Microbial compound bacterial fertilizer for improving saline alkali soil and increasing crop yield

Abstract

The invention discloses a microbial compound bacterial fertilizer for improving saline alkali soil and increasing the acting yield. A preparation method of the microbial compound bacterial fertilizer comprises the following steps: preparing a microbial agent containing phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, bacillus subtilis and actinomycetes; the preparation method comprises the following steps: preparing a sodium alginate solution, adding nano-hydroxyapatite and a microbial agent, uniformly mixing, dropwise adding a calcium chloride solution, and embedding an inner layer to obtain microbial embedded particles; uniformly mixing biochar, humic acid and attapulgite, taking a 2-3% HPMC solution as a binder, and carrying out middle-layer coating, so as to obtain prefabricated microbial fertilizer particles; and coating the chitosan-sodium alginate-nano ZnO outer layer to obtain the microbial compound bacterial fertilizer. The microbial compound bacterial fertilizer disclosed by the invention adopts a multi-layer and multifunctional collaborative design concept, realizes efficient protection and slow release of functional microorganisms in a saline-alkali environment, remarkably improves the physicochemical properties of soil and promotes the growth of crops.

Description

Technical Field

[0001] The present invention relates to the technical field of saline-alkali soil improvement, and particularly relates to a microbial compound fertilizer for improving saline-alkali soil and increasing crop yield. Background Art

[0002] Soil salinization is a severe ecological environment problem faced by humans at present. Therefore, how to improve and utilize saline-alkali land, accelerate vegetation restoration, improve plant salt tolerance, and promote the sustainable utilization of saline-alkali land are effective measures to solve the current shortage of land resources, improve land utilization rate, and improve the ecological environment.

[0003] Measures and technologies for saline-alkali land improvement can be mainly simply classified into three categories: physical methods, chemical methods, and biological methods. Physical methods mainly refer to irrigation for salt leaching, deep plowing and sunning of the soil, replacing the original soil with good soil, etc.; chemical methods mainly involve the use of chemical improvers to improve the soil structure or displace Na in the soil + , and promote salt leaching; biological methods include the selection and breeding of salt-tolerant plants and the utilization of microorganisms (sulfur-oxidizing bacteria, actinomycetes, AM (Arbuscular Mycorrhizal) fungi, and photosynthetic bacteria), etc. Among them, physical methods often have disadvantages such as resource waste, large investment, and complex engineering; chemical methods, although having quick effects, have problems such as high cost and secondary pollution; biological methods, although having slow effects and long cycles, integrate economic, environmental, and ecological benefits, meet the goals of the sustainable development strategy, have achieved certain results in saline-alkali land improvement and are receiving increasing attention, especially microbial improvement technology. Microbial improvement refers to the use of important functional microorganisms for saline-alkali soil improvement: phosphate-solubilizing and potassium-solubilizing bacteria, sulfur-oxidizing bacteria, actinomycetes, AM (Arbuscular Mycorrhizal) fungi, photosynthetic bacteria, and bacillus, etc. for saline-alkali soil improvement.

[0004] Applying microbial inoculants and fertilizers can effectively reduce the pH and salinity of the soil, increase the contents of available phosphorus, available potassium, total nitrogen, and organic matter in the soil, and improve the physical and chemical properties of saline-alkali soil. However, the action time of traditional microbial inoculants is limited, and it is difficult to continuously play an improvement role throughout the crop growth cycle, especially in moderately and severely saline-alkali lands with high salt back-seepage and alkalization degrees, and the improvement effect is difficult to maintain for a long time. Summary of the Invention

[0005] Based on the problems existing in the background technology, the present invention provides a microbial compound fertilizer for improving saline-alkali soil and increasing crop yield. The microbial compound fertilizer adopts a multi-level and multi-functional collaborative design concept, and realizes the efficient protection and slow release of functional microorganisms in a saline-alkali environment through a three-layer structure of inner encapsulation with sodium alginate-nano-hydroxyapatite, middle coating with biochar-humic acid-palygorskite, and outer coating with chitosan-sodium alginate-nano-ZnO. At the same time, it significantly improves the physical and chemical properties of the soil and promotes crop growth.

[0006] The present invention is implemented through the following technical solutions:

[0007] A microbial compound fertilizer for improving saline-alkali soil and increasing crop yield, and the preparation method of the microbial compound fertilizer includes the following steps:

[0008] S1. Activate and culture phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, Bacillus subtilis and actinomycetes separately, collect the cell precipitate and mix it evenly with a protective agent, and freeze-dry to obtain a microbial inoculant;

[0009] S2. Prepare a 2% sodium alginate solution, add nano-hydroxyapatite and the microbial inoculant, mix evenly, and then drop the mixture into calcium chloride solution through a nozzle with a diameter of 1-2 mm, stir for 15-20 minutes to complete cross-linking, filter and wash to obtain microbial embedded particles;

[0010] S3. Mix biochar, humic acid and palygorskite evenly, use a 2-3% HPMC solution as a binder, and form a carrier coating layer on the outer layer of the microbial embedded particles through a fluidized bed coating process to obtain prefabricated microbial fertilizer particles;

[0011] S4. Prepare a coating solution, immerse the prefabricated microbial fertilizer particles in the coating solution, then transfer them to a 1-3% calcium chloride solution for curing, and dry them by hot air circulation at 30-45 °C to obtain the microbial compound fertilizer.

[0012] Further, in step S1, the phosphate-solubilizing bacteria is Bacillus megaterium; the potassium-solubilizing bacteria is Bacillus mucilaginosus; the nitrogen-fixing bacteria is Azotobacter chroococcum; the actinomycetes is Streptomyces microflavus.

[0013] Further, in step S1, the viable count of phosphate-solubilizing bacteria in the microbial inoculant ≥ 2×10 9 CFU / g; the viable count of potassium-solubilizing bacteria ≥ 1×10 9 CFU / g; the viable count of nitrogen-fixing bacteria ≥ 2×10 9 CFU / g; the viable count of Bacillus subtilis ≥ 5×10 9 CFU / g; the viable count of actinomycetes ≥ 2×10 9 CFU / g.

[0014] Furthermore, in step S1, the mass ratio of the bacterial cell precipitate to the protective agent is 1:1 - 1:2, and the protective agent is composed of skim milk, trehalose, and glycerol in a mass ratio of (5 - 8):(2 - 4):(1 - 3).

[0015] Furthermore, in step S2, the addition amount of nano-hydroxyapatite is 1 - 5% of the weight of sodium alginate, the addition amount of the microbial inoculant is 15 - 20% of the weight of sodium alginate, and the concentration of the calcium chloride solution is 2 - 4%.

[0016] Furthermore, in step S3, the mass ratio of biochar, humic acid, and attapulgite is (4 - 6):(2 - 4):(1 - 3).

[0017] Furthermore, the process parameters of fluidized bed coating in step S3 are: inlet air temperature 40 - 45°C, spraying rate 3 - 5 mL / min, and material bed temperature 35 - 38°C.

[0018] Furthermore, the coating solution in step S4 is composed of sodium alginate with a mass concentration of 2 - 4%, chitosan with 0.5 - 1.5%, and nano-zinc oxide with 0.05 - 0.2%, and the pH value is 5.5 - 6.5.

[0019] Furthermore, the pH adaptability of the microbial composite fertilizer is 8.0 - 9.5, and the conductivity (EC) tolerance range is 4 - 8 dS / m.

[0020] Furthermore, the particle size of the microbial composite fertilizer is 2 - 4 mm, the application rate is 300 - 500 kg / ha, and it is mixed and applied in the tillage layer of 0 - 20 cm.

[0021] Advantages of the present invention:

[0022] 1. Through the multi-layer core-shell structure design of the microbial fertilizer in this application, the microbial composite fertilizer can continuously release functional flora and establish a long-term microbial ecosystem. The synergistic effect of multiple functional microorganisms forms a complete soil-plant growth promotion system. Phosphorus-solubilizing bacteria and potassium-solubilizing bacteria can effectively activate insoluble phosphorus and potassium elements in the soil and convert them into forms that can be absorbed and utilized by plants, improving nutrient availability; nitrogen-fixing bacteria provide nitrogen sources for plants through biological nitrogen fixation, reducing the application of chemical fertilizers; Bacillus subtilis produces a variety of bioactive substances and antibacterial substances, enhancing plant stress resistance and disease resistance; actinomycetes promote the decomposition of organic matter and improve soil structure. The synergistic effect of multi-functional flora improves soil microbial diversity, and the acid produced by the metabolism of the flora (oxalic acid / lactic acid) synergistically releases H + , reducing the pH of the surface soil, increasing the soil buffer capacity, and reducing the pH fluctuation range.

[0023] 2. In this application, the microbial fertilizer uses sodium alginate-nano-hydroxyapatite as the inner carrier, which not only provides a physical protection barrier for the microorganisms, reducing the direct damage of the saline-alkali environment to the microorganisms, but also the nano-hydroxyapatite can serve as a slow-release phosphorus source and enhance the mechanical strength of the microspheres at the same time.

[0024] 3. The biochar-humic acid-palygorskite composite material in the middle layer of the microbial fertilizer in this application has a significant effect on improving the soil structure. The porous structure of the biochar improves the physical properties of the soil, enhances the water retention capacity of the soil, increases the aggregate content, and makes the soil more loose and breathable; and the three-dimensional pores of the biochar provide a shelter for the microbial flora, increasing the survival rate of the microbial flora; the humic acid adsorbs sodium ions through ion exchange, reducing the content of exchangeable sodium in the soil and reducing the soil salt damage; the layered structure of palygorskite can enhance the soil ion exchange capacity, avoid salt accumulation, and prevent secondary salinization.

[0025] 4. The chitosan-sodium alginate-nano-ZnO coating on the outer layer of the microbial fertilizer in this application is designed to be pH-responsive, forming a slow-release protective film with excellent mechanical strength and biocompatibility. At the same time, nano-ZnO provides the necessary trace elements and antibacterial properties, further enhancing the stability of the product. Detailed implementation manners

[0026] The technical solutions of the present invention will be further described in detail below in combination with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0027] The specific information of the microbial inoculant used in the examples and comparative examples of this application is as follows:

[0028] The phosphate-solubilizing bacterium is Bacillus megaterium (LJP-106), which was deposited on April 26, 2010 at the General Microbiological Center of the China Committee for Culture Collection of Microorganisms, address: No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, and the deposit number of the strain is CGMCC No. 3770.

[0029] The potassium-solubilizing bacterium is Bacillus mucilaginosus (JDzhs-bh), which was deposited on March 20, 2019 at the General Microbiological Center of the China Committee for Culture Collection of Microorganisms, address: No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, and the deposit number of the strain is CGMCC No. 17376.

[0030] The nitrogen-fixing bacterium is Azotobacter chroococcum (LGN-09), which was deposited with the General Microbiological Center of the China Committee for Culture Collection of Microorganisms on April 26, 2010. The address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing. The deposit number of the strain is CGMCC No. 3768.

[0031] The Bacillus subtilis is Bacillus subtilis (B3), which was deposited with the General Microbiological Center of the China Committee for Culture Collection of Microorganisms on June 4, 2024. The address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing. The deposit number of the strain is CGMCC NO. 30857.

[0032] The actinomycete is Streptomyces microflavus, which was purchased from Shanghai Meiyan Biotechnology Co., Ltd. The deposit number of the strain is AS 4.1428.

[0033] Example 1

[0034] A microbial compound fertilizer for improving saline-alkali soil and increasing crop yield. The preparation method of the microbial compound fertilizer comprises the following steps:

[0035] S1. The phosphorus-solubilizing bacterium, potassium-solubilizing bacterium, nitrogen-fixing bacterium, Bacillus subtilis and actinomycete are separately activated and cultured, and the collected cell precipitates are mixed evenly with a protective agent (skim milk, trehalose and glycerol in a mass ratio of 6:3:2) at a mass ratio of 1:1, and then freeze-dried to obtain a microbial inoculant; the viable count of the phosphorus-solubilizing bacterium in the final microbial inoculant is ≥2×10 9 CFU / g; the viable count of the potassium-solubilizing bacterium is ≥1×10 9 CFU / g; the viable count of the nitrogen-fixing bacterium is ≥2×10 9 CFU / g; the viable count of Bacillus subtilis is ≥5×10 9 CFU / g; the viable count of the actinomycete is ≥2×10 9 CFU / g;

[0036] S2. Prepare a 2% sodium alginate solution, add nano-hydroxyapatite and the microbial inoculant. The addition amount of nano-hydroxyapatite is 2% of the weight of sodium alginate, and the addition amount of the microbial inoculant is 16% of the weight of sodium alginate. After mixing evenly, the mixture is dropped into a 3% calcium chloride solution through a nozzle with a diameter of 1 mm, and stirred for 20 minutes to complete cross-linking, then filtered and washed to obtain microbial embedded particles;

[0037] S3. Mix biochar, humic acid, and attapulgite clay evenly at a mass ratio of 5:3:2, use a 2% HPMC solution as a binder, and form a carrier coating layer on the outer layer of the microbial-embedded particles through a fluidized bed coating process. The process parameters of the fluidized bed coating are: inlet air temperature 40°C, spraying rate 4 mL / min, material bed temperature 36°C, and coating weight gain rate 15%, to obtain prefabricated microbial fertilizer particles;

[0038] S4. Prepare a coating solution composed of 3% sodium alginate, 1% chitosan, and 0.2% nano-zinc oxide by mass concentration, with a pH value of 6.5. Immerse the prefabricated microbial fertilizer particles in the coating solution, and then transfer them to a 2% calcium chloride solution for curing, and dry them by hot air circulation at 40°C to obtain the microbial compound fertilizer.

[0039] Further, when performing freeze-drying in S1, a freeze-drying device is used to perform freeze-drying treatment on the mixture. The freeze-drying device includes: an identification and confirmation module, a first processing module, a second processing module, a third processing module, and an inspection and analysis module; the freeze-drying device performing freeze-drying treatment on the mixture includes: the identification and confirmation module performing preliminary identification on the mixture to determine whether there is a mixture for which freeze-drying treatment is to be performed, and when there is a mixture for which freeze-drying treatment is to be performed, further identifying and confirming the mixture to determine the quantity and composition of the mixture, and moving the mixture to the processing chamber; the first processing module analyzing the freezing property according to the composition of the mixture to determine the target freezing temperature, and combining the quantity of the mixture to determine the estimated freezing time, and then adjusting the freezing environment of the processing chamber according to the estimated freezing time and the target freezing temperature, and realizing the freezing treatment of the mixture based on the adjusted freezing environment to obtain the frozen mixture; the second processing module performing vacuum treatment on the processing chamber during the freezing treatment process of the first processing module, so that the processing chamber is in a vacuum environment; the third processing module analyzing the heating sublimation property according to the composition of the mixture, and combining the target freezing temperature to determine the target heating temperature, and then, after the first processing module completes the freezing treatment and the second processing module completes the vacuum treatment, performing heating regulation on the processing chamber according to the target heating temperature through the third processing module, so that the processing chamber realizes the heating sublimation of the frozen mixture under vacuum conditions to obtain the mixture after heating sublimation treatment; the inspection and analysis module performing drying inspection on the mixture after heating sublimation treatment to judge whether the mixture after heating sublimation treatment is completely dry. When the mixture after heating sublimation treatment is completely dry, the mixture at this time is the final product microbial agent after freeze-drying. When the mixture after heating sublimation treatment is not completely dry, the second processing module further adjusts the pressure of the processing chamber based on the current vacuum environment to reduce the pressure of the processing chamber, and at the same time the third processing module regulates the target heating temperature to increase the target heating temperature, and continues to perform heating sublimation according to the regulated target heating temperature until the mixture after heating sublimation treatment is completely dry. The mixture at this time is the final product microbial agent after freeze-drying.

[0040] Among them, when the third processing module continues to perform heating sublimation according to the regulated target heating temperature, it is based on the vacuum environment after pressure adjustment. The regulated target heating temperature is slightly higher than the target heating temperature.

[0041] The above-mentioned freeze-drying of the mixture after the uniform mixing of the bacterial cell precipitate and the protective agent at a mass ratio of 1:1 by the freeze-drying device realizes the acquisition of the microbial inoculant, ensures the activity of the microbial inoculant, provides guarantee for the preparation of the microbial compound fertilizer, and moreover, through the recognition and confirmation module, the analysis of the mixture is realized. Not only can the freeze-drying device analyze and process when there is a mixture to be freeze-dried, but when there is no mixture to be freeze-dried, it does not need to respond, realizing the control of whether the freeze-drying device is enabled, and also realizing the preliminary recognition and confirmation of the mixture, clarifying the quantity and composition of the mixture, so that the first processing module and the third processing module can carry out corresponding regulation in combination with the actual situation of the mixture, avoiding waste of regulation resources and damage to the mixture. Through the first processing module, the freeze-drying property analysis is carried out according to the composition of the mixture and the freeze-drying estimated time is determined in combination with the quantity of the mixture, so as to carry out adaptive regulation for mixtures in different situations, avoiding waste of resources caused by long-term freeze-drying of a small amount of mixture or poor freeze-drying effect caused by short-term freeze-drying of a large amount of mixture, and at the same time avoiding the mismatch between the regulated freeze-drying environment and the bacterial cells in the mixture resulting in inactivation or deformation of the bacterial cells, ensuring the activity of the bacterial cells in the mixture after freeze-drying. Through the second processing module, the vacuum environment of the processing chamber is regulated, so that when the third processing module performs heat sublimation, it can be based on the vacuum environment, which not only provides convenience for the sublimation of water molecules and improves the efficiency of heat sublimation, but also helps to reduce the temperature of the material and can prevent the mixture from being damaged due to excessive temperature rise during sublimation. Through the third processing module, the heat sublimation property analysis is carried out according to the composition of the mixture and the target heating temperature is determined in combination with the target freeze-drying temperature, realizing the association with the mixture, so that heat sublimation is carried out in combination with the properties of the mixture, avoiding damage to the mixture caused by too high temperature and affecting the quality of the microbial inoculant. In addition, through the inspection and analysis module, further analysis is carried out on whether the microbial inoculant is thoroughly dried, ensuring that the final microbial inoculant is thoroughly dried, providing guarantee for the result output of the freeze-drying device.

[0042] Further, when transferring to the 2% calcium chloride solution for solidification, an image acquisition device is used to monitor and analyze the solidification process, including:

[0043] Obtain the monitored and collected images, perform optimization processing on the monitored and collected images, and lock the target area based on the optimized monitored and collected images;

[0044] Identify the physical image characteristics of the target area to obtain the current identification information of the target area;

[0045] Carry out solidification characteristic analysis on the current identification information of the target area to obtain the current solidification characteristics;

[0046] Analyze the curing change of the prefabricated microbial fertilizer granules impregnated coating solution by combining the current curing characteristics with the historical curing characteristics to obtain the current curing change information;

[0047] Determine whether the prefabricated microbial fertilizer granules impregnated coating solution is completely cured in a 2% calcium chloride solution according to the current curing change information to obtain the monitoring and analysis results;

[0048] According to the monitoring and analysis results, when the prefabricated microbial fertilizer granules impregnated coating solution is completely cured, perform hot air circulation drying at 40 °C to obtain the microbial compound fertilizer.

[0049] Among them, the target area is the area where the prefabricated microbial fertilizer granules impregnated coating solution exists in the 2% calcium chloride solution.

[0050] The visualization of the curing process is realized through the image acquisition device above, enabling the determination of whether it is completely cured based on the monitored and collected images, realizing the control of the curing process, avoiding incomplete curing from affecting the acquisition rate of the microbial compound fertilizer, and also avoiding waste of time caused by too long curing time. By optimizing the monitored and collected images, the quality of the monitored and collected images is improved, providing guarantee for identifying the physical characteristics of the target area and subsequent analysis based on the current recognition information of the target area. Moreover, by analyzing the curing change of the prefabricated microbial fertilizer granules impregnated coating solution by combining the current curing characteristics with the historical curing characteristics to clarify the current curing change information, it can not only provide data analysis support for determining whether it is completely cured, but also provide curing prediction for the case of incomplete curing, enabling relevant personnel to determine the progress of curing based on the current curing change information and better reflecting the detailed situation of the curing process.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that only the microbial agent is coated in sodium alginate-hydroxyapatite, without including the subsequent two-step coating processes of S3 and S4, and the compound fertilizer A is prepared.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 1 is that it does not include the step of impregnating with the coating solution in S4; the compound fertilizer B is prepared.

[0055] Comparative Example 3

[0056] The difference between this comparative example and Example 1 is that in step S3, only biochar is used as the carrier, without including humic acid and attapulgite; the rest of the preparation is the same as in Example 1, and the compound fertilizer C is prepared.

[0057] Comparative Example 4

[0058] The difference between this comparative example and Example 1 is that in step S4, only sodium alginate coating is used, excluding chitosan, and the rest of the preparation is the same as in Example 1, to obtain compound bacterial fertilizer D.

[0059] Test Example

[0060] One typical coastal saline-alkali land in this test example was used as the experimental subject to conduct the improvement experiment of microbial inoculants. The experimental time was one season of crops, and the crop yield and the changes in soil physical and chemical properties before and after application were measured.

[0061] 1. Experimental location: Dafeng coastal tidal flat test field, Yancheng, Jiangsu, GPS point: 32°59' north latitude, 120°49' east longitude.

[0062] 2. Experimental design

[0063] Deep trenches were used for isolation, and plots of 5×5m were designed to plant the green manure plant Melilotus officinalis. The designs included planting and not planting, applying inoculants, not applying and applying different groups of inoculants (the inoculants were used as base fertilizers, and the methods are shown in Table 1), with eight treatments, and each treatment had 3 replicates.

[0064] The experiment was carried out between April and July 2024. Melilotus officinalis was sown on April 10th, and the yield during the vigorous growth period was measured on July 15th. Soils in the tillage layer (0-20cm) before and after planting were collected to analyze the physical and chemical properties.

[0065] 3. Experimental results

[0066] The statistical results of each treatment are shown in Table 1

[0067] Table 1

[0068]

[0069] It can be seen from the data in Table 1 that for Treatment 2 with the application of the microbial inoculant in Example 1, compared with the blank Treatment 1, the soil pH decreased from 8.5 to 7.9, and the salinity decreased from 0.46% to 0.38%, indicating that the compound bacterial fertilizer effectively reduced the soil alkalinity and alleviated the soil salt damage; the nutrient contents (alkali-hydrolyzable nitrogen, available phosphorus, available potassium) all increased, mainly due to the transformation of microorganisms, and the organic matter content increased significantly (4.5→13.8g / kg), which was the result of the promotion of organic matter accumulation by microbial activities. In Treatment 3, planting Melilotus officinalis without applying the microbial inoculant could produce a yield of 113kg / mu, while after adding the microbial inoculant in Example 1, the yield increased to 167kg / mu, with an increase of 47.8%; combining the microbial inoculant and the planting of Melilotus officinalis could significantly reduce the soil pH (7.6) and salinity (0.23%), and the effect was better than using the microbial inoculant alone; the nutrient content and the organic matter content both increased significantly, indicating that there was a positive synergistic effect between the microbial inoculant and the green manure plant.

[0070] Treatment 5 applied compound bacterial fertilizer A, which only had an inner embedding and lacked the middle and outer protective structures. The effect of pH reduction was weak, the salinity reduction was limited, the nutrient content increase was small, and the organic matter content increase was also extremely limited. The whole data indicated that the compound bacterial fertilizer with a single-layer embedding structure had insufficient protection for microorganisms in the saline-alkali environment and limited active release.

[0071] Treatment 6 applied compound bacterial fertilizer B, which lacked the outermost coating protection. Overall, it was lower than Treatment 2 but higher than Treatment 5, indicating that the outer coating had an important protective effect on the long-term activity of microorganisms and nutrient release.

[0072] Treatment 7 applied compound bacterial fertilizer C, whose middle carrier only used biochar and lacked humic acid and attapulgite. The improvement of pH was weak, the salinity reduction was not obvious, the improvement of available phosphorus and available potassium contents was limited, and the organic matter content was higher than that of compound bacterial fertilizer A but still much lower than that of Example 1. The whole data showed that humic acid and attapulgite had a synergistic effect on microorganism activity and soil improvement.

[0073] Treatment 8 applied compound bacterial fertilizer D, whose outer layer only used sodium alginate coating and lacked chitosan. The pH dropped to 8.0, which was better than that of bacterial fertilizers A and C but weaker than that of Example 1. The improvement of salinity and nutrient levels was medium, and the organic matter content was the highest among all comparative examples but still lower than that of Example 1; it indicated that the pH-responsive performance of the chitosan-sodium alginate composite coating had a significant promoting effect on the exertion of microorganism activity.

[0074] The microbial bacterial fertilizer of the present invention adopts a core-shell structure design. The outer layer is a pH-responsive sodium alginate coating, which dissociates under alkaline conditions to form nanoscale pores, promoting water penetration; the amino group of chitosan loses protonation in the alkaline environment, weakening the electrostatic interaction with sodium alginate and further forming pores to increase the dissolution rate; the organic acids and buffer ions in the core functional layer are gradually released to reduce the soil pH and create a suitable environment for the survival of the microbial flora. The biochar-humic acid-attapulgite composite structure gels and swells after absorbing water in the soil; the nano-hydroxyapatite in the core layer gradually dissolves to provide a phosphorus source, and the bacterial flora gradually absorbs water and revives to ensure the long-term activity of the bacterial flora; the bacterial flora migrates along the three-dimensional pores of the biochar to form a dominant microbial flora; the porous structure of the organism provides a shelter for the bacterial flora and increases the survival rate of the bacterial flora.

[0075] Finally, it should be noted that the above embodiments only represent several implementation manners of the present invention and are not intended to limit the present invention. For those of ordinary skill in the art, any modifications, equivalent replacements, improvements, etc. made without departing from the concept of the present invention should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A microbial compound fertilizer for improving saline-alkali soil and increasing the yield, characterized in that: The preparation method of the microbial composite fertilizer comprises the following steps: S1. Activate and culture phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, Bacillus subtilis and actinomycetes separately, collect bacterial precipitates, mix them evenly with a protective agent, and freeze-dry them to obtain a microbial agent; S2. Prepare a 2% sodium alginate solution, add nano-hydroxyapatite and microbial agents, mix well, drop the mixture into a calcium chloride solution through a nozzle with a diameter of 1-2 mm, stir for 15-20 minutes to complete cross-linking, filter and wash to obtain microbial embedded particles; S3. The biochar, humic acid and attapulgite are evenly mixed, 2-3% HPMC solution is used as a binder, and a carrier coating layer is formed on the outer layer of the microorganism embedded particles by a fluidized bed coating process to obtain prefabricated microbial fertilizer particles; S4. Prepare coating solution, immerse the prefabricated microbial fertilizer particles in the coating solution, then transfer to 1-3% calcium chloride solution for solidification, and dry with hot air circulation at 30-45°C to obtain microbial composite fertilizer.

2. The microbial composite fertilizer according to claim 1, characterized in that: In step S1, the phosphate-solubilizing bacteria is Bacillus megaterium; the potassium-solubilizing bacteria is Bacillus colloids; the nitrogen-fixing bacteria is Azotobacter rotundifolia; and the actinomycetes is Streptomyces tenuifolius.

3. The microbial composite fertilizer according to claim 1, characterized in that: The number of viable phosphate-solubilizing bacteria in the microbial agent in step S1 is ≥ 2×10 9 CFU / g; viable count of potassium-dissolving bacteria ≥1×10 9 CFU / g; viable count of nitrogen-fixing bacteria ≥ 2×10 9 CFU / g; viable count of Bacillus subtilis ≥5×10 9 CFU / g; viable count of actinomycetes ≥2×10 9 CFU / g.

4. The microbial composite fertilizer according to claim 1, characterized in that: In step S1, the mass ratio of bacterial precipitate to protective agent is 1:1-1:2, and the protective agent is composed of skim milk, trehalose and glycerol in a mass ratio of (5-8):(2-4):(1-3).

5. The microbial composite fertilizer according to claim 1, characterized in that: In step S2, the amount of nano-hydroxyapatite added is 1-5% of the weight of sodium alginate, the amount of microbial agent added is 15-20% of the weight of sodium alginate, and the concentration of calcium chloride solution is 2-4%.

6. The microbial composite fertilizer according to claim 1, characterized in that: The mass ratio of biochar, humic acid and attapulgite in step S3 is (4-6):(2-4):(1-3).

7. The microbial composite fertilizer according to claim 1, characterized in that: The process parameters of fluidized bed coating in step S3 are: air inlet temperature 35-40°C, spray rate 3-5 mL / min, and bed temperature 35-38°C.

8. The microbial composite fertilizer according to claim 1, characterized in that: In step S4, the coating solution is composed of 2-4% sodium alginate, 0.5-1.5% chitosan and 0.05-0.2% nano zinc oxide in mass concentration, and the pH value is 5.5-6.

5.

9. The microbial composite fertilizer according to any one of claims 1 to 8, characterized in that: The pH adaptability of the microbial composite fertilizer is 8.0-9.5, and the electrical conductivity (EC) tolerance range is 4-8dS / m.

10. The microbial composite fertilizer according to any one of claims 1 to 8, characterized in that: The particle size of the microbial composite fertilizer particles is 2-4 mm, the application amount is 300-500 kg / hectare, and it is mixed and applied in a tillage layer of 0-20 cm.

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