A composite particle with both slow-release gas production and targeted release of microbial agents and its preparation method.

Abstract

This invention discloses a composite particle with both slow-release gas production and targeted release of microbial inoculants, and its preparation method. The composite particle is essentially a "three-layer core + three-layer isolation coating" structure. The innermost layer is a microbial inoculant core that can produce beneficial crop metabolites such as carbon dioxide. The second layer is an acid source middle layer, and the third layer is a carbonate outer layer. Coating materials are applied between the inoculant and the acid source, between the acid source and the carbonate, and on the outermost carbonate layer. The coating material is prepared through a unique chemical modification process and has good water solubility, biocompatibility, and isolation properties. It can effectively prevent the microbial inoculant from prematurely contacting and deactivating with the acid or alkali source. At the same time, it enables the coating to slowly dissolve upon contact with water, and the acid and alkali to gradually contact and produce gas, ultimately releasing the microbial inoculant. This achieves dual gas supply of "chemical gas production + microbial metabolic gas production," providing continuous carbon dioxide and beneficial microorganisms for crop growth, improving crop photosynthetic efficiency and soil fertility.

Description

Technical Field

[0001] This invention belongs to the field of agricultural microbial technology, and particularly relates to a composite particle with both slow-release gas production and targeted release of microbial agents, and its preparation method. Background Technology

[0002] CO2 is the primary cause of global warming due to the "greenhouse effect," but it is also an essential raw material for crop growth and a necessary material basis for plant photosynthesis. The concentration of carbon dioxide in greenhouses often fails to meet the needs of normal crop growth, and CO2 shortage in greenhouse production is a global problem. Countries have been working to increase CO2 levels in greenhouse cultivation to promote crop yields. Therefore, applying carbon dioxide fertilization within a suitable concentration range is essential for improving crop photosynthetic intensity, increasing dry matter accumulation, and ultimately increasing yield. According to existing domestic and international reports, the rational application of carbon dioxide fertilization can advance crop maturity by 7-10 days, extend the harvest period by 15-20 days, and increase yield by 20-50%, and in some cases, even double it.

[0003] Microbial inoculants are beneficial for promoting crop growth and protecting soil health. Through the activities of microorganisms, not only can the physical and chemical properties of the soil be improved, and the soil organic matter content and conversion efficiency be increased, but they also have the functions of potassium solubilization, phosphorus solubilization, and nitrogen fixation. At the same time, the metabolic products produced during the reproduction of microorganisms also include carbon dioxide, which can be used as a supplementary carbon dioxide fertilizer.

[0004] It is evident that combining carbon dioxide fertilizer and microbial inoculants for synergistic effects will undoubtedly become a hot topic in the development of environmentally friendly, value-added, and efficiency-enhancing fertilizers. However, the current main method of applying carbon dioxide fertilizer involves using a carbon dioxide generator to mix sulfuric acid or hydrochloric acid with ammonium bicarbonate to produce carbon dioxide. While this method is relatively simple, safe, and less expensive than other methods, it is currently the most widely used. However, because the acids are corrosive liquids, transportation and use are unsafe and can easily cause personal injury. Furthermore, since this method involves free release, it cannot achieve timed and quantitative slow release of carbon dioxide, thus posing certain ecological risks and potentially leading to carbon dioxide dependence in crops. If application is suddenly stopped after a period of time, it can easily cause premature aging of crops.

[0005] Currently, simply mixing carbon dioxide fertilizer and microbial agents mechanically, or preparing compound fertilizers through adsorption granulation, clearly fails to achieve synergistic effects. To overcome these technical shortcomings, slow-release and controlled-release carbon dioxide fertilizers and microbial agents have emerged. However, how to form a physical barrier on the surface of carbon dioxide fertilizer and microbial agents to delay the dissolution of carbon dioxide and microbial agents, and achieve dual gas supply through "chemical gas production + microbial metabolic gas production," is not yet disclosed in existing technologies. Summary of the Invention

[0006] This invention proposes a composite particle with both slow-release gas production and targeted release of microbial inoculants, and its preparation method. The composite particle is essentially a "three-layer core + three-layer isolation coating" structure. The innermost layer is a microbial inoculant core that can produce beneficial crop metabolites such as carbon dioxide. The second layer is an acid source middle layer, and the third layer is a carbonate outer layer. Coating materials are applied between the inoculant and the acid source, between the acid source and the carbonate, and on the outermost carbonate layer. The coating material is prepared through a unique chemical modification process and has good water solubility, biocompatibility, and isolation properties. It can effectively prevent the microbial inoculant from prematurely contacting and deactivating with the acid or alkali source. At the same time, it enables the coating to slowly dissolve upon contact with water, and the acid and alkali to gradually contact and produce gas, ultimately releasing the microbial inoculant. This achieves a dual gas supply of "chemical gas production + microbial metabolic gas production," providing continuous carbon dioxide and beneficial microorganisms for crop growth, improving crop photosynthetic efficiency and soil fertility.

[0007] The present invention proposes a composite particle that combines slow-release gas production and directional release of microbial agents. From the inside out, it comprises a microbial agent core, an acid source middle layer, and a carbonate outer layer. Furthermore, coating layers are provided between the microbial agent core and the acid source middle layer, between the acid source middle layer and the carbonate outer layer, and outside the carbonate outer layer. The microbial agent used in the microbial agent core is composed of Bacillus amyloliquefaciens, Enterobacter amyloliquefaciens, and Lactobacillus plantarum.

[0008] In this invention, by controlling the design of the coating layer structure, the composite particles are ensured to dissolve slowly after contact with water, avoiding the instantaneous contact and gas generation of acid sources and carbonates; at the same time, the isolation of the coating is improved to prevent the microbial agent from prematurely contacting and deactivating with acid sources and carbonates.

[0009] Preferably, the coating layer is a chitosan-pullulan composite gel material based on dynamic covalent cross-linking.

[0010] Preferably, the chitosan-pullulan composite gel material based on dynamic covalent crosslinking is obtained by phosphate grafting of quaternary ammonium salt modified chitosan and phosphorylated modified pullulan, followed by condensation reaction with thiamine disulfide under glutaraldehyde crosslinking agent.

[0011] In this invention, the coating material adopts "chitosan-pullulan graft modification + dynamic covalent crosslinking", which has biocompatibility, slow solubility and isolation properties; among them, chitosan and pullulan are natural polysaccharide base materials, which have good biocompatibility and biodegradability, avoiding soil pollution. At the same time, the combination of the two can improve the film-forming properties and toughness of the coating.

[0012] In this invention, chitosan can be electrophilically substituted with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) to obtain quaternary ammonium salt modified chitosan, thereby improving its water solubility and coating film-forming properties; pullulan can be obtained by reacting sodium tripolyphosphate and sodium trimetaphosphate to obtain phosphorylated modified pullulan; the two can be grafted by the ionic reaction of phosphate groups and amino groups to achieve phosphorylation ammoniumization, thereby integrating the advantages of the two polysaccharides, improving the film-forming properties and toughness of the coating material, avoiding the problems of brittleness and insufficient isolation of single polysaccharide coatings, and providing more active sites for subsequent cross-linking reactions; subsequently, thiamine disulfide is used. TS (as a dynamic crosslinking agent) undergoes imidization crosslinking with the amino groups on the grafted product under the crosslinking agent of glutaraldehyde, constructing a dynamic covalent network. This network is structurally stable in a dry state and has good isolation properties. Upon contact with water, the dynamic covalent bonds can slowly break, allowing the coating material to gradually dissolve and achieving a slow-dissolution effect. At the same time, the dynamic covalent bonds have self-healing capabilities, which can repair minor damage to the coating during preparation and transportation. Thus, the coating material improves the slow-dissolution and isolation properties of the coating, while also endowing the coating with a certain degree of self-healing ability, avoiding damage to the coating during preparation and transportation.

[0013] Preferably, the microbial agent core is formed by loading the microbial agent onto an organic carrier and a protectant; Preferably, the microbial agent is composed of Bacillus amyloliquefaciens, Enterobacter amyloliquefaciens, and Lactobacillus plantarum in a weight ratio of 2:1:1; the organic carrier is corn starch and diatomaceous earth; and the protective agent is trehalose and vitamin C.

[0014] In this invention, a compound microbial strain with both gas production and crop growth promotion functions is selected. The compound microbial strain formula is determined by combining the characteristics of existing agricultural microorganisms and gas production requirements, taking into account both gas production and growth promotion, which is different from the application of single microbial strains: Bacillus amyloliquefaciens can secrete growth-promoting substances and assist in gas production, Enterobacter aeruginosa can produce a large amount of carbon dioxide through the formic acid lysis pathway, and Lactobacillus plantarum can regulate the soil microecology and produce a small amount of carbon dioxide through metabolism. The three work together to ensure microbial metabolic gas production, promote crop growth, and improve the soil environment.

[0015] In this invention, the organic carriers are corn starch and diatomaceous earth. Corn starch and diatomaceous earth have good adsorption and shaping properties, which can adsorb the bacterial inoculum and form stable bacterial agent particles to carry the inoculum, improve the shaping and stability of the bacterial agent particles, and at the same time provide a small amount of carbon source for microorganisms. The protective agents are trehalose and vitamin C. Trehalose can form a protective film on the surface of microbial cells, and vitamin C has an antioxidant effect. The two work synergistically to protect microbial cells from damage caused by high temperature and mechanical action, maintain their activity, and protect the activity of microbial agents to prevent them from being deactivated by high temperature and mechanical action during the preparation process.

[0016] Preferably, the acid source middle layer is formed by granulating the acid source using a binder; The acid source is citric acid; the binder is sodium carboxymethyl cellulose.

[0017] Preferably, the carbonate outer layer is formed by granulating carbonate using a binder; The carbonate is ammonium bicarbonate; the binder is sodium carboxymethyl cellulose.

[0018] In this invention, the reaction between ammonium bicarbonate (alkali source) and citric acid (acid source) is slow, with no harmful byproducts, and the product can be utilized by crops; Ammonium bicarbonate, as a gas-producing alkali source, reacts with citric acid to produce carbon dioxide, ammonia, and water. Among these, carbon dioxide serves as a gaseous fertilizer, and ammonia can be converted into ammonium nitrogen for crop absorption, thus avoiding gas waste and environmental impact. At the same time, its reaction rate is mild, which can avoid instantaneous gas production that could impact the particle structure.

[0019] Citric acid, as a gas-producing acid source, reacts slowly with ammonium bicarbonate. By adjusting its dosage, the gas production rate can be precisely controlled. At the same time, citric acid itself can serve as an organic acid required for crop growth and increase soil acidity (suitable for alkaline soils).

[0020] Preferably, the particle size of the microbial agent core is 0.5-2 mm, the thickness of the acid source middle layer is 0.3-0.6 mm, the thickness of the carbonate outer layer is 0.3-0.6 mm, and the thickness of the coating layer is 50-100 μm.

[0021] This invention also proposes a method for preparing the above-mentioned composite particles with slow-release gas generation and directed release of microbial agents, comprising the following steps: S1. After granulating the components of the corresponding microbial agent core, a microbial agent core is formed; after coating the surface of the microbial agent core using a fluidized bed process, a coating layer is formed on the surface of the microbial agent core, resulting in a microbial agent core with a coating layer. S2. After granulating the components of the corresponding acid source middle layer and the microbial agent core with a coating layer, an acid source middle layer is formed on the surface of the microbial agent core with a coating layer; after coating the surface of the acid source middle layer using a fluidized bed process, a coating layer is formed on the surface of the acid source middle layer to obtain a microbial agent core coated with an acid source middle layer. S3. After granulating the components corresponding to the carbonate outer layer and the microbial agent core coating the acid source middle layer, a carbonate outer layer is formed; after coating the surface of the carbonate outer layer using a fluidized bed process, a coating layer is formed on the surface of the carbonate outer layer, thus obtaining the composite particles.

[0022] Preferably, the granulation temperature is 10-25℃ and the granulation speed is 40-50 r / min; the fluidized bed inlet air temperature is 40-45℃, the outlet air temperature is 30-35℃, and the air velocity is 1.5-2 m / s.

[0023] Preferably, the preparation method further includes: mixing and coating the composite particles and the anti-caking agent to obtain the final product.

[0024] Compared with the prior art, the present invention has the following technical effects: (1) Particle structure design: physical isolation of acid source, carbonate and microbial agent is achieved through layered coating to ensure the stability of each component; (2) Innovative synthesis of coating material: chitosan-pullulan graft modification combined with dynamic covalent bond crosslinking process is adopted, which is different from the existing single polysaccharide coating or ordinary polyurethane coating, and has the advantages of slow solubility, isolation and biodegradability; (3) Selection of gas generation system: ammonium bicarbonate and citric acid are selected as carbonate and acid source. The slow reaction rate of the two is utilized to avoid instantaneous gas generation leading to particle breakage or gas escape. At the same time, it is combined with microbial metabolic gas generation to achieve continuous and stable gas supply. Attached Figure Description

[0025] Figure 1 The following is a schematic diagram of the structure of the composite particles described in Embodiment 1 of the present invention: 1 is the microbial agent core, 2 is the first coating layer, 3 is the acid source middle layer, 4 is the second coating layer, 5 is the carbonate outer layer, and 6 is the third coating layer. Figure 2 This is the infrared spectrum of the coating material described in Embodiment 1 of the present invention. Detailed Implementation

[0026] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0027] Example 1 Reference Figure 1A composite particle that combines slow-release gas production and directional release of microbial agents comprises, from the inside out, a microbial agent core 1, an acid source middle layer 3, and a carbonate outer layer 5; and a first coating layer 2, a second coating layer 4, and a third coating layer 6 are respectively provided between the microbial agent core 1 and the acid source middle layer 3, between the acid source middle layer 3 and the carbonate outer layer 5, and outside the carbonate outer layer 5.

[0028] The aforementioned composite particles, which combine the functions of slow-release gas production and targeted release of microbial agents, are prepared using the following method: (1) Coating material Chitosan (degree of deacetylation ≥90%, molecular weight 50000-80000Da) was added to a 5wt% aqueous acetic acid solution and stirred until completely dissolved. After heating to 50℃, CHPTAC (4wt% of chitosan by weight) was added. The mixture was kept at this temperature and stirred for 4 hours. The pH of the resulting reaction solution was adjusted to 7 with a 10wt% sodium hydroxide solution. After centrifugation, the precipitate was collected, washed with deionized water, and dried under vacuum at 60℃ to obtain quaternary ammonium salt modified chitosan. Pullulan (molecular weight 20,000-30,000 Da) was added to deionized water, along with sodium tripolyphosphate at 3 times the mass of pullulan and sodium trimetaphosphate at 60 wt% of the mass of pullulan. After stirring and mixing, the pH was adjusted to 9 with 10 wt% sodium hydroxide solution. The temperature was raised to 80°C and stirred for 5 h. The resulting reaction solution was added to 95% ethanol to precipitate for 48 h. After centrifugation, the precipitate was collected, washed with deionized water, and freeze-dried to obtain phosphorylated pullulan. Quaternary ammonium salt-modified chitosan and phosphorylated pullulan were added to deionized water at a mass ratio of 2:1. The mixture was heated to 40°C and stirred at this temperature for 6 hours. Then, 20 wt% TS (by weight of quaternary ammonium salt-modified chitosan) and 10 wt% glutaraldehyde aqueous solution (50 wt% concentration) of quaternary ammonium salt-modified chitosan were added. The mixture was heated to 45°C and stirred at this temperature for 3 hours. The resulting reaction solution was vacuum dried at 60°C to remove the solvent, pulverized, and passed through an 80-mesh sieve to obtain a chitosan-pullulan composite gel material based on dynamic covalent bond crosslinking, which is the coating material. Its infrared spectrum is shown below. Figure 2 As shown; (2) Microbial agent core Bacillus amyloliquefaciens, Enterobacter alginate, and Lactobacillus plantarum were inoculated separately into LB medium and cultured at 37℃ and 180 r / min for 24 h with shaking to obtain activated bacterial cultures. The three activated bacterial cultures were mixed at a weight ratio of 2:1:1 to obtain a composite bacterial culture, and the concentration of the culture was adjusted to 1×10⁻⁶. 10 CFU / mL; Corn starch and diatomaceous earth were mixed at a mass ratio of 3:1 and used as a carrier. Trehalose (15 wt% of corn starch mass) and vitamin C (8 wt% of corn starch mass) were added as a protectant. After further mixing, a carrier-protectant mixture was obtained. The carrier-protectant mixture was added to a granulator, and a composite bacterial inoculum solution with a mass ratio of 1.5 times that of the carrier-protectant was slowly sprayed while stirring. The granulator speed was adjusted to 50 r / min and the granulation pressure to 0.3 MPa to prepare wet bacterial agent granules with a particle size of 2 mm. The wet bacterial agent granules were placed in a drying oven and dried at a constant temperature of 35℃ for 12 h (low temperature drying to avoid microbial inactivation). After drying, the granules were sieved to remove unqualified particles, and the microbial agent core was obtained. (3) Microbial agent core + first coating layer The microbial agent core was placed in a fluidized bed coating machine. The inlet air temperature of the fluidized bed was adjusted to 40℃, the outlet air temperature to 30℃, and the air velocity to 1.5m / s. The coating material and deionized water were mixed at a weight ratio of 1:5 and stirred until completely dissolved to obtain a coating solution. The coating solution was sprayed onto the surface of the microbial agent core at a rate of 1.0mL / min for 30min. After coating, the core was dried at a constant temperature of 35℃ for 6h to form a first coating layer with a thickness of 70μm, thus obtaining a microbial agent core with a coating layer. (4) Microbial agent core + first coating layer + acid source middle layer The microbial agent core with a coating layer is added to a granulator, and then citric acid powder (particle size 100-120 mesh, purity ≥99.5%) is added as an acid source. At the same time, a 5wt% sodium carboxymethyl cellulose solution is sprayed as a binder. The mixture is stirred and sprayed while the rotation speed is adjusted to 40 r / min, so that the citric acid powder is evenly coated on the surface of the first coating layer, forming an acid source middle layer with a thickness of 0.4 mm, thus obtaining the microbial agent core coated with the acid source middle layer. (5) Microbial agent core + first coating layer + acid source middle layer + second coating layer The microbial agent core coated with the acid source middle layer was placed in a fluidized bed coating machine. The inlet air temperature of the fluidized bed was adjusted to 40℃, the outlet air temperature to 30℃, and the air velocity to 1.5m / s. The coating material and deionized water were mixed at a weight ratio of 1:5 and stirred until completely dissolved to obtain a coating solution. The coating solution was sprayed onto the surface of the microbial agent core at a rate of 1.0mL / min for 25min. After coating, the core was dried at a constant temperature of 35℃ for 6h to form a second coating layer with a thickness of 60μm, thus obtaining the microbial agent core coated with the acid source middle layer. (6) Microbial agent core + first coating layer + acid source middle layer + second coating layer + carbonate outer layer The microbial agent core coated with an acid source middle layer is added to a granulator, and then ammonium bicarbonate powder (particle size 100-120 mesh, purity ≥99.5%) is added as carbonate. At the same time, a 5wt% sodium carboxymethyl cellulose solution is sprayed as a binder. The mixture is stirred and sprayed while the rotation speed is adjusted to 40 r / min, so that the ammonium bicarbonate powder is evenly coated on the surface of the second coating layer, forming a carbonate outer layer with a thickness of 0.4 mm, thus obtaining the microbial agent core coated with a carbonate outer layer. (7) Microbial agent core + first coating layer + acid source middle layer + second coating layer + alkali source outer layer + third coating layer The microbial agent core coated with a carbonate outer layer was placed in a fluidized bed coating machine. The inlet air temperature of the fluidized bed was adjusted to 40℃, the outlet air temperature to 30℃, and the air velocity to 1.5m / s. The coating material and deionized water were mixed at a weight ratio of 1:5 and stirred until completely dissolved to obtain a coating solution. The coating solution was sprayed onto the surface of the microbial agent core at a rate of 1.0mL / min for 30min. After coating, the core was dried at a constant temperature of 35℃ for 6h to form a third coating layer with a thickness of 70μm, thus obtaining a microbial agent core coated with a carbonate outer layer. The microbial agent core coated with a carbonate outer layer was added to a mixer, and talc powder was added as an anti-caking agent. After stirring for 10min, the talc powder was evenly coated on the particle surface. The particles were sieved to remove unqualified particles with a particle size of less than 2mm or greater than 3mm. The qualified particles were placed in sealed bags and stored in a cool, dry, and ventilated place, avoiding moisture and high temperature, to obtain the composite particles.

[0029] Comparative Example 1 A composite particle is formed by mixing and pressing citric acid powder and ammonium bicarbonate powder in the same mass ratio as in Example 1.

[0030] Comparative Example 2 A composite particle, identical to that of Example 1, except that the first and second coating layers are omitted.

[0031] Comparative Example 3 A composite particle, identical to that of Example 1, except that the coating material is prepared by the following method: The quaternary ammonium salt modified chitosan and pullulan (molecular weight 20000-30000 Da) were added to deionized water at a mass ratio of 2:1. After heating to 40°C, the mixture was stirred at a constant temperature for 6 hours. Then, 20 wt% TS and 10 wt% glutaraldehyde aqueous solution (concentration 50 wt%) of chitosan were added. After heating to 45°C, the mixture was stirred at a constant temperature for 3 hours. The resulting reaction solution was vacuum dried at 60°C to remove the solvent. After pulverizing, the solution was passed through an 80-mesh sieve to obtain the coating material.

[0032] Comparative Example 4 A composite particle, identical to that of Example 1, except that the coating material is prepared by the following method: The quaternary ammonium salt modified chitosan and phosphorylated pullulan were added to deionized water at a mass ratio of 2:1. The mixture was heated to 40°C and stirred at a constant temperature for 6 hours. The resulting reaction solution was vacuum dried at 60°C to remove the solvent, pulverized, and passed through an 80-mesh sieve to obtain the coating material.

[0033] Performance testing (1) Impact on CO2 release performance: To quantitatively verify the slow release and long-term sustained-release effect of the three-layer coated composite particles in the example upon contact with water, a parallel control was conducted with the uncoated citric acid + ammonium bicarbonate mixed powder of the same ratio in the comparative example, comparing the differences in instantaneous gas production, cumulative gas production, and duration of gas production.

[0034] The complete three-layer coated composite particles described in Example 1 were used as the experimental group; the uncoated citric acid and ammonium bicarbonate composite particles described in Comparative Example 1 were used as the control group; the composite particles described in Comparative Examples 2, 3, and 4 were used as control groups 1, 2, and 3, respectively; deionized water, anhydrous calcium chloride (for drying), and high-purity nitrogen (carrier gas) were used as other experimental instruments. The experimental instruments included a portable CO2 concentration detector (accuracy 0-5000ppm), a closed constant temperature reaction reactor (500mL sealed reaction bottle with sampling port), a constant temperature water bath, an electronic analytical balance, a pipette, a stopwatch, a data logger, and a gas drying tube.

[0035] During the test, a constant temperature water bath was turned on and set to 25℃, and preheated until the temperature remained constant. 5.00g of coated composite granules from the experimental group, 5.00g of uncoated acid-base mixed powder from the control group, and 5.00g of composite granules from the comparison group were weighed. A 500mL sealed reactor was cleaned, dried, and cooled to room temperature for later use. The CO2 concentration detector was calibrated, zeroed, and set to automatically record CO2 concentration data every 5 minutes. Additionally, 20mL of deionized water was injected into the empty sealed reactor, and it was sealed and allowed to stand for 10 minutes. The CO2 detector was connected, and the initial CO2 background concentration in the reactor was recorded as a blank baseline. Subsequent data were adjusted by subtracting the background value to eliminate ambient air interference.

[0036] Place 5.00g of the control group powder at the bottom of the sealed reactor, and quickly add 20mL of 25℃ deionized water using a pipette. Immediately seal the reactor to ensure airtightness and prevent leakage. Place the reactor in a 25℃ constant temperature water bath and maintain a constant temperature throughout the process. Start the CO2 data logger and begin timing. Record the CO2 concentration every 5 minutes as set, and monitor continuously for 120 hours. Observe and record: gas production start time, peak gas concentration, peak occurrence time, gas decay time, and time to complete cessation of gas production. After the experiment, clean the reactor, dry it, and repeat the experiment three times in parallel. Similarly, 5.00g of the test group composite particles were placed at the bottom of the sealed reactor, ensuring the particles remained intact; 20mL of 25℃ deionized water was added, and the reactor was quickly sealed to ensure airtightness and no leakage; the reactor was then fixed in a 25℃ constant temperature water bath; the same detection parameters, recording intervals, and monitoring duration of 120h were used as the control group; CO2 concentration, gas production start time, peak value, peak occurrence time, and gas production duration were recorded synchronously at each time point; the experiment was repeated three times in parallel to ensure repeatability; the same conditions were applied to control group 1, control group 2, and control group 3. Based on the volume of the closed reactor and the CO2 concentration at different time points, the instantaneous CO2 release per unit mass of sample and the cumulative CO2 release were calculated. The two sets of data were compared: peak gas production, peak time, and total duration of gas production. The results are shown in Tables 1-3 below. All experimental data are averages from three parallel experiments, after deducting the background CO2 concentration. Table 1 Instantaneous CO2 release concentration at different time points

[0037] Table 2 Cumulative CO2 Emissions for Each Time Period

[0038] Table 3 Comparison of CO2 emission performance

[0039] As can be seen from the comparison of key parameters of gas production characteristics in Table 1-3 above, the uncoated control group rapidly increased CO2 concentration within 5 minutes of contact with water, and the acid and alkali reacted violently and instantly. The layered coating structure of Example 1, through the inner isolation coating and the middle isolation coating, physically separates the bacterial agent, acid source, and alkali source, allowing water to penetrate slowly and preventing rapid contact between acid and alkali, thus completely avoiding instantaneous explosive gas production. At the same time, it protects the internal microbial agent from contact with acid and alkali throughout the process, ensuring the activity of the strain and the stability of the structure. The control group 1, because it only has an outer coating structure without layered coating, is also prone to premature mixing and reaction of acid and alkali, which also affects the core of the bacterial agent. The control groups 2 and 3, because the coating material cannot form an effective cross-linking structure, have a slower release effect than the Example.

[0040] The above clearly demonstrates that the layered coated particles of the present invention can significantly reduce the peak CO2 production, delay the peak time, and greatly extend the slow release time, thus achieving the design requirement of slow carbon dioxide release; at the same time, it verifies the technical advantages of the particle structure, modified coating material, and gas production system.

[0041] (2) Effects on plant growth and photosynthetic efficiency: To verify the dual gas supply efficiency, the dynamic changes in carbon dioxide concentration in the greenhouse were monitored to assess the slow-release gas production capacity of the composite particles and its actual contribution to improving crop photosynthetic efficiency. To evaluate physiological and yield performance, the promoting effect on strawberry growth was quantified by measuring indicators such as strawberry chlorophyll content and plant morphology. To evaluate the soil improvement effect, the colonization of microbial agents in the root zone and their effect on improving soil fertility were verified.

[0042] The experimental site was selected as a 60-meter long × 10-meter wide × 3.5-meter high greenhouse with a volume of about 2100 cubic meters and a planting area of ​​about 0.8-0.9 mu (approximately 0.2-0.3 hectares). The selected crop was the "Hongyan" strawberry variety.

[0043] A randomized block design was used, with a total of 6 treatments, each with 3 replicates. The planting area of ​​each plot was no less than 30 square meters. Except for differences in gas fertilizer and inoculant, the field management measures such as irrigation, fertilization (nitrogen, phosphorus and potassium), and pest and disease control were completely identical in all plots. The specific design is shown in Table 4 below: Table 4 Different treatment designs

[0044] The results of the experiment on the growth and photosynthetic efficiency of greenhouse strawberries are summarized in Table 5 below: Table 5. Experimental results of greenhouse strawberry growth and photosynthetic efficiency.

[0045] As shown in Table 5 above, from the perspective of environmental data, although the peak CO2 concentration in the morning of group T1 was slightly lower than that of group T2 (because T2 is a common chemical gas fertilizer, which reacts violently with water), its advantage lies in the fact that "the number of days with CO2 concentration > 600 ppm reached 28 days", far exceeding the 12 days of group T2. This confirms that the "modified coating material" of this invention has good water solubility and isolation properties, successfully achieving gradual contact between acid and alkali and slow gas production, avoiding the drawback of "strong at the beginning and weak at the end" of traditional gas fertilizers, and providing strawberries with a stable carbon source for nearly a month; while groups T4, T5, and T6, due to the lack of layered coating or the relatively poor slow-release effect of the coating material, could not maintain "the number of days with CO2 concentration > 600 ppm reached 28 days".

[0046] In terms of physiological indicators, the chlorophyll SPAD value (47.8) and net photosynthetic rate (13.8 μmol / m³) of group T1 were significantly higher. 2 The levels of ·s were significantly higher than those of other groups; compared with group T3 (only microbial agent), the additional chemical gas production in group T1 directly increased the intercellular CO2 concentration, removing the substrate limitation for photosynthesis; compared with group T2 (only chemical fertilizer), the microbial agent released by group T1 promoted the absorption of mineral elements by the roots, which in turn fed back to the synthesis of chlorophyll in the leaves; this dual effect of "above-ground carbon supplementation + underground root promotion" maximized the photosynthetic potential of strawberries.

[0047] The final economic traits showed that the yield per plant in the T1 group was about 51.6% higher than that of the control (CK) and about 18.3% higher than that of the group using only chemical gas fertilizer (T2). At the same time, the sugar content (soluble solids) of the fruit reached the optimal level of 11.5%. The continuous and sufficient supply of CO2 accelerated the accumulation of carbohydrates, while the improved rhizosphere environment by microorganisms ensured the efficient transport of nutrients. In contrast, the T4, T5, and T6 groups were inferior to the T1 group in terms of strawberry physiological indicators and rhizosphere microecology because they did not have layered coating or the coating material had a relatively poor slow-release effect.

[0048] 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 composite particle that combines the functions of slow-release gas production and targeted release of microbial agents, characterized in that, From the inside out, it includes a microbial agent core, an acid source middle layer, and a carbonate outer layer; at the same time, there are coating layers between the microbial agent core and the acid source middle layer, between the acid source middle layer and the carbonate outer layer, and outside the carbonate outer layer; the microbial agent used in the microbial agent core is composed of Bacillus amyloliquefaciens, Enterobacter amyloliquefaciens and Lactobacillus plantarum.

2. The composite particles with both slow-release gas production and directed release of microbial agents as described in claim 1, characterized in that, The coating layer is a chitosan-pullulan composite gel material based on dynamic covalent cross-linking.

3. The composite particles with both slow-release gas production and targeted release of microbial agents as described in claim 2, characterized in that, The chitosan-pullulan composite gel material based on dynamic covalent crosslinking is obtained by phosphate grafting of quaternary ammonium salt modified chitosan and phosphorylated modified pullulan, followed by condensation reaction with thiamine disulfide in the presence of glutaraldehyde crosslinking agent.

4. The composite particles with both slow-release gas production and directed release of microbial agents as described in any one of claims 1-3, characterized in that, The microbial agent core is formed by loading the microbial agent onto an organic carrier and a protectant. The microbial agent is composed of Bacillus amyloliquefaciens, Enterobacter amyloliquefaciens, and Lactobacillus plantarum in a weight ratio of 2:1:1; the organic carrier is corn starch and diatomaceous earth; and the protective agent is trehalose and vitamin C.

5. The composite particles with both slow-release gas production and directed release of microbial agents as described in any one of claims 1-3, characterized in that, The middle layer of the acid source is formed by granulating the acid source using a binder. The acid source is citric acid; the binder is sodium carboxymethyl cellulose.

6. The composite particles with both slow-release gas production and directed release of microbial agents as described in any one of claims 1-3, characterized in that, The outer carbonate layer is formed by granulating carbonate using a binder. The carbonate is ammonium bicarbonate; the binder is sodium carboxymethyl cellulose.

7. The composite particles with both slow-release gas production and directed release of microbial agents as described in any one of claims 1-3, characterized in that, The particle size of the microbial agent core is 0.5-2 mm, the thickness of the acid source middle layer is 0.3-0.6 mm, the thickness of the carbonate outer layer is 0.3-0.6 mm, and the thickness of the coating layer is 50-100 μm.

8. A method for preparing composite particles with both slow-release gas generation and directed release of microbial agents as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. After granulating the components of the corresponding microbial agent core, a microbial agent core is formed; after coating the surface of the microbial agent core using a fluidized bed process, a coating layer is formed on the surface of the microbial agent core, resulting in a microbial agent core with a coating layer. S2. After granulating the components of the corresponding acid source middle layer and the microbial agent core with a coating layer, an acid source middle layer is formed on the surface of the microbial agent core with a coating layer; after coating the surface of the acid source middle layer using a fluidized bed process, a coating layer is formed on the surface of the acid source middle layer to obtain a microbial agent core coated with an acid source middle layer. S3. After granulating the components corresponding to the carbonate outer layer and the microbial agent core coating the acid source middle layer, a carbonate outer layer is formed; after coating the surface of the carbonate outer layer using a fluidized bed process, a coating layer is formed on the surface of the carbonate outer layer, thus obtaining the composite particles.

9. The method for preparing the composite particles with both slow-release gas generation and directed release of microbial agents according to claim 8, characterized in that, The granulation temperature is 10-25℃ and the granulation speed is 40-50 r / min; the fluidized bed inlet air temperature is 40-45℃, the outlet air temperature is 30-35℃, and the air velocity is 1.5-2 m / s.

10. The method for preparing composite particles with both slow-release gas generation and directed release of microbial agents as described in claim 8 or 9, characterized in that, Also includes: The final product is obtained by mixing and coating the composite particles with an anti-caking agent.

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