Microbial synergistic slow-release fertilizer and preparation method thereof

Abstract

The invention discloses a microbial synergistic slow-release fertilizer and a preparation method thereof. The fertilizer comprises an organic-inorganic mixture, microbial agent microcapsules and a coating layer. The preparation method mainly comprises the following steps: firstly, through a sectional fermentation process, mixing corn straws with humic acid, adding an improved microbial inoculum for fermentation, and premixing biochar with ammonium dihydrogen phosphate and potassium sulfate to improve the nutrient adsorption efficiency; embedding beneficial microorganisms such as nitrogen-fixing bacteria, phosphate solubilizing bacteria and the like with the seaweed extract to prepare a microcapsule fungicide with high survival rate, and forming slow-release fertilizer particles with the organic-inorganic mixed material through a specific granulation process; and finally, coating the surfaces of the particles, forming a basic slow-release film by using a sodium alginate-diatomite mixed solution, and further wrapping environment-sensitive hydrogel, the microbial synergistic slow-release fertilizer disclosed by the invention is particularly suitable for planting crops such as rice in saline-alkali soil, and has remarkable agricultural application value and environmental friendliness.

Description

[0001] The invention relates to the technical field of pesticides, in particular to a microbial synergistic slow-release fertilizer and a preparation method thereof. Background Art

[0002] In the agricultural field, especially in the field of rice cultivation in saline-alkali land, the selection of fertilizers and soil improvement have always been the key links to improve crop yield and quality. Although traditional fertilizers can provide crops with necessary nutrients, their effects are often limited in the special environment of saline-alkali land. The soil in saline-alkali land contains high concentrations of salt, which not only restricts the normal growth of crops, but also may lead to the deterioration of soil structure, further affecting the yield and quality of crops. In recent years, with the rapid development of fields such as microbiology, ecology and materials science, microbial fertilizers, as a new and environmentally friendly form of fertilizer, have gradually attracted widespread attention in the agricultural community. Microbial fertilizers introduce beneficial microorganisms and utilize the metabolic activities and biotransformation functions of microorganisms to improve the soil environment and soil fertility, thereby promoting the growth and development of crops. In the cultivation of rice in saline-alkali land, the application of microbial fertilizers is particularly important. On the one hand, the beneficial microorganisms in microbial fertilizers can decompose organic matter in the soil, promote the formation of soil aggregate structure, and improve the air permeability and water retention of the soil, which is beneficial to the growth of rice roots and the absorption of nutrients. On the other hand, microorganisms can also neutralize the salt in the soil and reduce the pH value of the soil by producing metabolites such as organic acids, thus creating a more suitable environment for the growth of rice. However, existing microbial fertilizers still have some problems in practical applications. For example, the survival time of microorganisms in the soil is short, making it difficult for them to continue to play a role; the fertilizer effect of microbial fertilizers is released too quickly, making it difficult to meet the needs of the entire growth cycle of crops; and microbial fertilizers have poor adaptability to saline-alkali soils, making it difficult to fully exert their improvement effects.

[0003] In order to solve these problems, researchers began to explore the research and development of microbial synergistic slow-release fertilizers. This fertilizer not only combines the advantages of microbial fertilizers, but also achieves the slow release of fertilizer effect and the continuous survival of microorganisms by adding slow-release materials and optimizing the structure of microbial flora. At the same time, in view of the special environment of saline-alkali land, researchers have also screened out microbial strains with salt tolerance, phosphorus solubilization, potassium solubilization and other functions to improve the adaptability of fertilizers to saline-alkali soils. In summary, microbial synergistic slow-release fertilizers have broad application prospects in saline-alkali land rice cultivation. By continuously optimizing the preparation process, screening high-efficiency microbial strains, and improving the adaptability of fertilizers to soils, the fertilizer efficiency and utilization rate of microbial fertilizers can be further improved, providing strong support for the sustainable development of saline-alkali land rice. Summary of the invention

[0004] To achieve the above-mentioned purpose, the present invention provides a microbial synergistic slow-release fertilizer and a preparation method thereof, which solves the above-mentioned technical problems.

[0005] The invention provides a microbial synergistic slow-release fertilizer, comprising an organic-inorganic mixture, a bacterial agent microcapsule and a coating layer.

[0006] Furthermore, the organic-inorganic mixture includes fermented corn stalks, humic acid, biochar, diammonium phosphate and potassium sulfate.

[0007] Furthermore, the microbial agent microcapsules encapsulate nitrogen-fixing bacteria and phosphate-solubilizing bacteria.

[0008] Furthermore, the coating layer includes a pH-responsive sustained-release membrane and an environmentally sensitive hydrogel layer.

[0009] Furthermore, the weight ratio of organic components to inorganic components in the organic-inorganic mixture is 3:7; the organic components include corn stalks, humic acid and biochar, and the inorganic components include diammonium phosphate and potassium sulfate.

[0010] Furthermore, the nitrogen-fixing bacteria are salt-tolerant nitrogen-fixing bacteria, and the phosphate-solubilizing bacteria are halophilic phosphate-solubilizing bacteria.

[0011] Furthermore, the pH-responsive sustained-release membrane is a sodium alginate-diatomaceous earth mixed membrane, and the environmentally sensitive hydrogel layer is methacrylated sodium alginate.

[0012] The present invention provides a method for preparing a microbial synergistic slow-release fertilizer, comprising the following steps:

[0013] S1, segmented fermentation and mixing: corn straw is mixed with humic acid, improved bacterial agents are added for fermentation, and biochar, diammonium phosphate and potassium sulfate are mixed to form an organic-inorganic mixture;

[0014] S2, bacterial agent loading and granulation: nitrogen-fixing bacteria, phosphate-dissolving bacteria and seaweed extract containing fucoidan are embedded into microspheres, extruded and granulated to form bacterial agent microcapsules, and the organic-inorganic mixture and bacterial agent microcapsules are granulated into granules at a weight ratio of 7:3;

[0015] S3, coating and post-treatment: spraying a sodium alginate-diatomaceous earth mixture with a solid content of 20% on the surface of the particles, forming a pH-responsive sustained-release film after drying, and then coating with methacrylated sodium alginate.

[0016] Furthermore, the corn stalks and humic acid are mixed in a ratio of 3:1 by weight, and an improved bacterial agent is added, and fermented at 50-60°C for 12 days, with a degree of maturity of 95%. The biochar is mixed with diammonium hydrogen phosphate and potassium sulfate in a ratio of 1:2:1 by weight for 3 hours.

[0017] Furthermore, the nitrogen-fixing bacteria, phosphate-solubilizing bacteria and the seaweed extract containing fucoidan are embedded into microspheres by spray drying, and the organic-inorganic mixture and the bacterial agent microcapsules are granulated into granules in a weight ratio of 7:3 at a temperature of 40° C. using a double-roll extrusion granulator with a particle size of 2-4 mm.

[0018] The microbial synergistic slow-release fertilizer and the preparation method thereof proposed in the present invention have the following beneficial effects:

[0019] 1. The present invention is aimed at the coastal areas of the Lixiahe Plain, such as the newly reclaimed coastal areas, such as the coastal reclamation areas of Dongtai and Dafeng. The soil is alkaline due to the backflow of seawater and the influence of high-salt parent material, with a pH greater than 7 and less than 8.5. The content of available phosphorus in alkaline soil is extremely low (<5 mg / kg). Because calcium and magnesium ions combine with phosphate to form insoluble phosphates (such as hydroxyapatite), the organic matter content is usually less than 2.0%, the fertilizer retention capacity is weak, and the microbial activity is limited, the organic matter decomposes slowly, and the electrical conductivity (EC) in some areas is high (>3mS / cm) due to secondary salinization. The sodium ion content is high, which is easy to cause soil compaction. The bacterial community-hydrogel synergistic controlled release, the nitrogen-fixing bacteria and the phosphate-dissolving bacteria are compounded, and the survival rate is improved through the colonization of rice husk charcoal pores. The extracellular polysaccharides produced by bacterial community metabolism form a three-dimensional network with the sodium alginate hydrogel, so that the nitrogen slow-release period is extended; the methacrylylated sodium alginate automatically shrinks the pores when the soil salinity is high, reducing the nitrogen leaching in the rainy season;

[0020] 2. The fertilizer-rice husk charcoal synergistic soil improvement system is used. The high porosity of rice husk charcoal can absorb salt. Rice husk charcoal (pH 8.2) and coastal saline soil (pH 7.9-8.5) form a buffer system. Combined with humic acid (46% organic matter) in the fertilizer, the pH of the rhizosphere micro-domain is stabilized at 7.2-7.8, inhibiting the osmotic stress of salt on the root system.

[0021] 3. Microorganisms secrete extracellular polysaccharides (EPS) combined with humic acid to form stable aggregates (> 0.25mm aggregates increased by 20%), improve compaction, and seaweed active substances inhibit salt disease pathogens (such as Fusarium), reducing the incidence of soil-borne diseases by ≥ 30%; synergistic mechanism of each formula; microorganisms secrete extracellular polysaccharides (EPS) combined with humic acid to form stable aggregates, improve compaction; seaweed active substances inhibit salt disease pathogens (such as Fusarium), reduce the incidence of soil-borne diseases, and improve the effectiveness of bacterial agents. Adding can not only optimize the maturity, but also improve the adsorption capacity of organic matter in saline soil. Adding seaweed extract (including fucoidan) as a protective agent for bacterial agents can increase the survival rate by 15% at high temperature (50°C) compared with conventional microcapsules. The present application is a dual-responsive membrane structure, with the outer layer being MAAs hydrogel (salt response layer) and the inner layer being humic acid-modified diatomaceous earth (pH response layer). When the salt concentration is greater than 3dS / m, the permeability of the outer membrane increases, and when the pH is less than 7.5, the inner layer quickly disintegrates, achieving precise controlled release of dual environmental factors.

[0022] 4. Seaweed extract uses low-value brown algae (such as Sargassum) as raw material, which reduces the cost by 40%. The high temperature in Dongtai Port in summer (average temperature 26-28℃ from June to August) accelerates the mineralization of organic nitrogen, but the high salinity of coastal saline soil (EC 1-3dS / m) will inhibit the activity of nitrifying bacteria and further reduce the accumulation of nitrate nitrogen. The release rate of coated slow-release fertilizer (under flooding conditions is reduced (pH and anoxic environment affect the degradation of the coating) is better matched with the fertilizer requirement curve of rice. DETAILED DESCRIPTION

[0023] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0024] Unless otherwise specified, the examples and comparative examples are parallel tests with the same components, component contents, preparation steps and preparation parameters. The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0025] Unless otherwise stated, all reagents were used as received without further purification.

[0026] In the preparation examples and embodiments of the present invention, the “parts” are parts by weight unless otherwise specified, and the concentration percentages are concentrations by weight unless otherwise specified.

[0027] Core strains:

[0028] Salt-tolerant nitrogen-fixing bacteria: Azotobacter chroococcum, a salt-tolerant nitrogen-fixing bacterium, whose nitrogenase activity remains above 60% when the salt concentration is ≤2.5%, was purchased from Beijing Biobo Biotechnology Co., Ltd., model: Bio-05484; alkaliphilic phosphate-solubilizing bacteria: Pseudomonas sp. screened from coastal saline-alkali soil, which can dissolve calcium phosphate at pH 8.5 and release available phosphorus; stress-resistant growth-promoting bacteria, manufacturer: Shanghai Collection Biotechnology Center, model: SHBCC D80591 (ATCC 31554).

[0029] Methacryloyl sodium alginate was purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd., model: XFBM07; seaweed extract containing fucoidan was purchased from Qingdao Mingyue Seaweed Group Co., Ltd., model: BMSFu-Hp; sodium alginate-diatomaceous earth mixture was purchased from MY-Alg-DE20; corn straw was purchased from Zhengyang County Xintiandi Grass Industry Co., Ltd.; humic acid was purchased from Chiping County Jinshun Chemical Co., Ltd., model AA with a purity of 99%; improved bacterial agents were purchased from Zhongnong Fuyuan, strains: halotolerant Bacillus, halotolerant actinomycetes and halotolerant Trichoderma, activity: effective viable count ≥ 5 billion / g, salt tolerance threshold EC = 5dS / m; biochar was purchased from Henan Xingyuan Environmental Protection Materials Co., Ltd. with a purity of 99%.

[0030] Embodiment 1:

[0031] The preparation method of the microbial synergistic slow-release fertilizer comprises the following steps:

[0032] S1. Segmented fermentation and mixing: corn stalks and humic acid are mixed in a weight ratio of 3:1, and improved bacterial agents are added. The mixture is fermented in a trough-type turning machine at a temperature of 60°C for 12 days, and the degree of maturity is 95% to obtain an organic component; biochar with a particle size of 1.5 mm is premixed with diammonium phosphate and potassium sulfate in a weight ratio of 1:2:1 in a double-shaft differential speed mixer to obtain an inorganic component; the organic component and the inorganic component are mixed in a weight ratio of 3:7, and adsorbed for 3 hours to obtain an organic-inorganic mixture;

[0033] S2. Bacteria loading and granulation: salt-tolerant nitrogen-fixing bacteria, alkali-loving phosphate-dissolving bacteria and seaweed extract containing fucoidan (5% w / w) were embedded into microspheres by spray drying technology; the organic-inorganic mixture and the bacteria microcapsules were granulated in a weight ratio of 7:3 (particle size 3 mm) using a double-roll extrusion granulator at a temperature of 40°C;

[0034] S3. Coating and post-treatment: Spray a sodium alginate-diatomaceous earth mixture (solid content 20%) on the particle surface, form a pH-responsive slow-release membrane after drying, and coat with methacrylated sodium alginate to adjust the membrane permeability in response to changes in soil salt concentration to prevent nutrient leaching during the rainy season.

[0035] Embodiment 2:

[0036] The preparation method of the microbial synergistic slow-release fertilizer comprises the following steps:

[0037] S1. Segmented fermentation and mixing: corn stalks and humic acid are mixed in a weight ratio of 4:1, and improved bacterial agents are added. The mixture is fermented in a tank-type turning machine (temperature 55°C) for 10 days, and the degree of maturity is 93%; biochar with a particle size of 2 mm is premixed with ammonium dihydrogen phosphate and potassium sulfate in a weight ratio of 1:2:1 in a double-shaft differential speed mixer to obtain an inorganic component; the organic component and the inorganic component are mixed in a weight ratio of 3:7, and adsorbed for 3 hours to obtain an organic-inorganic mixture;

[0038] S2. Bacteria loading and granulation: salt-tolerant nitrogen-fixing bacteria, alkali-loving phosphate-dissolving bacteria and seaweed extract containing fucoidan (5% w / w) were embedded into microspheres by spray drying technology; the organic-inorganic mixture and the bacteria microcapsules were granulated in a weight ratio of 7:3 (particle size 4 mm) using a double-roll extrusion granulator at a temperature of 30°C;

[0039] S3. Coating and post-treatment: Spray a sodium alginate-diatomaceous earth mixture (solid content 20%) on the particle surface, form a pH-responsive slow-release membrane after drying, and coat with methacrylated sodium alginate to adjust the membrane permeability in response to changes in soil salt concentration to prevent nutrient leaching during the rainy season.

[0040] Embodiment 3:

[0041] The preparation method of the microbial synergistic slow-release fertilizer comprises the following steps:

[0042] S1. Segmented fermentation and mixing: corn stalks and humic acid are mixed in a weight ratio of 3:2, and improved bacterial agents are added. The mixture is fermented in a trough-type turning machine at a temperature of 50°C for 13 days, and the degree of maturity is 96%. Biochar with a particle size of 1 mm is premixed with ammonium dihydrogen phosphate and potassium sulfate in a weight ratio of 1:2:1 in a double-shaft differential speed mixer to obtain an inorganic component; the organic component and the inorganic component are mixed in a weight ratio of 3:7, and adsorbed for 4 hours to obtain an organic-inorganic mixture;

[0043] S2. Bacteria loading and granulation: salt-tolerant nitrogen-fixing bacteria, alkali-loving phosphate-dissolving bacteria and seaweed extract containing fucoidan (5% w / w) were embedded into microspheres by spray drying technology; the organic-inorganic mixture and the bacteria microcapsules were granulated in a weight ratio of 7:3 (particle size 2 mm) using a double-roll extrusion granulator at a temperature of 35°C;

[0044] S3. Coating and post-treatment: Spray a sodium alginate-diatomaceous earth mixture (solid content 20%) on the particle surface, form a pH-responsive slow-release membrane after drying, and coat with methacrylated sodium alginate to adjust the membrane permeability in response to changes in soil salt concentration to prevent nutrient leaching during the rainy season.

[0045] Comparative Example 1

[0046] Siweit fertilizers on the market.

[0047] Comparative Example 2

[0048] The difference from Example 1 is that in step S3, no methacrylated sodium alginate is used for coating, and a single-layer coated fertilizer is prepared, and the other steps are the same.

[0049] Comparative Example 3

[0050] The difference from Example 1 is that in step S3, the sodium alginate-diatomaceous earth mixed solution (solid content 20%) is not sprayed on the particle surface, and the other steps are the same.

[0051] Comparative Example 4

[0052] The difference from Example 1 is that ordinary activated carbon is used instead of biochar, and the rest are the same.

[0053] Comparative Example 5

[0054] The difference from Example 1 is the lack of salt-tolerant nitrogen-fixing bacteria and alkaliphilic phosphate-solubilizing bacteria, and the others are the same.

[0055] Comparative Example 6

[0056] The difference from Example 1 is the lack of salt-tolerant nitrogen-fixing bacteria, and the others are the same.

[0057] Comparative Example 7

[0058] The difference from Example 1 is the lack of alkaliphilic phosphate-solubilizing bacteria, and the others are the same.

[0059] Application of microbial synergistic slow-release fertilizer in rice cultivation: Use 15cm deep plowing machinery to mix microbial synergistic slow-release fertilizer (550kg / ha) and rice husk charcoal (2000kg / ha) in a ratio of 1:3.6 and apply them in layers to the tillage layer to form a "charcoal on top and fertilizer on the bottom" structure.

[0060] Performance Testing

[0061] The microbial synergistic slow-release fertilizers prepared in the examples and comparative examples were tested as follows: The test was conducted at the test base of Tiaozini Reclamation Area in Dongtai, 1 km from the coastline. The basic physical and chemical properties of the tested soil were as follows: pH 8.1, organic matter 1.5 g / kg, total nitrogen 0.9 g / kg, nitrate nitrogen 10.2 mg / kg, ammonium nitrogen 21.5 mg / kg, available phosphorus 11.4 mg / kg, available potassium 85.6 mg / kg, and the EC value of the shallow well water in the local well was 3.1 dS / m. The tested rice variety was "Nanjing 9108".

[0062] 1. Tests of nitrogen content, soil EC value, etc.: This test uses a lysmeter method to collect leaching solution. The lysmeter is 150 cm long, 80 cm wide, and 40 cm high, simulating the actual field tillage layer depth. The soil in the pool (soil pH 8.2) was dug out in layers (one layer every 5 cm) and backfilled before the test. The soil was surrounded by plastic cloth, and a leaching bucket (40 cm in diameter and 40 cm in height) was placed below. Two layers of 0.15 mm (100 mesh) nylon mesh were laid on the lid of the leaching bucket. The inside of the bucket was connected to the surface through a connecting pipeline, and the leaching solution was extracted using a vacuum pump. The irrigation method is drip irrigation, and the irrigation water source is local well water. The specific irrigation conditions are 75mm from June 10 to June 15, 2023, 180mm from June 16 to July 15, 2023, 145mm from July 16 to August 5, 2023, 90mm from August 6 to August 25, 2023, and 65mm from August 26 to September 10. Microbial synergistic slow-release fertilizer is used as base fertilizer, and ordinary urea is used as topdressing at a nitrogen content of 240kg N / ha. The ratio of base fertilizer to topdressing is 1:1, and the rice planting density is 300 ears / m 2 , and irrigation and pest control were carried out according to local routine field management. The leaching solution was collected 5 times during the entire rice growth period, with sampling dates on June 15, 2023 (tillering stage), July 15, 2023 (jointing stage), August 5, 2023 (booting stage), August 25, 2023 (heading stage) and September 10, 2023 (filling stage). The volume of the leaching solution was recorded each time, filtered and dispensed into polyethylene bottles, stored at 4°C in the dark, and ammonium nitrogen, nitrate nitrogen and total nitrogen in the leaching solution were determined using a flow analyzer (Beijing Jitian iFIA7). After the heading period, the soil was prepared and tilled, and soil samples from the 0-10 cm soil layer were collected using the five-point method. The total nitrogen content was determined by the concentrated sulfuric acid-hydrogen peroxide digestion Kjeldahl method, and the available phosphorus was determined by the vanadium molybdenum blue colorimetric method using the Beijing Jitian fully automatic flow injection analyzer iFIA7; the available potassium was determined by the flame photometer method using the Puxi General Atomic Absorption A3. Soil enzyme activity was determined using the Solarbio activity detection kit (BC0120, BC0240 and BC0100), and the formula used to calculate the cumulative leaching loss was: Among them, Q t is the cumulative leaching nitrogen loss (unit: kg N / ha); n is the total number of sampling times; C i is the nitrogen concentration in the ith leaching solution (unit: mg / L or kg / m 3 );V i is the volume of the ith shower solution (unit: L or m 3 ), the results are shown in Table 1.

[0063] Table 1:

[0064]

[0065]

[0066] As shown in Table 1, nitrogen migrates vertically rapidly from the jointing stage to the booting stage. Example 1 is synchronized with the nitrogen requirement of rice, reducing the residual soluble nitrogen in the soil, while Comparative Example 1 is easily converted into nitrate nitrogen under alkaline soil conditions (pH 8.2), and nitrate nitrogen has a weak adsorption force with the soil (rich in iron and aluminum oxides) due to its negative charge, and is more easily leached; and the proportion of ammonium nitrogen in Example 1 is higher than that in Comparative Example 1, so Example 1 delays the process of urea hydrolysis into ammonium nitrogen, and ammonium nitrogen can be adsorbed by iron and aluminum oxides in the soil, reducing further nitrification to generate NO3 that is easily leached. - , strong anti-leaching performance.

[0067] 2. Tests on rice yield, soil EC value, etc.: From the beginning of harvesting to the end of harvesting of facility rice, the rice harvested in each treatment was weighed and the rice yield of each harvest was recorded in detail; the soil EC value was measured using a four-electrode conductivity meter (HORIBALAQUA); soil pH value was measured: 10 cm tillage layer soil samples were collected at the tillering stage, heading stage and after harvest (rice maturity stage), and the samples were mixed using the five-point sampling method. The soil samples were naturally air-dried and passed through a 2 mm sieve, and a suspension was prepared at a soil-water ratio of 1:2.5. After standing for 30 minutes, the pH was measured using a pH meter (Mettler FE28), and the initial soil pH was 8.1; organic matter content was measured using the potassium dichromate oxidation-external heating method (GB 9834-88). Take 0.5g of soil sample passed through a 0.25mm sieve, add 5mL of 0.8mol / L K2Cr2O7 solution and 5mL of concentrated H2SO4, boil in an oil bath (170℃) for 5 minutes, use o-phenanthroline as an indicator, and titrate with 0.5mol / L FeSO4. The results are shown in Table 2.

[0068] Table 2:

[0069]

[0070] As shown in Table 2, due to the lack of pH-responsive slow-release membrane, nutrient release is not precise, resulting in a slightly higher EC value and a decreased pH regulation ability. The salt adsorption capacity of ordinary activated carbon is weaker than that of biochar. The lack of microbial synergy has the worst soil improvement effect. The lack of nitrogen-fixing bacteria leads to insufficient nitrogen supply. The lack of phosphate-solubilizing bacteria affects phosphorus release. The yield is lower than that of the embodiment but better than that of the comparative example 5 which has no microorganisms at all.

[0071] 3. Stability test

[0072] The survival rate of the bacterial agent was tested after storage for 30 days under the conditions of EC=3dS / m, temperature 50°C and humidity 80%. See Table 3.

[0073] Table 3

[0074]

[0075] As shown in Table 3, the lack of the inner pH-responsive membrane leads to a decrease in the protectiveness of the microcapsules. The pore structure of ordinary activated carbon is not as good as that of biochar, and the colonization effect of the bacterial agent is poor and the survival rate is low. In summary, Example 1 reduces leaching by synchronizing nutrient release with the rice fertilizer requirement curve, thereby achieving precise controlled release, and can also reduce EC value, adjust pH, and alleviate salt stress, thereby improving salinity. In addition, the coating structure and protective agent of Example 1 improve the survival rate of the bacterial agent, promote the accumulation of soil organic matter, and are conducive to the long-term maintenance of microbial activity.

[0076] The specific embodiments of the present invention are described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions made to the present invention are also within the scope of the present invention. Therefore, the equalization changes and modifications made without departing from the spirit and scope of the present invention should be included in the scope of the present invention.

Claims

1. A microbial synergistic slow-release fertilizer, characterized in that: It includes an organic-inorganic mixture, bacterial agent microcapsules and a coating layer.

2. The microbial synergistic slow-release fertilizer according to claim 1, characterized in that: The organic-inorganic mixture comprises fermented corn stalks, humic acid, biochar, diammonium phosphate and potassium sulfate.

3. The microbial synergistic slow-release fertilizer according to claim 1, characterized in that: The microcapsules of the bacterial agent encapsulate nitrogen-fixing bacteria and phosphate-solubilizing bacteria.

4. The microbial synergistic slow-release fertilizer according to claim 1, characterized in that: The coating layer comprises a pH-responsive sustained-release membrane and an environmentally sensitive hydrogel layer.

5. The microbial synergistic slow-release fertilizer according to claim 1, characterized in that: The weight ratio of the organic component to the inorganic component in the organic-inorganic mixture is 3:7; the organic component includes corn stalks, humic acid and biochar, and the inorganic component includes diammonium phosphate and potassium sulfate.

6. The microbial synergistic slow-release fertilizer according to claim 3, characterized in that: The nitrogen-fixing bacteria are salt-tolerant nitrogen-fixing bacteria, and the phosphate-solubilizing bacteria are halophilic phosphate-solubilizing bacteria.

7. The microbial synergistic slow-release fertilizer according to claim 4, characterized in that: The pH-responsive sustained-release membrane is a sodium alginate-diatomaceous earth mixed membrane, and the environmentally sensitive hydrogel layer is methacrylated sodium alginate.

8. The method for preparing the microbial synergistic slow-release fertilizer according to claim 1, characterized in that: The following steps are involved: S1, segmented fermentation and mixing: corn straw is mixed with humic acid, improved bacterial agents are added for fermentation, and biochar, diammonium phosphate and potassium sulfate are mixed to form an organic-inorganic mixture; S2, bacterial agent loading and granulation: nitrogen-fixing bacteria, phosphate-dissolving bacteria and seaweed extract containing fucoidan are embedded into microspheres, extruded and granulated to form bacterial agent microcapsules, and the organic-inorganic mixture and bacterial agent microcapsules are granulated into granules at a weight ratio of 7:3; S3, coating and post-treatment: spraying a sodium alginate-diatomaceous earth mixed solution with a solid content of 20% on the surface of the particles, forming a pH-responsive sustained-release film after drying, and coating the methacrylated sodium alginate.

9. The method for preparing the microbial synergistic slow-release fertilizer according to claim 8, characterized in that: The corn stalks and humic acid are mixed in a weight ratio of (3-4):(1-2), and an improved bacterial agent is added. The mixture is fermented at 50-60° C. for 10-13 days until the degree of maturity is 93-96%. The biochar, diammonium phosphate and potassium sulfate are mixed in a weight ratio of 1:2:1 for 2-4 hours.

10. The method for preparing the microbial synergistic slow-release fertilizer according to claim 8, characterized in that: The nitrogen-fixing bacteria, phosphate-dissolving bacteria and the seaweed extract containing fucoidan are embedded into microspheres through spray drying, and a double-roll extrusion granulator is used at a temperature of 30-50° C. to granulate the organic-inorganic mixture and the bacterial agent microcapsules in a weight ratio of 7:3 into granules with a particle size of 2-4 mm.

Images