Functional microbial composite double-layer coated controlled-release fertilizer and its preparation method

Abstract

This application provides a functional microbial composite double-layer coated controlled-release fertilizer and its preparation method, belonging to the field of controlled-release fertilizer technology. The functional microbial composite double-layer coated controlled-release fertilizer comprises, from the inside out, a core, a controlled-release layer, and a functional layer; wherein, the core is fertilizer granules; the controlled-release layer includes bio-based polymer materials and plasticizers; the functional layer includes functional microorganisms, stabilizers, and binders; the functional microorganisms include Rhizobium filamentosa, Flavobacterium tumefaciens, and Bacillus licheniformis.

Description

Technical Field

[0001] This application relates to the field of controlled-release fertilizer technology, specifically to a functional microbial composite double-layer coated controlled-release fertilizer and its preparation method, and more particularly to a functional microbial composite double-layer coated controlled-release fertilizer suitable for saline-alkali land and its preparation method. Background Technology

[0002] Coated controlled-release technology, as one of the core technologies for improving fertilizer utilization efficiency, has become a key pathway for reducing fertilizer application and increasing efficiency due to its advantage of precisely controlling the release rhythm. Its core technology lies in forming a dense or semi-permeable film on the surface of fertilizer granules using coating materials such as polyurethane, sulfur, and biomass-based materials. This allows nutrients such as nitrogen, phosphorus, and potassium in the fertilizer granules to be released slowly according to the needs of crops at different growth stages, fundamentally solving the problems of nutrient loss and soil pollution caused by the mismatch between the nutrient release rate of traditional fertilizers and the crop absorption rhythm. This coated controlled-release technology can not only increase fertilizer utilization by more than 30% compared to traditional fertilizers, but also reduce ecological problems such as eutrophication of water bodies and air pollution caused by nutrient leaching and volatilization, aligning with the core requirements of green agriculture for fertilizer conservation and environmental protection.

[0003] Microbial inoculants are a research and application hotspot in green agriculture. As a type of biofertilizer, their core value lies in optimizing both soil ecology and crop growth through the life activities of artificially selected and domesticated beneficial microorganisms (such as rhizobia, Bacillus subtilis, and phosphorus- and potassium-solubilizing bacteria). Unlike traditional chemical fertilizers that directly supplement nutrients, microbial inoculants have a comprehensive mechanism of action: after colonizing the soil, beneficial microorganisms secrete plant growth regulators such as auxins and gibberellins through metabolic activities, directly stimulating crop root development and enhancing the crop's ability to absorb water and nutrients; on the other hand, they secrete substances such as ironophiles and antibiotics, inhibiting the reproduction of pathogens in the soil and reducing the risk of crop diseases; more importantly, some functional microorganisms can secrete extracellular polysaccharides, which can bind tightly to soil particles, effectively improving soil aggregate structure, enhancing soil water and fertilizer retention capacity, and promoting the activation of insoluble nutrients in the soil, thus creating a favorable soil micro-ecological environment for crop growth and ultimately achieving the dual goals of increasing crop yield and optimizing agricultural product quality.

[0004] Combining microbial fertilizers with coated controlled-release technology to create compound fertilizers that possess both controlled-release function and biological activity can achieve synergistic effects of "precise nutrient release + soil ecological improvement," representing an important future development direction for the fertilizer industry. However, in practical applications, the integration of these two technologies still faces many technical challenges that urgently need to be overcome, limiting the industrialization, promotion, and application effectiveness of this type of compound fertilizer. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a functional microbial composite double-layer coated controlled-release fertilizer and its preparation method, aiming to at least partially solve the above-mentioned technical problems. The specific technical solution provided by this application is as follows.

[0006] As the first aspect of this application, a functional microbial composite double-layer coated controlled-release fertilizer is provided, comprising, from the inside out, a core, a controlled-release layer, and a functional layer; wherein, the core is fertilizer granules; the controlled-release layer comprises bio-based polymer materials and plasticizers; the functional layer comprises functional microorganisms, stabilizers, and binders; the functional microorganisms include Rhizobium filamentosa, Bacillus thuringiensis, and Bacillus licheniformis.

[0007] As a second aspect of this application, a method for preparing a functional microbial composite double-layer coated controlled-release fertilizer is provided, comprising:

[0008] A controlled-release coating solution containing bio-based polymer materials and plasticizers is coated onto the surface of fertilizer granules and dried to form a controlled-release layer on the surface of the fertilizer granules.

[0009] A mixed bacterial solution containing functional microorganisms is provided. A stabilizer and a binder are added to the mixed bacterial solution and mixed evenly to obtain a functional coating solution.

[0010] The functional coating liquid is coated onto the surface of the controlled-release layer and dried to obtain a functional microbial composite double-layer coated controlled-release fertilizer.

[0011] In this embodiment, fertilizer granules are arranged sequentially from the inside out as the core, controlled-release layer, and functional layer. The controlled-release layer utilizes bio-based polymer materials and plasticizers to achieve slow nutrient release, while the functional layer uses stabilizers and adhesives to fix Rhizobium filamentosa, Bacillus thuringiensis, and Bacillus licheniformis on the surface of the controlled-release layer, forming a physical barrier to prevent direct contact between the fertilizer granules and microorganisms. This effectively maintains the activity of functional microorganisms while ensuring the controlled-release performance of the fertilizer. Furthermore, the preparation method of forming the controlled-release layer first and then coating it with the functional coating liquid avoids damage to microorganisms during the coating process, ultimately obtaining a double-layer coated controlled-release fertilizer that combines nutrient controlled release and stable colonization of microorganisms. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of the functional microbial composite double-layer coated controlled-release fertilizer in the embodiments of this application;

[0013] Figure 2 This is a schematic diagram illustrating the process by which the functional microbial composite double-layered coated controlled-release fertilizer is applied to the soil in the embodiments of this application;

[0014] Figure 3 This is a flowchart illustrating the preparation method of the functional microbial composite double-layer coated controlled-release fertilizer in the embodiments of this application;

[0015] Figure 4 This is a schematic diagram of the fluidized bed equipment used in the preparation of functional microbial composite double-layer coated controlled-release fertilizer in the embodiments of this application;

[0016] Figure 5 This is a diagram of the functional microbial composite double-layered coated controlled-release fertilizer prepared in Example 1 of this application;

[0017] Figure 6 This is a graph showing the nitrogen release curve of the functional microbial composite double-layered coated controlled-release fertilizer in Example 1 of this application;

[0018] Figure 7 This is a comparison chart of wheat growth at the same time under different treatments in Example 1 of this application;

[0019] Figure 8 This is a comparison chart of the number of wheat tillers under different treatments in Example 1 of this application;

[0020] Figure 9 This is a comparison chart of wheat yields under different treatments in Example 1 of this application;

[0021] Figure 10 This is a comparison chart of soil electrical conductivity under different treatments in Example 1 of this application;

[0022] Figure 11 This is a diagram of the functional microbial composite double-layered coated controlled-release fertilizer prepared in Example 2 of this application;

[0023] Figure 12 This is a graph showing the nitrogen release curve of the functional microbial composite double-layered coated controlled-release fertilizer in Example 2 of this application;

[0024] Figure 13 This is a comparison chart of maize yields under different treatments in Example 2 of this application;

[0025] Figure 14 This is a comparison chart of soil electrical conductivity of maize under different treatments in Example 2 of this application.

[0026] Explanation of reference numerals in the attached figures:

[0027] F0 - Kernel, F1 - Controlled Release Layer, F2 - Functional Layer;

[0028] 1-Roots blower, 2-Gas buffer tank, 3-Heater, 4-Fluidized bed, 5-Constant temperature system, 6-Peristaltic pump, 7-Coating liquid storage tank, 8-Air compressor. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0030] In the practice of saline-alkali land management and improvement, the application value of microbial fertilizers is becoming increasingly prominent. The high salt and high pH characteristics of saline-alkali soils severely inhibit crop growth and disrupt the soil microbial community structure, becoming a core bottleneck for regional agricultural development. Screening functional microorganisms with salt and high pH tolerance and utilizing their metabolic activities to overcome the obstacles of saline-alkali land has become a cutting-edge direction in saline-alkali land management. These stress-resistant microorganisms can not only survive stably in extreme saline-alkali environments, but their secreted metabolites such as auxins and gibberellins can effectively alleviate the damage of salt and alkali stress to crop roots and promote deep root development; the extracellular polysaccharides they secrete can adsorb salt ions in the soil, reduce the salt concentration of the soil solution, regulate the soil pH, and improve the soil physicochemical properties; at the same time, the life activities of microorganisms can also enrich the microbial diversity of saline-alkali soils and gradually build a healthy soil micro-ecosystem.

[0031] However, microbial inoculants generally suffer from poor environmental tolerance and are prone to inactivation. Live microorganisms are extremely sensitive to environmental conditions during storage, transportation, and application: excessively high temperatures (above 35°C) can cause protein denaturation, while excessively low temperatures inhibit metabolism; high humidity environments easily breed other microorganisms, leading to clumping and deterioration of the inoculant; and a pH deviation from the suitable range in the soil or fertilizer system (most functional microorganisms thrive at pH 6.0-7.5) directly affects the survival and reproduction of microorganisms. These factors collectively cause the activity of microbial inoculants to continuously decline throughout the entire chain from production to application, with some inoculants having a survival rate of less than 30% after reaching the soil, severely reducing the stability and reliability of fertilizer efficacy.

[0032] Furthermore, the insufficient colonization and competitive ability of microorganisms in the soil restricts their effectiveness. Traditional microbial fertilizers often adopt a simple mixing model of "microorganisms + fertilizer" without considering the compatibility between microorganisms and fertilizer components and the soil environment. On the one hand, the high concentration of salt and some chemical components in the fertilizer may inhibit microbial activity during the mixing process. On the other hand, after being applied to the soil, the target microorganisms face fierce competition from native microorganisms (including competition for nutrients and inhibition by antibacterial substances), making it difficult for them to establish stable colonization in the crop rhizosphere and form a sufficient population. In most cases, they can only produce a short-term effect in the initial stage of application.

[0033] The poor compatibility between coating technology and microorganisms has become a core technological barrier to their integration. Currently, mainstream controlled-release coating technologies (such as melt coating and solvent coating) are mostly developed for chemical fertilizers, and their process conditions significantly contradict the survival requirements of microorganisms: melt coating requires temperatures above 100°C, which directly kills most living microorganisms; the organic solvents used in solvent coating (such as toluene and xylene) damage the cell membrane structure of microorganisms. Simultaneously, the air permeability and water permeability of existing coating materials are difficult to precisely match the respiration and metabolic needs of microorganisms: overly dense coatings hinder the entry of water and oxygen, inhibiting microbial activity; overly permeable coatings cannot achieve slow, controlled nutrient release. The degradation rate of some coating materials in the soil does not match the activity cycle of microorganisms, also affecting the synergistic effect of compound fertilizers.

[0034] Existing technologies include encapsulation methods that use microorganisms as the core, but these only achieve controlled release of microorganisms, resulting in a lag between nutrient release and microbial activity. Furthermore, the polymeric coatings used (such as polyolefins) require large amounts of toxic organic solvents or high-temperature melting, which can damage the microorganisms. Another method involves directly spraying the bacterial solution onto the surface of fertilizer granules. However, contact between the bacterial solution and high-concentration salt solutions significantly reduces activity, and the use of polyurethane membranes requires curing at 70-80℃, which also inactivates the bacteria.

[0035] In summary, the current production and preparation processes of microbial-fertilizer composite systems have the following shortcomings: First, they simply combine microorganisms and fertilizers without optimizing the compatibility between microbial activity and fertilizer components; second, the controlled-release membrane materials used in the controlled-release process do not take into account their potential harm to microorganisms; and third, the production equipment used is not specifically optimized for the characteristics of microorganisms.

[0036] To address the aforementioned technical problems, this application provides a functional microbial composite double-layer coated controlled-release fertilizer and its preparation method: by establishing different functional layers (core, controlled-release layer, and functional layer), both controlled-release performance and functional microbial activity are guaranteed; the proportions of bio-based polymer materials, mixed bacterial solution, stabilizer, and binder are precisely controlled to form a structurally stable microbial coating shell on the surface of fertilizer particles. This solution can effectively alleviate the problem of easy inactivation of microorganisms during production, storage, transportation, and application, and physically isolates the microorganisms from the fertilizer particles, significantly improving the stability of the application effect of microbial fertilizers, and providing a feasible technical path for the efficient combination of coating controlled-release technology and microbial fertilizers.

[0037] As the first aspect of this application, a functional microbial composite double-layer coated controlled-release fertilizer is provided, comprising, from the inside out, a core, a controlled-release layer, and a functional layer; wherein, the core is fertilizer granules; the controlled-release layer comprises bio-based polymer materials and plasticizers; the functional layer comprises functional microorganisms, stabilizers, and binders; the functional microorganisms include Rhizobium filamentosa, Bacillus thuringiensis, and Bacillus licheniformis.

[0038] In this embodiment, fertilizer granules are arranged sequentially from the inside out as the core, controlled-release layer, and functional layer. The controlled-release layer utilizes bio-based polymer materials and plasticizers to achieve slow nutrient release, while the functional layer uses stabilizers and adhesives to fix Rhizobium filamentosa, Bacillus thuringiensis, and Bacillus licheniformis on the surface of the controlled-release layer, forming a physical barrier to prevent direct contact between fertilizer granules and functional microorganisms. This effectively maintains the activity of functional microorganisms while ensuring the controlled-release performance of the fertilizer, resulting in a double-layered coated controlled-release fertilizer that combines nutrient controlled release and stable colonization of microorganisms.

[0039] In some embodiments, the contents of each component in the functional microbial composite double-layer coated controlled-release fertilizer are as follows, by weight: 1000 parts of fertilizer granules in the core; 10-30 parts of bio-based polymer material in the controlled-release layer; 1-3 parts of plasticizer; and 200-300 parts of mixed bacterial solution added in the functional layer, with 1-2 parts of stabilizer and 30-50 parts of binder.

[0040] In this embodiment, by reasonably limiting the weight ratio of each component, the proportion of bio-based polymer materials and plasticizers in the controlled-release layer is appropriate, enabling the formation of a structurally stable coating and the controlled release of nutrients. Simultaneously, the amounts of mixed bacterial solution, stabilizer, and binder in the functional layer are matched to ensure effective loading and fixation of functional microorganisms on the surface of the controlled-release layer, while avoiding the adverse effects of excessive components on microbial activity. This achieves a synergistic effect between the controlled-release layer and the functional layer, resulting in a double-layered coated controlled-release fertilizer that combines stable controlled-release performance with good microbial activity.

[0041] In some embodiments, the total concentration of viable bacteria in the mixed bacterial solution is 1×10⁻⁶. 8 -1×10 9 CFU / mL, wherein the ratio of viable counts of Rhizobium linearis, Flavobacterium tumefaciens, and Bacillus licheniformis is 1:(0.8-1.2):(0.8-1.2), preferably, the ratio of viable counts of Rhizobium linearis, Flavobacterium tumefaciens, and Bacillus licheniformis is 1:1:1.

[0042] In this embodiment, by controlling the total concentration of viable bacteria and the ratio of viable bacteria among *Rhizobium filamentosa*, *Flavobacterium tumefaciens*, and *Bacillus licheniformis* in the mixed bacterial solution, a synergistic effect is achieved among the three functional microorganisms. *Bacillus licheniformis* can form spores and possesses cellulase, amylase secretion, and phosphorus-solubilizing capabilities, which helps enhance microbial tolerance and promote nutrient conversion. *Flavobacterium tumefaciens*, as a highly abundant core group in the rhizosphere, has strong ecological adaptability and can stably colonize in complex soil environments. *Rhizobium filamentosa* can synthesize extracellular polysaccharides and has phosphorus-solubilizing and potassium-solubilizing functions, which is beneficial for improving the rhizosphere microenvironment of crops. The three coexist in the functional layer at appropriate concentrations and ratios, forming a stable and efficient functional microbial community on the surface of the controlled-release layer, thereby achieving synergistic improvement of the soil microecology while controlling the release of fertilizer nutrients.

[0043] In some embodiments, the stabilizer is selected from at least one of calcium carbonate, calcium chloride, superphosphate, and montmorillonite powder, preferably montmorillonite. The binder is selected from at least one of sodium carboxymethyl cellulose, sodium carboxymethyl starch, carboxymethyl chitosan, and sodium alginate, preferably sodium carboxymethyl cellulose.

[0044] In the embodiments of this application, by selecting montmorillonite and other materials as stabilizers and sodium carboxymethyl cellulose and other materials as binders, the stability of the functional layer and the stress resistance of functional microorganisms during storage and application can be significantly improved. At the same time, stabilizers such as montmorillonite can replace sodium ions in the soil and promote salt excretion. Furthermore, binders such as sodium carboxymethyl cellulose have better compatibility with bacterial solutions and can form a structurally stable functional layer. Thus, while ensuring the controlled-release performance of fertilizer, the activity of functional microorganisms can be effectively maintained and the soil environment can be improved.

[0045] In some embodiments, the bio-based polymer material is selected from at least one of ethyl cellulose, chitin, and lignin. The plasticizer is selected from at least one of phthalate, dibutyl sebacate, epoxidized soybean oil, chitosan, polyethylene glycol, glycerin, polycaprolactone, and polybutylene terephthalate.

[0046] In this embodiment, by selecting the above-mentioned bio-based polymer material and plasticizer to form a controlled-release layer, the slow release of fertilizer nutrients can be achieved. At the same time, the controlled-release layer and the functional layer containing functional microorganisms are physically isolated to avoid direct contact between fertilizer particles and microorganisms. Thus, the activity of functional microorganisms is effectively maintained while ensuring the controlled-release performance, and the synergistic effect between the controlled-release layer and the functional layer is achieved.

[0047] In some embodiments, the fertilizer granules are selected from at least one of potassium chloride, potassium sulfate, ammonium sulfate, ammonium nitrate, monoammonium phosphate, diammonium phosphate, urea, and compound nitrogen, phosphorus, and potassium fertilizers.

[0048] In this embodiment, the fertilizer granules serve as the core, providing crops with essential nutrients such as nitrogen, phosphorus, and potassium, and enabling the slow release of nutrients through the controlled-release layer. Simultaneously, the fertilizer granules and the functional microorganisms in the functional layer work synergistically. The nutrients released by the fertilizer granules provide nutritional support for the growth and metabolism of the functional microorganisms, while the metabolic activities of the functional microorganisms promote the transformation of nutrients in the soil and their absorption by the crops, thus achieving an organic combination of fertilizer supply and microbial synergy.

[0049] In some embodiments, a lubricant is coated on the surface of the fertilizer granules. The lubricant fills the gaps on the surface of the fertilizer granules to make the surface of the fertilizer granules smooth. The amount of lubricant used is 5-10 parts by weight. The lubricant is selected from at least one of liquid paraffin, ethylene glycol, glycerin, and silicone oil.

[0050] In this embodiment, by coating the surface of fertilizer particles with a lubricant, the interfacial friction between the fertilizer particles and the controlled-release layer can be reduced, the uniformity and adhesion of the coating can be improved, thereby enhancing the structural integrity of the controlled-release layer and facilitating the achievement of a stable nutrient release rate.

[0051] In some embodiments, a sealing agent is coated on the surface of the controlled-release layer. The sealing agent is used to fill the voids and defects in the controlled-release layer to improve its controlled-release effect. The amount of sealing agent used is 5-10 parts by weight. The sealing agent is selected from at least one of solid paraffin, polycaprolactone, ethylene-vinyl acetate copolymer, and polyethylene oxide.

[0052] In the embodiments of this application, by coating the surface of the controlled-release layer with a sealing agent, the micropore defects that may exist on the surface of the controlled-release layer can be sealed, further slowing down the nutrient release rate. At the same time, it provides a uniform and continuous adhesion interface for the functional layer, enhances the bonding force between the functional layer and the controlled-release layer, and thus improves the structural stability of the functional layer while ensuring the controlled-release performance.

[0053] Figure 1 This is a schematic diagram of the structure of the functional microbial composite double-layer coated controlled-release fertilizer in the embodiments of this application; Figure 2 This is a schematic diagram illustrating the process by which the functional microbial composite double-layer coated controlled-release fertilizer is applied to the soil in the embodiments of this application.

[0054] This application provides a functional microbial composite double-layer coated controlled-release fertilizer, comprising fertilizer granules as the core F0, bio-based polymer materials as the controlled-release layer F1, and functional microorganisms as the functional layer F2. Its structure and mechanism of action are as follows: Figures 1-2 As shown.

[0055] like Figure 1As shown, this functional microbial composite double-layered controlled-release fertilizer comprises, from the inside out, a core F0, a controlled-release layer F1, and a functional layer F2. The core F0 consists of fertilizer granules (such as urea) providing nutrients like nitrogen and phosphorus necessary for crop growth. The controlled-release layer F1 uses bio-based polymers such as ethyl cellulose to form a appropriately dense coating, controlling the slow release of nutrients. The functional layer F2 consists of an adhesive, a stabilizer, and functional microorganisms (Rhizobium filamentosa, Bacillus thuringiensis, and Bacillus licheniformis). The adhesive, bridged by the stabilizer, forms a network structure, within which the functional microorganisms are embedded, achieving stable loading and physical isolation.

[0056] like Figure 2 As shown, after this functional microbial composite double-layered coated controlled-release fertilizer is applied to the soil, the binder in the outer functional layer F2 quickly forms a hydrogel-soil water-retaining layer upon contact with water, which not only retains soil moisture but also provides a moist microenvironment for the functional microorganisms; at the same time, the stabilizer (such as montmorillonite) in the functional layer F2 releases Ca... 2+ , with Na in the soil solution + Ion exchange occurs, reducing the salt concentration in the root zone and achieving salt removal. During this process, functional microorganisms preferentially release nutrients from the functional layer F2 and colonize the rhizosphere within hours to days after application to the soil. Nutrients released from the core F0 fertilizer granules, however, must pass through the dense membrane of the controlled-release layer F1 and are released slowly over weeks to months, creating a significant time difference between the two. This design avoids the loss of activity caused by direct exposure of microorganisms to high salt concentrations or high osmotic pressure fertilizer granules in traditional simple "microorganism + fertilizer" mixtures, effectively protecting microbial activity and achieving a synergistic effect of "microorganism colonization first, nutrient supply later." After being released into the rhizosphere, the microorganisms interact with crop roots and native soil microorganisms, secreting metabolites such as auxins and extracellular polysaccharides, promoting crop root growth, improving soil aggregate structure, and enhancing crop salt tolerance and nutrient absorption efficiency. The controlled-release layer F1 continuously and slowly releases nutrients such as nitrogen, providing long-term nutritional support for crops and rhizosphere microorganisms.

[0057] Figure 3 This is a flowchart illustrating the preparation method of the functional microbial composite double-layer coated controlled-release fertilizer in the embodiments of this application.

[0058] As a second aspect of this application, a method for preparing a functional microbial composite double-layer coated controlled-release fertilizer is provided, such as... Figure 3 As shown, it includes steps S1-S3.

[0059] Step S1: Coat the surface of fertilizer granules with a controlled-release coating solution containing bio-based polymer materials and plasticizers and dry it to form a controlled-release layer on the surface of fertilizer granules.

[0060] Step S2: Provide a mixed bacterial solution containing functional microorganisms, add stabilizers and binders to the mixed bacterial solution and mix evenly to obtain a functional coating solution.

[0061] Step S3: Coat the surface of the controlled-release layer with the functional coating liquid and dry it to obtain the functional microbial composite double-layer coated controlled-release fertilizer.

[0062] In this embodiment, the step-by-step preparation method of first forming a controlled-release layer and then coating with a functional coating liquid effectively avoids damage to functional microorganisms during the high-temperature drying process when forming the controlled-release layer. At the same time, stabilizers and adhesives are used to fix the functional microorganisms on the surface of the controlled-release layer, forming physical isolation and stable load, thereby obtaining a double-layer coated controlled-release fertilizer with complete structure, good controlled-release performance and high microbial activity retention rate.

[0063] In some embodiments, the preparation method further includes: coating the surface of fertilizer particles with a lubricant before forming the controlled-release layer; and / or coating the surface of the controlled-release layer with a sealing agent before coating the functional microbial coating solution.

[0064] In this embodiment, by coating a lubricant before forming the controlled-release layer, the interfacial lubricity between the core and the controlled-release layer can be improved, thus enhancing coating uniformity and adhesion. By coating a sealing agent before applying the functional coating liquid, micropore defects on the surface of the controlled-release layer can be sealed, further slowing down the nutrient release rate and providing a smooth adhesion substrate for the functional layer. Using either or both simultaneously can enhance the integrity of the bilayer structure and the stability of the controlled-release performance.

[0065] Specifically, this application provides a method for preparing a functional microbial composite double-layer coated controlled-release fertilizer, including steps Q1-Q5.

[0066] Step Q1: Coat the surface of the fertilizer granules with lubricant.

[0067] Step Q2: Coat the surface of fertilizer granules coated with a controlled-release coating solution containing bio-based polymer materials and plasticizers, and dry it to form a controlled-release layer on the surface of the fertilizer granules.

[0068] Step Q3: Coat the surface of the controlled-release layer with a sealing agent.

[0069] Step Q4: Provide a mixed bacterial solution containing functional microorganisms, add stabilizers and binders to the mixed bacterial solution and mix evenly to obtain a functional coating solution.

[0070] Step Q5: Apply the functional coating liquid to the surface of the controlled-release layer that has been coated with the sealing agent and dry it to obtain the functional microbial composite double-layer coated controlled-release fertilizer.

[0071] Figure 4This is a schematic diagram of the fluidized bed equipment used in the preparation of functional microbial composite double-layer coated controlled-release fertilizer in the embodiments of this application.

[0072] In some embodiments, the preparation of the functional microbial composite double-layer coated controlled-release fertilizer in this application is carried out using methods such as... Figure 4 The fluidized bed equipment shown includes: a Roots blower 1, a gas buffer tank 2, a heater 3, a fluidized bed 4, a temperature control system 5, a peristaltic pump 6, a coating liquid storage tank 7, and an air compressor 8.

[0073] In some embodiments, the specific operation of coating the fertilizer granules with lubricant in step Q1 is as follows: the fertilizer granules are placed in the fluidized bed 4 and preheated at 50-70°C for 10-20 minutes. Then, while maintaining the heating condition at 50-70°C, the lubricant is added to the coating liquid storage tank 7 and delivered to the nozzle in the fluidized bed 4 by the peristaltic pump 6. The lubricant is atomized by the compressed air provided by the air compressor 8 and sprayed onto the surface of the fertilizer granules in the fluidized state in the fluidized bed 4.

[0074] In some embodiments, in step Q2, the controlled-release coating solution containing bio-based polymer materials and plasticizers is prepared by the following method: dissolving the bio-based polymer materials and plasticizers in a solvent and stirring until homogeneous to obtain the controlled-release coating solution.

[0075] For different bio-based polymer materials, the preferred solutions are as follows:

[0076] When the bio-based polymer material is ethyl cellulose, the plasticizer is preferably phthalate, dibutyl sebacate, or epoxidized soybean oil, and the solvent is preferably ethanol, methanol, isopropanol, ethyl acetate, or chloroform.

[0077] When the bio-based polymer material is chitin, the plasticizer is preferably triethanolamine, polyethylene glycol or glycerol, and the solvent is preferably NaOH / urea aqueous solution, N,N-dimethylacetamide (DMAC) / lithium chloride (LiCl), ionic liquid, etc.

[0078] When the bio-based polymer material is lignin, the plasticizer is preferably polycaprolactone, polyethylene glycol or polybutylene terephthalate, and the solvent is preferably NaOH / ammonia solution, dioxane or acetone.

[0079] More preferably, the bio-based polymer material is ethyl cellulose, the plasticizer is dibutyl sebacate, and the solvent is ethanol.

[0080] In some embodiments, the specific operation of coating the controlled-release coating liquid onto the surface of the fertilizer granules coated with lubricant in step Q2 is as follows: under heating conditions of 50-70°C, the peristaltic pump 6 is turned on to deliver the controlled-release coating liquid from the coating liquid storage tank 7 to the nozzle in the fluidized bed 4. At the same time, the air compressor 8 provides compressed air to atomize the controlled-release coating liquid and continuously spray it onto the surface of the fertilizer granules coated with lubricant in the fluidized state in the fluidized bed 4. After the spraying is completed, the fluidization continues for 20 minutes to allow the ethanol to evaporate completely and form a controlled-release layer on the surface of the fertilizer granules.

[0081] In some embodiments, the specific operation of coating the controlled-release layer surface with sealing agent in step Q3 is as follows: under heating conditions of 50-70°C, the sealing agent is melted into a liquid, and after the fluidization state is stable, it is slowly and evenly dripped into the surface of the fertilizer particles with the controlled-release layer in the fluidized bed 4; after the dripping is completed, the fluidization continues for 10-15 minutes to make the sealing agent uniformly solidify.

[0082] In some embodiments, in step Q4, the mixed bacterial solution containing functional microorganisms is prepared by the following method: the functional microorganisms are screened and isolated from the roots and rhizosphere soil of corn and wheat, including *Rhizobium filamentosa*, *Flavobacterium tumefaciens*, and *Bacillus licheniformis*; each strain is inoculated into a liquid culture medium for expansion culture, and then the bacterial solutions are mixed in proportion to obtain the mixed bacterial solution; the OD of the mixed bacterial solution is adjusted. 600 To 1.0, so that the total concentration of viable bacteria is 1×10⁻⁶. 8 -1×10 9 The concentration of CFU / mL is as follows, and the ratio of viable counts of Rhizobium linearis, Flavobacterium tumefaciens, and Bacillus licheniformis is 1:(0.8-1.2):(0.8-1.2), preferably 1:1:1.

[0083] In some embodiments, in step Q4, the specific operation of adding stabilizer and binder to the mixed bacterial solution and mixing evenly to obtain functional coating solution is as follows: take the above mixed bacterial solution, add stabilizer and stir evenly, then add binder and continue to stir thoroughly until the system is homogeneous to obtain functional coating solution.

[0084] In some embodiments, the specific operation of applying the functional coating liquid to the surface of the controlled-release layer coated with the sealing agent in step Q5 is as follows: The temperature inside the fluidized bed 4 is precisely controlled within the optimal growth temperature range (25-30℃) of the functional microorganisms by the constant temperature system 5 to avoid high temperature damage to the microbial activity. The functional coating liquid is added to the coating liquid storage tank 7 and delivered to the nozzle inside the fluidized bed 4 by the peristaltic pump 6. At the same time, the air compressor 8 is turned on to provide compressed air to atomize the sealing agent and continuously spray it onto the surface of the fertilizer granules with the controlled-release layer in the fluidized state inside the fluidized bed 4. Uniform coating is achieved by the rolling action of the granules. After spraying, fluidization continues for 10 minutes to ensure that the functional coating liquid is uniformly coated on the surface of the controlled-release layer. Then, drying is carried out in a low-temperature environment (25-30℃) to remove excess solvent without damaging the activity of the functional microorganisms. Finally, the functional microorganism composite double-layer coated controlled-release fertilizer product is collected.

[0085] In summary, this application provides a sustainable, continuous, and efficient method for preparing a functional microbial composite double-layer coated controlled-release fertilizer. This method uses fertilizer granules as the core, coating them with bio-based polymer materials to form a controlled-release layer, achieving controlled nutrient release. A functional coating solution is prepared using a specific ratio of mixed bacterial solution, binder, and stabilizer. A fluidized bed low-temperature coating process is then employed to uniformly coat the functional microorganisms onto the surface of the controlled-release layer, forming a functional layer. This enhances microbial stability, prolongs their survival time, and simultaneously improves the slow-release effect of the fertilizer in the soil, as well as its growth-promoting and stress-resistance functions on crops.

[0086] Specifically, a stable structural system of "fertilizer-controlled release-multifunctionality" is constructed on the surface of fertilizer granules by using a fluidized bed layer-by-layer spraying process, with bio-based polymer materials as the inner layer (controlled release layer) and functional microorganisms mixed with binders and stabilizers in a certain proportion as the outer layer (functional layer). This results in a coated controlled release fertilizer with multiple functions such as slow release, growth promotion, and salt excretion.

[0087] This application has the following significant beneficial effects:

[0088] 1. Multifunctional: This fertilizer can not only improve soil aggregate structure and promote crop root growth, but also increase the number of beneficial soil microorganisms and optimize the soil micro-ecological environment.

[0089] 2. Double-layer protection to extend storage period: Through the synergistic effect of bio-based polymer materials (controlled-release layer) and stabilizers and binders (functional layer), a double-layer protective film is formed on the surface of fertilizer granules, providing a relatively isolated environment for functional microorganisms, reducing the impact of environmental stresses such as temperature, humidity, and pH on microorganisms, and significantly extending the storage period of microbial fertilizer.

[0090] 3. Low-temperature coating process, suitable for industrial production: The fluidized bed low-temperature coating process ensures that the activity of microorganisms is not destroyed and that the functional layer is uniform and dense; the process has a high degree of automation and is suitable for large-scale continuous production.

[0091] 4. Synergistic effect after application to soil:

[0092] The adhesive (such as sodium carboxymethyl cellulose) in the outer functional layer forms a hydrogel matrix when it comes into contact with water, which protects the microbial community. At the same time, the complex microorganisms interact with the native microorganisms of the soil and roots, promoting the crop's salt and alkali resistance and improving the germination rate.

[0093] The inner controlled-release layer slowly releases nutrients, providing a stable and suitable environment for microorganisms while promoting nutrient absorption by crops.

[0094] 5. Microbial Source and Characteristics: The three tested microorganisms (Bacillus licheniformis, Flavobacterium tumefaciens, and Rhizobium fimbriatum) were all isolated from plant roots and rhizosphere soil, and showed good affinity with plants. Previous in vitro functional identification indicated:

[0095] Bacillus licheniformis can form spores and has the ability to secrete cellulase and amylase as well as phosphate solubility.

[0096] Flavobacterium tumefaciens is a core group with high abundance in the rhizosphere and strong ecological adaptability;

[0097] Linear rhizobia can synthesize extracellular polysaccharides (EPS) and have the functions of phosphate solubilization and potassium solubilization, which are beneficial to improving the rhizosphere microenvironment.

[0098] Plate confrontation experiments showed that there was no antagonistic effect among the three strains, and their symbiotic compatibility was good, laying the foundation for the construction of a multifunctional complex microbial community.

[0099] In summary, this functional microbial compound double-layer coated controlled-release fertilizer can improve crop nutrient absorption and soil microbial diversity, enhance crop stress resistance (such as salt tolerance and disease resistance), improve the root microenvironment, and ultimately achieve a dual improvement in crop yield and quality. This application fills the gap in the adaptability of existing microbial fertilizers to coating processes, providing efficient and stable fertilizer products and core preparation technologies for green agriculture and ecological agriculture.

[0100] The present application is further illustrated below through embodiments and related test experiments. In the detailed description below, numerous specific details are set forth for ease of explanation to provide a comprehensive understanding of the embodiments of the present application. However, it is apparent that one or more embodiments may be implemented without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict. All instruments, consumables, and reagents used in the following embodiments are commercially available unless otherwise specified.

[0101] Example 1

[0102] In this embodiment 1, a functional microbial composite double-layer coated controlled-release fertilizer was prepared according to the following method and applied to wheat planting.

[0103] The specific production process of functional microbial compound double-layer coated controlled-release fertilizer is as follows:

[0104] First, add 70g ethanol, 30g ethyl cellulose, and 1.5g dibutyl sebacate to a 500mL beaker and stir on a magnetic stirrer to obtain a controlled-release coating solution.

[0105] The second step involves adjusting the bacterial concentrations of the three functional microorganisms (Rhizobium filamentosa (ACCC No. 15082), Flavobacterium tumefaciens (CGMCC No. 31149), and Bacillus licheniformis (CGMCC No. 38142)) to OD using culture medium. 600 =1.0, then mix them at a volume ratio of 1:1:1 for later use. Weigh 300g of the mixed bacterial solution, 2g of montmorillonite powder, and 50g of sodium carboxymethyl cellulose, add them to another beaker and stir, keeping the beaker temperature at 25-30℃ to obtain the functional coating solution.

[0106] The third step is to turn on the Roots blower 1 after all the substances have completely dissolved. The airflow is buffered and balanced by the gas buffer tank 2, and then heated by the heater 3 before entering the fluidized bed 4. The circulation lasts for about 20 minutes, so that the temperature inside the fluidized bed 4 is stabilized at 55°C and the fluidized bed 4 is in working condition.

[0107] The fourth step is to add 1 kg of large urea particles with a diameter of 2-4 mm (purchased from Shandong Hualu Hengsheng Group Co., Ltd.) to fluidized bed 4, preheat for 10 minutes, and then add 5 g of liquid paraffin to lubricate the surface of the fertilizer particles.

[0108] Fifth step: Add controlled-release coating liquid to coating liquid storage tank 7, use peristaltic pump 6 to deliver it to nozzle, atomize it and spray it onto the surface of fertilizer granules.

[0109] Step 6: Atomize the controlled-release coating solution at a rate of 5 mL / min through the nozzle for 20 minutes, then fluidize for another 20 minutes to allow complete ethanol evaporation. Add 8 g of solid paraffin, maintain the coating temperature at 55°C, and fluidize for 10 minutes. Stop heating, turn on the cooler, adjust heater 3 to 30°C, and run it steadily for 5 minutes.

[0110] Step 7: Add functional coating liquid to coating liquid storage tank 7, use peristaltic pump 6 to deliver it to nozzle, atomize it and spray it onto the surface of fertilizer granules.

[0111] Step 8: The functional coating solution is atomized through the nozzle at a rate of 3 mL / min for 1 hour. Then, heating is stopped, the fertilizer is removed, and it is air-dried to obtain the desired product. Figure 5 The functional microbial composite double-layer coated controlled-release fertilizer shown.

[0112] Furthermore, the performance of the functional microbial composite double-layer coated controlled-release fertilizer prepared above was tested.

[0113] Referring to the international standard ISO 22398, the controlled-release performance was determined using the 25℃ water immersion method. The specific steps are as follows:

[0114] (1) Take 10g of functional microbial composite double-layer coating controlled-release fertilizer with uniform shape and size, put it into a 150μm (100 mesh) nylon mesh bag, seal it and put it into a 250mL plastic bottle;

[0115] (2) Add 200 mL of deionized water, seal and place in a 25°C constant temperature incubator;

[0116] (3) Each treatment was repeated 3 times. The sampling times were: days 1, 4, 7, 10, 14, 21 and 28 of culture, and then once every 7 days thereafter.

[0117] (4) The content of urea nitrogen in the solution was determined by p-dimethylaminobenzaldehyde-spectrophotometry (wavelength 420 nm), and the cumulative nutrient dissolution rate was calculated;

[0118] (5) The number of days required for the cumulative nutrient dissolution rate to reach 80% is taken as the controlled release period of the fertilizer.

[0119] Figure 6 This is a graph showing the nitrogen release curve of the functional microbial composite double-layered coated controlled-release fertilizer in Example 1 of this application.

[0120] like Figure 6 As shown, the functional microbial composite double-layer coated controlled-release fertilizer prepared in Example 1 of this application exhibits a gradual increase in the cumulative release rate of nitrogen (N) over time under static water immersion conditions at 25°C. The cumulative release rate was 0.13% on day 1, 1.93% on day 4, 4.95% on day 7, 7.91% on day 10, 11.63% on day 14, 18.03% on day 21, and 24.81% on day 28. This release curve indicates that the fertilizer releases nutrients slowly over 28 days, with the cumulative release rate not exceeding 25%. Based on the standard of the number of days required to achieve an 80% cumulative release rate as the controlled-release period, the controlled-release period of the functional microbial composite double-layer coated controlled-release fertilizer in Example 1 is 90 days, demonstrating excellent nutrient controlled-release performance.

[0121] The effective viable counts of Rhizobium linearis (ACCC No. 15082), Flavobacterium tumefaciens (CGMCC No. 31149), and Bacillus licheniformis (CGMCC No. 38142) were determined using the dilution plating method, and the viable count was used as an indicator to complete the microbial activity calibration.

[0122] The test results showed that the viable count of the three functional microorganisms in the fertilizer reached 2.78 × 10⁻⁶. 7 The CFU / L and viable bacteria count both meet the standards for microbial fertilizers (compound microbial fertilizer (NY / T 798-2015)), and can be used as a high-efficiency functional microbial fertilizer.

[0123] Furthermore, the functional microbial composite double-layer coated controlled-release fertilizer (denoted as CRFB) prepared above was used in wheat cultivation.

[0124] The fertilizer was mixed with phosphate and potassium fertilizers to form a special fertilizer for wheat. The application rate was 210-105-60 kg / ha based on N-P2O5-K2O. Fertilizer efficiency test was conducted in a slightly saline-alkali land (salinity of 0.34%). All fertilizers were applied as base fertilizer before wheat sowing, and no topdressing was applied later. The following comparative treatments were set up: (1) Conventional fertilization (CK): compound fertilizer (15-15-15) was applied as base fertilizer, and nitrogen fertilizer was applied as topdressing later. The total amount of nitrogen applied was the same as that of the CRFB treatment; (2) Ordinary controlled-release fertilizer (CRF): the application rate was the same as that of CRFB, applied once, and its preparation process was the same as that of CRFB but without the addition of bacterial solution. The experiment analyzed the effects of different treatments on wheat tiller number, wheat yield and soil electrical conductivity (EC).

[0125] Figure 7 This is a comparison chart of wheat growth at the same time under different treatments in Example 1 of this application; Figure 8 This is a comparison chart of the number of wheat tillers under different treatments in Example 1 of this application; Figure 9 This is a comparison chart of wheat yields under different treatments in Example 1 of this application; Figure 10 This is a comparison chart of soil electrical conductivity under different treatments in Example 1 of this application.

[0126] from Figures 7-10 It can be seen that the functional microbial composite double-layer coated controlled-release fertilizer prepared in Example 1 of this application has significant effects on wheat growth and soil improvement.

[0127] from Figure 7 The comparison chart of wheat growth shows that wheat plants treated with CRFB grew more vigorously, with dark green leaves, and their plant height and biomass were better than those treated with conventional fertilization (CK) and conventional controlled-release fertilizer (CRF), indicating that CRFB effectively promoted the vegetative growth of wheat.

[0128] from Figure 8The comparison chart of wheat tiller numbers shows that the tiller number in the CK treatment was 11.811 × 10⁻⁶. 4 The number of plants per mu (unit of land area) was 14.069 × 10⁻⁶. 4 The number of plants per mu (unit of land area) was 16.506 × 10⁶. 4 The number of tillers per acre was significantly increased in the CRFB treatment compared to the control (CK), with an increase of approximately 40%; compared to the CRF treatment, the increase was approximately 17%. This indicates that the introduction of functional microorganisms effectively promoted the tillering ability of wheat.

[0129] from Figure 9 The wheat yield comparison chart shows that, compared with the CK treatment, the CRFB treatment achieved a yield increase of 17.8%; compared with the CRF treatment, the CRFB treatment also showed a significant yield advantage. This indicates that the functional microbial composite double-layer coated controlled-release fertilizer prepared in Example 1 of this application significantly improved wheat yield through the synergistic effect of functional microorganisms on the basis of controlled release.

[0130] from Figure 10 The soil electrical conductivity (EC) comparison chart shows that the soil EC value of the CK treatment was 1335.75 μS / cm, while that of the CRF treatment decreased to 891 μS / cm, and that of the CRFB treatment was 972.75 μS / cm. Compared with the CK, the soil EC value of the CRFB treatment decreased significantly, by approximately 27%, indicating that this fertilizer can effectively reduce soil salinity and improve the rhizosphere saline-alkali environment.

[0131] In summary, compared with conventional fertilization and ordinary controlled-release fertilizers, the functional microbial compound double-layer coated controlled-release fertilizer of this application can significantly increase the number of wheat tillers, improve yield, and reduce soil electrical conductivity, demonstrating excellent yield-increasing and soil-remediating effects.

[0132] Example 2

[0133] In this embodiment 2, a functional microbial composite double-layer coated controlled-release fertilizer was prepared according to the following method and applied to corn planting.

[0134] The specific production process of functional microbial compound double-layer coated controlled-release fertilizer is as follows:

[0135] First, add 80g of ethanol, 20g of ethyl cellulose, and 1g of dibutyl sebacate to a 500mL beaker, and stir on a magnetic stirrer to obtain a controlled-release coating solution.

[0136] The second step involves adjusting the bacterial concentrations of the three functional microorganisms (Rhizobium filamentosa (ACCC No. 15082), Flavobacterium tumefaciens (CGMCC No. 31149), and Bacillus licheniformis (CGMCC No. 38142)) to OD using culture medium. 600=1.0, then mix them at a volume ratio of 1:1:1 for later use. Weigh 200g of the mixed bacterial solution, 1g of montmorillonite powder, and 30g of sodium carboxymethyl cellulose and add them to another beaker. Stir and control the beaker temperature to maintain at 25-30℃ to obtain the functional coating solution.

[0137] The third step is to turn on the Roots blower 1 after all the substances have completely dissolved. The airflow is buffered and balanced by the gas buffer tank 2, and then heated by the heater 3 before entering the fluidized bed 4. The circulation lasts for about 20 minutes, so that the temperature inside the fluidized bed 4 is stabilized at 55°C and the fluidized bed 4 is in working condition.

[0138] The fourth step is to add 1 kg of large urea particles to fluidized bed 4, preheat for 10 minutes, and then add 5 g of liquid paraffin to lubricate the surface of the fertilizer particles.

[0139] Fifth step: Add controlled-release coating liquid to coating liquid storage tank 7, use peristaltic pump 6 to deliver it to nozzle, atomize it and spray it onto the surface of fertilizer granules.

[0140] Step 6: Atomize the controlled-release coating solution at a rate of 5 mL / min through the nozzle for 20 minutes, then fluidize for another 20 minutes to allow complete ethanol evaporation. Add 8 g of solid paraffin, maintain the coating temperature at 55°C, and fluidize for 10 minutes. Stop heating, turn on the cooler, adjust heater 3 to 30°C, and run it steadily for 5 minutes.

[0141] Step 7: Add functional coating liquid to coating liquid storage tank 7, use peristaltic pump 6 to deliver it to nozzle, atomize it and spray it onto the surface of fertilizer granules.

[0142] Step 8: The functional coating solution is atomized through the nozzle at a rate of 3 mL / min for 1 hour. Then, heating is stopped, the fertilizer is removed, and it is air-dried to obtain the desired product. Figure 11 The functional microbial composite double-layer coated controlled-release fertilizer shown.

[0143] Furthermore, the performance of the functional microbial composite double-layer coated controlled-release fertilizer prepared above was tested.

[0144] Referring to the international standard ISO 22398, the controlled-release performance was determined using the 25℃ water immersion method. The specific steps are as follows:

[0145] (1) Take 10g of functional microbial composite double-layer coating controlled-release fertilizer with uniform shape and size, put it into a 150μm (100 mesh) nylon mesh bag, seal it and put it into a 250mL plastic bottle;

[0146] (2) Add 200 mL of deionized water, seal and place in a 25°C constant temperature incubator;

[0147] (3) Each treatment was repeated 3 times. The sampling times were: days 1, 4, 7, 10, 14, 21 and 28 of culture, and then once every 7 days thereafter.

[0148] (4) The content of urea nitrogen in the solution was determined by p-dimethylaminobenzaldehyde-spectrophotometry (wavelength 420 nm), and the cumulative nutrient dissolution rate was calculated;

[0149] (5) The number of days required for the cumulative nutrient dissolution rate to reach 80% is taken as the controlled release period of the fertilizer.

[0150] Figure 12 This is a graph showing the nitrogen release curve of the functional microbial composite double-layered coated controlled-release fertilizer in Example 2 of this application.

[0151] like Figure 12 As shown, the functional microbial composite double-layer coated controlled-release fertilizer prepared in Example 2 of this application exhibited a steady increase in the cumulative release rate of nitrogen (N) with prolonged soaking time under static water immersion conditions at 25°C. The cumulative release rate was 0.36% on day 1, 2.84% on day 4, 6.07% on day 7, 9.83% on day 10, 14.57% on day 14, 23.07% on day 21, and 34.88% on day 28. Based on the standard of the number of days required to achieve an 80% cumulative release rate as the controlled-release period, the controlled-release period of the functional microbial composite double-layer coated controlled-release fertilizer in Example 2 is 60 days, demonstrating excellent nutrient controlled-release performance.

[0152] The effective viable counts of *Rhizobium linearis* (ACCC No. 15082), *Flavobacterium tumefaciens* (CGMCC No. 31149), and *Bacillus licheniformis* (CGMCC No. 38142) were determined using the dilution plating method, and the viable counts were used as an indicator to determine the activity of the bacterial species.

[0153] The test results showed that the viable count of the three functional bacteria in the fertilizer reached 3.58 × 10⁻⁶. 7 The CFU / L and viable bacteria count both meet the standards for microbial fertilizers (compound microbial fertilizer (NY / T 798-2015)), and can be used as a high-efficiency functional microbial fertilizer.

[0154] Furthermore, the functional microbial composite double-layer coated controlled-release fertilizer (denoted as CRFB) prepared above was used in corn planting.

[0155] The fertilizer was mixed with phosphate and potassium fertilizers to form a special fertilizer for corn. The application rate was 180-60-60 kg / ha based on N-P2O5-K2O. Fertilizer efficiency test was conducted in a slightly saline-alkali land (salinity of 0.34%). All fertilizers were applied as base fertilizer before corn sowing, and no topdressing was applied later. The following comparative treatments were set up: (1) Conventional fertilization (CK): compound fertilizer (15-15-15) was applied as base fertilizer, and nitrogen fertilizer was applied later. The total amount of nitrogen applied was the same as that of the CRFB treatment; (2) Ordinary controlled-release fertilizer (CRF): the application rate was the same as that of CRFB, applied once, and its preparation process was the same as that of CRFB but without the addition of bacterial solution. The experiment analyzed the effects of different treatments on corn yield and soil electrical conductivity (EC).

[0156] Figure 13 This is a comparison chart of maize yields under different treatments in Example 2 of this application; Figure 14 This is a comparison chart of soil electrical conductivity under different treatments in Example 2 of this application.

[0157] from Figures 13-14 It can be seen that the functional microbial composite double-layer coated controlled-release fertilizer prepared in Example 2 of this application has a significant impact on corn yield and soil salinity.

[0158] from Figure 13 The comparison chart of maize yields shows that the maize yield under conventional fertilization (CK) was 9916.319 kg / hm². 2 The conventional controlled-release fertilizer (CRF) treatment was basically the same as the control (9783.137 kg / hm²). 2 The yield of maize treated with CRFB reached 11452.87 kg / hm². 2 Compared to the control (CK), the CRFB treatment increased yield by approximately 10%, indicating that the introduction of functional microorganisms further enhanced maize yield on the basis of controlled release.

[0159] from Figure 14 The soil electrical conductivity (EC) comparison chart shows that the soil EC value of the CK treatment was 330.6 μS / cm, while that of the CRF treatment decreased to 195.6 μS / cm, and that of the CRFB treatment was 294.7 μS / cm. Compared with the CK, the soil EC value of the CRFB treatment decreased significantly, by about 10%, indicating that this fertilizer can effectively reduce soil salinity and improve the rhizosphere saline-alkali environment.

[0160] In summary, the functional microbial composite double-layer coated controlled-release fertilizer prepared in this embodiment has a significant yield-increasing effect on corn (yield increase rate of up to 10%), and can also significantly reduce soil electrical conductivity, demonstrating good dual effects of yield increase and soil remediation.

[0161] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A functional microbial composite double-layer coated controlled-release fertilizer, characterized in that, The functional microbial composite double-layer membrane controlled-release fertilizer comprises, from the inside out, a core, a controlled-release layer, and a functional layer. The core is a fertilizer granule; The controlled-release layer comprises bio-based polymer materials and plasticizers; The functional layer includes functional microorganisms, stabilizers, and adhesives; The functional microorganisms include Rhizobium filamentosa, Flavobacterium tumefaciens, and Bacillus licheniformis.

2. The functional microbial composite double-layer coated controlled-release fertilizer according to claim 1, characterized in that, The contents of each component in the functional microbial composite double-layer coated controlled-release fertilizer, by weight, are as follows: The amount of fertilizer granules used in the core is 1000 parts; The amount of the bio-based polymer material in the controlled-release layer is 10-30 parts, and the amount of the plasticizer is 1-3 parts; The functional microorganisms in the functional layer are added in the form of a mixed bacterial solution, with an amount of 200-300 parts of the mixed bacterial solution, an amount of 1-2 parts of the stabilizer, and an amount of 30-50 parts of the adhesive.

3. The functional microbial composite double-layer coated controlled-release fertilizer according to claim 2, characterized in that, The total concentration of viable bacteria in the mixed bacterial solution is 1×10⁻⁶. 8 -1×10 9 CFU / mL, wherein the ratio of viable counts of Rhizobium linearis, Flavobacterium tumefaciens, and Bacillus licheniformis is 1:(0.8-1.2):(0.8-1.2).

4. The functional microbial composite double-layer coated controlled-release fertilizer according to claim 1, characterized in that, The stabilizer is selected from at least one of calcium carbonate, calcium chloride, superphosphate, and montmorillonite powder; The adhesive is selected from at least one of sodium carboxymethyl cellulose, sodium carboxymethyl starch, carboxymethyl chitosan, and sodium alginate.

5. The functional microbial composite double-layer coated controlled-release fertilizer according to claim 1, characterized in that, The bio-based polymer material is selected from at least one of ethyl cellulose, chitin, and lignin; The plasticizer is selected from at least one of phthalate, dibutyl sebacate, epoxidized soybean oil, chitosan, polyethylene glycol, glycerin, polycaprolactone, and polybutylene terephthalate.

6. The functional microbial composite double-layer coated controlled-release fertilizer according to claim 1, characterized in that, The fertilizer granules are selected from at least one of potassium chloride, potassium sulfate, ammonium sulfate, ammonium nitrate, monoammonium phosphate, diammonium phosphate, urea, and compound nitrogen, phosphorus and potassium fertilizers.

7. The functional microbial composite double-layer coated controlled-release fertilizer according to claim 1, characterized in that, The fertilizer granules are coated with a lubricant, which is used to fill the gaps on the surface of the fertilizer granules to make the surface of the fertilizer granules smooth. The amount of the lubricant used is 5-10 parts by weight; The lubricant is selected from at least one of liquid paraffin, ethylene glycol, glycerin, and silicone oil.

8. The functional microbial composite double-layer coated controlled-release fertilizer according to claim 1, characterized in that, A sealing agent is coated on the surface of the controlled-release layer to fill the gaps in the controlled-release layer and improve the controlled-release effect of the controlled-release layer. The amount of the sealing agent is 5-10 parts by weight. The sealing agent is selected from at least one of solid paraffin, polycaprolactone, ethylene-vinyl acetate copolymer, and polyethylene oxide.

9. A method for preparing a functional microbial composite double-layer coated controlled-release fertilizer as described in any one of claims 1-8, characterized in that, include: A controlled-release coating solution containing bio-based polymer materials and plasticizers is coated onto the surface of fertilizer granules and dried to form a controlled-release layer on the surface of the fertilizer granules. A mixed bacterial solution containing functional microorganisms is provided. A stabilizer and a binder are added to the mixed bacterial solution and mixed evenly to obtain a functional coating solution. The functional coating liquid is coated onto the surface of the controlled-release layer and dried to obtain a functional microbial composite double-layer coated controlled-release fertilizer.

10. The preparation method according to claim 9, characterized in that, The preparation method further includes: Before forming the controlled-release layer, a lubricant is coated onto the surface of the fertilizer granules; and / or Before coating the functional coating liquid, a sealing agent is coated on the surface of the controlled-release layer.

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