Coated slow-release solid water-soluble fertilizer, preparation method and application thereof

Abstract

The application discloses a kind of film-coated sustained-release solid water-soluble fertilizer and its preparation method and application, including the following weight fraction components: nitrogen source 15~20 parts, phosphorus source 8~12 parts, potassium source 15~25 parts, humic acid 3~8 parts, biochar powder 10~15 parts;Functional microorganism 0.5~1.5 parts, microbial metabolite 1~2 parts, seaweed extract 2~5 parts, chitosan-gelatin composite material 5~8 parts;The functional microorganism is adsorbed on the biochar powder bacillus subtilis, bacillus licheniformis and azotobacter.The film-coated sustained-release solid water-soluble fertilizer provided in the application has the effects of nutrient supply and prevention and control of soil-borne diseases, achieves one fertilizer multiple effects, can improve crop nutrient utilization rate, inhibit soil-borne diseases and promote soil microbial diversification.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, and more specifically to a coated slow-release solid water-soluble fertilizer, its preparation method, and its application. Background Technology

[0002] Soil-borne diseases refer to diseases caused by pathogens such as fungi, bacteria, nematodes, and viruses that live in the soil with diseased plant debris and attack crops through the roots or stems when conditions are suitable. Soil-borne diseases are a significant factor restricting agricultural production, seriously affecting crop yield and quality. Solid water-soluble fertilizers, by providing sufficient nutrition, enhance crop resistance and reduce the occurrence of soil-borne diseases. Furthermore, they are gaining increasing attention from agricultural growers because they improve fertilizer utilization and promote ecological environmental protection. However, traditional solid water-soluble fertilizers often use chemical control methods. While these methods can control soil-borne diseases to some extent, long-term use can easily lead to soil ecological imbalance, increased pathogen resistance, and adverse effects on the environment and human health.

[0003] Microbial fertilizers, as a novel type of fertilizer, contain specific living microorganisms that increase crop nutrient supply or promote crop growth through their life activities, thereby increasing yield, improving crop quality, and enhancing the agricultural ecological environment. However, microbial activity is easily affected by environmental factors, and the nutrient release rate is difficult to synchronize with crop needs. Therefore, it is necessary to prepare them in the form of slow-release compound fertilizers. Chinese invention patent CN 107011071A discloses a slow-release microbial compound fertilizer and its preparation method. However, the coating material of this patent uses a traditional combination of gelatin and polyvinyl alcohol, which has limited functionality and environmental friendliness, and its ability to control soil-borne diseases such as bacterial wilt and Fusarium wilt has not been studied in depth. Therefore, there is an urgent need to develop a slow-release microbial compound fertilizer that can both promote crop growth and prevent soil-borne diseases. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a coated slow-release solid water-soluble fertilizer, its preparation method, and the application of the coated slow-release solid water-soluble fertilizer provided by this invention.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] A coated slow-release solid water-soluble fertilizer comprises the following components in parts by weight: 15-20 parts nitrogen source, 8-12 parts phosphorus source, 15-25 parts potassium source, 3-8 parts humic acid, 10-15 parts biochar powder, 0.5-1.5 parts functional microorganisms, 1-2 parts microbial metabolites, 2-5 parts seaweed extract, and 5-8 parts chitosan-gelatin composite material; wherein the functional microorganisms are Bacillus subtilis, Bacillus licheniformis, and Nitrogenin spirochetes adsorbed on the biochar powder.

[0007] The coated slow-release solid water-soluble fertilizer provided by this invention has the effects of both nutrient supply and prevention of soil-borne diseases, achieving multiple benefits from one fertilizer. It can improve crop nutrient utilization, inhibit soil-borne diseases, and promote soil microbial diversity.

[0008] Furthermore, the preparation method of the functional microorganisms is as follows: biochar powder is soaked in a mixed bacterial solution, adsorbed, and then filtered dry to obtain the functional microorganisms; the effective viable counts in the mixed bacterial solution are 0.8-1.5 billion CFU / g for Bacillus subtilis, 0.09-0.13 billion CFU / g for Bacillus licheniformis, and 0.09-0.13 billion CFU / g for Azotobacter nigra.

[0009] The mixed bacterial solution must contain sufficient functional bacteria. Appropriate concentrations of these bacteria help enhance soil microbial diversity, competitively repel pathogens, reduce soil-borne diseases such as bacterial wilt and Fusarium wilt, and simultaneously improve crop disease resistance and growth vigor. Biochar powder, made from ordinary straw, provides attachment sites for functional microorganisms through its porous structure, promoting the growth of beneficial bacteria and certain functional bacteria. The adsorption and hydrolysis of signaling molecules by biochar affects interspecies communication among microorganisms, thereby altering the soil microbial community structure. The combination of biochar and complex microorganisms promotes the reproduction of beneficial microorganisms, increases microbial diversity and function, and enhances crop disease resistance.

[0010] Furthermore, the microbial metabolites are at least one of lactic acid bacteria metabolites and streptomycin secondary metabolites.

[0011] Lactic acid bacteria produce metabolites such as lactic acid and bacteriocins, while Streptomyces can produce various polysaccharides, enzymes, and plant hormones. These metabolites can promote crop root growth, enhance stress resistance, and control pests and diseases.

[0012] Furthermore, the preparation method of the seaweed extract includes: alkali hydrolysis of seaweed, followed by fermentation degradation using compound microbial enzymes.

[0013] Seaweed extract obtained through fermentation and degradation contains active substances such as alginic acid, polysaccharides, and oligosaccharides. Seaweed extract can act as a biostimulant, which can improve the adaptability of crops to environmental stress, enhance their resistance to adverse conditions and pests, and improve fertilizer effectiveness.

[0014] Furthermore, the compound microbial enzyme comprises 32-38 wt% cellulase, 13-18 wt% pectinase, 10-16 wt% hemicellulase, 10-15 wt% amylase, and 21-27 wt% protease.

[0015] Different microbial enzymes have their own unique fermentation methods and fermentation products. During fermentation, these enzymes interact and promote each other, producing various beneficial fermentation substances. After seaweed is fermented by the compound microorganisms of this application, the extract contains a variety of plant hormones and bioactive substances such as alginic acid, amino acids, and polysaccharides. These substances have enhanced activity after fermentation, significantly affecting the physiological processes of crops and contributing to their healthy growth.

[0016] Furthermore, the nitrogen source is at least one of urea, ammonium nitrate, and ammonium bicarbonate.

[0017] Urea contains up to 46% nitrogen, ammonium nitrate contains about 34% nitrogen, and ammonium bicarbonate contains about 17% nitrogen. These substances are rapidly absorbed by crops after being applied to the soil. As nitrogen sources, these three substances can quickly replenish the nitrogen needed by crops in the soil, increase the nutritional content of crops, and improve their quality and taste.

[0018] Furthermore, the phosphorus source is at least one of phosphorus pentoxide, diammonium phosphate, monoammonium phosphate, and ammonium polyphosphate.

[0019] The above-mentioned substances are suitable as phosphorus sources for various soils and crops, and can promote crop root development and flower bud differentiation, thereby increasing crop yield and quality.

[0020] Furthermore, the potassium source is at least one of potassium chloride, potassium sulfate, potassium nitrate, and potassium oxide.

[0021] Potassium chloride is inexpensive and readily soluble, making it suitable for field crops that are not sensitive to chloride ions, such as wheat and corn. Potassium sulfate provides sulfur in addition to potassium, making it suitable for crops that require more sulfur. Potassium nitrate is suitable for cash crops, such as tobacco, melons, fruits, and vegetables. Potassium oxide has a high potassium content and is suitable as a potassium source for various crops that require high potassium content.

[0022] Furthermore, the particle size of the biochar powder is 50–500 μm.

[0023] The size of biochar particles has a certain impact on their adsorption performance. Generally speaking, the smaller the particles, the larger the specific surface area, and therefore the better the adsorption performance. However, excessively small particles can also create too many pores and defects, affecting their adsorption performance. Biochar particles with a diameter of 50–500 μm have a porous structure suitable for complex microorganisms, providing attachment sites for them, while also enhancing soil microbial activity and promoting the growth of beneficial bacteria and certain functional bacteria.

[0024] Furthermore, the preparation method of the chitosan-gelatin composite material includes:

[0025] Chitosan solution was prepared by dissolving chitosan in a 2wt%–4wt% acetic acid solution;

[0026] Dissolve gelatin in water to make it swell, and prepare a gelatin solution with a mass fraction of 1% to 10%;

[0027] Chitosan solution and gelatin solution are mixed to obtain the chitosan-gelatin composite material.

[0028] Acetic acid solution is a weak acid, and a concentration of 2wt%–4wt% provides suitable solubility for chitosan while having limited degradation effects, thus maintaining the high molecular weight of chitosan and better exerting its biological activity and function. Gelatin fully swells in water, resulting in a chitosan-gelatin composite material with excellent slow-release fertilizer release, improving the absorption and utilization rate of fertilizer components by crops.

[0029] A method for preparing a coated slow-release solid water-soluble fertilizer according to the above, comprising:

[0030] S1: Mix nitrogen, phosphorus, and potassium sources with humic acid powder to prepare core particles;

[0031] S2: Add functional microorganisms to the microbial metabolic concentrate, add carboxymethyl cellulose, polyethylene glycol and polyvinyl alcohol to prepare a suspended biochar mixture; spray the suspended biochar mixture onto the surface of the core particles to form a functional microbial coating;

[0032] S3: Apply chitosan-gelatin composite material to the surface of the functional microbial coating, cure it to form a coating layer;

[0033] S4: Apply seaweed extract to the surface of the coating layer to form a biostimulant coating, thus obtaining a coated slow-release solid water-soluble fertilizer.

[0034] The coated slow-release solid water-soluble fertilizer of this application comprises a four-layer structure from the inside out: core particles, a functional microbial coating, a covering layer, and a biostimulant coating. The core particles, located in the innermost layer, reduce nutrient loss and improve the long-term utilization rate of the fertilizer. Humic acid, derived from weathered coal, lignite, and other organic matter, can form stable complexes with nitrogen, phosphorus, and potassium elements, facilitating the slow release of nutrients and continuous absorption by crops, increasing the crop's ability to absorb nutrients such as nitrogen, phosphorus, and potassium, promoting crop growth, and reducing nutrient loss. The functional microbial coating has antibacterial properties; carboxymethyl cellulose and polyethylene glycol provide good stability to the suspended biochar mixture, while polyvinyl alcohol increases the adhesion of the suspension mixture. The main function of the covering layer is to protect the inner components, control the release rate, and improve fertilization effectiveness. The functional microbial layer, located between the core particles and the covering layer, effectively resists interference from the external environment on the functional microorganisms. Seaweed extract, used as a biostimulant coating, increases the granular structure of the outermost layer. The large pores between the granules provide ample oxygen, promoting the activity of microorganisms within the coating. Furthermore, the biostimulant coating promotes crop growth and enhances crop resistance, increasing the activity of various beneficial microorganisms in the soil, thereby strengthening crop resistance to pests and diseases and enhancing fertilizer effectiveness. The coated slow-release solid water-soluble fertilizer gradually decomposes and releases nutrients from the outer layer to the inner layer. This not only continuously supplies nutrients to the crop, synchronizing the internal nutrient release rate with the crop's needs, but also allows beneficial microorganisms inside the coated fertilizer and in the soil to aggregate, thus regulating microbial activity.

[0035] Furthermore, the moisture content of the core particles is less than 2%.

[0036] The low moisture content of the core particles prevents the nutrients inside the coated slow-release solid water-soluble fertilizer from being released too quickly, which is conducive to the slow release of nutrients and continuous absorption by crops. This increases the long-term absorption of nutrients such as nitrogen, phosphorus, and potassium by crops, reduces nutrient loss, and improves the utilization rate of nutrients by crops.

[0037] Application of a coated slow-release solid water-soluble fertilizer based on the above in crop nutrient supply and soil-borne disease control.

[0038] This application utilizes slow-release coating technology to organically combine humic acid, functional microorganisms, microbial metabolites, and seaweed extracts, which can provide crops with sufficient nutrient supply. The functional microorganisms have significant effects on the prevention and control of soil-borne diseases, and can also enhance the diversity of beneficial microorganisms in the soil and improve the crop's disease resistance, thus achieving the goal of multiple benefits from one fertilizer.

[0039] Furthermore, the crops include at least one of chili peppers, tomatoes, cucumbers, corn, and eggplants.

[0040] Experiments have shown that the coated slow-release solid water-soluble fertilizer of this invention has good yield-increasing and disease-resistant capabilities in peppers, tomatoes, cucumbers, corn, and eggplants. The fertilizer in this application contains all the nutrients commonly needed by peppers, tomatoes, cucumbers, corn, and eggplants, such as nitrogen, phosphorus, and potassium. Furthermore, the fertilizer in this application has a control effect on common soil-borne pathogens and can be used on a variety of crops.

[0041] Furthermore, the soil-borne diseases include bacterial wilt and / or Fusarium wilt.

[0042] Bacterial wilt, a disease affecting a wide range of crops, is caused by pathogens such as *Ralstonia solanacearum*. Fusarium wilt, also known as blight, is caused by pathogens such as *Fusarium oxysporum*. The functional microorganisms in this application, *Bacillus subtilis* and *Bacillus licheniformis*, can secrete antibiotics, enzymes, and growth-promoting substances, effectively inhibiting the growth of soil-borne pathogens. *Azospirillum* provides a usable nitrogen source through nitrogen fixation, creating more favorable nutrient conditions for plant growth. The combination of these three beneficial bacteria with biochar powder synergistically enhances soil microbial diversity, competitively excludes pathogens of bacterial wilt and Fusarium wilt, and improves crop disease resistance.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] 1. The coated slow-release solid water-soluble fertilizer provided by this invention combines nutrient supply with the prevention and control of soil-borne diseases, achieving multiple benefits from a single fertilizer. It can improve crop nutrient utilization, inhibit soil-borne diseases, and promote soil microbial diversity. It is beneficial to maintaining soil ecological health, and the fertilizer effect is significantly enhanced. Specifically, by using slow-release coating technology to organically combine humic acid, functional microorganisms, microbial metabolites, and seaweed extract, a comprehensive improvement in fertilizer utilization, plant resistance, and soil health is achieved. The fertilizer of this application continuously releases nutrients such as nitrogen, phosphorus, and potassium during crop growth, reducing nutrient loss and improving fertilizer utilization efficiency; functional microorganisms and their metabolites effectively enhance plant disease resistance and stress resistance by inhibiting pathogens, decomposing organic matter, and improving the rhizosphere microbial community; seaweed extract, as a biostimulant, promotes plant growth and improves resistance. In addition, humic acid and biochar powder optimize soil structure, enhance water and fertilizer retention capacity, and further improve soil health.

[0045] 2. Functional microorganisms utilize the porous structure of biochar to provide attachment sites for complex microorganisms, promoting the growth of beneficial bacteria and certain functional bacteria. The adsorption and hydrolysis of signaling molecules by biochar affect interspecies communication among microorganisms, thereby altering the soil microbial community structure, promoting the reproduction of beneficial microorganisms, increasing microbial diversity and function, maintaining the stability of the soil ecological community, and enhancing crop disease resistance. Among the functional microorganisms, Bacillus subtilis and Bacillus licheniformis can secrete antibiotics, enzymes, and growth-promoting substances, effectively inhibiting the growth of soil-borne pathogens. Simultaneously, nitrogen-fixing spirochetes provide a usable nitrogen source through nitrogen fixation, creating more favorable nutrient conditions for crop growth. The synergistic effect of these three beneficial bacteria and biochar can enhance soil microbial diversity, competitively exclude pathogens, reduce the occurrence of soil-borne diseases such as bacterial wilt and Fusarium wilt, and simultaneously improve crop disease resistance and growth vigor. Detailed Implementation

[0046] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are all within the scope of protection of the present invention. Unless otherwise specified, the experimental materials, reagents, instruments, etc., used in the embodiments of the present invention are all commercially available; unless specifically specified, all technical means in the embodiments of the present invention are conventional means well known to those skilled in the art.

[0047] Example 1

[0048] This embodiment provides a method for preparing a coated slow-release solid water-soluble fertilizer, which is prepared using the following components: 15 kg of urea, 10 kg of monoammonium phosphate, 20 kg of potassium chloride, 5 kg of humic acid, 10 kg of biochar powder; 0.5 kg of mixed bacterial solution; 2 kg of microbial metabolites; 3 kg of seaweed extract; and 6 kg of coating solution.

[0049] The specific preparation method includes the following steps:

[0050] S1. Preparation of core particles: Urea, monoammonium phosphate, potassium chloride and humic acid powder are mixed evenly, an appropriate amount of water is added, and the mixture is stirred into granules. The granules are then dried until the moisture content is less than 2% to obtain core particles.

[0051] S2. Preparation of Functional Microorganisms: Bacillus subtilis and Bacillus licheniformis were fermented using a high-dissolved-oxygen liquid fermentation process. The fermentation medium contained glucose, peptone, and corn steep liquor, with a pH of 6.5–7.0. The mixture was cultured at 37°C for 48 hours with continuous stirring and aeration to ensure rapid cell proliferation, ultimately yielding high concentrations of Bacillus subtilis and Bacillus licheniformis. Azotospirobacter was fermented using sucrose as the carbon source at a pH of 6.8–7.2 at 28°C for 48–72 hours with appropriate aeration or gentle stirring, ultimately obtaining a highly active azotospirobacter bacterial solution. The above bacterial solutions were mixed to obtain a mixed bacterial solution with effective viable counts of: Bacillus subtilis 120 million CFU / g, Bacillus licheniformis 100 million CFU / g, and Azotospirobacter 100 million CFU / g. Straw was burned to produce biochar powder of 50–500 μm. The mixed bacterial solution was then mixed with the sterilized biochar powder for adsorption, yielding the functional microorganisms.

[0052] S3. Preparation of Microbial Metabolites: The lactic acid bacteria fermentation medium uses glucose as the carbon source, and adds nutrients such as peptone and yeast extract. The pH is controlled at 6.0–6.5, the fermentation temperature is 32℃, and the fermentation time is 48 hours. Suitable temperature and acidity are maintained during fermentation to promote rapid growth of lactic acid bacteria and efficient accumulation of lactic acid. During fermentation, lactic acid bacteria produce metabolites such as lactic acid and bacteriocins. After fermentation, the bacterial cells are separated from the fermentation broth using an industrial centrifuge or filtration device. The fermentation broth contains the metabolites of lactic acid bacteria. Microfiltration membrane separation technology is used to further filter the fermentation broth to remove residual bacterial cells and macromolecular impurities, purifying the desired metabolites. The filtered fermentation broth is concentrated under vacuum conditions to reduce water content and increase the concentration of effective components, obtaining a concentrated microbial metabolite solution.

[0053] S4. Preparation of suspension mixture: The functional microorganisms obtained in S2 are added to the concentrated microbial metabolites obtained in S3. Carboxymethyl cellulose and polyethylene glycol are added to suspend biochar particles. Polyvinyl alcohol is added to increase the adhesion of the suspension mixture to obtain the suspension mixture.

[0054] S5. Functional microbial spraying: The suspension mixture obtained in S4 is sprayed at low temperature onto the surface of the core particles obtained in S1 to form fertilizer particles with a functional microbial coating.

[0055] S6. Preparation of coating solution: Chitosan was dissolved in a 2% (w / w) acetic acid solution and stirred for 30 minutes to obtain a chitosan solution; gelatin was dissolved in deionized water, ultrasonically dispersed for 3 hours, and left at room temperature for 24 hours to allow it to fully swell, thus obtaining a 10% (w / w) gelatin solution. The chitosan solution and gelatin solution were mixed to obtain the coating solution for the chitosan-gelatin composite material.

[0056] S7. Slow-release coating treatment: The fertilizer granules prepared in S5 are preheated at 35℃~50℃, and then the coating liquid prepared in S6 is uniformly sprayed or rolled onto the surface of the functional microbial coating in a rotating drum or fluidized bed; the coating is cured by heating or drying to form a uniform coating layer.

[0057] S8. Preparation of Seaweed Extract: Fresh seaweed is washed to remove impurities, minced and homogenized, and the pH of the homogenate is adjusted. Alkaline hydrolysis under pressure is then performed to break down the seaweed cell walls and release internal components. A compound microbial enzyme containing 32% cellulase, 18% pectinase, 10% hemicellulase, 15% amylase, and 21% protease is used to ferment and degrade the alkaline-hydrolyzed seaweed. The fermentation conditions are: temperature 32–37℃, pH adjusted to approximately 6.5, reaction time 18–24 hours, and moderate stirring to ensure sufficient contact between the enzyme and the seaweed. Under these conditions, the compound enzyme can efficiently decompose the seaweed cell walls, forming a seaweed extract rich in nutrients and bioactive small molecules.

[0058] S9. Biostimulant Coating: The seaweed extract obtained in S8 is evenly sprayed onto the surface of the coating layer formed in S7 to form a biostimulant coating, which further enhances the fertilizer effect.

[0059] Example 2

[0060] This embodiment provides a method for preparing a coated slow-release solid water-soluble fertilizer, which is prepared using the following components: 20 kg of urea, 8 kg of monoammonium phosphate, 25 kg of potassium nitrate, 8 kg of humic acid, 15 kg of biochar powder; 1 kg of mixed bacterial solution; 1 kg of microbial metabolites; 5 kg of seaweed extract; and 8 kg of coating solution.

[0061] The specific preparation method includes the following steps:

[0062] S1. Preparation of core particles: Urea, monoammonium phosphate, potassium nitrate and humic acid powder are mixed evenly, an appropriate amount of water is added, and the mixture is stirred into granules. The granules are then dried until the moisture content is less than 2% to obtain core particles.

[0063] S2. Preparation of Functional Microorganisms: Bacillus subtilis and Bacillus licheniformis were fermented using a high-dissolved-oxygen liquid fermentation process. The fermentation medium contained glucose, peptone, and corn steep liquor, with a pH of 6.5–7.0. The mixture was cultured at 37°C for 48 hours with continuous stirring and aeration to ensure rapid cell proliferation, ultimately yielding high concentrations of Bacillus subtilis and Bacillus licheniformis. Azotospirobacter was fermented using sucrose as the carbon source at a pH of 6.8–7.2 at 28°C for 48–72 hours with appropriate aeration or gentle stirring, ultimately obtaining a highly active azotospirobacter bacterial solution. The above bacterial solutions were mixed to obtain a mixed bacterial solution with effective viable counts of: Bacillus subtilis 150 million CFU / g, Bacillus licheniformis 9 million CFU / g, and Azotospirobacter 13 million CFU / g. Straw was burned to produce biochar powder of 50–500 μm. The mixed bacterial solution was then mixed with sterilized biochar powder for adsorption, yielding the functional microorganisms.

[0064] S3. Preparation of Microbial Metabolites: The lactic acid bacteria fermentation medium uses glucose as the carbon source, and adds nutrients such as peptone and yeast extract. The pH is controlled at 6.0–6.5, the fermentation temperature is 32℃, and the fermentation time is 48 hours. Suitable temperature and acidity are maintained during fermentation to promote rapid growth of lactic acid bacteria and efficient accumulation of lactic acid. During fermentation, lactic acid bacteria produce metabolites such as lactic acid and bacteriocins. After fermentation, the bacterial cells are separated from the fermentation broth using an industrial centrifuge or filtration device. The fermentation broth contains the metabolites of lactic acid bacteria. Microfiltration membrane separation technology is used to further filter the fermentation broth to remove residual bacterial cells and macromolecular impurities, purifying the desired metabolites. The filtered fermentation broth is concentrated under vacuum conditions to reduce water content and increase the concentration of effective components, obtaining a concentrated microbial metabolite solution.

[0065] S4. Preparation of suspension mixture: The functional microorganisms obtained in S2 are added to the concentrated microbial metabolites obtained in S3. Carboxymethyl cellulose and polyethylene glycol are added to suspend biochar particles. Polyvinyl alcohol is added to increase the adhesion of the suspension mixture to obtain the suspension mixture.

[0066] S5. Functional microbial spraying: The suspension mixture obtained in S4 is sprayed at low temperature onto the surface of the core particles obtained in S1 to form fertilizer particles with a functional microbial coating.

[0067] S6. Preparation of coating solution: Chitosan was dissolved in a 3% (w / w) acetic acid solution and stirred for 30 minutes to obtain a chitosan solution; gelatin was dissolved in deionized water, ultrasonically dispersed for 3 hours, and left at room temperature for 24 hours to allow it to fully swell, thus obtaining a 5% (w / w) gelatin solution. The chitosan solution and gelatin solution were mixed to obtain the coating solution for the chitosan-gelatin composite material.

[0068] S7. Slow-release coating treatment: The fertilizer granules prepared in S5 are preheated at 35℃~50℃, and then the coating liquid prepared in S6 is uniformly sprayed or rolled onto the surface of the functional microbial coating in a rotating drum or fluidized bed; the coating is cured by heating or drying to form a uniform coating layer.

[0069] S8. Preparation of Seaweed Extract: Fresh seaweed is washed to remove impurities, minced and homogenized, and the pH of the homogenate is adjusted. Alkaline hydrolysis is then performed under pressure to break down the seaweed cell walls and release internal components. A compound microbial enzyme containing 38% cellulase, 13% pectinase, 16% hemicellulase, 10% amylase, and 27% protease is used to ferment and degrade the alkaline-hydrolyzed seaweed. The fermentation conditions are: temperature 32–37℃, pH adjusted to approximately 6.5, reaction time 18–24 hours, and moderate stirring to ensure sufficient contact between the enzyme and the seaweed. Under these conditions, the compound enzyme can efficiently decompose the seaweed cell walls, forming a seaweed extract rich in nutrients and bioactive small molecules.

[0070] S9. Biostimulant Coating: The seaweed extract obtained in S8 is evenly sprayed onto the surface of the coating layer formed in S7 to form a biostimulant coating, which further enhances the fertilizer effect.

[0071] Example 3

[0072] This embodiment provides a method for preparing a coated slow-release solid water-soluble fertilizer, which is prepared using the following components: 15 kg of urea, 8 kg of monoammonium phosphate, 15 kg of potassium chloride, 3 kg of humic acid, 10 kg of biochar powder; 0.5 kg of mixed bacterial solution; 2 kg of microbial metabolites; 2 kg of seaweed extract; and 5 kg of coating solution.

[0073] The specific preparation method includes the following steps:

[0074] S1. Preparation of core particles: Urea, monoammonium phosphate, potassium chloride and humic acid powder are mixed evenly, an appropriate amount of water is added, and the mixture is stirred into granules. The granules are then dried until the moisture content is less than 2% to obtain core particles.

[0075] S2. Preparation of Functional Microorganisms: Bacillus subtilis and Bacillus licheniformis were fermented using a high-dissolved-oxygen liquid fermentation process. The fermentation medium contained glucose, peptone, and corn steep liquor, with a pH of 6.5–7.0. The mixture was cultured at 37°C for 48 hours with continuous stirring and aeration to ensure rapid cell proliferation, ultimately yielding high concentrations of Bacillus subtilis and Bacillus licheniformis. Azotospirobacter was fermented using sucrose as the carbon source at a pH of 6.8–7.2 at 28°C for 48–72 hours with appropriate aeration or gentle stirring, ultimately obtaining a highly active azotospirobacter bacterial solution. The above bacterial solutions were mixed to obtain a mixed bacterial solution with effective viable counts of: Bacillus subtilis 0.8 billion CFU / g, Bacillus licheniformis 0.13 billion CFU / g, and Azotospirobacter licheniformis 0.09 billion CFU / g. Straw was burned to produce biochar powder of 50–500 μm. The mixed bacterial solution was then mixed with sterilized biochar powder for adsorption, yielding the functional microorganisms.

[0076] S3. Preparation of Microbial Metabolites: The lactic acid bacteria fermentation medium uses glucose as the carbon source, and adds nutrients such as peptone and yeast extract. The pH is controlled at 6.0–6.5, the fermentation temperature is 32℃, and the fermentation time is 48 hours. Suitable temperature and acidity are maintained during fermentation to promote rapid growth of lactic acid bacteria and efficient accumulation of lactic acid. During fermentation, lactic acid bacteria produce metabolites such as lactic acid and bacteriocins. After fermentation, the bacterial cells are separated from the fermentation broth using an industrial centrifuge or filtration device. The fermentation broth contains the metabolites of lactic acid bacteria. Microfiltration membrane separation technology is used to further filter the fermentation broth to remove residual bacterial cells and macromolecular impurities, purifying the desired metabolites. The filtered fermentation broth is concentrated under vacuum conditions to reduce water content and increase the concentration of effective components, obtaining a concentrated microbial metabolite solution.

[0077] S4. Preparation of suspension mixture: The functional microorganisms obtained in S2 are added to the concentrated microbial metabolites obtained in S3. Carboxymethyl cellulose and polyethylene glycol are added to suspend biochar particles. Polyvinyl alcohol is added to increase the adhesion of the suspension mixture to obtain the suspension mixture.

[0078] S5. Functional microbial spraying: The suspension mixture obtained in S4 is sprayed at low temperature onto the surface of the core particles obtained in S1 to form fertilizer particles with a functional microbial coating.

[0079] S6. Preparation of coating solution: Chitosan was dissolved in a 4% (w / w) acetic acid solution and stirred for 30 minutes to obtain a chitosan solution; gelatin was dissolved in deionized water, ultrasonically dispersed for 3 hours, and left at room temperature for 24 hours to allow it to fully swell, thus obtaining a 1% (w / w) gelatin solution. The chitosan solution and gelatin solution were mixed to obtain the coating solution for the chitosan-gelatin composite material.

[0080] S7. Slow-release coating treatment: The fertilizer granules prepared in S5 are preheated at 40℃~50℃, and then the coating liquid prepared in S6 is uniformly sprayed or rolled onto the surface of the functional microbial coating in a rotating drum or fluidized bed; the coating is cured by heating or drying to form a uniform coating layer.

[0081] S8. Preparation of Seaweed Extract: Fresh seaweed is washed to remove impurities, minced and homogenized, and the pH of the homogenate is adjusted. Alkaline hydrolysis is then performed under pressure to break down the seaweed cell walls and release internal components. A compound microbial enzyme containing 35% cellulase, 16% pectinase, 13% hemicellulase, 12% amylase, and 24% protease is used to ferment and degrade the alkaline-hydrolyzed seaweed. The fermentation conditions are: temperature 32–37℃, pH adjusted to approximately 6.5, reaction time 18–24 hours, and moderate stirring to ensure sufficient contact between the enzymes and the seaweed. Under these conditions, the compound enzyme can efficiently decompose the seaweed cell walls, forming a seaweed extract rich in nutrients and bioactive small molecules.

[0082] S9. Biostimulant Coating: The seaweed extract obtained in S8 is evenly sprayed onto the surface of the coating layer formed in S7 to form a biostimulant coating, which further enhances the fertilizer effect.

[0083] Comparative Example

[0084] Commercially available compound fertilizer with a nutrient element ratio of N:P:K = 15:15:15 was selected for testing.

[0085] Experimental Example 1

[0086] Pepper seedlings of uniform growth were selected, and the experiment was conducted in a greenhouse. To ensure a consistent root growth environment, all plants were cultivated in pots with substrate, with 10 pots per treatment and 3 replicates for each treatment. The blank control group received no fertilizer. Fertilizer was applied to all examples and comparative examples by mixing 20g of fertilizer into the soil per 10kg of soil. Other agronomic practices remained consistent. Leaf width, plant height, stem diameter, and chlorophyll content were measured 30 days after fertilization. The results are shown in Table 1. Different letters in the table represent different levels of significance, with 'a' representing the strongest significance, and letters from 'a' to 'e' indicating decreasing significance.

[0087] Table 1. Statistics on the growth of chili seedlings

[0088]

[0089] As shown in Table 1, compared with the blank control group, the leaf width, plant height, stem diameter, and chlorophyll content of each example showed a significant increasing trend. Among them, Example 2, containing a higher proportion of functional microorganisms by mass, showed the most significant increase in the overall growth indicators of the peppers. Compared with the blank control group, the leaf width, plant height, stem diameter, and chlorophyll content of Example 2 increased by 187.3%, 56.9%, 72.6%, and 16.9%, respectively; compared with the comparative example, the leaf width, plant height, stem diameter, and chlorophyll content of Example 2 increased by 32.3%, 14.8%, 13.1%, and 2.6%, respectively. The above results indicate that the coated slow-release solid water-soluble fertilizer prepared in this application has a good promoting effect on the growth of pepper seedlings, and that the functional microorganisms have a significant impact on the growth of pepper seedlings.

[0090] Experimental Example 2

[0091] The number of beneficial microorganisms that could be cultured in the rhizosphere soil of the pepper seedlings cultured in Experiment Example 1 was counted. The statistical results are shown in Table 2. Different letters in the table represent different significant differences, with 'a' representing the strongest significance and letters from 'a' to 'e' representing decreasing significance.

[0092] Table 2. Number of beneficial microorganisms that can be cultured in the rhizosphere soil of chili seedlings

[0093]

[0094]

[0095] As shown in Table 2, the fertilizers used in the examples significantly increased the abundance of beneficial microorganisms in the rhizosphere soil of crops. Example 2 contained a higher proportion of functional microorganisms by mass, with the most significant increase in the number of culturable microorganisms in the rhizosphere soil of chili seedlings. Compared with the blank control group, the number of culturable bacteria, actinomycetes, and fungi in Example 2 increased by 27.9%, 38.9%, 72.6%, and 42.3%, respectively. The conventional compound fertilizer used in Comparative Example 1 did not significantly change the number of microorganisms in the rhizosphere soil of chili seedlings compared to the blank control group.

[0096] It can be concluded that adding functional microorganisms to coated slow-release solid water-soluble fertilizers can enhance plant disease resistance through multiple mechanisms. Functional microorganisms rapidly colonize the plant rhizosphere, occupying ecological sites, limiting the living space and resources of pathogens, reducing their infection opportunities, and promoting the diversity of beneficial microorganisms in pepper roots. This increased diversity of pepper root microorganisms also ensures enhanced disease resistance. Some beneficial microorganisms can secrete antibacterial substances, such as antibiotics and enzymes, which can directly inhibit or kill pathogens, reducing disease incidence. Beneficial microorganisms can activate the plant's defense system, improving its resistance to pathogens and enhancing disease resistance. The abundance of beneficial microorganisms can improve soil fertility, improve soil structure, promote healthy crop growth, and thus enhance its disease resistance.

[0097] Experimental Example 3

[0098] The effects of the fertilizers prepared in each example and comparative example on the disease resistance of tomatoes were evaluated through field surveys. The experimental site was a general farmland in Zhucun Village, Zengcheng District, Guangzhou, with loam soil. The test crop was tomato. The experiment included five treatments: Example 1, Example 2, Example 3, comparative example, and blank control group. Each treatment had 100 plants, with five replicates, and a total of 500 plants for each treatment. Disease incidence was observed and recorded regularly throughout the tomato's growth period. The number of diseased plants in each treatment and the percentage of total plants were recorded. A disease severity score was calculated, and the statistical results are detailed in Table 3.

[0099] Table 3 Number of diseased tomato plants

[0100]

[0101]

[0102] Table 3 shows that the percentage of diseased tomato plants in the blank control group and the comparative treatment were 7.8% and 8.2%, respectively. All treatments in the examples showed a significant decrease in the number of diseased plants, with Example 2 having the lowest percentage at only 1.4%, while Examples 1 and 3 had percentages of 3.4% and 3.0%, respectively. The results confirm that the application of the water-soluble fertilizer of this application significantly reduced the disease incidence and disease index, indicating that the fertilizer of this application enhances crop disease resistance. The coated slow-release solid water-soluble fertilizer of this application can be used as basal fertilizer and top dressing, applied in furrows, or used in fertigation, with a dosage of 10-15 kg per acre. It can significantly promote crop growth, reduce the spread of soil-borne diseases, and improve the crop's stress resistance.

[0103] Experiment Example 4

[0104] The effects of the fertilizer of this invention on the weight of different parts of chili seedlings were determined to verify whether its slow-release performance can continuously and evenly meet the nutrient requirements of crops at different growth stages. The chili pot experiment was conducted in a greenhouse from May to September 2024. Each pot contained 5 kg of soil, fertilized with 180 mg / kg of pure nitrogen. Two chili seedlings were transplanted into each pot. During cultivation, soil moisture was adjusted by weight to maintain a soil moisture content of 60% of field capacity. There were five treatments: Example 1, Example 2, Example 3, comparative example, and blank control group. Each treatment was replicated three times. The weight of each part of the chili seedlings was recorded after growth, and the statistical results are shown in Table 4. Different letters in the table represent different levels of significance, with 'a' representing the strongest significance, and letters from 'a' to 'e' representing decreasing significance.

[0105] Table 4 Weight of different parts of chili seedlings

[0106]

[0107]

[0108] Table 4 shows that different treatments had varying effects on the different organs and total dry weight of the chili pepper plant. The overall dry weight of the plant organs was: fruit > leaves and stems > roots. Example 2 showed the best performance among all treatments, with its total dry weight exceeding the blank control group and the comparative group by 154.8% and 60.4%, respectively. Significant differences existed between the total dry weight and fruit dry weight of the chili peppers among the different fertilization treatments, with the example treatment showing significantly better results than the control (no fertilization) and the comparative group. The main reason is that ordinary compound fertilizers generally release large amounts of nutrients in a short time, but over time, due to volatilization and leaching, nutrient supply becomes insufficient in the later stages of growth, resulting in overall lower plant growth compared to the slow-release fertilizer used in the example. This invention's coated slow-release solid water-soluble fertilizer utilizes materials and technologies to control and slow nutrient release, enabling sustained nutrient release and maximizing fertilizer utilization efficiency. Simultaneously, the organic combination of functional microorganisms, microbial metabolites, and seaweed extracts broadens the sources of nutrient absorption for crops, promoting crop growth and yield.

[0109] Similarly, applying the coated slow-release solid water-soluble fertilizer of the present invention to the planting of cash crops such as cucumbers, corn, and eggplants also has similar effects.

[0110] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A coated slow-release solid water-soluble fertilizer, characterized in that, The product comprises the following components in parts by weight: 15-20 parts nitrogen source, 8-12 parts phosphorus source, 15-25 parts potassium source, 3-8 parts humic acid, 0.5-1.5 parts functional microorganisms, 1-2 parts microbial metabolites, 2-5 parts seaweed extract, and 5-8 parts chitosan-gelatin composite material; the functional microorganisms are prepared by soaking biochar powder in a mixed bacterial solution of Bacillus subtilis, Bacillus licheniformis, and Azotobacter azolam, followed by adsorption and filtration; the microbial metabolites are lactic acid bacteria metabolites. The preparation method of the coated slow-release solid water-soluble fertilizer includes: S1: Mix nitrogen, phosphorus, and potassium sources with humic acid powder to prepare core particles; S2: Add functional microorganisms to a microbial metabolite concentrate, and add carboxymethyl cellulose, polyethylene glycol and polyvinyl alcohol to prepare a suspended biochar mixture; spray the suspended biochar mixture onto the surface of the core particles to form a functional microbial coating; S3: Apply chitosan-gelatin composite material to the surface of the functional microbial coating, cure it to form a coating layer; S4: Apply seaweed extract to the surface of the coating layer to form a biostimulant coating, thus obtaining a coated slow-release solid water-soluble fertilizer.

2. The coated slow-release solid water-soluble fertilizer according to claim 1, characterized in that, The effective viable bacterial counts in the mixed bacterial solution were 0.8-1.5 billion CFU / g for Bacillus subtilis, 0.09-0.13 billion CFU / g for Bacillus licheniformis, and 0.09-0.13 billion CFU / g for Azotobacter nigra.

3. The coated slow-release solid water-soluble fertilizer according to claim 1, characterized in that, The preparation method of the seaweed extract includes: alkali hydrolysis of seaweed, followed by fermentation and degradation using compound microbial enzymes.

4. The coated slow-release solid water-soluble fertilizer according to claim 3, characterized in that, The compound microbial enzyme comprises 32-38 wt% cellulase, 13-18 wt% pectinase, 10-16 wt% hemicellulase, 10-15 wt% amylase, and 21-27 wt% protease.

5. The coated slow-release solid water-soluble fertilizer according to claim 1, characterized in that, The biochar powder has a particle size of 50–500 μm.

6. The coated slow-release solid water-soluble fertilizer according to claim 1, characterized in that, The preparation method of the chitosan-gelatin composite material includes: Chitosan solution was prepared by dissolving chitosan in a 2wt%–4wt% acetic acid solution; Dissolve gelatin in water to make it swell, and prepare a gelatin solution with a mass fraction of 1% to 10%. Chitosan solution and gelatin solution are mixed to obtain the chitosan-gelatin composite material.

7. The coated slow-release solid water-soluble fertilizer according to claim 1, characterized in that, The core particles have a moisture content of less than 2%.

8. The application of a coated slow-release solid water-soluble fertilizer according to any one of claims 1-7 in crop nutrient supply and soil-borne disease control.

9. The application according to claim 8, characterized in that, The crops include at least one of the following: chili peppers, tomatoes, cucumbers, corn, and eggplants.

10. The application according to claim 8, characterized in that, The soil-borne diseases include bacterial wilt and / or Fusarium wilt.

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