Culture soil, method for growing plants, and method for producing culture soil

Abstract

The present disclosure relates to a culture soil containing silica particles (100) and sterile soil, wherein the silica particles (100) have a median particle size of particles (101), which have a particle size of 100 nm or more, in a particle size distribution of the particles (101), which have a particle diameter of 100 nm or more, of 120 nm to 800 nm. The present disclosure further relates to a method for growing plants using the culture soil, and a method for producing the culture soil. According to the present disclosure, a culture soil that promotes the growth of plants, a method for growing plants using the same, and a method for producing the culture soil are provided.

Description

Culture soil, plant growth method, and culture soil manufacturing method

[0001] The present disclosure relates to a potting soil, a method for growing plants, and a method for producing the potting soil.

[0002] Patent Document 1 proposes an agent for preventing or ameliorating soil damage, which is capable of improving the inhibition of plant growth in damaged soil, and which contains bubbles having an average diameter of 100 μm or less in a liquid medium.

[0003] Japanese Patent Application Laid-Open No. 2020-63382

[0004] The agent for preventing or ameliorating soil damage described in Patent Document 1 has a soil disinfecting effect that may kill not only bacteria that cause soil damage but also bacteria that are beneficial to plant growth, which may make it difficult to promote plant growth.

[0005] An object of the present disclosure is to provide a culture soil that promotes plant growth, a method for growing plants using the same, and a method for manufacturing the culture soil.

[0006] A culture medium according to a first embodiment of the present disclosure is a culture medium comprising silica particles and sterilized soil, wherein the silica particles have a particle size of 100 nm or more and a median particle size of 120 nm to 800 nm in the particle size distribution of particles having a particle size of 100 nm or more.

[0007] A method for producing a culture medium according to a second embodiment of the present disclosure includes a soil preparation step of sterilizing soil to prepare sterilized soil, and a culture medium preparation step of blending silica particles with the sterilized soil to prepare the culture medium. The median particle size of silica particles having a particle size of 100 nm or more is 120 nm or more and 800 nm or less in the particle size distribution of particles having a particle size of 100 nm or more.

[0008] According to the first embodiment of the present disclosure, it is possible to provide a culture soil that promotes plant growth and a plant growth method using the same.

[0009] According to the second embodiment of the present disclosure, a method for producing a culture soil that promotes plant growth can be provided.

[0010] FIG. 1 is a schematic cross-sectional view illustrating an example of silica particles. FIG. 2 is a schematic flowchart illustrating an example of a method for producing silica particles. FIG. 3 is a schematic cross-sectional view illustrating a multi-layer structure of a culture medium. FIG. 4 is a diagram illustrating a method for spraying silica particles on soil. FIG. 5 is a diagram illustrating holes provided in the culture medium for placing seeds. FIG. 6 is a schematic flowchart illustrating an example of a method for producing a culture medium. FIG. 7 is a scanning electron microscope image of a silica particle. FIG. 8 is a scanning electron microscope image of a silica particle. FIG. 9 is a composite map (Si and N) of a silica particle obtained by energy dispersive X-ray spectroscopy. FIG. 10 is a scanning electron microscope image of silica particles immersed in water for one year. FIG. 11 is a diagram illustrating the growth results of grown spinach. FIG. 12 is a diagram illustrating the growth results of grown spinach. FIG. 13 is a diagram illustrating the growth results of grown spinach. FIG. 14 is a diagram illustrating a comparison of komatsuna harvest yields. FIG. 15 is a diagram illustrating a comparison of spinach harvest yields. Fig. 16 is a diagram showing temperature changes in the culture medium during the growth period. Fig. 17 is a diagram showing changes in moisture content in the culture medium during the growth period. Fig. 18 is a diagram showing a bar chart showing the abundance rate of each bacterium. Fig. 19 is a diagram showing a bar chart in which the abundance rate of bacteria A is rearranged from left to right in ascending order. Fig. 20 is a diagram showing a rarefaction curve of Observed_features. Fig. 21 is a diagram showing a box plot of Observed_features. Fig. 22 is a diagram showing the results of Jaccard principal coordinate analysis. Fig. 23 is a diagram showing the results of Unweighted_Unifrac principal coordinate analysis. Fig. 24 is a diagram showing the results of Weighted_Unifrac principal coordinate analysis.

[0011] <First embodiment> [Cultivation soil] The culture soil according to the first embodiment contains silica particles. The median particle size of the silica particles having a particle size of 100 nm or more (hereinafter also referred to as the first particles) is 120 nm or more and 800 nm or less in the particle size distribution of the first particles. By including the silica particles in the culture soil, bacteria that are beneficial to plant growth in the culture soil are proliferated, which results in the promotion of plant growth.

[0012] The silica particles are aggregates of a plurality of silica particles. The silica particles may be substantially spherical particles. The silica particles include first particles. The silica particles may include a plurality of first particles. The content of the first particles in the silica particles (when the first particles have second particles described below, the content of the first particles having the second particles) may be, for example, 40% by mass or more, 60% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0013] Silica particles will be described with reference to FIG. 1 . Silica particles 100 include first particles 101. The central particle size of the first particles 101 is 120 nm or more and 800 nm or less in the particle size distribution of the first particles 101. In this specification, the central particle size refers to the median value of particle sizes in the particle size distribution, and is the median diameter (D50). In FIG. 1 , the particle size of the first particles 101 is the length D. In this specification, the particle size refers to the longest particle size (longest diameter). In an image of the silica particles observed at 50,000 times with a scanning electron microscope (SEM), the particle size distribution is calculated from the longest diameters measured for 25 or more particles (first particles) with a particle size of 100 nm or more, and the central particle size of the first particles is the median calculated from the particle size distribution.

[0014] As shown in FIG. 1 , the silica particles may have particles 102 with a particle size of less than 100 nm on the surface of the first particles 101. In this specification, the particles 102 with a particle size of less than 100 nm that are included in the first particles 101 are also referred to as second particles. The median particle size of the second particles 102 is 10 nm or more and less than 100 nm in the particle size distribution of the second particles 102. The first particles may have multiple second particles. Having second particles on the surface of the first particles tends to increase the specific surface area of ​​the silica particles. The silica particles may include at least one of first particles with multiple second particles and first particles without second particles, or may include only first particles with multiple second particles and first particles without second particles, or may include only first particles with multiple second particles or first particles without second particles. The presence of second particles 102 in the first particles 101 can be confirmed, for example, by observation at 200,000x magnification using an SEM. The particle size distribution of the second particles is a particle size distribution obtained from the longest diameter measured for 25 or more particles (second particles) having a particle size of less than 100 nm in an SEM image of the silica particles observed at 200,000 magnification, and the central particle size of the second particles is the median value calculated from the particle size distribution.

[0015] When the silica particles contain second particles, the second particles may be attached to most or all of the first particles. When the second particles are attached to the outer surfaces of the first particles, the contact area of ​​the silica particles as a whole with the soil tends to be large, which tends to facilitate the proliferation of bacteria that are beneficial to plant growth through the silica particles. In this specification, "attached" means that the first particles 101 and the second particles 102 are integrated to such an extent that, for example, when water is poured over the silica particles 100, the second particles 102 do not fall off from the first particles 101. A chemical bond, such as a covalent bond, may exist between the first particles 101 and the second particles 102.

[0016] As shown in FIG. 1 , the first particle 101 may have voids 103 therein. The second particle 102 may also have voids 103 therein. When the porosity of a single particle is defined as the ratio of the area occupied by voids to the cross-sectional area of ​​a single silica particle in the cross section of the particle, the porosity of a single particle may be, for example, 0.2% to 6.0%, or 2.5% to 6.0%, or 0.2% to 2.0%, for example, 1.2%. The ratio of the voids 103 in the first particle 101 may be less than 0.2% or greater than 6.0%. The porosity of a single particle can also be measured, for example, by analyzing images captured by a transmission electron microscope (TEM).

[0017] The first particles 101 and the second particles 102 may be secondary particles (aggregated particles) composed of a plurality of primary particles. The average particle size of the primary particles may be, for example, 50 nm or less, 1 nm or more and 50 nm or less, or 10 nm or more and 40 nm or less. Furthermore, the fact that the first particles 101 and the second particles 102 are secondary particles composed of a plurality of primary particles can be confirmed by the following procedure. First, silica particles are immersed in an alkaline solution for 5 days. The alkaline solution may be a strong alkaline solution. Then, the surface or cross section of the silica particles removed from the alkaline solution is observed using SEM or TEM. This allows the presence of a primary particle or a boundary between multiple primary particles to be confirmed.

[0018] The first particles 101 may have cracks. The term "cracks" refers to a general term for linear images on the surfaces of the first particles 101 observed in an image observed at 150,000 magnifications using an SEM. The cracks may be groove-like depressions, linear scratches, steps, or the like that occur on the surfaces of the first particles 101.

[0019] The specific surface area of ​​the silica particles 100 is, for example, 15 m ２ / g or more 200m ２ / g or less, and ２ / g. The specific surface area is the value of the surface area per unit weight. The specific surface area of ​​silica particles is measured, for example, by a gas adsorption measurement method using the BET method. The BET method is a method for measuring the surface area of ​​particles by adsorbing a gas with a known adsorption occupation area onto the surface of the particles. The specific surface area of ​​silica particles 100 is 15 m within the range in which the effects of the present disclosure can be obtained. ２ / g or less than 200m ２ / g or more.

[0020] The silica particles may be amorphous. The crystallinity of the silica particles is confirmed by X-ray diffraction (XRD). Both the first particles and the second particles may be amorphous.

[0021] The coefficient of variation of the silica particles may be, for example, 0.30 or less. The coefficient of variation is the value obtained by dividing the standard deviation of the particle diameter of the silica particles by the average particle diameter of the silica particles. The coefficient of variation may be greater than 0.30 as long as the effects of the present disclosure are achieved.

[0022] The silica particles may not contain particles having a particle size of less than 100 nm other than the first particles and the second particles contained in the first particles, or may contain only a very small amount of particles having a particle size of less than 100 nm compared to the amount of the first particles 101. When the silica particles contain particles having a particle size of less than 100 nm, the number of particles having a particle size of less than 100 nm may be 1 / 100 or less of the number of the first particles 101.

[0023] Silica particles are SiO ２ As used herein, the term "main component" refers to the component with the largest content in terms of mass among the constituent components, and may be, for example, 90 mass % or more, 95 mass % or more, or 99 mass % or more based on the total mass of all constituent components. The first particles and the second particles may be particles containing SiO as the main component. ２ The SiO in the silica particles may be ２ The content of is measured by X-ray fluorescence analysis. In this specification, the remaining constituent components other than the main component are also referred to as minor components.

[0024] Silica particles are composed of carbon (C), diphosphorus pentoxide (P２ O ５ ), sulfur trioxide (SO ３ The silica particles may further contain one or more elements or compounds selected from the group consisting of chlorine (Cl), sodium (Na), and nitrogen (N) as minor components. Since Na, Cl, phosphorus (P), and sulfur (S) are nutrients for plant growth, the inclusion of the above elements or compounds in the silica particles as minor components tends to be advantageous for plant growth. The silica particles may further contain Na, Cl, P within a range in which the effects of the present disclosure can be obtained. ２ O ５ , S.O. ３ The content may not necessarily be any of the above, and is not limited to the examples of the content shown below.

[0025] When the silica particles contain C, the C content in the silica particles may be, for example, 5.0 mass% or less, 1.5 mass% or more, or even 1.5 mass%. The C content in the silica particles can be measured using a carbon-sulfur analyzer (CS analyzer). In carbon measurement using a CS analyzer, the silica particles are dissolved in a high-frequency heating furnace in an oxygen stream. At this time, the C component contained in the silica particles is dissolved in CO, CO ２ The carbon-derived gas is then measured using an infrared detector. This quantifies the amount of carbon contained in the silica particles. From the quantification results, the carbon content in the silica particles is calculated. The carbon content in the silica particles may be less than 1.5% or more than 5.0%, as long as the effects of the present disclosure are achieved.

[0026] Silica particles are P ２ O ５ When the silica particles contain ２ O ５ The content of may be, for example, 0.1 mass % or less, or may be 0.01 mass %. ３ When the silica particles contain ３The content of may be, for example, 0.1% by mass or less, or may be 0.04% by mass. When the silica particles contain Cl, the content of Cl in the silica particles may be, for example, 0.05% by mass or less, or may be 0.02% by mass. When the silica particles contain Na, the content of Na in the silica particles may be, for example, less than 0.01% by mass, or may be 0.01% by mass or more as long as the effects of the present disclosure are obtained. P in the silica particles ２ O ５ , S.O. ３ The Cl content is measured by, for example, X-ray fluorescence analysis, and the Na content is measured by, for example, emission spectroscopy.

[0027] When the silica particles contain N, the N content in the silica particles may be, for example, 1.0 mass% or less, 0.8 mass% or less, or 0.73 mass% or less. The N content in the silica particles is measured, for example, by an inert gas fusion method.

[0028] N is ammonia nitrogen (NH ４ N may exist as ammonia nitrogen (NH ４ When present as ammonia nitrogen (NH ４ The content of nitrate nitrogen (NO -N) may be, for example, 5.0 mg / 100 g or less, 4.0 mg / 100 g or less, 3.0 mg / 100 g or less, 1.6 mg / 100 g or less, or 1.5 mg / 100 g or less. ３ The silica particles may contain, for example, less than 0.1 mg / 100 g of nitrate nitrogen (NO -N), or less than 0.05 mg / 100 g of nitrate nitrogen (NO ３-N). The contents of ammonia nitrogen and nitrate nitrogen in silica particles are measured, for example, in accordance with the method described in "Soil Environmental Analysis Methods" (Soil Environmental Analysis Methods Editorial Committee, 1997). The content of ammonia nitrogen in silica particles can be measured, for example, by the indophenol method using potassium chloride solution as the extraction solution. The content of nitrate nitrogen in silica particles can be measured, for example, by extracting with potassium chloride solution, followed by alkali reduction, and then by the diazo dye method.

[0029] The content of available silicic acid in silica particles may be, for example, 30 mg / 100 g or less, 26.0 mg / 100 g or less, or 25.8 mg / 100 g. When the content of available silicic acid in silica particles is within the above range, they tend to be insoluble in water. The content of available silicic acid in silica particles is measured, for example, in accordance with the method described in "Soil, Water Quality and Plant Analysis Method" (Japan Soil Association, 2001). The content of available silicic acid in silica particles can be measured, for example, by the molybdenum blue method after extraction with a pH 6.2 phosphoric acid extract.

[0030] The silica particles may have a base exchange capacity (CEC) (also known as fertilizer retention capacity) of, for example, 1.0 meq / 100 g or less, 0.6 meq / 100 g or less, or 0.5 meq / 100 g or less. The CEC of the silica particles is measured, for example, in accordance with the method described in "Soil Environmental Analysis Methods" (Soil Environmental Analysis Methods Editorial Committee, 1997). The CEC of the silica particles can be measured, for example, by the indophenol method after extraction using the modified Schollenberger method.

[0031] Silica particles may be hardly dissolved in water, or may be insoluble in water.Therefore, silica particles are less likely to dissolve in the water contained in the culture soil, and are less likely to produce silicic acid.For example, when about 0.27g of silica particles are added per 1L of soil, a portion of the silica particles dissolves in water, and the silicic acid concentration in the culture soil can increase by about 21ppm compared to before the silica particles dissolve.Incidentally, silicic acid refers to orthosilicic acid (H ４ SiO ４), metasilicic acid (H ２ SiO ３ In soil, silicic acid refers to water-soluble compounds containing SiOH, such as calcium silicate (Ca ２ SiO ４ It may also exist as silicates such as sulphite.

[0032] The silica particles can be, for example, commercially available silica particles. Alternatively, the silica particles can be produced by a production method (hereinafter also referred to as a first production method) using silica particles produced during the production of electronic components, as described below.

[0033] FIG. 2 shows a flowchart of the first manufacturing method. In the laminate preparation step S11, a laminate, which is a rectangular parallelepiped element body, is prepared. For example, a plurality of ceramic sheets that will serve as the element body are prepared. The ceramic sheets may be thin plates. A conductive paste that will serve as electrodes and wiring is laminated on the ceramic sheets. A ceramic sheet that will serve as the element body is laminated on the laminated conductive paste. In this way, the ceramic sheets and the conductive paste are laminated. Then, an unfired laminate is formed by cutting to a predetermined size. The unfired laminate is then fired at a high temperature to prepare the laminate.

[0034] Next, a solvent introduction step S12 is performed. In the solvent introduction step S12, a solvent is introduced into the reaction vessel. The solvent may be any liquid that can disperse the metal alkoxide appropriately, such as 2-propanol.

[0035] Next, a catalyst introduction step S13 is performed. In the catalyst introduction step S13, first, stirring of the solvent in the reaction vessel is started. Then, ammonia water is introduced into the reaction vessel as an aqueous solution containing a catalyst. The catalyst is a hydroxide ion, and functions as a catalyst for promoting the hydrolysis of the metal alkoxide, which will be described later.

[0036] Next, an object introduction step S14 is performed. In the object introduction step S14, a plurality of element bodies formed in advance in the laminate preparation step S11 described above are introduced into the reaction vessel as objects.

[0037] Next, a polymer introduction step S15 is carried out. In the polymer introduction step S15, polyvinylpyrrolidone is introduced into the reaction vessel as a polymer. As a result, the polymer introduced into the reaction vessel is adsorbed onto the outer surface of the element body.

[0038] Next, a metal alkoxide introduction step S16 is performed. In the metal alkoxide introduction step S16, liquid tetraethyl orthosilicate is introduced into the reaction vessel as the metal alkoxide. Note that tetraethyl orthosilicate is also called tetraethoxysilane.

[0039] Next, the film-forming step S17 is performed. In the film-forming step S17, the stirring of the solvent, which began in the solvent-feeding step S12 described above, is continued for a predetermined time after the metal alkoxide is fed into the reaction vessel in the metal alkoxide-feeding step S16. As a result, the metal alkoxide is hydrolyzed by the hydroxide ions serving as a catalyst. When the metal alkoxide is hydrolyzed, the hydrolyzed metal alkoxide adheres to the surface of the element body. Then, the metal alkoxides attached to the surface of the element body dehydrate and condense with each other to form a glass film. Therefore, in the film-forming step S17, a sol-like glass film is formed by a liquid-phase reaction in the reaction vessel. Furthermore, the dehydration and condensation reaction between the metal alkoxides also progresses in the solution. As a result, sol-like silica particles are produced as a by-product.

[0040] Next, an element removal step S18 is performed. In this step, the element is removed from the reaction vessel. The element is then dried and fired to obtain an electronic component having a glass film formed on the outer surface of the element.

[0041] Next, a recovery step S19 is performed. In the recovery step S19, silica particles present in the solution in the reaction vessel are recovered. Specifically, the solvent in the reaction vessel is evaporated to recover the silica particles remaining in the reaction vessel. As described above, this solution contains sol-like silica particles. Note that tetraethyl orthosilicate and polyvinylpyrrolidone adhere to the outer surfaces of the recovered silica particles.

[0042] Next, a drying step S20 is performed. In the drying step S20, the sol-state silica particles recovered in the recovery step S19 are dried. This removes most of the liquid components, such as 2-propanol and water, from the recovered sol-state silica particles. Through this drying step S20, first particles having a particle size of 100 nm or more are generated as silica particles. The median particle size of the generated first particles is 120 nm or more and 800 nm or less in the particle size distribution of the first particles. The particle size of the generated first particles can be controlled, for example, by adjusting the time of the film-forming step S17.

[0043] Next, the baking step S21 is performed. In the baking step S21, the silica particles that have undergone the drying step S20 are baked at a temperature of 300°C to 450°C for 5 to 40 minutes. Specifically, the baking is performed at a temperature of 400°C for 30 minutes. As a result, the gel-like silica particles contained in the solution harden as the moisture and polymer evaporate. Through this baking step S21, second particles with a particle size of less than 100 nm are generated as silica particles. The median particle size of the generated second particles is 10 nm to 100 nm in the particle size distribution of the second particles. Furthermore, the generated second particles that are in contact with the first particles are sintered together with the first particles during the baking step S21. Therefore, the second particles adhere to the surfaces of the first particles. The particle size of the generated second silica particles can be controlled by adjusting the baking temperature and time in the baking step S21. In this manner, silica particles are produced that include first silica particles having a median particle size of 120 nm or more and 800 nm or less and second silica particles having a median particle size of 10 nm or more and less than 100 nm.

[0044] As mentioned above, silica particles can be produced using a solution containing industrial by-products. This eliminates the need for disposal of the solution and reduces the energy required for the process, which is environmentally friendly.

[0045] The silica particles may be produced during the process of forming a glass film on the object, and may not be produced during the process of manufacturing the electronic component. In other words, the object introduced into the reaction vessel 11 in the object introduction step S14 does not have to be an element body of an electronic component.

[0046] The solvent introduction step S12 may be performed after the catalyst introduction step S13 or the object introduction step S14. The solvent introduction step S12 may be performed before at least one of the metal alkoxide introduction step S16 and the catalyst introduction step S13. The solvent introduction step S12 may also be omitted. In this case, for example, if the amount of water contained in the aqueous solution containing the catalyst is appropriately large, the metal alkoxide will react in the liquid phase. Alternatively, the aqueous solution containing the catalyst may be introduced in a state where it is mixed with an organic solvent as a solvent.

[0047] Although the catalyst has been described as being added as an aqueous solution containing the catalyst, a solid compound containing the catalyst and water may be added separately to the reaction vessel, in which case the catalyst can be considered to have been added to the reaction vessel when it is produced in the reaction vessel. Alternatively, for example, a solid compound containing the catalyst may be added to the reaction vessel, and moisture in the air may be used as the water required for hydrolysis.

[0048] The object introduction step S14 may be performed before the catalyst introduction step S13. Furthermore, when the object introduction step S14 is performed before the catalyst introduction step S13, the metal alkoxide introduction step S16 may be performed before the catalyst introduction step S13 or the object introduction step S14. The object introduction step S14 may be performed before at least one of the metal alkoxide introduction step S16 and the catalyst introduction step S13.

[0049] In the metal alkoxide introduction step S16, the metal alkoxide may be generated in the reaction vessel, instead of being introduced into the reaction vessel after being generated outside the reaction vessel. For example, the metal alkoxide may be generated by reacting a metal salt with an alcohol. Therefore, even when a metal salt and an alcohol, which are metal alkoxide precursors, are introduced into the reaction vessel and reacted to generate the metal alkoxide, the metal alkoxide can be considered to have been introduced into the reaction vessel.

[0050] The metal alkoxide is not limited to tetraethyl orthosilicate. The alkoxy group of the metal alkoxide may be a methoxy group, a propoxy group, or the like, or may be modified with a functional group such as a long-chain alkyl group or an epoxy group, as in a coupling agent. Furthermore, the coordination number for the metal contained in the metal alkoxide is not limited to tetracoordination, but may be 3 or 2.

[0051] The element removal step S18 may be omitted. That is, the recovery step S19 may be performed while the element remains in the reaction vessel.

[0052] In the calcination step S21, the temperature at which the sol- or gel-like particles are calcined may be less than 300° C. or more than 450° C. The calcination time may be less than 5 minutes or more than 40 minutes. For example, even if the temperature is higher than 450° C., calcination for less than 5 minutes may be sufficient as long as silica particles having a median particle size of 120 nm to 800 nm can be produced.

[0053] In the recovery step S19, the silica particles may be recovered by, for example, evaporating the solvent by drying under reduced pressure. The particle size of the first silica particles generated in the drying step S20 and the firing step S21 may be controlled by the concentration of the materials in each step, etc.

[0054] The first particle 101 may be a multilayer particle having a core portion and an outer layer. A first particle that is a multilayer particle is also referred to as a first multilayer particle. The core portion is approximately spherical and includes the center of gravity of the silica particle. The core portion may have a void 103 therein. The outer layer is a portion that covers the core portion from the outside and includes the outer surface of the first particle 101. The first particle 101 has an outer layer on the surface side including the outer surface. The silica particle 100 may contain polyvinylpyrrolidone. When the silica particle 100 contains polyvinylpyrrolidone, the outer layer may contain polyvinylpyrrolidone. When the outer layer contains polyvinylpyrrolidone, the concentration of polyvinylpyrrolidone is higher than the concentration of polyvinylpyrrolidone in the portion of the silica particle excluding the outer layer, i.e., the core portion. Furthermore, when the silica particle is imaged using, for example, a field emission transmission electron microscope (FE-TEM), a substantially clear interface may be observed between the outer layer and the portion of the silica particle excluding the outer layer. The first multilayer particle may or may not have a second particle.

[0055] The ratio of the thickness T of the outer layer to the particle diameter D of the first particles 101 (also referred to as the T / D ratio) may be, for example, 2% or more. For example, when the particle diameter D of the first particles 101 is approximately 260 nm and the thickness T of the outer layer 105 is approximately 15 nm, the T / D ratio is approximately 5.2%. Polyvinylpyrrolidone has various properties, such as high hygroscopicity and viscosity increasing properties. Therefore, when the outer layer contains polyvinylpyrrolidone, it tends to be more effective in improving plant growth, such as preventing soil from drying out and sustained release of active ingredients.

[0056] The thickness T of the outer layer is defined as follows. First, an image of the first particle 101 is taken using an FE-TEM or the like. In the image, the dimension of the outer layer at an arbitrary point on the outer surface of the first particle 101 in a direction perpendicular to the outer surface is defined as the thickness T of the outer layer at that point. More specifically, "a direction perpendicular to the outer surface at an arbitrary point on the outer surface of the mother particle" refers to a direction perpendicular to a tangent line drawn to the first particle 101 with the arbitrary point as a contact point. The thickness of the outer layer is the distance from the arbitrary point to the interface in the perpendicular direction.

[0057] The first multilayer particles are produced, for example, by recovering silica particles from a solution after the steps from the laminate preparation step S11 to the drying step S20 in the first production method. That is, the first multilayer particles can be silica particles after the drying step S20 and before the firing step S21 in the first production method.

[0058] The silica particles may have an outer layer having a polyvinylpyrrolidone concentration equal to or lower than that of the core, and the ratio of the thickness T of the outer layer to the particle diameter D of the silica particles may be less than 2%. Even in these cases, the effects of the present disclosure can be obtained.

[0059] The first particles may have a T / D ratio of less than 2% or may not have an outer layer, i.e., the silica particles may not have a clear boundary between the core and the outer layer.

[0060] The silica particles may include both first particles having no multilayer structure and first multilayer particles. In other words, the silica particles may include both silica particles after the firing step S21 and silica particles after the drying step S20 without the firing step S21.

[0061] The culture medium can be prepared by mixing the silica particles and sterilized soil. The inclusion of sterilized soil in the culture medium facilitates the proliferation of bacteria that are beneficial to plant growth and are propagated by the silica particles, thereby facilitating the promotion of plant growth.

[0062] The sterilized soil may be, for example, soil that has been sterilized, or soil in which the number of bacteria in the soil has been reduced. The number of bacteria per mass in the culture medium or sterilized soil may be, for example, 0% to 50% of the number of bacteria per mass in the sterilized soil before sterilization, 0% to 30% or 0% to 10%, or even 0%. The smaller the number of bacteria in the culture medium or sterilized soil, the greater the room for bacteria that are beneficial to plant growth in the culture medium, and therefore the more likely bacteria that are beneficial to plant growth in the culture medium tend to proliferate. As long as the effects of the present disclosure are achieved, the number of bacteria per mass in the culture medium or sterilized soil may be 50% or more of the number of bacteria per mass in the sterilized soil before sterilization.

[0063] The sterilization treatment can be carried out, for example, by irradiating the soil with gamma rays. The gamma ray irradiation dose may be, for example, 30 kGY. The sterilization treatment may be carried out, for example, indoors or outdoors. The sterilization treatment may be carried out directly on the soil in, for example, a farm field.

[0064] The number of bacteria in the soil and culture medium can be measured, for example, by a bioburden test. The number of bacteria in the culture medium or sterilized soil measured by a bioburden test may be, for example, 0 cfu / g.

[0065] The culture medium may contain only sterilized soil, or may further contain non-sterilized soil. The non-sterilized soil may be sterilized soil before sterilization. When the soil further contains non-sterilized soil, the diversity of the bacterial flora in the culture medium is easily improved, and bacteria that are advantageous for plant growth are easily propagated. When the culture medium further contains non-sterilized soil, the mass ratio of the non-sterilized soil to the sterilized soil (non-sterilized soil / sterilized soil) may be, for example, 50 / 50 or more and 80 / 20 or less, preferably more than 50 / 50 and 80 / 20 or less, and more preferably 60 / 40 or more and 80 / 20 or less.

[0066] The sterilized soil and non-sterilized soil may be soil suitable for growing crops, such as sandy loam, loam, or clay loam. The sterilized soil and non-sterilized soil may be soil from agricultural land such as fields, or may be commercially available. The sterilized soil and non-sterilized soil may contain, as soil components, for example, Akadama soil, Kanuma soil, compost, and coconut shell materials.

[0067] Non-sterile soil may contain bacteria contained in the soil components. The bacterial flora in the soil may be diversified due to the competition for survival between the bacteria contained in the soil components and bacteria newly proliferated in the atmosphere, around seeds, in water, etc. during the growth process of plants. Non-sterile soil may have aerobic bacteria counts of 1 x 10 as measured in a bioburden test, for example. ８ The non-sterilized soil may be soil in which the number of anaerobic bacteria measured in a bioburden test is 1×10 or more. ５ cfu / g or more.

[0068] Sterilized soil can be soil having a different diversity compared to non-sterilized soil, for example. The diversity can be, for example, alpha diversity and beta diversity. Sterilized soil can be soil having a different alpha diversity and / or beta diversity compared to non-sterilized soil, for example, soil having a lower alpha diversity compared to non-sterilized soil.

[0069] Alpha diversity is an index that indicates the diversity of species within a certain sample, for example. This index indicates the diversity inherent to the sample, and a higher value indicates a higher diversity of species within the sample. In this specification, alpha diversity is an index that indicates the number of species actually observed in the sample, where Observed_features is the number of species. Observed_features directly reflects the diversity of the bacterial flora. A high value of Observed_features means that many species are observed in the sample. Generally, a high value indicates a diverse ecosystem or a healthy microbial environment, while a low value indicates a hostile environment or effective sterilization results.

[0070] β diversity is an index that indicates the degree of difference in species diversity between two samples. This index expresses the difference in composition between samples as the distance between two points, and the greater the distance, the more different the bacterial flora compositions of the two samples. β diversity can be evaluated using Jaccard principal coordinate analysis, Unweighted_Unifrac principal coordinate analysis, and Weighted_Unifrac principal coordinate analysis. β diversity can be evaluated for similarities and differences between samples using Jaccard distance, Bray-Curtis distance, and phylogenetic-based UniFrac distance.

[0071] Jaccard principal coordinate analysis is a method that does not consider abundance but relies on the number of common species. This method calculates distance based on the proportion of species that are commonly present between two samples. The more common species there are, the shorter the distance between the samples will be, and conversely, the fewer common species there are, the longer the distance will be.

[0072] Unweighted_Unifrac principal coordinate analysis is a method that weights only the phylogenetic tree distance. This method evaluates the evolutionary distance between different bacterial species by calculating the phylogenetic distance between samples. Based on the phylogenetic tree, the length of the common evolutionary branch is compared, and the distance is calculated based on the proportion of shared evolutionary history.

[0073] Weighted_Unifrac principal coordinate analysis is a method that uses weighting based on both phylogenetic distance and abundance. This method simultaneously considers the phylogenetic distance between samples and the relative abundance of each species. This allows for the evaluation of differences in species richness, not just phylogenetic differences.

[0074] The culture medium may contain bacteria that are beneficial to plant growth. For example, the culture medium may contain bacteria of a bacterial genus that promotes plant growth, and preferably contains at least one bacterial genus selected from the group consisting of Lysobacter and Planomicrobium.

[0075] The culture medium may contain, for example, bacteria of a bacterial genus having organic matter decomposition activity, and preferably contains at least one bacterium of a bacterial genus selected from the group consisting of the genera Hydrogenophaga and Sphingopyxis.

[0076] The compost may contain bacteria of a bacterial genus that has a biocontrol, e.g. antifungal, activity, and preferably contains bacteria of the genus Janthinobacterium.

[0077] The culture medium may contain, for example, bacteria of the genus Bacteria having phytopathogenicity, but preferably does not contain bacteria of the genus Bacteria having phytopathogenicity.The culture medium may contain, for example, bacteria of the genus Agrobacterium, but preferably does not contain bacteria of the genus Agrobacterium.

[0078] The culture medium may contain bacteria of at least one bacterial genus selected from the group consisting of Lysobacter, Planomicrobium, Hydrogenophaga, Sphingopyxis, Janthinobacterium, and Agrobacterium. From the viewpoint of plant growth, the culture medium preferably contains bacteria of at least one bacterial genus selected from the group consisting of Lysobacter, Planomicrobium, Hydrogenophaga, Sphingopyxis, and Janthinobacterium.

[0079] The soil alone may have, for example, a pH of 6.5±0.5 and an electrical conductivity of 1.0 mS / cm, and the pH and electrical conductivity can be adjusted appropriately depending on the crop being cultivated.

[0080] The culture soil may be a mixture of the above-mentioned silica particles and sterilized soil. The culture soil may also have a multi-layer structure as shown in FIG. 3. Multi-layer structure 200 is a multi-layer structure in which a layer 201 containing sterilized soil, a layer 202 containing silica particles, and a layer 203 containing sterilized soil are stacked in this order. The layer containing sterilized soil may also contain non-sterilized soil, may not contain silica particles, or may contain only sterilized soil. The layer containing silica particles may contain only silica particles. In the multi-layer structure, the layer containing sterilized soil and the layer containing silica particles may have a clear boundary, or may be mixed together in some areas.

[0081] When the culture medium has the above-mentioned multi-layer structure, it may have a multi-layer structure (hereinafter also referred to as the first multi-layer structure) in which at least a portion of the periphery of the multi-layer structure perpendicular to the stacking direction is covered with soil containing sterilized soil. The culture medium having the first multi-layer structure can be prepared, for example, by first forming a depression in the soil, scattering silica particles in the depression, and then covering it with soil. The soil containing sterilized soil may be soil that constitutes a layer containing sterilized soil.

[0082] The compost may be prepared in a container, such as a pot, planter, plug tray, or bowl, and may be made of plastic, ceramic, wood, paper, or glass.

[0083] For example, when preparing a culture medium in a planter with a rectangular opening, a linear depression of a predetermined depth is created in the center of the soil placed in the planter along the long side of the opening, and a predetermined amount of silica particles is evenly scattered on the bottom surface of the depression, as shown in Figure 4. Next, soil is placed in the depression on top of the silica particles, and the soil surface is flattened to prepare a culture medium having a first multi-layer structure.

[0084] The shape, size and depth of the depressions made in the soil can be appropriately set depending on, for example, the shape, size and depth of the container, the type of plant to be grown, etc.

[0085] The amount of silica particles to be added to the soil (hereinafter also referred to as the amount added) may be, for example, 0.2 g to 1.5 g, preferably 0.2 g to 0.4 g, per 1 L of sterilized soil (the total of sterilized and non-sterilized soil). The amount of silica particles contained in the culture medium may be more than 1.5 g per 1 L of sterilized soil (a mixture of sterilized and non-sterilized soil), as long as the effects of the present disclosure are achieved. Analysis of harvested plants has confirmed that even if the amount of silica particles contained in the culture medium is high, there is no direct damage to the plants caused by the silica particles, and no direct adverse effects on the plants.

[0086] When the sterilization treatment is carried out directly on the soil in a field, the silica particles can be directly sprayed on the surface of the soil. The silica particles may also be sprayed after planting seeds or seedlings in the soil. When the silica particles are sprayed on the surface of the soil, for example, the silica particles are sprayed over 1 m of the soil. ２ The growth improver can be applied at a rate of 5 to 100 g per 10 cm2 of surface area of ​​the potting soil. ２ The silica particles may be sprayed in an amount such that the concentration of silica particles in 1 L of culture soil collected from the area where the silica particles are present is 0.2 g to 1.5 g, preferably 0.2 g to 0.4 g.

[0087] The content of silica particles in the culture soil may be, for example, 0.001% by mass or more and 1% by mass or less, 0.01% by mass or more and 0.5% by mass or less, or 0.01% by mass or more and 0.2% by mass or less. The content of silica particles in the culture soil can be measured as follows. First, the amount of available silicic acid in the culture soil is measured. Available silicic acid can be measured by the method described in "Method for evaluating available silicic acid in paddy field soil by phosphate buffer solution extraction method" (Japanese Journal of Soil Science and Plant Nutrition, 2002, Vol. 73, No. 4, pp. 383-390). Next, the silica content in the culture soil is measured. The silica content refers to the SiO2 content including insoluble silica and water-soluble silica (available silicic acid). ２ The silica content refers to the content of all components derived from the soil. The silica content can be calculated by measuring the amount of silica eluted when silica in the soil is eluted with a high concentration of alkali using ICP atomic emission spectroscopy or atomic absorption spectroscopy. The silica particle content can be determined by subtracting the amount of available silicic acid from the silica content.

[0088] The content of ammonia nitrogen in the culture soil may be, for example, 3.3 mg / 100 g or more, or 3.7 mg / 100 g or more.

[0089] The content of nitrate nitrogen in the culture soil may be, for example, 0.2 mg / 100 g or more, 0.5 mg / 100 g or more, or 0.8 mg / 100 g or more.

[0090] The content of available silicon in the culture soil may be, for example, 164 mg / 100 g or less, or 161 mg / 100 g or less. Even if the culture soil has a relatively low content of available silicon within the above range, the culture soil of the present disclosure tends to promote plant growth.

[0091] The voltage generated by microbial power generation using culture soil can be, for example, 0.7 V or higher. If the voltage generated by microbial power generation in the culture soil is within the above range, microbial activity is vigorous, making the culture soil suitable for plant cultivation. Furthermore, the microorganisms tend to decompose nitrate nitrogen in the culture soil, increasing the amount of ammonia nitrogen that can be absorbed by plants. The voltage generated by microbial power generation can be measured as follows. Specifically, the culture soil was placed into a measuring device (microbial fuel cell experimental device, product number: MudWatt, Kenis). Then, two weeks after placement, the voltage generated between the electrodes of the microbial power generation measuring device was measured. Note that the voltage generated by microbial power generation may be less than 0.7 V as long as the effects of the present disclosure can be obtained.

[0092] The culture medium may further contain a water-retaining polymer. By including a water-retaining polymer, moisture in the atmosphere can be easily absorbed into the culture medium, making it easier for plants to grow even when water is not supplied to the culture medium during the plant growth period. Examples of water-retaining polymers include acrylic polymers. The water-retaining polymer may be in the form of particles, sheets, or the like.

[0093] In order to facilitate the promotion of the growth of microorganisms living in the culture medium, the culture medium may contain microbial materials.

[0094] The culture soil is suitable as a culture soil for growing plants. The culture soil can be a culture soil for growing plants outdoors. When the culture soil is used to grow plants outdoors, the diversity of the bacterial flora in the culture soil tends to improve, and bacteria that are advantageous for plant growth tend to easily grow.

[0095] The type of plant grown using the compost may be a dicotyledonous plant or a monocotyledonous plant. The compost is suitable for growing agricultural crops. The crops may be edible plants such as vegetables and fruits, and is suitable for growing plants that are expensive to grow or difficult to grow. The compost is suitable for growing agricultural crops that are, for example, luxury foodstuffs.

[0096] Examples of edible plants include plants from the Brassicaceae family, Amaranthaceae family, Solanaceae family, and Dioscorea family. Examples of Brassicaceae plants include komatsuna (Japanese mustard spinach) and daikon radish. Examples of Amaranthaceae plants include spinach. Examples of Solanaceae plants include tomatoes (tomatoes, cherry tomatoes). Examples of Dioscorea plants include Japanese yam and Chinese yam.

[0097] The culture soil is also suitable for growing non-edible plants. Examples of non-edible plants include ornamental plants (such as aquatic plants), plants for livestock feeding, and plants for fuel. Examples of non-edible plants include plants from the families Venusaceae, Utriculariaceae, Poaceae, and Asteraceae. Examples of plants from the Venusaceae family include Miniglossostigma. Examples of plants from the Utriculariaceae family include water lawn. Examples of plants from the Poaceae family include dent corn. Examples of plants from the Asteraceae family include sunflower.

[0098] The plant grown using the culture soil is preferably at least one selected from the group consisting of Japanese mustard spinach and spinach, and more preferably spinach. When the culture soil is used to grow Japanese mustard spinach, the yield (fresh weight) can be increased by about 1.01 to 1.4 times. When the culture soil is used to grow spinach, the yield (fresh weight) can be increased by, for example, about 1.01 to 6 times.

[0099] [Plant Growing Method] The plant growing method is a method for growing plants using the above-mentioned culture soil. The growing method can further include, for example, a sowing step of planting seeds or seedlings of the plant to be grown in the culture soil, and a growing step of spraying water.

[0100] In the sowing process, for example, holes or grooves can be made in the prepared potting soil, and the seeds or seedlings of the plants to be grown can be placed in the holes or grooves. The holes or grooves can be made at regular intervals on the surface of the potting soil. For example, if silica particles are sprayed along the long side of the opening of a planter as shown in FIG. 4, holes can be made in the potting soil at regular intervals along the long side as shown in FIG. 5. The depth of the holes can be shallower than the depth to which the silica particles are sprayed. The size and location of the holes or grooves can be appropriately determined depending on the size and shape of the container, the type of plant to be grown, etc. After planting the seeds or seedlings, the holes or grooves can be covered with sterilized soil, a mixture of sterilized soil and non-sterile soil, or potting soil.

[0101] During the growing process, water can be supplied. Fertilizer and the like can also be supplied to the culture soil. The amount and frequency of water and fertilizer to be sprayed can be determined taking into account the type of plant, growing environment, growth level, etc.

[0102] Water may be supplied, for example, daily after planting the plant seeds or seedlings, or once immediately after planting the plant seeds or seedlings, and then once every 10 days, once every 50 days, or once every 100 days. The water supply method can be set depending on the size of the plant to be grown, the container, etc. Water may be supplied, for example, by spraying with a ladle or watering can, or by spraying from the nozzle of a hose connected to a water source.

[0103] In the growing step, the volumetric water content (VWC) of the culture medium may be, for example, 70% or less, 60% or less, 50% or less, 40% or less, or 25% or less. The volumetric water content can be measured by a soil sensor that can measure temperature and moisture content.

[0104] During the growing process, the culture medium or the container can be covered with a cover. The cover has the function of protecting the plant from bad weather such as strong winds, snowfall, and heavy rain, as well as from pests and external impacts. The cover may be of a size and shape that can cover the opening of the container or that can cover the entire container.

[0105] The cover may be, for example, a thermoplastic resin sheet. Examples of thermoplastic resins include soft polyvinyl chloride, polyester, and polyolefin. Examples of polyolefins include polyethylene and polypropylene. The sheet may be a commercially available agricultural sheet, such as a sheet for greenhouses. From the viewpoint of plant growth, the sheet may preferably be a light-transmitting sheet, more preferably a transparent sheet.

[0106] Plants may be grown outdoors or indoors. From the viewpoint of improving the diversity of the soil bacterial flora, plants are preferably grown outdoors. The types of plants grown are the same as those exemplified above. The plant grown is preferably at least one species selected from the group consisting of Japanese mustard spinach and spinach.

[0107] <Second embodiment> [Method for manufacturing culture soil] The method for manufacturing culture soil according to the second embodiment of the present disclosure includes a soil preparation step of sterilizing soil to prepare sterilized soil, and a culture soil preparation step of blending silica particles and sterilized soil to prepare culture soil. The median particle size of silica particles having a particle size of 100 nm or more is 120 nm or more and 800 nm or less in the particle size distribution of particles having a particle size of 100 nm or more. The explanations in the first embodiment apply to the silica particles, sterilized soil, and culture soil.

[0108] Figure 6 shows a flowchart of a method for producing culture soil. In the soil preparation step, soil can first be sterilized to prepare sterilized soil. When the culture soil contains sterilized soil, it becomes easier to increase bacteria that are beneficial to plant growth and are propagated by silica particles, thereby making it easier to promote plant growth. The soil may be soil suitable for growing crops, such as sandy loam, loam, or clay loam. The soil may be soil from agricultural land such as fields, or commercially available soil. The soil may contain, for example, Akadama soil, Kanuma soil, compost, coconut shell materials, etc.

[0109] In the soil preparation process, sterilized soil can be prepared by sterilizing the soil until the number of bacteria per mass of the soil is, for example, 0% to 50%, or 0% to 30%, or 0% to 10%, or 0%. The lower the number of bacteria in the culture medium or sterilized soil, the greater the room for bacteria beneficial to plant growth in the culture medium, and therefore the more likely bacteria beneficial to plant growth tend to proliferate in the culture medium. As long as the effects of the present disclosure are achieved, sterilization does not necessarily require the number of bacteria per mass of the soil to be 50% or less.

[0110] In the soil preparation step, sterilized soil can be prepared by sterilizing the soil until the number of bacteria measured by a bioburden measurement test reaches 0 cfu / g.

[0111] The sterilization treatment for sterilizing the soil can be carried out, for example, by irradiating with gamma rays. The irradiation dose of gamma rays may be, for example, 30 kGY. The sterilization treatment may be carried out, for example, indoors or outdoors. The sterilization treatment may be carried out directly on the soil, for example, in a farm field.

[0112] In the soil preparation step, sterilized soil and non-sterilized soil can be mixed. When the culture medium further contains non-sterilized soil, the diversity of the culture medium's bacterial flora is easily improved, and bacteria that are beneficial to plant growth are easily propagated. When the culture medium further contains non-sterilized soil, the mixing ratio of the non-sterilized soil to the sterilized soil (non-sterilized soil / sterilized soil) may be, for example, 50 / 50 or more and 80 / 20 or less, preferably more than 50 / 50 and 80 / 20 or less, and more preferably 60 / 40 or more and 80 / 20 or less.

[0113] The sterilized soil and non-sterilized soil may be mixed, for example, in a container, or if the field has been sterilized directly, the sterilized soil on the surface can be mixed with the non-sterilized soil underneath by tilling the soil in the field. The container exemplified in the first embodiment is applicable.

[0114] Next, in the culture medium preparation step, silica particles and sterilized soil (a mixture of sterilized soil and non-sterilized soil) are mixed to prepare the culture medium. In the culture medium preparation step, silica particles and sterilized soil (a mixture of sterilized soil and non-sterilized soil) may be mixed to prepare the culture medium as a mixture of silica particles and sterilized soil (a mixture of sterilized soil and non-sterilized soil). In addition, in the culture medium preparation step, the culture medium having the above-mentioned multi-layer structure may be prepared. The culture medium having the multi-layer structure can be prepared, for example, by forming a depression in soil containing sterilized soil, scattering silica particles on the bottom surface of the depression, and then covering the depression with soil containing sterilized soil.

[0115] The culture soil preparation step can be carried out, for example, in a container. In the culture soil preparation step, the culture soil having the first multi-layer structure described above may be prepared. For example, when the culture soil is prepared in a planter with a rectangular opening, as shown in FIG. 4, a linear depression of a predetermined depth is formed in the center of the soil placed in the planter along the long side of the opening, and a predetermined amount of silica particles is evenly dispersed on the bottom surface of the depression. Next, soil is placed in the depression on top of the silica particles, and the soil surface is flattened to prepare the culture soil having the first multi-layer structure.

[0116] The amount of silica particles (hereinafter referred to as the blending amount) to be blended into soil containing sterilized soil may be, for example, 0.2 g to 1.5 g, preferably 0.2 g to 0.4 g, per 1 L of sterilized soil (a mixture of sterilized soil and non-sterilized soil). The amount of silica particles contained in the culture medium may be more than 1.5 g per 1 L of sterilized soil (a mixture of sterilized soil and non-sterilized soil), as long as the effects of the present disclosure are obtained. Analysis of harvested plants has confirmed that even if the soil contains a large amount of silica particles, there is no direct damage to plants caused by the silica particles, and no direct adverse effects on plants.

[0117] When the sterilization treatment is carried out directly on the soil in a field, the silica particles can be directly sprayed on the surface of the soil. The silica particles may also be sprayed after planting seeds or seedlings in the soil. When the silica particles are sprayed on the surface of the soil, for example, the silica particles are sprayed over 1 m of the soil. ２The growth improver can be applied at a rate of 5 to 100 g per 10 cm2 of surface area of ​​the potting soil. ２ The silica particles may be sprayed in an amount such that the concentration of silica particles in 1 L of culture soil collected from the area where the silica particles are present is 0.2 g to 1.5 g, preferably 0.2 g to 0.4 g.

[0118] The content of silica particles in the culture soil may be, for example, 0.001% by mass or more and 1% by mass or less, 0.01% by mass or more and 0.5% by mass or less, or 0.01% by mass or more and 0.2% by mass or less.

[0119] In the culture soil preparation step, at least one of a water-retentive polymer and a microbial material can be blended in. The explanations in the first embodiment apply to the water-retentive polymer and the microbial material.

[0120] The sterilized soil can be stored for a long period of time by, for example, placing it in a sterilized bag after sterilization and storing it in a sterile environment.

[0121] The soil preparation step and the culture medium preparation step can be carried out outdoors. By carrying out the soil preparation step and the culture medium preparation step outdoors, the diversity of the culture medium flora tends to be improved, and bacteria that are advantageous for plant growth tend to be more likely to grow.

[0122] The present invention will be described in more detail below with reference to examples.

[0123] [Preparation of Silica Particles] Silica particles were prepared according to the first production method described above. 2-Propanol was used as the solvent in the solvent introduction step S12. The sol-like silica particles obtained in the recovery step S19 were dried in the drying step S20, and then calcined at 400°C for 30 minutes in the calcination step S21 to obtain silica particles.

[0124] The silica particles were silica particles having particles (second particles) with a particle size of less than 100 nm on the surface of particles (first particles) with a particle size of 100 nm or more. The median particle size of the first particles in the particle size distribution of the first particles was 251 nm. Furthermore, the median particle size of the second particles in the particle size distribution of the second particles was 16 nm. The particle size distributions and median particle sizes of the first particles and second particles were determined as follows using SEM images of the silica particles at 50,000 and 200,000 magnifications. First, the particle size distribution was determined from the longest diameters measured for 25 or more first particles and second particles in each SEM image. Next, the median values ​​of the determined particle size distributions were determined to be the median particle sizes of the first particles and second particles.

[0125] The specific surface area of ​​the silica particles measured by the BET method is 163 m ２ The specific surface area of ​​the particles after drying and before calcination was 18.3 m2 as measured by the BET method. ２ / g.

[0126] The crystallinity of the silica particles was confirmed to be amorphous by X-ray diffraction (XRD). Scanning electron microscope (SEM) images of the silica particles are shown in Figures 7 and 8. A composite map (Si and N) of the silica particles obtained by energy dispersive X-ray spectroscopy (EDX) is shown in Figure 9. It was confirmed that the silica particles had multiple fine particles attached to the surface of the base particle. Furthermore, the results of component analysis of the silica particles are shown in Table 1. No heavy metals (arsenic, lead, cadmium, mercury, chromium, cyanide) were detected in the silica particles.

[0127] After immersing silica particles in a strong alkali for 5 days, the surfaces or cross sections of the silica particles removed from the alkali solution were examined using an SEM. The presence of multiple primary particles was confirmed in the first and second silica particles. The sizes of two of the multiple primary particles were measured in the SEM observation image and found to be 26 nm and 29 nm.

[0128]

[0129] Furthermore, an SEM image of the surface of silica particles after immersion in water for one year is shown in Fig. 10. Although some areas were observed where the second particles attached to the surfaces of the first particles had peeled off, no change in particle size of the first particles was observed, and no evidence of dissolution in water was observed.

[0130] Examples 1 to 8 [Culture Soil Preparation Process] Commercially available soil (manufactured by Togawa Heiwa Farm Co., Ltd.) containing Akadama soil, Kanuma soil, compost, and coconut shell material (trade name "COCOYUKI (registered trademark)") was prepared as non-sterile soil. Sterilized soil was prepared by irradiating the non-sterile soil with 30 kGy gamma rays. A bioburden measurement test was conducted according to the following procedure, and it was confirmed that the bacterial count (total number of aerobic bacteria and anaerobic bacteria) of the sterilized soil was 0 cfu / g in all dilutions. Bioburden Test: (1) A suspension of the sterilized soil and its diluted solution were smeared on a plate medium, and aerobic and anaerobic cultures were performed. (2) 1 g of sample was weighed and suspended in a Falcon tube containing 10 mL of PTS recovery solution to prepare a stock solution. (3) 1 mL was removed from the stock solution and diluted 10-fold with 9 mL of PTS recovery solution. This process was repeated six times. (4) 100 μL each from the 100-fold, 10,000-fold, and 1,000,000-fold diluted solutions was taken and smeared on an SCDA plate medium. After culturing aerobic bacteria for 7 days, the aerobic bacterial count was measured. (5) 100 μL each from the original solution and the 100-fold diluted solution was taken and smeared on an SCDA plate medium. After culturing anaerobic bacteria for 7 days, the anaerobic bacterial count was measured.

[0131] A total of 25 L of sterilized soil and non-sterilized soil were placed in a planter (depth 30 cm, width 63 cm, height 33 cm) outdoors, with the mass ratio of each being as shown in Table 1. The container was tapped to remove air. As shown in Figure 4, a linear depression was created in the center of the planter, along the long side of the opening, at a depth of 9 cm from the soil surface. A soil sensor capable of measuring temperature and moisture content was then installed in the culture medium, and silica particles were then spread on the surface of the bottom of the depression so that the mass ratio of soil to silica particles (soil:silica particles) was 25 L:6.5 g. This was then covered with soil to form the culture medium.

[0132] [Seeding step] As shown in Figure 5, 16 holes were made in the culture soil to a depth of 2 cm from the surface. Two seeds of the plants shown in Table 1 were placed in each hole, and the culture soil was placed on top of them.

[0133] [Growth Process] 1 L of pure water was sprayed onto the surface of the culture soil in which the seeds were planted. The planter was covered with a transparent polyethylene sheet. The sheet was left open when there was no snowfall or strong winds, and the planter was covered with the sheet in other weather conditions. Growth was continued for 3.5 months. During the growth period, no water was sprayed on the soil surface except for water sprayed on the soil surface 8 days after sowing. Figures 11 and 12 show the growth conditions of Example 1 (100% sterilized soil) and Example 4 (0% sterilized soil), respectively. The measurement results of fresh weight (yield) after harvest are shown in Table 2, Figure 14 (komatsuna), and Figure 15 (spinach). The right-hand vertical axes of Figures 14 and 15 represent the average and standard deviation (average value line graph with standard deviation) of the komatsuna yield (g) and spinach yield (g) divided by the number of harvested bundles per bundle, respectively, and the left-hand vertical axis represents the total yield (bar graph). 16 and 17 show the temperature and moisture content in the culture soil measured by the soil sensor during the growing period in Examples 1, 3 and 4.

[0134] Comparative Examples 1 to 8 Culture media were prepared in the mass ratios shown in Table 1 in the same manner as in Examples 1 to 8, except that silica particles were not added to the sterilized soil and non-sterilized soil, and the plants shown in Table 1 were grown. The growth conditions in Comparative Example 1 (100% sterilized soil) are shown in Figure 13. The results of measuring the fresh weight (yield) after harvest are shown in Figure 14 (Japanese mustard spinach) and Figure 15 (spinach). The temperature and moisture content in the culture media measured with a soil sensor during the growth periods of Comparative Examples 1, 3, and 4 are shown in Figures 16 and 17.

[0135]

[0136] As shown in Figure 16, there was no significant difference in the temperature in the culture medium regardless of the mass ratio of sterilized soil to non-sterilized soil in the culture medium or whether or not silica particles were added to the soil. On the other hand, as shown in Figure 17, there was variation in the moisture content in the culture medium even though the growth conditions were the same except for the presence or absence of silica particles and the proportion of sterilized soil.

[0137] 14 and 15 show that Examples 1, 2, and 4 to 8, which used culture soil containing silica particles, had higher yields than the corresponding Comparative Examples 1, 2, and 4 to 8. Also, as shown in Fig. 15, the yield tended to increase as the proportion of sterilized soil increased. This is presumably because the greater the proportion of sterilized soil, the greater the space available for bacterial growth in the culture soil, and the silica particles allowed bacteria that are beneficial to plant growth to grow in relatively large numbers in the culture soil.

[0138] Bioburden measurement tests were carried out on the culture soil samples at the time of harvest in Examples 1 to 8 and Comparative Examples 1 to 8, and the number of bacteria in the culture soil was measured. The number of aerobic bacteria in all samples except for the 1,000,000-fold diluted solution in Example 2 was 1 x 10 ８ cfu / g or more. In addition, the number of anaerobic bacteria in all samples was 1 × 10 ５ cfu / g or more. It was confirmed that bacteria proliferated in the sterilized soil and in the culture medium containing the sterilized soil, where the bacterial count measured by the bioburden measurement test was 0 cfu / g during plant growth. It is presumed that growing the plants outdoors further increased bacterial proliferation in the culture medium.

[0139] In Examples 1 to 8 and Comparative Examples 1 to 8, bacterial flora analysis was performed on samples collected from the culture medium at the start of growth (germination), the culture medium on the periphery of the planter at harvest, and the culture medium attached to the plant roots (rhizosphere). The bacterial flora analysis was performed according to the following procedure.

[0140] 1) Plant harvest and soil collection: The soil surface of the komatsuna and spinach was collected, and the komatsuna and spinach were harvested. Some of the soil adhering to the komatsuna and spinach was removed, and the rhizosphere (the soil space influenced by plant root secretions and soil bacteria) was collected with a brush. The collected soil was spread on aluminum foil, and 40 g of the soil alone, avoiding the fertilizer (yellow and white) and wood chips, was dispensed into a tube containing ceramic beads from a DNA extraction kit.

[0141] 2) The DNA extraction beads were mixed with the soil and cell lysis solution and then vigorously shaken. This caused the beads to detach microorganisms (bacteria) adhering to the soil, lyse the microorganisms, and release their DNA.

[0142] 3) Quantification of total DNA The amount of DNA contained in the solution obtained in the DNA extraction process (total DNA solution) was confirmed. A fluorescent dye that specifically binds to DNA was added, and the amount of DNA was quantified by measuring the fluorescence intensity. The experiment was performed using 3 μL of total DNA and 197 μL of staining solution, and it was confirmed that approximately 40 ng / μL had been extracted. The amount of reagents for the first PCR was determined based on the confirmed concentration.

[0143] 4) 1st PCR PCR was carried out by performing one cycle of thermal denaturation, annealing and extension reaction in this order.

[0144] 5) DNA Purification After removing unnecessary substances other than DNA (such as enzymes used in PCR) using magnetic beads, the magnetic beads and a solution for separating DNA were added.

[0145] 6) Gel preparation and electrophoresis A 2% agarose gel was prepared, and the agarose was dissolved in hot water and cooled to solidify. Electrophoresis confirmed that the target DNA region had been amplified by 1st-PCR.

[0146] 7) 2nd PCR: The same procedure as 1st PCR was performed, and an adapter sequence was added to the amplified target DNA region (creating a library). By adding the adapter sequence to the end of the DNA in each amplified sample, DNA amplification and sequence analysis were performed using a next-generation sequencer (a machine that analyzes DNA sequences). The adapter sequence contains a unique sequence that can distinguish sample numbers.

[0147] 8) Sequencing: First, the library concentration was measured using a Synergy H1 (Agilent Technologies) and a QuantiFluor dsDNA System. Next, the quality of the prepared library was confirmed using a Fragment Analyzer and a dsDNA 915 Reagent Kit (Agilent Technologies). Then, sequencing was performed using a MiSeq system and MiSeq Reagent Kit v3 (Illumina) at 2x300 bp.

[0148] 9) 16S rRNA data analysis First, reads that matched the primer sequence were extracted using FASTX-Toolkit (ver. 0.0.14). Next, the reads were combined using the paired-end read combination script FLASH (ver. 1.2.11). After removing chimeric sequences and noise sequences using Qiime2 (ver. 2024.2), a representative sequence was obtained, and the feature-classifier plugin was used to compare the obtained representative sequence with 97% OTU of Greengene (ver. 13_8) to estimate the phylogeny. The phylogenetic tree was created using the Alignment and phylogeny plugins.

[0149] Figure 18 shows a bar chart for each sample showing the abundance of each bacterial species collected from each sample. Figure 19 shows a bar chart in which the abundance of bacteria A (Rhodanobacter genus) in Figure 18 is rearranged from left to right in ascending order. In Figures 18 and 19, the abbreviations have the following meanings: An odd number at the beginning indicates a culture medium containing silica particles; an even number indicates a culture medium without silica particles. Furthermore, when the first number is 1 or 2, the ratio of sterilized soil is 100%, when it is 3 or 4, the ratio of sterilized soil is 76%, when it is 5 or 6, the ratio of sterilized soil is 50%, and when it is 7 or 8, the ratio of sterilized soil is 0% (100% non-sterilized soil). Furthermore, S and O represent the culture medium at the start of growth (germination) and the culture medium around the planter at harvest, respectively. K and H represent komatsuna and spinach. The numbers at the end indicate the level of samples taken from the culture medium (n=3).

[0150] As a result of the α diversity analysis, the rarefaction curve of Observed_features is shown in Figure 20. Also, a box plot of Observed_features is shown in Figure 21.

[0151] Principal coordinate analysis (PCoA) was used to visualize beta diversity. In PCoA, each plot represents one sample, and the closer the plots are to each other, the more similar the bacterial flora composition between the samples is. Figure 22 shows the results of Jaccard principal coordinate analysis. Figure 23 shows the results of Unweighted_Unifrac principal coordinate analysis. Figure 24 shows the results of Weighted_Unifrac principal coordinate analysis.

[0152] (Bar chart analysis) Figure 18 shows bar charts sorted by sample number. Tests were performed at each level (n = 3), and equivalent bacterial flora bar charts were obtained at the same conditions. This confirmed the reproducibility of the experiment.

[0153] Figure 19 shows a bar chart sorted from left to right by the abundance rate of bacteria A. The sample was divided into three sections (initial bacterial flora, 100% sterilized soil, and a group containing non-sterilized soil), each with a similar bacterial flora pattern. The "initial bacterial flora" section had a high bacterial flora diversity, with various bacterial species evenly distributed. The "100% sterilized soil" section showed significant changes in the composition of the bacterial flora over the period from sterilization to plant cultivation. Furthermore, the dominance of several specific bacterial species (e.g., bacteria B [Pseudomonas genus] and bacteria C [Flavobacterium genus]) increased, resulting in a decrease in bacterial flora diversity. The "group containing non-sterilized soil" section showed an increase in bacterial flora diversity. Furthermore, the plant-pathogenic genus Agrobacterium was detected as the top bacterial species when silica particles were not added, but was less likely to be detected when silica particles were added to 100% sterilized soil or non-sterilized soil. Furthermore, the addition of silica particles was confirmed to increase the number of bacteria in the genera Lysobacter, Planomicrobium, Hydrogenophaga, Sphingopyxis, and Janthinobacterium. These analytical results demonstrate that soil sterilization and subsequent plant cultivation have a significant impact on the bacterial flora.

[0154] (Analysis of α diversity) Figure 20 shows the rarefaction curve of bacterial flora diversity (Observed_features). Since the gene reading was performed to the point where the number of detected bacterial species did not change even when the number of gene readings was increased, it was confirmed that the amount of data to be analyzed in the analysis of α diversity was sufficient.

[0155] In Figure 21, the box plots show the distribution of bacterial flora diversity (Observed_features) for each sample. The vertical axis shows the number of observed species, which is used to evaluate the diversity of the bacterial flora. It can be seen that the diversity of the bacterial flora was significantly reduced at the 100% sterilized soil level. It was also confirmed that the addition of silica particles at the 100% sterilized soil level increased the number of bacterial species, and diversity tended to recover. On the other hand, no difference was observed between the presence and absence of silica particles at the 76% sterilized soil, 50% sterilized soil, and non-sterilized soil levels.

[0156] (Analysis of β diversity) (1) Jaccard principal coordinate analysis Jaccard principal coordinate analysis is a method that does not consider the abundance of each species, but rather depends on the number of common species. The Jaccard distance used in Jaccard principal coordinate analysis is expressed such that the greater the number of species commonly present between samples, the shorter the distance between samples, and conversely, the fewer common species, the longer the distance.

[0157] In Figure 22, the bacterial flora at the start of the experiment was separated into coordinates with distances corresponding to the degree of mixing of sterilized and non-sterilized soil. Regarding the soil bacterial flora at harvest, the specimen with 100% sterilized soil was shown to have the most significantly different bacterial flora from the start compared to the specimens harvested under the other conditions. Furthermore, clusters (i.e., bacterial flora with different compositions) were formed and separated at different coordinates depending on whether or not silica particles were added. These results indicate that soil that was 100% sterilized soil at the start formed unique bacterial flora at harvest, and that the presence or absence of silica particles significantly affected the formation of the bacterial flora.

[0158] On the other hand, just like with 100% sterilized soil, changes in the bacterial flora from the start of the experiment to harvest were observed in non-sterilized soil, and different bacterial flora compositions were formed depending on whether or not silica particles were added at that time, but the differences were closer than in the case of 100% sterilized soil. In the cases of 76% and 50% sterilized soil, the bacterial flora coordinates at the start and at harvest were located between those of 100% sterilized soil and non-sterilized soil, but the differences due to the presence or absence of added silica particles were small.

[0159] It can be seen that soil that was 100% sterilized at the start formed its own unique bacterial flora by the time plant cultivation was completed, and that the bacterial flora formation was significantly affected by the presence or absence of silica particles added. Considering that the results of the Examples and Comparative Examples show that the effect of the addition of silica on plant growth was greatest in 100% sterilized soil, was equal to or lower in non-sterilized soil than in 100% sterilized soil, and was far lower in 76% and 50% sterilized soil than non-sterilized soil, it can be seen that differences in bacterial flora reflect differences in plant growth.

[0160] (2) Unweighted Unifrac Principal Coordinate Analysis Unweighted Unifrac principal coordinate analysis is a method for evaluating the evolutionary distance between different bacterial species by calculating the phylogenetic distance (UniFrac distance) between samples and weighting them only by the phylogenetic tree distance.

[0161] Figure 23 shows that only the 100% sterilized soil level was significantly different from the coordinate range of the other samples. Furthermore, the 76% sterilized soil, 50% sterilized soil, and non-sterilized soil levels showed only small changes in the bacterial flora between the start and end of plant cultivation. These results suggest that the 100% sterilized soil level has bacterial flora that are phylogenetically very different. Furthermore, the 76% sterilized soil, 50% sterilized soil, and non-sterilized soil levels have bacterial flora composed of phylogenetically similar bacterial species.

[0162] (3) Weighted Unifrac Principal Coordinate Analysis Weighted Unifrac Principal Coordinate Analysis is a method of analysis that uses the phylogenetic distance between samples (UniFrac distance) and the distance indicating species abundance (Bray-Curtis distance) to weight both the phylogenetic tree distance and the abundance rate, and takes into account not only phylogenetic differences but also differences in species abundance in the evaluation.

[0163] As shown in Figure 24, differences were observed in the bacterial flora after plant cultivation in 100% sterilized soil depending on whether silica was added or not. Differences were also observed in the bacterial flora of the rhizosphere soil between cultivated plants. In the 76%, 50% sterilized, and non-sterilized soil levels, the bacterial flora at the start and end of plant cultivation were separated by Weighted Unifrac principal coordinate analysis, but the distances were very close, and there was little difference between the presence and absence of silica particles.

[0164] The 100% sterilized soil level had a microbial flora composed of significantly different species compared to the other conditions, and these differences were also confirmed to be significantly different in terms of phylogenetic development from the microbial flora under other conditions. This suggests that the soil, which had lost its microbial flora due to sterilization, acquired a new microbial flora and changed uniquely during the plant cultivation process. Furthermore, it was suggested that the presence of silica particles significantly affected the formation of the microbial flora during this process. Furthermore, the difference in the microbial flora with the addition of silica particles was significant between the 100% sterilized soil and the non-sterilized soil levels, and the difference in plant growth promotion effect was also significant at these levels. Conversely, when the 76% and 50% sterilized soil levels, where the two were mixed to start the experiment, the difference in both the microbial flora and plant growth promotion between the presence and absence of silica particles was small. This suggests that the effect of silica particles on the diversity of the microbial flora is strongly correlated with the plant growth promotion effect.

[0165] It was found that the bacterial flora improver of the present disclosure can directly or indirectly affect the formation of bacterial flora in soil during plant cultivation, and it was also suggested that the formation of bacterial flora may be correlated with the plant growth improvement effect.

[0166] From the above, it can be seen that in culture medium containing sterile soil, silica particles allow bacteria that are beneficial to plant growth to proliferate, and as a result, plant growth is better than when culture medium not containing sterile soil is used or when silica particles are not added to the soil.

[0167] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0168] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0169] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0170] (Item 1) A culture medium according to an embodiment of the present disclosure is a culture medium comprising silica particles and sterilized soil, wherein the silica particles have a particle size of 100 nm or more and a median particle size of 120 nm to 800 nm in a particle size distribution of particles having a particle size of 100 nm or more.

[0171] (Item 2) The culture medium according to item 1 further comprises non-sterilized soil.

[0172] (Item 3) In the culture medium according to item 2, the mass ratio of non-sterile soil to sterilized soil (non-sterilized soil / sterilized soil) is 50 / 50 or more and 80 / 20 or less.

[0173] (4) In the culture medium according to any one of paragraphs 1 to 3, the number of bacteria per mass in the culture medium or sterilized soil is 0% or more and 50% or less of the number of bacteria per mass in the sterilized soil before sterilization.

[0174] (Item 5) The culture soil according to any one of Items 1 to 4, wherein the culture soil is sterilized soil or soil containing sterilized soil, and the number of bacteria measured by a bioburden measurement test is 0 cfu / g. The culture soil according to claim 1.

[0175] (Item 6) The culture soil according to any one of Items 1 to 5 has a multi-layer structure in which a layer containing sterilized soil, a layer containing silica particles, and a layer containing sterilized soil are stacked in this order, and at least a portion of the periphery of the multi-layer structure on the side perpendicular to the stacking direction is covered with soil containing sterilized soil.

[0176] (7) A method for growing plants using the culture soil according to any one of items 1 to 6.

[0177] (Item 8) The method for growing plants according to item 7 is a method for growing plants outdoors.

[0178] (Item 9) In the method for growing a plant according to item 7 or 8, the plant is at least one species selected from the group consisting of Japanese mustard spinach and spinach.

[0179] (Item 10) A method for producing a culture medium according to another embodiment of the present disclosure includes a soil preparation step of sterilizing soil to prepare sterilized soil, and a culture medium preparation step of blending silica particles with the sterilized soil to prepare the culture medium. The median particle size of silica particles having a particle size of 100 nm or more is 120 nm or more and 800 nm or less in the particle size distribution of particles having a particle size of 100 nm or more.

[0180] (Item 11) In the method for producing a culture soil according to Item 10, sterilized soil and non-sterilized soil are mixed in the soil preparation step.

[0181] (Item 12) In the method for producing a culture soil according to Item 11, the mixing ratio of non-sterile soil to sterilized soil (non-sterilized soil / sterilized soil) is 50 / 50 or more and 80 / 20 or less.

[0182] (Item 13) In the method for producing culture soil according to any one of Items 10 to 12, in the soil preparation step, the soil is sterilized until the number of bacteria per mass of the soil is 0% or more and 50% or less.

[0183] (Item 14) In the method for producing culture soil according to any one of Items 10 to 13, in the soil preparation step, the soil is sterilized until the number of bacteria measured by a bioburden measurement test becomes 0 cfu / g.

[0184] (Item 15) In the method for producing culture soil according to any one of Items 10 to 14, in the culture soil preparation step, a depression is formed in soil containing sterilized soil, silica particles are scattered on the bottom surface of the depression, and then the culture soil is prepared by covering the depression with soil containing sterilized soil.

[0185] (Item 16) In the method for producing culture soil according to any one of Items 10 to 15, the culture soil preparation step is carried out in a container.

[0186] (Item 17) In the method for producing a culture soil according to any one of Items 10 to 16, the soil preparation step and the culture soil preparation step are carried out outdoors.

[0187] 100 Silica particles, 101 First particles, 102 Second particles, 103 Voids, 200 Multilayer structure, 201, 203 Layers containing soil, 202 Layers containing silica particles.

Claims

A culture medium comprising silica particles and sterilized soil, The silica particles have a median particle size of 120 nm or more and 800 nm or less in the particle size distribution of the particles having a particle size of 100 nm or more.

10. The potting soil of claim 1, further comprising non-sterile soil. 　 The culture soil according to claim 2, wherein the mass ratio of the non-sterile soil to the sterilized soil (non-sterile soil / sterilized soil) is 50 / 50 or more and 80 / 20 or less. 　 The number of bacteria per mass in the culture soil or the sterilized soil is 0% or more and 50% or less of the number of bacteria per mass in the sterilized soil before sterilization. The culture soil according to any one of claims 1 to 3. 　 The culture soil according to any one of claims 1 to 4, wherein the sterilized soil or the soil containing the sterilized soil has a bacterial count of 0 cfu / g as measured by a bioburden measurement test. 　 a multilayer structure in which a layer containing the sterilized soil, a layer containing the silica particles, and a layer containing the sterilized soil are laminated in this order; The culture soil according to any one of claims 1 to 5, wherein at least a portion of the periphery of the multilayer structure perpendicular to the lamination direction is covered with soil containing the sterilized soil. 　 A method for growing plants using the culture soil according to any one of claims 1 to 6.

8. The method for growing plants according to claim 7, wherein the plants are grown outdoors.

9. The method for growing a plant according to claim 7 or 8, wherein the plant is at least one species selected from the group consisting of Japanese mustard spinach and spinach. 　 A method for producing culture soil, a soil preparation step of sterilizing the soil and preparing sterilized soil; The method includes a culture soil preparation step of preparing culture soil by mixing silica particles and sterilized soil, A method for producing culture soil, wherein the median particle size of the silica particles having a particle size of 100 nm or more is 120 nm or more and 800 nm or less in the particle size distribution of the particles having a particle size of 100 nm or more. 　 The method for producing culture soil according to claim 10, wherein the sterilized soil and non-sterilized soil are mixed in the soil preparation step. 　 The method for producing culture soil according to claim 11, wherein the mixing ratio of the non-sterile soil to the sterilized soil (non-sterile soil / sterilized soil) is 50 / 50 or more and 80 / 20 or less. 　 The method for producing culture soil according to any one of claims 10 to 12, wherein in the soil preparation step, the soil is sterilized until the number of bacteria per mass of the soil is 0% or more and 50% or less. 　 The method for producing culture soil according to any one of claims 10 to 13, wherein in the soil preparation step, the soil is sterilized until the number of bacteria measured by a bioburden measurement test becomes 0 cfu / g. 　 In the culture soil preparation step, a depression is formed in the soil containing the sterilized soil, the silica particles are scattered on the bottom surface of the depression, and then the culture soil is prepared by covering the depression with soil containing the sterilized soil. The method for producing culture soil according to any one of claims 10 to 14. 　 The method for producing culture soil according to any one of claims 10 to 15, wherein the culture soil preparation step is carried out in a container. 　 The method for producing culture soil according to any one of claims 10 to 16, wherein the soil preparation step and the culture soil preparation step are carried out outdoors.

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