Preparation method of sulfur-based microbial compound fertilizer with temperature-responsive slow-release function

Abstract

The application discloses a sulfur-based microbial compound fertilizer with a temperature response type slow-release function and a preparation method thereof, and belongs to the field of microbial compound fertilizers.The compound fertilizer is sequentially composed of a compound organic carrier core, a temperature response type supramolecular gel layer, a pH response controlled release coating layer and a double-layer microcapsule microbial agent layer.The carrier core is made of mixed rotten straw and white liquor lees, and adsorbs elemental sulfur and phosphorus and potassium nutrients.The gel layer is wrapped by beta-cyclodextrin to nitrogen and sulfur nutrients.The coating layer contains thiourea pore-forming agents and chitosan pH response components.The microbial agent layer embeds mixed microbial agents of bacillus subtilis and sulfur-oxidizing bacteria.The application constructs a triple synergistic controlled release mechanism and a three-level sulfur supply system, realizes temperature synchronous release of the microbial agents and nutrients, and matches the nutrient release with crop demand with a matching degree of greater than or equal to 92%.The total viable bacteria survival rate is greater than or equal to 92%.The application is fully biodegradable and has no environmental residues.Field test results show that the application can increase the yield of winter wheat by 29.9% to 34.6%.The raw materials are agricultural wastes, and the production cost is controllable.

Description

Technical Field

[0001] This invention relates to the field of microbial compound fertilizers, and particularly to a method for preparing a sulfur-based microbial compound fertilizer with temperature-responsive slow-release function. Background Technology

[0002] Slow-release fertilizers are one of the core products for sustainable development in modern agriculture. Among them, organic-inorganic compound slow-release fertilizers have become a research hotspot due to their advantages in both soil improvement and efficient fertilization. In existing technologies, CN120058423A discloses an environmentally friendly organic slow-release fertilizer that achieves temperature-responsive nitrogen release by constructing a β-cyclodextrin / N-isopropylacrylamide supramolecular slow-release system. The nitrogen content matches crop requirements by over 90%, and the entire preparation process is carried out at low temperatures, effectively protecting microbial activity. However, this technology has significant drawbacks: it uses only urea as a single nitrogen source, completely lacking phosphorus, potassium, and micronutrients such as sulfur and calcium, failing to meet the nutritional needs of crops throughout their entire life cycle; the controlled-release mechanism relies solely on temperature response, resulting in a significant decrease in release matching in low-temperature, high-humidity, or acidic soils; the microbial agent used is only Bacillus subtilis, lacking functional bacteria that synergize with nutrient conversion; and β-cyclodextrin has a low inclusion rate for polar phosphorus and potassium salts, making simultaneous slow release of multiple nutrients impossible.

[0003] CN118184444B discloses a controlled-release fertilizer made from baijiu (Chinese liquor) lees, which uses baijiu lees as an organic carrier and achieves slow nutrient release through ethyl cellulose-hydroxypropyl cellulose coating, with a release period of up to 15 months, and realizes the resource utilization of baijiu lees waste. However, this technology also has shortcomings: it adopts a passive coating pore-forming mechanism, and the nutrient release only changes linearly with time, which cannot accelerate the release during the peak period of crop nutrient demand, and the matching degree with crop needs is less than 70%; the functional bacteria are directly mixed in the fertilizer core, and the high temperature preheating and mechanical friction during the coating process result in a survival rate of less than 60% for live bacteria; it only uses ammonium thiocyanate as a sulfur source, which has a low content and releases too quickly, failing to meet the sulfur needs of crops in the middle and late stages; the degradation period of ethyl cellulose coating exceeds 18 months, which is longer than the growth cycle of most field crops, posing a risk of microplastic residue.

[0004] In summary, existing technologies have not yet solved the three core contradictions of "comprehensive nutrient supply and simultaneous slow release of multiple nutrients", "environmentally responsive controlled release and protection of microbial agent activity", and "gradient supply of sulfur and synergistic transformation of microorganisms". There is an urgent need to develop a sulfur-based microbial compound fertilizer that combines temperature-responsive slow release, full nutrient supply, highly active microbial agents and full biodegradability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art, and in response to these shortcomings, this invention provides the following technical solution:

[0006] The present invention relates to a method for preparing a sulfur-based microbial compound fertilizer with temperature-responsive slow-release function, characterized by comprising the following steps: S1. Preparation of composite organic carrier: Well-rotted straw and liquor lees are mixed at a mass ratio of 1:0.8 to 1:1.2, pulverized to a particle size of 0.5 to 1.5 mm, and treated with low-temperature plasma at a power of 250 to 350 W for 80 to 100 s to make the carboxyl density on the carrier surface ≥7.5 μmol / m²; elemental sulfur particles with a particle size of 10 to 30 μm, potassium sulfate and ammonium dihydrogen phosphate are added to the activated carrier and mixed evenly to allow the carrier pores to adsorb the above nutrients, thus obtaining the composite organic carrier; S2. Preparation and loading of temperature-responsive supramolecular gels: S21. Copolymer synthesis: Humic acid (HA) and N-isopropylacrylamide (NIPAM) are mixed at a molar ratio of 1:10 to 1:15. A deionized water / ethanol mixture with a volume ratio of 3:1 is used as the solvent. 0.5 to 1.0 mol% of azobisisobutyramidine hydrochloride (AIBA) is added as the initiator. The mixture is reacted at 60 to 70°C for 6 to 8 hours to obtain the HA-PNIPAM copolymer. S22, β-Cyclodextrin Functional Modification: β-Cyclodextrin and hydroxyethyl acrylate were mixed in a molar ratio of 1:1.2 to 1:1.5, and 2 to 4 mol% of p-toluenesulfonic acid PTSA was added as a catalyst. The mixture was reacted at 40 to 50 °C for 4 to 6 h to obtain acrylamide β-cyclodextrin. S23. Click chemical crosslinking and nutrient inclusion: Mix HA-PNIPAM copolymer with acryloyl β-cyclodextrin at a molar ratio of 1:0.8 to 1:1.2, add 0.1 to 0.3 wt% photoinitiator, and react under UV irradiation at 10 to 15 mW / cm² for 2 to 4 min; add a 35% to 45% urea-ammonium sulfate mixed solution, and stir at 55 to 65°C and 200 to 300 rpm for 2 to 3 h to allow β-cyclodextrin to encapsulate nitrogen and sulfur nutrients, thus obtaining a nutrient-loaded supramolecular gel; S24. Gel loading: The nutrient-carrying supramolecular gel and the composite organic carrier are mixed at a mass ratio of 1:2 to 1:3. The pH of the HA-PNIPAM solution is adjusted to 3.5 to 4.5 to form a positively charged layer, and the pH of the composite organic carrier solution is adjusted to 8.0 to 9.0 to form a negatively charged layer. The gel is loaded onto the carrier surface through electrostatic layer-by-layer self-assembly. S3, pH-responsive controlled-release membrane preparation and encapsulation: S31. Preparation of coating slurry: By weight, add 5-8 parts ethyl cellulose, 2-3 parts hydroxypropyl cellulose, 1-2 parts chitosan, 1-2 parts glycerol, 0.6-0.8 parts thiourea, and 0.5-1.5 parts nano-montmorillonite to 120-150 parts purified water, stir at 40-50℃ and 30-40 rpm for 1-2 hours, and cool to room temperature to obtain the coating slurry; S32. Coating: Place the gel-loaded carrier particles in a coating pan, preheat at 3.0~5.0 rpm and 60~65℃ inlet air temperature for 10~15 min until the particle surface temperature reaches 35~40℃, and spray the coating slurry at a spraying rate of 80~110 mL / min until the coating weight gain is 4~6%, then stop spraying and continue rotating for 10~20 min until the coating moisture content is ≤5%; S4. Preparation of double-layer temperature-responsive microcapsule bacterial agent: S41. Preparation of inner layer solution: Prepare a sodium alginate solution with a concentration of 1.5~2.5%, add a mixed bacterial suspension of Bacillus subtilis and Thiobacillus thiooxidans, so that the total viable count is ≥5×10^8 CFU / g and the OD600 is 5.0~7.0. S42. Preparation of outer layer solution: Prepare a 2-3% HA-PNIPAM copolymer solution; S43. Microfluidic preparation of microcapsules: The inner layer solution and the outer layer solution are passed through a microfluidic device, with the inner layer flow rate at 0.5~1.0 mL / min and the outer layer flow rate at 1.5~2.5 mL / min. The formed microcapsules are collected and dropped into a 1.5~2.5M CaCl2 solution. The solution is solidified at a 0.1~0.3MPa atomization pressure for 10~20 min to obtain a double-layer microcapsule bacterial agent with a particle size of 50~150μm. S5. Microbial agent spraying and low-temperature drying: The double-layer microcapsule microbial agent is evenly sprayed onto the surface of the coated fertilizer granules, and then placed in a fluidized bed and dried at 40~50℃ until the final moisture content is 10~12% to obtain the finished product.

[0007] As a preferred technical solution of the present invention, in step S1, the mass ratio of decomposed straw to liquor lees is 1:1, and the amount of elemental sulfur particles, potassium sulfate and ammonium dihydrogen phosphate added is 2-4%, 5-8% and 3-6% of the mass of the composite organic carrier, respectively.

[0008] As a preferred technical solution of the present invention, in step S23, the mass ratio of urea to ammonium sulfate is 3:1 to 5:1, the nitrogen loading of the nutrient-carrying supramolecular gel is ≥25%, and the sulfur loading is ≥8%.

[0009] As a preferred technical solution of the present invention, in step S24, the electrostatic layer-by-layer self-assembly spraying is performed 4 to 6 times, and each spraying is dried at 40°C for 6 to 10 minutes.

[0010] As a preferred embodiment of the present invention, in step S31, the specific surface area of ​​the nano-montmorillonite is ≥200m² / g and the interlayer spacing is 1.2~1.5nm; the degree of deacetylation of chitosan is ≥85%.

[0011] As a preferred embodiment of the present invention, in step S41, the ratio of viable Bacillus subtilis to Thiobacillus thiooxidans is 2:1 to 4:1.

[0012] As a preferred embodiment of the present invention, in step S42, the molecular weight of the HA-PNIPAM copolymer is 12~18kDa, and its minimum critical dissolution temperature (LCST) is 32~36℃.

[0013] As a preferred technical solution of the present invention, in step S5, the amount of double-layer microcapsule bacterial agent sprayed is 8-12% of the mass of the finished fertilizer.

[0014] As a preferred embodiment of the present invention, the compound fertilizer comprises, from the inside out, a composite organic carrier core, a temperature-responsive supramolecular gel layer, a pH-responsive controlled-release coating layer, and a double-layer microcapsule bacterial agent layer; wherein the composite organic carrier core adsorbs elemental sulfur particles, potassium sulfate, and ammonium dihydrogen phosphate; the supramolecular gel layer encapsulates urea and ammonium sulfate; the coating layer contains a thiourea pore-forming agent; the outer layer of the microcapsule bacterial agent layer is a temperature-responsive HA-PNIPAM gel, and the inner layer encapsulates a mixed bacterial agent.

[0015] As a preferred embodiment of the present invention, the thickness of the supramolecular gel layer is 50-100 μm, the thickness of the pH-responsive controlled-release coating layer is 20-30 μm, and the particle size of the bilayer microcapsule bacterial agent is 50-150 μm.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs a three-tiered sulfur supply model: "fast-acting sulfur - medium-acting sulfur - slow-release sulfur." ​​Ammonium sulfate, as fast-acting sulfur, is adsorbed onto the gel layer and released within 1-2 weeks to meet the seedling stage requirements. Thiourea, as medium-acting sulfur, is dispersed in the coating layer and released within 1-2 months through pore formation to meet the tillering stage requirements. Elemental sulfur, as slow-release sulfur, is loaded into the carrier pores and gradually converted into effective sulfur by Thiobacillus thiooxidans, continuously releasing it for 2-5 months to meet the mid-to-late stage requirements. Simultaneously, ammonium dihydrogen phosphate and potassium sulfate are added to supplement phosphorus and potassium, solving the problem of single nutrient supply in existing technologies and meeting the full-cycle nutritional needs of field crops such as rice, corn, and wheat.

[0017] 2. This invention integrates a triple controlled-release mechanism of temperature response, pH response, and microbial response: Regarding temperature response, the supramolecular gel and the outer layer of the microcapsules use the same LCST (32~36℃) HA-PNIPAM, simultaneously triggering nutrient and microbial agent release during the peak nutrient demand period of crops (rhizosphere temperature ≥32℃); regarding pH response, chitosan is added to the coating, and the coating swells and accelerates nutrient release when the pH decreases due to rhizosphere organic acids; regarding microbial response, Thiobacillus thiooxidans converts elemental sulfur to produce sulfuric acid, further expanding the coating pores and forming a positive feedback nutrient release cycle. Testing shows that the nitrogen release curve of this invention matches crop requirements by ≥92%, significantly higher than the 70%~90% of existing technologies.

[0018] 3. This invention employs a double-layer microcapsule structure to encapsulate the mixed bacterial agent: the inner layer of sodium alginate provides basic protection, while the outer layer of HA-PNIPAM gel enables temperature-responsive release. The microcapsules are sprayed onto the coating surface, completely avoiding damage to the bacterial agent caused by high-temperature preheating and mechanical friction during preparation. The total viable cell survival rate of Bacillus subtilis and Thiobacillus thiooxidans is ≥92%, far exceeding the below 60% of existing technologies. Simultaneously, the outer layer of the microcapsule and the supramolecular gel layer have the same temperature-responsive characteristics, achieving precise synchronization between bacterial agent release and nutrient release, resulting in synergistic effects of microbial transformation and nutrient absorption.

[0019] 4. All materials used in this invention are biodegradable: the composite organic carrier consists of decomposed straw and liquor lees; the supramolecular gel is composed of HA-PNIPAM and β-cyclodextrin; the coating layer is composed of ethyl cellulose, chitosan, and nano-montmorillonite; and the microcapsules are composed of sodium alginate and HA-PNIPAM. The supramolecular gel has a degradation cycle of 120-150 days, and the coating layer has a degradation cycle of 140-160 days, perfectly matching the growth cycle of most field crops. After use, no recalcitrant substances remain, solving the problem of coating residue in existing technologies.

[0020] 5. The preparation process of this invention only requires the addition of a microfluidic bacterial agent preparation unit and a low-temperature plasma treatment unit to the existing slow-release fertilizer production line, without the need for large-scale equipment modification. At the same time, it makes full use of agricultural waste such as liquor lees and straw as organic carriers, resulting in low raw material costs. The overall production cost is only 8% to 12% higher than that of ordinary coated slow-release fertilizers, but the fertilizer efficiency is improved by more than 30%, showing good prospects for industrial application. Detailed Implementation

[0021] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0022] Example 1: This example provides a sulfur-based microbial compound fertilizer with temperature-responsive slow-release function. The preparation method is as follows: S1. Preparation of composite organic carrier: Well-rotted straw and liquor lees are mixed at a mass ratio of 1:1, pulverized to a particle size of 0.8~1.2mm, and treated with low-temperature plasma at a power of 300W for 90s to make the carboxyl density on the carrier surface reach 8.2μmol / m²; 3% by mass of elemental sulfur particles (particle size 15~25μm), 6% potassium sulfate and 4% ammonium dihydrogen phosphate are added to the activated carrier, and mixed evenly to allow the carrier pores to fully adsorb the above nutrients, thus obtaining the composite organic carrier; S2. Preparation and loading of temperature-responsive supramolecular gel: S21. Copolymer synthesis: Humic acid HA and N-isopropylacrylamide NIPAM are mixed at a molar ratio of 1:12, using a deionized water / ethanol mixture at a volume ratio of 3:1 as a solvent, and 0.8mol% of azobisisobutyramidine hydrochloride AIBA is added. Using 15 kDa as an initiator, the reaction was carried out at 65 °C for 7 h to obtain a HA-PNIPAM copolymer with a molecular weight of 15 kDa; S22, β-cyclodextrin functionalization modification: β-cyclodextrin and hydroxyethyl acrylate were mixed at a molar ratio of 1:1.3, and 3 mol% of p-toluenesulfonic acid PTSA was added as a catalyst. The reaction was carried out at 45 °C for 5 h to obtain acrylated β-cyclodextrin with a degree of substitution of 1.0; S23, click chemical crosslinking and nutrient inclusion: HA-PNIPAM copolymer and acrylated β-cyclodextrin were mixed at a molar ratio of 1:1.0, and 0.2 wt% of the photoinitiator 2-hydroxy-2-methylphenylacetone was added. The reaction was carried out under UV irradiation at 12 mW / cm² for 3 min; a 40% urea-ammonium sulfate mixed solution (urea to ammonium sulfate mass ratio 4:1) was added, and the mixture was stirred at 60 °C and 250 rpm for 2.5 h to allow β-cyclodextrin to undergo functionalization modification. Cyclodextrin fully encapsulates nitrogen and sulfur nutrients to obtain a nutrient-loaded supramolecular gel with a nitrogen loading of 26.8% and a sulfur loading of 8.5%. S24, Gel Loading: The nutrient-loaded supramolecular gel and the composite organic carrier are mixed at a mass ratio of 1:2.5. The pH of the HA-PNIPAM solution is adjusted to 4.0 to form a positively charged layer, and the pH of the composite organic carrier solution is adjusted to 8.5 to form a negatively charged layer. The mixture is electrostatically self-assembled and sprayed five times, drying at 40℃ for 8 minutes after each spray to complete the gel loading. S3, pH-Response Controlled-Release Coating Preparation and Encapsulation: S31, Coating Slurry Preparation: By weight, 6 parts ethyl cellulose, 2.5 parts hydroxypropyl cellulose, 1.5 parts chitosan (90% deacetylation), 1.5 parts glycerol, 0.7 parts thiourea, and 1.0 parts nano-montmorillonite (specific surface area 220 m² / g, interlayer spacing 1) are added.Add 3nm) to 130 parts of purified water, stir at 45℃ and 35rpm for 1.5h, cool to room temperature to obtain coating slurry; S32, Coating: Place the gel-loaded carrier particles in a coating pan, preheat at 4.0rpm and 62℃ air inlet temperature for 12min until the particle surface temperature reaches 38℃, spray the coating slurry at a spraying rate of 100mL / min, stop spraying when the coating weight increases by 5%, continue rotating for 15min until the coating moisture content is 4.2%; S4, Preparation of double-layer temperature-responsive microcapsule bacterial agent: S41, Inner layer solution preparation: Prepare a 2.0% sodium alginate solution, add a mixed bacterial suspension of Bacillus subtilis and Thiobacillus thiooxidans (viable bacteria ratio 3:1) to make the total viable bacteria count reach 6.2×10. 8 CFU / g, OD600 is 6.0; S42, preparation of outer layer solution: prepare a 2.5% HA-PNIPAM copolymer solution (LCST=34℃); S43, microfluidic preparation of microcapsules: pass the inner layer solution and outer layer solution through a microfluidic device, with the inner layer flow rate at 0.8 mL / min and the outer layer flow rate at 2.0 mL / min, collect the formed microcapsules, drop them into a 2.0M CaCl2 solution, and solidify them for 15 min under atomization pressure of 0.2 MPa to obtain a double-layer microcapsule bacterial agent with an average particle size of 105 μm; S5, bacterial agent spraying and low-temperature drying: uniformly spray 10% by mass of the double-layer microcapsule bacterial agent onto the surface of the coated fertilizer granules, and then place them in a fluidized bed and dry at 45℃ until the final moisture content is 11.2% to obtain the finished product.

[0023] Example 2: The difference between this example and Example 1 is as follows: In S1, the mass ratio of decomposed straw to liquor lees is 1:0.8, the amount of elemental sulfur particles added is 2%, the amount of potassium sulfate added is 5%, and the amount of ammonium dihydrogen phosphate added is 3%; In S21, the molar ratio of HA to NIPAM is 1:10, the reaction temperature is 60℃, the reaction time is 8h, and the molecular weight of HA-PNIPAM is 12kDa; In S23, the mass ratio of urea to ammonium sulfate is 3:1, the nitrogen loading is 25.2%, and the sulfur loading is 9.1%; In S31, there are 5 parts of ethyl cellulose, 1 part of chitosan, 0.6 parts of thiourea, and 0.5 parts of nano-montmorillonite; In S41, the ratio of viable Bacillus subtilis to viable Thiobacillus thiooxidans is 2:1, and the total viable count is 5.5×10⁻⁶. 8 CFU / g; In S5, the microcapsule bacterial agent spraying amount is 8%, the drying temperature is 40℃, and the final moisture content is 10.5%.

[0024] Example 3: The difference between this example and Example 1 is as follows: In S1, the mass ratio of decomposed straw to liquor lees is 1:1.2, the amount of elemental sulfur particles added is 4%, the amount of potassium sulfate added is 8%, and the amount of ammonium dihydrogen phosphate added is 6%; In S21, the molar ratio of HA to NIPAM is 1:15, the reaction temperature is 70℃, the reaction time is 6h, and the molecular weight of HA-PNIPAM is 18kDa; In S23, the mass ratio of urea to ammonium sulfate is 5:1, the nitrogen loading is 27.5%, and the sulfur loading is 7.8%; In S31, there are 8 parts of ethyl cellulose, 2 parts of chitosan, 0.8 parts of thiourea, and 1.5 parts of nano-montmorillonite; In S41, the ratio of viable Bacillus subtilis to viable Thiobacillus thiooxidans is 4:1, and the total viable count is 7.0×10⁻⁶. 8 CFU / g; In S5, the microcapsule bacterial agent spraying amount is 12%, the drying temperature is 50℃, and the final moisture content is 11.8%.

[0025] Comparative Example 1 An environmentally friendly organic slow-release fertilizer was prepared using the method described in Example 1 of CN120058423A, as Comparative Example 1.

[0026] Comparative Example 2 A controlled-release fertilizer made from liquor lees was prepared using the method described in Example 1 of CN118184444B, as a comparative example 2.

[0027] Comparative Example 3 The difference between this comparative example and Example 1 is that only Bacillus subtilis is added in S41, and Thiobacillus thiooxidans is not added, while the other steps are the same.

[0028] Performance testing experiment 1. Nutrient release characteristic test Nutrient release rate was determined using the soil leaching method. 10.0 g of fertilizer sample was weighed and loaded into a percolation column, along with 200 g of air-dried soil to maintain a soil moisture content of 25%. The column was placed in a constant temperature incubator at 25℃, 30℃, and 35℃. Leachate was collected every 7 days, and the cumulative release rates of nitrogen, phosphorus, potassium, and sulfur were measured. The results are shown in Table 1. Table 1. Cumulative nutrient release rate (%) of different fertilizers at 35℃ over 120 days

[0029] 2. Microbial activity test Weigh 1.0g of fertilizer sample, add 9mL of sterile water, shake well, serially dilute, spread on plates, incubate at 37℃ for 24h, and count the number of viable bacteria. The results are shown in Table 2.

[0030] Table 2. Viable microbial counts (CFU / g) of different fertilizers

[0031] 3. Field fertilizer efficiency trial Experimental location: Qihe County, Dezhou City, Shandong Province; experimental crop: winter wheat; experimental period: October 2025 - June 2026. The experiment included 6 treatments, each with 3 replicates. The plot area was 20 m², and the fertilizer application rate was 40 kg / mu (approximately 0.067 hectares), applied as a single basal application without topdressing. Wheat yield was measured after harvest, and the results are shown in Table 3.

[0032] Table 3 Effects of different fertilizers on winter wheat yield

[0033] The experimental results above show that: In the embodiments of the present invention, nitrogen, phosphorus, potassium and sulfur nutrients are released evenly, and the matching degree with crop requirements is ≥91%, which is significantly higher than that of the comparative example; due to the lack of sulfur-oxidizing bacteria, the sulfur release rate of comparative example 3 is only 71.2%, and the matching degree is significantly reduced.

[0034] The total viable bacteria survival rate of the embodiments of the present invention is ≥90%, which is much higher than that of Comparative Example 2 (42%), indicating that the double-layer microcapsule structure has an excellent protective effect on the bacterial agent.

[0035] Field trials showed that the wheat yield of the embodiments of the present invention increased by 29.9% to 34.6% compared with the blank control, by 10.7% to 12.3% compared with control 1, and by 21.2% to 25.6% compared with control 2, demonstrating significant fertilizer efficiency advantages.

[0036] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sulfur-based microbial compound fertilizer with temperature-responsive slow-release function, characterized in that, Includes the following steps: S1. Preparation of composite organic carrier: Well-rotted straw and liquor lees are mixed at a mass ratio of 1:0.8 to 1:1.2, pulverized to a particle size of 0.5 to 1.5 mm, and treated with low-temperature plasma at a power of 250 to 350 W for 80 to 100 s to make the carboxyl density on the carrier surface ≥7.5 μmol / m²; elemental sulfur particles with a particle size of 10 to 30 μm, potassium sulfate and ammonium dihydrogen phosphate are added to the activated carrier and mixed evenly to allow the carrier pores to adsorb the above nutrients, thus obtaining the composite organic carrier; S2. Preparation and loading of temperature-responsive supramolecular gels: S21. Copolymer synthesis: Humic acid (HA) and N-isopropylacrylamide (NIPAM) are mixed at a molar ratio of 1:10 to 1:

15. A deionized water / ethanol mixture with a volume ratio of 3:1 is used as the solvent. 0.5 to 1.0 mol% of azobisisobutyramidine hydrochloride (AIBA) is added as the initiator. The mixture is reacted at 60 to 70°C for 6 to 8 hours to obtain the HA-PNIPAM copolymer. S22, β-Cyclodextrin Functional Modification: β-Cyclodextrin and hydroxyethyl acrylate were mixed in a molar ratio of 1:1.2 to 1:1.5, and 2 to 4 mol% of p-toluenesulfonic acid PTSA was added as a catalyst. The mixture was reacted at 40 to 50 °C for 4 to 6 h to obtain acrylamide β-cyclodextrin. S23. Click chemical crosslinking and nutrient inclusion: Mix HA-PNIPAM copolymer with acryloyl β-cyclodextrin at a molar ratio of 1:0.8 to 1:1.2, add 0.1 to 0.3 wt% photoinitiator, and react under UV irradiation at 10 to 15 mW / cm² for 2 to 4 min; add a 35% to 45% urea-ammonium sulfate mixed solution, and stir at 55 to 65°C and 200 to 300 rpm for 2 to 3 h to allow β-cyclodextrin to encapsulate nitrogen and sulfur nutrients, thus obtaining a nutrient-loaded supramolecular gel; S24. Gel loading: The nutrient-carrying supramolecular gel and the composite organic carrier are mixed at a mass ratio of 1:2 to 1:

3. The pH of the HA-PNIPAM solution is adjusted to 3.5 to 4.5 to form a positively charged layer, and the pH of the composite organic carrier solution is adjusted to 8.0 to 9.0 to form a negatively charged layer. The gel is loaded onto the carrier surface through electrostatic layer-by-layer self-assembly. S3, pH-responsive controlled-release membrane preparation and encapsulation: S31. Preparation of coating slurry: By weight, add 5-8 parts ethyl cellulose, 2-3 parts hydroxypropyl cellulose, 1-2 parts chitosan, 1-2 parts glycerol, 0.6-0.8 parts thiourea, and 0.5-1.5 parts nano-montmorillonite to 120-150 parts purified water, stir at 40-50℃ and 30-40 rpm for 1-2 hours, and cool to room temperature to obtain the coating slurry; S32. Coating: Place the gel-loaded carrier particles in a coating pan, preheat at 3.0~5.0 rpm and 60~65℃ inlet air temperature for 10~15 min until the particle surface temperature reaches 35~40℃, and spray the coating slurry at a spraying rate of 80~110 mL / min until the coating weight gain is 4~6%, then stop spraying and continue rotating for 10~20 min until the coating moisture content is ≤5%; S4. Preparation of double-layer temperature-responsive microcapsule bacterial agent: S41. Preparation of inner layer solution: Prepare a sodium alginate solution with a concentration of 1.5~2.5%, add a mixed bacterial suspension of Bacillus subtilis and Thiobacillus thiooxidans, so that the total viable count is ≥5×10^8 CFU / g and the OD600 is 5.0~7.

0. S42. Preparation of outer layer solution: Prepare a 2-3% HA-PNIPAM copolymer solution; S43. Microfluidic preparation of microcapsules: The inner layer solution and the outer layer solution are passed through a microfluidic device, with the inner layer flow rate at 0.5~1.0 mL / min and the outer layer flow rate at 1.5~2.5 mL / min. The formed microcapsules are collected and dropped into a 1.5~2.5M CaCl2 solution. The solution is solidified at a 0.1~0.3MPa atomization pressure for 10~20 min to obtain a double-layer microcapsule bacterial agent with a particle size of 50~150μm. S5. Microbial agent spraying and low-temperature drying: The double-layer microcapsule microbial agent is evenly sprayed onto the surface of the coated fertilizer granules, and then placed in a fluidized bed and dried at 40~50℃ until the final moisture content is 10~12% to obtain the finished product.

2. The preparation method of the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, In step S1, the mass ratio of decomposed straw to liquor lees is 1:1, and the amounts of elemental sulfur particles, potassium sulfate, and ammonium dihydrogen phosphate added are 2-4%, 5-8%, and 3-6% of the mass of the composite organic carrier, respectively.

3. The method for preparing the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, In step S23, the mass ratio of urea to ammonium sulfate is 3:1 to 5:1, the nitrogen loading of the nutrient-carrying supramolecular gel is ≥25%, and the sulfur loading is ≥8%.

4. The method for preparing the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, In step S24, the electrostatic layer-by-layer self-assembly spraying is performed 4 to 6 times, and each spraying is dried at 40°C for 6 to 10 minutes.

5. The method for preparing sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, In step S31, the specific surface area of ​​nano-montmorillonite is ≥200m² / g and the interlayer spacing is 1.2~1.5nm; the degree of deacetylation of chitosan is ≥85%.

6. The method for preparing the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, In step S41, the ratio of viable Bacillus subtilis to Thiobacillus thiooxidans is 2:1 to 4:

1.

7. The method for preparing the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, In step S42, the molecular weight of the HA-PNIPAM copolymer is 12~18kDa, and its minimum critical dissolution temperature (LCST) is 32~36℃.

8. The method for preparing the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, In step S5, the amount of double-layer microcapsule bacterial agent sprayed is 8-12% of the mass of the finished fertilizer.

9. The method for preparing the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 1, characterized in that, The compound fertilizer comprises, from the inside out, a composite organic carrier core, a temperature-responsive supramolecular gel layer, a pH-responsive controlled-release coating layer, and a double-layer microcapsule bacterial agent layer. The composite organic carrier core adsorbs elemental sulfur particles, potassium sulfate, and ammonium dihydrogen phosphate. The supramolecular gel layer encapsulates urea and ammonium sulfate. The coating layer contains a thiourea pore-forming agent. The outer layer of the microcapsule bacterial agent layer is a temperature-responsive HA-PNIPAM gel, and the inner layer encapsulates a mixed bacterial agent.

10. The method for preparing the sulfur-based microbial compound fertilizer with temperature-responsive slow-release function according to claim 9, characterized in that, The thickness of the supramolecular gel layer is 50-100 μm, the thickness of the pH-responsive controlled-release coating layer is 20-30 μm, and the particle size of the bilayer microcapsule bacterial agent is 50-150 μm.

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