Humic acid extract and method for promoting growth of roots of plant

Abstract

Provided is a humic acid extract which contains humic acid having a mass average molecular weight of 400-1,000, has a total organic carbon concentration of 10,000-45,000 mg / L, and has a free nitric acid content of 1 mass% or less. Also provided is a method for promoting the growth of roots of a plant, the method including diluting the humic acid extract with water and applying the diluted solution to the plant.

Description

Humic acid extract and method for promoting plant root growth

[0001] The present invention relates to a humic acid extract and a method for promoting plant root growth. This application claims priority to Japanese Patent Application No. 2024-134953, filed on August 13, 2024, the contents of which are incorporated herein by reference.

[0002] Humic acid is a polymeric organic substance naturally present in soil and land water, and is classified into humin, which is the insoluble fraction; humic acid, which is alkali-soluble but acid-insoluble; and fulvic acid, which is acid-soluble. Humic acid can be naturally derived or industrially obtained. Humic acid is believed to have effects such as promoting plant growth, and its use as fertilizer has been proposed. Furthermore, techniques for extracting and liquefying humic acid for use as liquid fertilizer have also been proposed (Patent Documents 1 and 2).

[0003] Patent No. 6955335 Patent No. 7110456

[0004] Patent Documents 1 and 2 evaluate the effect of humic acid extracts on the above-ground parts of plants, but do not examine the effect on the roots.

[0005] An object of the present invention is to provide a humic acid extract having an excellent effect of promoting plant root growth, and a method for promoting plant root growth using the same.

[0006] The present invention has the following aspects. [1] A humic acid extract containing humic acid having a mass-average molecular weight of 400 to 1,000, a total organic carbon concentration of 10,000 to 45,000 mg / L, and a free nitric acid content of 1% by mass or less. [2] The humic acid extract according to [1] above, wherein the free nitric acid content is 0.1% by mass or more. [3] The humic acid extract according to [1] or [2] above, wherein the pH is 4.5 to 7.5. [3-2] The humic acid extract according to [1] or [2] above, wherein the pH is 4.5 to 9.5. [4] The humic acid extract according to any one of [1] to [3-1] above, containing an alkali metal salt of nitric acid, wherein the content of the alkali metal salt is 6 to 9% by mass in terms of potassium. [5] A humic acid extract containing humic acid having a mass-average molecular weight of 400 to 1,000, a total organic carbon concentration of 10,000 to 45,000 mg / L, and a free nitrate content of 3 mass% or less. [6] A method for promoting root growth of plants, comprising diluting the humic acid extract according to any one of [1] to [5] above with water and applying the diluted solution to plants.

[0007] According to the present invention, it is possible to provide a humic acid extract having an excellent effect of promoting plant root growth, and a method for promoting plant root growth using the same.

[0008] 1 is a graph showing the dry mass of the above-ground parts of komatsuna plants to which the humic acid extracts of Examples 1 to 3 were applied. 2 is a graph showing the dry mass of the underground parts (roots) of komatsuna plants to which the humic acid extracts of Examples 1 to 3 were applied.

[0009] In this specification, a numerical range expressed as "to" means a numerical range in which the numerical values ​​before and after "to" are the lower and upper limits. In this specification, "humic acid" is a general term for humic acid and fulvic acid. Humic acid is acid-insoluble but alkali-soluble, while fulvic acid is acid-soluble. A "humic acid extract" is obtained by extracting humic acid from a humic acid-containing raw material such as young charcoal using an extraction solvent. Hereinafter, an embodiment of the present invention will be described.

[0010] [Humic Acid Extract] The humic acid extract of this embodiment contains humic acid. The mass-average molecular weight (Mw) of the humic acid is 400 to 1,000, preferably 500 to 900, and more preferably 600 to 800. When the Mw is within the above range, precipitation is unlikely to form even when the humic acid extract is added to a concentrated liquid fertilizer containing the three elemental components, etc., making it useful for fertilizer applications. The Mw is measured by size exclusion chromatography (SEC method) using sodium polystyrene sulfonate as a standard. Details are as described in the Examples.

[0011] The total organic carbon concentration (TOC) of the humic acid extract is 10,000 to 45,000 mg / L, preferably 11,000 to 40,000 mg / L, more preferably 11,000 to 35,000 mg / L, and even more preferably 12,000 to 35,000 mg / L. There is a strong correlation between humic acid concentration and TOC, and TOC serves as an indicator of humic acid concentration. While varying depending on the type of raw material, the humic acid concentration is estimated to be approximately 1.4 to 1.8 times the TOC. A higher humic acid concentration is more useful for transportation and secondary product manufacturing. On the other hand, higher humic acid concentrations tend to gel more easily with decreases in temperature and pH. A TOC below the upper limit can adequately suppress gelation. TOC is measured using a total organic carbon analyzer using a combustion catalytic oxidation method.

[0012] The humic acid extract of this embodiment typically contains an extraction solvent, preferably water.

[0013] The humic acid extract of this embodiment may contain nitric acid. When the humic acid extract is produced by the production method described below, the obtained humic acid extract usually contains nitric acid. The nitric acid in the humic acid extract may be in the form of free nitric acid or a salt. It is preferable that at least a portion of the nitric acid in the humic acid extract is in the form of a salt. Examples of nitric acid salts include alkali metal salts such as sodium salts and potassium salts, and ammonium salts. From the viewpoint of storage stability, alkali metal salts are preferred.

[0014] The content of free nitric acid in the humic acid extract is 1% by mass or less, preferably 0.5% by mass or less, and may be 0% by mass, relative to the total mass of the humic acid extract. When the content of free nitric acid is less than the above upper limit, the plant root growth promoting effect is excellent. The content of free nitric acid is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, relative to the total mass of the humic acid extract. When the content of free nitric acid is greater than the above lower limit, the miscibility with liquid fertilizers and the like tends to be excellent. The range of the content of free nitric acid is, for example, preferably more than 0% by mass and less than 1% by mass, more preferably 0.1% by mass or more and less than 1% by mass, and even more preferably 0.2% by mass or more and less than 0.5% by mass or more, relative to the total mass of the humic acid extract. The content of free nitric acid is measured by potentiometric titration. Details are as described in the Examples.

[0015] When the humic acid extract contains an alkali metal salt of nitric acid, the content thereof is preferably 6 to 9 mass %, more preferably 6.5 to 8.5 mass %, and even more preferably 7 to 8 mass %, calculated as potassium, relative to the total mass of the humic acid extract. If the content of the alkali metal salt is equal to or greater than the lower limit, the content of free nitric acid is likely to be equal to or less than the upper limit, and if it is equal to or less than the upper limit, the solubility of humic acid tends to be excellent.

[0016] The pH of the humic acid extract is preferably 4.5 to 9.5, more preferably 4.5 to 7.5, more preferably 4.5 to 7, and even more preferably 5 to 7. If the pH is above the lower limit, the free nitric acid content is likely to be below the upper limit. If the pH is below the upper limit, the free nitric acid content is likely to be above the lower limit.

[0017] [Method for Producing Humic Acid Extract] The humic acid extract of this embodiment can be produced, for example, by a production method including the following steps (1) to (6): (1) Adding an aqueous solution of nitric acid to 20 parts by mass of young coal, ３(2) A step of reacting the mixture obtained in the step (1) at 70 to 80°C for 1 to 3 hours to prepare a crude humic acid product. (3) A step of adding water and an alkali to the crude humic acid product to prepare a mixture having a pH of 2.0 to 4.0 and a solid-liquid ratio of 1:4 to 1:6. (4) A step of subjecting the mixture obtained in the step (3) to an extraction treatment under conditions of a liquid temperature of 40 to 80°C for 0.5 hours or more. (5) A step of subjecting the mixture obtained after the extraction treatment to solid-liquid separation and recovering the separated liquid portion. (6) A step of adding an alkali to the liquid portion to adjust the free nitric acid content to 1 mass% or less.

[0018] Young coal is coal with a lower carbon content than bituminous coal and is defined as having a carbon content of 83% by mass or less. Young coal is, for example, peat, lignite, brown coal, subbituminous coal, etc., and one or a mixture of two or more of these can be used. The nitric acid concentration of the nitric acid aqueous solution added to the young coal is, for example, 40 to 60% by mass.

[0019] In step (3), for example, water is added to the humic acid crude product so that the solid-liquid ratio is equal to or less than the target, then an alkali is added to the humic acid crude product so that the pH is the target, and further water is added as necessary to obtain a mixture with the target pH and solid-liquid ratio. Here, the solid-liquid ratio is the ratio of the amount of raw material young coal used to prepare the humic acid crude product to the amount of extraction solvent. For example, when 100 parts by mass of extraction solvent (water) is added to humic acid crude product prepared from 20 parts by mass of young coal, the solid-liquid ratio is 1:5.

[0020] Examples of alkalis include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and ammonia. Among these, alkali metal hydroxides are preferred from the viewpoint of storage stability. Alkalis may be used alone or in combination of two or more. The alkali can be selected depending on the intended use, such as using potassium hydroxide, which can be used as a fertilizer component. The alkali is added while measuring the pH. Alternatively, a test can be conducted in advance in which different amounts of alkali are added to the humic acid crude product to determine the amount of alkali to be added to achieve the desired pH, and the determined amount of alkali can then be added.

[0021] The pH of the mixture obtained in step (3) is 2.0 to 4.0, preferably 2.0 to 3.0. When the pH is within this range, precipitation is less likely to occur during component adjustment after solid-liquid separation. The solid-liquid ratio of the mixture obtained in step (3) is 1:4 to 1:6, preferably 1:5 to 1:6. When the solid-liquid ratio is within the above range, handling properties and extraction efficiency tend to be excellent.

[0022] In step (4), the liquid temperature of the mixture is brought to 40-80°C using a hot water bath or the like, and after maintaining this temperature for 0.5 hours or more, it is cooled to 40°C or below and subjected to step (5). An extraction time of 0.5 hours or more does not significantly affect the extraction efficiency of humic acid, and in consideration of work efficiency, a range of 0.5 to 1 hour is preferable. In step (5), solid-liquid separation can be performed by known methods such as centrifugation or a filter press.

[0023] In step (6), by adding an alkali to the liquid portion, at least a portion of the free nitric acid is neutralized, and the content of free nitric acid is reduced. The content of free nitric acid can be adjusted by the amount of alkali added. Examples of alkali include those similar to those described above. The liquid portion with a free nitric acid content of 1% by mass or less can be used as the humic acid extract of this embodiment. If necessary, dilution or concentration may be performed to adjust the TOC.

[0024] [Method for Promoting Plant Root Growth] In the method for promoting plant root growth of this embodiment, the above-mentioned humic acid extract is diluted with water and applied to a plant. This can promote plant root growth (root formation, etc.). Promoting plant growth expands the rhizosphere, improving the plant's ability to absorb water and nutrients from soil, etc., leading to healthy plant growth and improved crop yield and quality.

[0025] The amount of water used to dilute the humic acid extract is, for example, 40,000 to 400,000 parts by mass, preferably 50,000 to 300,000 parts by mass, per 100 parts by mass of the humic acid extract. The pH of the water-diluted humic acid extract is, for example, 6.0 to 8.0.

[0026] The type of plant is not particularly limited, and examples thereof include leafy vegetables such as komatsuna, spinach, Chinese cabbage, and lettuce, and fruit vegetables such as tomatoes, eggplants, and bell peppers. From the viewpoint of promoting the growth cycle, leafy vegetables such as komatsuna, spinach, and lettuce are preferred. The cultivation form of the plant is also not particularly limited, and examples thereof include soil cultivation and hydroponic cultivation. Soil cultivation is preferred from the viewpoint of the greater usefulness of promoting root growth.

[0027] The timing of application of the water-diluted humic acid extract can be, for example, at the time of planting. The water-diluted humic acid extract can be applied once or twice or more times. When applied twice or more times, the application interval is, for example, 1 to 4 weeks.

[0028] Fertilizer may be applied together with the water-diluted humic acid extract, or before and / or after applying the water-diluted humic acid extract. Known fertilizers can be used depending on the plant. Examples include liquid fertilizers containing all fertilizer components: three elements (nitrogen, phosphorus, potassium), secondary elements (calcium, magnesium, sulfur), and trace elements (manganese, boron, iron, copper, zinc, molybdenum, and chlorine). When applying fertilizer together with the water-diluted humic acid extract, they may be applied separately or mixed in advance.

[0029] Although the present invention has been described above using embodiments, the present invention is not limited to the above embodiments. Each configuration and their combinations in the above embodiments are merely examples, and additions, omissions, substitutions, and other modifications of configurations are possible within the scope of the present invention. For example, the content of free nitrate in the humic acid extract may be 3% by mass or less, 2% by mass or less, or 1.5% by mass or less relative to the total mass of the humic acid extract.

[0030] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0031] <Measurement Method> [pH Measurement] pH was measured by the glass electrode method. The pH was measured while stirring the suspension containing the residue of the crude humic acid product with a magnetic stirrer.

[0032] [Mass average molecular weight] The mass average molecular weight (Mw) of humic acid is measured by HPSEC (High Pressure Size Exclusion Chromatography) method (GPC method) using a Waters ACQUITY APC SYSTEM. The column was manufactured by Waters, the standard sample was sodium polystyrene sulfonate, and the detection wavelength was 260 nm. The mobile phase was a 100 mmol / L sodium phosphate buffer solution containing 20% ​​by mass acetonitrile, the flow rate was 0.3 mL / min, and the column temperature was 40 ° C (column oven setting value).

[0033] [Total Organic Carbon Concentration] The total organic carbon concentration (TOC) was measured by a combustion catalytic oxidation method using a total organic carbon meter (TOC-L manufactured by Shimadzu Corporation).

[0034] [Free nitric acid content] For the humic acid extract, a potentiometric titration was performed using a potentiometric titrator (manufactured by HIRANUMA, trade name "COM-A19S", glass electrode: GE-1010B, reference electrode: RE201, thermistor electrode: TE403) according to the following procedure to determine the content of free nitric acid. 5 g of sample was weighed into a 100 mL beaker, and ultrapure water was added up to 50 mL to prepare a measurement sample. For the measurement sample, potentiometric titration was performed using a 0.1 M NaOH aqueous solution.

[0035] <Preparation of Humic Acid Extract> [Example 1] In a draft chamber, 20 g of lignite with a carbon content of 77% by mass was placed in a 500 mL beaker, and 50.0 g of a nitric acid aqueous solution with a nitric acid concentration of 48% by mass was added. An oxidation reaction was carried out in a water bath at 80 °C for 3 hours to obtain a crude humic acid. 80 mL of water was added to the obtained crude humic acid, and 10.0 g of potassium hydroxide was added and stirred. While stirring, a 1.0 mol / L aqueous potassium hydroxide solution was appropriately added while monitoring with a pH meter to adjust the pH to 3.5. The mixture was adjusted to a constant volume of 100 mL with water (solid-liquid ratio of 1:5) and extracted at 80 °C for 1 hour. The mixture was then cooled to below 40 °C, evaporative water was added to make the total volume 100 mL, and the mixture was centrifuged at 3,500 × g for 20 minutes, and the supernatant liquid was collected. This liquid was used as the humic acid extract of Example 1. The humic acid extract of Example 1 had a humic acid Mw of 640, a TOC of 12,000 mg / L, a free nitric acid content of 1.7 mass %, and a pH of 2.3.

[0036] [Example 2] Potassium hydroxide was added to the liquid portion obtained in the same manner as in Example 1 so that the pH was 5, to obtain a humic acid extract of Example 2. The humic acid extract of Example 2 had a free nitric acid content of 0.41% by mass. The Mw and TOC of the humic acid were the same as in Example 1.

[0037] [Example 3] Potassium hydroxide was added to the liquid portion obtained in the same manner as in Example 1 so that the pH was 9, to obtain a humic acid extract of Example 3. Free nitric acid was not detected in the humic acid extract of Example 3. The Mw and TOC of the humic acid were the same as in Example 1.

[0038] <Evaluation of Plant Root Growth> Using the humic acid extract of each example as a sample, plant root growth was evaluated according to the following procedure. Seven culture media (Takii seedling culture medium) were prepared for each sample, and Komatsuna seeds were sown in each (n = 7). Two and three weeks after sowing, a water dilution of 4.4 g of sample diluted with 1,996 g of water was sprayed onto the culture media. Four weeks after sowing, Komatsuna plants were collected from the seven culture media, and the dry mass of the aboveground and underground parts (roots) was measured, and the average value and standard deviation were calculated. The dry mass was measured after drying at 105 ° C for 24 hours.

[0039] The results are shown in Figures 1 and 2. Figure 1 is a graph showing the dry mass of the above-ground parts, and Figure 2 is a graph showing the dry mass of the underground parts. For the underground parts (roots), Examples 2 and 3 had an increased dry mass compared to Example 1. The results for Example 2 were particularly excellent. For the above-ground parts, at the 4-week point, Examples 1 to 3 had the same dry mass, but because the growth of the underground parts was promoted in Examples 2 and 3, it is expected that Examples 2 and 3 will have an increased dry mass for the above-ground parts in the future.

Claims

1. A humic acid extract containing humic acid having a mass average molecular weight of 400 to 1,000, a total organic carbon concentration of 10,000 to 45,000 mg / L, and a free nitrate content of 1 mass% or less.

2. The humic acid extract according to claim 1, wherein the content of free nitric acid is 0.1% by mass or more.

3. The humic acid extract according to claim 1, having a pH of 4.5 to 7.

5.

4. The humic acid extract according to claim 1, which contains an alkali metal salt of nitric acid, and the content of said alkali metal salt is 6 to 9 mass % in terms of potassium.

5. A humic acid extract containing humic acid having a mass average molecular weight of 400 to 1,000, a total organic carbon concentration of 10,000 to 45,000 mg / L, and a free nitrate content of 3 mass% or less.

6. A method for promoting root growth of plants, comprising diluting the humic acid extract according to any one of claims 1 to 5 with water and applying the diluted extract to plants.

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