Compound microbial agent for soil improvement and preparation method thereof

Abstract

The invention discloses a composite microbial agent for soil improvement and a preparation method thereof, and relates to the technical field of microbial agent preparation, the composite microbial agent comprises the following raw materials: a composite carrier, a functional material, modified xanthan gum, a strain fermentation broth and an adhesive; according to the invention, the composite carrier is added, silica sol-biomass ash modified bentonite provides a stable shelter for viable bacteria by virtue of a nano coating structure, and the composite carrier has the functions of water retention, stress resistance and heavy metal passivation; the charcoal provides a carbon source with a high specific surface area and improves the soil porosity; humic acid can adjust the pH value of soil and promote rhizosphere colonization of strains; the nano kaolin enhances the adsorption performance of the carrier through the original nano particle size, and Al < 3 + > is separated out to participate in the cross-linking reaction of the modified xanthan gum; the soil conditioner is high in viable bacterium loading rate, the granular structure and nutrient adsorption capacity of the soil are remarkably improved through the synergistic effect of all the components, and the soil conditioner is good in compatibility with strain fermentation liquor and functional materials and can adapt to various soil types such as acidity, salt and alkali, heavy metal pollution and the like.

Description

Technical Field

[0001] This invention relates to the field of microbial agent preparation technology, and in particular to a compound microbial agent for soil improvement and its preparation method. Background Technology

[0002] Microbial inoculants are active preparations made through artificial selection and propagation of microorganisms with specific functions. They typically contain effective microbial communities, carriers, and auxiliary components, and mainly act on soil, plants, or the environment. They exert their effects through the life activities of microorganisms, such as nitrogen fixation, phosphorus and potassium solubilization, pollutant degradation, pathogen inhibition, crop growth promotion, or ecological environment improvement.

[0003] Traditional compound microbial agents used for soil improvement suffer from poor stability of live bacteria during storage, short shelf life at room temperature, and easy inactivation of live bacteria during transportation. Furthermore, the activity of strains is easily lost in extreme soil environments such as acidic, saline-alkali, and heavy metal-contaminated soils. Traditional agents also exhibit slow effects, and the mismatch between nutrient release rates and strain activation rhythms leads to poor soil improvement results. Therefore, this invention provides a compound microbial agent for soil improvement and its preparation method. Summary of the Invention

[0004] The main objective of this invention is to provide a compound microbial agent for soil improvement with high survival rate of stored live bacteria and high number of live bacteria in the soil, which is applied in a compound microbial agent for soil improvement and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a compound microbial agent for soil improvement, comprising the following components: 65-75 parts of a composite carrier, 13-17 parts of functional materials, 4-6 parts of modified xanthan gum, 32.5-37.5 parts of bacterial fermentation broth, and 8-12 parts of binder.

[0006] The optimal mass-to-volume ratio of the composite carrier and the bacterial fermentation broth is 2 kg: 1 L.

[0007] live bacteria in the fermentation broth of the strain spore rate ≥85%, Trichoderma spores No antagonism.

[0008] Furthermore, the preparation of the composite carrier includes the following steps: mixing modified bentonite, biochar, humic acid and nano-kaolin evenly, placing it in an autoclave for sterilization, setting the temperature to 121℃ and the pressure to 0.1MPa, sterilizing for 2 hours, and then allowing the temperature to cool naturally to 30℃ to obtain the composite carrier; The mass ratio of the modified bentonite, biochar, humic acid and nano-kaolin is 1:1:1:0.5.

[0009] The biochar has a particle size of 100 mesh and, after anaerobic pyrolysis at 600℃, has a specific surface area ≥300m² / g. The porous structure formed by anaerobic pyrolysis at 600℃ has an ultra-large specific surface area, which can not only adsorb and fix functional strains and soil nutrients, but also improve soil aeration and fertilizer retention. It can also passivate heavy metals by synergistically modifying bentonite through surface functional groups. The advantages of this material are that the raw materials are widely available, the preparation cost is low, the pH is neutral to alkaline, which can neutralize acidic soils, and it has good compatibility with functional strains, without inhibiting the activity of strains. It can also promote the formation of soil aggregate structure and improve the long-term fertility of soil.

[0010] The humic acid has a particle size of 100 mesh, a humic acid content of ≥70%, and a water solubility of ≥30%. This material has good water solubility and disperses evenly after being mixed with the composite carrier, which can enhance the soil improvement efficiency of the microbial agent. It is also a natural organic matter, which can increase the humus content of the soil. Long-term application will not cause soil compaction. When used in synergy with modified bentonite and biochar, it can further enhance the remediation effect of soil physicochemical properties.

[0011] Nano-kaolin has a particle size of 200 mesh and a primary particle size ≤50nm; Al 3+ With a dissolution rate of ≥0.5%, this material can exert a nano-effect without additional modification. It is inexpensive and widely available, and has no antagonistic effect with the components of the carrier. It can optimize the physical properties of the bacterial agent and help improve the protective performance of modified xanthan gum on live bacteria, further extending the shelf life of the bacterial agent.

[0012] Furthermore, the preparation of the modified bentonite includes the following steps: S1. Sterilize bentonite under high pressure at a set temperature of 121℃ and a pressure of 0.1MPa for 2 hours to obtain sterile bentonite. Dry biomass ash at a set temperature of 105℃ for 2 hours to obtain dried biomass ash. S2. Add silica sol to the reactor and stir at 30 rpm. Add dried biomass ash and stir at 30 rpm for 8 minutes to obtain a suspension. S3. Add sterile bentonite to the suspension and stir at 30 rpm for 8 minutes. Let it stand for 1.5 hours, then dry it in a cool, ventilated place at 35°C with a wind speed of >2.0 m / s for 8-10 hours to obtain a mixture. Crush the mixture to 200 mesh to obtain modified bentonite. The silica sol is a sterile aqueous solution with a mass concentration of 5%. The mass ratio of the silica sol to the dried biomass ash is 18:1; The mass ratio of the sterile bentonite to the suspension is 1:1.8.

[0013] Silica sol can form a continuous and dense inorganic silicon nano-coating on the surface and between layers of bentonite. On the one hand, this coating can reconstruct the interlayer pore structure of bentonite, adjusting the pore size to a scale suitable for live bacteria loading, and significantly improving the live bacteria immobilization rate. On the other hand, the inorganic silanol structure of silica sol can enhance the mechanical strength and stress resistance of bentonite, while reducing the loss of live bacteria during storage and transportation through adsorption, and can also synergistically passivate heavy metal ions in the soil.

[0014] The bentonite has a particle size of 200 mesh.

[0015] Biomass ash, derived from straw combustion, has a particle size of 200 mesh and is rich in minerals such as silicon, calcium, and magnesium, which fill the pores of the silica sol coating. This process serves several purposes: first, it increases the porosity of the coating, providing more sheltered sites for live bacteria and improving the colonization efficiency of the strains in the soil; second, the released mineral ions enhance the pH buffering capacity of bentonite, making it suitable for various soil types, including acidic and saline-alkali soils; and third, the natural organic matter in the biomass ash acts as a slow-release carbon source for the strains, promoting their metabolic proliferation. Furthermore, its origin as an agricultural byproduct makes it environmentally friendly and inexpensive.

[0016] The dried biomass ash is sterile.

[0017] The moisture content of the mixture after ventilation and drying is ≤15%.

[0018] Further, the preparation of the modified xanthan gum includes the following steps: xanthan gum and seaweed oligosaccharide are added to deionized water and stirred at 60 rpm for 15 minutes; nano-kaolin suspension is added and stirred at 60 rpm for 10 minutes; the mixture is allowed to stand for 5 minutes; seaweed and vitamin C are added and stirred at 40 rpm for 8 minutes; the mixture is then filtered using a 0.22 μm filter membrane to remove particles, thereby obtaining the modified xanthan gum. The nano-kaolin suspension is a sterile aqueous solution with a mass concentration of 2%. The mass ratio of xanthan gum, seaweed oligosaccharide, deionized water, nano-kaolin suspension, trehalose, and vitamin C is 1.5:0.3:34.2:4.5:3:0.5.

[0019] The nano-kaolin suspension contains kaolin particles with a native particle size ≤50nm, exhibiting good dispersibility and capable of precipitating sufficient Al. 3+ Al 3+It can form ionic bonds with the carboxyl groups on the xanthan gum molecular chain and the hydroxyl groups on the seaweed oligosaccharide molecular chain, causing xanthan gum to transform from a linear molecule into a stable three-dimensional network structure. At the same time, nano-kaolin particles are embedded in the network as physical cross-linking points, enhancing the mechanical strength and shear resistance of xanthan gum and improving the targeted encapsulation effect on live bacteria. In addition, the adsorption properties of kaolin can also help adsorb nutrients in the fermentation broth of the strain, achieving synergistic encapsulation of live bacteria and nutrients, and further optimizing the sustained-release performance.

[0020] The viscosity of modified xanthan gum It is a three-dimensional network structure.

[0021] Xanthan gum is food grade.

[0022] Seaweed oligosaccharides have a molecular weight ≤1000 Da, are agricultural grade, and have short molecular chains and abundant active groups. They can first form a pre-bonded system with xanthan gum through hydrogen bonds, laying the foundation for subsequent ionic cross-linking. At the same time, as a natural plant-derived polysaccharide, seaweed oligosaccharides are non-toxic to functional strains and can also serve as a nutrient substrate for strains, improving their survival rate during drying and storage. In addition, the hydrophilicity of seaweed oligosaccharides can enhance the water solubility of modified xanthan gum, ensuring that the bacterial agent can quickly disperse in the soil after application, releasing live bacteria and nutrients, and shortening the time to effectiveness.

[0023] The nano-kaolin suspension is sterile.

[0024] Furthermore, the functional material is composed of coated urea and potassium dihydrogen phosphate mixed in a mass ratio of 2:1.

[0025] The coated urea has a particle size of 100 mesh, the coating material is modified starch, the total nitrogen content of the coated urea is ≥46.0% (dry basis), and the biuret content is ≤0.9%.

[0026] Potassium dihydrogen phosphate has a particle size of 100 mesh, a purity of ≥99%, P2O5 ≥52%, K2O ≥34%, moisture content ≤0.5%, and pH 4.4–4.7. It is a key material for supplementing phosphorus and potassium nutrients. Its high-purity phosphorus and potassium elements can be directly supplied to crop roots for absorption, promoting crop root development and photosynthesis. At the same time, it can provide essential nutrients for the metabolic proliferation of functional strains, enhancing the nitrogen fixation, phosphorus solubilization, and potassium solubilization activities of the strains. It has high purity and good water solubility, and has no antagonistic effect with other components of the inoculant. After application, it will not cause soil salinization. Moreover, it can synergistically regulate soil nutrient balance with coated urea, further shortening the effective period of the inoculant and improving the overall effect of soil improvement.

[0027] Furthermore, the fermentation broth of the strain is a mixture of Azotobacter chrysophyll, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum.

[0028] The number of viable bacteria in nitrogen-fixing bacteria liquid viable count of Bacillus megaterium in liquid The viable count of Bacillus mucilaginosus in the liquid was viable cell count of Bacillus subtilis in liquid viable cell count of Trichoderma harzianum solution .

[0029] Furthermore, the fermentation broth of the strain comprises Azotobacter chrysophyll, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum in a volume ratio of 2:4:2:2:1.

[0030] The fermentation broth of the strain contains Azotobacter chrysophagus, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum. When combined, they do not have antagonistic effects and can synergistically achieve functions such as atmospheric nitrogen fixation, activation of insoluble phosphorus and potassium in the soil, and antagonism of soil-borne pathogens. They can also secrete plant growth regulators to promote crop growth.

[0031] Furthermore, the preparation of the adhesive includes the following steps: adding starch and sodium alginate into deionized water and stirring in a water bath, setting the water bath temperature to 35°C and the rotation speed to 80 rpm, stirring for 10 minutes to obtain the adhesive.

[0032] Furthermore, the mass ratio of starch, sodium alginate, and deionized water is 7:3:112.5.

[0033] Secondly, a method for preparing a compound microbial agent for soil improvement, comprising the following steps: Step 1. Mix the composite carrier and functional materials at 100 rpm for 15 minutes. Add modified xanthan gum and stir. Reduce the speed to 80 rpm and stir for 20 minutes. Add the bacterial fermentation broth and stir. Reduce the speed to 60 rpm and stir for 15 minutes. Add the binder and stir at 60 rpm for 25 minutes to obtain material A. Step 2. Place material A into an extrusion granulator for granulation. Set the rotation speed to 300 rpm, the filter screen aperture to 2.5 mm, and the feeding speed to 5 kg / min to obtain material granules. Place the material granules into a forced-air drying oven for drying. Set the temperature to 60℃, the air speed to 1.5 m / s, and dry for 2.5 hours to obtain a compound microbial agent for soil improvement.

[0034] The present invention has the following beneficial effects: 1. In this invention, a composite carrier is added, wherein the silica sol-biomass ash modified bentonite provides a stable shelter for live bacteria with its nano-coating structure, and also has the functions of water retention, stress resistance, and heavy metal passivation; biochar provides a carbon source with its high specific surface area and improves soil porosity; humic acid can regulate soil pH and promote rhizosphere colonization of the strains; and nano-kaolin enhances the adsorption performance of the carrier through its native nanoparticle size, while simultaneously releasing Al. 3+It participates in the cross-linking reaction of modified xanthan gum; it has a high live bacteria loading rate, and the synergistic effect of each component significantly improves the soil aggregate structure and nutrient adsorption capacity. It also has good compatibility with bacterial fermentation broth and functional materials, and can be adapted to various soil types such as acidic, saline-alkali, and heavy metal polluted soils, laying a solid foundation for the bacterial agent to exert its improvement effect.

[0035] 2. In this invention, modified xanthan gum is added, which is a key material to ensure the stability of live bacteria and the formability of the formulation. After in-situ grafting modification with nano-kaolin and seaweed oligosaccharides, it forms a three-dimensional network structure, which can target and encapsulate live bacteria, protect the cell membrane of the strain from drying and environmental stress, and enhance the adsorption efficiency of the fermentation broth and the composite carrier, thus preventing the formulation from stratifying and clumping. Moreover, this adjuvant is prepared entirely from green raw materials, with no chemical residues, does not inhibit the activity of functional strains, can extend the shelf life of the bacterial agent at room temperature, improve the stress resistance of the bacterial agent in high-salt environments, and can also help enhance the cohesiveness of the sustained-release particles and optimize the physical properties of the formulation.

[0036] 3. In this invention, a binder is added, which is a compound of starch and sodium alginate. When prepared into an aqueous solution, it can effectively bind the carrier, nutrients and live bacteria to form structurally stable particles. The binder is completely biodegradable, leaves no soil residue, and will not damage the soil micro-ecological environment. At the same time, its binding performance is moderate. The particles formed after drying are not easily broken during transportation and application. Moreover, it can regulate the release rate of live bacteria and nutrients through the pore structure, further extending the field action period of the inoculant. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that all raw materials used in the following experiments are commercially available.

[0039] Example 1: A compound microbial agent for soil improvement, comprising the following raw materials: 65 parts of composite carrier, 13 parts of functional material, 4 parts of modified xanthan gum, 32.5 parts of bacterial fermentation broth, and 8 parts of binder.

[0040] The preparation of the composite carrier includes the following steps: the modified bentonite, biochar, humic acid and nano-kaolin are mixed evenly, put into an autoclave for sterilization, set the temperature to 121℃, the pressure to 0.1MPa, sterilize for 2 hours, and then let the temperature cool naturally to 30℃ to obtain the composite carrier. The mass ratio of modified bentonite, biochar, humic acid and nano-kaolin is 1:1:1:0.5.

[0041] The preparation of modified bentonite includes the following steps: S1. Sterilize bentonite under high pressure at a set temperature of 121℃ and a pressure of 0.1MPa for 2 hours to obtain sterile bentonite. Dry biomass ash at a set temperature of 105℃ for 2 hours to obtain dried biomass ash. S2. Add silica sol to the reactor and stir at 30 rpm. Add dried biomass ash and stir at 30 rpm for 8 minutes to obtain a suspension. S3. Add sterile bentonite to the suspension and stir at 30 rpm for 8 minutes. Let it stand for 1.5 hours, then dry it in a cool, ventilated place at 35°C with a wind speed of >2.0 m / s for 8 hours to obtain a mixture. Crush the mixture to 200 mesh to obtain modified bentonite. The silica sol was a sterile aqueous solution with a mass concentration of 5%. The mass ratio of silica sol to dried biomass ash is 18:1; The mass ratio of sterile bentonite to suspension is 1:1.8.

[0042] The moisture content of modified bentonite is ≤15%.

[0043] The preparation of modified xanthan gum includes the following steps: xanthan gum and seaweed oligosaccharide are added to deionized water and stirred at 60 rpm for 15 minutes. Nano-kaolin suspension is added and stirred at 60 rpm for 10 minutes. After standing for 5 minutes, seaweed and vitamin C are added and stirred at 40 rpm for 8 minutes. The mixture is then filtered using a 0.22 μm filter membrane to remove particles and obtain modified xanthan gum. The nano-kaolin suspension is a sterile aqueous solution with a mass concentration of 2%. The mass ratio of xanthan gum, seaweed oligosaccharide, deionized water, nano-kaolin suspension, trehalose, and vitamin C was 1.5:0.3:34.2:4.5:3:0.5.

[0044] The functional material is composed of coated urea and potassium dihydrogen phosphate mixed in a mass ratio of 2:1.

[0045] The fermentation broth of the strain was composed of a mixture of Azotobacter chrysophyll, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum.

[0046] The fermentation broth of the strain consisted of Azotobacter chrysophyte, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum in a volume ratio of 2:4:2:2:1.

[0047] The preparation of the binder includes the following steps: starch and sodium alginate are added to deionized water and stirred in a water bath at a temperature of 35°C and a speed of 80 rpm for 10 minutes to obtain the binder.

[0048] The mass ratio of starch, sodium alginate, and deionized water is 7:3:112.5.

[0049] Secondly, a method for preparing a compound microbial agent for soil improvement, comprising the following steps: Step 1. Mix the composite carrier and functional materials at 100 rpm for 15 minutes. Add modified xanthan gum and stir. Reduce the speed to 80 rpm and stir for 20 minutes. Add the bacterial fermentation broth and stir. Reduce the speed to 60 rpm and stir for 15 minutes. Add the binder and stir at 60 rpm for 25 minutes to obtain material A. Step 2. Place material A into an extrusion granulator for granulation. Set the rotation speed to 300 rpm, the filter screen aperture to 2.5 mm, and the feeding speed to 5 kg / min to obtain material granules. Place the material granules into a forced-air drying oven for drying. Set the temperature to 60℃, the air speed to 1.5 m / s, and dry for 2.5 hours to obtain a compound microbial agent for soil improvement.

[0050] Example 2: A compound microbial agent for soil improvement, comprising the following raw materials: 70 parts of composite carrier, 15 parts of functional material, 5 parts of modified xanthan gum, 35 parts of bacterial fermentation broth, and 10 parts of binder.

[0051] The preparation of the composite carrier includes the following steps: the modified bentonite, biochar, humic acid and nano-kaolin are mixed evenly, put into an autoclave for sterilization, set the temperature to 121℃, the pressure to 0.1MPa, sterilize for 2 hours, and then let the temperature cool naturally to 30℃ to obtain the composite carrier. The mass ratio of modified bentonite, biochar, humic acid and nano-kaolin is 1:1:1:0.5.

[0052] The preparation of modified bentonite includes the following steps: S1. Sterilize bentonite under high pressure at a set temperature of 121℃ and a pressure of 0.1MPa for 2 hours to obtain sterile bentonite. Dry biomass ash at a set temperature of 105℃ for 2 hours to obtain dried biomass ash. S2. Add silica sol to the reactor and stir at 30 rpm. Add dried biomass ash and stir at 30 rpm for 8 minutes to obtain a suspension. S3. Add sterile bentonite to the suspension and stir at 30 rpm for 8 minutes. Let it stand for 1.5 hours, then dry it in a cool, ventilated place at 35°C with a wind speed of >2.0 m / s for 9 hours to obtain a mixture. Crush the mixture to 200 mesh to obtain modified bentonite. The silica sol was a sterile aqueous solution with a mass concentration of 5%. The mass ratio of silica sol to dried biomass ash is 18:1; The mass ratio of sterile bentonite to suspension is 1:1.8.

[0053] The preparation of modified xanthan gum includes the following steps: xanthan gum and seaweed oligosaccharide are added to deionized water and stirred at 60 rpm for 15 minutes. Nano-kaolin suspension is added and stirred at 60 rpm for 10 minutes. After standing for 5 minutes, seaweed and vitamin C are added and stirred at 40 rpm for 8 minutes. The mixture is then filtered using a 0.22 μm filter membrane to remove particles and obtain modified xanthan gum. The nano-kaolin suspension is a sterile aqueous solution with a mass concentration of 2%. The mass ratio of xanthan gum, seaweed oligosaccharide, deionized water, nano-kaolin suspension, trehalose, and vitamin C was 1.5:0.3:34.2:4.5:3:0.5.

[0054] The functional material is composed of coated urea and potassium dihydrogen phosphate mixed in a mass ratio of 2:1.

[0055] The fermentation broth of the strain was composed of a mixture of Azotobacter chrysophyll, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum.

[0056] The fermentation broth of the strain consisted of Azotobacter chrysophyte, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum in a volume ratio of 2:4:2:2:1.

[0057] The preparation of the binder includes the following steps: starch and sodium alginate are added to deionized water and stirred in a water bath at a temperature of 35°C and a speed of 80 rpm for 10 minutes to obtain the binder.

[0058] The mass ratio of starch, sodium alginate, and deionized water is 7:3:112.5.

[0059] Secondly, a method for preparing a compound microbial agent for soil improvement, comprising the following steps: Step 1. Mix the composite carrier and functional materials at 100 rpm for 15 minutes. Add modified xanthan gum and stir. Reduce the speed to 80 rpm and stir for 20 minutes. Add the bacterial fermentation broth and stir. Reduce the speed to 60 rpm and stir for 15 minutes. Add the binder and stir at 60 rpm for 25 minutes to obtain material A. Step 2. Place material A into an extrusion granulator for granulation. Set the rotation speed to 300 rpm, the filter screen aperture to 2.5 mm, and the feeding speed to 5 kg / min to obtain material granules. Place the material granules into a forced-air drying oven for drying. Set the temperature to 60℃, the air speed to 1.5 m / s, and dry for 2.5 hours to obtain a compound microbial agent for soil improvement.

[0060] Example 3: A compound microbial agent for soil improvement, comprising the following raw materials: 75 parts of composite carrier, 17 parts of functional materials, 6 parts of modified xanthan gum, 37.5 parts of bacterial fermentation broth, and 12 parts of binder.

[0061] The preparation of the composite carrier includes the following steps: the modified bentonite, biochar, humic acid and nano-kaolin are mixed evenly, put into an autoclave for sterilization, set the temperature to 121℃, the pressure to 0.1MPa, sterilize for 2 hours, and then let the temperature cool naturally to 30℃ to obtain the composite carrier. The mass ratio of modified bentonite, biochar, humic acid and nano-kaolin is 1:1:1:0.5.

[0062] The preparation of modified bentonite includes the following steps: S1. Sterilize bentonite under high pressure at a set temperature of 121℃ and a pressure of 0.1MPa for 2 hours to obtain sterile bentonite. Dry biomass ash at a set temperature of 105℃ for 2 hours to obtain dried biomass ash. S2. Add silica sol to the reactor and stir at 30 rpm. Add dried biomass ash and stir at 30 rpm for 8 minutes to obtain a suspension. S3. Add sterile bentonite to the suspension and stir at 30 rpm for 8 minutes. Let it stand for 1.5 hours, then dry it in a cool, ventilated place at 35°C with a wind speed of >2.0 m / s for 10 hours to obtain a mixture. Crush the mixture to 200 mesh to obtain modified bentonite. The silica sol was a sterile aqueous solution with a mass concentration of 5%. The mass ratio of silica sol to dried biomass ash is 18:1; The mass ratio of sterile bentonite to suspension is 1:1.8.

[0063] The preparation of modified xanthan gum includes the following steps: xanthan gum and seaweed oligosaccharide are added to deionized water and stirred at 60 rpm for 15 minutes. Nano-kaolin suspension is added and stirred at 60 rpm for 10 minutes. After standing for 5 minutes, seaweed and vitamin C are added and stirred at 40 rpm for 8 minutes. The mixture is then filtered using a 0.22 μm filter membrane to remove particles and obtain modified xanthan gum. The nano-kaolin suspension is a sterile aqueous solution with a mass concentration of 2%. The mass ratio of xanthan gum, seaweed oligosaccharide, deionized water, nano-kaolin suspension, trehalose, and vitamin C was 1.5:0.3:34.2:4.5:3:0.5.

[0064] The functional material is composed of coated urea and potassium dihydrogen phosphate mixed in a mass ratio of 2:1.

[0065] The fermentation broth of the strain was composed of a mixture of Azotobacter chrysophyll, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum.

[0066] The fermentation broth of the strain consisted of Azotobacter chrysophyte, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum in a volume ratio of 2:4:2:2:1.

[0067] The preparation of the binder includes the following steps: starch and sodium alginate are added to deionized water and stirred in a water bath at a temperature of 35°C and a speed of 80 rpm for 10 minutes to obtain the binder.

[0068] The mass ratio of starch, sodium alginate, and deionized water is 7:3:112.5.

[0069] Secondly, a method for preparing a compound microbial agent for soil improvement, comprising the following steps: Step 1. Mix the composite carrier and functional materials at 100 rpm for 15 minutes. Add modified xanthan gum and stir. Reduce the speed to 80 rpm and stir for 20 minutes. Add the bacterial fermentation broth and stir. Reduce the speed to 60 rpm and stir for 15 minutes. Add the binder and stir at 60 rpm for 25 minutes to obtain material A. Step 2. Place material A into an extrusion granulator for granulation. Set the rotation speed to 300 rpm, the filter screen aperture to 2.5 mm, and the feeding speed to 5 kg / min to obtain material granules. Place the material granules into a forced-air drying oven for drying. Set the temperature to 60℃, the air speed to 1.5 m / s, and dry for 2.5 hours to obtain a compound microbial agent for soil improvement.

[0070] Comparative Example 1: The difference between this comparative example and Example 1 is that: Modified xanthan gum was used in this comparative example.

[0071] Comparative Example 2: The difference between this comparative example and Example 1 is that: Modified bentonite was not used in the composite carrier in this comparative example.

[0072] Comparative Example 3 differs from Example 1 in that: In this comparative example, the coating material of the functional material-coated urea is not modified starch.

[0073] Performance testing: The compound microbial agents for soil improvement prepared in Examples 1, 2, 3, Comparative Examples 1, 2, and 3 were tested.

[0074] Performance testing: The relevant performance of the composite microbial inoculant and its preparation method for soil improvement provided in Examples 1-3 and Comparative Examples 1-3 were tested respectively, and the test data are recorded in Table 1 below:

[0075] Based on the above data, the following conclusions can be drawn: Among them, the composite microbial agents for soil improvement prepared according to the test methods in GB20287-2006, namely Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3, were stored at 25°C for 15 months and the viable bacteria survival rate was tested. The number of viable bacteria in the soil prepared by the compound microbial agent for soil improvement in Examples 1, 2, 3, Comparative Examples 1, 2, and 3, using the test methods in GB20287-2006, was tested within 120 days. The cumulative nitrogen release rate of the compound microbial agents for soil improvement prepared in Examples 1, 2, 3, Comparative Examples 1, 2, and 3, prepared according to the test methods in GB / T23348-2009, was tested over 120 days.

[0076] Through the above demonstrations, the present invention is significantly superior to the control group in terms of the survival rate of live bacteria stored at 25℃ for 15 months, the number of live bacteria in the soil within 120 days, and the cumulative nitrogen release rate within 120 days, thus verifying the advanced nature and rationality of the preparation process.

[0077] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0078] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A compound microbial inoculant for soil improvement, characterized in that, The compound microbial agent for soil improvement comprises the following raw materials: 65-75 parts of composite carrier, 13-17 parts of functional materials, 4-6 parts of modified xanthan gum, 32.5-37.5 parts of bacterial fermentation broth, and 8-12 parts of binder.

2. The compound microbial agent for soil improvement according to claim 1, characterized in that, The preparation of the composite carrier includes the following steps: mixing modified bentonite, biochar, humic acid and nano-kaolin evenly, and sterilizing in an autoclave to obtain the composite carrier; The mass ratio of the modified bentonite, biochar, humic acid and nano-kaolin is 1:1:1:0.

5.

3. The compound microbial agent for soil improvement according to claim 2, characterized in that, The preparation of the modified bentonite includes the following steps: S1. Sterilize bentonite by high pressure to obtain sterile bentonite, and dry biomass ash to obtain dried biomass ash; S2. Add silica sol to the reactor and stir, then add dried biomass ash and stir to obtain a suspension; S3. Add sterile bentonite to the suspension and stir, dry at low temperature and ventilation to obtain a mixture, pulverize the mixture to obtain modified bentonite; The silica sol is a sterile aqueous solution with a mass concentration of 5%. The mass ratio of the silica sol to the dried biomass ash is 18:1; The mass ratio of the sterile bentonite to the suspension is 1:1.

8.

4. The compound microbial agent for soil improvement according to claim 1, characterized in that, The preparation of the modified xanthan gum includes the following steps: Xanthan gum and seaweed oligosaccharide were added to deionized water and stirred. Nano-kaolin suspension was added and stirred. The mixture was allowed to stand. Trehalose and vitamin C were added and stirred. The mixture was filtered through a filter membrane to remove particles and obtain modified xanthan gum. The nano-kaolin suspension is a sterile aqueous solution with a mass concentration of 2%. The mass ratio of xanthan gum, seaweed oligosaccharide, deionized water, nano-kaolin suspension, trehalose, and vitamin C is 1.5:0.3:34.2:4.5:3:0.

5.

5. The compound microbial agent for soil improvement according to claim 1, characterized in that, The functional material is composed of coated urea and potassium dihydrogen phosphate mixed in a mass ratio of 2:

1.

6. The compound microbial agent for soil improvement according to claim 1, characterized in that, The fermentation broth of the strain is a mixture of Azotobacter chrysophyll, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum.

7. The compound microbial agent for soil improvement according to claim 6, characterized in that, The fermentation broth of the strain consists of Azotobacter chrysophyll, Bacillus megaterium, Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum in a volume ratio of 2:4:2:2:

1.

8. The compound microbial agent for soil improvement according to claim 1, characterized in that, The preparation of the binder includes the following steps: adding starch and sodium alginate to deionized water and stirring in a water bath to obtain the binder.

9. The compound microbial agent for soil improvement according to claim 8, characterized in that, The mass ratio of starch, sodium alginate, and deionized water is 7:3:112.

5.

10. A method for preparing a compound microbial inoculant for soil improvement according to any one of claims 1-9, characterized in that, The process includes the following steps: Step 1. Mix the composite carrier and functional materials, add modified xanthan gum and stir, add the bacterial fermentation broth and stir, add the binder and stir to obtain material A; Step 2. Place material A into an extrusion granulator to granulate it, and then place the material particles into a forced-air drying oven to dry them, thereby obtaining a compound microbial agent for soil improvement.

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