Liquid fertilizer as well as preparation method and application thereof

Abstract

The invention discloses a liquid fertilizer as well as a preparation method and application thereof, and relates to the technical field of liquid fertilizers, the preparation method comprises the following steps: adding a flocculant into fermentation liquor containing organic acid and inositol, mixing to obtain mixed liquor, filtering and separating the mixed liquor, and collecting clear liquor; filtering the clear liquid through an ultrafiltration membrane to obtain ultrafiltration membrane clear liquid; adsorbing and eluting the ultrafiltration membrane clear liquid through anion exchange resin, and respectively collecting first effluent and eluent; mixing the first effluent and the eluent to obtain a compound liquid, adsorbing the compound liquid through a cationic resin column, and collecting a second effluent; performing concentration treatment on the second effluent through a nanofiltration membrane to obtain a concentrated solution, and performing heat concentration treatment on the concentrated solution to obtain a liquid fertilizer; the final liquid fertilizer prepared by the invention is extremely low in impurity content, is rich in organic acid and inositol, and can effectively relieve the stress effect of high salinity and high pH value on crops.

Description

Technical Field

[0001] This invention relates to the field of liquid fertilizer technology, and in particular to a liquid fertilizer, its preparation method, and its application. Background Technology

[0002] Saline soils are widely distributed throughout the world, and soil salinization is a global problem. Soil salinization leads to decreased soil fertility, difficulty for plant roots to absorb water, and hinders crop growth, resulting in significant yield reductions or even abandonment of cultivation, seriously affecting the sustainable development of agriculture and forestry. Therefore, it is urgent to carry out saline-alkali soil improvement and comprehensive utilization of saline-alkali land.

[0003] Generally speaking, the main factors in improving saline-alkali soil include soil pH, salinity, and groundwater level. There are also several key issues that deserve our attention in improving saline-alkali soil and planting crops on saline-alkali soil: (1) soil organic matter deficiency, especially water-soluble organic matter; (2) high degree of soil salinization, deterioration of soil physical and chemical properties, and serious abiotic stress on plants; (3) changes in soil microbial community structure, tending to be unbalanced, and easy formation of soil-borne diseases.

[0004] Current methods for improving saline-alkali soils mainly include salt leaching, screening for salt-tolerant crops, and enhancing crop salt tolerance. Studies have shown that inositol can regulate plant osmotic pressure, helping plants accumulate osmotic regulators such as proline in saline-alkali environments, thereby alleviating salt damage to cells. Simultaneously, it can reduce the accumulation of reactive oxygen species (ROS), protect cell membrane integrity, and mitigate oxidative damage caused by salt stress. It also plays a beneficial role in promoting plant growth and nutrient absorption, and improving the soil microenvironment.

[0005] Currently, there are reports of using inositol to alleviate salt stress and promote crop growth, but saline-alkali soils are usually not only high in salt but also have a high pH (about 8.0), and this acid-base environment is not suitable for the growth of most crops.

[0006] Therefore, it is particularly important to provide a fertilizer containing inositol that can simultaneously alleviate the stress of high salt and high pH levels on crops. Summary of the Invention

[0007] The purpose of this invention is to provide a liquid fertilizer, its preparation method, and its application. The liquid fertilizer preparation method of this invention can remove most of the salts, pigments, and other impurities from the fermentation liquid, resulting in extremely low impurity content in the final liquid fertilizer. At the same time, this liquid fertilizer is rich in organic acids and inositol, which can effectively alleviate the stress of high salt and high acidity / alkalinity on crops.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a liquid fertilizer, wherein the preparation method includes: A flocculant is added to a fermentation broth containing organic acids and inositol, and the mixture is mixed to obtain a mixture. The mixture is then filtered and the clear liquid is collected. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; The ultrafiltration membrane supernatant is adsorbed and eluted by anion exchange resin, and the first effluent and the eluent are collected separately. The first effluent and the eluent are mixed to obtain a compound liquid, which is then adsorbed through a cation exchange resin column to collect the second effluent. The second effluent is concentrated by nanofiltration membrane, and the concentrate is then concentrated by heat to obtain liquid fertilizer.

[0009] Compared with existing technologies, this invention obtains a first effluent containing inositol and an eluent containing organic acid and inositol by flocculation, ultrafiltration, and adsorption-elution with anion exchange resin after filtration of the fermentation broth containing organic acid and inositol. During the elution of organic acid, some anionic impurities (such as phosphate, sulfate, chloride, etc.) are still adsorbed on the anion exchange resin, thereby removing some anionic impurities. After mixing the first effluent and the eluent, it is adsorbed through a cation exchange resin column, which not only removes cationic impurities (such as sodium, magnesium, potassium, etc.) and reduces the conductivity of the second effluent, but also allows the organic acid salts to be converted back into organic acid. After concentration by nanofiltration, some ionic impurities are removed, and after thermal concentration, liquid fertilizer is obtained. The liquid fertilizer preparation method of this invention can remove most of the salts, pigments and other impurities in the fermentation liquid, resulting in an extremely low impurity content in the final liquid fertilizer. At the same time, the liquid fertilizer of this invention is rich in organic acids and inositol. Through the synergistic effect of organic acids and inositol, it can reduce the pH value of saline-alkali soil on the one hand, alleviate the damage of salt to cells on the other hand, promote plant growth and nutrient absorption, improve the soil microenvironment, and alleviate the stress of high salt and high acidity / alkalinity on crops.

[0010] Furthermore, the fermentation broth is obtained by fermentation of a mixed culture medium containing glucose, the mixed culture including Corynebacterium glutamicum, lactic acid bacteria and yeast.

[0011] Furthermore, in the fermentation broth, the content of the organic acid is 200-300 g / L, and the content of the inositol is 20-40 g / L.

[0012] Furthermore, the organic acid comprises at least one of amino acids, citric acid, acetic acid, lactic acid, and tartaric acid.

[0013] In this invention, when the content of organic acids and inositol in the fermentation broth, as well as the types of organic acids, meet the above-mentioned ranges, it is more conducive to obtaining liquid fertilizer with low impurity content and rich in organic acids and inositol, thereby further alleviating the stress of high salt and high acidity / alkalinity on crops.

[0014] Furthermore, the flocculant is selected from chitosan and / or polyacrylamide.

[0015] Furthermore, the flocculant is added to the fermentation broth in solution form, the concentration of the flocculant solution is 0.1-0.5 wt%, and the volume ratio of the flocculant solution to the fermentation broth is (0.2-0.5):1.

[0016] In this invention, when the type of flocculant, the concentration of the flocculant solution, and the ratio of the flocculant solution to the fermentation broth meet the above-mentioned ranges, it can effectively adsorb tiny particles, impurities, and negatively charged substances (such as proteins, pigments, bacterial cells, etc.) in the fermentation broth. Through electrostatic interaction, it forms larger flocs, which facilitates subsequent filtration by adding diatomaceous earth to form sediment or filter separation, thereby improving the solid-liquid separation efficiency. This is beneficial for obtaining liquid fertilizer with low impurity content and rich in organic acids and inositol.

[0017] Furthermore, the filtration separation of the mixture includes: adding diatomaceous earth to the mixture for filtration aid and collecting the clear liquid.

[0018] Furthermore, the pore size of the ultrafiltration membrane is 2000Da-3000Da, the operating temperature of the clarified liquid when filtered through the ultrafiltration membrane is 20-30℃, and the operating pressure is 0.1-0.5Mpa.

[0019] In this invention, when the pore size of the ultrafiltration membrane, the operating temperature during ultrafiltration, and the operating pressure meet the above-mentioned ranges, impurities in the clarified liquid can be effectively removed, which is beneficial to obtaining liquid fertilizer with low impurity content and rich in organic acids and inositol, thereby further alleviating the stress of high salt and high acidity / alkalinity on crops.

[0020] Further, the ultrafiltration membrane supernatant is adsorbed onto the anion exchange resin at an injection flow rate of 1-2 BV / h until saturation, the first effluent is collected, and then eluted with a sodium hydroxide solution of concentration of 2wt%-4wt%, with an injection volume of 2-3 BV, and the eluent is collected.

[0021] In this invention, when the injection flow rate of the ultrafiltration membrane supernatant, the concentration of the sodium hydroxide solution, and the injection volume of the sodium hydroxide solution meet the above-mentioned ranges, the efficiency of adsorption and elution can be improved. By using a sodium hydroxide solution with a concentration of 2wt%-4wt% for elution, some anionic impurities (such as phosphate, sulfate, chloride, etc.) will still be adsorbed on the anion exchange resin, further reducing the content of anionic impurities in the eluent. This is beneficial for obtaining a liquid fertilizer with low impurity content and rich in organic acids and inositol, thereby further alleviating the stress of high salt and high acidity / alkalinity on crops.

[0022] Furthermore, the mass ratio of organic acid to inositol in the compound liquid obtained by mixing the first effluent and the eluent is (15-20):1.

[0023] In this invention, when the mass ratio of organic acid and inositol in the compound liquid meets the above-mentioned range, the liquid fertilizer produced can contain a specific amount of organic acid and inositol, which can better improve the pH value of saline-alkali soil, alleviate the damage of salt to cells, further promote plant growth and nutrient absorption, improve the soil microenvironment, and alleviate the stress of high salt and high acidity / alkalinity on crops.

[0024] Furthermore, the compounded liquid is adsorbed onto a cation exchange resin column until saturation at an injection flow rate of 2-4 BV / h.

[0025] In this invention, when the injection flow rate of the compound solution meets the above-mentioned range, it can more effectively remove cationic impurities and collect a second effluent rich in organic acids and inositol.

[0026] Furthermore, the nanofiltration membrane used for the concentration of the second effluent has a pore size of 100-200 Da, an operating temperature of 20-30℃, an operating pressure of 1-3 MPa, and a solid content of 10-15 wt% in the concentrated solution.

[0027] Furthermore, the concentrated liquid is subjected to a heat concentration treatment at a temperature of 60-70°C, and the solid content of the liquid fertilizer is 40-45 wt%.

[0028] A second aspect of the present invention provides a liquid fertilizer prepared by the above-described liquid fertilizer preparation method.

[0029] Compared with existing technologies, the liquid fertilizer of the present invention is rich in organic acids and inositol. Through the synergistic effect of organic acids and inositol, it can reduce the pH value of saline-alkali soil on the one hand, alleviate the damage of salt to cells on the other hand, promote plant growth and nutrient absorption, improve the soil microenvironment, and alleviate the stress of high salt and high acidity / alkalinity on crops.

[0030] A third aspect of the present invention provides an application of the above-mentioned liquid fertilizer in alleviating the stress of high salt and high acidity / alkalinity on crops. Detailed Implementation

[0031] To make the technical problems, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0033] The first aspect of this invention provides a method for preparing a liquid fertilizer, wherein the preparation method includes: A flocculant is added to a fermentation broth containing organic acids and inositol, and the mixture is mixed to obtain a mixture. The mixture is then filtered and the clear liquid is collected. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; The ultrafiltration membrane supernatant is adsorbed and eluted by anion exchange resin, and the first effluent and the eluent are collected separately. The first effluent and the eluent are mixed to obtain a compound liquid, which is then adsorbed through a cation exchange resin column to collect the second effluent. The second effluent is concentrated by nanofiltration membrane, and the concentrate is then concentrated by heat to obtain liquid fertilizer.

[0034] Using the above technical solution, after flocculation, ultrafiltration, and adsorption-elution with anion exchange resin, fermentation broth containing organic acids and inositol is subjected to elution, resulting in a first effluent containing inositol and an eluent containing organic acid salts. During the elution of organic acids, some anionic impurities (such as phosphate, sulfate, and chloride ions) are still adsorbed onto the anion exchange resin, thus removing some anionic impurities. The first effluent and the eluent are then mixed and adsorbed through a cation exchange resin column, which not only removes cationic impurities (such as sodium, magnesium, and potassium ions) and reduces the conductivity of the second effluent, but also allows the organic acid salts to be converted back into organic acids. After concentration by nanofiltration, some ionic impurities are removed, and after thermal concentration, liquid fertilizer is obtained. The liquid fertilizer preparation method of this invention can remove most of the salts, pigments and other impurities in the fermentation liquid, resulting in an extremely low impurity content in the final liquid fertilizer. At the same time, the liquid fertilizer of this invention is rich in organic acids and inositol. Through the synergistic effect of organic acids and inositol, it can reduce the pH value of saline-alkali soil on the one hand, alleviate the damage of salt to cells on the other hand, promote plant growth and nutrient absorption, improve the soil microenvironment, and alleviate the stress of high salt and high acidity / alkalinity on crops.

[0035] In some embodiments, the fermentation broth is obtained by fermentation of a mixed culture medium containing glucose, the mixed culture including Corynebacterium glutamicum, lactic acid bacteria and yeast.

[0036] In this invention, there is no particular limitation on the type of yeast; for example, the yeast may be *Kluyveromyces martensii*. In this invention, a fermentation broth containing inositol and organic acids is obtained by fermenting *Corynebacterium glutamicum*, lactic acid bacteria, and yeast using glucose as a substrate.

[0037] In some embodiments, the method for preparing the fermentation broth includes the following steps: Corynebacterium glutamicum was inoculated into the first culture medium at an inoculation rate of 1-5% (v / v) for the first culture to obtain Corynebacterium glutamicum seed culture; Lactic acid bacteria are inoculated into the second culture medium at an inoculation rate of 1-5% (v / v) for a second culture to obtain lactic acid bacteria seed culture; Kluyveromyces martensii was inoculated into the third culture medium at an inoculation rate of 1-5% (v / v) for a third culture to obtain Kluyveromyces martensii seed culture. The Corynebacterium glutamicum seed solution, the lactic acid bacteria seed solution, and the Kluyveromyces martensii seed solution are mixed, and the resulting mixed bacterial solution is inoculated into the fermentation medium at an inoculation rate of 5-10% (v / v) for fermentation culture. After fermentation, the fermentation broth is obtained.

[0038] Using the above technical solution, Corynebacterium glutamicum, lactic acid bacteria and Kluyveromyces martensii are cultured respectively, and the three seed liquids are then mixed and inoculated into a fermentation medium for fermentation culture. This can improve the efficiency of fermentation culture, and the obtained fermentation broth can contain the organic acids and inositol required for liquid fertilizer.

[0039] In the method for preparing the fermentation broth, the conditions for inoculating Corynebacterium glutamicum into the first culture medium for the first culture include: culturing at a temperature of 25-35℃, a pH value maintained at 6.8-7.2, and a stirring speed of 150-220 rpm for 10-15 hours. In this invention, there is no specific limitation on the OD600 value at the end of the first culture of Corynebacterium glutamicum, as long as the culture time meets the above-mentioned requirements of this invention.

[0040] In the preparation method of fermentation broth, the glucose content in the first culture medium is 80-100 g / L, and the urea content is 5-10 g / L. The content is 1-2 g / L. The content of the first culture medium is 0.3-0.8 g / L, the content of biotin is 0.002-0.005 g / L, and the content of citric acid is 0.5-1 g / L; the pH value of the first culture medium is 7.0-7.2.

[0041] In the method for preparing the fermentation broth, the conditions for inoculating the lactic acid bacteria into the second culture medium for the second culture include: culturing at a temperature of 35-40℃, a pH value maintained at 6.3-6.7, and a stirring speed of 130-170 rpm for 10-15 hours. In this invention, there is no specific limitation on the OD600 value at the end of the second culture of the lactic acid bacteria, as long as the culture time meets the above requirements of this invention.

[0042] In the preparation method of the fermentation broth, the second culture medium contains 15-25 g / L of glucose, 5-15 g / L of peptone, and 3-8 g / L of beef extract. The content is 0.8-1.3 g / L. The concentration of the active ingredient was 0.3-0.8 g / L, and the pH of the second culture medium was 6.5-6.8.

[0043] In the preparation method of the fermentation broth, the third culture of *Kluyveromyces martensii* inoculated into the third culture medium includes: culturing at a temperature of 25-35℃, a pH maintained at 5.7-6.3, and a stirring speed of 80-130 rpm for 40-55 hours. In this invention, there is no particular limitation on the OD600 value at the end of the third culture of *Kluyveromyces martensii*, as long as the culture time meets the above requirements of this invention.

[0044] In the preparation method of fermentation broth, the third culture medium contains 5-10 g / L of glycerol, 7-13 g / L of glucose, 3-8 g / L of peptone, and 2-5 g / L of yeast extract. The content is 0.8-1.3 g / L. The concentration was 0.3-0.8 g / L, and the pH of the third culture medium was 6-6.4.

[0045] In the method for preparing the fermentation broth, the conditions for inoculating the fermentation medium and culturing it include: maintaining the pH of the fermentation medium at 6.8-7.2, an air flow rate of 1.2-1.8 m³ / L, a pressure of 0.03-0.08 MPa, a fermentation temperature of 30-36℃, a stirring speed of 180-300 rpm, and a culturing time of 24-72 h. In this invention, there is no specific limitation on the OD600 value at the end of the fermentation culture, as long as the culturing time meets the above requirements of this invention.

[0046] In the preparation of the fermentation broth, the pH value is maintained by adding 40-60 wt% ammonia water.

[0047] In the method for preparing the fermentation broth, the content of the Corynebacterium glutamicum seed liquid is 55-65% by volume percentage, the content of the lactic acid bacteria seed liquid is 15-25%, and the content of the Kluyveromyces martensii seed liquid is 15-25%.

[0048] In the method for preparing the fermentation broth, the fermentation medium contains 80-100 g / L of glucose, 5-10 g / L of glycerol, and 5-10 g / L of urea. The content is 1-2 g / L. The content of α-phosphorus is 0.3-0.8 g / L, the content of biotin is 0.002-0.005 g / L, the content of FeSO4·7H2O is 0.01-0.02 g / L, and the content of citric acid is 0.5-1 g / L.

[0049] In some embodiments, the content of the organic acid in the fermentation broth is 200-300 g / L, and the content of the inositol is 20-40 g / L.

[0050] For example, in the fermentation broth, the content of the organic acid can be 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L, 260 g / L, 270 g / L, 280 g / L, 290 g / L, or 300 g / L, or a range consisting of any two of the aforementioned values; the content of inositol can be 20 g / L, 22 g / L, 24 g / L, 26 g / L, 28 g / L, 30 g / L, 32 g / L, 34 g / L, 36 g / L, 38 g / L, or 40 g / L, or a range consisting of any two of the aforementioned values.

[0051] In some embodiments, the organic acid comprises at least one of amino acids, citric acid, acetic acid, lactic acid, and tartaric acid.

[0052] By adopting the above technical solution, when the content of organic acids and inositol in the fermentation broth, as well as the types of organic acids, meet the above range, it is more conducive to obtaining liquid fertilizer with low impurity content and rich in organic acids and inositol, thereby further alleviating the stress of high salt and high acidity / alkalinity on crops.

[0053] Preferably, the organic acid comprises an amino acid, and at least one selected from citric acid, acetic acid, lactic acid, and tartaric acid. Preferably, the amino acid content in the fermentation broth is 100-200 g / L. For example, the amino acid content can be 100 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, or 200 g / L, or a range consisting of any two of the aforementioned values.

[0054] In some embodiments, the flocculant is selected from chitosan and / or polyacrylamide.

[0055] In some embodiments, the flocculant is added to the fermentation broth in solution form, the concentration of the flocculant solution is 0.1-0.5 wt%, and the volume ratio of the flocculant solution to the fermentation broth is (0.2-0.5):1.

[0056] For example, the concentration of the flocculant solution may be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, or 0.5wt%, or a range consisting of any two of the aforementioned values; the volume ratio of the flocculant solution to the fermentation broth may be 0.2:1, 0.3:1, 0.4:1, or 0.5:1, or a range consisting of any two of the aforementioned values.

[0057] When the above technical solution is adopted, and the type of flocculant, the concentration of the flocculant solution, and the ratio of the flocculant solution to the fermentation broth meet the above range, it can effectively adsorb small particles, impurities, and negatively charged substances (such as proteins, pigments, bacterial cells, etc.) in the fermentation broth. Through electrostatic interaction, larger flocs are formed, which facilitates subsequent filtration by adding diatomaceous earth to form sediment or filter separation, thereby improving the solid-liquid separation efficiency. This is beneficial for obtaining liquid fertilizer with low impurity content and rich in organic acids and inositol.

[0058] Preferably, the concentration of the flocculant solution is 0.1-0.3 wt%, and the volume ratio of the flocculant solution to the fermentation broth is (0.3-0.5):1.

[0059] In some embodiments, the filtration separation of the mixture includes: adding diatomaceous earth to the mixture for filtration aid and collecting the clear liquid.

[0060] In some embodiments, the mass ratio of the mixture to the diatomaceous earth is 1:(0.03-0.05).

[0061] For example, the mass ratio of the mixture to the diatomaceous earth can be 1:0.03, 1:0.04, or 1:0.05, or a range consisting of any two of the aforementioned values.

[0062] In some embodiments, the pore size of the ultrafiltration membrane is 2000 Da-3000 Da, the operating temperature of the supernatant when filtered through the ultrafiltration membrane is 20-30°C, and the operating pressure is 0.1-0.5 MPa.

[0063] For example, the pore size of the ultrafiltration membrane can be 2000 Da, 2500 Da, or 3000 Da, or a range consisting of any two of the aforementioned values; the operating temperature of the supernatant during filtration through the ultrafiltration membrane can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, or 30°C, or a range consisting of any two of the aforementioned values; the operating pressure can be 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, or 0.5 MPa, or a range consisting of any two of the aforementioned values.

[0064] Preferably, the pore size of the ultrafiltration membrane is 2000 Da-2500 Da, the operating temperature of the clarified liquid when filtered through the ultrafiltration membrane is 20-25℃, and the operating pressure is 0.1-0.3 MPa.

[0065] By adopting the above technical solution, when the pore size of the ultrafiltration membrane, the operating temperature and operating pressure during ultrafiltration meet the above range, impurities in the clear liquid can be effectively removed, which is conducive to obtaining liquid fertilizer with low impurity content and rich in organic acids and inositol, thereby further alleviating the stress of high salt and high acidity / alkalinity on crops.

[0066] In some embodiments, the ultrafiltration membrane supernatant is adsorbed onto an anion exchange resin at an injection flow rate of 1-2 BV / h until saturation, the first effluent is collected, and then eluted with a sodium hydroxide solution of 2wt%-4wt% with an injection volume of 2-3 BV, and the eluent is collected.

[0067] By employing the above technical solution, when the injection flow rate of the ultrafiltration membrane supernatant, the concentration of the sodium hydroxide solution, and the injection volume of the sodium hydroxide solution meet the above ranges, the efficiency of adsorption and elution can be improved. By using a sodium hydroxide solution with a concentration of 2wt%-4wt% for elution, some anionic impurities (such as phosphate, sulfate, chloride, etc.) will still be adsorbed on the anion exchange resin, further reducing the content of anionic impurities in the eluent. This is beneficial for obtaining liquid fertilizer with low impurity content and rich in organic acids and inositol, thereby further alleviating the stress of high salt and high acidity / alkalinity on crops.

[0068] Preferably, the ultrafiltration membrane supernatant is adsorbed onto anion exchange resin at an injection flow rate of 1-1.5 BV / h until saturation, the first effluent is collected, and then eluted with a sodium hydroxide solution of 2wt%-3wt% at an injection volume of 2-2.5 BV, and the eluent is collected.

[0069] In some embodiments, the anion exchange resin is a weakly basic anion exchange resin. For example, the weakly basic anion exchange resin may be at least one of D315 resin, D304 resin, or D301 resin.

[0070] In some embodiments, the mass ratio of organic acid to inositol in the compound liquid obtained by mixing the first effluent and the eluent is (15-20):1.

[0071] Using the above technical solution, when the mass ratio of organic acid and inositol in the compound liquid meets the above range, the liquid fertilizer produced can contain a specific amount of organic acid and inositol, which can better improve the pH value of saline-alkali soil, alleviate the damage of salt to cells, further promote plant growth and nutrient absorption, improve the soil microenvironment, and alleviate the stress of high salt and high acidity / alkalinity on crops.

[0072] For example, the mass ratio of organic acid to inositol in the compound liquid obtained by mixing the first effluent and the eluent can be 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, or a range consisting of any of the above ratios.

[0073] Preferably, the mass ratio of organic acid to inositol in the compound liquid obtained by mixing the first effluent and the eluent is (15-18):1.

[0074] In some embodiments, the compounded liquid is adsorbed onto a cation exchange resin column until saturation at an injection flow rate of 2-4 BV / h.

[0075] By adopting the above technical solution, when the injection flow rate of the compound solution meets the above range, it is possible to more effectively remove cationic impurities and collect the second effluent rich in organic acids and inositol.

[0076] Preferably, the compounded liquid is adsorbed onto a cation exchange resin column until saturation at an injection flow rate of 2-3 BV / h.

[0077] In some embodiments, the cation exchange resin in the cation exchange resin column is a strongly acidic cation exchange resin and / or a weakly acidic cation exchange resin D113. For example, the strongly acidic cation exchange resin can be D001 resin and / or D75 resin, and the weakly acidic cation exchange resin can be D113 resin.

[0078] In some embodiments, the nanofiltration membrane used for concentrating the second effluent has a pore size of 100-200 Da, an operating temperature of 20-30°C, an operating pressure of 1-3 MPa, and a solid content of 10-15 wt% in the concentrated solution.

[0079] For example, the pore size of the nanofiltration membrane used for concentrating the second effluent can be 100 Da, 150 Da, or 200 Da, or a range consisting of any two of the above values; the operating temperature can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, or 30°C, or a range consisting of any two of the above values; the operating pressure can be 1 MPa, 2 MPa, or 3 MPa, or a range consisting of any two of the above values; and the solid content of the concentrate after nanofiltration membrane concentration can be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, or a range consisting of any two of the above values.

[0080] Preferably, the nanofiltration membrane used for the concentration of the second effluent has a pore size of 150-200 Da, an operating temperature of 20-25°C, an operating pressure of 1-3 MPa, and a solid content of 10-13 wt% in the concentrated solution.

[0081] In some embodiments, the temperature at which the concentrate is thermally concentrated is 60-70°C, and the solid content of the liquid fertilizer is 40-45 wt%.

[0082] For example, the temperature at which the concentrate is thermally concentrated can be 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, or 70°C, or a range consisting of any two of the aforementioned values; the solid content of the liquid fertilizer can be 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, or 45wt%, or a range consisting of any two of the aforementioned values.

[0083] Preferably, the temperature at which the concentrate is thermally concentrated is 65-70°C.

[0084] A second aspect of the present invention provides a liquid fertilizer prepared by the above-described liquid fertilizer preparation method.

[0085] Compared with existing technologies, the liquid fertilizer of the present invention is rich in organic acids and inositol. Through the synergistic effect of organic acids and inositol, it can reduce the pH value of saline-alkali soil on the one hand, alleviate the damage of salt to cells on the other hand, promote plant growth and nutrient absorption, improve the soil microenvironment, and alleviate the stress of high salt and high acidity / alkalinity on crops.

[0086] A third aspect of the present invention provides an application of the above-mentioned liquid fertilizer in alleviating the stress of high salt and high acidity / alkalinity on crops.

[0087] To better illustrate the technical solution of the present invention, the following specific embodiments are also provided.

[0088] Unless otherwise specified, all raw materials used in the examples and comparative examples were obtained commercially.

[0089] Example 1 Preparation of fermentation broth: Corynebacterium glutamicum was inoculated into the first culture medium at a rate of 2% (v / v) and cultured at 30°C, pH 7, and 200 rpm for 12 hours to obtain a Corynebacterium glutamicum seed culture. The first culture medium contained 90 g / L glucose and 7 g / L urea. The content is 1.5g / L. The concentrations of the first culture medium were 0.5 g / L, 0.004 g / L, and 0.8 g / L, respectively; the pH of the first culture medium was 7.

[0090] Lactic acid bacteria were inoculated into the second culture medium at an inoculum rate of 2% (v / v) and cultured at 37℃, pH 6.5, and a rotation speed of 150 rpm for 12 h to obtain a lactic acid bacteria seed culture. The second culture medium contained 20 g / L glucose, 10 g / L peptone, and 5 g / L beef extract. The content is 1g / L. The concentration of the substance was 0.5 g / L, and the pH of the second culture medium was 6.7.

[0091] Kluyveromyces martensii was inoculated into the third medium at a rate of 2% (v / v) and cultured at 30°C, pH 6, and 100 rpm for 48 h to obtain the Kluyveromyces martensii seed culture. The third medium contained 7 g / L glycerol, 10 g / L glucose, 5 g / L peptone, and 3 g / L yeast extract. The content is 1g / L. The concentration was 0.5 g / L, and the pH of the third culture medium was 6.2.

[0092] The seed cultures of *Corynebacterium glutamicum*, *Lactobacillus*, and *Kluyveromyces martensii* were mixed, and the resulting mixed culture was inoculated into the fermentation medium at an inoculum size of 8% (v / v). The culture conditions included: a pH of 7, an initial air flow rate of 1.5 m³ / L, a maintenance pressure of 0.05 MPa, a fermentation temperature of 33°C, and a stirring speed of 250 rpm. During fermentation, the pH was maintained by adding 50 wt% ammonia. The culture was carried out for 47 hours to obtain the fermentation broth. The fermentation medium contained 90 g / L glucose, 8 g / L glycerol, and 7 g / L urea. The content is 1.5g / L. The content of [unspecified substance] is 0.5 g / L, and the content of biotin is 0.004 g / L. The content of [unspecified substance] was 0.01 g / L, and the content of citric acid was 0.7 g / L; based on the volume percentage of the mixed bacterial culture, the content of Corynebacterium glutamicum seed culture was 60%, the content of Lactic acid bacteria seed culture was 20%, and the content of Kluyveromyces martensii seed culture was 20%.

[0093] Tests showed that the fermentation broth contained 200 g / L of organic acids and 30 g / L of inositol. The broth also contained amino acids, citric acid, acetic acid, lactic acid, and tartaric acid. Among these, the amino acid content was 100 g / L.

[0094] Preparation of liquid fertilizer: A flocculant solution (chitosan) was added to the fermentation broth, and the mixture was mixed to obtain a mixed solution. Then, diatomaceous earth was added for filtration. The mixed solution was filtered and separated, and the clear liquid was collected. The concentration of the flocculant solution was 0.3 wt%, and the volume ratio of the flocculant solution to the fermentation broth was 0.3:1. The mass ratio of the mixed solution to the diatomaceous earth was 1:0.04. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; wherein, the pore size of the ultrafiltration membrane is 2000 Da, and the operating temperature of the clarified liquid when filtering through the ultrafiltration membrane is 25°C and the operating pressure is 0.3 MPa; The ultrafiltration membrane supernatant was injected through an anion exchange resin (D304) at a flow rate of 1.5 BV / h until saturation. The first effluent was collected, and then eluted with a 3 wt% sodium hydroxide solution at an injection volume of 2 BV. The eluent was collected.

[0095] The first effluent and the eluent are mixed to obtain a compound liquid. The mass ratio of organic acid to inositol in the compound liquid is 18:1. The compound liquid is adsorbed through a cation exchange resin column (D001) at an injection flow rate of 3 BV / h, and the second effluent is collected. The second effluent was concentrated using a nanofiltration membrane (200 Da pore size) at 25°C and 2 MPa, resulting in a concentrate with a solid content of 13 wt%. This concentrate was then subjected to thermal concentration at 70°C to obtain a liquid fertilizer with a solid content of 43 wt%. The total content of organic acids and inositol in the liquid fertilizer was 400 g / L.

[0096] Example 2 Preparation of liquid fertilizer: A flocculant solution (chitosan) was added to the fermentation broth prepared in Example 1, and the mixture was mixed to obtain a mixed solution. Then, diatomaceous earth was added for filtration. The mixed solution was filtered and separated, and the clear liquid was collected. The concentration of the flocculant solution was 0.1 wt%, and the volume ratio of the flocculant solution to the fermentation broth was 0.5:1. The mass ratio of the mixed solution to the diatomaceous earth was 1:0.03. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; wherein, the pore size of the ultrafiltration membrane is 2000 Da, and the operating temperature of the clarified liquid when filtering through the ultrafiltration membrane is 20°C and the operating pressure is 0.1 MPa; The ultrafiltration membrane supernatant was injected through an anion exchange resin (D304) at a flow rate of 1 BV / h until saturation. The first effluent was collected and then eluted with a 2 wt% sodium hydroxide solution. The injection volume of the sodium hydroxide solution was 2 BV, and the eluent was collected.

[0097] The first effluent and the eluent are mixed to obtain a compound liquid. The mass ratio of organic acid to inositol in the compound liquid is 15:1. The compound liquid is adsorbed through a cation exchange resin column (D001) at an injection flow rate of 2 BV / h, and the second effluent is collected. The second effluent was concentrated using a nanofiltration membrane (200 Da pore size) at 20°C and 1 MPa, resulting in a concentrate with a solid content of 10 wt%. This concentrate was then subjected to thermal concentration at 70°C to obtain a liquid fertilizer with a solid content of 40 wt%. The total content of organic acids and inositol in the liquid fertilizer was 360 g / L.

[0098] Example 3 Preparation of liquid fertilizer: A flocculant solution (chitosan) was added to the fermentation broth prepared in Example 1, and the mixture was mixed to obtain a mixed solution. Then, diatomaceous earth was added for filtration. The mixed solution was filtered and separated, and the clear liquid was collected. The concentration of the flocculant solution was 0.5 wt%, and the volume ratio of the flocculant solution to the fermentation broth was 0.2:1. The mass ratio of the mixed solution to the diatomaceous earth was 1:0.05. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; wherein, the pore size of the ultrafiltration membrane is 2000 Da, and the operating temperature of the clarified liquid when filtering through the ultrafiltration membrane is 30°C and the operating pressure is 0.5 MPa; The ultrafiltration membrane supernatant was injected through an anion exchange resin (D304) at a flow rate of 2 BV / h until saturation. The first eluent was collected, and then eluted with a 4 wt% sodium hydroxide solution at an injection volume of 2 BV. The eluent was collected.

[0099] The first effluent and the eluent are mixed to obtain a compound liquid. The mass ratio of organic acid to inositol in the compound liquid is 20:1. The compound liquid is adsorbed through a cation exchange resin column (D001) at an injection flow rate of 3 BV / h, and the second effluent is collected. The second effluent was concentrated using a nanofiltration membrane (200 Da pore size) at 20°C and 3 MPa, resulting in a concentrate with a solid content of 15 wt%. This concentrate was then subjected to thermal concentration at 70°C to obtain a liquid fertilizer with a solid content of 45 wt%. The total content of organic acids and inositol in the liquid fertilizer was 420 g / L.

[0100] Example 4 Preparation of liquid fertilizer: A flocculant solution (chitosan) was added to the fermentation broth prepared in Example 1, and the mixture was mixed to obtain a mixed solution. Then, diatomaceous earth was added for filtration. The mixed solution was filtered and separated, and the clear liquid was collected. The concentration of the flocculant solution was 0.2 wt%, and the volume ratio of the flocculant solution to the fermentation broth was 0.4:1. The mass ratio of the mixed solution to the diatomaceous earth was 1:0.04. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; wherein, the pore size of the ultrafiltration membrane is 2000 Da, and the operating temperature of the clarified liquid when filtering through the ultrafiltration membrane is 25°C and the operating pressure is 0.3 MPa; The ultrafiltration membrane supernatant was injected through an anion exchange resin (D304) at a flow rate of 1.5 BV / h until saturation. The first eluent was collected, and then eluted with a 3 wt% sodium hydroxide solution at an injection volume of 2 BV. The eluent was collected.

[0101] The first effluent and the eluent are mixed to obtain a compound liquid. The mass ratio of organic acid to inositol in the compound liquid is 16:1. The compound liquid is adsorbed through a cation exchange resin column (D001) at an injection flow rate of 2 BV / h, and the second effluent is collected. The second effluent was concentrated using a nanofiltration membrane (200 Da pore size) at 25°C and 3 MPa, resulting in a concentrate with a solid content of 13 wt%. This concentrate was then subjected to thermal concentration at 70°C to obtain a liquid fertilizer with a solid content of 43 wt%. The total content of organic acids and inositol in the liquid fertilizer was 391 g / L.

[0102] Example 5 Preparation of fermentation broth: Referring to the preparation method of the fermentation broth in Example 1, the difference is that the seed cultures of *Corynebacterium glutamicum*, *Lactobacillus*, and *Kluyveromyces martensii* were mixed, and the resulting mixed bacterial culture was inoculated into the fermentation medium at an inoculum size of 10% (v / v). The culture conditions included: a pH of 7 in the fermentation medium, an initial air flow rate of 1.5 m³ / L, a maintenance pressure of 0.05 MPa, a fermentation temperature of 30°C, a stirring speed of 250 rpm, and the pH was maintained by adding 50 wt% ammonia water during fermentation. The culture was carried out for 47 hours to obtain the fermentation broth. The fermentation medium contained 90 g / L glucose, 8 g / L glycerol, and 7 g / L urea. The content is 1.5g / L. The content of [unspecified substance] is 0.5 g / L, and the content of biotin is 0.004 g / L. The content of [unspecified substance] was 0.01 g / L, and the content of citric acid was 0.7 g / L; based on the volume percentage of the mixed bacterial culture, the content of Corynebacterium glutamicum seed culture was 65%, the content of Lactic acid bacteria seed culture was 18%, and the content of Kluyveromyces martensii seed culture was 17%. Tests showed that the fermentation broth contained 220 g / L of organic acids and 35 g / L of inositol. The fermentation broth also contained amino acids, citric acid, acetic acid, lactic acid, and tartaric acid; among them, the amino acid content was 100 g / L.

[0103] Preparation of liquid fertilizer: A flocculant solution (chitosan) was added to the fermentation broth, and the mixture was mixed to obtain a mixed solution. Then, diatomaceous earth was added to aid filtration. The mixed solution was filtered and separated, and the clear liquid was collected. The concentration of the flocculant solution was 0.3 wt%, and the volume ratio of the flocculant solution to the fermentation broth was 0.4:1. The mass ratio of the mixed solution to the diatomaceous earth was 1:0.05. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; wherein, the pore size of the ultrafiltration membrane is 2000 Da, and the operating temperature of the clarified liquid when filtering through the ultrafiltration membrane is 25°C and the operating pressure is 0.3 MPa; The ultrafiltration membrane supernatant was injected through an anion exchange resin (D304) at a flow rate of 1 BV / h until saturation. The first eluent was collected, and then eluted with a 4 wt% sodium hydroxide solution at an injection volume of 2 BV. The eluent was collected.

[0104] The first effluent and the eluent are mixed to obtain a compound liquid. The mass ratio of organic acid to inositol in the compound liquid is 19:1. The compound liquid is adsorbed through a cation exchange resin column (D001) at an injection flow rate of 2 BV / h, and the second effluent is collected. The second effluent was concentrated using a nanofiltration membrane (200 Da pore size) at 25°C and 3 MPa, resulting in a concentrate with a solid content of 13 wt%. This concentrate was then subjected to thermal concentration at 70°C to obtain a liquid fertilizer with a solid content of 43 wt%. The total content of organic acids and inositol in the liquid fertilizer was 430 g / L.

[0105] Example 6 The fermentation broth was prepared according to the method described in Example 1; Referring to the liquid fertilizer preparation method in Example 1, the difference is that the first effluent and the eluent are mixed to obtain a compound liquid. The mass ratio of organic acid to inositol in the compound liquid is 13:1. The remaining preparation steps are the same as in Example 1. The total content of organic acid and inositol in the obtained liquid fertilizer is 392 g / L.

[0106] Comparative Example 1 The liquid fertilizer preparation method of Example 1 is the same as in Example 1, except that the clarified liquid is not subjected to ultrafiltration membrane filtration, but is directly adsorbed and eluted by anion exchange resin; the remaining preparation steps are the same as in Example 1. The total content of organic acids and inositol in the obtained liquid fertilizer is 400 g / L.

[0107] Comparative Example 2 Referring to the liquid fertilizer preparation method of Example 1, the difference is that the second effluent is not subjected to nanofiltration membrane concentration; instead, it is directly subjected to thermal concentration. The remaining preparation steps are the same as in Example 1. The total content of organic acids and inositol in the obtained liquid fertilizer is 410 g / L.

[0108] Comparative Example 3 The liquid fertilizer preparation method is the same as in Example 1, except that the ultrafiltration membrane supernatant is not adsorbed using anion exchange resin (D304). Instead, the supernatant is directly passed through a cation exchange resin column (D001) at an injection flow rate of 3 BV / h for adsorption, and the effluent is collected. The remaining preparation steps are the same as in Example 1. The total content of organic acids and inositol in the obtained liquid fertilizer is 420 g / L.

[0109] Comparative Example 4 Referring to the liquid fertilizer preparation method of Example 1, the difference is that the first effluent and the eluent are mixed, and the resulting compound liquid is not subjected to cation exchange resin column (D001) adsorption. Instead, the compound liquid is directly concentrated through a nanofiltration membrane (pore size of 200 Da). The remaining preparation steps are the same as in Example 1. The total content of organic acids and inositol in the obtained liquid fertilizer is 425 g / L.

[0110] Test case The liquid fertilizers containing inositol and organic acids prepared in Examples 1-6 and Comparative Examples 1-4 were tested.

[0111] The test methods include: The experimental site is located in Yingawati Village, Yingmaili Township, Jiashi County, Kashgar Prefecture. It has a temperate continental climate with an average annual temperature of 11.7℃, an average annual frost-free period of 233 days, an average annual sunshine duration of 2923.7 hours, an average annual precipitation of 64.6 mm, and an average annual evaporation of 2051.5 mm. The test crop was cotton, variety Xinluzhong 60. Six experimental groups, four control groups, and one blank control group were set up. Experimental groups 1-6 used the liquid fertilizers described in Examples 1-6, respectively; control groups 1-4 used the liquid fertilizers described in Comparative Examples 1-4, respectively; and the blank control group used local conventional fertilizers. Specifically, experimental group 1 used local conventional fertilizers and the liquid fertilizer from Example 1; and so on, up to experimental group 6, which used local conventional fertilizers and the liquid fertilizer from Example 6; control group 1 used local conventional fertilizers and the liquid fertilizer from Comparative Example 1; control group 2 used local conventional fertilizers and the liquid fertilizer from Comparative Example 2; control group 3 used local conventional fertilizers and the liquid fertilizer from Comparative Example 3; control group 4 used local conventional fertilizers and the liquid fertilizer from Comparative Example 4; and the blank control group used only local conventional fertilizers.

[0112] Each experimental group, control group, and blank control group had three replicates. Fertilization was performed via drip irrigation, with one application after cotton sowing and a second application 7 days after sowing. During the planting period, the amount of liquid fertilizer used in each of the experimental groups 1-6 and control groups 1-4 was the same, at 10 kg / mu, applied twice via drip irrigation (once after cotton sowing and 7 days after sowing). The amount of local conventional fertilizer used in each of the experimental groups 1-6, control groups 1-4, and blank control group was the same, at 78 kg / mu, applied in multiple stages (once after cotton sowing, 7 days after sowing, during the budding stage, boll-forming stage, and boll-opening stage). The fertilization times were the same for all experimental groups, control groups, and blank control group, and the fertilizer application amount was the same for each stage. Cotton was sown on April 16 and harvested in mid-October. Soil physicochemical properties and cotton yield per mu (a Chinese unit of area, approximately 0.067 hectares) were tested after harvesting. The test results are shown in Table 1.

[0113] Table 1 As shown in Table 1, compared with the control groups 1-4 and the blank control group, the liquid fertilizer prepared by the present invention in experimental groups 1-6 can effectively increase the soil CEC value and improve the soil's nutrient retention capacity; reduce the pH value of saline-alkali soil, bringing the soil pH value closer to 7, and lower the salt content in the soil. Furthermore, experimental groups 1-6 showed higher cotton yields. This demonstrates that the liquid fertilizer prepared by the present invention has lower impurity content and is rich in organic acids and inositol. Through the synergistic effect of organic acids and inositol, it can lower the pH value of saline-alkali soil, alleviate salt damage to cells, promote plant growth and nutrient absorption, and increase crop yield. Simultaneously, it can improve the soil microenvironment, enhance soil nutrient retention capacity, and reduce soil salinity. In contrast, Comparative Example 1 did not undergo ultrafiltration membrane filtration. The large molecular organic matter remaining in the clarified liquid was easily adsorbed or blocked on the resin surface and pores, leading to a decrease in the removal efficiency of anionic and cationic impurities, resulting in a relatively high impurity content in the liquid fertilizer. The second effluent, after being concentrated by nanofiltration, can further remove anionic impurities (such as phosphate, sulfate, and chloride ions) and cationic impurities (such as magnesium ions). Comparative Example 2, however, did not undergo nanofiltration concentration, resulting in a higher impurity content in the liquid fertilizer. This led to a low soil CEC value, high salinity, failure to improve soil pH, and low cotton yield. Comparative Example 3's ultrafiltration membrane effluent did not use anion exchange resin (D304) for adsorption; instead, it was directly adsorbed through a cation exchange resin column (D001). While this removed cations (such as sodium, magnesium, and potassium ions) from the ultrafiltration membrane effluent, the resulting liquid fertilizer contained a significant amount of anionic impurities (such as phosphate, sulfate, and chloride ions). Chloride and sulfate ions can combine with calcium and magnesium ions in the soil to form salts. These salts are not easily absorbed by crops and tend to accumulate on the soil surface, increasing soil osmotic pressure and causing salt damage. Phosphate ions combine with calcium ions to form calcium phosphate precipitates, which can damage soil structure and indirectly promote salt accumulation on the soil surface. In Comparative Example 4, the compound liquid was not adsorbed by a cation exchange resin column (D001), which prevented the organic acid salts from being converted back into organic acids. Furthermore, the fertilizer contained a large number of cations (such as sodium and potassium ions). Sodium and potassium ions are one of the main components of salt. Applying fertilizers containing sodium and potassium ions will increase the soil salinity, leading to salinization. This results in low soil CEC value, high salt content, and failure to improve soil pH, leading to low cotton yield.

[0114] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a liquid fertilizer, characterized in that, The preparation method includes: A flocculant is added to a fermentation broth containing organic acids and inositol, and the mixture is mixed to obtain a mixture. The mixture is then filtered and the clear liquid is collected. The clarified liquid is filtered through an ultrafiltration membrane to obtain an ultrafiltration membrane clarified liquid; The ultrafiltration membrane supernatant is adsorbed and eluted by anion exchange resin, and the first effluent and the eluent are collected separately. The first effluent and the eluent are mixed to obtain a compound liquid, which is then adsorbed through a cation exchange resin column to collect the second effluent. The second effluent is concentrated by nanofiltration membrane, and the concentrate is then concentrated by heat to obtain liquid fertilizer.

2. The preparation method according to claim 1, characterized in that, The fermentation broth is obtained by fermenting a mixture of bacteria in a glucose-containing culture medium, the mixture of bacteria including Corynebacterium glutamicum, lactic acid bacteria and yeast; In the fermentation broth, the content of the organic acid is 200-300 g / L, and the content of the inositol is 20-40 g / L; The organic acid comprises at least one of amino acids, citric acid, acetic acid, lactic acid, and tartaric acid.

3. The preparation method according to claim 1 or 2, characterized in that, The flocculant is selected from chitosan and / or polyacrylamide; The flocculant is added to the fermentation broth in solution form, with a flocculant solution concentration of 0.1-0.5 wt% and a volume ratio of flocculant solution to fermentation broth of (0.2-0.5):1; and / or, The filtration separation of the mixture includes: adding diatomaceous earth to the mixture for filtration aid and collecting the clear liquid.

4. The preparation method according to claim 1 or 2, characterized in that, The ultrafiltration membrane has a pore size of 2000 Da-3000 Da, and the operating temperature of the clarified liquid when filtered through the ultrafiltration membrane is 20-30℃ and the operating pressure is 0.1-0.5 MPa.

5. The preparation method according to claim 1 or 2, characterized in that, The ultrafiltration membrane supernatant is introduced through anion exchange resin at a flow rate of 1-2 BV / h until saturation. The first effluent is collected and then eluted with a sodium hydroxide solution of 2wt%-4wt%, with an injection volume of 2-3 BV. The eluent is then collected.

6. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of organic acid to inositol in the compound liquid obtained by mixing the first effluent and the eluent is (15-20):

1.

7. The preparation method according to claim 1 or 2, characterized in that, The compounded liquid is injected through a cation exchange resin column at a flow rate of 2-4 BV / h until it is saturated.

8. The preparation method according to claim 1 or 2, characterized in that, The second effluent is concentrated using a nanofiltration membrane with a pore size of 100-200 Da, an operating temperature of 20-30°C, and an operating pressure of 1-3 MPa. The concentrated solution after nanofiltration has a solid content of 10-15 wt%; and / or, The concentrated liquid is heat-concentrated at a temperature of 60-70°C, and the solid content of the liquid fertilizer is 40-45 wt%.

9. A liquid fertilizer, characterized in that, It is prepared by the liquid fertilizer preparation method according to any one of claims 1-8.

10. The application of the liquid fertilizer according to claim 9 in alleviating the stress of high salt and high acidity / alkalinity on crops.

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