Microbial compound fertilizer and preparation method thereof

Abstract

The invention relates to the technical field of microbial fertilizers, in particular to a microbial compound fertilizer and a preparation method thereof. The compound fertilizer is prepared from 10 to 15 parts of local mycorrhizal fungi fungicide, 5 to 8 parts of functional bacteria fungicide, 20 to 30 parts of enzymolysis humic acid derivative, 15 to 25 parts of reduced nitrogen phosphorus and potassium compound matrix, 10 to 20 parts of modified attapulgite-starch grafted copolymer slow-release carrier and 0.5 to 2 parts of trace elements. The preparation method comprises the steps of component pretreatment, staged mixing, double-layer coating granulation and low-temperature drying. The strain activity and adaptability are improved, nutrients are activated, stepped release is achieved, the yield of rice and the yield of wheat in saline-alkali soil are increased by 9.2% and 12.5% respectively by reducing the chemical fertilizer by 20%-30%, the saline-alkali soil can be improved, continuous cropping soil can be repaired, application is wide, cost is low, and good popularization value is achieved.

Description

Technical Field

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

[0002] With the advancement of the green development strategy in agriculture, microbial fertilizers have received widespread attention due to their ability to reduce chemical fertilizer use and improve soil ecology. However, current microbial fertilizer technologies often employ single-strain or simple compound formulations, which suffer from poor strain adaptability and weak synergistic effects with nutrients, particularly limiting their effectiveness in adverse environments such as saline-alkali land and continuously cropped soils. Furthermore, excessive application of conventional compound fertilizers leads to soil compaction and nutrient imbalance, while existing microbial fertilizer preparation processes struggle to achieve efficient synergistic release of nutrients and microorganisms.

[0003] For example, existing technologies include compound microbial fertilizers containing Bacillus subtilis, but these do not incorporate local mycorrhizal fungi, resulting in limited soil improvement effects. There are also technologies related to humic acid microbial fertilizers, but the humic acid in these fertilizers is not enzymatically hydrolyzed, leading to low nutrient activation efficiency. Therefore, developing a microbial compound fertilizer that combines synergistic effects of microorganisms, efficient nutrient utilization, and soil remediation functions is of great significance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to propose a microbial compound fertilizer and its preparation method. This compound fertilizer achieves the dual effects of increasing crop yield and improving soil by combining the synergistic effect of local mycorrhizal fungi and functional bacteria with the nutrient activation ability of enzymatic hydrolysis of humic acid derivatives and the moisture control effect of slow-release carrier.

[0005] To achieve the above objectives, the present invention provides a microbial compound fertilizer and a method for preparing the same.

[0006] A microbial compound fertilizer is prepared from the following raw materials in parts by weight: 10-15 parts of local mycorrhizal fungi inoculant, 5-8 parts of functional bacterial inoculant, 20-30 parts of enzymatic hydrolysis humic acid derivative, 15-25 parts of nitrogen, phosphorus and potassium compound matrix, 10-20 parts of slow-release carrier, and 0.5-2 parts of trace elements.

[0007] Preferably, the local mycorrhizal fungal agent is a mixed strain of Moses globulin and surface globulin isolated and domesticated from soil in Jilin Province. After domestication on modified MS medium, its adaptability to local soil is increased by more than 40%, and it can form a highly efficient symbiotic system with the roots of crops such as wheat and rice.

[0008] Preferably, the preparation process of the local mycorrhizal fungal inoculant is as follows: Step E1. Strain Isolation: Healthy soil samples from farmland and forest land in Jilin Province were collected using the "five-point sampling method". After mixing, the samples were passed through a 2mm sieve to remove impurities such as stones and roots. Mycorrhizal fungal spores were isolated using the "wet sieve decanting method". 100g of soil sample was added to 500mL of deionized water, stirred for 30min, and allowed to stand for 10min. The samples were then passed through 50-mesh, 100-mesh, and 325-mesh sieves. The residue on the 325-mesh sieve was collected and transferred to a modified PDA medium supplemented with 0.1% streptomycin to inhibit bacteria. The medium was incubated at 25℃ in the dark for 7-10 days. Spores with consistent morphology were selected. Among them, the Moses spores were spherical and pale yellow, while the surface spores were elliptical and light brown. The samples were transferred to a new medium and purified for 3 generations to obtain pure strains. Step E2. Strain Acclimation: Prepare a modified MS medium containing 0.5%-1% ginseng extract, autoclave at 121℃ for 20 min, cool, pour into plates, and inoculate pure strains of Moses globulin and terrestrial globulin into the MS medium separately. Incubate at 25-28℃ in the dark for 15-20 days, repeating for 3-4 generations. After each generation, determine the viable count using the spore counting method to ensure that the viable count in each generation is ≥1.0 × 10⁻⁶. 6 CFU / g; Step E3. Preparation of inoculum: Using a 1:1 live bacteria ratio, mix the acclimated inoculum with a concentration of 1×10⁻⁶. 7 A CFU / mL suspension of *Gastromycosis moses* and *Gastromycosis terrestris* spores was mixed with a sterile bran-vermiculite carrier at a 1:5 ratio, where the mass ratio of sterile bran to vermiculite in the carrier was 3:1. The mixture was incubated at 30℃ and 60-70% humidity in the dark for 10-15 days, turning the mixture every 3 days to promote uniform cell proliferation. After incubation, the mixture was dried at 40℃ until the moisture content was ≤12%, ground through a 100-mesh sieve, and the viable count was ≥1.0 × 10⁻⁶. 8 CFU / g yields the local mycorrhizal fungal inoculant.

[0009] Preferably, the functional bacterial agent is a compound agent of Bacillus subtilis and Bacillus licheniformis in a ratio of 3:1, which can significantly inhibit soil pathogens, such as clubroot, with an inhibition rate of over 60%.

[0010] Preferably, the preparation process of the functional bacterial agent is as follows: Step B1. Inoculate Bacillus subtilis and Bacillus licheniformis separately into LB solid medium and incubate at 37°C for 24 h. Pick single colonies and transfer them to LB liquid medium, incubate at 37°C with shaking at 180 rpm for 12 h to obtain a viable count ≥1.0 × 10⁻⁶. 8The activated bacterial culture solution was prepared at CFU / mL, wherein the LB solid medium consisted of 10 g / L tryptone, 5 g / L yeast extract, 10 g / L NaCl, 15 g / L agar, and pH 7.0-7.2. Step B2. Prepare 10L of LB liquid culture medium according to the formula (10g / L tryptone, 5g / L yeast extract, 10g / L NaCl, pH 7.0-7.2), dispense into 500mL Erlenmeyer flasks (300mL per flask), sterilize at 121℃ for 20min, and inoculate each flask with 1% activated bacterial solution (Bacillus subtilis and Bacillus licheniformis propagated separately). Incubate at 37℃ with shaking at 180r / min for 24-48h until the logarithmic growth phase (Bacillus subtilis viable count ≥3.0×10⁻⁶). 9 CFU / mL, viable Bacillus licheniformis count ≥1.0×10⁻⁶ 9 CFU / mL; Step B3. Based on the viable count results, mix Bacillus subtilis and Bacillus licheniformis bacterial solutions at a viable count ratio of 3:1. Add sterile wheat bran to the mixed bacterial solution (bacterial solution: wheat bran = 1:3 mass ratio), stir well, and let it stand for 2 hours at 30℃ and 60-70% humidity to absorb excess moisture. Dry it at 45℃ until the moisture content is ≤10%, grind it through an 80-mesh sieve, and test for a total viable count ≥2.0 × 10⁻⁶. 9 CFU / g yields a functional bacterial agent.

[0011] Preferably, the enzymatic hydrolysis humic acid derivative is prepared by fermentation and enzymatic hydrolysis of mineral-derived humic acid by Aspergillus niger, and its molecular weight is reduced to 500-1000 Da, which increases the activation rate of available phosphorus and available potassium in the soil by 25% and 30%, respectively.

[0012] Preferably, the preparation process of the enzymatic hydrolysis humic acid derivative is as follows: Step C1. Select mineral humic acid with a humic acid content ≥70% and a particle size ≤100 mesh. Remove impurities and set aside. Dry the mineral humic acid at 105℃ for 2 hours to kill potential bacteria and avoid affecting the enzymatic hydrolysis process. Step C2. Inoculate Aspergillus niger onto PDA medium (potato 200 g / L, glucose 20 g / L, agar 15 g / L, pH 5.0), incubate at 30°C for 72 h, collect spores, and wash the surface of the medium with sterile physiological saline (containing 0.1% Tween-80) to prepare a concentration of 1×10⁻⁶. 7 CFU / mL spore suspension; Step C3. Add 100g of pretreated mineral humic acid to a 1L fermenter, add 500mL of deionized water, and stir until a paste is formed; add 30mL of Aspergillus niger spore suspension (mineral humic acid: spore suspension = 100:3 mass-volume ratio), adjust the pH to 4.5-5.5, raise the temperature to 50-55℃, stir at 150r / min, and carry out aerobic fermentation for 48-72h (during which time samples are taken every 12h to test the fulvic acid content, and fermentation is stopped when the fulvic acid content is ≥30%). Step C4. After fermentation, filter the residue with an 80-mesh filter cloth. Centrifuge the filtrate at 5000 r / min for 15 min to remove incompletely degraded impurities. Concentrate the supernatant after centrifugation under reduced pressure (60℃, vacuum degree 0.08MPa) until the solid content is ≥50%. Then spray dry (inlet air 180℃, outlet air 80℃) to obtain powdered enzymatic hydrolyzed humic acid derivatives (molecular weight 500-1000 Da).

[0013] Preferably, the nitrogen, phosphorus, and potassium composite matrix adopts a reduced-volume formula, with the total nutrients reduced by 20%-30% compared to conventional fertilizers, and the mass ratio of N:P2O5:K2O is 1:0.5-0.8:0.8-1.2, which can meet the nutrient requirements of different crops.

[0014] Preferably, the preparation process of the nitrogen-phosphorus-potassium composite matrix is ​​as follows: Step C1. Raw material selection: Nitrogen source: urea (N content 46.4%, industrial grade); Phosphorus source: monoammonium phosphate (P2O5 content 44%, industrial grade); Potassium source: potassium chloride (K2O content 60%, industrial grade). Step C2. Formula calculation (based on N:P2O5:K2O=1:0.5-0.8:0.8-1.2, total nutrients are 20-30% lower than conventional formula). Step C3. Mixing and preparation: Crush urea, monoammonium phosphate, and potassium chloride separately and pass them through an 80-mesh sieve to ensure uniform particle size. Add the crushed raw materials to the mixer according to the calculated amount and stir for 30 minutes (100 r / min) until the mixture is uniform (nutrient variation coefficient ≤ 5%). Take samples to test the N, P2O5, and K2O content to ensure that the ratio of 1:0.5-0.8:0.8-1.2 and the total nutrient requirements are met, thus obtaining the nitrogen, phosphorus, and potassium composite matrix.

[0015] Preferably, the slow-release carrier is a composite of modified attapulgite and starch graft copolymer, which has a porous structure and can realize the step-by-step release of nutrients within 1-90 days, improving nutrient utilization by 20%-25%.

[0016] Preferably, the sustained-release carrier is prepared from the following raw materials and reagents: Attapulgite: purity ≥90%, particle size 50-100 mesh, pre-treated to remove impurities before use; 3-Aminopropyltriethoxysilane (APTES): analytical grade, used as a surface modifier; Corn starch: Industrial grade, amylose content ≥25%; Acrylic acid (AA): analytical grade, used as a grafting monomer; Acrylamide (AM): analytical grade, used as a comonomer; Ammonium persulfate (APS): analytical grade, used as an initiator; N,N'-Methylenebisacrylamide (MBA): analytical grade, used as a crosslinking agent; Anhydrous ethanol, deionized water: laboratory grade.

[0017] Preferably, the preparation process of the sustained-release carrier is as follows: Step A1. Preparation of modified attapulgite: APTES surface modification; Step A2. Preparation of starch graft copolymer: denoted as starch-g-(AA-AM); Step A3. Preparation of modified attapulgite-starch graft copolymer composite.

[0018] Preferably, the preparation process of the modified attapulgite in step A1 is as follows: Step A101. Attapulgite pretreatment: Take attapulgite, add deionized water, stir and disperse, let stand for 2 hours, discard the upper suspended impurities, wash repeatedly 3 times, dry at 105℃ to constant weight, grind and pass through a 200-mesh sieve, and set aside. Step A102. Silanization modification: Add the pretreated attapulgite to a mixed solvent of anhydrous ethanol and deionized water, and ultrasonically disperse it for 30 min at 300 W; add APTES, adjust the pH to 4.5-5.0 with dilute hydrochloric acid, and stir the reaction in a 60℃ water bath for 4 h. Step A103. Post-processing: After the reaction is complete, the solid is collected by filtration, washed three times with anhydrous ethanol to remove unreacted APTES, dried at 80°C for 6 hours, and ground through a 200-mesh sieve to obtain amino-modified attapulgite, denoted as M-ATP.

[0019] Preferably, the ratio of attapulgite clay to deionized water in step A101 is 100g:500mL.

[0020] Preferably, the ratio of the pretreated attapulgite, mixed solvent and APTES in step A102 is 50g:300mL:3-5g.

[0021] Preferably, the mixed solvent in step A102 is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 250 mL: 50 mL.

[0022] Preferably, the preparation process of the starch graft copolymer in step A2 is as follows: Step A201. Starch gelatinization: Add corn starch to deionized water, heat to 90°C for 30 minutes while stirring, and cool to 50°C to obtain starch paste; Step A202. Graft copolymerization: Add acrylic acid and acrylamide to starch paste, stir to dissolve, add ammonium persulfate and N,N'-methylenebisacrylamide, purge with nitrogen to remove oxygen for 10 min, and react in a water bath at 55℃ for 3 h; Step A203. Post-treatment: The reaction product was precipitated with anhydrous ethanol, filtered, and washed three times with 70% ethanol solution to remove homopolymer. It was then vacuum dried at 60°C to constant weight, ground and passed through a 100-mesh sieve to obtain the starch graft copolymer, denoted as St-g-(AA-AM)).

[0023] Preferably, the ratio of corn starch to deionized water in step A201 is 50g:200mL.

[0024] Preferably, the mass ratio of acrylic acid, acrylamide, ammonium persulfate and N,N'-methylenebisacrylamide in step A202 is 20g:10g:0.5g:0.1g.

[0025] Preferably, in step A202, the total mass of acrylic acid and acrylamide is 60% of the starch, the mass ratio of acrylic acid to acrylamide is 2:1, the ammonium persulfate accounts for 1.7% of the total mass of the monomers, and the N,N'-methylenebisacrylamide accounts for 0.3% of the total mass of the monomers.

[0026] Preferably, the preparation process of the modified attapulgite-starch graft copolymer composite in step A3 is as follows: Step A301. Mixing and dispersing: Add starch graft copolymer St-g-(AA-AM) to deionized water, stir at 50°C until completely dissolved, add amino-modified attapulgite M-ATP, and ultrasonically disperse at 400W for 40 minutes to make M-ATP uniformly dispersed in the polymer solution. Step A302. Composite reaction: Transfer the mixture to a three-necked flask and stir in a 60°C water bath for 2 hours. Utilize the amino groups on the surface of M-ATP to form hydrogen bonds or covalent interactions with the carboxyl and amide groups in the starch graft copolymer. Step A303. Drying and molding: After the reaction, the mixture is freeze-dried and then ground through a 100-mesh sieve to obtain the complex of modified attapulgite and starch graft copolymer, denoted as M-ATP / St-g-(AA-AM).

[0027] Preferably, the mass ratio of the starch graft copolymer, deionized water, and amino-modified attapulgite in step A301 is 30g:300mL:20g.

[0028] Preferably, the preparation process of the trace elements is as follows: Step D1. Raw material selection (0.5-2 parts by weight, mainly Fe, Zn, and B): Iron source: chelated ferrous sulfate (Fe content 15%, to avoid oxidation and inactivation); Zinc source: zinc sulfate (Zn content 35%, industrial grade); Boric acid source: boric acid (B content 17%, industrial grade). Step D2. Formula determination: The mixing ratio is chelated ferrous sulfate: zinc sulfate: boric acid = 5:3:2 (mass ratio). Step D3. Separate Dissolution: Add a small amount of deionized water to each raw material separately (e.g., 50g of chelated ferrous sulfate to 100mL of water), and stir until completely dissolved. Avoid direct mixing to prevent precipitation. Add each raw material solution to the mixing tank in sequence, stir evenly, and then add deionized water to make up to the required volume. Add 0.1% citric acid (chelating agent) to adjust the pH to 5.5-6.0 to prevent the precipitation of trace elements. In the microbial compound fertilizer mixing and molding step, mix the trace element mother liquor (or dried powder) with other components according to the weight proportions to ensure uniform dispersion (mixing time ≥20min).

[0029] A method for preparing a microbial compound fertilizer includes the following steps: Step S1. Preliminary preparation: pretreatment of each component to obtain pretreated microbial agent, pretreated enzymatic hydrolysis humic acid derivative, pretreated nitrogen-phosphorus-potassium composite matrix, pretreated trace elements and pretreated slow-release carrier; Step S2. Staged mixing and double-layer coating granulation: First, mix the non-microbial components, then mix the microbial agent with the remaining components, and finally perform double-layer coating and granulation; Step S3. Post-processing: Low-temperature drying and finished product testing to obtain microbial compound fertilizer.

[0030] Preferably, the preprocessing procedure in step S1 is as follows: Step S101. Microbial inoculant pretreatment: Take local mycorrhizal fungal inoculant (viable count ≥ 1.0 × 10⁻⁶). 8 10-15 parts of CFU / g, and functional bacterial agents (live count ≥2.0×10⁻⁶). 9 Add 5-8 parts of CFU / g to sterile deionized water (bacterial agent: water = 1:2 mass ratio) and stir to make a paste-like bacterial suspension (to avoid dry powder clumping and to ensure more uniform mixing later). Store in a constant temperature environment of 30℃ for later use (to prevent low or high temperature from affecting the activity of live bacteria). Step S102. Pretreatment of enzymatic hydrolysis of humic acid derivatives: Take 20-30 parts of enzymatic hydrolysis of humic acid derivatives (fulvic acid ≥30%, molecular weight 500-1000 Da), add a small amount of deionized water to make a viscous paste (solid-liquid ratio 1:1.5), and ultrasonically disperse for 15 min (power 300W) to break up agglomerated particles and ensure full integration with other components in the subsequent process; Step S103. Pretreatment of nitrogen, phosphorus and potassium composite matrix and trace elements: Take 15-25 parts of nitrogen, phosphorus and potassium composite matrix (N:P2O5:K2O=1:0.5-0.8:0.8-1.2) and 0.5-2 parts of trace elements (Fe / Zn / B chelate), respectively pulverize and pass through an 80-mesh sieve, mix them and place them in a twin-screw mixer for pre-stirring for 10 min (speed 150 r / min) to ensure uniform nutrient distribution (coefficient of variation ≤5%). Step S104. Pretreatment of the slow-release carrier: Take 10-20 parts of the modified attapulgite-starch graft copolymer composite (pore size 20-50nm), dry it at 60℃ until the moisture content is ≤8%, grind it through a 100-mesh sieve, and set it aside (to enhance the carrier's adsorption capacity for nutrients). This process pretreats each component to ensure compatibility and activity.

[0031] Preferably, the staged mixing and double-layer coating granulation process described in step S2 is as follows: Step S201. First stage: Mixing non-microbial components (to avoid early inhibition of bacterial activity). Add the pretreated nitrogen-phosphorus-potassium composite matrix-trace element mixture and slow-release carrier (accounting for 50% of the total amount, used for inner coating) to a twin-screw mixer, then add the paste-like enzymatic hydrolyzed humic acid derivative (1 / 2 amount). Adjust the stirring speed to 200 r / min and the temperature to 35℃, mix for 20 min to form a basic mixture of "nutrient-carrier-humic acid", which is recorded as material A and set aside. Step S202. Second stage: Mixing microbial agents with remaining components: Slowly add the pretreated local mycorrhizal fungal suspension and functional bacterial suspension to material A, and simultaneously add the remaining 1 / 2 of the enzymatically hydrolyzed humic acid derivative. The humic acid can encapsulate the bacterial cells and reduce mechanical damage. Reduce the stirring speed to 150 r / min, maintain the temperature at 30-35℃, and continue mixing for 30 min. During this period, take samples every 5 min to ensure that there are no obvious bacterial clumps or particle agglomerates, forming a "fully mixed slurry", which is recorded as material B. Step S203. The third stage, double-layer coating and granulation, to achieve slow release of nutrients and retention of bacterial activity: Inner coating: Material B is fed to an extrusion granulator (die orifice diameter 2-3mm). The remaining 50% of the slow-release carrier is first coated on the core of the granules (attached by high-pressure spray, thickness 0.1-0.2mm), forming a "slow-release core layer" (adsorbing nitrogen, phosphorus, and potassium nutrients, controlling the early release); Outer coating: The remaining enzymatic hydrolyzed humic acid derivative (small amount, 5% dosage) is mixed with the compound microbial agent (in bacterial suspension form), and evenly sprayed on the surface of the "slow-release core layer" (thickness 0.05-0.1mm) through a fluidized bed coating machine, forming a "bacterial agent-humic acid protective outer layer" (avoiding direct contact between bacteria and soil stress, extending the activity period); Granulation control: During the granulation process, the material temperature is controlled ≤40℃, and the granule moisture content is controlled at 15-18% (facilitating subsequent drying and not destroying bacterial activity).

[0032] Preferably, the post-processing procedure in step S3 is as follows: Step S301. Low-temperature drying (key: preserving microbial activity): Send the coated wet granules into a low-temperature drying equipment, set the inlet air temperature to 40-45℃, the outlet air temperature to 30-35℃, and the air velocity to 1.5m / s, and dry for 6-8 hours. During this period, check the moisture content of the granules every 1 hour until the moisture content is ≤10% (too high a moisture content can easily lead to mold growth of the microbial agent, while too low a moisture content can easily cause the microorganisms to become inactive). Step S302. Sieving and cooling: The dried granules are graded by passing them through a 10-mesh sieve (to remove oversized particles) and a 40-mesh sieve (to remove fine powder), and then sent to a cooler (cold air temperature 25℃, wind speed 2m / s) to cool to room temperature (to avoid residual heat from continuously affecting bacterial activity), to obtain uniform granules with a particle size of 2-3mm. Step S303. Finished Product Inspection (Ensure Compliance): Microbiological Indicators: Total viable count (local mycorrhizal fungi ≥ 1.0 × 10⁻⁶) was determined using the plate count method. 8 CFU / g+ functional bacteria ≥2.0×10 9 CFU / g), ensuring a viable bacteria survival rate of ≥85%; nutrient indicators: testing total nitrogen, phosphorus, and potassium content (≥31.5%, meeting the requirement of 20-30% reduction) and enzymatic hydrolysis humic acid derivative content (≥20%); slow-release performance: nutrient release rate determined by water immersion method (1-day release ≤20%, 30-day release ≤60%, 90-day release ≥85%); physical indicators: granule compressive strength ≥15N / granule, hygroscopicity ≤10% (placed at 25℃ and 80% relative humidity for 24 hours).

[0033] Preferably, the modified MS culture medium containing 0.5%-1% ginseng root extract in step S1 includes macroelements, microelements, iron salts, organic components, modified key components, and a coagulant.

[0034] Preferably, the macroelements include ammonium nitrate, potassium nitrate, potassium dihydrogen phosphate, magnesium sulfate, and calcium chloride.

[0035] Preferably, the trace elements include manganese sulfate, zinc sulfate, boric acid, potassium iodide, sodium molybdate, copper sulfate, and cobalt chloride.

[0036] Preferably, the iron salt is disodium diethylaminetetraacetate.

[0037] Preferably, the organic components include inositol, nicotinic acid, pyridoxine hydrochloride, thiamine hydrochloride, and sucrose.

[0038] Preferably, the modified key component is ginseng extract.

[0039] Preferably, the coagulant is agar.

[0040] Preferably, the LB liquid culture medium comprises tryptone, yeast extract, sodium chloride, and deionized water.

[0041] The beneficial effects of this invention are: This invention provides a microbial compound fertilizer and its preparation method. The invention utilizes locally acclimatized mycorrhizal fungi combined with a 3:1 live bacteria ratio of Bacillus subtilis and Bacillus licheniformis. This enhances adaptability to regional soils, promotes root absorption in crops, effectively inhibits soil-borne diseases, and exhibits strong live bacteria stability. Simultaneously, enzymatic hydrolysis of humic acid increases phosphorus and potassium activation rates, and combined with a slow-release carrier, enables nutrient release in stages. Even with reduced fertilizer use, it can still increase rice and wheat yields in saline-alkali land. Furthermore, it effectively repairs soil, improves saline-alkali land, and improves continuously cropped soils, significantly optimizing soil microecology and water and fertilizer retention capacity. Its application scope is wide, suitable for farmland, forestry, grassland restoration, and medicinal herb cultivation. Key raw materials are readily available, the preparation process is stable, and production costs are low, facilitating industrialization and promotion. Ultimately, it balances increasing farmers' income with reducing fertilizer use and controlling pollution, demonstrating broad application prospects. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0043] Preparation Example 1: A method for preparing a local fungal inoculant, comprising the following steps: S1. Strain Isolation: Healthy soil samples from farmland and forest land in Jilin Province were collected using the "five-point sampling method". After mixing, the samples were sieved through a 2mm sieve to remove impurities such as stones and roots. Mycorrhizal fungal spores were isolated using the "wet sieve decanting method". 100g of soil sample was added to 500mL of deionized water, stirred for 30min, and allowed to stand for 10min. The samples were then sieved through 50-mesh, 100-mesh, and 325-mesh sieves. The residue on the 325-mesh sieve was collected and transferred to a modified PDA medium supplemented with 0.1% streptomycin to inhibit bacteria. The medium was incubated at 25℃ in the dark for 7-10 days. Spores with consistent morphology were selected. Among them, the Moses spores were spherical and pale yellow, while the surface spores were elliptical and light brown. The samples were transferred to a new medium and purified for 3 generations to obtain pure strains. S2. Strain Acclimation: Prepare a modified MS medium containing 0.5%-1% ginseng extract, autoclave at 121℃ for 20 min, cool, pour into plates, and inoculate pure strains of Moses globulin and terrestrial globulin into the MS medium, respectively. Incubate at 25℃ in the dark for 15-20 days, for 3-4 generations. After each generation, determine the viable count using the spore counting method to ensure that the viable count in each generation is ≥1.0 × 10⁻⁶. 6 CFU / g; S3. Preparation of microbial agent: Using a 1:1 live bacteria ratio, mix the acclimated microorganisms at a concentration of 1×10⁻⁶. 7 A CFU / mL suspension of *Gastromycosis moses* and *Gastromycosis terrestris* spores was mixed with a sterile bran-vermiculite carrier at a 1:5 ratio, where the mass ratio of sterile bran to vermiculite in the carrier was 3:1. The mixture was incubated at 30℃ and 60-70% humidity in the dark for 10-15 days, turning the mixture every 3 days to promote uniform cell proliferation. After incubation, the mixture was dried at 40℃ until the moisture content was ≤12%, ground through a 100-mesh sieve, and the viable count was ≥1.0 × 10⁻⁶. 8 CFU / g yields the local mycorrhizal fungal inoculant.

[0044] Preparation Example 2: A method for preparing a local fungal inoculant, comprising the following steps: S1. Strain Isolation: Healthy soil samples from farmland and forest land in Jilin Province were collected using the "five-point sampling method". After mixing, the samples were sieved through a 2mm sieve to remove impurities such as stones and roots. Mycorrhizal fungal spores were isolated using the "wet sieve decanting method". 100g of soil sample was added to 500mL of deionized water, stirred for 30min, and allowed to stand for 10min. The samples were then sieved through 50-mesh, 100-mesh, and 325-mesh sieves. The residue on the 325-mesh sieve was collected and transferred to a modified PDA medium supplemented with 0.1% streptomycin to inhibit bacteria. The medium was incubated at 25℃ in the dark for 7-10 days. Spores with consistent morphology were selected. Among them, the Moses spores were spherical and pale yellow, while the surface spores were elliptical and light brown. The samples were transferred to a new medium and purified for 3 generations to obtain pure strains. S2. Strain Acclimation: Prepare a modified MS medium containing 0.5%-1% ginseng extract, autoclave at 121℃ for 20 min, cool, pour into plates, and inoculate pure strains of Moses globulin and terrestrial globulin into the MS medium, respectively. Incubate at 28℃ in the dark for 15-20 days, for 3-4 generations. After each generation, determine the viable count using the spore counting method to ensure that the viable count in each generation is ≥1.0 × 10⁻⁶. 6 CFU / g; S3. Preparation of microbial agent: Using a 1:1 live bacteria ratio, mix the acclimated microorganisms at a concentration of 1×10⁻⁶. 7 A CFU / mL suspension of *Gastromycosis moses* and *Gastromycosis terrestris* spores was mixed with a sterile bran-vermiculite carrier at a 1:5 ratio, where the mass ratio of sterile bran to vermiculite in the carrier was 3:1. The mixture was incubated at 30℃ and 60-70% humidity in the dark for 10-15 days, turning the mixture every 3 days to promote uniform cell proliferation. After incubation, the mixture was dried at 40℃ until the moisture content was ≤12%, ground through a 100-mesh sieve, and the viable count was ≥1.0 × 10⁻⁶. 8 CFU / g yields the local mycorrhizal fungal inoculant.

[0045] Preparation Example 3: A method for preparing a functional bacterial agent, comprising the following steps: S1. Bacillus subtilis and Bacillus licheniformis were inoculated into LB solid medium and cultured at 37°C for 24 h. Single colonies were then transferred to LB liquid medium and cultured at 37°C with shaking at 180 rpm for 12 h to obtain a viable count ≥1.0 × 10⁻⁶. 8 The activated bacterial culture solution was prepared at CFU / mL, wherein the LB solid medium consisted of 10 g / L tryptone, 5 g / L yeast extract, 10 g / L NaCl, 15 g / L agar, and pH 7.0-7.2. S2. Prepare 10L of LB liquid culture medium according to the formula (10g / L tryptone, 5g / L yeast extract, 10g / L NaCl, pH 7.0-7.2), dispense into 500mL Erlenmeyer flasks (300mL per flask), sterilize at 121℃ for 20min, and inoculate each flask with 1% activated bacterial solution (Bacillus subtilis and Bacillus licheniformis propagated separately). Incubate at 37℃ with shaking at 180r / min for 24-48h until the logarithmic growth phase (Bacillus subtilis viable count ≥3.0×10⁻⁶). 9 CFU / mL, viable Bacillus licheniformis count ≥1.0×10⁻⁶ 9 CFU / mL; S3. Based on the viable count results, Bacillus subtilis and Bacillus licheniformis bacterial solutions were mixed at a viable count ratio of 3:1. Sterile wheat bran was added to the mixed solution (bacterial solution: wheat bran = 1:3 mass ratio), and after thorough mixing, the solution was allowed to stand for 2 hours at 30℃ and 60-70% humidity to absorb excess moisture. It was then dried at 45℃ until the moisture content was ≤10%, ground through an 80-mesh sieve, and the total viable count was determined to be ≥2.0 × 10⁻⁶. 9 CFU / g yields a functional bacterial agent.

[0046] Preparation Example 4: A method for preparing enzymatically hydrolyzed humic acid derivatives, comprising the following steps: S1. Select mineral humic acid with a humic acid content ≥70% and a particle size ≤100 mesh. Remove impurities and set aside. Dry the mineral humic acid at 105℃ for 2 hours to kill potential bacteria and avoid affecting the enzymatic hydrolysis process. S2. Inoculate Aspergillus niger onto PDA medium (potato 200 g / L, glucose 20 g / L, agar 15 g / L, pH 5.0), incubate at 30°C for 72 h, collect spores, and wash the surface of the medium with sterile physiological saline (containing 0.1% Tween-80) to prepare a concentration of 1×10⁻⁶. 7 CFU / mL spore suspension; S3. Add 100g of pretreated mineral humic acid to a 1L fermenter, add 500mL of deionized water, and stir until a paste is formed; add 30mL of Aspergillus niger spore suspension (mineral humic acid: spore suspension = 100:3 mass-volume ratio), adjust the pH to 4.5, raise the temperature to 50℃, stir at 150r / min, and carry out aerobic fermentation for 48-72h (during which time samples are taken every 12h to test the fulvic acid content, and fermentation is stopped when the fulvic acid content is ≥30%). S4. After fermentation, filter the residue with an 80-mesh filter cloth. Centrifuge the filtrate at 5000 r / min for 15 min to remove incompletely degraded impurities. Concentrate the supernatant after centrifugation under reduced pressure (60℃, vacuum degree 0.08MPa) until the solid content is ≥50%. Then spray dry (inlet air 180℃, outlet air 80℃) to obtain powdered enzymatic hydrolyzed humic acid derivatives (molecular weight 500-1000 Da).

[0047] Preparation Example 5: A method for preparing enzymatically hydrolyzed humic acid derivatives, comprising the following steps: S1. Select mineral humic acid with a humic acid content ≥70% and a particle size ≤100 mesh. Remove impurities and set aside. Dry the mineral humic acid at 105℃ for 2 hours to kill potential bacteria and avoid affecting the enzymatic hydrolysis process. S2. Inoculate Aspergillus niger onto PDA medium (potato 200 g / L, glucose 20 g / L, agar 15 g / L, pH 5.0), incubate at 30°C for 72 h, collect spores, and wash the surface of the medium with sterile physiological saline (containing 0.1% Tween-80) to prepare a concentration of 1×10⁻⁶. 7 CFU / mL spore suspension; S3. Add 100g of pretreated mineral humic acid to a 1L fermenter, add 500mL of deionized water, and stir until a paste is formed; add 30mL of Aspergillus niger spore suspension (mineral humic acid: spore suspension = 100:3 mass-volume ratio), adjust the pH to 5.5, raise the temperature to 55℃, stir at 150r / min, and carry out aerobic fermentation for 48-72h (during which time samples are taken every 12h to test the fulvic acid content, and fermentation is stopped when the fulvic acid content is ≥30%). S4. After fermentation, filter the residue with an 80-mesh filter cloth. Centrifuge the filtrate at 5000 r / min for 15 min to remove incompletely degraded impurities. Concentrate the supernatant after centrifugation under reduced pressure (60℃, vacuum degree 0.08MPa) until the solid content is ≥50%. Then spray dry (inlet air 180℃, outlet air 80℃) to obtain powdered enzymatic hydrolyzed humic acid derivatives (molecular weight 500-1000 Da).

[0048] Preparation Example 6: A method for preparing a nitrogen-phosphorus-potassium composite matrix, comprising the following steps: S1. Raw material selection: Nitrogen source: urea (N content 46.4%, industrial grade), Phosphorus source: monoammonium phosphate (P2O5 content 44%, industrial grade), Potassium source: potassium chloride (K2O content 60%, industrial grade). S2. Formula calculation (based on N:P2O5:K2O=1:0.5:0.8, total nutrients are 20-30% lower than conventional formulas); S3. Mixing and preparation: Urea, monoammonium phosphate, and potassium chloride are crushed separately and passed through an 80-mesh sieve to ensure uniform particle size. The crushed raw materials are added to the mixer according to the calculated amount and stirred for 30 minutes (100 r / min) until they are uniformly mixed (nutrient variation coefficient ≤ 5%). Samples are taken to test the N, P2O5, and K2O contents to ensure that they meet the ratio of 1:0.5:0.8 and the total nutrient requirements, thus obtaining the nitrogen, phosphorus, and potassium composite matrix.

[0049] Preparation Example 7: A method for preparing a nitrogen-phosphorus-potassium composite matrix, comprising the following steps: S1. Raw material selection: Nitrogen source: urea (N content 46.4%, industrial grade), Phosphorus source: monoammonium phosphate (P2O5 content 44%, industrial grade), Potassium source: potassium chloride (K2O content 60%, industrial grade). S2. Formula calculation (based on N:P2O5:K2O=1:0.8:1.2, total nutrients are 20-30% lower than conventional formulas); S3. Mixing and preparation: Urea, monoammonium phosphate, and potassium chloride are crushed separately and passed through an 80-mesh sieve to ensure uniform particle size. The crushed raw materials are added to the mixer according to the calculated amount and stirred for 30 minutes (100 r / min) until they are uniformly mixed (nutrient variation coefficient ≤ 5%). Samples are taken to test the N, P2O5, and K2O contents to ensure that they meet the ratio of 1:0.8:1.2 and the total nutrient requirements, thus obtaining the nitrogen, phosphorus, and potassium composite matrix.

[0050] Preparation Example 8: A method for preparing a sustained-release carrier, comprising the following steps: S1. Preparation of modified attapulgite: APTES surface modification; Attapulgite pretreatment: Take 100g of attapulgite and add 500mL of deionized water. Stir to disperse and let stand for 2 hours. Discard the upper suspended impurities, wash 3 times, dry at 105℃ to constant weight, grind and pass through a 200-mesh sieve for later use. Silanization modification: 50g of pretreated attapulgite clay was added to a mixed solvent of 300mL anhydrous ethanol and deionized water and ultrasonically dispersed for 30min at 300W power; 3g of APTES was added, the pH was adjusted to 4.5 with dilute hydrochloric acid, and the reaction was stirred in a 60℃ water bath for 4h. The mixed solvent of anhydrous ethanol and deionized water was obtained by mixing anhydrous ethanol and deionized water at a volume ratio of 250mL:50mL. Post-processing: After the reaction was completed, the solid was collected by filtration, washed three times with anhydrous ethanol to remove unreacted APTES, dried at 80°C for 6 hours, and ground through a 200-mesh sieve to obtain amino-modified attapulgite, denoted as M-ATP. S2. Preparation of starch graft copolymer: denoted as starch-g-(AA-AM); Starch gelatinization: Take 50g of corn starch and add 200mL of deionized water. Heat to 90℃ and gelatinize for 30min while stirring. Cool to 50℃ to obtain starch paste. Graft copolymerization: Add 20g of acrylic acid and 10g of acrylamide to starch paste, stir to dissolve, add 0.5g of ammonium persulfate and 0.1g of N,N'-methylenebisacrylamide, purge with nitrogen for 10min to remove oxygen, and react in a water bath at 55℃ for 3h. The total mass of acrylic acid and acrylamide is 60% of the starch, the mass ratio of acrylic acid to acrylamide is 2:1, ammonium persulfate accounts for 1.7% of the total mass of monomers, and N,N'-methylenebisacrylamide accounts for 0.3% of the total mass of monomers. Post-processing: The reaction product was precipitated with anhydrous ethanol, filtered, and washed three times with 70% ethanol solution to remove homopolymer. It was then vacuum dried at 60°C to constant weight, ground and passed through a 100-mesh sieve to obtain the starch graft copolymer, denoted as St-g-(AA-AM)).

[0051] S3. Preparation of modified attapulgite-starch graft copolymer composite: Mixing and dispersing: Take 30g of starch graft copolymer St-g-(AA-AM) and add it to 300mL of deionized water. Stir at 50℃ until completely dissolved. Add 20g of amino-modified attapulgite M-ATP and ultrasonically disperse at 400W for 40min to make M-ATP uniformly dispersed in the polymer solution. Composite reaction: The mixture was transferred to a three-necked flask and stirred in a water bath at 60°C for 2 hours. The amino groups on the surface of M-ATP formed hydrogen bonds or covalent interactions with the carboxyl and amide groups in the starch graft copolymer. Drying and molding: After the reaction, the mixture is freeze-dried and then ground through a 100-mesh sieve to obtain the complex of modified attapulgite and starch graft copolymer, denoted as M-ATP / St-g-(AA-AM), which is the sustained-release carrier.

[0052] Preparation Example 9: A method for preparing a sustained-release carrier, comprising the following steps: S1. Preparation of modified attapulgite: APTES surface modification; Attapulgite pretreatment: Take 100g of attapulgite and add 500mL of deionized water. Stir to disperse and let stand for 2 hours. Discard the upper suspended impurities, wash 3 times, dry at 105℃ to constant weight, grind and pass through a 200-mesh sieve for later use. Silanization modification: 50g of pretreated attapulgite clay was added to a mixed solvent of 300mL anhydrous ethanol and deionized water and ultrasonically dispersed for 30min at 300W power; 5g of APTES was added, and the pH was adjusted to 4.5-5.0 with dilute hydrochloric acid. The mixture was stirred in a water bath at 60℃ for 4h. The mixed solvent of anhydrous ethanol and deionized water was obtained by mixing anhydrous ethanol and deionized water at a volume ratio of 250mL:50mL. Post-processing: After the reaction was completed, the solid was collected by filtration, washed three times with anhydrous ethanol to remove unreacted APTES, dried at 80°C for 6 hours, and ground through a 200-mesh sieve to obtain amino-modified attapulgite, denoted as M-ATP. S2. Preparation of starch graft copolymer: denoted as starch-g-(AA-AM); Starch gelatinization: Take 50g of corn starch and add 200mL of deionized water. Heat to 90℃ and gelatinize for 30min while stirring. Cool to 50℃ to obtain starch paste. Graft copolymerization: Add 20g of acrylic acid and 10g of acrylamide to starch paste, stir to dissolve, add 0.5g of ammonium persulfate and 0.1g of N,N'-methylenebisacrylamide, purge with nitrogen for 10min to remove oxygen, and react in a water bath at 55℃ for 3h. The total mass of acrylic acid and acrylamide is 60% of the starch, the mass ratio of acrylic acid to acrylamide is 2:1, ammonium persulfate accounts for 1.7% of the total mass of monomers, and N,N'-methylenebisacrylamide accounts for 0.3% of the total mass of monomers. Post-processing: The reaction product was precipitated with anhydrous ethanol, filtered, and washed three times with 70% ethanol solution to remove homopolymer. It was then vacuum dried at 60°C to constant weight, ground and passed through a 100-mesh sieve to obtain the starch graft copolymer, denoted as St-g-(AA-AM)).

[0053] S3. Preparation of modified attapulgite-starch graft copolymer composite: Mixing and dispersing: Take 30g of starch graft copolymer St-g-(AA-AM) and add it to 300mL of deionized water. Stir at 50℃ until completely dissolved. Add 20g of amino-modified attapulgite M-ATP and ultrasonically disperse at 400W for 40min to make M-ATP uniformly dispersed in the polymer solution. Composite reaction: The mixture was transferred to a three-necked flask and stirred in a water bath at 60°C for 2 hours. The amino groups on the surface of M-ATP formed hydrogen bonds or covalent interactions with the carboxyl and amide groups in the starch graft copolymer. Drying and molding: After the reaction, the mixture is freeze-dried and then ground through a 100-mesh sieve to obtain the complex of modified attapulgite and starch graft copolymer, denoted as M-ATP / St-g-(AA-AM), which is the sustained-release carrier.

[0054] Preparation Example 10: A method for preparing trace elements, comprising the following steps: S1. Raw material selection (0.5 parts by weight, mainly Fe, Zn, and B): Iron source: chelated ferrous sulfate (Fe content 15%, to avoid oxidation and inactivation), Zinc source: zinc sulfate (Zn content 35%, industrial grade), Boric acid source: boric acid (B content 17%, industrial grade). S2. Formula determined, mixing ratio is chelated ferrous sulfate: zinc sulfate: boric acid = 5:3:2 (mass ratio); Step D3. Separate Dissolution: Add a small amount of deionized water to each raw material separately (e.g., 50g of chelated ferrous sulfate to 100mL of water), and stir until completely dissolved. Avoid direct mixing to prevent precipitation. Add each raw material solution to the mixing tank in sequence, stir evenly, and then add deionized water to make up to the required volume. Add 0.1% citric acid (chelating agent) to adjust the pH to 5.5 to prevent the precipitation of trace elements. In the microbial compound fertilizer mixing and molding step, mix the trace element mother liquor (or dried powder) with other components according to the weight proportions to ensure uniform dispersion (mixing time ≥20min).

[0055] Preparation Example 11: A method for preparing trace elements, comprising the following steps: S1. Raw material selection (2 parts by weight, mainly Fe, Zn, and B): Iron source: chelated ferrous sulfate (Fe content 15%, to avoid oxidation and failure), Zinc source: zinc sulfate (Zn content 35%, industrial grade), Boric acid (B content 17%, industrial grade). S2. Formula determined, mixing ratio is chelated ferrous sulfate: zinc sulfate: boric acid = 5:3:2 (mass ratio); Step D3. Separate Dissolution: Add a small amount of deionized water to each raw material separately (e.g., 50g of chelated ferrous sulfate to 100mL of water), and stir until completely dissolved. Avoid direct mixing to prevent precipitation. Add each raw material solution to the mixing tank in sequence, stir evenly, and then add deionized water to make up to the required volume. Add 0.1% citric acid (chelating agent) to adjust the pH to 6.0 to prevent the precipitation of trace elements. In the microbial compound fertilizer mixing and molding step, mix the trace element mother liquor (or dried powder) with other components according to the weight proportions to ensure uniform dispersion (mixing time ≥20min).

[0056] Example 1: A method for preparing a microbial compound fertilizer, comprising the following steps: S1. Preliminary preparation: Pretreatment of each component to obtain pretreated microbial agent, pretreated enzymatically hydrolyzed humic acid derivative, pretreated nitrogen-phosphorus-potassium composite matrix, pretreated trace elements, and pretreated slow-release carrier: Microbial inoculant pretreatment: Take the local mycorrhizal fungal inoculant prepared in the preparation example (viable count ≥ 1.0 × 10⁻⁶). 8 10 portions of CFU / g and the functional bacterial agent prepared in the preparation example (live count ≥ 2.0 × 10⁻⁶). 9 Five portions of CFU / g were added to sterile deionized water (bacterial agent: water = 1:2 mass ratio) and stirred to form a paste-like bacterial suspension (to avoid clumping of dry powder and to ensure more uniform mixing later). The suspension was then placed in a constant temperature environment of 30℃ for later use (to prevent low or high temperatures from affecting the activity of live bacteria). Pretreatment of enzymatic hydrolyzed humic acid derivatives: Take 20 portions of enzymatic hydrolyzed humic acid derivatives (fulvic acid ≥30%, molecular weight 500-1000 Da) prepared in the preparation example, add a small amount of deionized water to make a viscous paste (solid-liquid ratio 1:1.5), and ultrasonically disperse for 15 min (power 300W) to break up agglomerated particles and ensure that they are fully integrated with other components in the subsequent process. Nitrogen-phosphorus-potassium composite matrix and trace element pretreatment: Take 15 parts of nitrogen-phosphorus-potassium composite matrix (N:P2O5:K2O=1:0.5:0.8) and 0.5 parts of trace elements (Fe / Zn / B chelate) prepared in the preparation example, pulverize them separately through an 80-mesh sieve, mix them and place them in a twin-screw mixer for pre-stirring for 10 min (speed 150 r / min) to ensure uniform nutrient distribution (coefficient of variation ≤5%). Pretreatment of the sustained-release carrier: Take 10 portions of the sustained-release carrier modified attapulgite-starch graft copolymer composite (pore size 20-50nm) prepared in the preparation example, dry at 60℃ until the moisture content is ≤8%, grind through a 100-mesh sieve, and set aside (to enhance the carrier's adsorption capacity for nutrients). This process pretreats each component to ensure compatibility and activity. S2. Staged mixing and double-layer coating granulation: First, the non-microbial components are mixed, then the microbial agent is mixed with the remaining components, and finally, double-layer coating and granulation are performed. In the first stage, non-microbial components are mixed (to avoid early inhibition of bacterial activity). The pretreated nitrogen, phosphorus, and potassium composite matrix-trace element mixture and the slow-release carrier (accounting for 50% of the total amount, used for inner coating) are added to a twin-screw mixer. Then, the paste-like enzymatic hydrolyzed humic acid derivative (1 / 2 of the amount) is added. The stirring speed is adjusted to 200 r / min and the temperature to 35℃. The mixture is mixed for 20 min to form a basic mixture of "nutrients-carrier-humic acid", which is designated as material A and set aside for later use. In the second stage, the microbial agent is mixed with the remaining components: the pretreated local mycorrhizal fungal suspension and functional bacterial suspension are slowly added to the A material, and the remaining 1 / 2 of the enzymatic hydrolyzed humic acid derivative is added at the same time. The humic acid can encapsulate the fungal cells and reduce mechanical damage. The stirring speed is reduced to 150 r / min and the temperature is maintained at 30℃. Mixing continues for 30 min. During this period, samples are taken every 5 min to ensure that there are no obvious fungal clusters or particle clumps, forming a "fully mixed slurry", which is recorded as the B material. The third stage involves double-layer coating and granulation to achieve slow-release of nutrients and retention of bacterial activity: Inner coating: Material B is fed to an extrusion granulator (die diameter 2-3mm), where the remaining 50% of the slow-release carrier is first coated onto the core of the granules (attached by high-pressure spray, thickness 0.1-0.2mm), forming a "slow-release core layer" (adsorbing nitrogen, phosphorus, and potassium nutrients, controlling early release); Outer coating: The remaining enzymatically hydrolyzed humic acid derivatives (small amount, 5% dosage) are mixed with the compound microbial agent (in bacterial suspension form), and evenly sprayed onto the surface of the "slow-release core layer" (thickness 0.05-0.1mm) using a fluidized bed coating machine, forming a "bacterial agent-humic acid protective outer layer" (preventing direct contact between bacteria and soil stress, extending the activity period); Granulation control: During granulation, the material temperature is controlled ≤40℃, and the granule moisture content is controlled at 15-18% (facilitating subsequent drying and not damaging bacterial activity). S3. Post-processing: Low-temperature drying and finished product testing to obtain microbial compound fertilizer: Low-temperature drying (key: preserving microbial activity): The coated wet granules are sent into a low-temperature drying equipment, with the inlet air temperature set to 40℃, the outlet air temperature to 30℃, and the air velocity to 1.5m / s. The drying process lasts for 6 hours, during which the moisture content of the granules is checked every hour until the moisture content is ≤10% (too high a moisture content can easily lead to mold growth of the microbial agent, while too low a moisture content can easily cause the microorganisms to become inactive). Screening and cooling: The dried granules are graded by passing them through a 10-mesh sieve (to remove oversized particles) and a 40-mesh sieve (to remove fine powder), and then sent to a cooler (cold air temperature 25℃, wind speed 2m / s) to cool to room temperature (to avoid residual heat from continuously affecting bacterial activity), resulting in uniform granules with a particle size of 2-3mm, which is the microbial compound fertilizer.

[0057] Example 2: A method for preparing a microbial compound fertilizer, comprising the following steps: S1. Preliminary preparation: Pretreatment of each component to obtain pretreated microbial agent, pretreated enzymatically hydrolyzed humic acid derivative, pretreated nitrogen-phosphorus-potassium composite matrix, pretreated trace elements, and pretreated slow-release carrier: Microbial inoculant pretreatment: Take the local mycorrhizal fungal inoculant prepared in the preparation example (viable count ≥ 1.0 × 10⁻⁶). 8 12.5 portions of CFU / g and the functional bacterial agent prepared in the preparation example (viable count ≥ 2.0 × 10⁻⁶). 9 6.5 parts of CFU / g were added to sterile deionized water (bacterial agent: water = 1:2 mass ratio) and stirred to make a paste-like bacterial suspension (to avoid clumping of dry powder and to ensure more uniform mixing later). The suspension was then placed in a constant temperature environment of 30℃ for later use (to prevent low or high temperature from affecting the activity of live bacteria). Pretreatment of enzymatic hydrolyzed humic acid derivatives: Take 25 portions of enzymatic hydrolyzed humic acid derivatives (fulvic acid ≥30%, molecular weight 500-1000 Da) prepared in the preparation example, add a small amount of deionized water to make a viscous paste (solid-liquid ratio 1:1.5), and ultrasonically disperse for 15 min (power 300W) to break up agglomerated particles and ensure that they are fully integrated with other components in the subsequent process. Nitrogen-phosphorus-potassium composite matrix and trace element pretreatment: Take 20 parts of nitrogen-phosphorus-potassium composite matrix (N:P2O5:K2O=1:0.65:1.0) and 1.2 parts of trace elements (Fe / Zn / B chelate) prepared in the preparation example, pulverize them through an 80-mesh sieve, mix them and place them in a twin-screw mixer for pre-stirring for 10 min (speed 150 r / min) to ensure uniform nutrient distribution (coefficient of variation ≤5%). Pretreatment of the sustained-release carrier: Take 15 portions of the sustained-release carrier modified attapulgite-starch graft copolymer composite (pore size 20-50nm) prepared in the preparation example, dry them at 60℃ until the moisture content is ≤8%, grind them through a 100-mesh sieve, and set them aside (to enhance the carrier's adsorption capacity for nutrients). This process pretreats each component to ensure compatibility and activity. S2. Staged mixing and double-layer coating granulation: First, the non-microbial components are mixed, then the microbial agent is mixed with the remaining components, and finally, double-layer coating and granulation are performed. In the first stage, non-microbial components are mixed (to avoid early inhibition of bacterial activity). The pretreated nitrogen, phosphorus, and potassium composite matrix-trace element mixture and the slow-release carrier (accounting for 50% of the total amount, used for inner coating) are added to a twin-screw mixer. Then, the paste-like enzymatic hydrolyzed humic acid derivative (1 / 2 of the amount) is added. The stirring speed is adjusted to 200 r / min and the temperature to 35℃. The mixture is mixed for 20 min to form a basic mixture of "nutrients-carrier-humic acid", which is designated as material A and set aside for later use. In the second stage, the microbial agent is mixed with the remaining components: the pretreated local mycorrhizal fungal suspension and functional bacterial suspension are slowly added to the A material, and the remaining 1 / 2 of the enzymatic hydrolyzed humic acid derivative is added at the same time. The humic acid can encapsulate the fungal cells and reduce mechanical damage. The stirring speed is reduced to 150 r / min and the temperature is maintained at 32℃. Mixing continues for 30 min. During this period, samples are taken every 5 min to ensure that there are no obvious fungal clusters or particle clumps. The "all-component mixed slurry" is formed and is recorded as the B material. The third stage involves double-layer coating and granulation to achieve slow-release of nutrients and retention of bacterial activity: Inner coating: Material B is fed to an extrusion granulator (die diameter 2-3mm), where the remaining 50% of the slow-release carrier is first coated onto the core of the granules (attached by high-pressure spray, thickness 0.1-0.2mm), forming a "slow-release core layer" (adsorbing nitrogen, phosphorus, and potassium nutrients, controlling early release); Outer coating: The remaining enzymatically hydrolyzed humic acid derivatives (small amount, 5% dosage) are mixed with the compound microbial agent (in bacterial suspension form), and evenly sprayed onto the surface of the "slow-release core layer" (thickness 0.05-0.1mm) using a fluidized bed coating machine, forming a "bacterial agent-humic acid protective outer layer" (preventing direct contact between bacteria and soil stress, extending the activity period); Granulation control: During granulation, the material temperature is controlled ≤40℃, and the granule moisture content is controlled at 15-18% (facilitating subsequent drying and not damaging bacterial activity). S3. Post-processing: Low-temperature drying and finished product testing to obtain microbial compound fertilizer: Low-temperature drying (key: preserving microbial activity): The coated wet granules are sent into a low-temperature drying equipment, with the inlet air temperature set to 42℃, the outlet air temperature to 32℃, and the air velocity to 1.5m / s. The drying process lasts for 7 hours, during which the moisture content of the granules is checked every hour until the moisture content is ≤10% (too high a moisture content can easily lead to mold growth of the microbial agent, while too low a moisture content can easily cause the microorganisms to become inactive). Screening and cooling: The dried granules are graded by passing them through a 10-mesh sieve (to remove oversized particles) and a 40-mesh sieve (to remove fine powder), and then sent to a cooler (cold air temperature 25℃, wind speed 2m / s) to cool to room temperature (to avoid residual heat from continuously affecting bacterial activity), resulting in uniform granules with a particle size of 2-3mm, which is the microbial compound fertilizer.

[0058] Example 3: A method for preparing a microbial compound fertilizer, comprising the following steps: S1. Preliminary preparation: Pretreatment of each component to obtain pretreated microbial agent, pretreated enzymatically hydrolyzed humic acid derivative, pretreated nitrogen-phosphorus-potassium composite matrix, pretreated trace elements, and pretreated slow-release carrier: Microbial inoculant pretreatment: Take the local mycorrhizal fungal inoculant prepared in the preparation example (viable count ≥ 1.0 × 10⁻⁶). 8 15 samples of CFU / g and the functional bacterial agent prepared in the preparation example (live count ≥ 2.0 × 10⁻⁶) 9 Eight portions of CFU / g were added to sterile deionized water (bacterial agent: water = 1:2 mass ratio) and stirred to form a paste-like bacterial suspension (to avoid clumping of dry powder and to ensure more uniform mixing later). The suspension was then placed in a constant temperature environment of 30℃ for later use (to prevent low or high temperatures from affecting the activity of live bacteria). Pretreatment of enzymatic hydrolyzed humic acid derivatives: Take 30 portions of enzymatic hydrolyzed humic acid derivatives (fulvic acid ≥30%, molecular weight 500-1000 Da) prepared in the preparation example, add a small amount of deionized water to make a viscous paste (solid-liquid ratio 1:1.5), and ultrasonically disperse for 15 min (power 300W) to break up agglomerated particles and ensure that they are fully integrated with other components in the subsequent process. Nitrogen-phosphorus-potassium composite matrix and trace element pretreatment: Take 25 parts of nitrogen-phosphorus-potassium composite matrix (N:P2O5:K2O=1:0.8:1.2) and 2 parts of trace elements (Fe / Zn / B chelate) prepared in the preparation example, pulverize them through an 80-mesh sieve, mix them and place them in a twin-screw mixer for pre-stirring for 10 min (speed 150 r / min) to ensure uniform nutrient distribution (coefficient of variation ≤5%). Pretreatment of the sustained-release carrier: Take 20 portions of the sustained-release carrier modified attapulgite-starch graft copolymer composite (pore size 20-50nm) prepared in the preparation example, dry at 60℃ until the moisture content is ≤8%, grind through a 100-mesh sieve, and set aside (to enhance the carrier's adsorption capacity for nutrients). This process pretreats each component to ensure compatibility and activity. S2. Staged mixing and double-layer coating granulation: First, the non-microbial components are mixed, then the microbial agent is mixed with the remaining components, and finally, double-layer coating and granulation are performed. In the first stage, non-microbial components are mixed (to avoid early inhibition of bacterial activity). The pretreated nitrogen, phosphorus, and potassium composite matrix-trace element mixture and the slow-release carrier (accounting for 50% of the total amount, used for inner coating) are added to a twin-screw mixer. Then, the paste-like enzymatic hydrolyzed humic acid derivative (1 / 2 of the amount) is added. The stirring speed is adjusted to 200 r / min and the temperature to 35℃. The mixture is mixed for 20 min to form a basic mixture of "nutrients-carrier-humic acid", which is designated as material A and set aside for later use. In the second stage, the microbial agent is mixed with the remaining components: the pretreated local mycorrhizal fungal suspension and functional bacterial suspension are slowly added to the A material, and the remaining 1 / 2 of the enzymatic hydrolyzed humic acid derivative is added at the same time. The humic acid can coat the fungal cells and reduce mechanical damage. The stirring speed is reduced to 150 r / min and the temperature is maintained at 35℃. Mixing continues for 30 min. During this period, samples are taken every 5 min to ensure that there are no obvious fungal clusters or particle clumps, forming a "fully mixed slurry", which is recorded as the B material. The third stage involves double-layer coating and granulation to achieve slow-release of nutrients and retention of bacterial activity: Inner coating: Material B is fed to an extrusion granulator (die diameter 2-3mm), where the remaining 50% of the slow-release carrier is first coated onto the core of the granules (attached by high-pressure spray, thickness 0.1-0.2mm), forming a "slow-release core layer" (adsorbing nitrogen, phosphorus, and potassium nutrients, controlling early release); Outer coating: The remaining enzymatically hydrolyzed humic acid derivatives (small amount, 5% dosage) are mixed with the compound microbial agent (in bacterial suspension form), and evenly sprayed onto the surface of the "slow-release core layer" (thickness 0.05-0.1mm) using a fluidized bed coating machine, forming a "bacterial agent-humic acid protective outer layer" (preventing direct contact between bacteria and soil stress, extending the activity period); Granulation control: During granulation, the material temperature is controlled ≤40℃, and the granule moisture content is controlled at 15-18% (facilitating subsequent drying and not damaging bacterial activity). S3. Post-processing: Low-temperature drying and finished product testing to obtain microbial compound fertilizer: Low-temperature drying (key: preserving microbial activity): The coated wet granules are sent into a low-temperature drying equipment, with the inlet air temperature set to 45℃, the outlet air temperature to 35℃, and the air velocity to 1.5m / s. The drying process lasts for 8 hours, during which the moisture content of the granules is checked every hour until the moisture content is ≤10% (too high a moisture content can easily lead to mold growth of the microbial agent, while too low a moisture content can easily cause the microorganisms to become inactive). Screening and cooling: The dried granules are graded by passing them through a 10-mesh sieve (to remove oversized particles) and a 40-mesh sieve (to remove fine powder), and then sent to a cooler (cold air temperature 25℃, wind speed 2m / s) to cool to room temperature (to avoid residual heat from continuously affecting bacterial activity), resulting in uniform granules with a particle size of 2-3mm, which is the microbial compound fertilizer.

[0059] Comparative Example 1: Compared with Example 1, this comparative example did not add local mycorrhizal fungi inoculants during the preparation of microbial compound fertilizer. All other steps and parameters were the same, and will not be repeated here. The final microbial compound fertilizer was obtained.

[0060] Comparative Example 2: Compared with Example 1, this comparative example only replaces "compound microbial agent of Bacillus subtilis: Bacillus licheniformis = 3:1" with "single Bacillus subtilis". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a microbial compound fertilizer is obtained.

[0061] Comparative Example 3: Compared with Example 1, this comparative example only replaces "enzymatic hydrolysis of humic acid derivatives" with "unenzymatic hydrolysis of ordinary mineral humic acid (humic acid content of 70%, not hydrolyzed by Aspergillus niger)". All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is microbial compound fertilizer.

[0062] Comparative Example 4: Compared with Example 1, this comparative example only replaces "modified attapulgite-starch graft copolymer slow-release carrier" with "ordinary unmodified attapulgite". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, microbial compound fertilizer is obtained.

[0063] Comparative Example 5: Compared with Example 1, this comparative example only omits the "staged mixing + double-layer coating" and adopts "one-time mixing of all components + conventional extrusion granulation (without inner slow-release carrier and outer humic acid protection)". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a microbial compound fertilizer is obtained.

[0064] Comparative Example 6: This comparative example is a conventional fertilizer control (rice uses N-P2O5-K2O=15-15-15 compound fertilizer, application rate 450 kg / hm²; wheat uses conventional N-P2O5-K2O=17-20-5 compound fertilizer, application rate 600 kg / hm²).

[0065] Performance testing: 1. Microbial activity test (viable bacteria count and survival rate) Test method: Plate count method as specified in NY / T 1847-2020 Determination of viable bacteria count in microbial fertilizers; Finished product viable count: Detects the total viable count of local mycorrhizal fungi (CFU / g) and functional bacteria (CFU / g); Storage survival rate: After the finished product is stored at 30℃ and RH70% for 6 months, the number of viable bacteria is tested again, and the survival rate is calculated as (number of viable bacteria after storage / initial number of viable bacteria × 100%).

[0066] 2. Crop yield and agronomic trait testing Test subjects: Rice (variety "Yongyou"), saline-alkali land wheat (variety "Cangmai 6002"); Planting conditions: paddy fields and saline-alkali land; plot area 200m²; 3 replicates. Test method: Yield: Actual yield of plots harvested at the harvest period, converted to kg / hm²; Agronomic traits: number of effective panicles in rice (10,000 panicles / hm²), plant height in wheat (cm), and root dry weight (g / plant) were determined using the "five-point sampling method" (20 plants were sampled at each point).

[0067] 3. Soil physicochemical property testing Test parameters: pH value, EC value (soluble salt concentration), available phosphorus, and available potassium; Test method: pH value: 《NY / T 1121.2-2006 Determination of soil pH value》 (soil-water ratio 1:2.5); EC value: 《NY / T 1121.16-2006 Determination of Soil Electrical Conductivity》; Available phosphorus: 《NY / T 1121.7-2014 Determination of available phosphorus in soil by molybdenum blue colorimetric method》; Available potassium: 《NY / T 1121.8-2021 Determination of available potassium in soil by flame spectrophotometry》.

[0068] 4. Nutrient slow-release performance test Test method: The water immersion method in GB / T 23348-2020 slow-release fertilizers was adopted; Test procedure: Take 5g of sample and place it in 500mL of distilled water. Take samples at 1d, 30d and 90d respectively, and determine the contents of N, P2O5 and K2O in the leachate. Calculate the cumulative release rate (cumulative leachate / total nutrient content × 100%).

[0069] 5. Soil-borne disease incidence test Test indicators: Rice sheath blight, vegetable clubroot; Test method: During the harvest period, the number of diseased plants was investigated using the "five-point sampling method", and the incidence rate was calculated as (number of diseased plants / total number of plants × 100%).

[0070] III. Performance Test Data Tables for Examples and Comparative Examples Table 1. Microbial activity test data

[0071] Table 2. Rice yield and agronomic traits test data

[0072] Table 3. Test data on wheat yield and agronomic traits

[0073] Table 4. Soil physicochemical property test data (paddy field / saline-alkali land)

[0074] Table 5. Test data on nutrient slow-release performance and disease incidence.

[0075] Test data analysis: 1. Microbial activity: Initial total viable count in Examples 1-3 was 2.2-2.5 × 10⁻⁶. 9CFU / g, with a survival rate of 84%-87% after 6 months of storage, significantly higher than all comparative examples. The core reason is that the 3:1 complex of local mycorrhizal fungi and functional bacteria forms a symbiotic protective system, reducing the environmental sensitivity of a single species; the double-layer coating process (outer layer of humic acid protection) isolates the bacteria from external humidity and temperature damage, while comparative example 5, which omitted this process, had an initial viable count of only 1.5 × 10⁻⁶. 9 The survival rate was only 66.7% with CFU / g. In contrast, the survival rate of Comparative Example 3 (common humic acid) dropped to 68.2% because the humic acid macromolecules were not enzymatically hydrolyzed and thus encapsulated the fungal cells. Comparative Example 1 (mycorrhizal fungi) had a survival rate of 77.8% due to the lack of symbiotic fungi, which confirms the "protective" role of local mycorrhizal fungi.

[0076] 2. Crop Yield and Agronomic Traits: In Examples 1-3, rice yield was 11129-11350 kg / hm², an increase of 10.7%-12.9% compared to Comparative Example 6 (conventional fertilizer); wheat yield in saline-alkali land was 7941-8120 kg / hm², an increase of 22.2%-24.9% compared to Comparative Example 6. Key Driving Factors: Local mycorrhizal fungi promoted root growth (wheat root dry weight 1.004-1.050 g / plant, 18.1%-23.5% higher than Comparative Example 1), increasing nutrient absorption area; enzymatic hydrolysis of humic acid activated phosphorus and potassium (available phosphorus 25.8-26.5 mg / kg, 32.3%-35.9% higher than Comparative Example 3), meeting the crop's needs during its vigorous growth period. In contrast, Comparative Example 4 (ordinary attapulgite soil) lacked slow-release function, resulting in nutrient loss in the early stage and insufficient nutrients in the later stage. The effective number of rice panicles was only 1.942 million panicles / hm², which was 6.2% lower than that of Example 1. Comparative Example 2 (single Bacillus subtilis) lacked the stress resistance of Bacillus licheniformis, resulting in a wheat plant height of 76.10 cm, which was 3.4% lower than that of Example 1.

[0077] 3. Soil physicochemical properties: The pH value of paddy fields in Examples 1-3 was 5.75-5.80, which alleviated acidification compared to Comparative Example 6 (5.40); the EC value of saline-alkali land was 235-239 μS / cm, which was 11.9%-13.0% lower than that of Comparative Example 6 (270). Key mechanism: The acidic groups of humic acid are neutralized by enzymatic hydrolysis, while the modified slow-release carrier adsorbs sodium ions (water-soluble sodium is reduced by 42-47 mg / kg, patent data); the improved microbial community (mycorrhizal fungi + compound bacteria) promotes the formation of soil aggregate structure, and the CEC value is increased by 0.57-0.8 cmol / kg, enhancing fertilizer retention capacity. In contrast, Comparative Example 6 (conventional fertilizer) caused soil acidification and salinization due to long-term application, with an effective phosphorus content of only 18.2 mg / kg, which is 29.5% lower than that of Example 1, confirming the "soil remediation" advantage of microbial compound fertilizer.

[0078] 4. Slow-release and disease control: Examples 1-3 showed a 1-day nutrient release rate of 17.8%-18.5% (avoiding seedling burn), a 30-day release rate of 50.5%-52.3% (matching the vigorous growth period), and a 90-day release rate of 88.7%-90.2% (meeting the entire growth period), fully complying with the GB / T23348-2020 standard; while Comparative Example 4 (ordinary attapulgite soil) had a 1-day release rate of 25.3%, which easily led to nutrient excess in the seedling stage, and a 30-day release rate of 68.5%, resulting in nutrient depletion in the later stages. The incidence rate of rice sheath blight in Examples 1-3 was 2.8%-3.2%, a decrease of 50.8%-56.9% compared to Comparative Example 6 (6.5%); the incidence rate of clubroot disease in Chinese cabbage was 1.9%-2.1%, a decrease of 50.0%-54.8% compared to Comparative Example 6 (4.2%). The core reason is the 3:1 combination of functional bacteria (Bacillus subtilis producing antimicrobial peptides + Bacillus licheniformis enhancing stress resistance), while the comparative ratio 2 (single Bacillus subtilis) has a 15%-20% lower inhibition rate.

[0079] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0080] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A microbial compound fertilizer, characterized in that, It is prepared from the following raw materials in parts by weight: 10-15 parts of local mycorrhizal fungi inoculant, 5-8 parts of functional bacterial inoculant, 20-30 parts of enzymatic hydrolysis of humic acid derivatives, 15-25 parts of nitrogen, phosphorus and potassium composite matrix, 10-20 parts of slow-release carrier, and 0.5-2 parts of trace elements. The local mycorrhizal fungal agent is a mixed strain of Moses globulin and surface globulin isolated and domesticated from soil in Jilin Province; The functional bacterial agent is a compound agent of Bacillus subtilis and Bacillus licheniformis, and the effective live bacteria ratio of Bacillus subtilis and Bacillus licheniformis is 3:

1. The enzymatically hydrolyzed humic acid derivative was prepared by enzymatic hydrolysis of mineral-derived humic acid through fermentation with Aspergillus niger. The nitrogen-phosphorus-potassium composite matrix adopts a reduced-volume formula, and the mass ratio of N:P2O5:K2O is 1:0.5-0.8:0.8-1.2; The slow-release carrier is a composite of modified attapulgite and starch graft copolymer, and has a porous structure.

2. The microbial compound fertilizer according to claim 1, characterized in that, The sustained-release carrier was prepared from the following raw materials and reagents: attapulgite, 3-aminopropyltriethoxysilane, corn starch, acrylic acid, acrylamide, ammonium persulfate, N,N'-methylenebisacrylamide, anhydrous ethanol, and deionized water.

3. The microbial compound fertilizer according to claim 1, characterized in that, The preparation process of the sustained-release carrier is as follows: Step A1. Preparation of modified attapulgite: APTES surface modification; Step A2. Preparation of starch graft copolymer: denoted as starch-g-(AA-AM); Step A3. Preparation of modified attapulgite-starch graft copolymer composite.

4. The microbial compound fertilizer according to claim 3, characterized in that, The preparation process of the modified attapulgite in step A1 is as follows: Step A101. Attapulgite pretreatment: Take attapulgite, add deionized water, stir and disperse, let stand for 2 hours, discard the upper suspended impurities, wash repeatedly 3 times, dry at 105℃ to constant weight, grind and pass through a 200-mesh sieve, and set aside. Step A102. Silanization modification: Add the pretreated attapulgite to a mixed solvent of anhydrous ethanol and deionized water, ultrasonically disperse at 300W for 30min, add APTES, adjust the pH to 4.5-5.0 with dilute hydrochloric acid, and stir in a 60℃ water bath for 4h. Step A103. Post-processing: After the reaction is complete, the solid is collected by filtration, washed three times with anhydrous ethanol, dried at 80℃ for 6 hours, and ground through a 200-mesh sieve to obtain amino-modified attapulgite, denoted as M-ATP.

5. The microbial compound fertilizer according to claim 4, characterized in that, The ratio of attapulgite clay to deionized water in step A101 is 100g:500mL; The ratio of the pretreated attapulgite, mixed solvent, and APTES in step A102 is 50g:300mL:3-5g; The mixed solvent mentioned in step A102 is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 250 mL: 50 mL.

6. The microbial compound fertilizer according to claim 3, characterized in that, The preparation process of the starch graft copolymer described in step A2 is as follows: Step A201. Starch gelatinization: Add corn starch to deionized water, heat to 90°C for 30 minutes while stirring, and cool to 50°C to obtain starch paste; Step A202. Graft copolymerization: Add acrylic acid and acrylamide to the starch paste and stir to dissolve; add ammonium persulfate and N,N'-methylenebisacrylamide, purge with nitrogen to remove oxygen for 10 min, and react in a water bath at 55℃ for 3 h; Step A203. Post-processing: The reaction product was precipitated with anhydrous ethanol, filtered, washed three times with 70% ethanol solution, dried under vacuum at 60°C to constant weight, and ground through a 100-mesh sieve to obtain the starch graft copolymer, denoted as St-g-(AA-AM)).

7. The microbial compound fertilizer according to claim 6, characterized in that, The ratio of corn starch to deionized water used in step A201 is 50g:200mL; The mass ratio of acrylic acid, acrylamide, ammonium persulfate, and N,N'-methylenebisacrylamide in step A202 is 20g:10g:0.5g:0.1g; In step A202, the total mass of acrylic acid and acrylamide is 60% of the starch, the mass ratio of acrylic acid to acrylamide is 2:1, the ammonium persulfate accounts for 1.7% of the total mass of the monomers, and the N,N'-methylenebisacrylamide accounts for 0.3% of the total mass of the monomers.

8. The microbial compound fertilizer according to claim 3, characterized in that, The preparation process of the modified attapulgite-starch graft copolymer composite described in step A3 is as follows: Step A301. Mixing and dispersing: Add starch graft copolymer St-g-(AA-AM) to deionized water and stir at 50°C until completely dissolved; add amino-modified attapulgite M-ATP and ultrasonically disperse at 400W for 40 minutes to ensure that M-ATP is uniformly dispersed in the polymer solution. Step A302. Composite reaction: Transfer the mixture to a three-necked flask and stir in a 60°C water bath for 2 hours; Step A303. Drying and molding: After the reaction, the mixture is freeze-dried and then ground through a 100-mesh sieve to obtain the complex of modified attapulgite and starch graft copolymer, denoted as M-ATP / St-g-(AA-AM).

9. The microbial compound fertilizer according to claim 8, characterized in that, The mass ratio of starch graft copolymer, deionized water and amino-modified attapulgite in step A301 is 30g:300mL:20g.

10. A method for preparing a microbial compound fertilizer, characterized in that, Includes the following steps: Step S1. Preliminary preparation: pretreatment of each component to obtain pretreated microbial agent, pretreated enzymatic hydrolysis humic acid derivative, pretreated nitrogen-phosphorus-potassium composite matrix, pretreated trace elements and pretreated slow-release carrier; Step S2. Staged mixing and double-layer coating granulation: First, mix the non-microbial components, then mix the microbial agent with the remaining components, and finally perform double-layer coating and granulation; Step S3. Post-processing: Low-temperature drying and finished product testing to obtain microbial compound fertilizer.

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