was 179.1 [mg / g], and the total soluble sugar content was 792.1 [mg / piece].

[0057] According to the results of Example 5 of the present invention, the fresh weight was 80.6 [g / piece], the chlorophyll content was 9.0 [mg / g], the carotenoid content was 3.8 [mg / g], the soluble sugar content was 164.3 [mg / g], and the total soluble sugar content was 688.9 [mg / piece].

[0058] According to the results of Comparative Example 1, the fresh weight was 54.6 [g / piece], the chlorophyll content was 6.2 [mg / g], the carotenoid content was 2.6 [mg / g], the soluble sugar content was 108.2 [mg / g], and the total soluble sugar content was 305.7 [mg / piece].

[0059] According to the results of Comparative Example 2, the fresh weight was 54.4 [g / piece], the chlorophyll content was 6.2 [mg / g], the carotenoid content was 2.6 [mg / g], the soluble sugar content was 107.1 [mg / g], and the total soluble sugar content was 303.2 [mg / piece].

[0060] According to the results of Example 6 of the present invention, the fresh weight was 82.1 [g / piece], the chlorophyll content was 7.4 [mg / g], the carotenoid content was 3.1 [mg / g], the soluble sugar content was 107.1 [mg / g], and the total soluble sugar content was 473.5 [mg / piece].

[0061] According to the results of Example 7 of the present invention, the fresh weight was 80.7 [g / piece], the chlorophyll content was 6.7 [mg / g], the carotenoid content was 2.8 [mg / g], the soluble sugar content was 96.8 [mg / g], and the total soluble sugar content was 423.3 [mg / piece].

[0062] According to the results of Example 8 of the present invention, the fresh weight was 72.0 [g / piece], the chlorophyll content was 6.0 [mg / g], the carotenoid content was 2.6 [mg / g], the soluble sugar content was 95.1 [mg / g], and the total soluble sugar content was 370.2 [mg / piece].

[0063] According to the results of Comparative Example 3, the fresh weight was 55.4 [g / piece], the chlorophyll content was 5.1 [mg / g], the carotenoid content was 2.1 [mg / g], the soluble sugar content was 71.0 [mg / g], and the total soluble sugar content was 211.7 [mg / piece].

[0064] According to the results of Comparative Example 4, the fresh weight was 53.3 [g / piece], the chlorophyll content was 4.9 [mg / g], the carotenoid content was 2.0 [mg / g], the soluble sugar content was 67.8 [mg / g], and the total soluble sugar content was 194.8 [mg / piece].

[0065] According to the results of Comparative Example 5, the fresh weight was 19.0 [g / piece], the chlorophyll content was 2.6 [mg / g], the carotenoid content was 1.7 [mg / g], the soluble sugar content was 283.5 [mg / g], and the total soluble sugar content was 323.5 [mg / piece].

[0066] According to the results of Comparative Example 6, the fresh weight was 6.0 [g / piece], the chlorophyll content was 1.7 [mg / g], the carotenoid content was 1.0 [mg / g], the soluble sugar content was 301.1 [mg / g], and the total soluble sugar content was 187.3 [mg / piece].

[0067] In Examples 1 to 5 of the present invention, an alkaline agent 131 was supplied to the nutrient solution 111 to produce an adjusted nutrient solution 121 with a pH of 6.0 to 6.9. That is, the pH of the nutrient solution 111 was adjusted to 6.0 to 6.9 by supplying the alkaline agent 131. As a result, compared with Comparative Example 1, in which the upper limit of the pH adjustment range was adjusted to be greater than 6.9, and with Comparative Example 2, in which the lower limit of the pH adjustment range was adjusted to be less than 6.0, the fresh weight, chlorophyll content, carotenoid content, soluble sugar content, and total soluble sugar content increased significantly. Furthermore, compared with Comparative Example 5, in which no pH adjustment was performed, and with Comparative Example 6, in which no raw material digestate was used, the fresh weight, chlorophyll content, carotenoid content, and total soluble sugar content increased significantly. Thus, according to Examples 1 to 5 of the present invention, the weight and quality of hydroponically grown plant A can be improved, and the productivity of the hydroponic cultivation system 1 using raw material digestate can be improved.

[0068] Furthermore, according to Examples 4 and 5 of the present invention, adjusting the pH of the nutrient solution 111 to 6.0 or higher and 6.3 or lower results in a more significant improvement in the weight and quality of hydroponically grown plant A compared to Examples 1 to 3 of the present invention, making it more preferable.

[0069] In Examples 6 to 8 of the present invention, a prepared digestate 141 was supplied to the nutrient solution 111 to produce a prepared nutrient solution 121 with a pH of 6.0 to 6.3. That is, the pH of the nutrient solution 111 was adjusted to 6.0 to 6.3 by supplying the prepared digestate 141. As a result, compared with Comparative Example 3, in which the upper limit of the pH adjustment range was adjusted to over 6.4, and Comparative Example 4, in which the lower limit of the pH adjustment range was adjusted to less than 6.0, the fresh weight, chlorophyll content, carotenoid content, soluble sugar content, and total soluble sugar content increased significantly. Furthermore, compared with Comparative Example 5, in which no pH adjustment was performed, and Comparative Example 6, in which no raw material digestate was used, the fresh weight, chlorophyll content, carotenoid content, and total soluble sugar content increased significantly. Thus, according to Examples 6 to 8 of the present invention, the weight and quality of hydroponically grown plant A can be improved, and the productivity of the hydroponic cultivation system 1 using raw material digestate can be improved.

[0070] Furthermore, in Examples 4 and 5 of the present invention, where the pH was adjusted to between 6.0 and 6.3, the fresh weight, chlorophyll content, carotenoid content, soluble sugar content, and total soluble sugar content tended to be higher compared to Examples 6 and 8 of the present invention, which were under the same pH adjustment conditions. This is thought to be because external pH adjustment with the alkaline agent 131 resulted in a more stable pH in the rhizosphere than when pH adjustment was made by the pH buffering effect of the prepared digestate 141 itself, thus maintaining an optimal pH range for plant A. As a result, the toxicity of ammoniacal nitrogen to plant A was reduced and nitrogen absorption was promoted, the solubility of trace elements such as iron and manganese in the prepared nutrient solution 121 was maintained at a high level, chlorophyll synthesis proceeded smoothly, and the pH of the prepared nutrient solution 121 shifted towards the acidic side, and HCO3 in the water followed the chemical equilibrium of the carbonate system. - It is thought that CO2 was generated from the plant, and plant A took in that CO2, improving photosynthetic efficiency and activity, which in turn promoted carbohydrate assimilation and increased soluble sugar content.

[0071] In Comparative Example 1, an alkaline agent 131 was supplied to the nutrient solution 111 to produce a nutrient solution 121 with a pH of 6.0 to 7.0. That is, the upper limit of the pH adjustment range of the nutrient solution 111 was adjusted to be greater than 6.9 by supplying the alkaline agent 131. In Comparative Example 2, an alkaline agent 131 was supplied to the nutrient solution 111 to produce a nutrient solution 121 with a pH of 5.9 to 6.9. That is, the lower limit of the pH adjustment range of the nutrient solution 111 was adjusted to be less than 6.0 by supplying the alkaline agent 131. As a result, although the fresh weight, chlorophyll content, and carotenoid content were higher compared to Comparative Examples 5 and 6, which did not have their pH adjusted, no significant increase was observed compared to Examples 1 to 5 of the present invention. Therefore, there is a concern that Comparative Examples 1 and 2 cannot reliably improve the weight and quality of hydroponically grown plant A, and that the productivity of the hydroponic cultivation system 1 using raw material digestate cannot be improved.

[0072] In Comparative Example 3, adjusted digestate 141 was supplied to nutrient solution 111 to produce adjusted nutrient solution 121 with a pH of 6.0 to 6.4. That is, the upper limit of the pH adjustment range of nutrient solution 111 was adjusted to be greater than 6.3 by supplying adjusted digestate 141. In Comparative Example 4, adjusted digestate 141 was supplied to nutrient solution 111 to produce adjusted nutrient solution 121 with a pH of 5.9 to 6.4. That is, the lower limit of the pH adjustment range of nutrient solution 111 was adjusted to be less than 6.0 by supplying adjusted digestate 141. As a result, although the fresh weight, chlorophyll content, and carotenoid content were higher compared to Comparative Examples 5 and 6, which did not have their pH adjusted, no significant increase was observed compared to Examples 6 to 8 of the present invention. Therefore, there is a concern that Comparative Examples 3 and 4 cannot reliably improve the weight and quality of hydroponically grown plant A, and that the productivity of the hydroponic cultivation system 1 using raw material digestate cannot be improved.

[0073] Furthermore, Comparative Examples 5 and 6 showed a tendency for higher soluble sugar content compared to Examples 1-8 of the present invention. This is thought to be because the growth of plant A was suppressed and the leaves became smaller in Comparative Examples 5 and 6, resulting in easier accumulation and concentration of soluble sugars. However, when comparing the total soluble sugar content per plant, which reflects the overall amount of photosynthetic products of plant A, the value is lower than that of Examples 1-8 of the present invention. Therefore, there are concerns that a reliable improvement in the quality of hydroponically grown plant A cannot be achieved, and the productivity of the hydroponic cultivation system 1 using the raw material digestate cannot be improved.

[0074] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0075] 1. Hydroponic cultivation system 11 Hydroponic cultivation tanks 111 Nutrient Solution 12 Adjustment tank 121 Prepared Nutrient Solution 13. Alkaline agent supply unit 131 Alkaline agent 14 Adjusted digestive fluid supply section 141 Adjusted Digestive Juice A plant

Claims

1. A method for preparing nutrient solutions in hydroponics, which involves preparing nutrient solutions using digestive fluids, Mix an alkaline agent into the nutrient solution supplied to plants containing at least one of the following: Asteraceae, Amaranthaceae, Amaryllidaceae, Apiaceae, or Brassicaceae, and repeatedly supply the nutrient solution to the plants while adjusting the pH of the nutrient solution to 6.0 or higher and 6.9 or lower. A method for preparing nutrient solution for hydroponics characterized by the following.

2. A method for preparing nutrient solutions in hydroponics, which involves preparing nutrient solutions using digestive fluids, Mix a prepared digestate into the nutrient solution supplied to plants containing at least one of the following: Asteraceae, Amaranthaceae, Amaryllidaceae, Apiaceae, or Brassicaceae, and repeatedly supply the nutrient solution to the plants while adjusting the pH of the nutrient solution to 6.0 or higher and 6.3 or lower. A method for preparing nutrient solution in hydroponics characterized by the following.

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