Preparation method and application of compound microbial agent based on soil improvement

Abstract

The invention discloses a preparation method and application of a compound microbial agent based on soil improvement, and relates to the technical field of agricultural microorganisms, and the preparation method comprises the following steps: respectively inoculating each microbial strain into an activation culture medium, and culturing for 45-50 hours to obtain a seed solution of each strain; respectively inoculating the obtained seed liquid of each strain into an amplification culture medium, and culturing and diffusing for 45-50 hours to obtain fermentation liquid of each strain; the preparation method comprises the following steps: adding a carrier into fermentation broth of each strain for adsorption, performing constant-temperature drying after adsorption to obtain microbial agent powder of each strain, and mixing the obtained microbial agent powder of each strain according to a mass ratio to obtain the compound microbial agent, the microbial strains comprise phosphate solubilizing bacteria strains, nitrogen-fixing bacteria strains and antagonistic bacteria strains; the carrier is chitosan / urea intercalation modified montmorillonite. The compound microbial agent provided by the invention has a good improvement effect.

Description

Technical Field

[0001] This application relates to the field of agricultural microbial technology, and particularly to a preparation method and application of a compound microbial inoculant based on soil improvement. Background Art

[0002] Soil is the material basis for crop growth. Factors such as its organic matter content, fertilizer retention capacity, air permeability, and soil solution balance play a decisive role in plant growth. Soil mainly consists of three parts: minerals, organic matter, and microorganisms. Among them, the activity of soil microorganisms is crucial for plant root nutrition. Beneficial microorganisms directly participate in the formation of soil fertility, including the transformation of matter and energy, the formation and decomposition of humus, nutrient release, and nitrogen fixation. However, in a pure natural state, the quantity and effect of beneficial microorganisms are relatively limited. In addition, the damage caused by plant pathogens has caused huge losses to crops, resulting in reduced yields at best and complete crop failures at worst, seriously affecting the economic interests of farmers. To prevent diseases and increase yields, farmers have to use a large amount of fungicides and fertilizers. However, the long-term and large-scale use of these chemical substances will damage the soil structure, leading to soil compaction, arable land degradation, shallowing of the plough layer, and a decline in water and fertilizer retention capacity, thereby polluting the ecological environment. This not only affects the continuous increase in crop yields, the improvement of the quality and efficiency of agriculture, and the cost reduction and income increase of farmers, but also threatens the quality and safety of agricultural products. At the same time, the accumulation of fungicides in plants will also harm the health of humans and livestock through the food chain.

[0003] In recent years, the application of microorganisms in agricultural production has become increasingly widespread. By artificially adding beneficial microorganisms to the soil, the quantity and overall activity of microorganisms in the soil can be significantly increased, thereby effectively improving soil fertility. However, most of the microbial inoculants currently used in agriculture are cultivated from single strains. However, the performance of single strains is relatively single, and the use effect is not stable enough. To improve the use effect, the prior art has developed compound microbial inoculants through strain combinations. However, research shows that there may be antagonistic effects between different strains in compound microbial inoculants, such as competing for nutrients and secreting inhibitory substances. These antagonistic effects may weaken the overall function of the inoculant. In addition, the inoculant is also vulnerable to the influence of high temperature, strong light, or high humidity environments during storage, resulting in a decrease in the number of viable bacteria. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, this application provides a preparation method and application of a compound microbial inoculant based on soil improvement.

[0005] The preparation method of the compound microbial inoculant based on soil improvement provided by this application adopts the following technical solutions:

[0006] The preparation method of the compound microbial inoculant based on soil improvement includes the following steps:

[0007] S1. Inoculate each microbial strain into the activation medium under the conditions of 28 - 38 °C and 100 - 200 rpm, and culture for 45 - 50 h to obtain the seed liquid of each strain;

[0008] S2. Inoculate the obtained seed liquid of each strain into the amplification medium under the conditions of 28 - 38 °C and 100 - 200 rpm, and culture and spread for 45 - 50 h to obtain the fermentation broth of each strain;

[0009] S3. Add a carrier to the fermentation broth of each strain for adsorption, and after adsorption, perform constant - temperature drying to obtain the microbial agent powder of each strain. After mixing the obtained microbial agent powders of each strain according to the mass ratio, the compound microbial agent is obtained;

[0010] The above - mentioned each microbial strain includes phosphate - solubilizing bacteria strain, nitrogen - fixing bacteria strain, and antagonistic bacteria strain;

[0011] The carrier is chitosan / urea - intercalated modified montmorillonite.

[0012] Preferably, the phosphate - solubilizing bacteria strain is one or more of Bacillus megaterium, Bacillus mucilaginosus, Pseudomonas fluorescens, Serratia marcescens, and Erwinia.

[0013] Preferably, the nitrogen - fixing bacteria strain is one or more of Rhizobium japonicum, Azospirillum, cyanobacteria, Rhodospirillum, and Azoarcus.

[0014] Preferably, the antagonistic bacteria strain is one or more of Bacillus subtilis, Trichoderma harzianum, Streptomyces, and Bacillus licheniformis.

[0015] Preferably, the mass ratio of the microbial agent powders of each strain is phosphate - solubilizing bacteria agent powder : nitrogen - fixing bacteria agent powder : antagonistic bacteria agent powder = (2 - 4) : (5 - 7) : 1.

[0016] Preferably, the microbial strains include Bacillus subtilis, Azoarcus, and Glomus claroideum; the mass ratio of Pseudomonas fluorescens, Azoarcus microbial agent powder, and Bacillus subtilis microbial agent powder is 3 : 6 : 1.

[0017] Preferably, the preparation method of the chitosan / urea - intercalated modified montmorillonite includes the following steps:

[0018] S1. Add sodium bicarbonate and montmorillonite into water and disperse evenly. The mass ratio of sodium bicarbonate, montmorillonite, and water is 1 : 15 - 25 : 300 - 400; then carry out an ion - exchange reaction at 75 - 85 °C for 5 - 7 h to obtain sodium - based montmorillonite;

[0019] S2. Add deionized water to sodium-based montmorillonite. The mass ratio of the sodium-based montmorillonite to the deionized water is 1:100 - 150. Ultrasonically disperse for 30 - 50 min to obtain a sodium-based montmorillonite suspension; adjust the pH of the sodium-based montmorillonite suspension to 6 - 7;

[0020] S3. Dissolve urea in deionized water according to a mass ratio of 1:2.3 - 3, and mix evenly to obtain a urea solution; under the water bath condition of 50 - 60 °C, drop the urea solution into the sodium-based montmorillonite suspension. After dropping, continue stirring for 20 - 25 h; after centrifugation, washing, and drying, obtain urea intercalated and modified montmorillonite;

[0021] S4. Disperse chitosan at a solid-liquid ratio of 1:50 - 60 in an acetic acid aqueous solution with a mass fraction of 5%, and stir at 30 - 40 °C for 16 - 20 h to obtain a chitosan solution; add the urea intercalated and modified montmorillonite to the chitosan solution, stir at 30 - 40 °C for 14 - 18 h, add an equal amount of 2 mol / L sodium hydroxide aqueous solution as the acetic acid aqueous solution, wash the product with deionized water and dry to obtain chitosan / urea intercalated and modified montmorillonite.

[0022] Preferably, the mass ratio of the urea to the sodium-based montmorillonite is 1:3 - 4.

[0023] Preferably, the mass ratio of the chitosan to the urea intercalated and modified montmorillonite is 1:1 - 1.2.

[0024] Application of the composite microbial inoculant obtained by the preparation method of the composite microbial inoculant for soil improvement in soil improvement.

[0025] In summary, the present application includes at least one of the following beneficial technical effects:

[0026] 1. By optimizing the strain combination, through the synergistic effect of "nitrogen-fixing bacteria + phosphorus-solubilizing bacteria + antagonistic bacteria", and cooperating with the chitosan / urea intercalated and modified montmorillonite carrier technology, the present application constructs an efficient soil nutrient supply system, effectively improves the soil biomass content, increases soil aeration and water retention, and improves soil fertility and biological activity.

[0027] 2. The carrier chitosan / urea intercalated and modified montmorillonite provided by the present application embeds urea molecules between the layers of montmorillonite to achieve slow release of nitrogen sources and provide continuous nutrition for microorganisms; the surface cross-links chitosan to form a cross-linked network, which can regulate the release rate of the microbial inoculant, extend the action time of microorganisms, and improve the utilization efficiency. Detailed implementation manners

[0028] The following further elaborates the present application in detail with reference to examples.

[0029] The chemical reagents used in the preparation examples, examples and comparative examples provided by the present invention are all commercially available products.

[0030] Preparation Example 1

[0031] S1. Add 1 g of sodium bicarbonate and 15 g of montmorillonite to 300 g of water and disperse evenly; then carry out an ion exchange reaction at 75 °C for 5 h to obtain sodium-based montmorillonite.

[0032] S2. Add 3 g of sodium-based montmorillonite to 300 g of deionized water and ultrasonically disperse for 30 min to obtain a sodium-based montmorillonite suspension; adjust the pH of the sodium-based montmorillonite suspension to 6 with dilute hydrochloric acid.

[0033] S3. Dissolve 1 g of urea in 2.3 g of deionized water at room temperature and mix evenly to obtain a urea solution; under the water bath condition of 50 °C, drop the urea solution into the sodium-based montmorillonite suspension. After dropping, continue stirring for 20 h; after centrifugation, washing and drying, urea intercalated modified montmorillonite is obtained.

[0034] S4. Disperse 5 g of chitosan in 250 mL of acetic acid aqueous solution with a mass fraction of 5% and stir at 30 °C for 16 h to obtain a chitosan solution; add 5 g of urea intercalated modified montmorillonite to the chitosan solution and stir at 30 °C for 14 h, then add 250 mL of sodium hydroxide aqueous solution with a concentration of 2 mol / L. After washing the product with deionized water and drying, chitosan / urea intercalated modified montmorillonite is obtained.

[0035] Preparation Example 2

[0036] S1. Add 1 g of sodium bicarbonate and 20 g of montmorillonite to 350 g of water and disperse evenly; then carry out an ion exchange reaction at 80 °C for 6 h to obtain sodium-based montmorillonite.

[0037] S2. Add 3.5 g of sodium-based montmorillonite to 420 g of deionized water and ultrasonically disperse for 40 min to obtain a sodium-based montmorillonite suspension; adjust the pH of the sodium-based montmorillonite suspension to 6.5 with dilute hydrochloric acid.

[0038] S3. Dissolve 1 g of urea in 2.6 g of deionized water at room temperature and mix evenly to obtain a urea solution; under the water bath condition of 55 °C, drop the urea solution into the sodium-based montmorillonite suspension. After dropping, continue stirring for 22.5 h; after centrifugation, washing and drying, urea intercalated modified montmorillonite is obtained.

[0039] S4. Disperse 5 g of chitosan in 275 mL of 5% acetic acid aqueous solution, stir at 35 °C for 18 h to obtain a chitosan solution; add 5.5 g of urea-intercalated modified montmorillonite to the chitosan solution, stir at 35 °C for 16 h, add 275 mL of 2 mol / L sodium hydroxide aqueous solution, wash the product with deionized water and dry to obtain chitosan / urea-intercalated modified montmorillonite.

[0040] Preparation Example 3

[0041] S1. Add 1 g of sodium bicarbonate and 25 g of montmorillonite to 400 g of water and disperse evenly; then carry out an ion exchange reaction at 85 °C for 7 h to obtain sodium-based montmorillonite;

[0042] S2. Add 4 g of sodium-based montmorillonite to 600 g of deionized water, ultrasonically disperse for 50 min to obtain a sodium-based montmorillonite suspension; adjust the pH of the sodium-based montmorillonite suspension to 7 with dilute hydrochloric acid;

[0043] S3. Dissolve 1 g of urea in 3 g of deionized water at room temperature and mix evenly to obtain a urea solution; under the water bath condition of 60 °C, drop the urea solution into the sodium-based montmorillonite suspension, and after dropping, continue to stir for 25 h; after centrifugation, washing and drying, obtain urea-intercalated modified montmorillonite;

[0044] S4. Disperse 5 g of chitosan in 300 mL of 5% acetic acid aqueous solution, stir at 40 °C for 20 h to obtain a chitosan solution; add 6 g of urea-intercalated modified montmorillonite to the chitosan solution, stir at 40 °C for 18 h, add 300 mL of 2 mol / L sodium hydroxide aqueous solution, wash the product with deionized water and dry to obtain chitosan / urea-intercalated modified montmorillonite.

[0045] Example 1

[0046] S1. Inoculate Bacillus megaterium, Rhizobium japonicum, and Bacillus subtilis into MacConkey agar medium at 28 °C and 100 rpm respectively, and culture for 45 h to obtain the seed liquid of each strain;

[0047] S2. Inoculate the obtained seed liquid of each strain into LB liquid medium at 28 °C and 100 rpm respectively, and culture and spread for 45 h to obtain the fermentation broth of each strain;

[0048] S3. Take 10 mL of the fermentation broth of each strain, and add 8 g of the chitosan / urea intercalated modified montmorillonite carrier prepared in Preparation Example 1 to the fermentation broth of each strain for adsorption. After adsorption, dry at a constant temperature of 30 °C to obtain the microbial agent powder of each strain. Mix the obtained Bacillus megaterium agent powder, Rhizobium japonicum agent powder, and Bacillus subtilis agent powder according to a mass ratio of 2:5:1 to obtain the composite microbial agent.

[0049] Example 2

[0050] S1. Inoculate Bacillus megaterium, Halomonas nitrogenfixans, and Trichoderma harzianum into MacConkey agar medium at 33 °C and 150 rpm respectively, and culture for 48 h to obtain the seed solution of each strain;

[0051] S2. Inoculate the obtained seed solution of each strain into LB liquid medium at 33 °C and 150 rpm respectively, and culture and spread for 48 h to obtain the fermentation broth of each strain;

[0052] S3. Take 10 mL of the fermentation broth of each strain, and add 10 g of the chitosan / urea intercalated modified montmorillonite carrier prepared in Preparation Example 2 to the fermentation broth of each strain for adsorption. After adsorption, dry at a constant temperature of 30 °C to obtain the microbial agent powder of each strain. Mix the obtained Bacillus megaterium agent powder, Halomonas nitrogenfixans agent powder, and Trichoderma harzianum agent powder according to a mass ratio of 3:6:1 to obtain the composite microbial agent.

[0053] Example 3

[0054] S1. Inoculate Pseudomonas fluorescens, Azospirillum, and Bacillus subtilis into MacConkey agar medium at 38 °C and 200 rpm respectively, and culture for 50 h to obtain the seed solution of each strain;

[0055] S2. Inoculate the obtained seed solution of each strain into LB liquid medium at 38 °C and 200 rpm respectively, and culture and spread for 50 h to obtain the fermentation broth of each strain;

[0056] S3. Take 10 mL of the fermentation broth of each strain, and add 12 g of the chitosan / urea intercalated modified montmorillonite carrier prepared in Preparation Example 3 to the fermentation broth of each strain for adsorption. After adsorption, dry at a constant temperature of 30 °C to obtain the microbial agent powder of each strain. Mix the obtained Pseudomonas fluorescens agent powder, Azospirillum agent powder, and Bacillus subtilis agent powder according to a mass ratio of 4:7:1 to obtain the composite microbial agent.

[0057] Example 4

[0058] S1. Serratia marcescens, Azotobacter salexigens, and Bacillus subtilis were respectively inoculated into MacConkey agar medium at 33°C and 150 rpm, and cultured for 48 h to obtain the seed solutions of each strain.

[0059] S2. The obtained seed solutions of each strain were respectively inoculated into LB liquid medium at 33°C and 150 rpm, and cultured and diffused for 48 h to obtain the fermentation broths of each strain.

[0060] S3. 10 mL of the fermentation broth of each strain was taken, and 10 g of the chitosan / urea intercalated modified montmorillonite carrier prepared in Preparation Example 2 was added to the fermentation broth of each strain for adsorption. After adsorption, it was dried at a constant temperature of 30°C to obtain the microbial agent powders of each strain. The obtained Serratia marcescens agent powder, Azotobacter salexigens agent powder, and Bacillus subtilis agent powder were mixed according to a mass ratio of 3:6:1 to obtain the composite microbial agent.

[0061] Example 5

[0062] S1. Pseudomonas fluorescens, Azotobacter salexigens, and Bacillus subtilis were respectively inoculated into MacConkey agar medium at 33°C and 150 rpm, and cultured for 48 h to obtain the seed solutions of each strain.

[0063] S2. The obtained seed solutions of each strain were respectively inoculated into LB liquid medium at 33°C and 150 rpm, and cultured and diffused for 48 h to obtain the fermentation broths of each strain.

[0064] S3. 10 mL of the fermentation broth of each strain was taken, and 10 g of the chitosan / urea intercalated modified montmorillonite carrier prepared in Preparation Example 2 was added to the fermentation broth of each strain for adsorption. After adsorption, it was dried at a constant temperature of 30°C to obtain the microbial agent powders of each strain. The obtained Pseudomonas fluorescens agent powder, Azotobacter salexigens agent powder, and Trichoderma harzianum agent powder were mixed according to a mass ratio of 3:6:1 to obtain the composite microbial agent.

[0065] Comparative Example 1

[0066] S1. Pseudomonas fluorescens and Azotobacter salexigens were respectively inoculated into MacConkey agar medium at 33°C and 150 rpm, and cultured for 48 h to obtain the seed solutions of each strain.

[0067] S2. The obtained seed solutions of each strain were respectively inoculated into LB liquid medium at 33°C and 150 rpm, and cultured and diffused for 48 h to obtain the fermentation broths of each strain.

[0068] S3. Take 10 mL of the fermentation broth of each strain, and add 10 g of the chitosan / urea intercalated modified montmorillonite carrier prepared in Preparation Example 2 to the fermentation broth of each strain for adsorption. After adsorption, dry at a constant temperature of 30 °C to obtain the microbial agent powder of each strain. Mix the obtained Pseudomonas fluorescens microbial agent powder and Azotobacter salinestris microbial agent powder according to a mass ratio of 3:6 to obtain the composite microbial agent.

[0069] Comparative Example 2

[0070] S1. Inoculate Azotobacter salinestris and Bacillus subtilis into MacConkey agar medium at 33 °C and 150 rpm respectively, and culture for 48 h to obtain the seed liquid of each strain.

[0071] S2. Inoculate the obtained seed liquid of each strain into LB liquid medium at 33 °C and 150 rpm respectively, and culture and spread for 48 h to obtain the fermentation broth of each strain.

[0072] S3. Take 10 mL of the fermentation broth of each strain, and add 10 g of the chitosan / urea intercalated modified montmorillonite carrier prepared in Preparation Example 2 to the fermentation broth of each strain for adsorption. After adsorption, dry at a constant temperature of 30 °C to obtain the microbial agent powder of each strain. Mix the obtained Azotobacter salinestris microbial agent powder and Trichoderma harzianum microbial agent powder according to a mass ratio of 6:1 to obtain the composite microbial agent.

[0073] Comparative Example 3

[0074] The difference between Comparative Example 3 and Example 5 is that the carrier used in Comparative Example 3 is montmorillonite.

[0075] Comparative Example 4

[0076] The difference between Comparative Example 4 and Example 5 is that the carrier used in Comparative Example 4 is urea intercalated modified montmorillonite; the preparation method of the urea intercalated modified montmorillonite includes the following steps:

[0077] S1. Add 1 g of sodium bicarbonate and 20 g of montmorillonite to 350 g of water and disperse evenly; then carry out an ion exchange reaction at 80 °C for 6 h to obtain sodium-based montmorillonite.

[0078] S2. Add 420 g of deionized water to 3.5 g of sodium-based montmorillonite, and ultrasonically disperse for 40 min to obtain a sodium-based montmorillonite suspension; adjust the pH of the sodium-based montmorillonite suspension to 6.5 with dilute hydrochloric acid.

[0079] S3. Dissolve 1 g of urea in 2.6 g of deionized water at room temperature, mix evenly to obtain a urea solution; under the water bath condition of 55 °C, drop the urea solution into the sodium-based montmorillonite suspension. After dropping, continue to stir for 22.5 h; after centrifugation, washing and drying, obtain the urea intercalated modified montmorillonite.

[0080] Performance detection test

[0081] I. Detect the improvement and restoration effects of the composite microbial inoculants obtained in Examples 1-5 and Comparative Examples 1-4 of the present application on the physical and chemical properties of soil:

[0082] Test soil: Collected from the Shisanlitang Base of the Duolun Restoration Ecology Experimental and Demonstration Research Station of the Institute of Botany, Chinese Academy of Sciences in Duolun County, Xilingol League, Inner Mongolia Autonomous Region. The soil texture is sandy loam;

[0083] Test soil: Leymus chinensis;

[0084] Experimental environment: Glass greenhouse, natural light, temperature in the greenhouse is 20-35 °C, humidity is 22-38%;

[0085] Experimental groups: 9 groups, respectively applying the composite microbial inoculants obtained in Examples 1-5 and Comparative Examples 1-4 of the present application. After application, plow the soil, and the application amount is 200 g / m 2 ;

[0086] Control group: 1 group, without applying the composite microbial inoculant;

[0087] Detection method:

[0088] (1) Soil pH, determined by the potentiometric method;

[0089] (2) Soil available nitrogen content, determined by the Kjeldahl method;

[0090] (3) Soil available potassium content, determined by the ammonium acetate extraction-flame photometer method;

[0091] (4) Soil available phosphorus content, determined by the sodium bicarbonate extraction-molybdenum antimony resistance spectrophotometry method;

[0092] (5) Soil bulk density, detected by the method of NY / T 1121.4-2006 "Soil Testing - Part 4: Determination of Soil Bulk Density";

[0093] The results are shown in Table 1.

[0094] The specific detection results are as follows:

[0095] Table 1 Detection results

[0096]

[0097] It can be seen from the detection results in Table 1 that after applying the compound microbial inoculant provided by the present invention, the soil bulk density is lower than before, indicating that the soil porosity has increased compared to before, and the air permeability, water permeability and water retention capacity of the soil have been improved; the soil pH approaches neutrality, indicating that the compound microbial inoculant provided by the present invention has a significant effect on improving the soil acidity and alkalinity; at the same time, the contents of available nitrogen, available phosphorus and available potassium have all increased to varying degrees, indicating that applying the microbial soil improvement and repair agent of the present invention can improve the air permeability of the soil, reduce the soil acidity, increase the contents of available nitrogen, available phosphorus and available potassium in the soil, indirectly improve the fertilizer utilization rate of the soil, and have a good promoting effect on the growth and development of plants.

[0098] This specific embodiment is only an interpretation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. Preparation method of composite microbial inoculum based on soil improvement, characterized in that: It includes the following steps: S1. Inoculate each microbial strain into an activation medium at 28 - 38°C and 100 - 200 rpm, and culture for 45 - 50 h to obtain the seed liquid of each strain; S2. Inoculate the obtained seed liquid of each strain into an amplification medium at 28 - 38°C and 100 - 200 rpm, and culture and spread for 45 - 50 h to obtain the fermentation broth of each strain; S3. Add a carrier to the fermentation broth of each strain for adsorption, and after adsorption, perform constant-temperature drying to obtain the microbial agent powder of each strain. After mixing the obtained microbial agent powders of each strain according to the mass ratio, a composite microbial agent is obtained; Each of the microbial strains includes a phosphate-solubilizing bacterium strain, a nitrogen-fixing bacterium strain, and an antagonistic bacterium strain; The carrier is chitosan / urea intercalated modified montmorillonite.

2. The preparation method of the composite microbial inoculum based on soil improvement according to claim 1, characterized in that: The phosphate-solubilizing bacterium strain is one or more of Bacillus megaterium, Bacillus mucilaginosus, Pseudomonas fluorescens, Serratia marcescens, and Erwinia; 3. The preparation method of the composite microbial inoculum based on soil improvement according to claim 1, characterized in that: The nitrogen-fixing bacterium strain is one or more of Rhizobium japonicum, Azospirillum, Cyanobacteria, Rhodospirillum, and Azoarcus; 4. The preparation method of the composite microbial inoculum based on soil improvement according to claim 1, characterized in that: The antagonistic bacterium strain is one or more of Bacillus subtilis, Trichoderma harzianum, Streptomyces, and Bacillus licheniformis; 5. The preparation method of the composite microbial inoculum based on soil improvement according to claim 1, characterized in that: The mass ratio of the microbial agent powders of each strain is phosphate-solubilizing bacterium agent powder : nitrogen-fixing bacterium agent powder : antagonistic bacterium agent powder = (2 - 4) : (5 - 7) :

1.

6. The preparation method of the composite microbial inoculum based on soil improvement according to claim 1, characterized in that: The microbial strains include Bacillus subtilis, Azoarcus, and Glomus claroideum; the mass ratio of Pseudomonas fluorescens, Azoarcus microbial agent powder, and Bacillus subtilis microbial agent powder is 3 : 6 :

1.

7. The preparation method of the composite microbial inoculum based on soil improvement according to claim 1, characterized in that: The preparation method of the chitosan / urea intercalated modified montmorillonite includes the following steps: S1. Add sodium bicarbonate and montmorillonite to water and disperse evenly. The mass ratio of sodium bicarbonate, montmorillonite, and water is 1 : 15 - 25 : 300 - 400; then carry out an ion exchange reaction at 75 - 85°C for 5 - 7 h to obtain sodium-based montmorillonite; S2. Add deionized water to the sodium-based montmorillonite. The mass ratio of sodium-based montmorillonite to deionized water is 1 : 100 - 150, and ultrasonically disperse for 30 - 50 min to obtain a sodium-based montmorillonite suspension; adjust the pH of the sodium-based montmorillonite suspension to 6 - 7; S3. Dissolve urea in deionized water according to a mass ratio of 1 : 2.3 - 3, mix evenly to obtain a urea solution; under the water bath condition of 50 - 60°C, drop the urea solution into the sodium-based montmorillonite suspension. After dropping, continue to stir for 20 - 25 h; after centrifugation, washing, and drying, urea intercalated modified montmorillonite is obtained; S4. Disperse chitosan at a solid-liquid ratio of 1 : 50 - 60 in a 5% acetic acid aqueous solution, and stir at 30 - 40°C for 16 - 20 h to obtain a chitosan solution; add the urea intercalated modified montmorillonite to the chitosan solution, stir at 30 - 40°C for 14 - 18 h, add a 2 mol / L sodium hydroxide aqueous solution equal in amount to the acetic acid aqueous solution, and wash and dry the product with deionized water to obtain chitosan / urea intercalated modified montmorillonite.

8. The preparation method of the composite microbial inoculum based on soil improvement according to claim 7, characterized in that: The mass ratio of urea to sodium-based montmorillonite is 1 : 3 - 4.

9. The preparation method of the composite microbial inoculum based on soil improvement according to claim 7, characterized in that: The mass ratio of the chitosan and urea intercalated modified montmorillonite is 1:1 - 1.

2.

10. Application of compound microbial inoculum based on soil improvement, characterized in that: Application of the composite microbial inoculum obtained by the preparation method according to any one of claims 1 - 9 in soil improvement.

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