Composite microbial fertilizer and preparation method thereof

Abstract

The application relates to the technical field of biological fertilizer, and particularly discloses a compound microbial fertilizer and a preparation method thereof. The Klebsiella pneumoniae, Bacillus megaterium, Bacillus mycoides and Bacillus subtilis are compounded, the Klebsiella pneumoniae converts nitrogen in the air into nitrogen available for plants, the Bacillus megaterium decomposes insoluble phosphorus in soil into effective phosphorus, the Bacillus mycoides decomposes potassium silicate minerals in soil to release effective potassium, the Bacillus subtilis produces biological substances to stimulate root growth and secretes antibacterial substances to inhibit pathogenic bacteria in roots. The modified biochar carrier is used to provide stable living space for the compound microbial fertilizer, so that the compound microbial fertilizer is sustainable, efficient and green.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biological fertilizer, in particular to a compound microbial fertilizer and a preparation method thereof. BACKGROUND

[0002] In the past agricultural production practice, chemical fertilizer has long occupied a core position and become an important means to ensure crop yield. However, with the continuous increase of chemical fertilizer, a series of ecological and production problems have gradually emerged. Soil degradation phenomena such as hardening, acidification and salinization occur, and soil fertility declines; crop diseases and insect pests occur frequently, which not only affects the growth state, but also leads to the decline of agricultural product quality; more importantly, the agricultural non-point source pollution caused by excessive use of chemical fertilizer has gradually become a key factor to aggravate the environmental burden. In this real demand, microbial fertilizer as a new green fertilizer emerges as the times require. This kind of fertilizer is rich in various beneficial microorganisms, which can play a key role in nitrogen fixation, phosphorus solubilization and potassium solubilization in soil environment, which can not only optimize the soil ecology, but also reduce the negative effects of chemical input, and provides a new idea to solve the problem caused by the dependence on chemical fertilizer.

[0003] Microbial fertilizer has multiple core advantages in agricultural production. The beneficial bacteria such as bacillus and actinomycetes contained in it can form a dominant community in the crop root system, inhibit pathogenic bacteria, reduce soil-borne diseases, and improve soil micro-ecology; the polysaccharides produced by microbial metabolism can improve the soil water retention capacity to help drought resistance, and enhance the cold resistance and disease resistance of crops, and reduce the use of pesticides. In addition, the organic acids produced by beneficial microorganisms can release the insoluble nutrients in the soil, supplement the organic matter, improve the soil aeration and fertilizer retention, and alleviate the soil degradation. Some microorganisms can also symbiotically with crop roots, expand the nutrient absorption range, and decompose macromolecular nutrients to help crops absorb fertilizer efficiently.

[0004] CN104446708A belongs to the field of fertilizer, and relates to a microbial fertilizer and a preparation method and application thereof. The microbial fertilizer is prepared by mixing a bacterial strain, an additive and a carrier according to specific weight proportions: the bacterial strain is selected from at least three kinds of bacillus subtilis, bacillus megaterium and silicate bacteria, and the amount of each bacterial strain ranges from 0.1 to 5 weight proportions; the additive is one of red sugar, molasses or sucrose, and accounts for 0.2-5 weight proportions; the carrier is an organic matter carrier or a water-soluble solvent carrier, and accounts for 72-97.9 weight proportions. The microbial fertilizer can improve the soil nutrient utilization rate, enhance the disease resistance of crops, reduce the occurrence of diseases, improve the yield of crops and reduce the production cost.

[0005] CN114560734A discloses a biochar carrier and microbial fertilizer, wherein the biochar carrier is prepared by limiting oxygen pyrolysis of crop straw at 300-800 DEG C. The microbial fertilizer uses the biochar as an adsorption substrate to load potassium-dissolving bacteria or phosphorus-dissolving bacteria. The biochar has a significant adsorption effect on bacterial cells, and the methemoglobin production rate increases with the culture time. The biochar can not only fully release nutrients but also provide sufficient living space for bacterial strains. After loading the bacterial strains, the surface functional groups of the biochar increase, and the biochar can achieve sustained adsorption. The microbial fertilizer has a significant effect on plant growth and development, especially when the biochar is combined with potassium-dissolving bacteria or the biochar is combined with potassium-dissolving bacteria and potassium mineral materials. The combination can help reduce the use of potassium fertilizer and alleviate the shortage of potassium fertilizer.

[0006] Microbial fertilizer can not only improve soil quality but also improve crop growth quality. However, the soil environment is complex, and direct addition of microbial agents may cause rapid inactivation of bacterial strains, making it difficult to inhibit pathogenic bacteria and transform nutrients. Therefore, microbial agents generally need to be used with carriers. Carriers can provide a stable living space for beneficial bacteria to avoid rapid inactivation. In addition, carriers can promote bacterial colonization and help bacterial strains to concentrate around the crop root system and form a dominant bacterial population. SUMMARY

[0007] In view of the above defects of the prior art, the technical problem to be solved by the present application is to provide a composite microbial fertilizer and a preparation method thereof.

[0008] Biochar is an excellent soil conditioner and is often used as a carrier for microorganisms. However, the surface of raw biochar usually lacks sufficient functional groups that can specifically bind to the cell membranes of microorganisms. Microorganisms are difficult to stably colonize and form biofilms on the surface of biochar, resulting in low bacterial activity and easy loss.

[0009] The application modifies the biochar, first forms a layer of firm active film rich in o-diphenol, quinone and amino on the surface of the biochar through polydopamine (PDA) deposition, covalently reacts with the electron mediator by using the active sites on the PDA, and precisely and firmly anchors the quinone molecules on the surface of the biochar through the covalent bond. The quinone group is a high-efficiency electron transfer mediator in nature, the unmodified biochar mainly plays the role of physical adsorption and carrier, and the electron transfer capacity of the quinone group is used to transfer the electrons in the microbial cells, so that the activity and nitrogen fixation efficiency of the microorganism are improved. And the functionalization is carried out through the covalent bond, the function is durable. The PDA coating is firmly combined with the biochar substrate, which ensures the long-term stability of the modified material in a complex environment. The PDA coating simulates the natural adhesive protein, greatly promotes the adhesion of the microorganism and the formation of the biofilm, and creates a better survival environment for the microorganism. The modified biochar is no longer a simple carrier, but also can accelerate nitrogen fixation, significantly improve the survival rate and colonization ability of the bacterial population, and enhance the stress resistance and stability of the bacterial fertilizer, so that more durable and efficient fertilizer efficiency is realized.

[0010] The application complexly uses Klebsiella pneumoniae, Bacillus megaterium, Paenibacillus mucilaginosus and Bacillus subtilis, Klebsiella pneumoniae converts nitrogen in the air into plant available nitrogen, and Bacillus megaterium decomposes soil insoluble phosphorus into available phosphorus.

[0011] Paenibacillus mucilaginosus decomposes potassium silicate minerals in the soil to release available potassium, and Bacillus subtilis produces biological substances to stimulate root growth and secretes antibacterial substances to inhibit root pathogenic bacteria. By constructing a functionally complementary microbial environment and using modified biochar carriers to provide stable living space, a sustainable, efficient and green compound microbial fertilizer is obtained.

[0012] To achieve the above object, the application provides a preparation method of a compound microbial fertilizer, comprising the following steps:

[0013] S1, Klebsiella pneumoniae, Bacillus megaterium, Paenibacillus mucilaginosus and Bacillus subtilis are inoculated on a plate, and after 24-48h of inverted culture at 27-29 DEG C, single colonies are picked and inoculated into LB liquid medium, and placed in a shaking bed, and cultured at 27-30 DEG C, 150-200rpm for 12-18h to obtain a primary seed liquid;

[0014] S2, the primary seed liquid is inoculated into LB liquid medium at a inoculation amount of 2%(v / v) for secondary expansion culture, and the viable cell count is controlled to be 1.0*109 / mL-1.0*1010 / mL. Then, the culture solutions of Klebsiella pneumoniae, Bacillus megaterium, Paenibacillus mucilaginosus and Bacillus subtilis are mixed in a volume ratio of 2-3:2-3:2-3:1-2 to obtain a mixed bacterial solution, which is added to the modified biochar, fully stirred, and cultured at 25-30℃ for 24-36h, and then dried at low temperature to obtain the compound microbial fertilizer.

[0015] Further, the ratio of the modified biochar to the mixed bacterial solution is 0.8-1.5:1g / mL.

[0016] Further, the temperature of the low-temperature drying is <35℃.

[0017] The preparation method of the modified biochar comprises the following steps:

[0018] X1, the biochar is added to 1wt% hydrogen peroxide solution and ultrasonically treated for 20-40min, and then filtered, washed and dried to obtain the pretreated biochar;

[0019] X2, dopamine hydrochloride is added to Tris-HCl buffer solution, stirred until dissolved, and then the pretreated biochar is added, ultrasonically dispersed for 10-15min, and then stirred in the dark for 20-26h, filtered, washed and dried to obtain the polydopamine composite biochar;

[0020] X3, the polydopamine composite biochar is added to 60wt% N,N-dimethylformamide aqueous solution, ultrasonically dispersed for 10-15min, and then an electron mediator is added, the pH is adjusted to weak alkaline, and then stirred at elevated temperature for 6-10h, filtered, washed and dried to obtain the modified biochar.

[0021] Further, the mass ratio of the biochar to the hydrogen peroxide solution is 1:10-15.

[0022] Further, the mass ratio of the dopamine hydrochloride to the Tris-HCl buffer solution and the pretreated biochar is 0.2-0.5:10:4-8.

[0023] Further, the mass ratio of the polydopamine composite biochar to the N,N-dimethylformamide aqueous solution and the electron mediator is 1:10-25:0.01-0.05.

[0024] Further, the electron mediator is one of 2-aminoanthraquinone, 1,4-diaminoanthraquinone and 2-amino-3-chloro-1,4-naphthoquinone.

[0025] Further, the temperature range of the elevated temperature is 60-70℃.

[0026] Preferably, the preparation method of the modified biochar comprises the following steps:

[0027] X1, the biochar is added to 1wt% hydrogen peroxide aqueous solution and ultrasonic treated for 20-40min, the mass ratio of biochar to hydrogen peroxide aqueous solution is 1:10-15, after filtration, washing and drying, the pretreated biochar is obtained;

[0028] X2, the dopamine hydrochloride is added to Tris-HCl buffer solution, after stirring to dissolve, the pretreated biochar is added, the mass ratio of dopamine hydrochloride to Tris-HCl buffer solution and pretreated biochar is 0.2-0.5:10:4-8, after ultrasonic dispersion for 10-15min, the stirring is carried out in dark for 20-26h, after filtration, washing and drying, the polydopamine composite biochar is obtained;

[0029] X3, the polydopamine composite biochar is added to 60wt% N,N-dimethylformamide aqueous solution, after ultrasonic dispersion for 10-15min, the electron mediator is added, the mass ratio of polydopamine composite biochar to N,N-dimethylformamide aqueous solution and electron mediator is 1:10-25:0.01-0.05, the pH is adjusted to weak alkaline, the stirring is carried out at 60-70℃ for 6-10h, after filtration, washing and drying, the modified biochar is obtained.

[0030] The application further provides a composite microbial fertilizer prepared by the above method.

[0031] The application has the following beneficial effects:

[0032] The Klebsiella pneumoniae, Bacillus megaterium, Paenibacillus mucilaginosus and Bacillus subtilis are compounded, a functional complementary microbial environment is constructed, and the modified biochar carrier is used to provide a stable and more efficient living space, so that the green composite microbial fertilizer is obtained. DETAILED DESCRIPTION

[0033] The Klebsiella pneumoniae has a preservation number of CGMCC No.32396, and the microorganism is disclosed in the patent CN119799689A, the preservation date is October 28, 2024, and the preservation unit is China General Microbiological Culture Collection Center.

[0034] The Bacillus megaterium is CICC 21458, a commercially available product, and is from China Industrial Microbial Culture Collection Management Center.

[0035] The Paenibacillus mucilaginosus is CICC 20666, a commercially available product, and is from China Industrial Microbial Culture Collection Management Center.

[0036] The Bacillus subtilis is CICC 20522, a commercially available product, and is from China Industrial Microbial Culture Collection Management Center.

[0037] LB liquid medium: tryptone 10 g / L, yeast extract 5 g / L, K2HPO4 1 g / L, KH2PO4 1 g / L, MgSO4·7H2O 0.5 g / L, NaCl 5 g / L, pH = 7.0.

[0038] Tris-HCl buffer solution, 6.057 g of Tris was dissolved in 400 mL of water, 0.1 mol / L dilute HCl was added to adjust the pH to 8.5.

[0039] Biochar is peanut shell biochar, 200 mesh.

[0040] 2-amino-3-chloro-1, 4-naphthoquinone, CAS: 2797-51-5.

[0041] Example 1

[0042] A preparation method of a composite microbial fertilizer, comprising the following steps:

[0043] S1, Klebsiella pneumoniae, Bacillus megaterium, jelly-like Paenibacillus and Bacillus subtilis were inoculated on plates and cultured at 28℃ for 24h, then single colonies were picked and inoculated into LB liquid medium, and placed in a shaking bed, Klebsiella pneumoniae was cultured at 28℃, 180rpm for 16h, Bacillus megaterium and Bacillus subtilis were cultured at 30℃, 200rpm for 12h, and jelly-like Paenibacillus was cultured at 30℃, 180rpm for 18h, to obtain a primary seed liquid;

[0044] S2, the primary seed liquid was inoculated into the LB liquid medium at an inoculation amount of 2%(v / v) for secondary expansion culture, and the viable cell count was Then the culture liquids of Klebsiella pneumoniae, Bacillus megaterium, jelly-like Paenibacillus and Bacillus subtilis were mixed in a volume ratio of 3:2.5:2:1 to obtain a mixed bacterial liquid, which was added to modified biochar, and the ratio of modified biochar to mixed bacterial liquid was 1:1 g / mL, and then fully stirred and cultured at 28℃ for 36h, and then low-temperature dried at <35℃ to obtain the composite microbial fertilizer.

[0045] The preparation method of the modified biochar comprises the following steps:

[0046] X1, the biochar was added to 1wt% hydrogen peroxide solution and ultrasonicated for 30min, the mass ratio of biochar to hydrogen peroxide solution was 1:12, and the pretreated biochar was obtained after filtration, washing and drying;

[0047] X2. Add dopamine hydrochloride to Tris-HCl buffer, stir until dissolved, then add pretreated biochar. The mass ratio of dopamine hydrochloride to Tris-HCl buffer and pretreated biochar is 0.3:10:5. After ultrasonic dispersion for 15 min, stir in the dark for 24 h. After filtration, washing and drying, polydopamine composite biochar is obtained.

[0048] X3. Add polydopamine composite biochar to 60wt% N,N-dimethylformamide aqueous solution, ultrasonically disperse for 15 min, then add 2-aminoanthraquinone. The mass ratio of polydopamine composite biochar to N,N-dimethylformamide aqueous solution and 2-aminoanthraquinone is 1:20:0.03. Adjust the pH to 7.5, heat to 70℃ and stir for 8 h. Filter, wash and dry to obtain modified biochar.

[0049] Example 2

[0050] It is basically the same as Example 1, except that 2-aminoanthraquinone is replaced with 1,4-diaminoanthraquinone.

[0051] Example 3

[0052] It is basically the same as Example 1, except that 2-aminoanthraquinone is replaced with 2-amino-3-chloro-1,4-naphthoquinone.

[0053] Compare with Example 1

[0054] A method for preparing a compound microbial fertilizer includes the following steps:

[0055] S1. Klebsiella pneumoniae, Bacillus megaterium, Bacillus subtilis and Bacillus subtilis were inoculated onto plates and incubated upside down at 28°C for 24 hours. Single colonies were then picked and inoculated into LB liquid medium and placed on a shaker. Klebsiella pneumoniae was incubated at 28°C and 180 rpm for 16 hours, Bacillus megaterium and Bacillus subtilis were incubated at 30°C and 200 rpm for 12 hours, and Bacillus subtilis was incubated at 30°C and 180 rpm for 18 hours to obtain the primary seed culture.

[0056] S2. Inoculate the primary seed culture into LB liquid medium at an inoculation rate of 2% (v / v) for secondary scale-up culture until the viable cell count reaches a certain level. Then, the culture solutions of Klebsiella pneumoniae, Bacillus megaterium, Bacillus spp. and Bacillus subtilis were mixed in a volume ratio of 3:2.5:2:1 to obtain a mixed bacterial solution, which was added to biochar at a ratio of 1:1 g / mL. The mixture was stirred thoroughly and cultured at 28°C with shaking for 36 hours. Then, it was dried at a low temperature of <35°C to obtain the compound microbial fertilizer.

[0057] Compare with Example 2

[0058] A preparation method of a composite microbial fertilizer, comprising the following steps:

[0059] S1, Klebsiella pneumoniae, Bacillus megaterium, Paenibacillus mucilaginosus and Bacillus subtilis were inoculated on plates, and after 24h of inverted culture at 28℃, single colonies were picked and inoculated into LB liquid medium in a shaker, Klebsiella pneumoniae was cultured at 28℃, 180rpm for 16h, Bacillus megaterium and Bacillus subtilis were cultured at 30℃, 200rpm for 12h, and Paenibacillus mucilaginosus was cultured at 30℃, 180rpm for 18h, to obtain a primary seed liquid;

[0060] S2, the primary seed liquid was inoculated into a culture medium at an inoculation amount of 2%(v / v) for secondary expansion culture, and the culture was carried out until the viable bacterial count reached 1.0x109CFU / mL; Then, the culture liquids of Klebsiella pneumoniae, Bacillus megaterium, Paenibacillus mucilaginosus and Bacillus subtilis were mixed in a volume ratio of 3:2.5:2:1 to obtain a mixed bacterial liquid, which was added to modified biochar, and the ratio of modified biochar to mixed bacterial liquid was 1:1g / mL, and after sufficient stirring, the mixture was cultured at 28℃ for 36h, and then low-temperature drying was carried out at <35℃ to obtain the composite microbial fertilizer.

[0061] The preparation method of the modified biochar comprises the following steps:

[0062] X1, biochar was added to 1wt% hydrogen peroxide aqueous solution and ultrasonicated for 30min, the mass ratio of biochar to hydrogen peroxide aqueous solution was 1:12, and after filtration, washing and drying, pretreated biochar was obtained;

[0063] X2, dopamine hydrochloride was added to Tris-HCl buffer solution, stirred until dissolved, and then the pretreated biochar was added, the mass ratio of dopamine hydrochloride to Tris-HCl buffer solution and pretreated biochar was 0.3:10:5, ultrasonic dispersion was carried out for 15min, and then the mixture was stirred in the dark for 24h, and after filtration, washing and drying, modified biochar was obtained.

[0064] Test Example 1

[0065] The composite microbial fertilizers prepared in the examples and the control example were applied to continuous cropping tomatoes, and field tests were carried out in a tomato field that had been continuously cropped for 3 years. The test adopted a randomized block design, and a total of 5 treatment groups were set, each treatment group had 3 repetitions, and a total of 15 test plots were set.

[0066] The area of each test plot was 21.12 m 2 , and the tomatoes were planted in a single ridge double row planting way with a planting row distance of 60cm and a plant distance of 40cm. The application amount of the composite microbial fertilizer was uniformly 1500 kg / hm 2, the total amount of fertilizer is 70% as base fertilizer, and the remaining 30% is applied during the fruit expansion period of tomatoes. The test tomatoes are planted in a greenhouse mode, and are cultivated for two seasons a year. During the growth period, routine field management measures are implemented.

[0067] After 40 days of tomato planting, 5 tomato plants are randomly selected from each plot, and the plant height and stem diameter are measured. The yield is determined by weighing the single fruit, and after 3 times of continuous cropping, the single yield is converted to yield per hectare to evaluate the effect of microbial fertilizer on tomato yield.

[0068] Table 1

[0069]

[0070] In crop planting, long-term continuous cropping can cause accumulation of pathogenic bacteria in the soil and imbalance of soil nutrients, thereby causing problems such as poor crop growth, frequent occurrence of diseases and pests, and continuous cropping obstacles.

[0071] As can be seen from Table 1, the compound microbial fertilizer of the application can reproduce in large quantities around the tomato root system, form a dominant bacterial population, inhibit the growth and reproduction of harmful pathogenic bacteria, reduce the occurrence of soil-borne diseases, and make the tomato grow stably and healthily.

[0072] Among them, Klebsiella pneumoniae converts nitrogen in the air into nitrogen available to plants, Bacillus megaterium decomposes insoluble phosphorus in the soil and converts it into available phosphorus. Gumbo-like Bacillus pasteurii decomposes potassium silicate minerals in the soil and releases available potassium. Bacillus subtilis produces a biological substance that stimulates root growth and also secretes antibacterial substances to inhibit root pathogens. And the biochar can improve the soil structure and the environment of nutrient absorption, and promote nutrient absorption.

[0073] Compared with the control example, the biochar is modified in the embodiment, so that the biochar not only serves as a nutrient and carrier, but also can accelerate nitrogen fixation, significantly improve the survival rate and colonization ability of the bacterial population, and enhance the stress resistance and stability of the microbial fertilizer, thereby realizing more persistent and efficient fertilizer efficiency.

[0074] Compared with examples 1 and 2, the tomato of example 3 grows better, which may be due to the fact that the electron mediator contains chlorine. Chlorine atom is a strong electron-withdrawing group, so it can further improve the efficiency of electron transfer, thereby improving energy metabolism and strengthening nitrogen fixation rate and bacterial activity. Therefore, the growth of tomatoes is better than that of examples 1-2.

[0075] Test Example 2

[0076] In test example 1, after the tomato fruits mature, the soil samples of 20 cm soil layer in the test plot are collected by five-point method, the collected samples are fully mixed and naturally dried, and are used for determination of soil physical and chemical properties. The alkali hydrolysis nitrogen content is determined by alkali hydrolysis diffusion method, the available phosphorus content is determined by molybdenum-antimony anti-colorimetric method, and the available potassium content is determined by flame photometer method. The total nitrogen content is determined by semi-micro Kelvin method, and the soil pH value is determined by water-soil ratio method.

[0077] Table 2

[0078]

[0079] As can be seen from Table 2, the composite microbial fertilizer prepared by the application can effectively improve the fertility of the soil, because the application of the microbial fertilizer can effectively supplement the types and amounts of carbon sources required for microbial metabolism, improve the micro-ecological environment and soil structure, and improve the root nutrient utilization efficiency. The Klebsiella pneumoniae converts nitrogen in the air into nitrogen available to plants, the Bacillus megaterium decomposes insoluble phosphorus in the soil to convert it into available phosphorus, the Bacillus mucilaginosus decomposes potassium silicate minerals in the soil to release available potassium, and the Bacillus subtilis produces biological substances to stimulate root growth and at the same time secretes antibacterial substances to inhibit root pathogenic bacteria. The combined action of the several bacteria effectively improves the soil fertility.

[0080] Compared with control example 1, the soil fertility of control example 2 is better, which may be due to the fact that the PDA coating is rich in functional groups such as phenolic hydroxyl and amino groups, which greatly increases the negative charge and complexation sites on the surface of the biochar. This makes the modified biochar have a much higher ability to adsorb and store nutrient cations such as potassium, calcium and magnesium than the original biochar, effectively reducing nutrient leaching.

[0081] Compared with the control example, the anthraquinone group can improve nitrogen fixation and the survival rate and colonization ability of the bacterial population, so the improvement of the soil is more significant.

[0082] The above describes in detail the preferred embodiments of the application. It should be understood that those skilled in the art can make many modifications and changes to the application without creative labor based on the concept of the application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment based on the prior art according to the concept of the application shall be within the protection scope determined by the claims.

Claims

1. A method for preparing a compound microbial fertilizer, characterized in that, Includes the following steps: S1. Klebsiella pneumoniae, Bacillus megaterium, Bacillus spp. and Bacillus subtilis were inoculated onto plates and incubated upside down at 27-29℃ for 24-48 hours. Single colonies were then picked and inoculated into LB liquid medium and placed on a shaker. The medium was then incubated at 27-30℃ and 150-200 rpm for 12-18 hours to obtain the primary seed culture. S2. Inoculate the primary seed culture into LB liquid medium at an inoculation rate of 2% (v / v) for secondary scale-up culture until the viable count is >1 × 10⁻⁶. 9 The concentration of CFU / mL was determined by mixing the culture media of Klebsiella pneumoniae, Bacillus megaterium, Bacillus spp. and Bacillus subtilis in a volume ratio of 2-3:2-3:2-3:1-2 to obtain a mixed bacterial solution. This solution was then added to modified biochar, stirred thoroughly, and cultured at 25-30℃ with shaking for 24-36 hours. Finally, the solution was dried at low temperature to obtain the composite microbial fertilizer. The Klebsiella pneumoniae strain mentioned has the accession number CGMCC No. 32396. This microorganism has been disclosed in patent CN119799689A, with an accession date of October 28, 2024. The depositary institution is the China General Microbiological Culture Collection Center. The method for preparing the modified biochar includes the following steps: X1. Add biochar to a 1 wt% hydrogen peroxide aqueous solution and sonicate for 20-40 min. After filtration, washing and drying, the pretreated biochar is obtained. X2. Add dopamine hydrochloride to Tris-HCl buffer, stir until dissolved, then add pretreated biochar, sonicate for 10-15 min, stir in the dark for 20-26 h, filter, wash, and dry to obtain polydopamine composite biochar. X3. Add polydopamine composite biochar to a 60wt% N,N-dimethylformamide aqueous solution, ultrasonically disperse for 10-15 min, add an electron mediator, adjust the pH to weakly alkaline, heat and stir for 6-10 h, filter, wash and dry to obtain modified biochar. The mass ratio of the biochar to the hydrogen peroxide aqueous solution is 1:10-15; The mass ratio of dopamine hydrochloride to Tris-HCl buffer and pretreated biochar is 0.2-0.5:10:4-8; The mass ratio of the polydopamine composite biochar to N,N-dimethylformamide aqueous solution and electron mediator is 1:10-25:0.01-0.05; The electron mediator is one of 2-aminoanthraquinone, 1,4-diaminoanthraquinone, and 2-amino-3-chloro-1,4-naphthoquinone; The temperature range for the heating is 60-70℃.

2. The method for preparing the compound microbial fertilizer as described in claim 1, characterized in that, The ratio of modified biochar to mixed bacterial solution is 0.8-1.5:1 g / mL.

3. The method for preparing the compound microbial fertilizer as described in claim 1, characterized in that, The temperature for the low-temperature drying is <35℃.

4. A compound microbial fertilizer, characterized in that, Prepared by the method described in any one of claims 1-3.

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