JP6747731B1 - Method for producing nutrient solution for plant cultivation and method for plant cultivation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an organic substance-degrading bacterium and nitrifying bacterium by individually controlling them in a method for producing a nutrient solution for plant cultivation in which the reaction of decomposing organic matter in water to obtain nitrate ion is carried out in the same system (tank). Reduce the possibility that harmful bacteria will be mixed in the nutrient solution. SOLUTION: As a microbial source, a microbial agent 3 of organic matter decomposing bacteria and a microbial agent 4 of nitrifying bacteria are separately prepared. To the tank 1 containing water, fish liquid fertilizer as an organic fertilizer 2 is added in an amount of more than 0.5 g/L, and two kinds of microbial agents 3 and 4 are simultaneously added in the same amount. The amount of each of the microbial agents 3 and 4 added is 0.01% to 1.5% per 1 L of water. After the addition of the fish liquid fertilizer 2 and the microbial agents 3 and 4, there is provided a period in which the decomposition of organic substances and the nitrification in the water in the tank 1 proceed. The liquid in the tank 1 is diluted during or after nitrification, and additional fertilization is performed simultaneously with or after the dilution. A period during which decomposition of organic matter and nitrification are advanced is provided for the liquid after dilution and topdressing. [Selection diagram] Figure 2

Description

The present invention relates to a method for producing a nutrient solution for plant cultivation and a method for plant cultivation.

Conventionally, in hydroponics such as hydroponic cultivation, a technique is known in which an organic substance is directly added to water and the added organic substance (organic nitrogen) is decomposed by a microorganism to obtain nitrate nitrogen that is easily absorbed by plants. (See, for example, Patent Documents 1 and 2). Microorganisms used in this technology include those that perform ammonia formation that decomposes organic matter to produce ammonia (ammonia-forming bacteria, organic matter-decomposing bacteria), and microorganisms that perform nitrification formation that converts ammonia into nitric acid (nitrifying bacteria). .. Nitrifying bacteria include bacteria that oxidize ammonia to produce nitrite (ammonia-oxidizing bacteria) and bacteria that oxidize nitrite to produce nitric acid (nitrite-oxidizing bacteria). In water, ammonia exists as ammonium ion (NH ₄ ⁺ ), nitric acid exists as nitrate ion (NO ₃ ⁻ ), and nitrous acid exists as nitrite ion (NO ₂ ⁻ ).

Patent Documents 1 and 2 propose a technique (parallel compound mineralization reaction) in which ammonia formation and nitric acid formation are performed in parallel in the same reaction solution. In the technique of Patent Document 1, soil or bark compost is used as a microorganism source. Further, in the technique of Patent Document 2, soil, compost, activated sludge, or water collected from nature is used as a microorganism source. Further, in Patent Document 2, a biofilm is formed on a solid surface in contact with water containing the above-mentioned microbial source, the biofilm is recovered, and the recovered biofilm is used as an inoculum of a microbial group of a parallel compound mineralization reaction. It is described to be used.

Japanese Patent No. 5071897 Patent No. 5388096

By the way, in order to efficiently obtain nitrate ions from organic substances, it is desirable to control the addition of organic substance-degrading bacteria and nitrifying bacteria individually, but in the techniques of Patent Documents 1 and 2, the types of microorganisms contained as a microbial source Since soils that are not sorted are used, it is not possible to individually control the addition of organic substance degrading bacteria and nitrifying bacteria. In addition, since the microbial sources of Patent Documents 1 and 2 contain miscellaneous microorganisms, in addition to useful microorganisms such as organic substance degrading bacteria and nitrifying bacteria, they are harmful to organic substances degrading or nitrifying, or harmful to plants. There is a possibility that various bacteria are mixed.

The present invention has been made in view of the above circumstances, in a method for producing a nutrient solution for plant cultivation, in which the reaction of decomposing organic matter in water to obtain nitrate ions is performed in the same system (tank), an organic matter degrading bacterium and nitrification are used. It is an object of the present invention to provide a method for producing a nutrient solution for plant cultivation, which can individually control the addition of bacteria and reduce the possibility that harmful bacteria are mixed in the nutrient solution produced.

In order to solve the above problems, the method for producing a nutrient solution for plant cultivation of the present invention,
An organic matter adding step of adding fish manure as an organic matter to water in an amount of more than 0.5 g per 1 L of water;
In the water, a microbial agent of an organic substance-decomposing bacterium that decomposes organic nitrogen to generate ammonium ion, a bacterium that oxidizes ammonium ion to generate nitrite ion and nitrite ion to oxidize nitrate ion Microbial agent addition step in which the same amount of the microbial agent of nitrifying bacteria that is a bacterium is added at the same time, and an amount of 0.01% or more and 0.1% or less per 1 L of water is added, respectively.
A nitrification step of advancing nitrification to the liquid after the organic matter addition step and the microbial agent addition step,
Equipped with
This is a method for obtaining a nutrient solution for plant cultivation having a nitrate ion concentration of 100 ppm or more .

According to the present invention, an organic substance-degrading microbial agent and a nitrifying bacterium microbial agent are separately prepared as microbial sources, and these two microbial agents are added to water together with the organic substance. This makes it possible to individually control the addition of the organic substance-degrading bacteria and the nitrifying bacteria. Further, since the microbial agent containing the selected microorganisms is used, it is possible to reduce the possibility that harmful bacteria are mixed in the produced nutrient solution. The microbial agent in the present invention refers to a liquid containing a selected specific microorganism, a powder, a solid, etc., a soil containing miscellaneous miscellaneous microorganisms, compost, activated sludge, and water collected from nature. Not including

The microbial agents of microbial agents and nitrifying bacteria organic matter degrading bacteria in the present invention is added the same amount at the same time. According to this, it becomes easy to control the addition of the organic substance degrading bacteria and the nitrifying bacteria.

Also an amount of respectively 0.01% -0.1% of the volume per 1L of water addition amount of the microbial agents of microbial agents and nitrifying bacteria organic matter degrading bacteria in the present invention. According to this, the amount of the microbial agent added can be suppressed, so that the cost can be reduced.

Also, the organic material in the present invention is a fish fertilizer, the amount added is an amount greater than 0.5g per water 1L. According to this, since the fish liquid fertilizer that is easily available is used, the nutrient solution can be efficiently produced. In addition, the concentration of nitrate ion can be increased by setting the addition amount of the fish liquid fertilizer to be more than 0.5 g per 1 L of water.

Further, in the present invention, in the organic matter addition step, fish liquid fertilizer may be added in an amount of more than 1.0 g per 1 L of water . By setting the addition amount of each microbial agent and fish manure to this condition, the nitrification rate and nitrate ion concentration can be further improved.

The present invention also provides the nitrification step as a first nitrification step,
A diluting step of diluting the liquid during or after nitrification in the first nitrification step,
A second nitrification step in which nitrification is advanced to the diluted solution so that the concentration of nitrate ions in the solution is 100 ppm or more;
May be further provided. According to this, the concentration of nitrite ions in the liquid can be reduced by diluting the liquid. A high nitrite ion concentration is harmful to nitrifying bacteria and may reduce the activity of nitrifying bacteria. By reducing the nitrite ion concentration, nitrate ions can be efficiently generated.

Further, the present invention may further include a supplemental fertilization step of adding fish fertilizer as an additional organic substance in an amount of more than 0.5 g per 1 L of water at the same time as or after the dilution in the dilution step. According to this, organic matter decomposing bacteria and nitrifying bacteria can be activated by topdressing, and the nitrate ion concentration can be increased. Further, by performing both the dilution and the additional fertilization, the amount of the nutrient solution to be produced can be increased and the cost can be reduced while suppressing the amount of the microbial agent added.

Further, in the present invention, the dilution in the diluting step is performed after the nitrification in the first nitrification step is completed, when the nitrate ion concentration in the liquid rises to 100 ppm or more, or the nitrate ion concentration is lower than the nitrite ion concentration. It may be performed when the state is reversed to a high state, or when the nitrite ion concentration drops from a state of 50 ppm or more to less than 50 ppm. When the nitrate ion concentration in the liquid is 100 ppm or more, it is considered that the microorganisms responsible for nitrification are sufficiently increased in the liquid. By performing the dilution after waiting for the increase of the microorganisms, nitrification can be promoted even after the dilution.

Further, in the present invention, the dilution in the diluting step is performed during the nitrification in the first nitrification step when the concentration of nitrate ion in the liquid is 100 ppm or less, or when the concentration of nitrite ion is higher than the concentration of nitrate ion, or Performed when the nitrate ion concentration is 50 ppm or more,
The addition amount of the microbial agent of the organic substance-degrading bacterium and the microbial agent of the nitrifying bacterium may be an amount having a volume larger than 0.01% per 1 L of water . The present inventors have found that when the amount of the microbial agent added in the initial stage is 0.01% or less and the dilution is performed without waiting for the increase of the microorganisms responsible for nitrification, the nitrate ion concentration does not increase much after the dilution. have. Therefore, when the dilution is carried out without waiting for the increase of the microorganisms responsible for nitrification, the amount of the microbial agent added in the initial stage should be an amount which is larger than 0.01% per 1 L of water. This allows nitrification to proceed even after dilution.

The plant cultivation method of the present invention cultivates a plant using the nutrient solution obtained by the method for producing a nutrient solution for plant cultivation of the present invention. According to this, since the cultivation is performed using the nutrient solution in which the harmful bacteria are prevented from being mixed, the plant can be smoothly grown.

It is a flowchart which shows the manufacturing process of the nutrient solution for plant cultivation. It is the figure which showed a mode that the organic fertilizer and two kinds of microbial agents were added to the tank in which water was put. 6 is a flowchart showing an additional process following the process of FIG. 1. It is the figure which showed a mode that the liquid in the middle of nitrification or after nitrification was diluted, and the fertilizer was further applied to the diluted liquid. It is the figure which showed a mode that the manufactured nutrient solution was supplied to the tank of hydroponics. It is a figure which shows the result of experiment 1. It is a figure which shows the result of experiment 2. It is a figure which shows the result of experiment 3. It is a figure which shows the result of experiment 4. It is a figure which shows the result of experiment 5. It is a figure which shows the result of experiment 6. It is a figure which shows the result of experiment 7. It is a figure which shows the result of experiment 8. It is a figure which shows the result of experiment 9. It is a figure which shows the result of experiment 10. It is a figure which shows the result of experiment 11.

Hereinafter, a method for producing a nutrient solution for plant cultivation according to the present embodiment will be described with reference to the drawings. The nutrient solution for plant cultivation of the present embodiment is a nutrient solution for organic cultivation. FIG. 1 shows a manufacturing process of the nutrient solution for plant cultivation of the present embodiment. FIG. 2 shows how the nutrient solution for plant cultivation is manufactured. During the process of FIG. 1, the plant is not cultivated in the tank 1 of FIG. 2, that is, the process of FIG. 1 is a process before the plant cultivation. First, as shown in FIG. 2, a tank 1, a bubbling section 5 for generating bubbling of air (oxygen), a supply section 6 for supplying air (oxygen), and the like are prepared as equipment used for nutrient solution production (S1). .. The bubbling portion 5 is put in the tank 1. The supply unit 6 is connected to the bubbling unit 5 and supplies air to the bubbling unit 5. In addition, a temperature adjusting unit (heater) (not shown) for adjusting the temperature of the water contained in the tank 1 and a filter 7 are also prepared if necessary.

Next, water is put into the tank 1 (S2). The initial amount of water may be any amount, but in order to suppress the amount of the microbial agent added in step S4 described below, it is better not to increase the initial amount of water, and for example, it may be about 1 L. The water put in the tank 1 may be natural water (water collected from nature) or artificial water (tap water, etc.).

Next, the organic fertilizer 2 (see FIG. 2) containing an organic substance is added to the water in the tank 1 (S3). The organic fertilizer 2 to be added is, for example, a liquid fertilizer, and more specifically, fish liquid fertilizer can be used. By adding the liquid fertilizer, when the produced nutrient solution is supplied to the cultivation tank by a machine (pump), it is possible to prevent the machine from having a problem (for example, the pump is clogged with foreign matter). The fish manure is, for example, an extract (for example, fish broth) extracted from fish such as horse mackerel and sardines, or a product obtained by further concentrating or purifying the extract. In addition, fish manure may be made from the residues such as the built-in fish market and processing facilities. The ratio of organic nitrogen contained in the fish manure is, for example, 5% to 10%. Further, the organic fertilizer 2 may include other fertilizer components such as phosphoric acid, potassium, and lime, in addition to organic substances such as fish manure (in other words, organic nitrogen, amino acids, proteins). Further, the organic fertilizer 2 may include a naturally derived material (for example, oyster shell (oyster shell)) for the purpose of supplying minerals, in addition to the fish liquid fertilizer. Oysters can supply minerals as nutrients that support the growth of microorganisms (organic matter degrading bacteria, nitrifying bacteria).

Further, the organic fertilizer 2 may be added to the tank 1 in a state of being undiluted, or may be diluted with water and then added to the tank 1. Further, the organic fertilizer 2 may be added to the tank 1 after being filtered by the filter 7 (see FIG. 2). By adding the diluted or filtered organic fertilizer 2, when the manufactured nutrient solution is supplied to the cultivation tank by a machine (pump), it is possible to further suppress the occurrence of a malfunction in the machine.

When using fish manure as the organic fertilizer 2, the amount of fish manure initially added is, for example, more than 0.5 g per liter of water, and more preferably more than 1.0 g. If it is less than 0.5 g/L, the concentration of nitrate ions produced will be low. The upper limit of the initial amount of fish manure can be 2.0 g per 1 L of water, for example. If the amount is more than 2.0 g/L, a part of the added fish liquid fertilizer may not be decomposed and may remain as an organic matter in the produced nutrient solution. In addition, when the organic fertilizer 2 contains fish liquid fertilizer and other fertilizer components or when the organic fertilizer 2 is diluted with water, the amount of fish liquid fertilizer (stock solution) contained in the organic fertilizer 2 is 0.5 g/L. The addition amount of the organic fertilizer 2 is set so as to be more than 2.0 g/L.

At the same time as or slightly before or after the addition of the organic fertilizer 2 to the tank 1, the water in the tank 1 contains a microbial agent 3 for organic matter-decomposing bacteria (see FIG. 2) and a microbial agent 4 for nitrifying bacteria (see FIG. 2). Is added (S4). It is desirable that these two kinds of microbial agents 3 and 4 be added in the same amount at the same time. According to this, addition control becomes easier than when the microbial agents 3 and 4 are added at different times or different amounts, and the nitrate ion concentration is equal to or higher than that when the microbial agents 3 and 4 are added at different times or different amounts. A nutrient solution containing the can be obtained.

Here, the microbial agent 3 includes, as organic matter-decomposing bacteria, one or more kinds of bacteria (ammonia-forming bacteria) that decompose organic nitrogen (amino acids, proteins, etc.) to generate ammonia (ammonium ion). ing. Examples of the organic substance-decomposing bacteria include protozoa, bacteria, filamentous fungi, and the like, and more specifically, Bacillus and Pseudomonas can be mentioned. It should be noted that the microbial agent 3 does not contain microorganisms (such as nitrifying bacteria) other than organic substance-decomposing bacteria.

The microbial agent 4 includes, as nitrifying bacteria, one or more kinds of bacteria (ammonia-oxidizing bacteria, nitrite-producing bacteria) that oxidize ammonia (ammonium ion) to generate nitrite (nitrite ion), Both one kind or plural kinds of bacteria (nitrite-oxidizing bacteria, nitric acid-producing bacteria) that oxidize nitrite to generate nitric acid (nitrate ion) are included. The microbial agent 4 may contain, for example, the same number of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, or the number of one bacterium may be twice or more the number of the other bacterium. Specifically, the above-mentioned equivalent number means that when the number of ammonia-oxidizing bacteria is X and the number of nitrite-oxidizing bacteria is Y, the ratio of the number X of ammonia-oxidizing bacteria to the total number (=X+Y) is, for example, It means 40% to 60%.

Examples of ammonia-oxidizing bacteria include genus Nitrosomonas, genus Nitrosococcus, genus Nitrosospira (including genus Nitrosolobus and genus Nitrosovibrio). Examples of the nitrite-oxidizing bacteria include genus Nitrobacter and genus Nitrospira. It should be noted that the microbial agent 4 does not include microorganisms other than nitrifying bacteria (for example, organic substance degrading bacteria).

As the microbial agents 3 and 4, for example, commercially available microbial agents for purification of wastewater from food factories can be used. The microbial agents 3 and 4 may be in a liquid state, a solid state, a powder state, or the like in the raw material state, but it is preferable to add them to the tank 1 in the liquid state. That is, when the microbial agents 3 and 4 are raw materials other than liquid, it is desirable that the microbial agents 3 and 4 be dissolved in water to be in a liquid state and then added to the water in the tank 1.

Before adding the microbial agents 3 and 4 to the water in the tank 1, it is preferable to activate the microorganisms contained in the microbial agents 3 and 4 in advance and add the activated microbial agents 3 and 4 to the water in the tank 1. desirable. As a result, the microorganisms can be rapidly activated in the water of the tank 1, and thus the decomposition and nitrification of the organic fertilizer 2 can be promoted rapidly. The microorganisms are activated, for example, by adding a predetermined amount of the microbial agent (the microbial agent 3 or the microbial agent 4) to lukewarm water at about 30° C., stirring the mixture well, and leaving it for a certain period of time.

The initial addition amounts of the microbial agents 3 and 4 are set to amounts of 0.01% or more and 1.5% or less per 1 L of water, respectively, and the addition amount of the microbial agent 3 and the addition amount of the microbial agent 4 are It is desirable to set the same amount to each other. According to this, a nutrient solution having a high nitrate ion concentration can be obtained. In addition, by suppressing the addition amount of the microbial agents 3 and 4 to be 1.5%/L or less, it is possible to suppress high cost. When the microbial agents 3 and 4 are diluted with water and the diluted solution is added to the water in the tank 1 to activate the microorganisms, etc., the microbial agents 3 and 4 contained in the diluted solution are The addition amount of the diluent is set so that the amount is 0.01%/L or more and 1.5%/L or less.

After adding the organic fertilizer 2 and the microbial agents 3 and 4, the organic matter contained in the organic fertilizer 2 is decomposed by the microorganisms contained in the microbial agent 3 in the water of the tank 1, and the ammonium ion generated by this decomposition is contained in the microbial agent 4. A step of converting nitrite ions to nitrate ions by the microorganisms thus formed is carried out (S5). Step S5 is also a step of adjusting the environment of organic matter-decomposing bacteria and nitrifying bacteria in water, in addition to the decomposition and nitrification of organic matter, that is, when the nutrient solution obtained in step S5 is supplementally fertilized. It also plays a role in preparing the microbial environment so that organic substances can be rapidly decomposed and converted into nitrate ions.

In step S5, specifically, the liquid in the tank 1 is maintained in a predetermined environment so that the decomposition and nitrification of organic substances proceed. As the predetermined environment, specifically, for example, the temperature of the liquid in the tank 1 is maintained by a temperature adjusting unit (heater) at a temperature predetermined as a temperature at which microorganisms act. The temperature is preferably 20° C. or higher, more preferably 25° C. to 35° C. Further, as the predetermined environment, air (oxygen) is continuously supplied into the liquid in the tank 1 by the bubbling unit 5 and the supply unit 6 (see FIG. 2) during the period of decomposition and nitrification of organic substances.

During the decomposition and nitrification of organic substances, it is desirable to monitor changes in the respective concentrations of ammonium ion, nitrite ion and nitrate ion in the liquid in the tank 1 with a semi-quantitative test strip or an ion concentration detector. In addition, when the dissolved oxygen amount and pH (hydrogen ion index) in which microorganisms are likely to act are set, it is necessary to monitor changes in the dissolved oxygen amount and pH and to control them so that they are not out of regulation. desirable.

The process of step S5 is performed until, for example, it can be determined that all the organic substances contained in the organic fertilizer 2 are decomposed and nitrification is completed. Specifically, the step S5 is performed until, for example, ammonium ions in the liquid in the tank 1 are below a predetermined value, nitrite ions are below a predetermined value, and nitrate ions are above a predetermined value. The nitric acid ion concentration at the completion of nitrification is, for example, 50 ppm or more, preferably 100 ppm or more. The ammonium ion concentration at the completion of nitrification is, for example, 20 ppm or less. When the process of FIG. 3 described later is performed, step S5 does not have to wait for the completion of nitrification.

Here, if the concentration of nitrite ions is high, the activity of nitrifying bacteria may be reduced and the efficient production of nitrate ions may be hindered. Therefore, it is desirable to reduce the nitrite ion concentration promptly. It is also desirable to be able to produce the nutrient solution in larger quantities or at lower cost. Therefore, in such a case, the step of FIG. 3 may be performed subsequent to the step S5 of FIG.

The process of FIG. 3 may be performed before the nitrification is completed (during the nitrification) in step S5, or after the nitrification is completed. The case where the step of FIG. 3 is performed before the completion of nitrification includes, for example, the case where the nitrite ion concentration is high in step S5 of FIG. 1 and nitrification does not progress easily. More specifically, as a step for determining before nitrification completion (during nitrification), the nitrate ion concentration is below a predetermined value (for example, 100 ppm), the nitrite ion concentration is higher than the nitrate ion concentration, and Even if the step of determining whether or not at least one or all that the nitrate ion concentration is equal to or higher than a predetermined value (for example, 50 ppm) is satisfied and the affirmative determination is made in the step, the process of FIG. 3 is performed. Good.

Further, the case where the step of FIG. 3 is carried out after the completion of nitrification includes the case where it is desired to obtain the nutrient solution in a larger amount or at a lower cost. More specifically, as a step for determining the completion of nitrification, the nitrate ion concentration has risen to a predetermined value (for example, 100 ppm) or more, and the nitrate ion concentration is reversed from a state lower than the nitrite ion concentration to a high state. And a step of determining whether or not at least one or all of the fact that the nitrite ion concentration has fallen from a state of being equal to or higher than a predetermined value (for example, 50 ppm) to less than the predetermined value is provided, and affirmative in that step. If determined, the process of FIG. 3 may be performed. Note that the plant is not cultivated in the tank 8 (see FIG. 4) during the process of FIG. 3, that is, the process of FIG. 3 is a process before the plant cultivation.

In the process of FIG. 3, first, in step S5 of FIG. 1, the liquid in the tank 1 during or after nitrification is diluted with water (S6). The degree of dilution can be appropriately set according to the target amount of nutrient solution, but can be, for example, 10-fold dilution. In step S6, specifically, for example, a tank 8 (see FIG. 4) larger than the tank 1 of FIG. 2 is prepared, and a predetermined amount of water is put into the tank 8. For example, when the liquid in the tank 1 is 1 L and the liquid is diluted 10 times (when the liquid is 10 L), 9 L of water is put in the tank 8. Then, the liquid in the tank 1 is put into the tank 8 containing water (see FIG. 4). If the tank 1 of FIG. 2 is large enough to contain the diluted solution, a predetermined amount of water may be added to the tank 1 of FIG. It should be noted that step S6 is synonymous with newly producing a nutrient solution using the nutrient solution obtained in the process of FIG. 1 as an inoculum (microorganism source).

Simultaneously with or after the dilution in step S6, additional organic fertilizer 9 (see FIG. 4) is added to the liquid in the tank 8 (S7). As the organic fertilizer 9, for example, the same organic fertilizer 2 (see FIG. 2) as the organic fertilizer 2 added in step S3 of FIG. 1 (for example, fish liquid fertilizer) may be used. The addition amount of the organic fertilizer 9 may be the same as that of the organic fertilizer 2 added in step S3, or may be different. When the organic fertilizer 9 is fish liquid fertilizer, the addition amount thereof may be, for example, more than 0.5 g/L and not more than 2.0 g/L, like the addition amount of the organic fertilizer 2. By the additional fertilization in step S7, the nutrient source of the microorganisms (organic substance decomposing bacteria, nitrifying bacteria) existing in the diluted liquid can be added.

The liquid in the tank 8 after the dilution in step S6 and the supplemental fertilization in step S7 is allowed to proceed with the decomposition and nitrification of organic substances (S8). Specifically, as in step S5 of FIG. 1, the liquid in the tank 8 is maintained in a predetermined environment so that the decomposition and nitrification of organic substances proceed. As the predetermined environment, specifically, for example, the temperature of the liquid in the tank 8 is set at a predetermined temperature (for example, 20° C. or higher, preferably 25° C. to 35° C.) as the temperature at which the microorganisms are activated by the temperature adjusting unit (heater). C)). Further, as the predetermined environment, air (oxygen) is continuously supplied into the liquid in the tank 8 by the bubbling section 5 and the supply section 6 (see FIG. 4) during the period of decomposition and nitrification of organic substances.

Further, in step S8, it is desirable to monitor changes in the respective concentrations of ammonium ions, nitrite ions and nitrate ions in the liquid in the tank 8 in the same manner as in step S5. Also, changes in the amount of dissolved oxygen and pH may be monitored.

The process of step S8 is performed until, for example, it is determined that the organic substances in the liquid in the tank 8 are all decomposed and nitrification is completed. Specifically, the step S8 is performed until, for example, ammonium ions in the liquid in the tank 8 are below a predetermined value, nitrite ions are below a predetermined value, and nitrate ions are above a predetermined value. The nitric acid ion concentration at the completion of nitrification is, for example, 50 ppm or more, preferably 100 ppm or more. The ammonium ion concentration at the completion of nitrification is, for example, 20 ppm or less.

The nutrient solution obtained by the process of FIG. 1 or the process of FIG. 3 is used, for example, as a nutrient solution for hydroponic cultivation. In this case, for example, as shown in FIG. 5, the nutrient solution obtained in the step of FIG. 1 or the step of FIG. 3 is put into the aeration tank 10 and the nutrient solution is sent to the cultivation tank 12 by the pump 11, At 12, the plants are cultivated. On the water surface of the cultivation tank 12, a floating member 13 on which plants are fixed is provided. As the aeration tank 10, the tank 1 of FIG. 1 or the tank 8 of FIG. 4 may be used as it is. Further, the nutrient solution may be circulated between the cultivation tank 12 and the aeration tank 10 as described below. That is, the nutrient solution in the cultivation tank 12 is collected in the aeration tank 10, and an organic fertilizer (for example, fish manure) is added to the nutrient solution collected in the aeration tank 10. If necessary, in addition to the organic fertilizer, the same microbial agent for decomposing organic substances and microbial agent for nitrifying bacteria as those used in step S3 of FIG. 1 are added as a microbial source for decomposing the same. Then, while aeration is performed, a process of decomposing organic substances contained in the organic fertilizer to generate nitrate ions is performed in the aeration tank 10.

Various verifications (experiments) related to the present invention were performed. This will be explained below.

<Experiment A: Comparison between the case where organic matter-decomposing bacteria and nitrifying bacteria are added stepwise and the case where they are added simultaneously>
(Experiment 1: When organic matter degrading bacteria and nitrifying bacteria are added in stages)
Fish liquid manure (1.5 g/L) was added as an organic fertilizer to a tank containing 1 L of water. "Potapota liquid fertilizer No. 2" manufactured by Royal Industries Co., Ltd. was used as the fish liquid fertilizer. Potapota liquid fertilizer No. 2 is 100% organic liquid fertilizer. In addition, oysters were added to the same tank so that the amount of oysters would be 1.0 g per 1 L of water for the purpose of supplying minerals.

Simultaneously with the addition of the fish liquid fertilizer, the microbial agent of the organic matter-decomposing bacteria was added in an amount of 1% volume (that is, 10 mL) per 1 L of water. "BFL5100HP" manufactured by BioFuture Ltd. was used as a microbial agent for the organic substance-decomposing bacteria. "BFL5100HP" is a microbial agent with organic matter-degrading bacteria fixed to a cereal base. When the microbial agent is added, first, in order to activate the microorganisms contained in the microbial agent, the amount of lukewarm water at about 30° C. is 10 for every 1 amount of the microbial agent. To the mixture was added lukewarm water, stirred well and allowed to stand for a certain period of time. Then, 100 mL (10 mL of the microbial agent contained therein) was added to 1 L of water in the tank, containing a 10% microbial agent dilution solution.

Seven days after the addition of the fish liquid fertilizer and the microbial agent of the organic matter-decomposing bacteria, the microbial agent of the nitrifying bacteria was added in an amount of 1% volume (that is, 10 mL) with respect to 1 L of water in the tank. The ammonium ion concentration in water when the nitrifying bacteria were added was about 100 ppm. As a microbial agent for nitrifying bacteria, "BFL5800NTB" manufactured by BioFuture Ltd. was used. "BFL5800NTB" is a liquid microbial agent. In addition, "BFL5800NTB" has the same number of bacteria that oxidize ammonia to produce nitrite (ammonia-oxidizing bacteria) and bacteria that oxidize nitrite to produce nitric acid (nitrite-oxidizing bacteria). It is a microbial agent formulated as follows. When adding this microbial agent, first add lukewarm water to the microbial agent so that the amount of lukewarm water at about 30° C. is 10 per 1 of the microbial agent, stir well, and leave for a certain period of time. Let Then, 100 mL (10 mL of the microbial agent contained therein) was added to 1 L of water in the tank, containing a 10% microbial agent dilution solution.

Then, changes in the ammonium ion concentration, the nitrite ion concentration, the nitrate ion concentration, the amount of dissolved oxygen and the pH in the water with respect to the number of days elapsed after the addition of the fish manure and the microbial agent of the organic matter-decomposing bacteria were measured. Aeration was continued during this measurement period. The water temperature during the measurement period was adjusted to 30 to 38°C. FIG. 6 shows the measurement result. The vertical axis on the left side of FIG. 6 is the axis of ion concentration (unit is ppm). The vertical axis on the right side is a common axis of the amount of dissolved oxygen (unit is ppm) and pH (there is no unit). Further, in FIG. 6 and FIGS. 7 to 16 described below, the amount of dissolved oxygen is indicated by “DO”.

As shown in FIG. 6, the ammonium ion concentration increased to 100 ppm by 7 days after the start of the experiment, and it is considered that the organic substances were decomposed smoothly. After addition of nitrifying bacteria, a large amount of nitrite ions were produced by the ammonia-oxidizing bacteria, while the nitrate ion concentration was about 50 ppm at 28 days after the start of the experiment. The change with time of the nitrate ion concentration tended to decrease with the lapse of time after 28 days from the start of the experiment (downward trend).

(Experiment 2: When the organic substance degrading bacteria and nitrifying bacteria are added at the same time)
The nitrifying bacteria microbial agent is not added after the addition of the organic substance-decomposing bacteria, but the same amount (1% volume relative to 1 L of water) is added at the same time as the addition of the organic substance-decomposing bacteria microbial agent. Conducted an experiment under the same conditions as Experiment 1. FIG. 7 shows this result.

As shown in FIG. 7, generation of ammonium ions, nitrite ions, and nitrate ions was confirmed immediately after the start of the experiment. From this, it is considered that nitrifying bacteria can act even when organic matter remains in the water (in other words, even when BOD (Biochemical oxygen demand) is high). Further, the nitrite ion concentration was about 270 ppm after 28 days from the start of the experiment, which was about 2/3 of the result of FIG. Further, the nitrate ion concentration was about 70 ppm after 28 days from the start of the experiment, which was equal to or slightly higher than the result of FIG. In addition, the change with time of the nitrate ion concentration tended to increase with the passage of time at the point of 28 days from the start of the experiment (the tendency to increase to the right).

(Summary of Experiment A (Experiments 1 and 2))
From the results of FIGS. 6 and 7, when the same amount of the organic matter-degrading bacteria and the nitrifying bacteria were added at the same time, the nitrification rate and the nitrate ion concentration were equal to or higher than those when the organic substance-degrading bacteria and the nitrifying bacteria were added stepwise I found out that

<Experiment B: Verification of time-dependent change of each ion concentration when the addition amount of the microbial agent is changed>
(Experiment 3: When the amount of the microbial agent added is 0.1%)
Similar to Experiment 2, the same amount of microbial agent of organic matter-decomposing bacteria and microbial agent of nitrifying bacteria are added at the same time, but the amount of each microbial agent is 0.1% volume to 1 L of water (that is, 1 mL). ) And other conditions were the same as in Experiment 2. FIG. 8 shows the result.

As shown in FIG. 8, the nitrate ion concentration rapidly increased after 16 days from the start of the experiment, reached 100 ppm at 20 days, and approached 200 ppm at 23 days (about 180 ppm). Arrived In addition, the change with time of the nitrate ion concentration tended to increase to the right at 23 days after the start of the experiment. On the other hand, the nitrite ion concentration gradually decreased after 16 days from the start of the experiment, and was a value lower than 150 ppm (about 130 ppm) after 23 days. In addition, the change with time of the nitrite ion concentration tended to decrease to the right after 23 days from the start of the experiment.

(Experiment 4: When the addition amount of the microbial agent is 0.01%)
Similar to Experiments 2 and 3, the same amount of the microbial agent of the organic matter degrading bacterium and the microbial agent of the nitrifying bacterium are added at the same time, but the amount of each microbial agent added is 0.01% by volume relative to 1 L of water ( That is, 0.1 mL) was set, and the other conditions were the same as those in Experiments 2 and 3. FIG. 9 shows the result.

As shown in FIG. 9, the nitrate ion concentration rapidly increased after 14 days from the start of the experiment, reached 100 ppm after 17 days, reached 250 ppm after 20 days, and remained almost flat thereafter. Was about 250 ppm after 26 days. On the other hand, the nitrite ion concentration gradually decreased after 11 days from the start of the experiment, became almost 0 ppm at the time of 20 days, became almost flat thereafter, and was almost 0 ppm at the time of 26 days.

(Summary of Experiment B (Experiments 2, 3, 4))
From the results shown in FIGS. 7, 8 and 9, the nitrification rate and the nitrate ion concentration were improved when the addition amount of each microbial agent was 0.1% or 0.01% rather than 1%. It has been found that it is desirable to suppress the addition amount to less than 1%, preferably 0.5% or less, and more preferably 0.1% or less, from the viewpoints of cost reduction, nitrification rate and nitrate ion concentration improvement. However, even if the amount of microbial agents added is 1%, the concentration of nitrate ions tends to increase upwards after about 1 month (see FIG. 7). Or, even if the value is slightly larger than 1% (for example, a value of 1.5% or less), it is considered that a relatively high nitrification rate and a nitrate ion concentration (for example, a concentration of 50 ppm or more after a lapse of about one month) are obtained. ..

<Experiment C: Verification of improvement in nitrification rate and nitrate ion concentration when the amount of nitrifying bacteria added is larger than that of organic substance-decomposing bacteria>
(Experiment 5: When the addition amount of the microbial agent of nitrifying bacteria was set to 2%)
The microbial agent for organic substance-degrading bacteria and the microbial agent for nitrifying bacteria are added at the same time. The amount of microbial agent for organic substance-degrading bacteria is 1% of the volume of 1 L of water (10 mL). The amount added was 2% with respect to 1 L of water (20 mL). Other than that, the experiment was performed under the same conditions as in Experiment 2. This Experiment 5 is an experiment in which the amount of nitrifying bacteria added was twice the amount of organic substance-degrading bacteria for the purpose of improving the nitrification rate and nitrate ion concentration. FIG. 10 shows the result.

As shown in FIG. 10, by doubling the addition amount of nitrifying bacteria, only the nitrite ion concentration increased, and no remarkable change in the nitrate ion concentration was observed. It is considered that a high concentration of nitrite ion reduced the activity of nitrifying bacteria, and this inhibited the increase of nitrate ion concentration.

(Summary of Experiment C (Experiments 2, 5))
Comparing the results of FIG. 7 (Experiment 2) and the results of FIG. 10 (Experiment 5), the results of FIG. 7 have a higher nitrification rate and nitrate ion concentration, and a lower nitrite ion concentration. From this, it is desirable to add the same amount of the microbial agent of the organic matter degrading bacterium and the microbial agent of the nitrifying bacterium from the viewpoint of improving the nitrification rate and the concentration of nitrate ion, and from the viewpoint of facilitating the addition control of the microbial agent. Can be said.

<Experiment D: Verification of decrease in nitrite ion concentration when diluted midway>
(Experiment 6: When diluted 10 times on the way)
The same amount (1% of the amount of 1 L of water) of the microbial agent of the organic matter-decomposing bacteria and the microbial agent of the nitrifying bacteria were added at the same time, and the solution in the tank was diluted 10 times with water on the 9th day from the start of the experiment (specifically, The amount of water was expanded to 10 L). The nitrite ion concentration just before dilution reached 100 ppm. The experiment was performed under the same conditions as in Experiment 2 except that the dilution was performed on the way. In Experiment 6, additional fertilization was not performed at the same time as or after dilution. FIG. 11 shows the result.

As shown in FIG. 11, the nitrite ion concentration was significantly reduced by diluting the liquid on the way. From this, it can be said that diluting the solution is effective for reducing the nitrite ion concentration.

<Experiment E: In addition to diluting the liquid, verification of whether nitrification progresses when topdressing is applied>
In the result of FIG. 11 described above, the nitrite ion concentration was decreased by diluting the liquid, but the nitrate ion concentration was not significantly increased. Therefore, the following Experiments 7, 8, 9, and 10 were performed to verify whether it is possible to increase the nitrate ion concentration while lowering the nitrite ion concentration by adding fertilizer in addition to dilution.

(Experiment 7: When the addition amount of the microbial agent is 0.1% and the fertilizer is added at the same time as the dilution)
Fish liquid manure (1.5 g/L) was added as an organic fertilizer to a tank containing 1 L of water. "Potapota liquid fertilizer No. 2" manufactured by Royal Industries Co., Ltd. was used as the fish liquid fertilizer. Simultaneously with the addition of the fish liquid fertilizer, a microbial agent for organic matter-decomposing bacteria and a microbial agent for nitrifying bacteria were added in amounts of 0.1% by volume (1 mL) per 1 L of water. "BFL5100HP" manufactured by BioFuture Ltd. was used as a microbial agent for the organic substance-decomposing bacteria. In addition, “BFL5800NTB” manufactured by BioFuture Ltd. was used as a microbial agent for nitrifying bacteria.

On the 31st day from the start of the experiment, the liquid in the tank was diluted 10 times with water (specifically, the amount of water was expanded to 10 L). Simultaneously with the dilution, 1.5 g of fish liquid fertilizer (“Potapota liquid fertilizer No. 2” manufactured by Royal Industries Co., Ltd.) was added per 1 L of water (15 g for 10 L of water). Immediately before dilution and top fertilization, the nitrate ion concentration was about 200 ppm, the ammonium ion concentration and the nitrite ion concentration were about 0 ppm, and nitrification was completed.

Then, as in each of the above experiments, changes in the ammonium ion concentration, the nitrite ion concentration, the nitrate ion concentration, the amount of dissolved oxygen, and the pH with respect to the number of days elapsed from the start of the experiment were measured. Aeration was continued during this measurement period. The water temperature during the measurement period was adjusted to 30 to 38°C. FIG. 12 shows the result.

As shown in FIG. 12, immediately after the dilution, the nitrite ion concentration and the nitrate ion concentration significantly decreased. Furthermore, since top fertilization is performed at the same time as dilution, each microorganism is activated by this top fertilization, and thus a remarkable change is observed in each ion concentration. Specifically, the ammonium ion concentration showed a tendency of gradually increasing with time after dilution and decreasing with time after 38 days from the start of the experiment. The nitrite ion concentration gradually increased with the passage of time after dilution, and tended to decrease with the passage of time after 42 days from the start of the experiment, and became almost 0 ppm after 51 days. Immediately after the dilution, the nitrate ion concentration was almost flat at around 50 ppm, and tended to sharply increase with time after 42 days from the start of the experiment. The nitrate ion concentration was about 250 ppm at 51 days after the start of the experiment, which was higher than the concentration immediately before dilution.

(Experiment 8: When the addition amount of the microbial agent was 0.1% and the fertilizer was added after the dilution)
Fish liquid manure (1.5 g/L) was added as an organic fertilizer to a tank containing 1 L of water. "Potapota liquid fertilizer No. 2" manufactured by Royal Industries Co., Ltd. was used as the fish liquid fertilizer. Simultaneously with the addition of the fish liquid fertilizer, a microbial agent for organic matter-decomposing bacteria and a microbial agent for nitrifying bacteria were added in amounts of 0.1% by volume (1 mL) per 1 L of water. "BFL5100HP" manufactured by BioFuture Ltd. was used as a microbial agent for the organic substance-decomposing bacteria. In addition, “BFL5800NTB” manufactured by BioFuture Ltd. was used as a microbial agent for nitrifying bacteria.

On the 7th day from the start of the experiment, the liquid in the tank was diluted 10 times with water (specifically, the amount of water was expanded to 10 L). Immediately before the dilution, the nitrite ion concentration reached 150 ppm, the nitrate ion concentration was less than 50 ppm, and nitrification was not yet completed. On the 31st day from the start of the experiment, 1.5 g of fish liquid fertilizer (“Potapota liquid fertilizer No. 2” manufactured by Royal Industries Co., Ltd.) was added as an additional fertilizer per 1 L of water (15 g for 10 L of water).

Then, similarly to each of the above experiments, changes in ammonium ion concentration, nitrite ion concentration, nitrate ion concentration, dissolved oxygen amount and pH with respect to the number of days elapsed from the start of the experiment were measured. Aeration was continued during this measurement period. The water temperature during the measurement period was adjusted to 30 to 38°C. FIG. 13 shows the result.

As shown in FIG. 13, immediately after the dilution, the nitrite ion concentration dropped significantly. It should be noted that the nitrate ion concentration slightly increased immediately after the dilution, but it is considered that this is because the nitrate ions originally contained in the water used for the dilution were added to the low-concentration nitrate ions immediately before the dilution. .. During the period from dilution to additional fertilization, changes in nitrite ion concentration and nitrate ion concentration are small, probably due to lack of nutrition of microorganisms. After topdressing, a remarkable change is seen in each ion concentration. Specifically, the ammonium ion concentration gradually increased with the passage of time after topdressing, decreased with the passage of time on the 38th day from the start of the experiment, and slightly increased after the 45th day. .. The nitrite ion concentration gradually increased with the passage of time after topdressing, and tended to decrease with the passage of time on the 42nd day from the start of the experiment, and became about 50 ppm at the time of the passage of 51 days. The nitrate ion concentration was almost flat at a value of less than 50 ppm immediately after top fertilization, but tended to increase sharply with the lapse of time after 42 days from the start of the experiment. The concentration of nitrate ion was about 200 ppm at 51 days after the start of the experiment, which was significantly increased from the concentration immediately before dilution and immediately before topdressing.

(Experiment 9: When the addition amount of the microbial agent is set to 0.01% and the dilution and the additional fertilization are simultaneously performed after nitrification is completed)
The amounts of the microbial agent for organic matter-decomposing bacteria and the microbial agent for nitrifying bacteria to be added in the initial stage were adjusted to 0.01% by volume (0.1 mL) with respect to 1 L of water, respectively. The liquid was diluted 10 times with water, and additional fertilization was performed at the same time as the dilution, and the experiment was performed under the same conditions as in Experiment 7 except for that. In other words, Experiment 9 is different from Experiment 7 in that the addition amount of the microbial agent is 0.01%/L, the timing of dilution and topdressing is the 26th day from the start of the experiment, and other than that, it is the same as Experiment 7. is there. Experiment 9 is an experiment in which the experiment 4 was diluted and topdressed on the 26th day. Immediately before dilution and top fertilization, the nitrate ion concentration was about 250 ppm, the ammonium ion concentration and the nitrite ion concentration were about 0 ppm, and nitrification was completed. FIG. 14 shows the result.

In FIG. 14, from the start of the experiment to the 26th day, it is the same as the result of the experiment 4 (FIG. 9). As shown in FIG. 14, the tendency of each ion concentration after dilution was almost the same as in Experiment 7. The nitrate ion concentration was about 250 ppm 47 days after the start of the experiment, which was the same as immediately before the dilution. Further, the nitrite ion concentration became almost 0 ppm 47 days after the start of the experiment.

(Experiment 10: When the addition amount of the microbial agent is 0.01% and the dilution and the supplemental fertilization are simultaneously performed during nitrification)
Dilution and supplemental fertilization were performed on the 7th day from the start of the experiment, and the experiment was performed under the same conditions as in Experiment 9 except for the above. Immediately before dilution and top fertilization, the nitrite ion concentration was a value approaching 100 ppm (about 80 ppm), while the nitrate ion concentration was less than 50 ppm, and nitrification was not yet completed. FIG. 15 shows the result.

As shown in FIG. 15, the nitrite ion concentration dropped sharply immediately after dilution, but then rapidly increased (after the 11th day from the start of the experiment) and reached 150 ppm or higher on the 13th day, and thereafter. Has almost leveled off. On the other hand, the nitrate ion concentration after dilution increased to about 50 ppm on the 14th day, but then gradually decreased to about 20 ppm at the 26th day.

(Summary of Experiment E (Experiments 7, 8, 9, 10))
The following can be said from the results of FIGS. 12, 13, 14, and 15.
-By adding fertilizer in addition to dilution, nitrification can be further promoted for the diluted liquid, while suppressing nitrite ions, it is possible to obtain a nitrate ion concentration equal to or higher than that before dilution, A larger amount of nutrient solution can be obtained. Moreover, since the amount of the microbial agent added in the initial stage can be suppressed, the nutrient solution can be obtained at low cost.
The dilution is carried out after the nitrification is completed, specifically when the nitrate ion concentration is increased to 100 ppm or more, preferably 150 ppm or more, more preferably 200 ppm or more, or from the state where the nitrate ion concentration is lower than the nitrite ion concentration. When it is reversed to a high state or when the concentration of nitrite ion drops from 50 ppm or more to less than 50 ppm, it is considered that the microorganisms responsible for nitrification are sufficiently increased. On the other hand, nitrification can be promoted without adding a microbial agent, and high-concentration nitrate ions can be generated (see FIGS. 12 and 14).
-The dilution may be performed during nitrification (before completion of nitrification). Specifically, when the nitrate ion concentration is 100 ppm or less, or when the nitrite ion concentration is higher than the nitrate ion concentration, or when the nitrite ion concentration is You may perform it when it is 50 ppm or more. However, in this case, if the amount of the microbial agent added in the initial stage is 0.01%/L or less, it may cause the nitrite to remain high after dilution, which may adversely affect the production of nitrate ions. (See FIG. 15) It is desirable that the amount of the microbial agent is more than 0.01%, preferably 0.1%/L or more (see FIG. 13).

-A high concentration of nitrate ion can be obtained whether the additional fertilization is performed at the same time as the dilution or after the dilution (see FIGS. 12 and 13).
-By performing the supplemental fertilizer at the same time as the dilution, it is possible to facilitate the control of the dilution timing and the supplemental fertilization timing, and to promote nitrification immediately after the dilution (see FIGS. 12 and 14).
-By performing the supplemental fertilization after the dilution, it is possible to change the timing and the addition amount of the supplemental fertilizer according to the progress of nitrification after the dilution (see FIG. 13).
-Nitrification can be promoted even when the amount of the microbial agent added is 0.1%/L or less (see FIGS. 12, 13, and 14).
-Nitrification can be promoted even when the amount of liquid in the tank is increased to 10 times by dilution (see FIGS. 12, 13, and 14).

<Experiment F: Verification of temporal change of each ion concentration when the addition amount of organic fertilizer is changed>
(Experiment 11: When the amount of fish manure added was 0.5 g/L)
An experiment was conducted under the same conditions as in Experiment 2 except that the amount of fish manure added was 0.5 g/L. FIG. 16 shows the result. As shown in FIG. 16, only the nitrite ion concentration increased, and the nitrate ion was hardly detected.

(Summary of Experiment F (Experiments 2 and 11))
Comparing the result of FIG. 7 and the result of FIG. 16, the result of FIG. 7 has a higher nitrate ion concentration. Therefore, the amount of fish liquid fertilizer added is preferably more than 0.5 g/L, and more preferably more than 1.0 g/L.

As described above, in the present embodiment, the ammonia formation and the nitric acid formation (nitrification) are performed in the same tank, so that the production process of the nutrient solution can be simplified and the nutrient solution can be efficiently produced. In addition, since a commercially available microbial agent is used as a microorganism source, it is possible to prevent various microorganisms (harmful bacteria) from being mixed in the nutrient solution. Moreover, since the microbial agent for organic substance-degrading bacteria and the microbial agent for nitrifying bacteria are separately prepared, addition control of organic substance-degrading bacteria and addition control of nitrifying bacteria can be performed separately. Further, by simultaneously adding the same amount of the microbial agent of the organic substance-decomposing bacteria and the microbial agent of the nitrifying bacteria, it is possible to obtain a nitrate ion concentration equal to or higher than that in the case of adding it stepwise, and to control the addition of the organic substance-degrading bacteria. The addition control of nitrifying bacteria can be facilitated.

Since a microbial agent containing both ammonia-oxidizing bacteria and nitrite-oxidizing bacteria is used as the microbial agent for nitrifying bacteria, nitrate ions can be efficiently produced from ammonium ions through nitrite ions.

In addition, by setting the addition amount of each microbial agent to 0.01%/L to 1%/L, it is possible to obtain a nitrate ion concentration of 50 ppm or more about one month after the start of decomposition and nitrification of organic substances. (See FIGS. 7, 8 and 9) Since the amount of the microbial agent added is suppressed, the cost can be reduced. In particular, by setting the addition amount to 0.1%/L or less, a higher concentration of nitrate ion can be obtained (see FIGS. 8 and 9).

Further, by carrying out the process of FIG. 3, a large amount of nutrient solution having a high concentration of nitrate ions can be obtained at low cost.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the claims. For example, in each of the above experiments, the initial amount of water was 1 L, but a water amount other than 1 L may be used. In addition, in the experiments 6, 7, 8, 9, and 10 described above, an example in which the liquid was diluted 10 times was shown, but it may be diluted at other ratios. In addition, in Experiments 7, 8, 9, and 10 above, an example was shown in which the amount of additional fish manure added was the same as the initial amount added, but the initial addition amount and the additional addition amount were different. Good. Further, in each of the above experiments, an example in which the fish liquid manure was used as the organic fertilizer was shown, but an organic fertilizer other than the fish liquid manure may be used.

1, 8 Tank 2, 9 Organic fertilizer 3 Microbial agent of organic matter decomposing bacteria 4 Microbial agent of nitrifying bacteria 5 Bubbling section 6 Oxygen supply section

Claims (10)

An organic matter adding step of adding fish manure as an organic matter to water in an amount of more than 0.5 g per 1 L of water;
In the water, a microbial agent of an organic substance-decomposing bacterium that decomposes organic nitrogen to produce ammonium ion, a bacterium that oxidizes ammonium ion to produce nitrite ion and nitrite ion to produce nitrate ion Microbial agent addition step in which the same amount of the microbial agent of nitrifying bacteria that is a bacterium is added at the same time, and an amount of 0.01% or more and 0.1% or less per 1 L of water is added, respectively.
A nitrification step of advancing nitrification to the liquid after the organic matter addition step and the microbial agent addition step,
Equipped with
A method for producing a nutrient solution for plant cultivation, which obtains a nutrient solution for plant cultivation having a nitrate ion concentration of 100 ppm or more. The method for producing a nutrient solution for plant cultivation according to claim 1, wherein, in the organic matter addition step, fish liquid fertilizer is added in an amount of more than 1.0 g per 1 L of water. The nitrification step is referred to as a first nitrification step,
A diluting step of diluting the liquid during or after nitrification in the first nitrification step,
A second nitrification step in which nitrification is advanced to the diluted solution so that the concentration of nitrate ions in the solution is 100 ppm or more;
The method for producing a nutrient solution for plant cultivation according to claim 1 or 2, further comprising: The method for producing a nutrient solution for plant cultivation according to claim 3, further comprising a supplemental fertilization step of adding fish fertilizer as an additional organic matter in an amount of more than 0.5 g per 1 L of water at the same time as or after the dilution in the dilution step. The dilution in the diluting step is performed after the nitrification in the first nitrification step is completed, when the nitrate ion concentration in the liquid rises to 100 ppm or more, or when the nitrate ion concentration is higher than the nitrite ion concentration. The method for producing a nutrient solution for plant cultivation according to claim 4, which is performed when the concentration of nitrite ion is decreased from 50 ppm or more to less than 50 ppm. The dilution in the diluting step is performed during the nitrification in the first nitrification step when the nitrate ion concentration in the liquid is 100 ppm or less, or when the nitrite ion concentration is higher than the nitrate ion concentration, or when the nitrite ion concentration is Perform when 50ppm or more,
The method for producing a nutrient solution for plant cultivation according to claim 4, wherein the amounts of the microbial agent of the organic substance-degrading bacterium and the microbial agent of the nitrifying bacterium are amounts that are more than 0.01% per 1 L of water. The dilution is performed when the nitrate ion concentration is 100 ppm or less, the nitrite ion concentration is higher than the nitrate ion concentration, and the nitrite ion concentration is 50 ppm or more. A method for producing the nutrient solution for plant cultivation described. The method for producing a nutrient solution for plant cultivation according to any one of claims 1 to 7, wherein the microbial agent of the organic substance decomposing bacterium and the microbial agent of the nitrifying bacterium are commercially available microbial agents for purifying wastewater. The microbial agent adding step activates microorganisms contained in the microbial agent of the organic substance-degrading bacterium and the microbial agent of the nitrifying bacterium in advance before adding the microbial agent of the organic substance-degrading bacterium and the microbial agent of the nitrifying bacterium to the water. The method for producing a nutrient solution for plant cultivation according to any one of claims 1 to 8, further comprising a step of activating the nutrient solution. A plant cultivation method for cultivating a plant using the nutrient solution obtained by the method for producing a nutrient solution for plant cultivation according to any one of claims 1 to 9.