A compound microbial fertilizer based on microbial metabolic synergy and a preparation method thereof

Abstract

The present application relates to the technical field of microbial fertilizer, in particular to a compound microbial fertilizer based on microbial flora metabolic synergy and a preparation method thereof, which comprises the following raw materials: compound microbial flora, modified biochar, seaweed extract, graphite powder, metabolic synergistic agent, ammonium sulfate and potassium dihydrogen phosphate; the modified biochar is prepared by impregnating primary biochar with potassium carbonate, then microwave-carbon dioxide synergistic activation and coating with polyglutamic acid. After being applied to soil, rhamnolipid as a biological surfactant induces the secretion of extracellular polymers by the flora, and cooperates with graphite powder to construct a micro-area electrically active biological membrane; relying on the local micro-conductive bridge formed by the dispersion of graphite powder in the pores of biochar and the extracellular polymer network, the electron transfer between microbial species is accelerated; 5-amino-ketoglutaric acid cooperates with chelated iron as the core precursor of hemoglobin and cytochrome, improving the nitrogen fixation efficiency. This mechanism significantly improves the survival rate of live bacteria and nutrient supply in a salinized environment.

Description

Technical Field

[0001] This invention relates to the field of microbial fertilizer technology, and more specifically, to a compound microbial fertilizer based on synergistic microbial community metabolism and its preparation method. Background Technology

[0002] In recent years, with the continuous development of modern agriculture, the planting scale of precious Chinese medicinal herbs (such as ginseng, Panax notoginseng, and Dendrobium officinale), high-quality specialty fruits and vegetables, and high-end facility agriculture (greenhouses) has been expanding. These high-value-added cash crops have extremely high requirements for soil micro-ecological environment, precision of nutrient supply, and stress resistance. However, in actual production, due to long-term intensive planting, excessive application of chemical fertilizers, and lack of natural rainwater leaching in greenhouses, planting areas generally face serious problems of secondary soil salinization and soil compaction and acidification. Under the stress of high salt and high osmotic pressure, the root development of high-value-added crops is hindered, disease resistance decreases, resulting in insufficient accumulation of effective components in precious Chinese medicinal herbs and degradation of the quality of high-end fruits and vegetables.

[0003] Applying microbial fertilizers is an ideal way to remediate secondary salinized soils and improve crop yield and quality. However, existing traditional microbial fertilizers face insurmountable technical bottlenecks when applied to the aforementioned high-salt stress environments: First, traditional microbial fertilizers mostly use natural humic substances such as peat moss and humic acid as carriers, which have low specific surface area, coarse pore structure, and unstable batch-to-batch physicochemical properties. In secondary salinized soils, the large accumulation of competing ions such as sodium ions easily occupies the adsorption sites on the carrier surface, leading to a sharp decline in the carrier's ability to slowly release and retain available nitrogen and phosphorus, making it difficult to provide a stable habitat microenvironment and energy supply for microorganisms. In addition, under saline-alkali osmotic stress, conventional microorganisms have difficulty proliferating after entering the soil, and the survival rate of live bacteria is extremely low. More importantly, even if some salt-tolerant strains can survive, the lack of effective intercellular communication mechanisms prevents the establishment of a synergistic metabolic network among the microbial community, resulting in extremely slow effects.

[0004] For the cultivation of high-value-added cash crops, traditional microbial fertilizers can no longer meet the needs of modern high-end agriculture. Summary of the Invention

[0005] The purpose of this invention is to provide a compound microbial fertilizer based on synergistic microbial metabolism and its preparation method, in order to solve the problems mentioned in the background art. Traditional carriers such as peat moss and humic acid can provide basic support, but their specific surface area is low, their pore structure is coarse, their batch physicochemical properties are unstable, and their ability to release and retain readily available nutrients is limited in saline-alkali environments. As a result, microorganisms have difficulty proliferating, have low survival rates of live bacteria, and have difficulty forming stable metabolic synergistic networks under conditions of lack of stable habitat microenvironment and sufficient energy supply. This invention is particularly suitable for saline-alkali land, secondary salinized soil, and medium- and low-yield fields that have become compacted and acidified due to long-term application of chemical fertilizers.

[0006] This invention provides a compound microbial fertilizer based on synergistic microbial metabolism, comprising the following raw materials: compound microbial flora, modified biochar, seaweed extract, graphite powder, metabolic synergist, ammonium sulfate, and potassium dihydrogen phosphate; The modified biochar is prepared by microwave-carbon dioxide gas synergistic activation of primary biochar, followed by coating modification with polyglutamic acid.

[0007] In this invention, the metabolic synergist refers to a composition composed of 5-aminolevulinic acid, tetrahydropyrimidine, rhamnolipid, sodium zinc chelate ethylenediaminetetraacetic acid, and iron chelate citrate.

[0008] Preferably, the composite microbial community is a mixed fermentation broth obtained by co-fermentation of various strains, and its total effective viable count is not less than 1×10⁻⁶. 9 CFU / mL; by weight, the composite microbial community consists of 10-20 parts by weight, modified biochar 30-50 parts by weight, seaweed extract 3-5 parts by weight, graphite powder 2-5 parts by weight, metabolic synergist 1.1-4.0 parts by weight, ammonium sulfate 10-15 parts by weight, and potassium dihydrogen phosphate 8-12 parts by weight.

[0009] Preferably, the composite microbial community is prepared by co-fermentation of the following strains, and during co-fermentation, each strain is added in the following ratio of effective viable bacteria at the time of inoculation: Paenibacillus mucilaginosus: Bacillus velezensis: Halobacillus sp.: Bacillus amyloliquefaciens = (4-6): (2-6): (2-3): (2-5).

[0010] Preferably, the metabolic synergist comprises: 0.1-0.2 parts by weight of 5-aminolevulinic acid, 0.2-0.4 parts by weight of tetrahydropyrimidine, 0.1-0.4 parts by weight of rhamnolipid, 0.2-1.0 parts by weight of sodium zinc chelate ethylenediaminetetraacetic acid, and 0.5-2.0 parts by weight of iron chelate citrate.

[0011] 5-Aminolevulinic acid (5-ALA) is a common precursor in the microbial tetrapyrrole synthesis pathway. It can upregulate the synthesis of heme and respiratory chain cytochromes, and promote the formation of biofilms and the secretion of extracellular polymers in microorganisms, thereby enhancing the spatial synergy of the bacterial community under salt stress. Iron chelated with citrate is an essential iron source for nitrogenase iron-molybdenum cofactors and cytochrome heme. Synergistically with 5-ALA, it can improve nitrogenase activity and the respiratory protection capacity of bacteria. Simultaneously, the hydrolysis of iron citrate can lower the pH value of the granular microenvironment, shifting the ammonia-ammonia balance towards the ammonium nitrogen side, reducing ammonia volatilization loss, and supplementing plants with iron to maintain the activity of antioxidant enzymes such as iron-superoxide dismutase and peroxidase, thus alleviating oxidative damage caused by salt stress. Sodium zinc chelated with EDTA is a precursor for alkaline phosphatase, carbonic anhydrase, and DNA polymerase. Zinc-containing cofactors, such as enzymes, can enhance the phosphatase activity of microbial communities, promoting the mineralization of soil organic phosphorus and the dissolution and release of insoluble inorganic phosphorus. This invention uses chelated zinc instead of inorganic zinc salts such as zinc sulfate because the fertilizer also contains potassium dihydrogen phosphate, and is applied to saline-alkali soils and secondary salinized soils with high pH and high carbonate content. Inorganic zinc salts are easily converted into insoluble zinc phosphate or zinc carbonate after granulation, storage, and application to the soil, or are fixed by clay minerals and lose their effectiveness. Ethylenediaminetetraacetic acid chelated zinc sodium exists in a stable chelated state, which can continuously maintain the available state of zinc under the above conditions, thereby achieving precise supply at a trace level of 0.2-1.0 parts by weight. This allows the fertilizer of this invention to maintain the metabolic activity of microbial communities and efficiently supply nutrients in saline-alkali and secondary salinized soils.

[0012] Preferably, the modified biochar is prepared by the following method: Straw is pyrolyzed at 600-800℃ under nitrogen protection for 2-4 hours to obtain primary biochar. The primary biochar is then impregnated in a 10-20% potassium carbonate solution at a mass ratio of 1:6 for 2-6 hours, i.e., the mass ratio of potassium carbonate to primary biochar is 0.6-1.2:1. After impregnation, solid-liquid separation is performed, and the impregnated biochar is dried at 105℃ to constant weight to obtain impregnated char. The impregnated char is placed in a microwave reactor under nitrogen protection and microwave irradiated at a power of 600-1000W for 20-40 minutes. Subsequently, it is transferred to a tube furnace and activated at 600-800℃ with carbon dioxide gas at a flow rate of 0.5-1L / min for 0.5-1.5 hours. After activation, it is washed with deionized water until the pH of the washing solution is not higher than 9.0 and the conductivity is not higher than 200μS / cm. The activated biochar is then dried at 105℃. The activated biochar was immersed in a 0.1 mol / L potassium hydroxide solution for 1 hour, washed and dried, and then immersed in a polyglutamic acid solution at a mass ratio of 1:4. The solution was stirred at 300-400 rpm for 1-2 hours at 40-60℃. Then, tannic acid at 5-8% of the mass of the polyglutamic acid solute was added, and the solution was stirred at 300-400 rpm for 0.5-1 hour. After washing, the solution was vacuum dried at 60℃ to constant weight to obtain modified biochar.

[0013] Preferably, the activated water washing is carried out in a segmented collection and countercurrent reuse manner: the washing liquid with a pH higher than 10 obtained in the first stage of washing is collected separately, and its potassium content is determined before being used to prepare the next batch of potassium carbonate or potassium hydroxide soaking solution. That is, this washing liquid replaces an equal volume of deionized water and the amount of potassium carbonate or potassium hydroxide added is reduced accordingly; the washing liquid obtained in the last stage of washing, which has reached a pH not higher than 9.0 and a conductivity not higher than 200 μS / cm, is used as the water for the first stage of washing the next batch of primary biochar. Thus, the potassium that is not embedded in the carbon skeleton in the activator and is removed in the water washing is recycled within the carrier preparation process, which avoids the discharge of potassium-containing alkaline waste liquid and eliminates the need for a separate evaporation and concentration process to recover this part of the potassium. It should be noted that the washing liquid is not incorporated into the fertilizer formulation for the following reasons: First, the conductivity of the washing liquid at the washing endpoint is no higher than 200 μS / cm, and the potassium content is very low. Even if it is concentrated and incorporated into the formulation, the recovered potassium is negligible compared to the 8-12 parts by weight of potassium dihydrogen phosphate in the formulation, while the energy consumption and equipment investment of the concentration process are far higher than its potassium value. Second, the washing liquid is alkaline and contains residual potassium carbonate. If it is incorporated into the calcium chloride solution sprayed in the subsequent granulation process, the carbonate ions will immediately react with the calcium ions to form calcium carbonate precipitate. This will not only consume the calcium ions used to form an ionic cross-linking network with the alginate in the seaweed extract and weaken the surface micro-cross-linking curing effect, but also easily clog the atomizing nozzle. At the same time, it will increase the pH of the granulation micro-area, promote the decomposition of ammonium sulfate and release ammonia, and damage the live bacteria loaded on the carrier. Therefore, the potassium in the finished fertilizer product of this invention is provided by potassium dihydrogen phosphate in the formula, and the potassium remaining and enriched in the pores of modified biochar is used as a quick-acting potassium supplement. The potassium removed by water washing is recovered by using it in the process. The destinations of the two are clear and they are not confused with each other.

[0014] The synergistic effect of potassium carbonate impregnation and microwave-carbon dioxide gas activation significantly increased the specific surface area of ​​biochar, forming a rich nanoscale porous structure, thereby enhancing its adsorption capacity for ammonium nitrogen. During the activation process, potassium carbonate partially decomposes into potassium oxide and carbon dioxide at high temperature (K2CO3→K2O+CO2). On the other hand, potassium carbonate and its decomposition product potassium oxide undergo a reduction etching reaction with the carbon skeleton (K2CO3+2C→2K+3CO, K2O+C→2K+CO). While etching the carbon skeleton, potassium vapor is generated and embedded into the interlayer of graphite microcrystals to create pores. This process is similar to the subsequent introduction of carbon dioxide. The carbonization etching process, triggered by carbonization, involves the superposition of C+CO2→2CO vaporization and etching phases, resulting in the simultaneous development of micropores and mesopores on the same carbon skeleton. Since the activator used is a potassium salt, its residue is potassium, an essential element for plants, rather than heavy metals. After activation, only water washing is required, without acid leaching. This avoids introducing exogenous heavy metals into the fertilizer and produces acidic wastewater containing heavy metals. The potassium removed by water washing can be reused within the carrier preparation process as described above, while the potassium remaining in the pores directly enters the fertilizer along with the carrier as a readily available potassium supplement. The potassium carbonate can also be replaced with alkaline activators such as potassium hydroxide, which also leave potassium residues, or alternatively, if additional acid leaching and corresponding wastewater can be tolerated. In liquid treatment processes, replacing activators with zinc chloride, phosphoric acid, or other activators can yield activated biochar with a high specific surface area. However, using zinc chloride or phosphoric acid will result in the loss of the advantage that the residues themselves are nutrients. Before coating, the activated biochar is soaked in potassium hydroxide solution, which deprotonates the carboxyl and phenolic hydroxyl groups on the carbon surface and converts them into potassium salts. This improves the hydrophilicity of the carbon surface and the wettability of the polyglutamic acid solution to the pores, resulting in a more uniform coating layer distribution. The added tannic acid, through its multiple phenolic hydroxyl groups, forms multi-point hydrogen bonds with the carboxyl and amide groups on the polyglutamic acid chains, fixing the coating layer so that it can swell in water without rapidly dissolving. The network allows it to maintain its barrier function even after granulation, spraying, and application into the soil. Furthermore, the introduction of the polyglutamic acid coating layer constructs a hydrophilic barrier, effectively reducing competition for adsorption sites from sodium ions in the soil, thereby alleviating environmental osmotic stress on microorganisms. The carboxyl and amino functional groups of polyglutamic acid synergistically work with oxygen-containing functional groups such as C=O and CO on the biochar surface, reducing the content of exchangeable sodium through ion exchange. Simultaneously, the quinone / hydroquinone groups and edge defect sites retained and enriched on the carbon skeleton during the activation process possess redox activity, serving as acceptor and donor sites for extracellular electron transfer, thus promoting microbial energy metabolism.

[0015] Preferably, the mass concentration of the polyglutamic acid solution is 2-5%.

[0016] On the other hand, the present invention provides a method for preparing a compound microbial fertilizer based on synergistic microbial community metabolism, used to prepare the compound microbial fertilizer based on synergistic microbial community metabolism as described in any of the above claims, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 10-20 parts by weight of compound microbial flora, 30-50 parts by weight of modified biochar, 3-5 parts by weight of seaweed extract, 2-5 parts by weight of graphite powder, 1.1-4.0 parts by weight of metabolic synergist, 10-15 parts by weight of ammonium sulfate and 8-12 parts by weight of potassium dihydrogen phosphate. S1.2. Seed cultures of *Bacillus lentigines* and *Bacillus belye* were inoculated into liquid culture medium and fermented in liquid form at pH 7.0 and 30°C for 48 hours. Then, sterile sodium chloride solution (20-25% by mass) was added to the fermentation broth in 3-5 increments, with each addition increasing the sodium chloride concentration by no more than 1.0%, and the interval between two additions being 0.5-1 hour, until the sodium chloride concentration reached 3-5%, and the cumulative volume of each addition did not exceed 15% of the initial fermentation broth volume. Then, seed cultures of *Bacillus halophilus* and *Bacillus amyloliquefaciens*, pre-acclimated to sodium chloride and cultured to the late logarithmic growth stage, were inoculated and fermented for another 24 hours at pH 7.5 and 35°C to obtain a total viable count of not less than 1×10⁻⁶. 9 A mixed fermentation broth with a CFU / mL concentration and a total weight of 10-20 parts; S1.3. The mixed fermentation broth is uniformly sprayed onto the modified biochar; then the loaded modified biochar, seaweed extract, graphite powder, ammonium sulfate, potassium dihydrogen phosphate, and rhamnolipin from the metabolic synergist are fed into a disc granulator and granulated at 35-40℃. During the granulation process, a calcium chloride solution with a concentration of 0.05-0.1mol / L is atomized and sprayed onto the surface of the material to perform surface micro-crosslinking and solidification. The amount of calcium chloride solution sprayed is 3-6% of the total mass of the granulated material. After granulation, fertilizer particles with a particle size of 2-4mm are collected by sieving, and the unqualified particles are returned to the disc granulator for regranulation. S1.4. The remaining components of the metabolic synergist are prepared into an aqueous solution with a mass concentration of 5-10%. The aqueous solution is sprayed onto the surface of the fertilizer granules obtained in S1.3 under light-protected conditions using a fluidized bed. Finally, the mixture is fluidized and dried at 35°C to obtain a compound microbial fertilizer based on synergistic metabolism of microbial communities.

[0017] Preferably, in step S1.3, the spraying conditions are: inlet air temperature 40-45℃, outlet air temperature 30-35℃, and atomization pressure 0.15-0.25MPa.

[0018] Preferably, in step S1.3, after spraying the calcium chloride solution, the mixture is continuously rolled and cured for 10-20 minutes.

[0019] Preferably, in step S1.4, the fluidized bed spraying conditions are: inlet air temperature 40-45℃, atomization pressure 0.8-1.2 bar, and spraying rate 5-10 mL / min.

[0020] Preferably, in step S1.4, the moisture content of the fertilizer granules is not higher than 30% by mass after fluidized drying; the resulting fertilizer granules have a particle size of 2-4 mm, an effective viable bacteria count of not less than 0.20 billion / g, and a total nutrient (N+P2O5+K2O) mass fraction of 8%-25%.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention utilizes modified biochar through potassium carbonate impregnation, microwave-carbon dioxide gas synergistic activation, and polyglutamic acid coating to form a high specific surface area and nanoscale porous structure. This provides a stable microenvironment for microorganisms, free from environmental stress, significantly enhancing the colonization ability of the microbial community and thus greatly improving the survival rate of live bacteria. Simultaneously, the activator used is a salt of potassium, an essential plant nutrient. After activation, only water washing is required, without acid washing. This avoids introducing exogenous heavy metals into the fertilizer and generating acidic wastewater containing heavy metals. The potassium removed by water washing is collected in stages and reused in the carrier preparation process for the next batch of impregnation and washing, eliminating the need for external discharge or a separate concentration process. The potassium remaining and enriched in the charcoal pores directly enters the fertilizer along with the carrier, becoming a readily available potassium supplement. This ensures that the potassium in the activator is utilized in both the process cycle and as a nutrient in the product, balancing process economy and product safety. 2. The quinone groups and other redox active sites enriched by the modified biochar after activation in this invention can serve as mediators for extracellular electron transfer. Combined with the improved interfacial hydrophilicity and cell adhesion properties of the carboxyl and amino groups introduced by polyglutamic acid, it promotes electron transfer in the micro-ecosystem and thereby enhances nitrogenase activity. 3. This invention utilizes rhamnolipids as a biosurfactant. After being applied to the soil, it induces the microbial community to secrete large amounts of extracellular polymers, which synergistically with graphite powder to construct a highly spatially structured, locally electroactive biofilm. This biofilm, relying on the excellent conductivity of graphite powder as microelectrode nodes, constructs short-range electron transport channels within fertilizer particles and rhizosphere microregions, accelerating the electron transport rate between microbial species and within the microenvironment. Simultaneously, 5-aminolevulinic acid (5-ALA) synergistically with chelated iron, as a core precursor to heme and cytochrome, further enhances nitrogen fixation efficiency from the substrate perspective; tetrahydropyrimidine, as a compatible solute, effectively maintains intracellular osmotic pressure balance under high-salt conditions; and ethylenediaminetetraacetic acid chelated zinc sodium, as a cofactor for zinc-containing enzymes such as alkaline phosphatase, promotes the mineralization of soil organic phosphorus and the dissolution and release of insoluble inorganic phosphorus. These physical protection and multiple metabolic synergistic mechanisms significantly improve the survival rate of viable bacteria and the continuous nutrient supply capacity of fertilizers in saline and other adverse soil conditions. Detailed Implementation

[0022] 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.

[0023] This invention provides a compound microbial fertilizer based on synergistic microbial metabolism, comprising the following raw materials: compound microbial flora, modified biochar, seaweed extract, graphite powder, metabolic synergist, ammonium sulfate, and potassium dihydrogen phosphate; The graphite powder was purchased from Qingdao Haoyu Graphite Products Co., Ltd., and the particle size was 1-5μm. The modified biochar is prepared by microwave-carbon dioxide gas synergistic activation of primary biochar, followed by coating modification with polyglutamic acid.

[0024] Polyglutamic acid (CAS: 25513-46-6) was purchased from Shaanxi Chenming Biotechnology Co., Ltd.

[0025] The main active components of seaweed extracts include polysaccharides (fucosan, alginate, alginic acid), alginate esters, nitrogen-containing compounds (mannitol, alginic acid), and minerals (such as trace elements like potassium, iodine, zinc, and selenium). The seaweed extracts used in this invention contain at least 25% (w / w) gelatable polysaccharides, calculated as alginate (sodium alginate), to ensure the gelatinous content of Ca in S1.3. 2+ Sufficient ion cross-linking network was formed to stabilize particle formation; the seaweed extract was purchased from Hubei Jiangmin Taihua Chemical Co., Ltd.

[0026] The complex microbial community was prepared by co-fermentation of the following strains: Paenibacillus mucilaginosus, Bacillus velezensis, Halobacillus sp., and Bacillus amyloliquefaciens.

[0027] Paenibacillus mucilaginosus is deposited at the China Center for Type Culture Collection (CCTCC, Wuhan University, Wuhan, China), accession number CCTCC M20231473; Bacillus velezensis is deposited at the China Center for Type Culture Collection, accession number CCTCC M2022130 (SF327); Halobacillus sp. is deposited at the China Industrial Microbial Culture Collection Center (CICC, Beijing, China), accession number CICC 10447; Bacillus amyloliquefaciens is deposited at the China Center for Type Culture Collection, accession number CCTCC M2018433; all of the above strains were obtained from their respective collection institutions.

[0028] The metabolic synergists include: 5-aminolevulinic acid, tetrahydropyrimidine, rhamnolipid, sodium zinc chelate ethylenediaminetetraacetic acid, and iron chelate citrate.

[0029] 5-Aminolevulinic acid (CAS: 147852-84-4) was purchased from Hubei Weishi Chemical Reagent Co., Ltd.; sodium zinc chelate ethylenediaminetetraacetic acid (CAS: 14025-21-9) was purchased from Kandis Chemical (Hubei) Co., Ltd.; ferric citric acid chelate was purchased from Shaanxi Chenming Biotechnology Co., Ltd.; tetrahydropyrimidine was purchased from Guangzhou Aorida Biotechnology Co., Ltd.

[0030] Rhamnose glycolipid, powder, purchased from Shaanxi Deguan Biotechnology Co., Ltd.

[0031] The culture medium used was LB liquid medium, purchased from Shanghai Weidi Biotechnology Co., Ltd., which consisted of 10 g / L tryptone, 5 g / L yeast extract, and 10 g / L sodium chloride, meaning that the initial sodium chloride mass fraction of the fermentation system was approximately 1.0%.

[0032] Preparation of seed culture for each strain: The above strains were inoculated into LB liquid medium and cultured with shaking at 30℃ and 180 r / min until the late logarithmic growth stage, yielding effective viable cell counts of not less than 1×10⁻⁶. 9 CFU / mL seed culture; wherein, 1.5% sodium chloride was added to the seed culture medium of Bacillus halophilus and Bacillus amyloliquefaciens for pre-acclimatization.

[0033] The sterile sodium chloride solution for replenishment is prepared as follows: Dissolve sodium chloride in deionized water to prepare a 25% (w / w) solution, sterilize at 121°C for 20 min, and then cool to room temperature for later use. When replenishing at this concentration, the amount of sodium chloride required to increase the mass fraction of the system by 0.5% is approximately 2.1%-2.3% of the mass of the initial fermentation broth. The cumulative amount of replenishment for four replenishments is approximately 9% of the initial fermentation broth mass. The dilution is limited and can be quantitatively calculated. The relative proportions of the various nutrient components in the culture medium do not change due to replenishment.

[0034] It should be noted that the ratio of effective viable cell counts of each strain in this invention refers to the inoculation ratio during co-fermentation, which is a directly measurable and controllable process parameter. Because the generation time, salt tolerance, and response to gradient salt stress differ among the four strains—*Bacillus spp.* has a longer generation time and relatively weaker salt tolerance, and its proportion tends to decrease after the sodium chloride mass fraction in the system rises above 3%; *Bacillus halophilus* has a growth advantage at this salinity, and its proportion tends to increase—the actual effective viable cell count ratio of each strain in the mixed fermentation broth at the fermentation endpoint will inevitably deviate relative to the inoculation ratio, and this deviation varies with the specific conditions of each batch. Therefore, this invention does not use the strain ratio at the fermentation endpoint as a control indicator, but rather the inoculation ratio and the total effective viable cell count at the fermentation endpoint (not less than 1×10⁻⁶). 9 The inoculation ratio (CFU / mL) was used as the control indicator. Within the above inoculation ratio range, all four strains were stably detected and coexisted at the fermentation endpoint, and their metabolic complementarity did not change due to the shift in the ratio. The viable count of each strain at the fermentation endpoint could be identified by colony morphology observation combined with 16S rRNA gene sequence, or by real-time quantitative PCR using strain-specific primers.

[0035] The straw used in this invention is corn straw, which is crushed, passed through a 40-mesh sieve, and dried at 105°C to constant weight before use. Potassium carbonate, potassium hydroxide, tannic acid, calcium chloride, sodium chloride, ammonium sulfate, and potassium dihydrogen phosphate are all commercially available analytical grade or industrial grade products. Unless otherwise specified, all raw materials used in this invention are commercially available, and all methods used are conventional methods in the field.

[0036] In the preparation of modified biochar in each embodiment, the washing solution after activation was collected and reused in stages as follows: the activated carbon was washed several times with deionized water. The washing solutions with a pH higher than 10 obtained from the first 2-3 washes were combined and collected separately. After determining the potassium content (calculated as K2O), the washing solution was used to prepare the next batch of potassium carbonate impregnation solution. That is, the washing solution replaced an equal volume of deionized water, and the amount of potassium carbonate to be added was reduced accordingly based on the measured potassium content. Subsequently, washing was continued with deionized water until the pH of the washing solution reached 8.5 and the conductivity was 150 μS / cm. This final washing solution was used as the pre-wash water for the next batch of primary biochar. The above washing solutions were not included in the fertilizer formulation. The potassium in the fertilizer in each embodiment was provided by the potassium dihydrogen phosphate weighed in S1.1 and the potassium remaining in the pores of the modified biochar.

[0037] Example 1: A method for preparing a compound microbial fertilizer based on synergistic microbial community metabolism, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 10 parts by weight of compound microbial flora, 30 parts by weight of modified biochar, 3 parts by weight of seaweed extract, 2 parts by weight of graphite powder, 1.1 parts by weight of metabolic synergist, 10 parts by weight of ammonium sulfate and 8 parts by weight of potassium dihydrogen phosphate. The metabolic synergist comprises: 0.1 parts by weight of 5-aminolevulinic acid, 0.2 parts by weight of tetrahydropyrimidine, 0.1 parts by weight of rhamnolipid, 0.2 parts by weight of sodium zinc chelate ethylenediaminetetraacetic acid, and 0.5 parts by weight of iron chelate citrate.

[0038] S1.2. At a viable viable count ratio of 4:2, seed cultures of *Bacillus jellyeris* and *Bacillus belye* were inoculated into LB liquid medium at a total inoculum of 5% (volume fraction). Liquid fermentation was carried out at pH 7.0, 30℃, and 180 r / min for 48 h. Subsequently, a 25% (w / w) sterile sodium chloride solution was added to the fermentation broth in four separate additions, increasing the sodium chloride concentration by 0.5% each time, with a 1 h interval between each addition, gradually increasing the sodium chloride concentration from the 1.0% present in the LB liquid medium to 3.0%. Then, at a viable viable count ratio of 2:2, pre-acclimated and cultured *Bacillus halophilus* and *Bacillus amyloliquefaciens* seed cultures (total inoculum 5%, volume fraction) were inoculated into the medium. Fermentation was continued at pH 7.5 and 35℃ for 24 h to obtain a total viable viable count of not less than 1 × 10⁻⁶. 9 The mixed fermentation broth, with a total volume of 10 parts by weight and a CFU / mL concentration, was prepared; the inoculation ratio of the four strains, based on the effective viable cell count, was 4:2:2:2. S1.3. The mixed fermentation broth is sprayed onto the modified biochar with an inlet air temperature of 40℃, an outlet air temperature of 30℃, and an atomization pressure of 0.2MPa. Then, the loaded modified biochar, along with seaweed extract, graphite powder, ammonium sulfate, potassium dihydrogen phosphate, and rhamnolipin from the metabolic synergist, are fed into a disc granulator. Low-temperature rolling granulation is performed at 35℃. During the granulation process, a 0.1mol / L calcium chloride solution is atomized and sprayed onto the surface of the material at a rate of 5% of the total mass of the granulated material. The granulation continues for 15 minutes to solidify. After solidification, fertilizer granules with a particle size of 3mm are collected by sieving. Unqualified granules are returned to the disc granulator for regranulation. S1.4 The remaining components of the metabolic synergist, namely 5-aminolevulinic acid, tetrahydropyrimidine, ethylenediaminetetraacetic acid chelated zinc sodium, and citrate chelated iron, are prepared into an 8% aqueous solution. This solution is then sprayed onto the surface of the fertilizer granules obtained in S1.3 using a fluidized bed under light-protected conditions. The inlet air temperature is 40℃, the atomization pressure is 1.0 bar, and the spraying rate is 8 mL / min. Finally, the solution is fluidized and dried at 35℃ until the moisture content of the material is 25%, thus obtaining a compound microbial fertilizer based on synergistic microbial metabolism.

[0039] Furthermore, the preparation method of modified biochar is as follows: Straw was pyrolyzed at 600℃ under nitrogen protection for 4 hours to obtain primary biochar. The primary biochar was then impregnated in a 15% potassium carbonate solution at a mass ratio of 1:6 for 6 hours, i.e., the mass ratio of potassium carbonate to primary biochar was 0.9:1. After impregnation, the biochar was separated by filtration and dried at 105℃ to constant weight to obtain impregnated char. The impregnated char was placed in a microwave reactor under nitrogen protection and microwaved at 800W for 30 minutes. Subsequently, it was transferred to a tube furnace and activated at 800℃ with carbon dioxide gas at a flow rate of 0.5L / min for 1 hour. After activation, the char was washed with deionized water until the pH of the washing liquid was 8.5 and the conductivity was 150μS / cm. The char was then dried at 105℃ to obtain activated biochar. The resulting washing liquid was collected in segments as described above and reused for the next batch of impregnation and washing, but was not included in the fertilizer formulation of this embodiment. The activated biochar was immersed in a 0.1 mol / L potassium hydroxide solution for 1 hour, washed and dried. Then, it was immersed in a 2% polyglutamic acid solution at a mass ratio of 1:4 and stirred at 400 rpm for 2 hours at 50°C. Tannic acid, accounting for 6% of the mass of the polyglutamic acid solute, was added, and stirring was continued at 400 rpm for 1 hour. After washing, it was vacuum dried at 60°C to constant weight to obtain modified biochar.

[0040] Example 2: A method for preparing a compound microbial fertilizer based on synergistic microbial community metabolism, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 15 parts by weight of compound microbial flora, 40 parts by weight of modified biochar, 4 parts by weight of seaweed extract, 4 parts by weight of graphite powder, 2.4 parts by weight of metabolic synergist, 13 parts by weight of ammonium sulfate and 10 parts by weight of potassium dihydrogen phosphate. The metabolic synergist comprises: 0.1 parts by weight of 5-aminolevulinic acid, 0.2 parts by weight of tetrahydropyrimidine, 0.1 parts by weight of rhamnolipid, 1.0 part by weight of sodium zinc chelate ethylenediaminetetraacetic acid, and 1.0 part by weight of iron chelate citrate.

[0041] S1.2. At a viable viable count ratio of 5:4, seed cultures of *Bacillus jellyeris* and *Bacillus belye* were inoculated into LB liquid medium at a total inoculum of 5% (volume fraction). Liquid fermentation was carried out at pH 7.0, 30℃, and 180 r / min for 48 h. Subsequently, a 25% (w / w) sterile sodium chloride solution was added to the fermentation broth in four separate additions, increasing the sodium chloride concentration by 0.5% each time, with a 1 h interval between each addition, gradually increasing the sodium chloride concentration from the 1.0% present in the LB liquid medium to 3.0%. Then, at a viable viable count ratio of 3:3, pre-acclimated and cultured *Bacillus halophilus* and *Bacillus amyloliquefaciens* seed cultures (total inoculum 5%, volume fraction) were inoculated into the medium. Fermentation was continued at pH 7.5 and 35℃ for 24 h to obtain a total viable viable count of not less than 1 × 10⁻⁶. 9 The mixed fermentation broth, with a total volume of 15 parts by weight and a CFU / mL concentration, was prepared; the inoculation ratio of the four strains, based on the effective viable cell count, was 5:4:3:3. S1.3. The mixed fermentation broth is sprayed onto the modified biochar with an inlet air temperature of 40℃, an outlet air temperature of 30℃, and an atomization pressure of 0.2MPa. Then, the loaded modified biochar, along with seaweed extract, graphite powder, ammonium sulfate, potassium dihydrogen phosphate, and rhamnolipin from the metabolic synergist, are fed into a disc granulator. Low-temperature rolling granulation is performed at 35℃. During the granulation process, a 0.1mol / L calcium chloride solution is atomized and sprayed onto the surface of the material at a rate of 5% of the total mass of the granulated material. The granulation continues for 15 minutes to solidify. After solidification, fertilizer granules with a particle size of 3mm are collected by sieving. Unqualified granules are returned to the disc granulator for regranulation. S1.4 The remaining components of the metabolic synergist, namely 5-aminolevulinic acid, tetrahydropyrimidine, ethylenediaminetetraacetic acid chelated zinc sodium, and citrate chelated iron, are prepared into an 8% aqueous solution. This solution is then sprayed onto the surface of the fertilizer granules obtained in S1.3 using a fluidized bed under light-protected conditions. The inlet air temperature is 40℃, the atomization pressure is 1.0 bar, and the spraying rate is 8 mL / min. Finally, the solution is fluidized and dried at 35℃ until the moisture content of the material is 25%, thus obtaining a compound microbial fertilizer based on synergistic microbial metabolism.

[0042] Furthermore, the preparation method of modified biochar is as follows: Straw was pyrolyzed at 600℃ under nitrogen protection for 4 hours to obtain primary biochar. The primary biochar was then impregnated in a 15% potassium carbonate solution at a mass ratio of 1:6 for 6 hours, i.e., the mass ratio of potassium carbonate to primary biochar was 0.9:1. After impregnation, the biochar was separated by filtration and dried at 105℃ to constant weight to obtain impregnated char. The impregnated char was placed in a microwave reactor under nitrogen protection and microwaved at 800W for 30 minutes. Subsequently, it was transferred to a tube furnace and activated at 800℃ with carbon dioxide gas at a flow rate of 0.5L / min for 1 hour. After activation, the char was washed with deionized water until the pH of the washing liquid was 8.5 and the conductivity was 150μS / cm. The char was then dried at 105℃ to obtain activated biochar. The resulting washing liquid was collected in segments as described above and reused for the next batch of impregnation and washing, but was not included in the fertilizer formulation of this embodiment. The activated biochar was immersed in a 0.1 mol / L potassium hydroxide solution for 1 hour, washed and dried. Then, it was immersed in a 3% polyglutamic acid solution at a mass ratio of 1:4 and stirred at 400 rpm for 2 hours at 50°C. Tannic acid, accounting for 6% of the mass of the polyglutamic acid solute, was added, and stirring was continued at 400 rpm for 1 hour. After washing, it was vacuum dried at 60°C to constant weight to obtain modified biochar.

[0043] Example 3: A method for preparing a compound microbial fertilizer based on synergistic microbial community metabolism, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 20 parts by weight of compound microbial flora, 50 parts by weight of modified biochar, 5 parts by weight of seaweed extract, 5 parts by weight of graphite powder, 3.9 parts by weight of metabolic synergist, 15 parts by weight of ammonium sulfate and 12 parts by weight of potassium dihydrogen phosphate. The metabolic synergist comprises: 0.2 parts by weight of 5-aminolevulinic acid, 0.4 parts by weight of tetrahydropyrimidine, 0.3 parts by weight of rhamnolipid, 1.0 part by weight of sodium zinc chelate ethylenediaminetetraacetic acid, and 2.0 parts by weight of iron chelate citrate.

[0044] S1.2. At a viable viable count ratio of 6:6, seed cultures of *Bacillus jellyeris* and *Bacillus belye* were inoculated into LB liquid medium at a total inoculum of 5% (volume fraction). Liquid fermentation was carried out at pH 7.0, 30℃, and 180 r / min for 48 h. Subsequently, a 25% sterile sodium chloride solution was added to the fermentation broth in four separate additions, increasing the sodium chloride concentration by 0.5% each time, with a 1 h interval between each addition, gradually increasing the sodium chloride concentration from the 1.0% present in the LB liquid medium to 3.0%. Then, at a viable viable count ratio of 3:5, pre-acclimated and cultured *Bacillus halophilus* and *Bacillus amyloliquefaciens* seed cultures (total inoculum 5%, volume fraction) were inoculated into the medium. Fermentation was continued at pH 7.5 and 35℃ for 24 h to obtain a total viable viable count of not less than 1 × 10⁻⁶. 9 The mixed fermentation broth, with a total volume of 20 parts by weight and a concentration of CFU / mL, was prepared; the inoculation ratio of the four strains, based on the effective viable cell count, was 6:6:3:5. S1.3. The mixed fermentation broth is sprayed onto the modified biochar with an inlet air temperature of 40℃, an outlet air temperature of 30℃, and an atomization pressure of 0.2MPa. Then, the loaded modified biochar, along with seaweed extract, graphite powder, ammonium sulfate, potassium dihydrogen phosphate, and rhamnolipin from the metabolic synergist, are fed into a disc granulator. Low-temperature rolling granulation is performed at 35℃. During the granulation process, a 0.1mol / L calcium chloride solution is atomized and sprayed onto the surface of the material at a rate of 5% of the total mass of the granulated material. The granulation continues for 15 minutes to solidify. After solidification, fertilizer granules with a particle size of 3mm are collected by sieving. Unqualified granules are returned to the disc granulator for regranulation. S1.4 The remaining components of the metabolic synergist, namely 5-aminolevulinic acid, tetrahydropyrimidine, ethylenediaminetetraacetic acid chelated zinc sodium, and citrate chelated iron, are prepared into an 8% aqueous solution. This solution is then sprayed onto the surface of the fertilizer granules obtained in S1.3 using a fluidized bed under light-protected conditions. The inlet air temperature is 40℃, the atomization pressure is 1.0 bar, and the spraying rate is 8 mL / min. Finally, the solution is fluidized and dried at 35℃ until the moisture content of the material is 25%, thus obtaining a compound microbial fertilizer based on synergistic microbial metabolism.

[0045] Furthermore, the preparation method of modified biochar is as follows: Straw was pyrolyzed at 600℃ under nitrogen protection for 4 hours to obtain primary biochar. The primary biochar was then impregnated in a 15% potassium carbonate solution at a mass ratio of 1:6 for 6 hours, i.e., the mass ratio of potassium carbonate to primary biochar was 0.9:1. After impregnation, the biochar was separated by filtration and dried at 105℃ to constant weight to obtain impregnated char. The impregnated char was placed in a microwave reactor under nitrogen protection and microwaved at 800W for 30 minutes. Subsequently, it was transferred to a tube furnace and activated at 800℃ with carbon dioxide gas at a flow rate of 0.5L / min for 1 hour. After activation, the char was washed with deionized water until the pH of the washing liquid was 8.5 and the conductivity was 150μS / cm. The char was then dried at 105℃ to obtain activated biochar. The resulting washing liquid was collected in segments as described above and reused for the next batch of impregnation and washing, but was not included in the fertilizer formulation of this embodiment. The activated biochar was immersed in a 0.1 mol / L potassium hydroxide solution for 1 hour, washed and dried, and then immersed in a 5% polyglutamic acid solution at a mass ratio of 1:4. The mixture was stirred at 400 rpm for 2 hours at 50 °C. Then, tannic acid at 6% of the mass of the polyglutamic acid solute was added, and the mixture was stirred at 400 rpm for 1 hour. After washing, the modified biochar was vacuum dried at 60 °C to constant weight to obtain the modified biochar.

[0046] Example 4: A method for preparing a compound microbial fertilizer based on synergistic microbial community metabolism, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 15 parts by weight of compound microbial flora, 45 parts by weight of modified biochar, 4 parts by weight of seaweed extract, 4 parts by weight of graphite powder, 2.4 parts by weight of metabolic synergist, 13 parts by weight of ammonium sulfate and 10 parts by weight of potassium dihydrogen phosphate. The metabolic synergist comprises: 0.1 parts by weight of 5-aminolevulinic acid, 0.2 parts by weight of tetrahydropyrimidine, 0.1 parts by weight of rhamnolipid, 1.0 part by weight of sodium zinc chelate ethylenediaminetetraacetic acid, and 1.0 part by weight of iron chelate citrate.

[0047] S1.2. At a viable viable count ratio of 5:4, seed cultures of *Bacillus jellyeris* and *Bacillus belye* were inoculated into LB liquid medium at a total inoculum of 5% (volume fraction). Liquid fermentation was carried out at pH 7.0, 30℃, and 180 r / min for 48 h. Subsequently, a 25% (w / w) sterile sodium chloride solution was added to the fermentation broth in four separate additions, increasing the sodium chloride concentration by 0.5% each time, with a 1 h interval between each addition, gradually increasing the sodium chloride concentration from the 1.0% present in the LB liquid medium to 3.0%. Then, at a viable viable count ratio of 3:3, pre-acclimated and cultured *Bacillus halophilus* and *Bacillus amyloliquefaciens* seed cultures (total inoculum 5%, volume fraction) were inoculated into the medium. Fermentation was continued at pH 7.5 and 35℃ for 24 h to obtain a total viable viable count of not less than 1 × 10⁻⁶.9 The mixed fermentation broth, with a total volume of 15 parts by weight and a CFU / mL concentration, was prepared; the inoculation ratio of the four strains, based on the effective viable cell count, was 5:4:3:3. S1.3. The mixed fermentation broth is sprayed onto the modified biochar with an inlet air temperature of 40℃, an outlet air temperature of 30℃, and an atomization pressure of 0.2MPa. Then, the loaded modified biochar, along with seaweed extract, graphite powder, ammonium sulfate, potassium dihydrogen phosphate, and rhamnolipin from the metabolic synergist, are fed into a disc granulator. Low-temperature rolling granulation is performed at 35℃. During the granulation process, a 0.1mol / L calcium chloride solution is atomized and sprayed onto the surface of the material at a rate of 5% of the total mass of the granulated material. The granulation continues for 15 minutes to solidify. After solidification, fertilizer granules with a particle size of 3mm are collected by sieving. Unqualified granules are returned to the disc granulator for regranulation. S1.4 The remaining components of the metabolic synergist, namely 5-aminolevulinic acid, tetrahydropyrimidine, ethylenediaminetetraacetic acid chelated zinc sodium, and citrate chelated iron, are prepared into an 8% aqueous solution. This solution is then sprayed onto the surface of the fertilizer granules obtained in S1.3 using a fluidized bed under light-protected conditions. The inlet air temperature is 40℃, the atomization pressure is 1.0 bar, and the spraying rate is 8 mL / min. Finally, the solution is fluidized and dried at 35℃ until the moisture content of the material is 25%, thus obtaining a compound microbial fertilizer based on synergistic microbial metabolism.

[0048] Furthermore, the preparation method of modified biochar is as follows: Straw was pyrolyzed at 600℃ under nitrogen protection for 4 hours to obtain primary biochar. The primary biochar was then impregnated in a 15% potassium carbonate solution at a mass ratio of 1:6 for 6 hours, i.e., the mass ratio of potassium carbonate to primary biochar was 0.9:1. After impregnation, the biochar was separated by filtration and dried at 105℃ to constant weight to obtain impregnated char. The impregnated char was placed in a microwave reactor under nitrogen protection and microwaved at 800W for 30 minutes. Subsequently, it was transferred to a tube furnace and activated at 800℃ with carbon dioxide gas at a flow rate of 0.5L / min for 1 hour. After activation, the char was washed with deionized water until the pH of the washing liquid was 8.5 and the conductivity was 150μS / cm. The char was then dried at 105℃ to obtain activated biochar. The resulting washing liquid was collected in segments as described above and reused for the next batch of impregnation and washing, but was not included in the fertilizer formulation of this embodiment. The activated biochar was immersed in a 0.1 mol / L potassium hydroxide solution for 1 hour, washed and dried, and then immersed in a 3% polyglutamic acid solution at a mass ratio of 1:4. The mixture was stirred at 400 rpm for 2 hours at 50°C. Then, tannic acid at 6% of the mass of the polyglutamic acid solute was added, and the mixture was stirred at 400 rpm for 1 hour. After washing, the modified biochar was vacuum dried at 60°C to constant weight to obtain the modified biochar.

[0049] Example 5: A method for preparing a compound microbial fertilizer based on synergistic microbial community metabolism, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 15 parts by weight of compound microbial flora, 50 parts by weight of modified biochar, 4 parts by weight of seaweed extract, 4 parts by weight of graphite powder, 2.4 parts by weight of metabolic synergist, 13 parts by weight of ammonium sulfate and 10 parts by weight of potassium dihydrogen phosphate. The metabolic synergist comprises: 0.1 parts by weight of 5-aminolevulinic acid, 0.2 parts by weight of tetrahydropyrimidine, 0.1 parts by weight of rhamnolipid, 1.0 part by weight of sodium zinc chelate ethylenediaminetetraacetic acid, and 1.0 part by weight of iron chelate citrate.

[0050] S1.2. At a viable viable count ratio of 5:4, seed cultures of *Bacillus jellyeris* and *Bacillus belye* were inoculated into LB liquid medium at a total inoculum of 5% (volume fraction). Liquid fermentation was carried out at pH 7.0, 30℃, and 180 r / min for 48 h. Subsequently, a 25% (w / w) sterile sodium chloride solution was added to the fermentation broth in four separate additions, increasing the sodium chloride concentration by 0.5% each time, with a 1 h interval between each addition, gradually increasing the sodium chloride concentration from the 1.0% present in the LB liquid medium to 3.0%. Then, at a viable viable count ratio of 3:3, pre-acclimated and cultured *Bacillus halophilus* and *Bacillus amyloliquefaciens* seed cultures (total inoculum 5%, volume fraction) were inoculated into the medium. Fermentation was continued at pH 7.5 and 35℃ for 24 h to obtain a total viable viable count of not less than 1 × 10⁻⁶. 9 The mixed fermentation broth, with a total volume of 15 parts by weight and a CFU / mL concentration, was prepared; the inoculation ratio of the four strains, based on the effective viable cell count, was 5:4:3:3. S1.3. The mixed fermentation broth is sprayed onto the modified biochar with an inlet air temperature of 40℃, an outlet air temperature of 30℃, and an atomization pressure of 0.2MPa. Then, the loaded modified biochar, along with seaweed extract, graphite powder, ammonium sulfate, potassium dihydrogen phosphate, and rhamnolipin from the metabolic synergist, are fed into a disc granulator. Low-temperature rolling granulation is performed at 35℃. During the granulation process, a 0.1mol / L calcium chloride solution is atomized and sprayed onto the surface of the material at a rate of 5% of the total mass of the granulated material. The granulation continues for 15 minutes to solidify. After solidification, fertilizer granules with a particle size of 3mm are collected by sieving. Unqualified granules are returned to the disc granulator for regranulation. S1.4 The remaining components of the metabolic synergist, namely 5-aminolevulinic acid, tetrahydropyrimidine, ethylenediaminetetraacetic acid chelated zinc sodium, and citrate chelated iron, are prepared into an 8% aqueous solution. This solution is then sprayed onto the surface of the fertilizer granules obtained in S1.3 using a fluidized bed under light-protected conditions. The inlet air temperature is 40℃, the atomization pressure is 1.0 bar, and the spraying rate is 8 mL / min. Finally, the solution is fluidized and dried at 35℃ until the moisture content of the material is 25%, thus obtaining a compound microbial fertilizer based on synergistic microbial metabolism.

[0051] Furthermore, the preparation method of modified biochar is as follows: Straw was pyrolyzed at 600℃ under nitrogen protection for 4 hours to obtain primary biochar. The primary biochar was then impregnated in a 15% potassium carbonate solution at a mass ratio of 1:6 for 6 hours, i.e., the mass ratio of potassium carbonate to primary biochar was 0.9:1. After impregnation, the biochar was separated by filtration and dried at 105℃ to constant weight to obtain impregnated char. The impregnated char was placed in a microwave reactor under nitrogen protection and microwaved at 800W for 30 minutes. Subsequently, it was transferred to a tube furnace and activated at 800℃ with carbon dioxide gas at a flow rate of 0.5L / min for 1 hour. After activation, the char was washed with deionized water until the pH of the washing liquid was 8.5 and the conductivity was 150μS / cm. The char was then dried at 105℃ to obtain activated biochar. The resulting washing liquid was collected in segments as described above and reused for the next batch of impregnation and washing, but was not included in the fertilizer formulation of this embodiment. The activated biochar was immersed in a 0.1 mol / L potassium hydroxide solution for 1 hour, washed and dried, and then immersed in a 3% polyglutamic acid solution at a mass ratio of 1:4. The mixture was stirred at 400 rpm for 2 hours at 50°C. Then, tannic acid at 6% of the mass of the polyglutamic acid solute was added, and the mixture was stirred at 400 rpm for 1 hour. After washing, the modified biochar was vacuum dried at 60°C to constant weight to obtain the modified biochar.

[0052] Comparative Example 1: Using the method of Example 2, in the preparation method of a compound microbial fertilizer based on synergistic microbial metabolism, no modified biochar was used, and primary biochar that had not been activated or coated was used directly. The remaining steps were the same as in Example 2.

[0053] Comparative Example 2: Using the method of Example 2, in a method for preparing a compound microbial fertilizer based on synergistic microbial metabolism, no synergistic synergist was added, that is, rhamnolipin was not added in S1.3, and the remaining synergist components were not sprayed and loaded in S1.4. The remaining steps were the same as in Example 2.

[0054] Comparative Example 3: Using the method of Example 2, in the preparation method of modified biochar, the primary biochar was impregnated with potassium carbonate solution and dried at 105°C. It was then directly washed with water and dried at 105°C without microwave radiation and carbon dioxide gas activation. The remaining steps were the same as in Example 2.

[0055] This invention relates to a composite microbial fertilizer based on synergistic microbial metabolism, prepared using modified biochar. The performance indicators and testing standards for this composite microbial fertilizer are as follows: After aliquoting the fertilizer samples, they were stored in a 25℃ incubator for 0 days (initial), 30 days, 90 days, and 180 days, respectively. After storage, 10g of 10g of each sample was added to 90mL of sterile physiological saline, shaken at 30℃ for 30min, and then serially diluted to 10⁻⁶. -5 -10 -7 Concentration; take 100 μL of the dilution and spread it on a plate, incubate at 30℃ for 48 h, and count the number of single colonies; the calculation formula is: viable cell survival rate (%) = (number of viable cells after storage / number of viable cells at the beginning) × 100%; the viable cell survival rates listed in Table 1 below are all the results of the measurement after 180 days of storage.

[0056] Secondary salinized greenhouse soil (0-20cm topsoil layer, salt content 0.3% (mass fraction), pH 8.2) was used as the test soil, and greenhouse cucumber was used as the test crop. The nutrient input for each fertilization treatment was 240 kg / hm² (nitrogen equivalent). 2 The experiment involved setting up fertilization zones: applying the target fertilizer (compound microbial fertilizer); and a blank control zone: receiving no fertilizer at all (relying solely on basic soil nutrients). Each treatment was replicated three times to minimize error. After crop maturity, the economic yield of the crops in both zones was measured, and the nitrogen uptake per unit economic yield was determined according to crop type. The total nitrogen uptake in both zones was calculated: nitrogen uptake in the fertilization zone (U1) = yield in the fertilization zone × nitrogen uptake per unit yield; nitrogen uptake in the blank control zone (U0) = yield in the blank control zone × nitrogen uptake per unit yield. The fertilizer utilization rate of this invention was calculated using the difference method based on nitrogen: fertilizer utilization rate (%) = [(U1-U0) / nitrogen input] × 100%.

[0057] The compound microbial fertilizers based on synergistic microbial metabolism prepared in Examples 1-5 and Comparative Examples 1-3 were tested according to the above standards, and the data obtained are shown in Table 1: Table 1 Performance data of compound microbial fertilizers in Examples 1-5 and Comparative Examples 1-3

[0058] As can be seen from Examples 2 and 4-5, when the weight of modified biochar is increased to an excessive amount while other components remain unchanged in the compound microbial fertilizer based on synergistic microbial metabolism, the survival rate of live bacteria in the compound microbial fertilizer and the fertilizer utilization rate of crops in the fertilization area continuously decrease. The hierarchical porous structure of modified biochar provides a physical shelter for microorganisms, helping them avoid direct damage from environmental stresses such as drought and salinity. Simultaneously, the functional groups (such as carboxyl and hydroxyl groups) on the surface of biochar can adsorb nutrients such as ammonium nitrogen and available phosphorus, delaying their loss and extending the time for microorganisms to utilize nutrients. Furthermore, biochar obtained from the high-temperature pyrolysis of straw at 600-800℃ is rich in alkali metal / alkaline earth metal oxides and carbonates such as K₂O, CaO, and Na₂O, and its potassium content is further enriched after activation with potassium carbonate. It is weakly alkaline (typically pH 8-10), which helps neutralize soil acidity and maintain a suitable pH range, thereby promoting the metabolic activity of the microbial community. However, excessive application of biochar can lead to overly dense fertilizer particles, hindering oxygen diffusion, creating a localized anaerobic environment, and inhibiting the proliferation of aerobic bacteria (such as Bacillus). Additionally, excessive biochar can adsorb NH₄⁺. + K + Plasma makes it difficult for microorganisms to desorb and utilize it, thereby reducing the content of readily available nutrients.

[0059] Based on the above test experiments, Example 2 is considered the optimal example. A comparison of Example 2 and Comparative Example 1 shows that when biochar is used directly without modified biochar, the survival rate of live bacteria in the compound microbial fertilizer and the fertilizer utilization rate of crops in the fertilization area are significantly reduced. Modified biochar, through microwave-carbon dioxide gas activation and polyglutamic acid coating, significantly increases its specific surface area and optimizes its pore structure, thereby enhancing its adsorption capacity for nutrients such as ammonium nitrogen and effectively reducing their loss. In contrast, unmodified biochar, due to its low specific surface area and coarse pore structure, has a weaker nutrient adsorption capacity, leading to the easy erosion or volatilization of nutrients such as nitrogen and phosphorus by rainwater. In addition, the polyglutamic acid coating layer can form a physical barrier, delaying nutrient release and achieving sustained fertilizer effect. Unmodified biochar, lacking a coating layer, releases nutrients too quickly, resulting in a low proportion absorbed by crops in the short term and reduced utilization. At the same time, the high porosity of modified biochar provides a protected habitat for microorganisms, while the low porosity of unmodified biochar makes the microbial community more susceptible to environmental stresses (such as drought and high temperature), leading to a lower survival rate.

[0060] A comparison of Example 2 and Comparative Example 2 shows that without the addition of a metabolic synergist, the survival rate of viable bacteria in the compound microbial fertilizer decreased from 84.6% to 66.0%, and the fertilizer utilization rate decreased from 60.8% to 37.2%, both significantly reduced. This is because the absence of rhamnolipids leads to hydrophobic aggregation of graphite powder, preventing the formation of an effective biofilm; the absence of tetrahydropyrimidine reduces the permeability of the bacteria; and the absence of 5-aminolevulinic acid and chelated iron / zinc reduces nitrogen fixation and phosphorus / potassium solubilization efficiency, preventing the effective release of insoluble phosphorus and potassium, ultimately resulting in an overall decrease in nitrogen, phosphorus, and potassium utilization.

[0061] A comparison of Example 2 and Comparative Example 3 shows that: without microwave-carbon dioxide gas synergistic activation, the survival rate of live bacteria in the compound microbial fertilizer is significantly reduced; microwave-carbon dioxide gas synergistic activation can significantly improve the specific surface area and microporous structure of biochar; unactivated primary biochar has a low specific surface area and fewer microbial attachment sites, making it difficult for the microbial community to stably colonize on the carrier surface; in addition, the survival rate of bacteria decreases under environmental stress (such as dehydration and pH fluctuations), which is one of the main problems faced by traditional carriers; during the microwave-carbon dioxide gas activation process, carbon dioxide gas reacts with the carbon material at high temperature, generating gas and gradually corroding its surface, thereby increasing the complexity of the pore structure and improving the specific surface area and adsorption capacity; at the same time, this method can also introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups, providing necessary chemical groups for subsequent polyglutamic acid coating, thereby forming an effective protective layer and enhancing the survival rate and colonization ability of microorganisms.

[0062] To further illustrate the effect of the activation process on the pore structure of the carrier, the biochar samples mentioned above were subjected to nitrogen adsorption-desorption measurements at 77K using an automated specific surface area and porosity analyzer. Specific surface area was calculated according to the BET equation, micropore volume was calculated using the t-plot method, and total pore volume was expressed as the amount of nitrogen adsorbed at a relative pressure of 0.99. Potassium content was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after microwave digestion and expressed as K₂O. The mass concentrations of the polyglutamic acid solution used in Examples 1, 2, 4, 5, and 3 were 2%, 3%, and 5%, respectively. The biochar in Comparative Example 3 was impregnated with potassium carbonate without microwave radiation or carbon dioxide activation. The measurement results are shown in Table 2. Table 2. Pore structure and potassium content of each biochar sample

[0063] As shown in Table 2, the specific surface area of ​​primary biochar is only 87 m². 2 / g, after being impregnated with potassium carbonate and activated by microwave radiation and carbon dioxide gas, the specific surface area increased to 1058m². 2 / g, total pore volume is 0.062cm³ 3 / g increased to 0.655cm3 / g, the micropore volume ratio increased from 42.3% to 71.2%, indicating that the chemical etching of potassium carbonate and the vapor etching of carbon dioxide produced a synergistic pore-forming effect on the same carbon skeleton; Comparative Example 3 was only impregnated with potassium carbonate without microwave and carbon dioxide activation, and its specific surface area decreased to 68m² instead of increasing. 2 / g indicates that simple impregnation does not create pores; instead, the impregnation residue and coating layer clog the original pores, which is the direct reason why the survival rate of viable bacteria in Comparative Example 3 was only 55.0%. Polyglutamic acid coating occupies some pores; when the mass concentration of the coating solution increases from 2% to 5%, the specific surface area of ​​the modified biochar increases from 812 m² / g. 2 / g decreased to 681m 2 The concentration of polyglutamic acid is too high, which is not conducive to maintaining the pore capacity of the carrier. This is one of the reasons why the survival rate of live bacteria in Example 3 is slightly lower than that in Example 2. In addition, the potassium content (calculated as K2O) in each modified biochar is 3.4%-3.5%, which is higher than the 2.8% of primary biochar. This indicates that some potassium is still retained in the pores of the char after washing and is applied to the soil along with the fertilizer. This confirms that when potassium carbonate is used as an activator, the residue is a nutrient rather than a pollutant. This part of potassium is the potassium in the activator that is finally applied to the soil with the product. The potassium removed by washing is collected in stages as described above and used in the carrier preparation process. It does not enter the fertilizer formula. The destinations of the two are clear and can be calculated separately.

[0064] 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 preferred examples and are not intended to limit 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 the present invention is defined by the appended claims and their equivalents.

Claims

1. A compound microbial fertilizer based on synergistic microbial community metabolism, characterized in that, The ingredients include: compound microbial flora, modified biochar, seaweed extract, graphite powder, metabolic synergist, ammonium sulfate and potassium dihydrogen phosphate; The modified biochar is prepared by impregnating primary biochar with potassium carbonate, followed by microwave-carbon dioxide gas synergistic activation, and then coating and modifying it with polyglutamic acid.

2. The compound microbial fertilizer based on synergistic microbial metabolism according to claim 1, characterized in that, The composite microbial community is a mixed fermentation broth obtained by co-fermentation of various strains, and its total effective viable count is not less than 1×10⁻⁶. 9 CFU / mL; by weight, the composite microbial community consists of 10-20 parts by weight, modified biochar 30-50 parts by weight, seaweed extract 3-5 parts by weight, graphite powder 2-5 parts by weight, metabolic synergist 1.1-4.0 parts by weight, ammonium sulfate 10-15 parts by weight, and potassium dihydrogen phosphate 8-12 parts by weight.

3. The compound microbial fertilizer based on synergistic microbial metabolism according to claim 2, characterized in that, The composite microbial community was prepared by co-fermentation of the following strains, and each strain was added during co-fermentation in the following ratio of effective viable counts at inoculation: Gelatinous Bacillus: Bacillus belye: Bacillus halophilus: Bacillus amyloliquefaciens = (4-6):(2-6):(2-3):(2-5).

4. The compound microbial fertilizer based on synergistic microbial metabolism according to claim 2, characterized in that, The metabolic synergist comprises: 0.1-0.2 parts by weight of 5-aminolevulinic acid, 0.2-0.4 parts by weight of tetrahydropyrimidine, 0.1-0.4 parts by weight of rhamnolipid, 0.2-1.0 parts by weight of sodium zinc chelate ethylenediaminetetraacetic acid, and 0.5-2.0 parts by weight of iron chelate citrate.

5. The compound microbial fertilizer based on synergistic microbial metabolism according to claim 2, characterized in that, The modified biochar is prepared as follows: Straw is pyrolyzed at 600-800℃ under nitrogen protection for 2-4 hours to obtain primary biochar. The primary biochar is then impregnated in a 10-20% potassium carbonate solution at a mass ratio of 1:6 for 2-6 hours, i.e., the mass ratio of potassium carbonate to primary biochar is 0.6-1.2:

1. After impregnation, solid-liquid separation is performed, and the impregnated biochar is dried at 105℃ to constant weight to obtain impregnated char. The impregnated char is placed in a microwave reactor under nitrogen protection and microwave irradiated at a power of 600-1000W for 20-40 minutes. Subsequently, it is transferred to a tube furnace and activated at 600-800℃ with carbon dioxide gas at a flow rate of 0.5-1L / min for 0.5-1.5 hours. After activation, the biochar was washed with deionized water until the pH of the washing solution was not higher than 9.0 and the conductivity was not higher than 200 μS / cm. It was then dried at 105℃ to obtain activated biochar. The activated biochar was immersed in a 0.1 mol / L potassium hydroxide solution for 1 hour, washed and dried, and then immersed in a polyglutamic acid solution at a mass ratio of 1:

4. The solution was stirred at 300-400 rpm for 1-2 hours at 40-60℃. Then, tannic acid at 5-8% of the mass of the polyglutamic acid solute was added, and the solution was stirred at 300-400 rpm for 0.5-1 hour. After washing, the solution was vacuum dried at 60℃ to constant weight to obtain modified biochar.

6. The compound microbial fertilizer based on synergistic microbial metabolism according to claim 5, characterized in that, The mass concentration of the polyglutamic acid solution is 2-5%.

7. A method for preparing a compound microbial fertilizer based on synergistic microbial metabolism, used to prepare the compound microbial fertilizer based on synergistic microbial metabolism as described in any one of claims 1-6, characterized in that, The preparation method of the compound microbial fertilizer based on synergistic microbial community metabolism is as follows: S1.1 Weigh the following raw materials in parts by weight: 10-20 parts by weight of compound microbial flora, 30-50 parts by weight of modified biochar, 3-5 parts by weight of seaweed extract, 2-5 parts by weight of graphite powder, 1.1-4.0 parts by weight of metabolic synergist, 10-15 parts by weight of ammonium sulfate and 8-12 parts by weight of potassium dihydrogen phosphate. S1.

2. Seed cultures of *Bacillus lentigines* and *Bacillus belye* were inoculated into liquid culture medium and fermented in liquid form at pH 7.0 and 30°C for 48 hours. Then, sterile sodium chloride solution (20-25% by mass) was added to the fermentation broth in 3-5 increments, with each addition increasing the sodium chloride concentration by no more than 1.0%, and the interval between two additions being 0.5-1 hour, until the sodium chloride concentration reached 3-5%, and the cumulative volume of each addition did not exceed 15% of the initial fermentation broth volume. Then, seed cultures of *Bacillus halophilus* and *Bacillus amyloliquefaciens*, pre-acclimated to sodium chloride and cultured to the late logarithmic growth stage, were inoculated and fermented for another 24 hours at pH 7.5 and 35°C to obtain a total viable count of not less than 1×10⁻⁶. 9 A mixed fermentation broth with a CFU / mL concentration and a total weight of 10-20 parts; S1.

3. The mixed fermentation broth is uniformly sprayed onto the modified biochar; then the loaded modified biochar, seaweed extract, graphite powder, ammonium sulfate, potassium dihydrogen phosphate, and rhamnolipin from the metabolic synergist are fed into a disc granulator and granulated at 35-40℃. During the granulation process, a calcium chloride solution with a concentration of 0.05-0.1mol / L is atomized and sprayed onto the surface of the material to perform surface micro-crosslinking and solidification. The amount of calcium chloride solution sprayed is 3-6% of the total mass of the granulated material. After granulation, fertilizer particles with a particle size of 2-4mm are collected by sieving, and the unqualified particles are returned to the disc granulator for regranulation. S1.

4. The remaining components of the metabolic synergist are prepared into an aqueous solution with a mass concentration of 5-10%. The aqueous solution is sprayed onto the surface of the fertilizer granules obtained in S1.3 under light-protected conditions using a fluidized bed. Finally, the mixture is fluidized and dried at 35°C to obtain a compound microbial fertilizer based on synergistic metabolism of microbial communities.

8. The method for preparing a compound microbial fertilizer based on synergistic microbial metabolism according to claim 7, characterized in that, In step S1.3, the spraying conditions are: inlet air temperature 40-45℃, outlet air temperature 30-35℃, and atomization pressure 0.15-0.25MPa.

9. The method for preparing a compound microbial fertilizer based on synergistic microbial metabolism according to claim 7, characterized in that, In step S1.4, the fluidized bed spraying conditions are: inlet air temperature 40-45℃, atomization pressure 0.8-1.2 bar, and spraying rate 5-10 mL / min.

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