Soil conditioners and their use

Abstract

The present invention provides soil conditioners, nitrification inhibitors, fertilizers, and methods for inhibiting nitrification, which can be used in a wide range of regions from tropical to temperate zones and utilize compounds or derivatives thereof that can be easily obtained from naturally derived materials. [Solution] A soil conditioner comprising one or more compounds selected from the group consisting of 5-hydroxy-2-methyl-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, and 2,7-dimethoxy-1,4-naphthoquinone, or salts thereof, or solvates thereof, as an active ingredient.

Description

[Technical Field]

[0001] This invention relates to a soil conditioner and its use. More specifically, it relates to a soil conditioner, a fertilizer, a method for producing the active ingredient of a soil conditioner, and a method for inhibiting nitrification. [Background technology]

[0002] Ammonia nitrogen, including ammonia, ammonium salts, and urea contained in chemical fertilizers, as well as ammonia nitrogen produced by the decomposition of organic fertilizers, is easily converted into nitrate nitrogen in the soil, especially under oxidative conditions such as the surface layer of fields and paddy fields.

[0003] This process, called nitrification, occurs through the action of nitrifying bacteria such as nitrite bacteria and nitrate bacteria, as well as archaea. The resulting nitrite and nitrate ions are not adsorbed by soil colloids, but are released into groundwater as nitrate nitrogen, or, through denitrification in the soil, are released into the atmosphere as nitrous oxide, a powerful greenhouse gas that is a major concern. For this reason, in oxidative soil conditions with strong nitrification, the utilization rate of applied nitrogen fertilizer by crops is very low, and the diffusion of nitrate nitrogen and nitrous oxide produced by nitrification into the environment is also a cause of natural environment pollution.

[0004] However, since the application of chemical fertilizers that chemically fix nitrogen from the air is the most reliable method for dramatically increasing crop production, a considerable amount of nitrogen fertilizer is applied to farmland. For this reason, under limited environmental conditions, compounds with nitrification-inhibiting activity, or fertilizers containing these compounds, such as nitrapyrin (2-chloro-6-trichloromethylpyridine) or synthetic agents such as dicyandiamide described in Patent Document 1, have been conventionally used.

[0005] In tropical regions, it is known that nitrification is suppressed in soil where creeping signal grass (Brachiaria humidicola), a tropical grass forage crop, grows (Non-Patent Document 1), and the invention described in Patent Document 2, which utilizes this phenomenon, is known. In addition, among common grains, sorgoleon secreted from the roots of sorghum is known to have nitrification-inhibiting activity (Non-Patent Document 2). Furthermore, the invention described in Patent Document 3, which utilizes the nitrification-inhibiting activity of fatty acids and fatty acid derivatives, is also known. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] GV Subbarao, T. Ishikawa, O. Ito, K. Nakahara, HY Wang, WL Berry, A bioluminescence assay to detect nitrification inhibitors released from plant roots: a case study with Brachiaria humidicola. Plant and Soil 288(1-2), 101-112, 2006. [Non-Patent Document 2] T. Tesfamariam, H. Yoshinaga, SP Deshpande, PS Rao, KL Sahrawat, Y. Ando, ​​K, Nakahara, CT Hash, GV Subbarao, Biological nitrification inhibition in sorghum; the role of sorgoleone production. Plant and Soil 379 (1-2), 325-335, 2014. [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-278973 [Patent Document 2] Patent No. 5408478 [Patent Document 3] Patent No. 5067520 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, nitrapyrine is highly volatile and is known to be largely ineffective at soil temperatures above 20°C, so dicyandiamide has been primarily used. Dicyandiamide can be used at higher temperatures compared to nitrapyrine. However, it requires high concentrations and is expensive, significantly impacting agricultural production costs. Therefore, the use of dicyandiamide is limited to specific regions. Furthermore, following the detection of dicyandiamide in New Zealand dairy products in 2013, New Zealand has regulated the use of dicyandiamide-containing fertilizers on pastures. Conventional nitrification inhibitors are synthetic drugs and not found in nature, so there is growing expectation for alternative nitrification inhibitors derived from natural sources that are expected to have a relatively low environmental impact.

[0009] There have been no reports on the inhibition of nitrification in maize, an important grain produced in fields with oxidized soil. Furthermore, there are no reports on the nitrification inhibitory activity of 1,4-naphthoquinones, which have been isolated from various plants and exhibit diverse physiological activities.

[0010] In view of the above problems, the present invention aims to provide a soil conditioner, nitrification inhibitor, fertilizer, and method for inhibiting nitrification that can be used in a wide area from tropical to temperate regions and utilize compounds or derivatives thereof that can be easily obtained from naturally derived materials. Furthermore, having found that the content of this substance differs greatly among maize varieties, the invention aims to inhibit soil nitrification by utilizing appropriate maize varieties. [Means for solving the problem]

[0011] The present invention includes the following embodiments. [1] A soil conditioner comprising a compound represented by the following formula (1), a salt thereof, or a solvate thereof as an active ingredient.

[0012] [ka] [In formula (1), R 1 ~R 6 Each of these independently represents a C1-C5 hydrocarbon group which may have substituents, a C1-C5 alkoxy group which may have substituents, an amino group, a hydroxyl group, a halogen atom, or a hydrogen atom.

[0013] [2] The compound represented by formula (1) is one or more selected from the group consisting of 1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 5-hydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 5-hydroxy-2-methyl-1,4-naphthoquinone, 2,3-dichloro-1,4-naphthoquinone, 2-methoxy-1,4-naphthoquinone, 2-amino-3-chloro-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, 6-methyl-1,4-naphthoquinone, 2-chloro-1,4-naphthoquinone, and 2,7-dimethoxy-1,4-naphthoquinone. [1] The soil conditioner described above. [3] A soil conditioner according to [1] or [2] that has a nitrification inhibitory effect. A fertilizer containing any of the soil conditioners listed in [4], [1], or [3]. [5] A method for producing the active ingredient of a soil conditioner according to any one of [1] to [3], comprising immersing the root surface of corn in an organic solvent to obtain a root extract and purifying the root extract by chromatography. A method for inhibiting soil nitrification, comprising cultivating a plant that produces the active ingredient of a soil conditioner described in any of [6][1] to [3]. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide soil conditioners, nitrification inhibitors, fertilizers, and methods for inhibiting nitrification that can be used in a wide range of regions from tropical to temperate zones and utilize compounds or derivatives thereof that can be easily obtained from naturally derived materials. [Brief explanation of the drawing]

[0015] [Figure 1] This is the ultraviolet-visible absorption spectrum of a compound produced from an extract of the surface of corn roots. [Figure 2] This is the electrospray ionization mass spectrum of a compound produced from an extract of the surface of corn roots. [Figure 3] This is the 1H-NMR spectrum of a compound produced from an extract of the surface of corn roots. [Figure 4] This is the 13C-NMR spectrum of a compound produced from an extract of the surface of corn roots. [Figure 5] This is a dose-response curve for nitrification inhibition by 2,7-dimethoxy-1,4-naphthoquinone. [Figure 6] This graph shows the content of 2,7-dimethoxy-1,4-naphthoquinone obtained from the roots of 11 maize varieties. [Modes for carrying out the invention]

[0016] The inventors of this invention have observed that a hydrophobic extract from the surface of corn roots has a strong inhibitory effect on nitrification. Based on this observation, they hypothesized that some kind of nitrification-inhibiting substance is released from corn roots and have been diligently conducting research. As a result, we isolated and obtained a nitrification-inhibiting substance, determined its chemical structure, and further confirmed that the isolated compound has a nitrification-inhibiting effect, thus completing the invention. Specifically, the isolated compound of the present invention is a 1,4-naphthoquinone derivative represented by the following formula (2), namely 2,7-dimethoxy-1,4-naphthoquinone (hereinafter sometimes referred to as "zeanone").

[0017] [ka]

[0018] Furthermore, as described later in the examples, the nitrification inhibitory activity of derivatives structurally similar to 2,7-dimethoxy-1,4-naphthoquinone (zeanone) was investigated. As a result, nitrification inhibitory activity was observed in the derivatives shown in Table 1. These 1,4-naphthoquinone derivatives can also be used for nitrification inhibition, similar to zeanone. In Table 1, R 1 ~R 6 These are, respectively, R in the general formula (1) above. 1 ~R 6 That is the case.

[0019] [Table 1]

[0020] 2,7-Dimethoxy-1,4-Naphthoquinone (Zeanone) is a substance isolated from corn grown in fields with widely fertilized conditions and where the soil is oxidized and prone to nitrification. Because Zeanone has low volatility, it is thought to be less affected by nitrification inhibition due to ambient temperature, making it more versatile than nitrapyrin and other compounds already in use. Many derivatives of this compound have also been reported as plant components, and as will be described later in the examples, they have been confirmed to have nitrification-inhibiting effects. By selecting appropriate plants containing these substances, it is possible to suppress soil nitrification, increase nitrogen utilization efficiency, and prevent adverse effects of nitrification such as the generation of nitrous oxide from the soil and the runoff of nitrate nitrogen into groundwater.

[0021] [Soil conditioner] In one embodiment, the present invention provides a soil conditioner comprising a compound represented by the following formula (1), a salt thereof, or a solvate thereof as an active ingredient. The soil conditioner of this embodiment, by containing this active ingredient, provides a practically useful nitrification inhibitory effect. In this specification, the compound represented by the following formula (1) may be referred to as a 1,4-naphthoquinone derivative.

[0022] [Chemical formula] [In formula (1), R 1 ~R 6 each independently represents a hydrocarbon group having 1 to 5 carbon atoms which may have a substituent, an alkoxy group having 1 to 5 carbon atoms which may have a substituent, an amino group, a hydroxy group, a halogen atom, or a hydrogen atom.]

[0023] In the above general formula (1), the hydrocarbon group having 1 to 5 carbon atoms which may have a substituent in R 1 ~R 6 is a saturated hydrocarbon group or an unsaturated hydrocarbon group, and is preferably a saturated hydrocarbon group. The hydrocarbon group having 1 to 5 carbon atoms which may have a substituent may be linear, branched, or cyclic. The hydrocarbon group is preferably linear or branched, and more preferably linear. As the hydrocarbon group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms is preferable. Examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, and the like. The number of carbon atoms of the hydrocarbon group is preferably 1 to 3. The hydrocarbon group is more preferably a methyl group or an ethyl group, and still more preferably a methyl group. When the hydrocarbon group has a substituent, examples of the substituent include a halogen atom.

[0024] In the above general formula (1), as the alkoxy group having 1 to 5 carbon atoms which may have a substituent (-OR) in R 1 ~R 6 , the R part of -OR is the same as those of the hydrocarbon groups having 1 to 5 carbon atoms which may have a substituent described above. The alkoxy group (-OR) is more preferably a methoxy group or an ethoxy group, and even more preferably a methoxy group.

[0025] In the above general formula (1), R 1 ~R 6 The halogen atom in may be a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, with a chlorine atom being preferable.

[0026] In the above general formula (1), R 1 It is preferable that the group is a group other than a hydroxyl group.

[0027] The compound represented by the above general formula (1) may be one compound alone or two or more compounds.

[0028] From the viewpoint of nitrification inhibitory activity, the following compounds (1-1), (1-2), and (1-3) are preferred as compounds represented by the above general formula (1). Compound (1-1):R 3 ~R 6 at least one of them is a hydroxyl group Compound (1-2):R 1 or R 2 Those whose atoms are halogen atoms Compound (1-3):R 3 ~R 6 At least one of them is a C1-C5 alkyl group which may have substituents. I will explain these in detail.

[0029] <Compound (1-1)> Compound (1-1) is a compound represented by the above general formula (1), where R 3 ~R 6 At least one of them is a hydroxyl group. In compound (1-1), R 3 It is preferable that it is a hydroxyl group.

[0030] R3 If is a hydroxyl group, then R 1 and R 2 Each of these may be a hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, or a hydrogen atom. R 1 and R 2 However, if both are hydrogen atoms, R 6 It is preferable that this is a hydroxyl group or a hydrogen atom. Furthermore, R 4 and R 5 Each of these is preferably a hydrogen atom, R 4 and R 5 It is more preferable that all of these are hydrogen atoms.

[0031] Alternatively, R 3 If is a hydroxyl group, compound (1-1) may be as follows: R 1 and R 2 Each of these is preferably a hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, and R 1 and R 2 Either one of them is a hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, and the other is more preferably a hydrogen atom, R 1 R is a hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, and 2 It is more preferable that R is a hydrogen atom. 6 It is preferable that it be a hydrogen atom. R 1 and R 2 In this, the hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, is either a saturated hydrocarbon group or an unsaturated hydrocarbon group, and is preferably a saturated hydrocarbon group. The hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, may be linear, branched, or cyclic. The hydrocarbon group is preferably linear or branched, and more preferably linear. As the hydrocarbon group having 1 to 5 carbon atoms, alkyl groups having 1 to 5 carbon atoms are preferred. Examples of alkyl groups having 1 to 5 carbon atoms include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, isopentyl, and neopentyl groups. The number of carbon atoms in the hydrocarbon group is preferably 1 to 3. The hydrocarbon group is more preferably a methyl group or an ethyl group, and even more preferably a methyl group. If the hydrocarbon group has substituents, examples of substituents include halogen atoms. Furthermore, R 4 and R 5 Each of these is preferably a hydrogen atom, R 4 and R 5 It is more preferable that all of these are hydrogen atoms.

[0032] Alternatively, R 3 If is a hydroxyl group, compound (1-1) may be as follows: R 1 ~R 2 These may each be a halogen atom or a hydrogen atom. R 1 ~R 2 Each of these is preferably a halogen atom, R 1 and R 2 Preferably, all of them are halogen atoms. R 1 and R 2 These are all halogen atoms, and furthermore, R 6 It is preferable that it is a hydroxyl group. The halogen atom may be a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, with a chlorine atom being preferred. Furthermore, R 4 and R 5 Each of these is preferably a hydrogen atom, R 4 and R 5 It is more preferable that all of these are hydrogen atoms.

[0033] Examples of compound (1-1) include 5-hydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 5-hydroxy-2-methyl-1,4-naphthoquinone, and 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone. Among these, 5-hydroxy-2-methyl-1,4-naphthoquinone and 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone are preferred.

[0034] <Compound (1-2)> Compounds (1-2) are compounds represented by the above general formula (1), where R 1 or R 2 However, these are halogen atoms. R 1 ~R 2 R 1 and R 2 Preferably, at least one of them is a halogen atom, R 1 and R 2 It is more preferable that all of them are halogen atoms. The halogen atom may be a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, with a chlorine atom being preferred.

[0035] Furthermore, R 3 It is preferably a hydroxyl group or a hydrogen atom, and more preferably a hydroxyl group. Furthermore, R 4 and R 5 Each of these is preferably a hydrogen atom, R 4 and R 5 It is more preferable that all of them are hydrogen atoms. Furthermore, R 6 It is preferably a hydroxyl group or a hydrogen atom, and more preferably a hydroxyl group.

[0036] Examples of compounds (1-2) include 2,3-dichloro-1,4-naphthoquinone, 2-amino-3-chloro-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, and 2-chloro-1,4-naphthoquinone. Among these, 2,3-dichloro-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, and 2-chloro-1,4-naphthoquinone are preferred. Among these, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone is more preferred.

[0037] <Compound (1-3)> Compounds (1-3) are compounds represented by the above general formula (1), where R 3 ~R 6 At least one of these is a hydrocarbon group having 1 to 5 carbon atoms, which may have substituents. In compounds (1-3), R 4 and R 5 Each of these is preferably a hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, and R 4 and R 5 It is more preferable that one of the members is a hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, and the other is a hydrogen atom.

[0038] A hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, is either a saturated hydrocarbon group or an unsaturated hydrocarbon group, and is preferably a saturated hydrocarbon group. The hydrocarbon group having 1 to 5 carbon atoms, which may have substituents, may be linear, branched, or cyclic. The hydrocarbon group is preferably linear or branched, and more preferably linear. As the hydrocarbon group having 1 to 5 carbon atoms, alkyl groups having 1 to 5 carbon atoms are preferred. Examples of alkyl groups having 1 to 5 carbon atoms include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, isopentyl, and neopentyl groups. The number of carbon atoms of the hydrocarbon group is preferably 1 to 3. The hydrocarbon group is more preferably a methyl group or an ethyl group, and even more preferably a methyl group. When the hydrocarbon group has a substituent, examples of the substituent include a halogen atom.

[0039] Furthermore, R 3 and R 6 are each preferably a hydrogen atom, and it is more preferable that both R 3 and R 6 are hydrogen atoms. Furthermore, R 1 and R 2 are each preferably a hydrogen atom, and it is more preferable that both R 1 and R 2 are hydrogen atoms.

[0040] Examples of the compound (1-3) include 6-methyl-1,4-naphthoquinone.

[0041] Among the above-mentioned compounds (1-1), compound (1-2), and compound (1-3), from the viewpoint of further enhancing the nitrification inhibitory activity of the compound, the compound represented by the general formula (1) is preferably compound (1-1) or compound (1-2), and more preferably compound (1-1).

[0042] The compound represented by the general formula (1) may be one or more selected from the group consisting of 1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 5-hydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 5-hydroxy-2-methyl-1,4-naphthoquinone, 2,3-dichloro-1,4-naphthoquinone, 2-methoxy-1,4-naphthoquinone, 2-amino-3-chloro-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, 6-methyl-1,4-naphthoquinone, 2-chloro-1,4-naphthoquinone, and 2,7-dimethoxy-1,4-naphthoquinone (zeanon) shown in Table 1.

[0043] As described later in the examples, the inventors measured the nitrification inhibitory activity of the above-mentioned compounds. From the viewpoint of preferring compounds with high nitrification inhibitory activity, the compound represented by the above general formula (1) is preferably one or more selected from the group consisting of 1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 5-hydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 5-hydroxy-2-methyl-1,4-naphthoquinone, 2,3-dichloro-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, 6-methyl-1,4-naphthoquinone, and 2-chloro-1,4-naphthoquinone. It is more preferable that it be one or more selected from the group consisting of 5-hydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 5-hydroxy-2-methyl-1,4-naphthoquinone, 2,3-dichloro-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, and 6-methyl-1,4-naphthoquinone, and even more preferable that it be one or more selected from the group consisting of 5-hydroxy-2-methyl-1,4-naphthoquinone and 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone.

[0044] In crop cultivation, it is important to suppress soil nitrification and improve nitrogen utilization efficiency. Nitrification inhibitors should preferably be naturally derived and easy to use. As mentioned above, 2,7-dimethoxy-1,4-naphthoquinone (zeanone) is secreted from the roots of corn, so cultivating corn can suppress soil nitrification. In addition, zeanone has low volatility and is not easily affected by ambient temperature. From this viewpoint, the compound represented by the above general formula (1) is preferably 2,7-dimethoxy-1,4-naphthoquinone (zeanone).

[0045] As for salts, there are no particular restrictions as long as they are agriculturally permissible. Examples of such salts include inorganic salts such as hydrochloride, sulfate, and nitrate; organic salts such as acetate and methanesulfonate; alkali metal salts such as sodium and potassium salts; alkaline earth metal salts such as magnesium and calcium salts; and quaternary ammonium salts such as dimethylammonium and triethylammonium.

[0046] Zeanone, represented by the following formula (2), is a newly identified naturally occurring compound. As described later in the examples, the inventors found that zeanone has excellent nitrification inhibitory properties. Zeanone can be used as a soil conditioner, nitrification inhibitor, and fertilizer, particularly in tropical to temperate regions. Since zeanone is secreted from the roots of corn, cultivating corn can suppress soil nitrification. In addition, zeanone has low volatility and is not easily affected by ambient temperature.

[0047] [ka]

[0048] 1,4-Naphthoquinone derivatives are a group of compounds that have long been known to be found in plants and microorganisms, and are known to possess various physiological activities. However, there have been no reports of zeanones, which have methoxy groups at positions 2 and 7, being isolated as naturally occurring compounds. Furthermore, there have been no previous reports of zeanones having nitrifying activity.

[0049] 2,7-Dimethoxy-1,4-Naphthoquinone (Zeanone) or the 1,4-Naphthoquinone derivatives shown in Table 1 can be added to inorganic materials such as lime or fertile soils such as Andosol to serve as soil conditioners. The amount to be added can be selected and determined as needed. For example, the amount of zeanone to be added is in the range of 15 to 50 μg per gram of soil. As described later in the examples, the nitrification inhibitory activity of the 1,4-naphthoquinone derivatives shown in Table 1 is equivalent to or greater than that of zeanone. The amount of these derivatives added may be determined by referring to the nitrification inhibitory activity of each derivative. The amount of derivatives added may be, for example, 0.5 μg or more, 2 μg or more, 5 μg or more, 10 μg or more, 20 μg or more, or 50 μg or less, 20 μg or less, 10 μg or less, 5 μg or less, or 2 μg or less per gram of soil. The upper and lower limits of the amount of derivatives added can be combined arbitrarily.

[0050] Soil conditioners containing 2,7-dimethoxy-1,4-naphthoquinone (zeanone) or the 1,4-naphthoquinone derivatives shown in Table 1 have a nitrification inhibitory effect, thereby suppressing the nitrification of nitrogen components and preventing the deterioration of the soil environment. The effects obtained by using the soil conditioner of this embodiment may include effects other than nitrification, as long as they promote plant growth.

[0051] [fertilizer] In one embodiment, the present invention provides a fertilizer containing a compound represented by the above general formula (1), a salt thereof, or a solvate thereof as a soil conditioner.

[0052] Because the fertilizer contains the aforementioned soil conditioner, it has a nitrification-inhibiting effect. This suppresses the nitrification of nitrogen components and prevents the deterioration of the soil environment.

[0053] Examples of fertilizers containing the aforementioned soil conditioners include inorganic fertilizers and organic fertilizers, and mixtures thereof are also acceptable. Inorganic fertilizers include nitrogenous fertilizers such as urea, ammonium sulfate, and ammonium chloride; phosphate fertilizers such as superphosphate; and potassium fertilizers such as potassium sulfate and potassium chloride. Organic fertilizers include bone meal and compost.

[0054] [Manufacturing method] In one embodiment, the present invention provides a method for producing an active ingredient of a soil conditioner, comprising immersing the root surface of corn in an organic solvent to obtain a root extract, and purifying the active ingredient of the soil conditioner contained in the root extract by chromatography.

[0055] As described later in the examples, the inventors isolated zeanone, which has nitrification-inhibiting properties, from corn roots. Since zeanone is a hydrophobic compound, it can be extracted into an organic solvent by immersing the corn roots in an organic solvent.

[0056] Examples of organic solvents used for extraction include alcohol, acetonitrile, diethyl ether, dichloromethane, chloroform, and ethyl acetate. Based on the relationship between the purity of the extracted compound and the recovery rate, using acetic acid-containing dichloromethane is the most efficient method.

[0057] Methods for purifying soil conditioners from organic solvents exuded from corn roots include, but are not limited to, partition chromatography, normal-phase chromatography, and reverse-phase chromatography. Any known chromatography method that can purify the hydrophobic substance zeanone is acceptable. The obtained organic solvent extract can be fractionated by partition adsorption column chromatography to obtain 2,7-dimethoxy-1,4-naphthoquinone (zeanone).

[0058] 2,7-Dimethoxy-1,4-Naphthoquinone (Zeanone) and the 1,4-Naphthoquinone derivatives shown in Table 1 exhibit outstanding nitrification inhibitory activity and can be used as nitrification inhibitors by adding them to soil conditioners, fertilizers, etc. Furthermore, 2,7-Dimethoxy-1,4-Naphthoquinone (Zeanone), used as a nitrification inhibitor, can be produced from corn. Therefore, soil conditioners containing nitrification inhibitors can be manufactured at low cost, and their activity is expected to be exerted in areas where nitrification is occurring in the soil.

[0059] [Nitrification suppression method] In one embodiment, the present invention provides a method for inhibiting soil nitrification, which includes cultivating plants that produce active ingredients for a soil conditioner.

[0060] In soil where corn has been cultivated, zeanone naturally inhibits soil nitrification by seeping into the soil. This prevents the deterioration of the soil environment.

[0061] As will be described later in the examples, the zeanone content varies greatly depending on the corn variety. By cultivating corn that contains a large amount of zeanone, it is possible to suppress the nitrification of nitrogen components in the soil, prevent the deterioration of the soil environment, and carry out agricultural production.

[0062] Because corn is a plant that is cultivated over a large area, it is expected that cultivating corn that contains a large amount of active ingredients in soil conditioners can suppress nitrification in vast cultivated fields.

[0063] Furthermore, the plants that produce the active ingredients of the soil conditioner are not limited to corn; any plant that contains a large amount of the active ingredients of the soil conditioner may be used. [Examples]

[0064] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0065] [Experimental Example 1] (Isolation and purification of xeanone) Compounds exhibiting nitrification-inhibiting activity were isolated and purified from extracts obtained from the surface of cultivated corn roots, and their structures were determined.

[0066] Corn plants were grown in a greenhouse for 20 days, and the roots of 200 plants were immersed in 200 mL of dichloromethane containing 10% acetic acid to obtain a hydrophobic extract from the root surface.

[0067] Next, the extract was concentrated using a rotary evaporator, and the concentrate was dissolved in a small amount of methanol. This was then fractionated using a reverse-phase solid-phase extraction cartridge (Waters, Sep-Pak C18 plus). Activity was detected in the 50% methanol fraction. The activity was measured using the method described later in Experimental Example 2.

[0068] This active fraction was further fractionated by high-performance liquid chromatography using a column (TSKgel Super ODS, manufactured by Tosoh Corporation), and finally, one active substance was purified.

[0069] The obtained compounds were subjected to ultraviolet spectroscopy and electrospray ionization mass spectrometry. 1 H-NMR analysis, 13 The spectra were analyzed by 13C-NMR analysis. These results are shown in Figures 1 to 4. Figure 1 is the ultraviolet-visible absorption spectrum, Figure 2 is the electrospray ionization mass spectrum, and Figure 3 is 1 Figure 4 shows the H-NMR spectrum. 13 This is a 1C-NMR spectrum.

[0070] Furthermore, 2,7-dimethoxynaphthalene was chromato-oxidized to synthesize 2,7-dimethoxy-1,4-naphthoquinone (for example, RD Wilson, Naphthaquinones - I: The molecular structures of some halogeno-2:7-dihydroxynaphthalenes. (1958) Tetrahedron, 3(3), 236-242).

[0071] UV-Vis absorption spectrum and electrospray ionization mass spectrum of active substances obtained from corn root surface extract. 1 H-NMR spectrum and 13 The 1C-NMR spectrum matched that of chemically synthesized 2,7-dimethoxy-1,4-naphthoquinone. This result revealed that the active substance obtained from the maize root surface extract is 2,7-dimethoxy-1,4-naphthoquinone.

[0072] This marks the first instance of 2,7-dimethoxy-1,4-naphthoquinone being isolated in nature.

[0073] [Experimental Example 2] (Zeanone's nitrification inhibitory effect) The nitrification inhibitory effect of 2,7-dimethoxy-1,4-naphthoquinone was analyzed using nitrifying bacteria in vitro (T. Iizumi, M. Mizumoto, K. Nakamura, A Bioluminescence assay using Nitrosomonas europaea for rapid and sensitive detection of nitrification inhibitors (1998) Appl. Environment. Microbiol., 64, 3656-3662).

[0074] Nitrifying bacteria (Nitrosomonas europaea IFO14298) into which a bacterial luciferase gene (luxAB) was introduced were cultured aerobically in P medium containing kanamycin (25 mg / 1 L) at 30°C for 7 to 9 days. After washing the obtained nitrifying bacteria, a suspension of nitrifying bacteria was prepared by suspending them in fresh P medium. This suspension of nitrifying bacteria was left to stand in the dark for at least 30 minutes before the experiment.

[0075] The composition of the P medium was as follows: (NH4)2SO4 2.5g, KH2PO4 0.7g, Na2HPO4 13.5g, NaHCO3 0.5g, MgSO4 / 7H2O 100mg, CaCl2 / 2H2O 5mg, Fe-EDTA 1mg, and water 1L, with a pH of 8.0.

[0076] Nitrification was evaluated by measuring the amount of bioluminescence associated with the nitrification reaction during incubation at 15°C for 30 minutes after mixing an aqueous solution of a nitrifying bacteria suspension consisting of 0.25 mL of the above-mentioned nitrifying bacteria suspension and 0.2 mL of water with 0.01 mL of a sample solution of 2,7-dimethoxy-1,4-naphthoquinone at various concentrations in a test tube using a luminometer (manufactured by Turner Designs, model name TD20 / 20).

[0077] The amount of bioluminescence associated with the nitrification reaction decreases if a nitrification inhibitory substance is present in the sample solution. Therefore, the nitrification inhibition rate was defined as the value obtained by dividing the amount of luminescence when a sample solution of 2,7-dimethoxy-1,4-naphthoquinone at various concentrations was added to the aqueous solution of the nitrifying bacteria suspension by the amount of luminescence when only the aqueous solution of the cell suspension was used without adding the sample solution. The results of measuring the nitrification inhibitory activity of this compound at various concentrations are shown in Fig. 5. From these results, it was revealed that ED 50 is 4.2 μM and ED 80 is 16.1 μM.

[0078] In addition, similar measurements were conducted on the nitrification inhibitory activity of 1,4-naphthoquinone derivatives. The results are shown in Table 2. In Table 2, R 1 ~R 6 are, respectively, R 1 ~R 6 in the following formula (1).

[0079]

Table 2

[0080]

Chemical formula

[0081] These results reveal that 1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 5-hydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 5-hydroxy-2-methyl-1,4-naphthoquinone, 2,3-dichloro-1,4-naphthoquinone, 2-methoxy-1,4-naphthoquinone, 2-amino-3-chloro-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, 6-methyl-1,4-naphthoquinone, 2-chloro-1,4-naphthoquinone, and 2,7-dimethoxy-1,4-naphthoquinone (zeanone) possess nitrification inhibitory activity. Furthermore, it was revealed that 2-hydroxy-1,4-naphthoquinone does not possess nitrification inhibitory activity.

[0082] [Experimental Example 3] (Zeanone content in corn) Eleven randomly selected maize strains (International Maize and Wheat Improvement Center) were cultivated, and the 2,7-dimethoxy-1,4-naphthoquinone content in the hydrophobic extract obtained from the roots was analyzed.

[0083] We obtained maize seeds with strain numbers 17528, 17529, 17531, 17540, 17542, 17544, 17546, 17548, 17549, 17550, and 17556 from the International Center for Maize and Wheat Improvement. The seeds were grown in a greenhouse for 20 days, and the roots of the resulting maize plants were immersed in 20 mL of 10% acetic acid-containing dichloromethane to obtain a hydrophobic extract from the root surface.

[0084] The extract was filtered through a 0.45 μm filter, concentrated to dryness, and dissolved in 1 mL of acetonitrile to prepare the sample. 10 μL of the sample was analyzed using a high-performance liquid chromatography-mass spectrometer connected to a column (TSKgel Super ODS, Tosoh Corporation).

[0085] For each sample, the peak area of ​​the molecular ion peak of 2,7-dimethoxy-1,4-naphthoquinone at m / z=219 was calculated, and the 2,7-dimethoxy-1,4-naphthoquinone content in each system was estimated. The results are shown in Figure 6.

[0086] Figure 6 shows the content of 2,7-dimethoxy-1,4-naphthoquinone in hydrophobic extracts obtained from the roots of 11 maize strains. In Figure 6, the horizontal axis represents the content of 2,7-dimethoxy-1,4-naphthoquinone (the compound), and the vertical axis represents the number of maize strains within each content range. As a result, it became clear that the content of 2,7-dimethoxy-1,4-naphthoquinone varied greatly depending on the maize variety. [Industrial applicability]

[0087] According to the present invention, it is possible to provide soil conditioners, nitrification inhibitors, fertilizers, and methods for inhibiting nitrification using compounds or derivatives thereof that can be used in a wide range of regions from tropical to temperate zones and are easily obtained from naturally derived materials. Furthermore, according to the present invention, it is possible to provide a nitrification inhibitor that has higher utilization efficiency and lower environmental impact compared to conventional nitrogen fertilizers.

Claims

1. A soil conditioner comprising one or more compounds selected from the group consisting of 5-hydroxy-2-methyl-1,4-naphthoquinone, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone, and 2,7-dimethoxy-1,4-naphthoquinone, or salts thereof, or solvates thereof, as an active ingredient.

2. A soil conditioner according to claim 1, which has a nitrification inhibitory effect.

3. A fertilizer containing the soil conditioner described in claim 1 or 2.

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