Application of composite solid phosphorus-solubilizing bacterial agent in repairing cadmium-contaminated soil and improving soil quality

Abstract

The application relates to the field of environment, resource utilization and agricultural biotechnology, and particularly relates to application of a composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-polluted soil and improving soil quality, wherein the composite solid phosphorus-solubilizing bacterial agent comprises phosphorus-solubilizing bacteria, bone charcoal, culture medium and organic matrix; the phosphorus-solubilizing bacteria are Pantoea agglomerans CT-3 and Enterobacter hormaechei HS-6; the composite solid phosphorus-solubilizing bacterial agent is applied to Cd-polluted soil, and the biological availability of Cd in the soil is reduced by Pantoea agglomerans CT-3, Enterobacter hormaechei HS-6 and micron-nanometer multi-stage bone charcoal, and meanwhile, the soil quality is improved. The application can effectively promote the transformation of insoluble phosphate into soluble phosphate, so that the content of effective soil phosphorus is increased by 98.19%; on the other hand, the application can fix soil heavy metal Cd, so that the content of effective Cd in the soil is reduced by about 52.50%, has excellent Cd-fixing capacity, and can relieve the Cd stress of crops, and has good application value in repairing farmland Cd pollution, improving soil quality and environmental protection.

Description

Technical Field

[0001] This invention relates to the fields of environmental protection, resource utilization, and agricultural biotechnology, specifically to the application of a compound solid phosphate-solubilizing agent for the remediation of cadmium-contaminated soil and improvement of soil quality. Background Technology

[0002] Soil cadmium (Cd) pollution has become a global environmental problem, placing a heavy burden on ecosystems, agricultural production, and human health. Rice, as one of the world's major food crops, has a strong capacity to accumulate Cd.

[0003] Traditional Cd-contaminated paddy soil remediation technologies, such as chemical leaching, can reduce soil Cd content to some extent, but they damage soil structure, leading to decreased soil fertility, and the use of chemical reagents can easily cause secondary pollution. Topsoil replacement methods are costly, extremely difficult to implement on a large scale, and can also damage the ecological environment of the soil extraction area. Therefore, developing green, efficient, low-cost, and sustainable remediation technologies is of great significance for the safe production of crops.

[0004] Phosphate-solubilizing bacteria (PSBs) are a group of functional microorganisms that can convert insoluble phosphorus in the soil into available phosphorus that plants can absorb and utilize. They participate in soil nutrient cycling and transformation, increase the content of available nutrients in the soil, improve the structure of the soil microbial community, and enhance soil fertility and quality. For the remediation of soil heavy metal Cd pollution, PSBs are a bioremediation method that is lower in cost and does not produce secondary pollution compared to chemical remediation methods. However, the growth and activity of PSBs are usually limited by environmental factors, which significantly reduces the remediation effect.

[0005] In addition, microbial agents are gradually being used for the remediation of Cd-contaminated soil. However, there are not many microbial agents that can be effectively used for the remediation of Cd-contaminated soil, and the remediation effect is not outstanding. Therefore, the development of microbial agents needs to be strengthened to enrich the resources of microbial agents for the remediation of Cd-contaminated soil and promote the remediation of Cd-contaminated soil. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the present invention aims to provide an application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality. This composite solid phosphate-solubilizing agent is highly effective in reducing the bioavailability of Cd and increasing the available phosphorus content in the soil, resulting in a significant improvement in soil quality. It also helps maintain soil ecological balance and promotes plant growth by enhancing soil fertility.

[0007] To achieve the objectives of the invention described above, the technical solution adopted by the present invention is as follows:

[0008] This invention provides an application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality. The composite solid phosphate-solubilizing agent includes phosphate-solubilizing bacteria, bone char, culture medium, and organic matrix. The phosphate-solubilizing bacteria include Enterobacter holmieae HS-6 and Pantotheca cumulus CT-3.

[0009] The classification name of the Enterobacter HS-6 is... Enterobacter hormaechei It was deposited at the China General Microbiological Culture Collection Center (CGMCC) on October 19, 2023, with accession number CGMCC NO.: 28680;

[0010] The classification name of the pantothecin CT-3 is... Pantoea agglomerans It was deposited at the China General Microbiological Culture Collection Center on January 8, 2025, with accession number CGMCC NO.: 33335;

[0011] When the composite solid phosphate-solubilizing agent is applied to Cd-contaminated soil, the bioavailability of Cd in the soil is reduced by the synergistic effect of Enterobacter holmieae HS-6, Pantothecin CT-3, and bone char, while improving soil quality.

[0012] Furthermore, the 16S rDNA gene sequence of the *Enterobacter holmieae* HS-6 is shown in SEQ ID No. 1;

[0013] The 16S rDNA gene sequence of the clump-forming pantothecin CT-3 is shown in SEQ ID No. 2.

[0014] Furthermore, the particle size of the bone char is 30 nm to 2 μm.

[0015] Furthermore, the organic matrix is ​​at least one of wheat bran, rice straw, or corn cob.

[0016] Furthermore, the application of the composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality includes the following steps:

[0017] S1. Preparation of micro / nano bone char: Animal bone was thermally pyrolyzed and cooled, then ball-milled to obtain micro / nano multi-level bone char;

[0018] S2. Activation of the strains: Enterobacter horneri HS-6 and Pantotheca cumulus CT-3 were inoculated into LB medium and then cultured in a constant temperature shaker at 28°C with shaking at 180 r / min until OD. 600 =0.6~0.8, to obtain HS-6 bacterial suspension and CT-3 bacterial suspension;

[0019] S3. Preparation of liquid bacterial agent: The HS-6 bacterial suspension and CT-3 bacterial suspension obtained in step S2 are mixed to form a composite bacterial solution. The micron-nano multi-level bone char obtained in step S1 is sterilized by irradiation and then added to the composite bacterial solution into NBRIP medium. The medium is then placed in a constant temperature shaker at 28°C and shaken at 180 r / min for 44 h to 50 h to obtain the liquid bacterial agent.

[0020] S4. Organic matrix carrier treatment: After rinsing the organic matrix with deionized water, add deionized water to cover the organic matrix and soak it. Then, sterilize it under high temperature and high pressure to obtain the treated organic matrix carrier.

[0021] S5. Preparation of solid bacterial agent: The liquid bacterial agent obtained in step S3 is added to the organic matrix carrier obtained in step S4, and cultured at 28℃ for 2-4 days to obtain the composite solid phosphate-solubilizing bacterial agent.

[0022] S6. Remediation of Cd-contaminated soil: The composite solid phosphate-solubilizing agent is applied to Cd-contaminated soil.

[0023] Further, in step S1, the animal bone is heated to 440℃~460℃ at a heating rate of 8℃ / min~12℃ / min for 100min~140min for thermal decomposition. After cooling, large pieces of bone char are obtained. The large pieces of bone char are then ball-milled at 440rpm~460rpm for 4h~6h to obtain micron-nano-level multi-grade bone char; and / or

[0024] In the ball mill, zirconium oxide particles are used to ball mill large bone char, and ethanol is added as a grinding aid; the weight ratio of zirconium oxide particles to large bone char is (15~20):1; the mass ratio of ethanol to large bone char is (1.5~2):1.

[0025] Furthermore, in step S2, the effective viable cell counts of the prepared HS-6 bacterial suspension and CT-3 bacterial suspension are 1×10⁻⁶ and 1×10⁻⁶, respectively. 10 CFU / mL ~9×10 10 CFU / mL.

[0026] Further, in step S3, the mass-to-volume ratio of the bone char to the NBRIP culture medium is 0.5% to 2.5%; and / or

[0027] The volume ratio of the HS-6 bacterial suspension to the CT-3 bacterial suspension is 1:1;

[0028] The inoculation amount of the composite bacterial solution in the NBRIP medium is 1% of the volume percentage of the NBRIP medium; and / or

[0029] The irradiation sterilization dose is 3.0 kGy to 6.0 kGy.

[0030] Furthermore, in step S4, after rinsing the organic matrix three times with deionized water, the organic matrix is ​​soaked in deionized water that covers it for 10-20 hours, and then sterilized under high temperature and high pressure to obtain the treated organic matrix carrier.

[0031] The conditions for high-temperature and high-pressure sterilization are: 121℃, 104KPa, 20min.

[0032] Further, in step S5, the liquid bacterial agent obtained in step S3 is added to the organic matrix carrier obtained in step S4, packed into a polyethylene bag and sealed. Five to eight air holes are punched on the surface of the polyethylene bag with a sterile needle. Then, it is placed in a constant temperature shaker at 28°C and shaken at 180 r / min for 2 to 4 days to obtain the composite solid phosphate-solubilizing bacterial agent.

[0033] In step S5, the mass ratio of the liquid bacterial agent to the organic matrix carrier is 15:(70~100).

[0034] In step S6, the mass ratio of the composite solid phosphate-solubilizing agent to the Cd-contaminated soil is 3:(250~350).

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) An application of a composite solid phosphate-solubilizing agent of the present invention for remediating cadmium-contaminated soil and improving soil quality. The composite solid phosphate-solubilizing agent includes phosphate-solubilizing bacteria, bone char, culture medium and organic matrix; the phosphate-solubilizing bacteria include Enterobacter holmium HS-6 and Pantotheca cumulus CT-3; when the composite solid phosphate-solubilizing agent is applied to Cd-contaminated soil, Enterobacter holmium HS-6, Pantotheca cumulus CT-3 and bone char synergistically reduce the bioavailability of Cd in the soil, while improving soil quality and increasing the available phosphorus content in the soil. On the one hand, this application can effectively promote the conversion of insoluble phosphates into soluble phosphates, thereby increasing the available phosphorus content in the soil by 98.19%; on the other hand, it can fix the heavy metal Cd in the soil, thereby reducing the available Cd content in the soil by about 52.50%, showing excellent Cd fixation ability, and can alleviate Cd stress in crops (e.g., rice). It has great application value in remediating Cd pollution in farmland, improving soil quality and protecting the environment.

[0037] (2) The application of a composite solid phosphate-solubilizing agent of the present invention for remediating cadmium-contaminated soil and improving soil quality is different from the existing Cd pollution remediation technology that only focuses on a single mechanism. The application technology of the present invention adopts the combined remediation technology of Enterobacter holmium HS-6, Pantotheca cumulus CT-3 and bone char. Through the rich pore structure, huge specific surface area and strong ion exchange capacity of the micron and nano-level bone char in the phosphate-solubilizing agent, it can efficiently and quickly adsorb Cd ions in the soil and has an excellent ability to fix Cd in the soil. It can also provide a stable habitat and rich nutrients for Enterobacter holmium HS-6 and Pantotheca cumulus CT-3, protect Enterobacter holmium HS-6 and Pantotheca cumulus CT-3 from adverse environmental factors, enhance the survival ability and activity of Enterobacter holmium HS-6 and Pantotheca cumulus CT-3 in the polluted environment, and thus improve the remediation ability of Enterobacter holmium HS-6 and Pantotheca cumulus CT-3 for heavy metals. Therefore, the synergistic effect of *Enterobacter holmieae* HS-6, *Pantotheca acuminata* CT-3, and micron- and nano-scale bone char significantly improves the removal and fixation efficiency of Cd, greatly reducing the bioavailability of Cd in soil and mitigating its harm to the ecological environment and crops. Furthermore, the metabolites produced by *Enterobacter holmieae* HS-6 and *Pantotheca acuminata* CT-3 during phosphorus dissolution can form stable complexes or precipitates with Cd ions, further reducing Cd bioavailability. Therefore, compared to using physical or chemical adsorption methods alone, this invention has a more significant remediation effect in reducing the bioavailability of Cd in soil.

[0038] (3) The application of the composite solid phosphate-solubilizing agent of the present invention for remediating cadmium-contaminated soil and improving soil quality is superior to traditional chemical remediation methods that use large amounts of chemical agents, which are prone to causing agent residues and secondary pollution. The remediation technology of the present invention uses Enterobacter holmieae HS-6, Pantotheca cumulus CT-3, and micron-nano multi-level bone char, all of which are of natural origin or biodegradable materials. They will not introduce harmful chemicals into the soil and are more friendly to the soil and the surrounding ecological environment. In addition, Enterobacter holmieae HS-6 and Pantotheca cumulus CT-3 can improve the soil microbial community structure and promote the growth and reproduction of beneficial microorganisms. Micron-nano multi-level bone char can provide a good habitat for soil microorganisms and jointly maintain the soil ecological balance, which is difficult to achieve with many traditional remediation technologies. Therefore, the application of the present invention has the advantage of being green and environmentally friendly.

[0039] (4) The application of a composite solid phosphate-solubilizing agent of the present invention to remediate cadmium-contaminated soil and improve soil quality. Since the Enterobacter holmium HS-6 and Pantotheca cumulus CT-3 in the phosphate-solubilizing agent can convert the insoluble phosphorus in the soil into available phosphorus, thereby increasing the phosphorus nutrition of the soil, while the micron and nano multi-level bone char can improve the pH value and cation exchange capacity of the soil and enhance the soil's water and fertilizer retention capacity, the combination of the three can comprehensively improve soil fertility and create good nutritional conditions for crop growth.

[0040] (5) The application of the composite solid phosphate-solubilizing agent of the present invention for remediating cadmium-contaminated soil and improving soil quality, through the synergistic effect of Enterobacter holmium HS-6, Pantothecin CT-3, and micron-nano multi-level bone char, reduces the toxic effects of Cd on crops in the soil and enhances the crop's resistance to stress. This is a function that simple physical or chemical remediation technologies do not possess. On the other hand, micron-nano multi-level bone char is rich in various nutrients such as calcium, nitrogen, phosphorus, and magnesium, which are precisely the nutrients necessary for plant growth. Therefore, the micron-nano multi-level bone char of the present invention can also act as fertilizer, replenishing soil fertility, promoting the vigorous growth of crops, and thus improving agricultural productivity. In summary, the application of the present invention has advantages in promoting plant growth. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a scanning electron microscope image of Enterobacter HS-6 of the present invention.

[0043] Figure 2 This is a scanning electron microscope image of Enterobacter HS-6 of the present invention after reaction with bone char.

[0044] Figure 3 This is a scanning electron microscope image of the CT-3 cluster of pantothecin bacteria according to the present invention.

[0045] Figure 4 This is a scanning electron microscope image of the clump-forming pantothecin CT-3 of the present invention after interaction with bone char.

[0046] Figure 5 This is a graph showing the soil pH measurement results of samples collected from different experimental groups at different times.

[0047] Figure 6 This is a graph showing the results of soil cation exchange capacity measurements from samples collected at different times in different experimental groups.

[0048] Figure 7 This is a graph showing the results of soil available phosphorus content determination for samples collected from different experimental groups at different time periods.

[0049] Figure 8 This is a graph showing the results of soil available Cd content determination for samples collected from different experimental groups at different time periods.

[0050] Figure 9 This is a graph showing the results of soil catalase activity assays for samples collected from different experimental groups at different time periods.

[0051] Figure 10 This is a graph showing the results of soil sucrase activity assays on samples collected from different experimental groups at different time periods.

[0052] Figure 11 This is a graph showing the results of soil urease activity measurements from samples collected at different times in different experimental groups.

[0053] Figure 12 This is a graph showing the results of soil acid phosphatase activity measurements from samples collected at different times in different experimental groups.

[0054] Figure 13 This is a graph showing the results of rice plant height measurements using soil samples from different experimental groups.

[0055] Figure 14 This is a graph showing the results of root length measurement of rice cultivated from soil samples in different experimental groups.

[0056] Figure 15 This is a graph showing the results of measuring the fresh weight of the aboveground parts of rice grown from soil samples in different experimental groups.

[0057] Figure 16 This is a graph showing the results of measuring the fresh weight of the underground parts of rice grown from soil samples in different experimental groups. Detailed Implementation

[0058] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0059] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. In this invention, the singular forms “a,” “the,” and “the” as used in the embodiments and appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0060] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0061] The culture medium formulations described in the following examples are as follows:

[0062] LB medium (g / L): 10g peptone, 5g yeast extract, 10g NaCl, pH 7.0~7.2.

[0063] LB solid medium: Add 18g~20g of agar powder to every 1L of LB medium.

[0064] NBRIP medium (g / L): glucose 10g, MgCl2·6H2O 5g, MgSO4·7H2O 0.25g, FeSO4·7H2O 0.01g, KCl 0.2g, (NH4)2SO4 0.1g, Ca3(PO4)2 5.0g, pH 7.0~7.4.

[0065] NBRIP solid medium: Add 18g~20g of agar powder to every 1L of NBRIP-P medium. Example 1

[0066] An application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality is disclosed. This composite solid phosphate-solubilizing agent comprises phosphate-solubilizing bacteria, bone char, culture medium, and wheat bran; the phosphate-solubilizing bacteria include *Enterobacter holmium* HS-6 and *Pantothecin* CT-3. The taxonomic name of *Enterobacter holmium* HS-6 is... Enterobacter hormaechei It was deposited on October 19, 2023, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC NO.: 28680, located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing. The scanning electron microscope image of *Enterobacter horneri* HS-6 is shown below. Figure 1 As shown. The classification name of this cluster of pantothecin CT-3 is... Pantoea agglomerans It was deposited on January 8, 2025, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC NO.: 33335, located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing. The scanning electron microscope image of *Enterobacter horneri* HS-6 is shown below. Figure 3 As shown.

[0067] This application uses a compound solid phosphate-solubilizing agent to treat Cd-contaminated soil. It reduces the bioavailability of Cd in the soil through the synergistic effect of Enterobacter holmieae HS-6, Pantothecin CT-3, and bone char, while improving soil quality.

[0068] The 16S rDNA gene sequence of Enterobacter holmieae HS-6 is shown in SEQ ID No. 1. The gene sequence length is 1476.

[0069] The 16S rDNA gene sequence of the pantothecin CT-3 is shown in SEQ ID No. 2. The length of the gene sequence is 1411.

[0070] In this embodiment, the particle size of bone char is 30 nm to 2 μm.

[0071] The application of this compound solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality includes the following steps:

[0072] S1. Preparation of micro- and nano-sized bone char: Animal bone was heated to 450℃ at a heating rate of 10℃ / min for 120 min and then cooled to obtain large pieces of bone char. The large pieces of bone char were ball-milled at 450 rpm for 5 h to obtain micro- and nano-sized multi-level bone char.

[0073] In the ball mill, zirconium oxide particles are used to ball mill large bone char pieces, and ethanol is added as a grinding aid; the weight ratio of zirconium oxide particles to large bone char pieces is 17:1; the mass ratio of ethanol to large bone char pieces is 1.8:1.

[0074] S2. Activation of the strains: Enterobacter horneri HS-6 and Pantotheca cumulus CT-3 were inoculated into LB medium and then cultured in a constant temperature shaker at 28°C with shaking at 180 r / min until OD. 600 =0.6~0.8, to obtain HS-6 bacterial suspension and CT-3 bacterial suspension; wherein, the effective viable bacteria count of the prepared HS-6 bacterial suspension and CT-3 bacterial suspension is 1×10 10 CFU / mL ~9×10 10 CFU / mL.

[0075] S3. Preparation of liquid bacterial agent: The HS-6 bacterial suspension and CT-3 bacterial suspension obtained in step S2 are mixed to form a composite bacterial solution. The micron-nano multi-level bone char obtained in step S1 is sterilized by irradiation and then added to the composite bacterial solution into NBRIP medium. The medium is then placed in a constant temperature shaker at 28°C and shaken at 180 r / min for 48 h to obtain the liquid bacterial agent.

[0076] In this embodiment, the mass-to-volume ratio of bone char to NBRIP culture medium is 0.5%; the volume ratio of HS-6 bacterial suspension to CT-3 bacterial suspension is 1:1; the inoculation amount of the composite bacterial solution in NBRIP culture medium is 1% of the volume percentage of NBRIP culture medium; in this embodiment, the irradiation sterilization dose is 5.0 kGy.

[0077] S4. Organic matrix carrier treatment: After rinsing the organic matrix three times with deionized water, soak the organic matrix in deionized water that covers it for 15 hours, and then sterilize it under high temperature and high pressure to obtain the treated organic matrix carrier; the conditions for high temperature and high pressure sterilization are: 121℃, 104KPa, 20min.

[0078] S5. Preparation of solid bacterial agent: The liquid bacterial agent obtained in step S3 is added to the organic matrix carrier obtained in step S4, packed into a polyethylene bag and sealed. Five air holes are punched on the surface of the polyethylene bag with a sterile needle. Then, it is placed in a constant temperature shaker at 28°C and shaken at 180 r / min for 3 days to obtain a composite solid phosphate-solubilizing bacterial agent. In this embodiment, the mass ratio of liquid bacterial agent to organic matrix carrier is 15:85.

[0079] S6. Remediation of Cd-contaminated soil: A compound solid phosphate-solubilizing agent is applied to the Cd-contaminated soil. In this embodiment, the mass ratio of the compound solid phosphate-solubilizing agent to the Cd-contaminated soil is 3:300. Example 2

[0080] An application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality is disclosed. The difference between this embodiment and Example 1 is that in step S3, the mass-to-volume ratio of bone char to NBRIP culture medium is 1%, the irradiation sterilization dose is 3.0 kGy, and the culture is incubated with shaking for 44 h. All other conditions and methods in this embodiment are the same as in Example 1. Example 3

[0081] An application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality is disclosed. The difference between this embodiment and Example 1 is that in this embodiment, the organic substrate is rice straw; in step S3, the mass-to-volume ratio of bone char to NBRIP medium is 2%, the irradiation sterilization dose is 4.0 kGy, and the culture is shaken for 46 h. All other conditions and methods in this embodiment are the same as in Example 1. Example 4

[0082] An application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality is disclosed. The difference between this embodiment and Example 1 is that in this embodiment, the organic substrate is corn cob; in step S3, the mass-to-volume ratio of bone char to NBRIP medium is 2.5%, the irradiation sterilization dose is 6.0 kGy, and the culture is shaken for 50 h. All other conditions and methods in this embodiment are the same as in Example 1. Example 5

[0083] An application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality. The difference between this embodiment and Embodiment 1 is that in this embodiment, step S1, preparation of micro-nano bone char: animal bone is heated to 440℃ at a heating rate of 8℃ / min and thermally decomposed for 140min. After cooling, large pieces of bone char are obtained. The large pieces of bone char are ball-milled at 440rpm for 6h to obtain micron-nano multi-level bone char.

[0084] In the ball mill, zirconium oxide particles are used to ball mill large bone char pieces, and ethanol is added as a grinding aid; the weight ratio of zirconium oxide particles to large bone char pieces is 15:1; the mass ratio of ethanol to large bone char pieces is 1.7:1.

[0085] The remaining conditions and methods in this embodiment are the same as in Embodiment 1. Example 6

[0086] An application of a composite solid phosphate-solubilizing agent for remediating cadmium-contaminated soil and improving soil quality. The difference between this embodiment and Embodiment 1 is that in this embodiment, step S1, preparation of micro-nano bone char: animal bone is heated to 460℃ at a heating rate of 12℃ / min and thermally decomposed for 100min. After cooling, large pieces of bone char are obtained. The large pieces of bone are ball-milled at 460rpm for 4h to obtain micron-nano multi-level bone char.

[0087] In the ball mill, zirconium oxide particles are used to ball mill large bone char pieces, and ethanol is added as a grinding aid; the weight ratio of zirconium oxide particles to large bone char pieces is 20:1; the mass ratio of ethanol to large bone char pieces is 2:1; and the irradiation sterilization dose is 6.0 kGy.

[0088] The remaining conditions and methods in this embodiment are the same as in Embodiment 1. Example 7

[0089] An application of a composite solid phosphate-solubilizing bacterial agent for remediating cadmium-contaminated soil and improving soil quality is disclosed. The difference between this embodiment and Embodiment 1 is that in this embodiment, in step S4, the organic matrix is ​​soaked in deionized water for 10 hours. In step S5, six air holes are punched in the surface of a polyethylene bag using a sterile needle, and then the bag is placed in a constant temperature shaker at 28°C and shaken at 180 r / min for 2 days to obtain the composite solid phosphate-solubilizing bacterial agent. In this embodiment, the mass ratio of liquid bacterial agent to organic matrix carrier is 15:70. In step S6, the mass ratio of the composite solid phosphate-solubilizing bacterial agent to Cd-contaminated soil is 3:250.

[0090] The remaining conditions and methods in this embodiment are the same as in Embodiment 1. Example 8

[0091] An application of a composite solid phosphate-solubilizing bacterial agent for remediating cadmium-contaminated soil and improving soil quality is disclosed. The difference between this embodiment and Embodiment 1 is that in this embodiment, in step S4, the organic matrix is ​​soaked in deionized water for 20 hours. In step S5, eight air holes are punched in the surface of a polyethylene bag using a sterile needle, and then the bag is placed in a constant temperature shaker at 28°C and shaken at 180 r / min for 4 days to obtain the composite solid phosphate-solubilizing bacterial agent. In this embodiment, the mass ratio of liquid bacterial agent to organic matrix carrier is 15:100. In step S6, the mass ratio of the composite solid phosphate-solubilizing bacterial agent to Cd-contaminated soil is 3:350.

[0092] The remaining conditions and methods in this embodiment are the same as in Embodiment 1.

[0093] Experimental testing:

[0094] I. Scanning electron microscopy examination

[0095] For a scanning electron microscope image of the *Enterobacter holmieae* strain HS-6 of this invention, please refer to [link to image]. Figure 1 .in, Figure 1 (b) is Figure 1 (a) A magnified view of the area within the dashed box. (e.g.) Figure 1 As shown, Enterobacter holmieae HS-6 is a rod-shaped bacterium 1 μm long.

[0096] In addition, scanning electron microscopy was performed on *Enterobacter holmieae* HS-6 after reaction with bone char. Please refer to [link to relevant documentation]. Figure 2 ,in Figure 2 (b) is Figure 2 (a) Enlarged view of the area within the dashed box. (From...) Figure 2 As can be seen, Enterobacter holmieae HS-6 is adsorbed on the surface of bone char, and the morphology of Enterobacter holmieae HS-6 is intact and full, indicating that bone char provides favorable conditions for the growth and physiological state of Enterobacter holmieae HS-6.

[0097] For a scanning electron microscope image of the pantothenic acid CT-3 strain of the present invention, please refer to [link to image]. Figure 3 .in, Figure 3 (b) is Figure 3 (a) A magnified view of the area within the dashed box. (e.g.) Figure 3 As shown, the CT-3 cluster of pantothecin bacteria consists of rod-shaped bacteria 1 μm long.

[0098] In addition, scanning electron microscopy was performed on the clumps of pantothenic acid CT-3 after interaction with bone char. Please refer to [link to relevant documentation]. Figure 4 ,in Figure 4 (b) is Figure 4 (a) Enlarged view of the area within the dashed box. (From...) Figure 4 As can be seen, clustered pantothenic acid CT-3 is adsorbed on the surface of bone char, and the morphology of the clustered pantothenic acid CT-3 is intact and full, indicating that bone char provides favorable conditions for the growth and physiological state of clustered pantothenic acid CT-3.

[0099] II. Remediation of Cd-contaminated soil

[0100] 1. Soil collection

[0101] The soil used in the experiment was collected from the topsoil layer (0cm-20cm) of paddy fields in Huadu District, Guangzhou (23.415°N, 113.047°E). Before use, the soil was air-dried, ground, and sieved through a 2mm mesh.

[0102] 2. Experimental Sample Design Scheme

[0103] The specific design scheme for the experimental samples is shown in Table 1 below.

[0104] Table 1. Experimental Sample Design Scheme

[0105]

[0106] The four experimental groups in Table 1 were each set up in quadruplicates. The total weight of the samples in each experimental group was 300g, and they were placed in brown wide-mouth bottles for incubation. The bottles were placed in a constant temperature environment of 25℃, and water was added daily to maintain a constant moisture content of 60%. Soil samples were collected on days 0, 3, 10, 18, and 30, dried, ground, and passed through a 100-mesh sieve for subsequent testing.

[0107] The soil pH, soil cation exchange capacity (CEC), soil available phosphorus content, soil available Cd content, and soil enzyme activity of the samples from the above experimental groups were measured respectively.

[0108] (a) Determination of soil pH in different experimental groups

[0109] The soil pH values ​​of the samples collected at different time periods according to the design in Table 1 (four parallel samples for each sample) were determined according to the "Polypotential Method for Determination of Soil pH" (HJ 962-2018). The results can be found in [link to relevant documentation]. Figure 5 . Figure 5 In the text, “Cd” represents the Cd soil group, “Cd MNBC” represents the Cd MNBC soil group, and “Cd MNBC CT-3&HS-6” represents the CdMNBC CT-3&HS-6 soil group.

[0110] Depend on Figure 5 The results showed that the pH values ​​of the samples from the blank control group and the Cd soil group were approximately 4.5 at each sampling time, while the pH values ​​of the samples from the Cd MNBC soil group and the Cd MNBC CT-3 & HS-6 soil group were approximately 6 at each sampling time. This indicates that the soil with added bone char or with added bone char, Pantotheca acuminata CT-3 and Enterobacter horneri HS-6 had a higher pH value compared to the blank control group, which can improve acidic soil.

[0111] in addition, Figure 5 During the study, the soil pH generally showed a trend of first increasing and then decreasing, reaching its highest point on day 10. This indicates that the application of bone char or the application of bone char, Pantotheca acuminata CT-3 and Enterobacter holmieae HS-6 significantly increased the soil pH.

[0112] Numerous studies have shown that the activity of some phosphate-solubilizing bacteria may be inhibited in acidic soils (pH < 6), but many phosphate-solubilizing bacteria exhibit high activity in neutral (pH 6-7) or slightly alkaline (pH > 7) soils, which is conducive to phosphorus release. Therefore, the application of a composite solid phosphate-solubilizing agent to remediate cadmium-contaminated soil and improve soil quality can bring the soil closer to neutral, thereby increasing the activity of *Pantotheca agglutinosa* CT-3 and *Enterobacter holmieae* HS-6, and promoting an increase in the available phosphorus content of the soil. Therefore, applying the composite solid phosphate-solubilizing agent of this invention to the soil, in combination with the effects of bone char, *Pantotheca agglutinosa* CT-3, and *Enterobacter holmieae* HS-6, is beneficial for the survival of *Pantotheca agglutinosa* CT-3 and *Enterobacter holmieae* HS-6 in paddy soil and for them to better exert their phosphate-solubilizing effects.

[0113] (II) Determination of soil cation exchange capacity in different experimental groups

[0114] Soil cation exchange capacity (CEC) was determined using samples collected at different time periods according to the design in Table 1 (four parallel samples were set up for each sample). The results can be found in [link to table]. Figure 6 The determination of soil cation exchange capacity was carried out in accordance with the "Determination of Soil Cation Exchange Capacity by Hexaamminecobalt Trichloride Extraction-Spectrophotometric Method" (HJ 889-2017). Figure 6 In the text, “Cd” represents the Cd soil group, “Cd MNBC” represents the Cd MNBC soil group, and “Cd MNBC CT-3&HS-6” represents the Cd MNBCCT-3&HS-6 soil group.

[0115] Depend on Figure 6 The results showed that, compared with the blank control group and the Cd MNBC soil group, the soil cation exchange capacity of samples from all sampling time periods in both the Cd MNBC soil group and the Cd MNBC CT-3 & HS-6 soil group was significantly increased. The soil cation exchange capacity generally showed a trend of first increasing and then decreasing, reaching its peak on day 10, indicating that the application of bone char or the application of bone char, *Pantotheca acuminata* CT-3, and *Enterobacter holmieae* HS-6 significantly increased the soil cation exchange capacity.

[0116] (III) Determination of available phosphorus content in soil samples from different experimental groups

[0117] The available phosphorus content in the soil was determined using samples collected at different time periods according to the design in Table 1 (four parallel samples were set up for each sample). The determination results can be found in [link to table]. Figure 7 . Figure 7 In the text, “Cd” represents the Cd soil group, “Cd MNBC” represents the Cd MNBC soil group, and “Cd MNBC CT-3&HS-6” represents the Cd MNBC CT-3&HS-6 soil group.

[0118] Depend on Figure 7 The results showed that the available phosphorus content in the Cd MNBC soil group and the Cd MNBC CT-3&HS-6 soil group was significantly increased compared to the blank control group and the Cd soil group, indicating that the application of micron- and nano-level bone char and phosphate-solubilizing bacteria to the soil can significantly increase the available phosphorus content. Interestingly, compared with the Cd MNBC soil group, the available phosphorus content in the Cd MNBC CT-3&HS-6 soil group increased by 16.51% on day 3 under the combined action of micron- and nano-level bone char, Pantothecin CT-3, and Enterobacter horneri HS-6, indicating that under Cd pollution, the application of this invention—micron- and nano-level bone char, Pantothecin CT-3, and Enterobacter horneri HS-6 synergistically—is more effective in increasing the available phosphorus content in the soil. After 30 days, the available phosphorus content in the Cd MNBC CT-3&HS-6 soil group increased by 98.19%.

[0119] (iv) Determination of available Cd content in soil samples from different experimental groups

[0120] The available Cd content in the soil was determined using samples collected at different time periods according to the design in Table 1 (four parallel samples were set up for each sample). The determination results can be found in [link to table]. Figure 8 . Figure 8 In the text, “Cd” represents the Cd soil group, “Cd MNBC” represents the Cd MNBC soil group, and “Cd MNBC CT-3&HS-6” represents the Cd MNBC CT-3&HS-6 soil group.

[0121] The determination of available Cd content in soil was carried out according to the "Determination of 8 Available Elements in Soil: Diethylenetriaminepentaacetic Acid Extraction-Inductively Coupled Plasma Atomic Emission Spectrometry" (HJ 804-2016). 5.00 g of freeze-dried and sieved soil sample was weighed and placed in a 50 mL centrifuge tube. 20 mL of diethylenetriaminepentaacetic acid (DTPA)-calcium chloride (CaCl2)-triethanolamine (TEA) extractant (pH 7.3) was added. The sample was extracted at room temperature with reciprocating shaking at 160 r / min for 2 h. After centrifugation, the supernatant was filtered through a 0.22 μm filter membrane and then tested.

[0122] Depend on Figure 8The results showed that, compared to the Cd soil group, the available Cd content in both the Cd MNBC soil group and the Cd MNBC CT-3 & HS-6 soil group was significantly reduced. In particular, the Cd MNBC CT-3 & HS-6 soil group showed a greater reduction in available Cd content compared to the Cd MNBC soil group, indicating that the combined treatment with micron- and nano-level bone char (using Pantothecin CT-3 and Enterobacter horneri HS-6) was more effective in reducing available Cd content in the soil. Analysis on day 3 compared to the Cd soil group revealed that the available Cd content in the Cd MNBC soil group and the Cd MNBC CT-3 & HS-6 soil group decreased by 39.88% and 43.19%, respectively. After 30 days of treatment with micron- and nano-level bone char (using Pantothecin CT-3 and Enterobacter horneri HS-6), the available Cd content in the Cd MNBC CT-3 & HS-6 soil group decreased by 52.50%. Figure 8 Analysis showed that in the early stage (days 0-10) of the Cd MNBC soil group and the Cd MNBC CT-3 & HS-6 soil group, bone char likely dominated Cd adsorption; in the middle stage (days 10-18), the biochemical regulatory role of phosphate-solubilizing bacteria became prominent, further enhancing Cd fixation; in the long stage (days 18-30), the Cd MNBC CT-3 & HS-6 soil group maintained lower Cd availability by continuously activating soil nutrients and optimizing Cd speciation. This demonstrates that the application of the composite solid phosphate-solubilizing agent of this invention for remediating cadmium-contaminated soil and improving soil quality can significantly reduce the available Cd content, exhibiting a more significant effect in reducing the bioavailability of Cd in soil.

[0123] (v) Determine the available Cd content in soil samples from single and double bacteria.

[0124] A single-strain phosphate-solubilizing agent was prepared as a comparative sample. The difference between the preparation of the single-strain phosphate-solubilizing agent and the preparation of the composite solid phosphate-solubilizing agent in Example 1 is that the strain Pantotheca cumulus CT-3 was not used, but only Enterobacter holmium HS-6 was used. All other methods were the same as in Example 1.

[0125] The design schemes for single-strain and double-strain samples are shown in Table 2 below.

[0126] Table 2. Sample design schemes for single-strain and double-strain experiments.

[0127]

[0128] The three experimental groups in Table 2 were each set up in quadruplicates. The total weight of the samples in each experimental group was 300g, and they were placed in brown wide-mouth bottles for incubation. The bottles were placed in a constant temperature environment of 25℃, and water was added daily to maintain a constant moisture content of 60%. Soil samples were collected on days 0, 3, 10, 18, and 30, dried, ground, and passed through a 100-mesh sieve. The available Cd content in the soil was then determined.

[0129] Compared with the Cd soil group, the available Cd content in the Cd MNBC HS-6 soil group and the Cd MNBC CT-3&HS-6 soil group was significantly reduced, as shown in Table 3 below.

[0130] Table 3. Data on the decrease in available Cd content in soil samples from single-strain and double-strain experiments.

[0131]

[0132] As shown in Table 3, compared with the Cd MNBC HS-6 soil group, the Cd MNBC HS-6 soil group showed a greater decrease in available Cd content in the early stage (days 3-10) and a greater decrease in the long stage (days 18-30). This indicates that the application of the composite solid phosphate-solubilizing agent of this invention for remediating cadmium-contaminated soil and improving soil quality demonstrates a more significant long-term effect in remediating Cd-contaminated soil.

[0133] (vi) Determination of soil enzyme activity in samples from different experimental groups

[0134] Soil catalase, sucrase, urease, and acid phosphatase activities were measured using samples collected at different time periods according to the design in Table 1 (four parallel samples were set up for each sample). The measurement results can be found in the respective tables. Figure 9 , Figure 10 , Figure 11 and Figure 12 .

[0135] The method for determining soil enzyme activity is as follows: Using the kit from Iseku Biotechnology Co., Ltd. (China) according to the manufacturer's instructions, and using a multifunctional enzyme marker (Synergy HTX, BioTek, USA), the activities of four typical soil enzymes—catalase, sucrase, urease, and acid phosphatase—were determined.

[0136] Figures 9 to 12 In the text, “Cd” represents the Cd soil group, “Cd MNBC” represents the Cd MNBC soil group, and “Cd MNBC CT-3&HS-6” represents the Cd MNBC CT-3&HS-6 soil group.

[0137] Urease, sucrase, and catalase are important soil enzymes widely used to evaluate the impact of soil conditioners on soil biological functions. Urease and sucrase participate in the decomposition and mineralization of carbohydrates in the soil, providing nutrients for soil microorganisms and crop growth, while catalase can degrade H2O2 in the soil, reducing its toxic effects on organisms. Figures 9 to 12 It is evident that, compared with the Cd soil group, the micron-nano multi-level bone char combined with Pantotheca CT-3 and Enterobacter horneri HS-6 significantly enhanced the activities of catalase, sucrase, urease and acid phosphatase in Cd-contaminated soil, increasing them by 13.30%, 340.38%, 473.29% and 108.59%, respectively.

[0138] Furthermore, acid phosphatase is a class of enzymes that catalyze the mineralization of soil organic phosphorus. Its activity directly affects the decomposition, transformation, and bioavailability of organic phosphorus in the soil, serving as an indicator of the direction and intensity of soil phosphorus biotransformation. Acid phosphatase activity is significantly influenced by soil carbon and nitrogen content, available phosphorus content, and pH. Therefore, micron- and nano-scaled bone char combined with clustered *Plasmophytosporum* CT-3 and *Enterobacter horneri* HS-6 enhances acid phosphatase activity in Cd-contaminated soil. This enhancement may be closely related to the unique properties of micron- and nano-scaled bone char. Bone char is an additional source of C and P elements, providing more suitable habitat conditions for clustered *Plasmophytosporum* CT-3 and *Enterobacter horneri* HS-6 in the soil and promoting their growth.

[0139] III. Experiments to Promote Crop Growth

[0140] The selected rice variety was Xiuzhan 15. The rice seedlings were first cultivated in a plant culture box for 14 days. Then, uniformly sized seedlings were transplanted into four experimental groups (as designed in Table 1) for pot cultivation. Six replicates were prepared for each group. The plants were placed at room temperature for a 28-day exposure experiment. The rice plants were harvested, and plant height, root length, aboveground fresh weight, and underground fresh weight were measured. The results are shown in the respective tables. Figure 13 , Figure 14 , Figure 15 and Figure 16 .

[0141] Figures 13 to 16 In the text, “Cd” represents the Cd soil group, “Cd MNBC” represents the Cd MNBC soil group, and “Cd MNBC CT-3&HS-6” represents the Cd MNBC CT-3&HS-6 soil group.

[0142] Depend on Figures 13 to 16The results showed that, compared with the blank control group, the plant height, root length, aboveground fresh weight, and underground fresh weight of rice cultivated in the Cd soil group were significantly reduced, by 22.55%, 25.87%, 25.23%, and 32.00%, respectively, indicating that Cd-contaminated soil seriously affected crop growth. Compared with the Cd soil group, both the Cd MNBC soil group and the Cd MNBC CT-3&HS-6 soil group significantly increased the plant height, root length, and aboveground fresh weight of rice. Specifically, the Cd MNBC CT-3&HS-6 soil group increased the plant height, root length, and aboveground fresh weight of rice by 16.05%, 31.99%, and 49.46%, respectively, compared with the Cd soil group. This demonstrates that the application of a composite solid phosphate-solubilizing agent to remediate cadmium-contaminated soil and improve soil quality can promote robust crop growth and thus enhance agricultural productivity.

[0143] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An application of a composite solid phosphorus-solubilizing bacterial agent for remediation of cadmium-contaminated soil and improvement of soil quality, characterized by, The composite solid phosphorus-solubilizing bacterial agent comprises phosphorus-solubilizing bacteria, micron-nanometer multi-level bone charcoal, culture medium and organic matrix; the phosphorus-solubilizing bacteria comprise Enterobacter hormaechei HS-6 and Pantoea agglomerans CT-3; The classification name of the Enterobacter hormaechei HS-6 is Enterobacter hormaechei , which was preserved in the China General Microbiological Culture Collection Center on October 19, 2023, with a preservation number of CGMCC NO. 28680. The taxonomic name of the Pantoea agglomerans CT-3 is Pantoea agglomerans , which was preserved in the China General Microbiological Culture Collection Center on January 8, 2025, with a preservation number of CGMCC NO. 33335; The composite solid phosphorus-solubilizing bacterial agent is applied to Cd-contaminated soil, and the bioavailability of Cd in the soil is reduced by the synergistic effect of Enterobacter hormaechei HS-6, Pantoea agglomerans CT-3 and bone charcoal, and the soil quality is improved.

2. The application of a composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 1, characterized in that, The micron-nanometer multi-level bone charcoal has a particle size of 30 nm to 2 μm.

3. The application of the composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 1, characterized in that, The organic matrix is at least one of wheat bran, rice straw or corn cob.

4. The application of the composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 1, characterized in that, The application comprises the following steps: S1, preparation of micron-nanometer multi-level bone charcoal: after being thermally cracked, the animal bone is cooled and ball milled to obtain micron-nanometer multi-level bone charcoal; S2, Activation of the strains: Enterobacter cloacae HS-6 and Pantoea agglomerans CT-3 were inoculated into LB medium respectively, and then put into a constant temperature shaker at 28°C to culture at 180 r / min until OD 600 = 0.6~0.8, to obtain HS-6 bacterial suspension and CT-3 bacterial suspension; S3, preparation of liquid bacterial agent: the HS-6 bacterial suspension and the CT-3 bacterial suspension obtained in step S2 are mixed to form a composite bacterial liquid, the micron-nanometer multi-level bone charcoal prepared in step S1 is sterilized by irradiation, and then the sterilized micron-nanometer multi-level bone charcoal and the composite bacterial liquid are added into NBRIP culture medium, and then the mixture is placed in a constant-temperature shaker at 28 ℃ and oscillated at 180 r / min for 44 h to 50 h to obtain a liquid bacterial agent; S4, treatment of organic matrix carrier: after being washed with deionized water, the organic matrix is soaked in deionized water that does not submerge the organic matrix, and then the soaked organic matrix is sterilized by high-temperature and high-pressure to obtain a treated organic matrix carrier; S5, preparation of solid bacterial agent: the liquid bacterial agent obtained in step S3 is added into the organic matrix carrier obtained in step S4, and then the mixture is cultured at 28 ℃ for 2 d to 4 d to obtain the composite solid phosphorus-solubilizing bacterial agent; S6, remediation of Cd-contaminated soil: the composite solid phosphorus-solubilizing bacterial agent is applied to Cd-contaminated soil.

5. The application of the composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 4, characterized in that, In step S1, the animal bone is thermally cracked at a heating rate of 8 ℃ / min to 12 ℃ / min to 440 ℃ to 460 ℃ for 100 min to 140 min, and then cooled to obtain large bone charcoal, and then the large bone charcoal is ball milled at 440 rpm to 460 rpm for 4 h to 6 h by using a ball mill to obtain micron-nanometer multi-level bone charcoal; In the ball mill, zirconium oxide particles are used to ball mill the large bone charcoal, and ethanol is added as a grinding aid; the weight ratio of the zirconium oxide particles to the large bone charcoal is (15-20):1; and the mass ratio of the ethanol to the large bone charcoal is (1.5-2):

1.

6. The application of the composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 4, characterized in that, In step S2, the effective viable cell number of the prepared HS-6 bacterial suspension and CT-3 bacterial suspension was 1 x 10 10 CFU / mL ~ 9 x 10 10 CFU / mL.

7. The application of the composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 4, characterized in that, In step S3, the mass-volume ratio of the micron-nanometer multi-level bone charcoal to the NBRIP culture medium is 0.5% to 2.5%; The volume ratio of the HS-6 bacterial suspension to the CT-3 bacterial suspension is 1:1; The inoculation amount of the composite bacterial liquid in the NBRIP culture medium is 1% of the volume percentage of the NBRIP culture medium; The dose of the sterilization by irradiation is 3.0 kGy to 6.0 kGy.

8. The application of the composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 4, characterized in that, In step S4, after the organic matrix is washed with deionized water for three times, the organic matrix is soaked in deionized water that does not submerge the organic matrix for 10 h to 20 h, and then the soaked organic matrix is sterilized by high-temperature and high-pressure to obtain a treated organic matrix carrier; The high-temperature and high-pressure sterilization is performed at 121 ℃, 104 KPa for 20 min.

9. The application of the composite solid phosphorus-solubilizing bacterial agent for repairing cadmium-contaminated soil and improving soil quality according to claim 4, characterized in that, In step S5, the liquid bacterial agent obtained in step S3 is added to the organic substrate carrier obtained in step S4, sealed in a polyethylene bag, 5-8 air holes are punched on the surface of the polyethylene bag with a sterile needle, and then placed in a constant temperature shaker at 28℃ for 2-4 days of culture at 180r / min to obtain the composite solid phosphorus-dissolving bacterial agent; In step S5, the mass ratio of the liquid bacterial agent to the organic substrate carrier is 15: (70-100); In step S6, the mass ratio of the composite solid phosphorus-dissolving bacterial agent to the Cd-contaminated soil is 3: (250-350).

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