Microbial inoculant and slow-release device for soil improvement

Abstract

The application discloses a kind of microbial inoculants and slow-release device for soil improvement, and relates to the technical field of soil improvement and microbial fertilizer.A kind of microbial inoculants for soil improvement, including strain inner core, slow-release layer and external coating, the strain inner core is the freeze-resistant bacteria powder core that spindly lysine bacillus and bacillus subtilis are mixed into with composite freeze-drying protective agent, and slow-release layer is coated in the outside of strain inner core.The microbial inoculants for soil improvement and slow-release device of the application, by spindly lysine bacillus and bacillus subtilis respectively preparing optimized composite freeze-drying protective agent, and making independent bacteria powder core by vacuum freeze-drying, two bacteria powder cores are in physical separation state in slow-release layer, effectively avoid the antagonistic inhibition of bacillus subtilis to spindly lysine bacillus, and realize the synergistic effect of two functional bacteria.

Description

[0001] This invention relates to the field of soil improvement and microbial fertilizer technology, and in particular to a microbial agent and slow-release device for soil improvement. Background Technology

[0002] With global climate change and the advancement of intensive agricultural production, soil degradation in freeze-thaw zones is becoming increasingly prominent. These areas experience multiple freeze-thaw cycles annually, leading to soil structure deterioration, aggregate destruction, reduced porosity, and accelerated nutrient loss. This is compounded by salinization and organic matter depletion, severely hindering sustainable agricultural development and ecological restoration in these regions. Existing technologies, including some patents, disclose microbial agents for saline-alkali land improvement and their application in general soil improvement. However, these existing technologies still have the following shortcomings: There is a lack of specialized microbial agents for soils in freeze-thaw zones. Soils in freeze-thaw zones are characterized by low average annual temperatures and frequent freeze-thaw cycles. Conventional microbial agents have low survival rates and short durations of effectiveness in such extreme environments, making it difficult for them to effectively improve soil conditions. Second, existing sustained-release technologies lack freeze-thaw responsive release mechanisms. Most existing sustained-release devices for microbial agents are designed for ambient temperature or saline-alkali environments, but none of them are designed with freeze-thaw cycle responsive release mechanisms.

[0003] Third, there is a lack of slow-release device designs that maintain the fluidity of bacterial suspensions in low-temperature environments. Existing slow-release devices do not consider the problem of bacterial suspensions freezing and failing to release under the low-temperature conditions of freeze-thaw zones, and lack heating, insulation, and anti-sedimentation designs for bacterial suspensions, which limits the practical application of slow-release devices in freeze-thaw zones. Summary of the Invention

[0004] The purpose of this invention is to provide a microbial agent and slow-release device for soil improvement. It solves the problems mentioned in the background art by formulating optimized composite freeze-drying protectants for Bacillus fusiformis and Bacillus subtilis, and then freeze-drying them under vacuum to form independent bacterial powder cores.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a microbial agent for soil improvement, comprising a microbial core, a slow-release layer, and an outer coating. The microbial core is a freeze-resistant microbial powder core made by mixing Bacillus fusiformis and Bacillus subtilis with a composite freeze-drying protectant. The slow-release layer covers the outside of the microbial core and uses polyvinyl alcohol cryogel as the slow-release material to achieve the slow-release target of low-temperature locking and temperature-release. The outer coating is made of composite material to cover the slow-release layer. The outer coating absorbs moisture and forms a physical insulation layer.

[0006] Preferably, the microbial core comprises a first microbial powder core and a second microbial powder core, wherein the first microbial powder core is prepared by vacuum freeze-drying a mixture of *Bacillus fusiformis* and a first composite freeze-drying protectant, and the second microbial powder core is prepared by vacuum freeze-drying a mixture of *Bacillus subtilis* and a second composite freeze-drying protectant. The mass ratio of the first microbial powder core to the second microbial powder core is (1-10):1, and the effective viable count of both the first and second microbial powder cores is not less than 1×10⁻⁶. 8 CFU / g. The first and second bacterial powder cores are physically separated in the slow-release layer, and spatial isolation between the bacterial species is achieved through an independent freeze-drying protective shell, avoiding the antagonistic inhibition of Bacillus subtilis on Bacillus fusiformis.

[0007] Preferably, the preparation method of the first bacterial powder core is as follows: the first composite freeze-drying protectant is prepared according to the following weight percentages: 10-20% skim milk powder, 8-15% trehalose, 4-10% sucrose, 1-3% monosodium glutamate, 1-3% glycerol, and the remainder is sterile water. The spindle-shaped lysine Bacillus is subjected to three-stage liquid fermentation, the bacterial cells are collected, and the bacterial sludge is collected after centrifugation at 8000-12000 rpm for 10-20 minutes. The spindle-shaped lysine Bacillus sludge and the first composite freeze-drying protectant are mixed evenly at a volume ratio of 1:(1-3), equilibrated at 4℃ for 40-60 minutes, pre-frozen at -40℃ for 3-8 hours, transferred to a vacuum freeze dryer, and freeze-dried at a pressure of 4-12 Pa for 18-24 hours to obtain the first bacterial powder core.

[0008] Preferably, the preparation method of the second bacterial powder core is as follows: the second composite freeze-drying protectant is prepared according to the following weight percentages: maltodextrin 3-8%, sucrose 3-6%, trehalose 0.5-2%, Tween-80 0.1-0.5%, and the remainder is sterile water. Bacillus subtilis is subjected to three-stage liquid fermentation, the bacterial cells are collected, and the bacterial sludge is collected after centrifugation at 8000-12000 rpm for 10-20 minutes. The Bacillus subtilis sludge and the second composite freeze-drying protectant are mixed evenly at a volume ratio of 1:(1-3), equilibrated at 4℃ for 40-60 minutes, pre-frozen at -40℃ for 3-8 hours, transferred to a vacuum freeze dryer, and freeze-dried at a pressure of 4-12 Pa for 18-24 hours to obtain the second bacterial powder core.

[0009] Preferably, the polyvinyl alcohol cryogel is a mixed gel made of polyvinyl alcohol, sodium alginate, diatomaceous earth, and waterborne polyurethane. The mass concentration of polyvinyl alcohol in the mixed gel is 8-12%, the mass concentration of sodium alginate is 0.5-2%, the mass concentration of diatomaceous earth is 1-3%, and the mass concentration of waterborne polyurethane is 0.5-2%. The addition of sodium alginate helps to form a denser network structure and slow down the release rate. The addition of diatomaceous earth forms a network pore structure inside the composite gel, optimizing the porous structure. The waterborne polyurethane can enhance the mechanical and mass transfer properties of the gel.

[0010] Preferably, the preparation method of the sustained-release layer is as follows: polyvinyl alcohol, sodium alginate, diatomaceous earth and waterborne polyurethane are dissolved in deionized water in proportion, heated to 90-100℃ and stirred evenly, cooled to 30-40℃, the first bacterial powder core and the second bacterial powder core are added, stirred evenly, the mixture is injected into a mold, frozen at -20℃ to -40℃ for 12-24 hours, thawed at room temperature, and a polyvinyl alcohol cryogel with a porous three-dimensional network structure is formed, thus obtaining the sustained-release layer.

[0011] Preferably, the outer coating is a composite material comprising the following raw materials in parts by weight: 30-50 parts weathered coal, 15-30 parts cellulose, 10-20 parts soybean meal powder, 10-20 parts corn cob powder, 5-15 parts chitosan, 3-10 parts carrageenan, and 3-8 parts diatomaceous earth. Cellulose, diatomaceous earth, and carrageenan absorb soil moisture, providing a moisture environment for the internal microorganisms. The weathered coal and organic materials form an insulating layer in the soil, buffering the impact of low external temperatures on the slow-release layer and the microorganisms. The outer coating acts as the first barrier, delaying the entry of moisture into the internal slow-release layer, thus achieving a step-by-step release.

[0012] Preferably, the preparation process of the outer coating is as follows: weathered coal, cellulose, soybean meal powder, corn cob powder, and diatomaceous earth are pulverized through a 100-200 mesh sieve and mixed evenly; chitosan and carrageenan are dissolved in a 1-3% acetic acid solution to prepare a coating solution; the above mixed powder and coating solution are mixed at a mass ratio of 1:(0.5-1.5) and stirred evenly; the mixture is sprayed or dipped onto the surface of the slow-release layer and dried at a low temperature of 40-60℃ to obtain the outer coating.

[0013] Another technical problem to be solved by the present invention is to provide a slow-release device for microbial agents used in soil improvement, including an outer casing. The outer casing contains a dosing tank and a drive assembly. The dosing tank includes a stirring inner tank, a heating jacket, and an insulated outer tank that are sequentially nested together. The microbial agent mixed with water is stirred evenly in the stirring inner tank. The heating jacket and the insulated outer tank heat and insulate the stirring inner tank to maintain the fluidity of the bacterial suspension in a low-temperature environment. The drive assembly includes a drive motor, a four-bar linkage, a stirring paddle, and a slow-release tube. The stirring paddle is located inside the stirring inner tank. The slow-release tube is connected to the lower end of the stirring inner tank. The drive motor drives the four-bar linkage to rotate. One end of the four-bar linkage controls the rotation of the stirring paddle, and the other end of the four-bar linkage drives the slow-release tube to slowly release the microbial agent.

[0014] Preferably, the four-bar linkage structure includes a parallel linkage array, a crank rod obliquely traversing the linkage array, a first transmission assembly, and a second transmission assembly. The crank rod has short rotating shafts at both ends. One short rotating shaft is fixedly connected to the output end of a drive motor via a bearing seat, and the other short rotating shaft is connected to the first transmission assembly. Limiting plates are provided at both ends of the linkage array. The center of one limiting plate is movably connected to the inner wall of the outer casing via a short shaft, and the center of the other limiting plate is connected to the second transmission assembly. The second transmission assembly is connected to a slow-release tube. A slow-release plate is provided inside the slow-release tube, and a first release hole is provided on the slow-release plate. A movable plate is movably connected to one side of the slow-release plate, and a second release hole corresponding to the position of the first release hole is provided on the movable plate. Sealing strips are symmetrically arranged on both sides of the movable plate, engaging with the slow-release tube. A movable hole is provided on the outer wall of the slow-release tube. A connecting rod is provided on the side of the movable plate near the movable hole, and the connecting rod is connected to the second transmission assembly.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The microbial agent and slow-release device for soil improvement of the present invention, by formulating optimized composite freeze-drying protectants for Bacillus fusiformis and Bacillus subtilis respectively, and preparing independent bacterial powder cores by vacuum freeze-drying, Bacillus fusiformis and Bacillus subtilis are respectively wrapped in independent composite freeze-drying protectant shells to form a first bacterial powder core and a second bacterial powder core. The two bacterial powder cores are physically separated in the slow-release layer, which effectively avoids the antagonistic and inhibitory effect of Bacillus subtilis on Bacillus fusiformis, and realizes the synergistic effect of the two functional bacteria. This invention uses a composite cryogel made of polyvinyl alcohol, sodium alginate, diatomaceous earth, and waterborne polyurethane as a sustained-release layer. By utilizing the low-temperature freezing and room-temperature thawing characteristics of polyvinyl alcohol, the sustained-release target of low-temperature locking and temperature-release is achieved. The addition of diatomaceous earth to the gel forms a network of pores inside the composite gel, optimizing the porous structure. Sodium alginate helps to form a denser network structure and slows down the release rate. Waterborne polyurethane can enhance the mechanical strength and mass transfer performance of the gel.

[0016] In this invention, the cellulose, diatomaceous earth, and carrageenan in the outer coating absorb soil moisture, providing a moisture environment for the internal microorganisms; the weathered coal and organic materials form a physical insulation layer in the soil, buffering the impact of low external temperatures on the slow-release layer and microorganisms; the outer coating acts as the first barrier, delaying the entry of moisture into the internal slow-release layer, thus achieving a step-by-step release.

[0017] The slow-release device of this invention achieves heating and insulation of the bacterial suspension through a three-layer nested structure of an inner stirring tank, a heating jacket, and an outer insulated tank, effectively maintaining the fluidity of the bacterial suspension under low-temperature conditions. The drive motor controls the continuous rotation of the stirring paddle and the intermittent release of the slow-release tube simultaneously through a four-bar linkage structure: the continuous rotation of the stirring paddle prevents the bacterial powder core from settling in the water, ensuring the uniformity of the bacterial suspension; the reciprocating deflection of the linkage array drives the gap between the movable plates to open the first release hole, realizing the intermittent quantitative release of the bacterial suspension. Attached Figure Description

[0018] Figure 1 This is an overall structural diagram of the slow-release device for soil improvement microbial agents of the present invention; Figure 2 This is a structural diagram of the slow-release device for soil improvement microbial agents of the present invention. Figure 3 This is a structural diagram of the driving component of the present invention; Figure 4 This is an overall view of the four-bar linkage structure of the present invention; Figure 5 This is a diagram showing the internal structure of the slow-release tube of the present invention; Figure 6 For the present invention Figure 5 Exploded view.

[0019] In the diagram: 1. Outer casing; 2. Feeding tank; 21. Inner mixing tank; 211. Feeding port; 212. Cover; 213. Vent; 22. Heating jacket; 23. Insulated outer tank; 3. Drive assembly; 31. Drive motor; 32. Four-bar linkage; 321. Linkage array; 3211. Limiting plate; 322. Crank rod; 3221. Rotating short shaft; 323. First transmission assembly; 324. Second transmission assembly; 33. Stirring paddle; 34. Slow-release tube; 341. Slow-release plate; 3411. First release hole; 342. Movable plate; 3421. Second release hole; 3422. Sealing strip; 3423. Linkage rod; 343. Movable hole. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0021] Microbial agents for soil improvement are prepared using the following methods: First bacterial powder core preparation: The first compound freeze-drying protectant was prepared by weight percentage as follows: 15% skim milk powder, 10% trehalose, 7% sucrose, 2% L-glutamate, 2% glycerol, and the remainder being sterile water. *Bacillus fusiformis* was subjected to tertiary liquid fermentation. The bacterial cells were collected, centrifuged at 10,000 rpm for 15 minutes, and the bacterial sludge was collected. The sludge was mixed with the first compound freeze-drying protectant at a volume ratio of 1:2, equilibrated at 4℃ for 50 minutes, pre-frozen at -40℃ for 5 hours, transferred to a vacuum freeze dryer, and freeze-dried at a pressure of 8 Pa for 20 hours to obtain the first bacterial powder core with an effective viable count of 2.5 × 10⁻⁶. 8 CFU / g.

[0022] Second microbial powder core preparation: The second compound freeze-drying protectant was prepared by weight percentage as follows: 5% maltodextrin, 4% sucrose, 0.8% trehalose, 0.2% Tween-80, with the remainder being sterile water. Bacillus subtilis was subjected to tertiary liquid fermentation. The bacterial cells were collected, centrifuged at 10,000 rpm for 15 minutes, and the bacterial sludge was collected. The sludge was mixed with the second compound freeze-drying protectant at a volume ratio of 1:2, equilibrated at 4℃ for 50 minutes, pre-frozen at -40℃ for 5 hours, transferred to a vacuum freeze dryer, and freeze-dried at 8 Pa for 20 hours to obtain the second bacterial powder core with an effective viable count of 3.0 × 10⁻⁶. 8 CFU / g, the first mycelium powder core and the second mycelium powder core are mixed at a mass ratio of 3:1 to form the mycelium core.

[0023] Preparation of sustained-release layer: Prepare a mixed gel solution with polyvinyl alcohol (10% by mass), sodium alginate (1% by mass), diatomaceous earth (2% by mass), and waterborne polyurethane (1% by mass), with the remainder being deionized water. Heat the solution to 95°C and stir until homogeneous. Cool the solution to 35°C, add the microbial inoculum core, stir until homogeneous, and pour the mixture into a spherical mold. Freeze the solution at -30°C for 18 hours and thaw at room temperature to form a slow-release gel layer.

[0024] Preparation of outer coating: Weigh out the following components by weight: 40 parts weathered coal, 20 parts cellulose, 15 parts soybean meal powder, 15 parts corn cob powder, 10 parts chitosan, 6 parts carrageenan, and 5 parts diatomaceous earth. Crush the weathered coal, cellulose, soybean meal powder, corn cob powder, and diatomaceous earth through a 150-mesh sieve and mix them evenly. Dissolve the chitosan and carrageenan in a 2% acetic acid solution to prepare a coating solution. Mix the powder and coating solution at a 1:1 mass ratio and stir evenly. Spray the mixture onto the surface of the slow-release layer and dry it at a low temperature of 50°C to obtain the finished microbial agent granules.

[0025] Simulated freeze-thaw cycle conditions were set up: freezing at -15℃ for 24 hours, thawing at 5℃ for 24 hours, and repeated 5 times. After the obtained bacterial agent granules were placed under simulated freeze-thaw cycle conditions, the survival rate of the bacterial strain was 81.7%. After application to the freeze-thaw zone soil in Northeast China with pH 8.2 and organic matter content of 1.2%, the soil pH dropped to 7.6 after 60 days, the organic matter content increased to 1.7%, and the available phosphorus content increased by 26%. Example

[0026] Microbial agents for soil improvement are prepared using the following methods: First bacterial powder core preparation: The first composite freeze-drying protectant was prepared by weight percentage as follows: 18% skim milk powder, 12% trehalose, 8% sucrose, 2.5% monosodium glutamate (MSG), 2.5% glycerol, and the remainder being sterile water. The first bacterial core was prepared according to the method in Example 1, with an effective viable count of 3.2 × 10⁻⁶. 8 CFU / g.

[0027] Second microbial powder core preparation: The second composite freeze-drying protectant was prepared by weight percentage as follows: 6% maltodextrin, 5% sucrose, 1.0% trehalose, 0.3% Tween-80, with the remainder being sterile water. The second bacterial core was prepared according to the method in Example 1, with an effective viable count of 2.8 × 10⁻⁶. 8 CFU / g, the first mycelium powder core and the second mycelium powder core are mixed at a mass ratio of 5:1 to form the mycelium core.

[0028] Preparation of sustained-release layer: Prepare a mixed gel solution comprising 9% polyvinyl alcohol, 1.5% sodium alginate, 2.5% diatomaceous earth, 1.2% waterborne polyurethane, and the remainder being deionized water. Heat to 95°C and stir until homogeneous. Cool to 35°C, add the inoculum core, and stir until homogeneous. Pour the mixture into a spherical mold and freeze at -35°C for 20 hours. Thaw at room temperature to form a slow-release layer.

[0029] Preparation of outer coating: Weigh out the following components by weight: 35 parts weathered coal, 25 parts cellulose, 12 parts soybean meal powder, 12 parts corn cob powder, 8 parts chitosan, 5 parts carrageenan, and 6 parts diatomaceous earth. Coat according to the method in Example 1 and dry at a low temperature of 45°C.

[0030] The survival rate of the obtained microbial agent granules under the same freeze-thaw cycle conditions as in Example 1 was 79.2%. After application to coastal saline-alkali freeze-thaw zone soil with pH 8.8 and total salt content of 0.5%, the soil pH dropped to 8.1, the total salt content dropped to 0.32%, and the soil exchangeable sodium content decreased by 32% after 45 days. Example

[0031] Please see Figures 1-6 A slow-release device for microbial agents used for soil improvement includes an outer casing 1. Inside the outer casing 1, there is a dosing tank 2 and a drive assembly 3. The dosing tank 2 includes a stirring inner tank 21, a heating jacket 22, and an insulated outer tank 23, which are connected in sequence. The microbial agent mixed with water is stirred evenly in the stirring inner tank 21. The heating jacket 22 and the insulated outer tank 23 heat and insulate the stirring inner tank 21 to maintain the fluidity of the bacterial suspension in a low-temperature environment. The heating jacket 22 adopts a heating resistance wire structure. The drive assembly 3 includes a drive motor 31, a four-bar linkage 32, a stirring paddle 33, and a slow-release tube 34. The stirring paddle 33 is set inside the stirring inner tank 21. The slow-release tube 34 is connected to the lower end of the stirring inner tank 21. The drive motor 31 drives the four-bar linkage 32 to rotate. One end of the four-bar linkage 32 controls the rotation of the stirring paddle 33, and the other end of the four-bar linkage 32 drives the slow-release tube 34 to slowly release the microbial agent.

[0032] Specifically, the top of the inner mixing tank 21 is provided with a feeding port 211, which extends to the upper end of the outer casing 1. A cover 212 is provided on the feeding port 211. When feeding, the cover 212 is opened. After feeding, the cover 212 is closed. A vent 213 is also provided on the cover 212. After feeding, the vent 213 can be opened to ensure that the pressure inside the inner mixing tank 21 is balanced with the outside. The microbial agent inside the inner mixing tank 21 is automatically discharged from the slow-release tube 34 under the action of gravity. The bottom of the inner mixing tank 21 has a conical structure. In addition, one end of the slow-release tube 34 is connected to the center of the bottom of the inner mixing tank 21 to facilitate the complete discharge of liquid.

[0033] More specifically, the four-bar linkage 32 includes a parallel linkage array 321, a crank 322 obliquely traversing the linkage array 321, a first transmission assembly 323, and a second transmission assembly 324. The crank 322 has two rotating short shafts 3221 at its ends. One rotating short shaft 3221 is fixedly connected to the output end of the drive motor 31 via a bearing seat, and the other rotating short shaft 3221 is connected to the first transmission assembly 323. When the drive motor 31 operates, it drives the rotating short shaft 3221 to rotate. The control crank 322 pushes the connecting rod array 321 to deflect. Limiting plates 3211 are provided at both ends of the connecting rod array 321. The center of one limiting plate 3211 is movably connected to the inner wall of the outer housing 1 via a short shaft, and the center of the other limiting plate 3211 is connected to the second transmission assembly 324. The deflection of the connecting rod array 321 causes the limiting plate 3211 to swing back and forth around its center, controlling the second transmission assembly 324 to rotate back and forth. The second transmission assembly 324 is connected to the slow-release tube 34, which contains... A slow-release plate 341 is provided, and a first release hole 3411 is provided on the slow-release plate 341. A movable plate 342 is movably connected to one side of the slow-release plate 341. A second release hole 3421 corresponding to the position of the first release hole 3411 is provided on the movable plate 342. Sealing strips 3422 are symmetrically arranged on both sides of the movable plate 342. The sealing strips 3422 are engaged with the slow-release tube 34. A movable hole 343 is provided on the outer wall of the slow-release tube 34. A [missing information - likely a typo, should be "likely ... Linkage rod 3423 is connected to the second transmission assembly 324. When the second transmission assembly 324 reciprocates, it synchronously drives the movable plate 342 to rotate. When the second release hole 3421 rotates to correspond to the position of the first release hole 3411, the slow-release tube 34 is in communication with the outside and can export the microbial agent. When the second release hole 3421 rotates to be misaligned with the first release hole 3411, the first release hole 3411 is blocked and the microbial agent cannot be exported.

[0034] Furthermore, the first transmission assembly 323 and the second transmission assembly 324 use a combination of pulleys and belts or a combination of sprockets and chains. The first transmission assembly 323 transmits the continuous rotational force of the crank 322 to the stirring paddle 33, causing the stirring paddle 33 to rotate continuously and stir continuously, preventing the microbial agent from settling in the water. The second transmission assembly 324 transmits the reciprocating rotational force of the connecting rod array 321 to the movable plate 342, controlling the opening of the gap of the first release hole 3411 to slowly release the microbial agent.

[0035] It should be understood that the slow-release tube 34 penetrates the outer box 1, and the tube wall of the slow-release tube 34, which is located outside the outer box 1, has micropores with a pore diameter of 0.5-2mm. The tube is filled with a porous ceramic carrier to further slow-release the microbial agent.

[0036] The microbial agent prepared in Example 1 is used in conjunction with the sustained-release device of the present invention, as follows: The microbial agent granules prepared in Example 1 are fed into the mixing tank 21 through the feeding port 211. An appropriate amount of water is added, and the mass ratio of agent to water is 1:50-1:100. The cover 212 is closed and the vent 213 is opened. Start the heating jacket 22 to maintain the temperature inside the stirring inner tank 21 at 15-25℃, and the heat-insulating outer tank 23 to reduce heat loss, ensuring that the bacterial suspension remains fluid even when the external ambient temperature is below 0℃. Start the drive motor 31. The drive motor 31 drives the crank 322 to rotate through the rotating short shaft 3221. The continuous rotation of the crank 322 is transmitted to the stirring paddle 33 through the first transmission component 323, so that the stirring paddle 33 rotates continuously in the stirring tank 21, which fully mixes the microbial agent with water and prevents the core of the bacterial powder from settling. The crank 322 simultaneously pushes the connecting rod array 321 to deflect, causing the limiting plate 3211 to swing back and forth around its center, and the reciprocating rotational force is transmitted to the connecting rod 3423 of the movable plate 342 through the second transmission component 324. The movable plate 342 reciprocates under the action of the linkage rod 3423: when the second release hole 3421 rotates to correspond to the position of the first release hole 3411, the slow release tube 34 is in communication with the stirring inner tank 21, and the bacterial suspension is discharged from the conical structure at the bottom of the stirring inner tank 21 through the slow release tube 34 under the action of gravity; when the second release hole 3421 rotates to be misaligned with the first release hole 3411, the first release hole 3411 is blocked, and the release of the bacterial suspension is suspended. The bacterial suspension discharged from the slow-release tube 34 flows through the tube section located outside the outer casing 1. The tube section has micropores with a diameter of 0.5-2 mm on its wall and is filled with a porous ceramic carrier. The bacterial suspension is continuously and slowly released into the surrounding soil during the flow, achieving uniform distribution of the bacterial agent in the soil.

[0037] A small-plot experiment was conducted on degraded grasslands in Northeast China with an average annual temperature of 1.5℃ and a freeze-thaw period of up to 5 months. A control group without microbial agents, a group treated with an equal amount of free microbial powder and a group using conventional microbial agents were compared. The results showed that the available phosphorus in the soil of the group using the invention was 32% higher than that of the control group, and the available potassium was 28% higher. The soil aggregate structure was 45% better than that of the control group. The grassland vegetation cover increased from 42% to 78% before the experiment, and the aboveground biomass increased by 55%. The effective release period of the microbial agent reached 75 days, which was better than the 21 days of the conventional microbial agent group.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A microbial inoculant for soil improvement, comprising a microbial core, a slow-release layer, and an outer coating, characterized in that, The core of the strain is a freeze-resistant bacterial powder core made by mixing Bacillus fusiformis and Bacillus subtilis with a composite freeze-drying protectant. The slow-release layer is coated on the outside of the bacterial core, and the slow-release layer uses polyvinyl alcohol cryogel as the slow-release material to achieve the slow-release target of low temperature locking and temperature rise release. The outer coating is made of composite material to coat the slow-release layer. The outer coating absorbs moisture and forms a physical heat insulation layer.

2. The microbial inoculant for soil improvement according to claim 1, characterized in that, The microbial core comprises a first microbial powder core and a second microbial powder core. The first microbial powder core is prepared by mixing *Bacillus fusiformis* with a first composite freeze-drying protectant and then freeze-drying under vacuum. The second microbial powder core is prepared by mixing *Bacillus subtilis* with a second composite freeze-drying protectant and then freeze-drying under vacuum. The mass ratio of the first microbial powder core to the second microbial powder core is (1-10):

1. The effective viable count of both the first and second microbial powder cores is not less than 1×10⁻⁶. 8 CFU / g.

3. A microbial inoculant for soil improvement according to claim 2, characterized in that, The preparation method of the first bacterial powder core is as follows: The first composite freeze-drying protectant is prepared according to the following weight percentages: 10-20% skim milk powder, 8-15% trehalose, 4-10% sucrose, 1-3% sodium L-glutamate, 1-3% glycerol, and the remainder is sterile water. The spindle-shaped lysine Bacillus is subjected to three-stage liquid fermentation, and the bacterial cells are collected. After centrifugation at 8000-12000 rpm for 10-20 minutes, the bacterial sludge is collected. The spindle-shaped lysine Bacillus sludge and the first composite freeze-drying protectant are mixed evenly at a volume ratio of 1:(1-3), equilibrated at 4℃ for 40-60 minutes, pre-frozen at -40℃ for 3-8 hours, transferred to a vacuum freeze dryer, and freeze-dried at a pressure of 4-12 Pa for 18-24 hours to obtain the first bacterial powder core.

4. A microbial inoculant for soil improvement according to claim 3, characterized in that, The preparation method of the second bacterial powder core is as follows: The second composite freeze-drying protectant is prepared according to the following weight percentages: maltodextrin 3-8%, sucrose 3-6%, trehalose 0.5-2%, Tween-80 0.1-0.5%, and the remainder is sterile water. Bacillus subtilis is subjected to three-stage liquid fermentation, and the bacterial cells are collected. After centrifugation at 8000-12000 rpm for 10-20 minutes, the bacterial sludge is collected. The Bacillus subtilis sludge and the second composite freeze-drying protectant are mixed evenly at a volume ratio of 1:(1-3), equilibrated at 4℃ for 40-60 minutes, pre-frozen at -40℃ for 3-8 hours, transferred to a vacuum freeze dryer, and freeze-dried at a pressure of 4-12 Pa for 18-24 hours to obtain the second bacterial powder core.

5. A microbial inoculant for soil improvement according to claim 1, characterized in that, The polyvinyl alcohol cryogel is a mixed gel made of polyvinyl alcohol, sodium alginate, diatomaceous earth and waterborne polyurethane. The mass concentration of polyvinyl alcohol in the mixed gel is 8-12%, the mass concentration of sodium alginate is 0.5-2%, the mass concentration of diatomaceous earth is 1-3%, and the mass concentration of waterborne polyurethane is 0.5-2%.

6. A microbial inoculant for soil improvement according to claim 5, characterized in that, The method for preparing the sustained-release layer is as follows: Polyvinyl alcohol, sodium alginate, diatomaceous earth and waterborne polyurethane are dissolved in deionized water in proportion, heated to 90-100℃ and stirred evenly, cooled to 30-40℃, the first bacterial powder core and the second bacterial powder core are added, stirred evenly, the mixture is injected into a mold, frozen at -20℃ to -40℃ for 12-24 hours, and thawed at room temperature to form a polyvinyl alcohol cryogel with a porous three-dimensional network structure, which is the sustained-release layer.

7. A microbial inoculant for soil improvement according to claim 1, characterized in that, The outer coating is made of composite material comprising the following raw materials in parts by weight: 30-50 parts weathered coal, 15-30 parts cellulose, 10-20 parts soybean meal powder, 10-20 parts corn cob powder, 5-15 parts chitosan, 3-10 parts carrageenan, and 3-8 parts diatomaceous earth.

8. A microbial inoculant for soil improvement according to claim 7, characterized in that, The preparation process of the outer coating is as follows: weathered coal, cellulose, soybean meal powder, corn cob powder, and diatomaceous earth are pulverized through a 100-200 mesh sieve and mixed evenly; chitosan and carrageenan are dissolved in a 1-3% acetic acid solution to prepare a coating solution; the above mixed powder and coating solution are mixed at a mass ratio of 1:(0.5-1.5) and stirred evenly; the mixture is sprayed or dipped onto the surface of the slow-release layer and dried at a low temperature of 40-60℃ to obtain the outer coating.

9. A slow-release device for a microbial inoculant for soil improvement as described in claim 1, characterized in that, The system includes an outer casing (1), inside which is a dosing tank (2) and a drive assembly (3). The dosing tank (2) includes a stirring inner tank (21), a heating jacket (22), and an insulated outer tank (23) connected in sequence. The microbial agent mixed with water is stirred evenly in the stirring inner tank (21). The heating jacket (22) and the insulated outer tank (23) heat and insulate the stirring inner tank (21) to maintain the fluidity of the bacterial suspension in a low-temperature environment. The drive assembly... The component (3) includes a drive motor (31), a four-bar linkage (32), a stirring paddle (33), and a slow-release tube (34). The stirring paddle (33) is installed inside the stirring inner tank (21), and the slow-release tube (34) is connected to the lower end of the stirring inner tank (21). The drive motor (31) drives the four-bar linkage (32) to rotate. One end of the four-bar linkage (32) controls the rotation of the stirring paddle (33), and the other end of the four-bar linkage (32) drives the slow-release tube (34) to slowly release the microbial agent.

10. A slow-release device for a microbial inoculant for soil improvement as described in claim 9, characterized in that, The four-bar linkage (32) includes a parallel linkage array (321), a curved rod (322) obliquely passing through the linkage array (321), a first transmission assembly (323), and a second transmission assembly (324). The curved rod (322) has two rotating short shafts (3221) at both ends. One rotating short shaft (3221) is fixedly connected to the output end of the drive motor (31) via a bearing seat, and the other rotating short shaft (3221) is connected to the first transmission assembly (323). Limiting plates (3211) are provided at both ends of the linkage array (321). The center of one limiting plate (3211) is movably connected to the inner wall of the outer housing (1) via a short shaft, and the center of the other limiting plate (3211) is connected to the second transmission assembly (324). The component (324) is connected to the slow-release tube (34). The slow-release tube (34) is provided with a slow-release plate (341). The slow-release plate (341) is provided with a first release hole (3411). A movable plate (342) is movably connected to one side of the slow-release plate (341). A second release hole (3421) corresponding to the position of the first release hole (3411) is provided on the movable plate (342). A sealing strip (3422) is symmetrically provided on both sides of the movable plate (342). The sealing strip (3422) is engaged with the slow-release tube (34). A movable hole (343) is provided on the outer wall of the slow-release tube (34). A connecting rod (3423) is provided on the side of the movable plate (342) near the movable hole (343). The connecting rod (3423) is connected to the second transmission component (324).

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