Phosphorus-dissolving nitrogen-fixing type soil improvement and yield increase microbial inoculum

Abstract

The invention discloses a phosphorus-dissolving and nitrogen-fixing type soil improvement and yield increase microbial agent, and particularly relates to the technical field of agricultural biology. The microbial inoculum takes sulfur modified porous ceramic microbeads as a carrier matrix, and a manganese / iron co-doped zeolite nanosheet and a functional layer of nano calcium carbonate coated with a lignin derived porous carbon shell are compounded on the surface of the carrier matrix. The preparation method comprises the following steps: carrying out sintering and vapor deposition to obtain elemental sulfur-loaded porous ceramic microbeads, preparing manganese / iron co-doped zeolite nanosheets, synthesizing a porous carbon shell coated nano calcium carbonate composite material, compounding the components to form a carrier, and finally loading a mixed bacteria solution of phosphorus-dissolving microorganisms and nitrogen-fixing microorganisms on the carrier, thereby obtaining the nitrogen-containing phosphorus-dissolving nitrogen-fixing composite material. And embedding and immobilizing to obtain the microbial inoculum. Competition and inhibition among strains are effectively reduced, the storage stability of the microbial inoculum and the lasting activity in soil are remarkably improved, and the microbial inoculum is suitable for soil improvement and crop yield increase.

Description

Technical Field

[0001] This invention relates to the field of agricultural biotechnology, and in particular to a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-enhancing microbial agent. Background Technology

[0002] The field of microbial fertilizer technology encompasses the preparation and application of agricultural inputs that utilize the life activities and metabolic products of beneficial microorganisms to improve crop nutrient supply, promote growth, increase yield, or improve quality. The core of this technology lies in screening and cultivating microbial strains with specific functions, such as nitrogen-fixing bacteria, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, and growth-promoting bacteria, and preparing them into live bacterial preparations that can be stably stored and applied through fermentation processes. This paper systematically introduces a series of technical aspects involved in this field, including the isolation and identification of microbial strains, functional verification, culture medium optimization, fermentation process control, selection of microbial carriers, preparation processing technology, and field application methods.

[0003] Microbial fertilizers, as an environmentally friendly agricultural input, focus on efficiently delivering beneficial microorganisms with specific functions, such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria, to the crop rhizosphere and maintaining their activity. To improve efficiency, different functional microbial strains are often used in combination. However, current technologies face serious challenges: during the preparation, storage, and initial application of microbial agents, different microbial strains, such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria, are prone to cross-inhibition of metabolites, nutrient competition, or direct antagonism due to close physical contact. This leads to a rapid decline in the activity of some microbial strains, making it difficult to maintain the synergistic effect of compound microbial agents in a sustained and stable manner.

[0004] Patent CN121085681A discloses a composite soil amendment fertilizer and its preparation process, suitable for improving degraded soils. The modified biochar carrier is produced through anaerobic pyrolysis of agricultural waste, citric acid modification, and mineral loading. The composite microbial agent contains three strains of bacteria, including phosphate-solubilizing Pseudomonas, with a viable count meeting standards. The organic fermentation substrate is prepared by aerobic-anaerobic staged fermentation of bacterial residue, activated sludge, and corn cobs. The inorganic mineral component consists of a specific ratio of attapulgite and dolomite powder. Applied twice, it can simultaneously improve the physical, chemical, and microbial ecology of the soil, enhancing nutrient utilization.

[0005] Patent CN102795944A relates to a soil-improving bio-fertilizer and its preparation method. The porous inorganic materials in the raw materials are selected from vermiculite, zeolite, etc. The compound microbial agent is made by fermentation of six specific strains. The organic fertilizer is obtained by composting crop straw powder and animal manure. In the preparation process, each strain is first cultured and made into an agent. Then, all raw materials are mixed in proportion, granulated, and dried at low temperature. The product can be used as a base fertilizer, which can increase the nitrogen content of the soil, improve the soil structure, and improve the utilization rate of chemical fertilizers and the yield and quality of crops.

[0006] Patent CN120424663A provides an acidified soil conditioner, its preparation method, and its application. The core of this method involves combining solid waste such as steel slag and phosphogypsum with functional materials. This conditioner employs a core-shell structure to achieve multi-level regulation, rapidly neutralizing soil acidity and maintaining long-term pH stability, thus solving the problem of room-temperature storage for bacterial conditioners. It increases the pH and base saturation of acidified soils, reduces available manganese content, and increases rice yield, with effects lasting for two planting years.

[0007] In existing technologies, compound microbial agents often directly mix or co-load microorganisms with different functions, such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria, onto the same carrier. This leads to competition for nutrients, cross-inhibition of metabolites, or direct antagonism between microbial species, which seriously affects the activity and functional durability of the microbial agent. The carriers used mostly focus on providing physical adsorption or protection, such as biochar, zeolite, and vermiculite, and lack the ability to systematically regulate the growth environment of microorganisms. For example, the integration of functions such as pH buffering, slow release of trace elements, and carbon source supply is insufficient. They are easily inactivated during storage, are greatly affected by the environment after being applied to the soil, and have a short survival time for functional microorganisms, making it difficult to achieve long-term effects.

[0008] Therefore, this invention proposes a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent. Summary of the Invention

[0009] The main objective of this invention is to provide a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent, which can effectively solve the problems of low activity and functional persistence of the above-mentioned microbial agents, short survival time of functional microorganisms, difficulty in achieving long-term effects, and lack of systematic regulation of the microbial growth environment by the carrier.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-enhancing microbial agent includes the following steps: S1: The carrier is a composite material carrier prepared by using sulfur-modified porous ceramic microspheres as the matrix and attaching a lignin-derived porous carbon shell to the outer surface of the microspheres to coat nano-calcium carbonate as the second functional layer. S2: The microbial inoculum containing phosphorus-solubilizing and nitrogen-fixing microorganisms is loaded onto a composite material carrier to prepare the phosphorus-solubilizing and nitrogen-fixing soil amendment and yield-increasing microbial agent.

[0011] The preferred step S1 involves the following steps in preparing the composite material carrier: A1: Phosphogypsum, binder and pore-forming agent are mixed, granulated and sintered at 850-950℃ to form porous ceramic microspheres. Then, elemental sulfur is loaded into the pores at 120-150℃ by vapor deposition to modify the porous ceramic microspheres. A2: Natural zeolite is made into nanosheets and subjected to ion exchange reaction with manganese salt and ferrous salt solution at 50-70℃ for 2-6 hours to obtain doped zeolite nanosheets, which are then dispersed in water to form a suspension. A3: Add calcium salt solution, carbonize lignin and SiO2 nanospheres at 600-800℃ under an inert atmosphere, and then carry out a carbonation reaction with hydrofluoric acid solution and CO2 to obtain the composite material. A4: Immerse the sulfur-modified porous ceramic microspheres obtained in step A1 into the suspension obtained in step S2, and after vacuum impregnation and drying, obtain the intermediate product loaded with zeolite nanosheets. A5: The intermediate product obtained in step A4 is mechanically mixed with the composite material powder obtained in step A3 to obtain a composite material carrier.

[0012] Preferably, in step A1, the particle size of the sulfur-modified porous ceramic microspheres is 100-500 μm, and the loading of elemental sulfur is 5-15% of the total mass of the sulfur-modified porous ceramic microspheres.

[0013] Preferably, the manganese salt in step A2 is MnCl2 and the ferrous salt is FeSO4; in the manganese and iron co-doped zeolite nanosheets, the total doping amount of manganese and iron is 3-10 wt% of the dry weight of the zeolite nanosheets.

[0014] Preferably, the specific surface area of ​​the porous carbon shell in the composite material in step A3 is 300-800 m². 2 / g, the content of nano-calcium carbonate is 10-30wt% of the total mass of the composite material.

[0015] Preferably, the binder in step A1 is one of bentonite and diatomaceous earth; the pore-forming agent is one of starch, ammonium carbonate, and polyethylene glycol.

[0016] Preferably, the mass ratio of phosphogypsum, binder, and pore-forming agent in step A2 is (5-7):(2-4):(0.5-1.5).

[0017] Preferably, in step S2, the loading method is an adsorption-embedding combination method, in which the microbial liquid is adsorbed onto the composite material carrier and embedded and fixed in a sodium alginate solution with a mass concentration of 2-4%.

[0018] Preferably, the phosphate-solubilizing microorganism in step S2 is a species of Pseudomonas or Bacillus; the nitrogen-fixing microorganism is a species of Azospirobacter or Azotobacter.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention uses sulfur-modified porous ceramic microspheres as a matrix. The elemental sulfur loaded inside can be slowly released to continuously supply sulfur elements. At the same time, the porous structure provides independent colonization space for phosphate-solubilizing bacteria and nitrogen-fixing bacteria, effectively reducing direct competition and metabolic inhibition between bacterial species, thereby significantly improving the biocompatibility and long-term stability of the compound bacterial agent.

[0020] This invention employs a carrier with manganese / iron co-doped zeolite nanosheets on its outer surface and lignin-derived porous carbon shells coated with nano-calcium carbonate, forming a superior second structural layer. This layer possesses a high specific surface area, providing ample interface for microbial adsorption and colonization. It can also slowly release trace elements such as manganese and iron through ion exchange, and utilize the pH buffering effect of calcium carbonate and the slow-release carbon source characteristics of porous carbon to continuously optimize the rhizosphere microenvironment, enhancing the activity maintenance and functional expression of microorganisms in the soil. Attached Figure Description

[0021] Figure 1 A schematic diagram of the process for preparing a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to the present invention; Detailed Implementation The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise range thresholds, and these range thresholds should be understood to include values ​​close to these range thresholds. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0022] The preparation of a phosphorus-solubilizing and nitrogen-fixing soil amendment and yield-increasing microbial agent provided in the embodiments of this specification will be described in detail below with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the preparation process of a phosphorus-solubilizing and nitrogen-fixing soil amendment and yield-increasing microbial agent is as follows, with specific preparation steps as shown below.

[0024] Example 1 S1: Phosphogypsum, diatomaceous earth, and starch were mixed evenly in a mass ratio of 5:2:0.5, granulated, and sintered at 900℃ for 2 hours to obtain porous ceramic microspheres. These microspheres were then placed in a sulfur vapor atmosphere and subjected to vapor deposition at 135℃ for 4 hours to load elemental sulfur into the micropores, resulting in sulfur-modified porous ceramic microspheres. The microsphere particle size was determined to be 300 μm, and the sulfur loading was 10% of the total mass.

[0025] Natural zeolite was mechanically exfoliated into nanosheets. 10 g of zeolite nanosheets were dispersed in 200 mL of deionized water, and a mixed solution of 0.5 mol / L MnCl2 and 0.3 mol / L FeSO4 was added. The mixture was subjected to an ion exchange reaction at 60 °C for 4 hours. After the reaction, the nanosheets were centrifuged, washed, and dried to obtain manganese / iron co-doped zeolite nanosheets. The total loading of manganese and iron was 6 wt% of the dry weight of the zeolite nanosheets. These nanosheets were then redispersed in water to form a 5% (w / w) suspension for later use.

[0026] 10g of lignin, 5g of SiO2 nanospheres, and 50mL of calcium chloride solution were mixed thoroughly and carbonized at 700℃ for 2 hours under nitrogen protection. The carbonized product was then treated with 10% hydrofluoric acid to remove the SiO2 template, followed by carbonation with CO2 to obtain a porous carbon shell-coated nano-calcium carbonate composite material. Its specific surface area was 550 m² / g. 2 / g, with a nano calcium carbonate content of approximately 20wt%.

[0027] Sulfur-modified porous ceramic microspheres were immersed in the zeolite nanosheet suspension prepared in step 2 and vacuum impregnated for 30 minutes. After removal, they were dried at 80°C. The dried product was then mechanically mixed with the composite material powder obtained in step 3 at a mass ratio of 7:3 to obtain the final composite material carrier.

[0028] S2: Culture Bacillus megaterium and Azotobacter brasiliensis separately, adjust the ratio of viable bacteria to 1:2 to 2:1, mix the composite material carrier with the microbial liquid at a mass ratio of 1:5, adsorb for 30 minutes, drain the excess liquid, and then spray and embed it evenly with a 3% sodium alginate solution. After cross-linking and curing with calcium chloride solution, the finished microbial agent is obtained after drying.

[0029] In Example 1, the phosphate-solubilizing microorganism was Bacillus megaterium, a species of Bacillus, and the nitrogen-fixing microorganism was Azotospira brasiliensis, a species of Azotospira.

[0030] Example 2 S1: Phosphogypsum, bentonite, and ammonium carbonate were mixed evenly in a mass ratio of 6:2:1, granulated, and sintered at 850℃ for 2 hours to obtain porous ceramic microspheres. These microspheres were then placed in a sulfur vapor atmosphere and subjected to vapor deposition at 120℃ for 4 hours to load elemental sulfur into the micropores, resulting in sulfur-modified porous ceramic microspheres. The microsphere particle size was determined to be 100 μm, and the sulfur loading was 5% of the total mass.

[0031] Natural zeolite was mechanically exfoliated into nanosheets. 10 g of zeolite nanosheets were dispersed in 200 mL of deionized water, and a mixed solution of 0.5 mol / L MnCl2 and 0.3 mol / L FeSO4 was added. The mixture was subjected to an ion exchange reaction at 50 °C for 2 hours. After the reaction, the nanosheets were centrifuged, washed, and dried to obtain manganese / iron co-doped zeolite nanosheets. The total loading of manganese and iron was 6 wt% of the dry weight of the zeolite nanosheets. These nanosheets were then redispersed in water to form a 5% (w / w) suspension for later use.

[0032] 10g of lignin, 5g of SiO2 nanospheres, and 50mL of calcium chloride solution were mixed thoroughly and carbonized at 600℃ for 2 hours under nitrogen protection. The carbonized product was treated with 10% hydrofluoric acid to remove the SiO2 template, followed by carbonation with CO2 to obtain a porous carbon shell-coated nano-calcium carbonate composite material. Its specific surface area was 300 m² / g, and the nano-calcium carbonate content was approximately 10 wt%.

[0033] Sulfur-modified porous ceramic microspheres were immersed in the zeolite nanosheet suspension prepared in step 2 and vacuum impregnated for 30 minutes. After removal, they were dried at 80°C. The dried product was then mechanically mixed with the composite material powder obtained in step 3 at a mass ratio of 7:3 to obtain the final composite material carrier.

[0034] S2: Bacillus megaterium and Azotobacter brasiliensis were cultured separately, and the ratio of live bacteria was adjusted to 1:2. The composite material carrier and the microbial liquid were mixed at a mass ratio of 1:5. After adsorption for 30 minutes, the excess liquid was drained, and then the mixture was evenly sprayed and embedded with a 2% sodium alginate solution. After cross-linking and curing with calcium chloride solution, the finished microbial agent was obtained after drying.

[0035] In Example 2, the phosphate-solubilizing microorganism is Bacillus megaterium, a species of Bacillus, and the nitrogen-fixing microorganism is Azotospira brasiliensis, a species of Azotospira.

[0036] Example 3 S1: Phosphogypsum, clay, and starch were mixed evenly in a mass ratio of 7:4:1.5, granulated, and sintered at 950℃ for 2 hours to obtain porous ceramic microspheres. These microspheres were then placed in a sulfur vapor atmosphere and subjected to vapor deposition at 150℃ for 4 hours to load elemental sulfur into the micropores, resulting in sulfur-modified porous ceramic microspheres. The microsphere particle size was determined to be 500 μm, and the sulfur loading was 15% of the total mass.

[0037] Natural zeolite was mechanically exfoliated into nanosheets. 10g of zeolite nanosheets were dispersed in 200mL of deionized water, and a mixed solution of 0.5mol / L MnCl2 and 0.3mol / L FeSO4 was added. The mixture was subjected to an ion exchange reaction at 70℃ for 2-6 hours. After the reaction, the nanosheets were centrifuged, washed, and dried to obtain manganese / iron co-doped zeolite nanosheets. The total loading of manganese and iron was 6wt% of the dry weight of the zeolite nanosheets. These nanosheets were then redispersed in water to form a 5% (w / w) suspension for later use.

[0038] 10g of lignin, 5g of SiO2 nanospheres, and 50mL of calcium chloride solution were mixed thoroughly and carbonized at 800℃ for 2 hours under nitrogen protection. The carbonized product was treated with 10% hydrofluoric acid to remove the SiO2 template, followed by carbonation with CO2 to obtain a porous carbon shell-coated nano-calcium carbonate composite material. Its specific surface area was 800 m² / g, and the nano-calcium carbonate content was approximately 30 wt%.

[0039] Sulfur-modified porous ceramic microspheres were immersed in the zeolite nanosheet suspension prepared in step 2 and vacuum impregnated for 30 minutes. After removal, they were dried at 80°C. The dried product was then mechanically mixed with the composite material powder obtained in step 3 at a mass ratio of 7:3 to obtain the final composite material carrier.

[0040] S2: Culture Bacillus megaterium and Azotobacter brasiliensis separately, adjust the ratio of live bacteria to 1:2 to 2:1, mix the composite material carrier with the microbial liquid at a mass ratio of 1:5, adsorb for 30 minutes, drain the excess liquid, and then spray and embed it evenly with a sodium alginate solution with a mass concentration of 2-4%. After cross-linking and curing with calcium chloride solution, the finished microbial agent is obtained after drying.

[0041] Comparative Example 1 This comparative example uses conventional carrier materials with simple physical mixing, and does not include the sulfur-modified porous ceramic microspheres and composite material structure of the present invention. The remaining steps are the same as in Example 1.

[0042] Comparative Example 2 This comparative example uses only ordinary porous ceramic microspheres as the matrix, without sulfur modification or loading of manganese / iron co-doped zeolite nanosheets, and the remaining steps are the same as in Example 1.

[0043] Comparative Example 3 This comparative example uses a single carrier material and does not have the composite structure of sulfur-modified porous ceramic microspheres in this invention. The remaining steps are the same as in Example 1.

[0044] The following performance tests were performed on Examples 1-3 and Comparative Examples 1-3 described above: 1. Storage stability test: Take three equal portions of the finished bacterial agents prepared in Examples 1-3 and Comparative Examples 1-3, put them into sterile sealed aluminum foil bags, and store the bacterial agents at room temperature under sealed conditions for 6 months. The viable count retention rate is then determined.

[0045] 2. Soil Simulation Release Test: In a simulated soil environment, that is, 10 mg / gram of soil is inoculated with the soil. 6 CFU was cultured at a constant temperature for 30 days, and its phosphorus solubilization and nitrogen fixation activities were measured periodically.

[0046] 3. Pot verification experiment: 2 kg of soil was placed in each pot and applied to corn potted plants. 10 mg of soil was inoculated per kilogram of soil. 7 CFU inoculant was applied, and the soil was watered regularly after sowing to maintain soil moisture at 70% of field capacity. The available phosphorus and available nitrogen content, plant dry weight, and root length in the soil were measured after 60 days.

[0047] The performance test results of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1: Table 1: Performance Results of Examples and Comparative Examples After 6 months of storage at room temperature in a sealed environment, the viable cell count retention rate of Example 1 reached 80.0%, while that of Comparative Example 1 was only 40.0%, and that of Comparative Example 2 was 50.0%. The data indicate that using sulfur-modified porous ceramic microspheres as a matrix, combined with a surface-composite manganese / iron co-doped zeolite nanosheet and a lignin-derived porous carbon shell-coated nano-calcium carbonate functional layer, can provide physically isolated colonization space for phosphate-solubilizing bacteria and nitrogen-fixing bacteria, effectively reducing direct competition between bacterial species and inhibition of metabolites. In a 30-day soil simulated release test, the Example group showed a slowly decreasing phosphate-solubilizing and nitrogen-fixing activity curve, indicating that the slow release of elements such as sulfur, manganese, and iron from the carrier continuously nourishes the microorganisms, the porous structure adsorbs water and nutrients, and calcium carbonate regulates the rhizosphere pH.

[0048] In a 30-day soil simulation release experiment, the phosphorus solubilization and nitrogen fixation activities of Example 1 remained at 85% and 78% of their initial values, respectively, significantly higher than those of Comparative Example 1 (45% and 40%) and Comparative Example 2 (60% and 55%). This result is attributed to the slow-release characteristics of elements such as sulfur, manganese, and iron in the carrier, as well as the buffering effect of nano-calcium carbonate on rhizosphere pH. Manganese / iron co-doped zeolite nanosheets gradually release trace elements through ion exchange, promoting microbial metabolic activity; the porous carbon shell serves as a high-quality interface for microbial attachment and continuously provides an organic carbon source.

[0049] In a maize pot experiment, after 60 days of treatment with the microbial agent from Example 1, the available phosphorus and available nitrogen contents in the soil reached 45.2 mg / kg and 120.5 mg / kg, respectively. The plant dry weight and root length were 35.6 g and 28.4 cm, respectively, representing increases of 43% and 34% compared to Comparative Example 1, and increases of 77% and 54% compared to the blank control. These data indicate that the microbial agent of this invention can not only significantly increase the content of available nutrients in the soil, but also promote crop root development and biomass accumulation by improving the rhizosphere microecology, achieving a synergistic effect of soil improvement, growth promotion, and yield increase.

[0050] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-enhancing microbial agent, characterized in that, Includes the following steps: S1: The carrier is a composite material carrier prepared by using sulfur-modified porous ceramic microspheres as the matrix and attaching a lignin-derived porous carbon shell to the outer surface of the microspheres to coat nano-calcium carbonate as the second functional layer. S2: The microbial inoculum containing phosphorus-solubilizing and nitrogen-fixing microorganisms is loaded onto a composite material carrier to prepare the phosphorus-solubilizing and nitrogen-fixing soil amendment and yield-increasing microbial agent.

2. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 1, characterized in that, The preparation of the composite material carrier in step S1 includes the following steps: A1: Phosphogypsum, binder and pore-forming agent are mixed, granulated and sintered at 850-950℃ to form porous ceramic microspheres. Then, elemental sulfur is loaded into the pores at 120-150℃ by vapor deposition to modify the porous ceramic microspheres. A2: Natural zeolite is made into nanosheets and subjected to ion exchange reaction with manganese salt and ferrous salt solution at 50-70℃ for 2-6 hours to obtain doped zeolite nanosheets, which are then dispersed in water to form a suspension. A3: Add calcium salt solution, carbonize lignin and SiO2 nanospheres at 600-800℃ under an inert atmosphere, and then carry out a carbonation reaction with hydrofluoric acid solution and CO2 to obtain the composite material. A4: Immerse the sulfur-modified porous ceramic microspheres obtained in step A1 into the suspension obtained in step S2, and after vacuum impregnation and drying, obtain the intermediate product loaded with zeolite nanosheets. A5: The intermediate product obtained in step A4 is mechanically mixed with the composite material powder obtained in step A3 to obtain a composite material carrier.

3. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 2, characterized in that, In step A1, the particle size of the sulfur-modified porous ceramic microspheres is 100-500 μm, and the loading of elemental sulfur is 5-15% of the total mass of the sulfur-modified porous ceramic microspheres.

4. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 2, characterized in that, In step A2, the manganese salt is MnCl2 and the ferrous salt is FeSO4; in the manganese and iron co-doped zeolite nanosheets, the total doping amount of manganese and iron is 3-10 wt% of the dry weight of the zeolite nanosheets.

5. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 2, characterized in that, In step A3, the specific surface area of ​​the porous carbon shell in the composite material is 300-800 m². 2 / g, the content of nano-calcium carbonate is 10-30wt% of the total mass of the composite material.

6. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 2, characterized in that, In step A1, the binder is one of bentonite and diatomaceous earth; the pore-forming agent is one of starch, ammonium carbonate, and polyethylene glycol.

7. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 2, characterized in that, The mass ratio of phosphogypsum, binder, and pore-forming agent in step A2 is (5-7):(2-4):(0.5-1.5).

8. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 1, characterized in that, In step S2, the loading method adopted is an adsorption-embedding combination method, in which the microbial liquid is adsorbed onto the composite material carrier and embedded and fixed in a sodium alginate solution with a mass concentration of 2-4%.

9. The preparation method of a phosphorus-solubilizing and nitrogen-fixing soil-improving and yield-increasing microbial agent according to claim 1, characterized in that, The phosphate-solubilizing microorganism in step S2 is one of the species of Pseudomonas or Bacillus; the nitrogen-fixing microorganism is one of the species of Azospirobacter or Azotobacter.

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