Classifications

• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
  • A01G22/00—Cultivation of specific crops or plants not otherwise provided for
  • A01G22/20—Cereals
  • A01G22/22—Rice
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K17/00—Soil-conditioning materials or soil-stabilising materials
  • C09K17/14—Soil-conditioning materials or soil-stabilising materials containing organic compounds only
  • C09K17/18—Prepolymers; Macromolecular compounds
  • C09K17/32—Prepolymers; Macromolecular compounds of natural origin, e.g. cellulosic materials

Definitions

• the present disclosure relates to iron reducing agents containing humic acid extracts, uses of the humic acid extracts, and reduction methods.
• alkaline soil which is considered unsuitable for farming, and in particular alkaline calcareous soil (calcareous alkaline soil).
• Iron is present in large quantities on the earth's surface as iron ore and iron oxide, but in calcareous alkaline soil, iron, a trace element essential for plant survival, exists as ferric hydroxide (III) and is insoluble in water.
• Insoluble trivalent iron is in a form that is difficult for plants to absorb, so in calcareous alkaline soil, plants are unable to absorb iron and are prone to iron deficiency.
• the problem of trace element deficiency in calcareous alkaline soil which accounts for 35% of cultivated land, is difficult to solve by fertilization.
• Iron is an essential trace element for plants, and contributes to various functions such as chlorophyll biosynthesis, photosynthesis, and respiration.
• crops cannot absorb iron in alkaline soil, and so they die from iron deficiency (chlorosis, a yellowing of the leaves), resulting in reduced yield and quality.
• chelated iron such as ferric ethylenediaminetetraacetate (Fe-EDTA), Fe-EDDHA, or Fe-HBED.
• Fe-EDTA ferric ethylenediaminetetraacetate
• Fe-HBED Fe-HBED
• Chelated iron is a form of iron that is easily absorbed by crops, and is therefore commonly used to improve iron deficiency (Patent Document 1).
• Chelate iron such as Fe-EDTA which is used to supply iron to crops, has excellent iron supplying properties.
• chelate compounds such as Fe-EDTA are poorly biodegradable, and unabsorbed chelate iron remains in the environment.
• ethylenediaminetetraacetic acid (EDTA) captures and solubilizes harmful heavy metals in the environment when released into the environment.
• EDTA ethylenediaminetetraacetic acid
• There are concerns that the heavy metal chelates produced may cause groundwater pollution, and are subject to regulations in Europe.
• EDDHA and HBED which are also used as iron chelating agents, are very expensive and have low versatility as agricultural materials. Therefore, there is a need to develop materials that can be used in place of such chelate compounds.
• the objective of this disclosure is to provide a material that can improve the form of iron in alkaline soil.
• an example of this embodiment is as follows.
• An iron reducing agent for reducing trivalent iron in soil to divalent iron in alkaline soil cultivation comprising a humic acid extract containing at least one selected from fulvic acid and humic acid extracted from a crude humic acid obtained by oxidizing young charcoal with nitric acid.
• the iron reducing agent according to (1) or (2), wherein the melanic index of the humic acid crude product is 2.0 to 3.
• the iron reducing agent according to any one of (1) to (3), wherein the alkaline soil cultivation is the cultivation of a grass family plant.
• the use according to (6), wherein the young coal is lignite.
• the use according to (6) or (7), wherein the alkaline soil cultivation is the cultivation of a grass family plant.
• the alkaline soil is a soil containing a calcareous component.
• This embodiment is an iron reducing agent for reducing trivalent iron to divalent iron in soil cultivated in alkaline soil, comprising a humic acid extract containing at least one selected from fulvic acid and humic acid extracted from crude humic acid obtained by oxidizing young charcoal with nitric acid.
• the insoluble trivalent iron can be reduced to divalent iron to make it easier to solubilize.
• the insolubilization of trivalent iron refers to the formation of a water-insoluble or poorly soluble compound such as hydroxide or oxide of iron (trivalent iron), and the solubilization of divalent iron refers to the ionization of iron (divalent iron) with a valence of +2 and elution as Fe 2+ .
• Divalent iron exists in the soil as a water-soluble compound such as a hydroxide compound or an oxide compound.
• soluble divalent iron compounds include iron (II) chloride, iron (II) sulfate, or iron (II) hydroxide.
• insoluble trivalent iron compounds (insoluble trivalent iron) include iron (III) chloride, iron (III) oxide, or iron (III) hydroxide.
• the iron reducing agent according to this embodiment includes a humic acid extract containing at least one selected from fulvic acid and humic acid extracted from a crude humic acid obtained by oxidizing young charcoal with nitric acid.
• the humic acid extract has excellent iron reducing power, and when applied to alkaline soil, it can effectively reduce trivalent iron in the alkaline soil to divalent iron, which is easily absorbed by crops. Therefore, when the iron reducing agent according to this embodiment is applied to alkaline soil, it is possible to reduce trivalent iron to divalent iron, improve the form of iron, and improve the supply of iron to crops.
• the iron reducing agent according to this embodiment can be produced from a naturally derived raw material (young charcoal), and therefore does not impose a burden on the environment. Furthermore, the iron reducing agent according to this embodiment is also excellent in terms of cost, since it can be produced inexpensively.
• alkaline soil refers to soil with a pH greater than 7.
• the soil pH can be obtained by adding 25 ml of distilled water to 10 g of air-dried soil, shaking for 1 hour, and measuring the pH of the resulting suspension.
• Alkaline soils include not only inherently alkaline soils, but also alkaline soils that have been made alkaline by fertilization or desertification.
• Examples of inherently alkaline soils include soils that contain various calcareous components, such as shell fossil soil, calcareous soil, and coralline soil. These calcareous components may be contained in one type, or in two or more types.
• mixed soils of alkaline soils containing these various calcareous components and non-alkaline soils, which are alkaline soils overall, are also included.
• the pH of alkaline soil is 7 or more, more than 7, preferably 7.5 or more, preferably 8 or more.
• the iron component exists as trivalent iron, so the iron reducing agent according to this embodiment can be effectively used.
• the pH of alkaline soil is, for example, 11 or less, preferably 10 or less. When the pH of alkaline soil is 11 or less, it is preferable from the viewpoint of promoting plant growth.
• alkaline soil cultivation simply means the cultivation of plants in alkaline soil.
• Soil cultivation means cultivation using natural soil or artificial soil.
• Soil cultivation includes, for example, cultivation forms such as open-field cultivation, greenhouse cultivation, and vinyl greenhouse cultivation.
• Soil cultivation also includes flooded cultivation, in which plants are grown in soil filled with water.
• the iron reducing agent according to this embodiment includes a humic acid extract containing at least one selected from fulvic acid and humic acid extracted from a crude humic acid product obtained by oxidizing young charcoal with nitric acid.
• Young coal is coal with a lower carbon content than bituminous coal and is defined as having a carbon content of 83% or less by mass.
• the carbon content of young coal is preferably 78% or less by mass. When the carbon content is 78% or less by mass, coalification is still in progress, there are still few aromatic condensed rings in the components, the proportion of condensation polymerization is small, the proportion of aliphatic hydrocarbon side chains and main chains is high, and oxidative decomposition by nitric acid is likely to proceed.
• young coal examples include brown coal (lignite), peat, and subbituminous coal. Young coal may be used alone or in combination of two or more types. Of these, brown coal (lignite) is preferably used as young coal.
• the humic acid extract contained in the iron reducing agent according to this embodiment is obtained by extracting fulvic acid and/or humic acid from a crude humic acid product obtained by oxidizing young charcoal with nitric acid.
• Humic acid can be classified into humin, which is a fraction that is insoluble in both acid and alkali, humic acid, which is soluble in alkali but insoluble in acid, and fulvic acid, which is soluble in acid.
• humic acid fraction and the fulvic acid fraction are important, and both, which have almost continuous characteristics, are collectively referred to as humic acid.
• Nitric acid oxidation of young coal can be carried out, for example, by adding 50 to 200 parts by mass of nitric acid, calculated as anhydrous, per 100 parts by mass of young coal and mixing.
• nitric acid oxidation can be carried out by adding 60 to 180 parts by mass of concentrated nitric acid, calculated as anhydrous, per 100 parts by mass of young coal and mixing. That is, the blending ratio (mass ratio) of young coal to nitric acid is, for example, 1:0.5 to 1:2, preferably 1:0.6 to 1:1.8.
• the reaction time is, for example, 20 to 180 minutes, preferably 30 to 120 minutes. After the reaction, the water can be removed by drying or the like, and crude humic acid can be obtained in a solid state.
• the melanic index of the resulting humic acid crude product can be set in the range of 2.0 to 3.
• the melanic index of the resulting humic acid crude product is 2.0 or higher, a large amount of water-soluble humic acid with active groups such as alcoholic hydroxyl groups and methoxyl groups is produced, and the extraction rate is improved.
• the melanic index is 3 or less, excessive oxidation reactions can be suppressed, and this leads to reduced costs for using nitric acid.
• the melanic index of natural humic acid is generally 1.7 or less.
• the melanic index is an index used to classify soil humic acid, and is the ratio of absorbance at wavelengths of 450 nm and 520 nm in the absorption spectrum of a sodium hydroxide extract ( Ky ⁇ ichi Kumada, Chemistry of Soil Organic Matter, 2nd Edition, Academic Press Center (1981), Japanese Journal of Soil and Plant Nutrition, Vol. 71, No. 1, pp. 82-85 (2000)).
• the Melanic Index is a method used to classify soil humic acid, but can also be applied to the analysis of crude humic acid.
• the Melanic Index in this specification is calculated by the following method.
• the sample is crushed into a 250 ⁇ m sieve using a mortar and a 250 ⁇ m sieve.
• about 0.10 g of the 250 ⁇ m sieve and 45 ml of 0.5 mol/L sodium hydroxide are placed in a 50 ml centrifuge tube, and the tube is shaken back and forth at a speed of about 100 rpm for about 1 hour at room temperature of 20°C.
• centrifugation is performed for about 10 minutes at 3,500 x g.
• the supernatant after centrifugation is filtered through filter paper (e.g., No. 5C made by Advantec).
• the absorbance of the filtrate at 450 nm and 520 nm is measured, using distilled water as a blank. In this case, if the absorbance at 450 nm is 1.0 or more, add 0.1 mol/L sodium hydroxide aqueous solution to adjust the absorbance to 0.8 or more and less than 1.0, and then measure the absorbance at 520 nm.
• the ratio of (absorbance at 450 nm/absorbance at 520 nm) is calculated and used as the melanic index.
• the melanic index can be adjusted by the amount of nitric acid and the reaction time during the production of the humic acid crude product. For example, the more nitric acid is added, the higher the melanic index tends to be. As the oxidation of young charcoal with nitric acid progresses, more humic acid having active groups such as alcoholic hydroxyl groups and methoxyl groups is produced, and the average molecular weight of the compounds produced by oxidation also becomes smaller, so that the melanic index of the resulting humic acid crude product tends to be higher.
• the melanic index of the humic acid crude product is 3.0 or less.
• the humic acid extract in this embodiment contains fulvic acid and/or humic acid extracted from the above-mentioned humic acid crude product.
• the extraction of humic acid from the humic acid crude product is not particularly limited, but can be performed at a pH of 8 or less (preferably 7 or less).
• humic acid can be extracted by adding water to the humic acid crude product and adding an alkali such as potassium hydroxide while measuring the pH to a pH of 5 to 8 (preferably 6 to 7).
• the liquid temperature is not particularly limited, but can be, for example, 40 to 90°C.
• the extraction time is not particularly limited, but can be, for example, 0.5 to 3 hours.
• the extraction can be performed under stirring. After extraction, it is preferable to cool the liquid temperature to 40°C or less.
• the unreacted residue can be separated into solid and liquid by centrifugation, filter press, etc. to obtain an extract.
• the obtained extract itself can be used as a humic acid extract, or it can be used as a humic acid extract after optionally performing purification, concentration and/or drying treatment.
• the humic acid extract of this embodiment has high solubility in water even when dehydrated and powdered, and can be powdered and used by spray drying or freeze drying.
• the humic acid extract of this embodiment may be in a liquid form (extract) or a solid form, and the concept includes both liquid and solid forms.
• humic acid By extracting humic acid from crude humic acid at, for example, a pH of 6 to 8 (preferably, pH 6.5 to 7.5), an extract containing fulvic acid and humic acid fractions can be obtained. Also, by extracting humic acid from crude humic acid at, for example, a pH of 1 to 2, a humic acid fraction can be obtained as a precipitate, and a fulvic acid fraction can be obtained as a supernatant.
• the humic acid used in the present embodiment preferably contains humic acid extracted from a crude humic acid product having a melanic index of 2.3 to 2.8, and more specifically, it preferably contains humic acid obtained by the following production method: (1) Mixing young charcoal and nitric acid in a mass ratio of 1:0.8 to 1:1.6 (nitric acid is calculated as anhydrous) to prepare a crude humic acid product having a melanic index of 2.3 to 2.8; (2) A method for producing a humic acid extract, comprising the steps of: (1) adding water and an alkali to a crude humic acid product to obtain an extract at a pH of 6 to 8; and (3) subjecting the extract obtained in (2) to solid-liquid separation to obtain a humic acid extract.
• the mixture of young charcoal and nitric acid can be reacted, for example, at 40 to 95°C (preferably 60 to 90°C) for 0.5 to 6 hours (preferably 1 to 3 hours).
• humic acid crude product preparation process it is preferable to mix young charcoal and nitric acid in a mass ratio of 1:1 to 1:1.5 (nitric acid is calculated as anhydrous).
• the melanic index of the crude humic acid product (1) is preferably 2.4 or more, and is preferably 2.7 or less, or 2.6 or less.
• the solid-liquid ratio of the humic acid crude product to water is preferably 1:3 or more.
• the solid-liquid ratio of the humic acid crude product to water is preferably 1:3 to 1:12, and more preferably 1:5 to 1:10.
• the solid-liquid ratio is the amount of extraction solvent relative to the amount of raw young coal. For example, when 100 g (100 mL) of solvent (water) is added to humic acid crude product prepared from 10 g of young coal, the solid-liquid ratio is 1:10.
• the extraction temperature is, for example, 40 to 95°C (preferably 60 to 90°C), and the extraction time is, for example, 0.5 to 24 hours.
• the total organic carbon (TOC) concentration of the extract can be measured, for example, by the following method.
• the supernatant obtained by centrifuging the humic acid extract at 3,000 x g is measured using a total organic carbon meter (TOC-L manufactured by Shimadzu Corporation) using a combustion catalytic oxidation method.
• the total organic carbon concentration is not a direct quantitative value of humic acid.
• TOC which is easily quantifiable, can be used as an indicator of humic acid concentration.
• the amount of humic acid can generally be estimated to be 1.4 to 1.8 times the amount of the total organic carbon concentration.
• the total organic carbon concentration of the extract can be adjusted by changing the solid-liquid ratio of the humic acid crude product and the solvent.
• the higher the melanic index, the higher the extraction rate, and this method can also be used to adjust the amount of organic carbon in the extract.
• the iron reducing agent according to this embodiment contains the humic acid extract and can be used to reduce trivalent iron in soil in alkaline soil cultivation to divalent iron.
• the iron reducing agent according to this embodiment can be a composition containing the humic acid extract.
• the iron reducing agent according to this embodiment may be in a solid form or in a liquid form.
• the iron reducing agent according to this embodiment may be in a concentrated liquid form, and may be diluted and applied at the time of use.
• the iron reducing agent according to this embodiment may be in a form containing only the humic acid extract alone, or may further contain any other material in addition to the humic acid extract as long as the effect of this embodiment is not substantially impaired.
• other materials include solvents, carriers, pH adjusters, surfactants, fertilizer components such as minerals, pesticide components, binders, or bulking agents.
• components that are generally used in pesticides or fertilizers can be used as these components. These may be used alone or in combination of two or more types.
• the carrier when the iron reducing agent according to this embodiment is in a solid form, the carrier may be an inorganic material such as vermiculite, talc, diatomaceous earth, kaolin, calcium carbonate, clay, calcium hydroxide, white earth, silica gel, or a solid carrier such as wheat flour or starch.
• the solvent as the other material is preferably water or an alcohol (e.g., ethanol or ethylene glycol).
• the iron reducing agent according to this embodiment is in a solid form
• its shape and size are not particularly limited, but from the standpoint of ease of production, ease of spreading on soil, etc., it is preferable for it to be in the form of granules with a particle size of 1 to 10 mm (preferably 2 to 4 mm).
• the humic acid extract used in the iron reducing agent of this embodiment is more useful when it is transported or used to manufacture secondary products, as long as it has a high concentration.
• a total organic carbon concentration of 5,000 to 50,000 mg/L is preferred, and 10,000 to 45,000 mg/L is more preferred.
• the iron reducing agent according to the present embodiment can reduce trivalent iron in alkaline soil to divalent iron by application to alkaline soil.
• the humic acid extract according to the present embodiment has an excellent iron reducing action, and can effectively reduce trivalent iron to divalent iron.
• divalent iron that is easily soluble is generated, and Fe 2+ , which is a form available to plants, is increased, so that iron deficiency symptoms in plants can be treated, improved, prevented, suppressed or alleviated.
• various iron deficiency symptoms in crop cultivation in alkaline soil containing calcareous components can be improved, prevented, suppressed or alleviated.
• Iron deficiency symptoms refer to various growth disorders that occur when the content of iron, an element essential for plant survival, is insufficient, or when iron is present in a form that is difficult to utilize due to oxidation or the formation of a compound with some substance, making it impossible for plants to use it for vital activities.
• Symptoms include chlorosis, in which the synthesis of chloroplasts is hindered and leaves turn yellowish white, and reduced crop yield and quality caused by nutritional deficiency due to chlorosis.
• Application to soil is not particularly limited, but can be done, for example, by spraying, dripping, irrigation, or mixing into soil.
• the plants to be cultivated are not particularly limited, and may be monocotyledonous or dicotyledonous plants. They may also be trees or herbs. They may also be wild plants, or agricultural, horticultural, or forestry plants. Agricultural, horticultural, or forestry plants include, for example, crops (including fruit vegetables), grains, ornamental plants, flowers, and fruit trees.
• the target plants are not particularly limited, but examples thereof include Gramineae, Liliaceae, Palmaceae, Solanaceae, Brassicaceae, Apiaceae, Asteraceae, Amaryllidaceae, Amaranthaceae, Leguminosae, Cucurbitaceae, etc.
• examples of such plants include the following: Gramineae: rice (Oryza sativa), corn (Zea mays), barley (Hordeum vulgare), wheat (Triticum aestivum), rye (Secale cereale), pearl barley (Coix lacryma-jobi var.
• Palm family oil palm (Elaeis guineensis, Elaeis oleifera), coconut palm (Cocos nucifera), date palm (Phoenix dactylifera), wax palm (Copernicia).
• Solanaceae tomato (Solanum lycopersicum), eggplant (Solanum melongena), pepper (Capsicum annuum), potato (Solanum tuberosum).
• Brassicaceae cabbage (Brassica oleracea), bok choy (Brassica rapa). Apiaceae; Carrot (Daucus carota).
• Asteraceae Lettuce (Lactuca sativa).
• Amaryllidaceae onion (Allium cepa), leek (Allium fistulosum).
• Amaranthaceae Spinach (Spinacia oleracea).
• Legumes soybean (Glycine max), adzuki bean (Vigna angularis).
• Cucurbitaceae cucumber (Cucumis sativus), pumpkin (Cucurbita sp.).
• the amount of the iron reducing agent used in this embodiment is not particularly limited, and can be set appropriately depending on the concentration of the active ingredient (humic acid extract), application time, weather conditions, number of applications, plant type, cultivation density, growth stage, application method, etc.
• the iron reducing agent according to this embodiment may be applied together with or mixed with fertilizers (three-element fertilizer, dolomite lime, shell fossils, calcium silicate, bark compost, etc.) and soil conditioners (zeolite, diatomaceous earth, green tuff, humic acid materials, vermiculite, peat moss, etc.) typically used in agricultural work.
• fertilizers three-element fertilizer, dolomite lime, shell fossils, calcium silicate, bark compost, etc.
• soil conditioners zeolite, diatomaceous earth, green tuff, humic acid materials, vermiculite, peat moss, etc.
• Another aspect of this embodiment is the use of a humic acid extract containing at least one selected from fulvic acid and humic acid extracted from a crude humic acid product obtained by oxidizing young charcoal with nitric acid, in order to reduce trivalent iron in soil cultivated in alkaline soil to divalent iron.
• the humic acid extract in this embodiment has excellent iron reducing power, and therefore can be used to reduce trivalent iron in soil cultivated in alkaline soil to divalent iron.
• one aspect of this embodiment is a method for reducing trivalent iron in soil cultivated in alkaline soil to divalent iron, the method including a step of applying to the soil a humic acid extract containing at least one selected from fulvic acid and humic acid extracted from a crude humic acid obtained by oxidizing young charcoal with nitric acid.
• the humic acid extract in this embodiment has excellent iron reducing power, and therefore, by applying the humic acid extract to soil cultivated in alkaline soil, trivalent iron can be reduced to divalent iron.
• humic acid extract E1 (humic acid extract E1)
• nitric acid nitric acid with a concentration of 48% by mass was added.
• an oxidation reaction with nitric acid was carried out in a water bath at 70° C. for about 1 hour, the mixture was dried at 105° C. to obtain a crude humic acid product.
• the melanic index was measured by the above-mentioned method and found to be 2.2.
• Example 2 Human acid extract E2
• the amount of nitric acid added was 1350 g, and about 100 mL of potassium hydroxide solution (0.5 mol/L) was added during extraction, and an appropriate amount of potassium hydroxide solution (1.0 mol/L) was added to adjust the pH to 2.0.
• An extract was prepared in the same manner as in Example 1 (humic acid extract E2). The melanic index of the humic acid crude product was 2.5.
• Example 3 Human Acid Extract E3 and Humic Acid Extract E4
• a humic acid extract was prepared in the same manner as in Example 1, except that the amount of nitric acid added was 1,350 g.
• the obtained humic acid extract was purified according to the International Humic Substances Society method (IHSS method) and fractionated and purified into a humic acid fraction (Example 3) or a fulvic acid fraction (Example 4).
• IHSS method International Humic Substances Society method
• the humic acid fraction may also be referred to as purified humic acid
• the fulvic acid fraction may also be referred to as purified fulvic acid.
• humic acid extract E3 6N hydrochloric acid was added to the obtained humic acid extract to adjust the pH to approximately 1.0, and the mixture was stirred for 1 hour and then centrifuged (3000g, 10 minutes) to obtain a precipitate fraction. Next, distilled water was added to the precipitate fraction, and the mixture was centrifuged at 3000g for 10 minutes to obtain a precipitate fraction, which was then washed. This washing process was performed three times in total. The precipitate fraction obtained after the three washes was dissolved in water and obtained as a purified humic acid fraction (humic acid extract E3) (Example 3).
• the supernatant obtained by the above centrifugation (3000 g, 10 minutes) was passed through a column (volume ⁇ 2.5 ⁇ 20 cm) packed with XAD-8 resin to adsorb the colored substances, and the resin was washed with 0.65 column volumes of distilled water.
• the flow rate was 15 bed volumes per hour, and the non-adsorbed fraction and the washing fraction were discarded.
• 1 column volume of sodium hydroxide aqueous solution (0.1 N) and then 2 to 3 column volumes of distilled water were passed through the column to desorb the adsorbed fraction, and a purified fulvic acid fraction (humic acid extract E4) was obtained (Example 4).
• the TOC (total organic carbon) concentrations of the humic acid extracts E1 and E2 prepared in Examples 1 and 2, the humic acid extract E3 (purified humic acid) prepared in Example 3, the humic acid extract E4 (purified fulvic acid) prepared in Example 4, and the humic acid extract C1 prepared in Comparative Example 1 are shown in Table 1. The concentrations are listed as TOC concentrations.
• Test 1 (Test 1-1: Humic acid extract E1)
• the test crop was rice (variety: Hitomebore), and a cultivation test of the humic acid extract was conducted using hydroponic cultivation.
• iron (III) chloride was added to the above hydroponic solution (Table 2) to a concentration of 50 ⁇ M
• humic acid extract E1 prepared in Example 1 was added to a TOC concentration of 20 mg/L
• the pH was adjusted to 8.0 with sodium hydroxide solution.
• the cultivation period was 28 days, the pH was adjusted to 8.0 every day with sodium hydroxide solution, and the hydroponic solution was replaced with the same hydroponic solution every 3 days.
• the crops were evaluated after cultivation (28 days after sowing). Specifically, the SPAD value (measured with a Konica Minolta SPAD-502Plus chlorophyll meter), number of tillers, plant height, and dry weight were measured as evaluation items, and the total iron concentration in the upper and lower leaves of the plant body was also measured (evaluation of iron absorption).
• the total iron content of the leaves was measured using the following method. Five upper leaves and five lower leaves were crushed to prepare samples. 30-50 mg of the crushed sample was weighed into a beaker, 5 ml of nitric acid and 0.2 ml of sulfuric acid were added, and the mixture was heated and decomposed on a hot plate, then the volume was adjusted to 10 ml to prepare the test solution. The iron content of the test solution was measured using ICP atomic emission spectrometry (Agilent 5110VDV).
• Test 1-2 Humic acid extract E2
• Crops were grown hydroponically and evaluated in the same manner as in Test 1-1, except that, instead of adding the humic acid extract E1 prepared in Example 1 to the hydroponic solution so that the TOC concentration was 20 mg/L, the humic acid extract E2 prepared in Example 2 was added to the hydroponic solution so that the TOC concentration was 20 mg/L.
• Test 1-3 Control
• Crops were grown hydroponically and evaluated in the same manner as in Test 1-1, except that the humic acid extract E1 prepared in Example 1 was not added to the hydroponic solution.
• humic acid extracts E1 and E2 were found to maintain normal leaf color when rice was grown under alkaline conditions. Iron deficiency symptoms were characterized by upper leaves turning yellowish-white and a decrease in SPAD value. Whereas the SPAD value of upper leaves in the control decreased, the application of humic acid extracts E1 or E2 maintained a high SPAD value for upper leaves.
• Test 2 The test crop was rice (variety: Hitomebore), and a cultivation test was carried out using the humic acid extract in hydroponic cultivation.
• the hydroponic solution was prepared by dissolving each material in ion-exchanged water so as to have the composition shown in Table 2.
• Test 2-2 Humic acid extract E4
• Crops were grown hydroponically and evaluated in the same manner as in Test 2-1, except that, instead of adding the humic acid extract E3 prepared in Example 3 to the hydroponic solution so that the TOC concentration was 25 mg/L or 50 mg/L, the humic acid extract E4 prepared in Example 4 was added to the hydroponic solution so that the TOC concentration was 20 mg/L.
• Test 2-3 Crops were hydroponically grown and evaluated in the same manner as in Test 2-1, except that the humic acid extract E3 prepared in Example 3 was not added to the hydroponic solution.
• humic acid extracts E3 and E4 maintained normal leaf color when rice was grown under alkaline conditions. Iron deficiency symptoms were characterized by upper leaves turning yellowish-white and a decrease in SPAD value. Whereas the SPAD value of upper leaves in the control decreased, the application of humic acid extracts E3 or E4 maintained a high SPAD value in upper leaves.
• Test 3 The test crop was rice (variety: Hitomebore), and a cultivation test was carried out using the humic acid extract in hydroponic cultivation.
• the hydroponic solution was prepared by dissolving each material in ion-exchanged water so as to have the composition shown in Table 2.
• Test 3-1 Humic acid extract E3
• ion-exchanged water was placed in a 5 L plastic container, and the seeds that had been subjected to the germination treatment were sown on a stainless steel cultivation plate. From the 7th day after sowing, the seeds were cultivated in 3.5 L of the above hydroponic solution (Table 2).
• the above hydroponic solution (Table 2) was used with iron (III) chloride added to a concentration of 50 ⁇ M, humic acid extract E3 (purified humic acid) prepared in Example 3 added to a TOC concentration of 25 mg/L, and the pH adjusted to 8.0 with sodium hydroxide solution.
• the cultivation period was 28 days, with the pH adjusted to 8.0 every day using sodium hydroxide solution, and the hydroponic solution was replaced every 3 days.
• the SPAD value was also measured three times a week from the 14th day after sowing.
• Test 3-2 Control
• Crops were grown hydroponically and evaluated in the same manner as in Test 3-1, except that, instead of adding the humic acid extract E3 prepared in Example 3 so that the TOC concentration was 25 mg/L, the humic acid extract C1 prepared in Comparative Example 1 was added so that the TOC concentration was 25 mg/L.
• Test 3-3 Reference
• Fe-EDTA which is known as an iron chelating agent
• 50 ⁇ M iron (III) hydroxide
• Test 3-4 Control
• Crops were hydroponically grown and evaluated in the same manner as in Test 3-1, except that the humic acid extract E3 prepared in Example 3 was not added to the hydroponic solution.
• humic acid extract E3 has the effect of maintaining the leaf color of the newest leaves until the end of cultivation, even when cultivated under alkaline conditions.
• This purified humic acid showed the same effect as Fe-EDTA, which is known to supply iron to plants through its iron chelating effect.
• humic acid extract E3 showed an effect of increasing the number of tillers even when cultivated under alkaline conditions.
• humic acid extract E3 showed an effect of increasing plant height when cultivated under alkaline conditions.
• humic acid extract E3 increased aboveground dry weight compared to the control when grown under alkaline conditions.
• humic acid extract E3 showed an increase in underground dry matter weight compared to the control when grown under alkaline conditions.
• Test 4-1 Humic acid extract E3
• the seedlings were grown in water for 5 days and transplanted one by one into one pot. Two pots were placed in a 5 L plastic container, and water was added so that the soil surface was completely submerged. The amount of water was adjusted so that the water level was always 3 cm above the soil surface.
• humic acid extract E3 was added to the water in an amount that resulted in 25 mg of TOC per liter (25 mg/L addition amount) or 50 mg of TOC per liter (50 mg/L addition amount) to allow the water to contain humic acid extract. No decrease in pH was observed due to the addition of humic acid extract E3 and Na-EDTA.
• Test 4-2 Reference
• Crops were grown in soil and evaluated in the same manner as in Test 4-1, except that instead of adding the humic acid extract E3 prepared in Example 3 to the water, Na-EDTA, known as an iron chelating agent, was added to the water at a concentration of 30 ⁇ M.
• Test 4-3 Control
• Crops were grown in soil and evaluated in the same manner as in Test 4-1, except that the humic acid extract E3 prepared in Example 3 was not added to the water.
• humic acid extract E3 As shown in Table 22, when grown in alkaline calcareous soil, application of humic acid extract E3 was found to have an effect of increasing plant height compared to the control. Application of humic acid extract E3 also showed the same effect as application of Na-EDTA.
• humic acid extract E3 As shown in Table 24, when grown in alkaline calcareous soil, application of humic acid extract E3 increased underground dry matter weight compared to the control. Application of humic acid extract E3 also showed the same effect as application of Na-EDTA.
• the cultivated crop was wheat, and the variety used was Norin 61.
• the soil used was a mixture of shell fossil soil (pH 8.9, containing 1.7% iron, Nihonkai Fertilizer Co., Ltd.) and perlite (Fuyolite No. 2) (Fuyo Perlite Co., Ltd.) in a volume ratio of 7:3, and the fertilizer component was ELT40.
• the pot used for cultivation was a polyvinyl chloride pot ( ⁇ 12 cm, height 10 cm, capacity 830 cm) (Tokai Chemical Industry Co., Ltd.), and the pot was used for cultivation with a mixture of soil (shell fossil soil 620.12 g, perlite 23.39 g: 764.3 cm 3 ) and the above fertilizer ELT40 (1.14 g).
• the pH after the addition of the fertilizer components was 8.8.
• Test 5-1 Humic acid extract E3
• Wheat seeds were soaked in RO water in the dark at 10°C for 3 days, and then placed under light at 25°C for about 1 day to promote acclimation and germination. Germinated seeds were sown one by one in pots, and 10 pots were cultivated per test plot. Irrigation was performed by bottom irrigation, and the water level was maintained at about 0.5 to 1 cm so that the bottom of the pot was always submerged in water.
• humic acid extract E3 was added in an amount that resulted in a TOC content of 50 mg/L or 200 mg/L (50 mg/L and 200 mg/L addition areas).
• Test 5-2 Reference
• Na-EDTA which functions as a chelating agent for iron ions
• Test 5-3 Control
• the iron reducing power of the humic acid extracts E1 to E4 and C1 prepared in Examples 1 to 4 and Comparative Example 1 was measured.
• an Oxi Select TM FRAP assay kit (Cosmo Bio Co., Ltd.) was used.
• a reduction reaction from trivalent iron to divalent iron is carried out by the electron donor in the humic acid extract tested.
• the amount of divalent iron produced is shown in the table as the iron reducing power.
• the humic acid extracts E1 to E4 of Examples 1 to 4 exhibited higher iron reducing power than the humic acid extract of Comparative Example 1, and in particular, the humic acid extract E3 (purified humic acid) of Example 3 exhibited high iron reducing power. It was found that the humic acid extracts of the Examples are iron reducing agents that increase the availability of iron to plants by reducing insoluble trivalent iron present in alkaline soils such as calcareous soils to soluble divalent iron.
• the orthophenanthroline colorimetric method was used to measure divalent iron. This method utilizes the color produced by the chelate between orthophenanthroline and divalent iron to quantify the amount of divalent iron.
• the humic acid extract of this embodiment has an excellent iron-reducing effect, and has the ability to reduce insoluble trivalent iron in alkaline soil to divalent iron, thereby solubilizing iron and promoting healthy plant growth.
• application of a humic acid extract improves chlorosis, a typical iron deficiency symptom in plants, and the humic acid extract has high activity in reducing trivalent iron to divalent iron, increasing the divalent iron content in alkaline soil, and application of humic acid under alkaline conditions improves the iron absorption ability of plants.
• the humic acid extract of this embodiment has an iron-reducing effect in calcareous alkaline soil. Therefore, the humic acid extract of this embodiment can be used as an excellent iron reducing agent.
• the upper and/or lower limit values of the numerical ranges described in this specification can be arbitrarily combined to define a preferred range.
• the upper and lower limit values of the numerical ranges can be arbitrarily combined to define a preferred range
• the upper limit values of the numerical ranges can be arbitrarily combined to define a preferred range
• the lower limit values of the numerical ranges can be arbitrarily combined to define a preferred range.

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