Preparation method of efficient organic fertilizer based on microbial agent

Abstract

The invention relates to the field of fertilizer microorganisms, and provides an efficient organic fertilizer based on a fungicide and a preparation method of the efficient organic fertilizer. The process comprises the following steps: regulating and controlling a pre-rotten substrate; preparing an alginate-containing mother solution at low temperature, carrying out crosslinking in a single kettle by adopting CaCO and GDL, and carrying out COin-situ foaming to form gel; phytic acid-Fe and chitosan are used for constructing a reversible shell microcapsule; and then three-phase layering granulation is carried out according to the steps of low-salt nutrition core-decomposed transition layer-outer layer roll coating of microcapsules, the water phase EC in the whole process is less than or equal to 1.5 mS / cm, and the Cl is less than or equal to 0.1%. The method realizes viable bacteria gated release and long-term stability, reduces salt / heat / shear stress, realizes green production, is free of multivalent salt external bath and water washing, adapts to multiple flora and different soil scenes, and improves the emergence rate, root growth and yield.

Description

Technical Field

[0001] This invention relates to the field of fertilizer microorganisms, specifically to a method for preparing a high-efficiency organic fertilizer based on microbial agents. Background Technology

[0002] Existing bio-organic fertilizers typically use well-rotted organic matter as a base, combined with beneficial microorganisms such as Bacillus subtilis, Bacillus licheniformis, Bacillus phosphate-solubilizing bacteria, silicate bacteria, Trichoderma, and growth-promoting Pseudomonas, applied in powder or granular form. Industrial production often employs processes such as composting, inoculation, drying, granulation, and coating; common binding systems include starch, lignin sulfonate, molasses, and alginate; microbial loading methods include carrier adsorption, spray bonding, gel embedding, and film coating. To improve storage and application shock resistance, some processes introduce sodium alginate-calcium salt gel embedding and chitosan coating. Alginate gels are often formed by "external cross-linking" with CaCl2 aqueous solution, followed by washing and drying.

[0003] Although the above technologies have improved product stability and field utilization to some extent, the following common shortcomings and technical bottlenecks still exist: Large fluctuations in live bacteria survival and shelf life: Heat load, mechanical shear, excessively rapid water loss rate during granulation and drying, as well as direct contact with high-salt binders or inorganic salts, can easily cause osmotic stress and activity decay; CFU / g tends to decline rapidly over time during room temperature circulation storage, resulting in insufficient batch-to-batch consistency.

[0004] High salt / chloride ion load: To meet the requirements of process intensity and fast-acting nutrients, potassium chloride, ammonium chloride, or high ionic strength solutions are commonly used; high EC and Cl⁻ environments are not conducive to the short-term survival and colonization of sensitive strains.

[0005] Compatibility issues caused by external cross-linking and water washing: Traditional CaCl2 external baths require a high osmotic pressure environment and include a water washing step, which can easily cause cell extravasation, gel network non-uniformity, and batch differences; water washing and drying also increase energy consumption and time costs.

[0006] The release behavior lacks the "rhizosphere triggering" characteristic: most encapsulated / coated structures release passively through diffusion, making it difficult to bind to soil signals such as rhizosphere pH decrease and phytase to achieve targeted unsealing, resulting in early release loss or release-demand asynchrony.

[0007] Insufficient spatial coupling design of "nutrient-microorganism": The interior of the particles is often a mixture or a simple surface spraying, lacking a layered plan for the low-salt nutrient core, the transitional organic layer and the outer layer of live bacteria, which easily leads to the local high concentration of nutrient ions affecting the live bacteria at close range or the antagonistic substances.

[0008] Multi-microbial compatibility and narrow process window: There are significant differences in the optimal water activity, pH, shear and salt tolerance of different bacterial genera; it is difficult to take into account both spore-type and vegetative bacteria with the same process parameters, and antagonism or "superiority" may easily occur, leading to incompatibility.

[0009] Green production and cost pressures: High-salt external bathing, water washing and high-temperature drying processes increase wastewater, energy consumption and time, which is not conducive to green, low-carbon and large-scale stable production.

[0010] Challenges in quality control and standardization: The representativeness of CFU / g online and offline testing, the uniformity of encapsulation, the integrity of the outer layer, and the release curve are difficult to control stably in existing mass production processes, affecting product consistency and market trust.

[0011] In summary, the industry urgently needs a new process for preparing microbial organic fertilizer that can complete the shaping and coating under low-salt, low-temperature, and low-shear conditions, while also possessing shelf stability and rhizosphere-triggered release. At the same time, it should achieve a reasonable spatial configuration of nutrient core-transition layer-live bacteria layer at the particle scale to reduce ion and osmotic stress, improve multi-microbial compatibility and field consistency, and meet the consistency requirements of green production and large-scale production. Summary of the Invention

[0012] In view of the shortcomings of the prior art, the present invention provides a method for preparing a high-efficiency organic fertilizer based on microbial agents, so as to solve the problems mentioned in the background art.

[0013] A method for preparing a high-efficiency organic fertilizer based on microbial inoculants includes the following steps: S1. Raw material pretreatment: Receive well-rotted organic substrate and adjust the C / N ratio to 20-25 and the water content to 50-60%; S2. Pre-composting: Aerobic fermentation at 38–45℃ and 55±5% moisture content until GI≥0.8, pile temperature≤40℃, pH6.5–7.5, and then cooled to 12–20% moisture content; S3. Preparation of microbial agents: Purchase finished microbial agents that meet the requirements for titer and limit of contaminating microorganisms, weigh the microbial agents directly according to the target loading amount, and disperse the powder directly in the S4 microcapsule mother liquor under the condition of ≤10℃; S4. Microcapsule stock solution: Dissolve trehalose, pullulan polysaccharide, sodium alginate, γ-polyglutamic acid, maltodextrin and ascorbic acid at ≤10℃ to form a solution with a solid content of 10-15% based on the total mass of the stock solution, add the bacterial agent described in S3 and mix with low shear. S5. Low-temperature “internal crosslinking + in-situ foaming” gelation: Calcium carbonate micro powder is dispersed in the microcapsule mother liquor described in S4 and gluconate-δ-lactone is added. At ≤12℃, the internal crosslinking of alginate and in-situ foaming of CO2 are completed simultaneously in a single reactor with a molar ratio of CaCO3:GDL of 1:1 to 1:1.5. Then, it is dried at 30-35℃ until the moisture content is ≤8% to obtain microcapsule particles A. S6. Reversible shell film formation: The microcapsule particles A are immersed in phytic acid-ferric complex solution for 1-3 min, drained, and then coated with chitosan-lactate with a mass fraction of 0.2-0.5% to form a reinforcing layer and dried at room temperature to obtain reversible shell microcapsule particles B; S7. Low-salt nutrient core: Using low-chlorine nitrogen, phosphorus and potassium as nutrient components, the total nutrient mass fraction is 4-8% based on the dry basis of low-salt nutrient core. Starch or sodium alginate is used as a binder. Sodium alginate is gently solidified in the GDL and CaCO3 system, or a cold bonding process is used to obtain 1-2 mm core particles. S8. Three-phase layered granulation: The 1-2 mm core particles obtained in S7 are used as the core to sequentially coat the mature transition layer and the microcapsule particles B are rolled on the outermost layer. Sodium alginate aqueous solution is used for cold bonding during the roll coating to obtain 2-4 mm particles. S9. Low-temperature drying and sieving: Dry at 30-35℃ until the moisture content of the finished product is ≤10%, and sieve to obtain 2-4 mm particle size; During steps S5 to S8, the aqueous phase in direct contact with the live bacteria satisfies EC ≤ 1.5 mS / cm and Cl⁻ mass fraction ≤ 0.1%; in step S6, the reversible shell unseales and releases the live bacteria when pH ≤ 6.2 or in the presence of phytase.

[0014] Furthermore, by mass fraction, the decomposed transition layer in S8 consists of 100 parts by mass of the pre-decomposed matrix of S2, 8-12 parts by mass of biochar, 4-8 parts by mass of zeolite, and 3-6 parts by mass of humate.

[0015] Furthermore, the microcapsule mother liquor of S4 is formulated by mass as follows: trehalose 3-8 parts, pullulan polysaccharide 0.5-1.5 parts, sodium alginate 1.0-2.0 parts, γ-polyglutamic acid 0.3-0.8 parts, maltodextrin 2-5 parts, and ascorbic acid 0.05-0.2 parts.

[0016] Furthermore, the calcium carbonate in S5 is a micro powder with a D50 of 5–10 μm.

[0017] Furthermore, the sodium alginate aqueous solution used for S8 roller coating has a mass fraction of 0.5% to 2.0% and is applied by atomized spraying.

[0018] Furthermore, the microbial agent described in S3 includes at least four of the following: Bacillus subtilis, Bacillus licheniformis, Bacillus phosphate-solubilizing bacteria, silicate bacteria, Trichoderma, and Pseudomonas aeruginosa.

[0019] Furthermore, the microbial community is fine-tuned for different scenarios without changing the process sequence and limiting conditions of S5 to S8; in the case of saline soil, the loading of silicate bacteria is increased and the chloride ion content of the finished product is controlled to ≤0.3%; in the case of low nitrogen dry land, free nitrogen-fixing bacteria are added.

[0020] To avoid ambiguity, in this invention: Unless otherwise specified, "%" refers to mass fraction; S4 "solid content 10-15%" is based on the total mass of the mother liquor; in S6, the concentrations of chitosan-lactate and sodium alginate solutions are based on the total mass of the solution; "water content / moisture content" is a wet basis mass fraction (w / w, wet basis); the drying endpoint "moisture ≤ 8%" and the finished product "moisture ≤ 10%" are both based on a wet basis; EC is measured at 25℃, unit mS / cm; "Cl⁻ mass fraction ≤ 0.1%" refers to the chloride ion mass fraction in the aqueous phase that is in direct contact with live bacteria; "total nutrients 4-8%" is based on a nucleus-particle dry basis in the context of S7; "low chlorine" means that potassium chloride, ammonium chloride, and other chlorine-containing raw materials are preferably not used and the chloride ion level is controlled; GI is the seed germination index, and GI ≥ 0.8 is the criterion for pre-fermentation readiness.

[0021] This invention provides a method for preparing a high-efficiency organic fertilizer based on microbial inoculants. It has the following beneficial effects: 1. Long-term preservation: Microcapsule formation through a combination of low-temperature internal cross-linking and in-situ foaming, and a shell system reinforced with phytic acid-Fe³⁺ complex layer and chitosan, film formation and drying are completed without exposure to high-salt external baths, reducing the inactivation rate of live bacteria during manufacturing and storage.

[0022] 2. Rhizosphere-triggered release: The reversible shell is unsealed when the rhizosphere is slightly acidified or phytase is present, which is conducive to the concentrated release and rapid colonization of live bacteria and improves field uniformity.

[0023] 3. Low salt stress: The EC and Cl⁻ content in the aqueous phase in contact with the live bacteria is limited from S5 to S8, and a low-chlorine nutrient core is constructed to reduce the adverse effects of osmotic pressure changes and chloride ions.

[0024] 4. Green and low energy consumption: Integrated low-temperature forming of internal cross-linking / pore formation is achieved at ≤12℃, and the subsequent drying temperature is ≤35℃, which reduces energy consumption and minimizes damage to heat-sensitive strains.

[0025] 5. Industrially controllable: Key process windows such as mother liquor solid content, GDL addition time and temperature, spray concentration, drying temperature / endpoint moisture, and upper limits of EC and Cl⁻ are clearly defined, facilitating large-scale and stable production.

[0026] 6. Adaptable to multiple scenarios: By fine-tuning the microbial community without changing the core process chain, it can cover different usage environments such as low-nitrogen dry land and slightly saline soil. Attached Figure Description

[0027] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0028] To enable those skilled in the art to understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0029] The present invention will now be described in detail with reference to the accompanying drawings: Example 1 (refer to) Figure 1 This embodiment provides a method for preparing a high-efficiency organic fertilizer based on microbial inoculants, and the specific implementation method is as follows: S1 Raw Material Pretreatment After receiving the compostable organic substrate, impurities are removed and samples are taken for testing. Based on the test results, the carbon-nitrogen ratio of the substrate is adjusted to 22, and the moisture content is adjusted to 55%. When the carbon-nitrogen ratio is too high, high-nitrogen raw materials such as qualified livestock and poultry manure, protein residue, or a small amount of urea or ammonium sulfate are added first. When the carbon-nitrogen ratio is too low, high-carbon raw materials such as straw powder, sawdust, or biochar are added. After each addition, the materials are thoroughly mixed and retested until the target range is reached. If the moisture content is insufficient, clean water is sprayed evenly to replenish the water. If the moisture content is too high, the water content is reduced by strengthening ventilation to ensure that the final moisture content is stable at 55% ± 2%. After completing the dual calibration of carbon-nitrogen ratio and moisture content, 10 parts of biochar, 6 parts of zeolite, and 4 parts of humate are added to the batch of substrate in the following mass ratio. "Parts" refers to mass parts and is only used to illustrate the process ratio. The actual substrate reference mass entering the granulation process shall be determined by the subsequent S8 step.

[0030] S2 Pre-fermentation The raw materials, mixed in the aforementioned proportions, are piled into windrows and subjected to aerobic fermentation under a combination of ventilation and turning. The initial moisture content is adjusted to 55%; if too high, it is reduced by mixing in dry materials or increasing ventilation; if too low, it is replenished by evenly spraying clean water. Ventilation should aim for uniform oxygen supply, preferably using intermittent ventilation, accumulating 15 minutes of ventilation per hour, and turning the pile once a day during fermentation to ensure uniform temperature and moisture distribution within the pile. The fermentation temperature is controlled at 40℃. After 3 days of continuous operation, samples are taken and tested according to standard methods: GI≥0.8, core temperature≤40℃, and pH of the water extract 6.5~7.5, indicating that the pre-fermentation state has been reached. Ventilation is then stopped, the material is spread thinly and allowed to cool naturally, and ventilation is used to bring the moisture content to 15%. The matrix for the granulation process is prepared according to the target moisture content of 15%. The dry basis mass is calculated to be 58.333 kg, corresponding to a wet material mass of 15% moisture content of 68.04 kg. The pre-composted substrate should be packaged and labeled, and sent to the subsequent granulation step as soon as possible; if stored for a short period of time, it should be covered to prevent dust and moisture and to avoid temperature fluctuations.

[0031] S3 bacterial agent preparation Bacillus subtilis, Bacillus licheniformis, Bacillus phosphate-solubilizing bacteria, silicate bacteria (spore formation rate ≥90%); Trichoderma harzianum (spore form), Pseudomonas fluorescens (lat logarithmic phase); The finished bacterial inoculum was purchased from Qingdao Weilande Biotechnology and was not propagated in-house. The supply format and titer for each variety are as follows: Bacillus subtilis, powder / spore powder, = 1 × 10¹¹ CFU / g, moisture ≤ 8%; Bacillus licheniformis, powder / spore powder, = 1 × 10¹¹ CFU / g, moisture ≤ 8%; Bacillus megaterium, powder / spore powder, = 5 × 10¹¹ CFU / g. 0 CFU / g, moisture ≤8%; silicate bacteria (B. mucilaginosus), powder / spore powder, = 5 × 10¹ 0 CFU / g, moisture ≤8%; Trichoderma harzianum, spores, =1×10¹ 0 Spores / g, moisture ≤8%; growth-promoting pseudomonocytes (Pseudomonas fluorescens), stable suspension, =1×10¹ 0 CFU / mL.

[0032] The target loading amount of Bacillus subtilis per 1 kg of dry microcapsules is 2.5 × 10¹. 0 CFU / kg; Bacillus licheniformis: 1.5 × 10¹ 0CFU / kg; Bacillus phosphate solubilizer: 1.5 × 10¹ 0 CFU / kg; Silicate bacteria: 1.5 × 10¹ 0 CFU / kg; Trichoderma: 7.5×10 9 Spores / kg; Promoting pseudomonocytes: 7.5 × 10⁻⁶ 9 CFU / kg.

[0033] In this embodiment, S4 plans to prepare 4.434 kg of microcapsules (dry weight). The required dosage and weighing of each bacterium are as follows: B. subtilis: Target activity = 2.5 × 10¹ 0 ×4.434=1.1085×10¹¹CFU, weigh 1.11 g.

[0034] B. licheniformis: 1.5 × 10¹ 0 ×4.434=6.651×10¹ 0 CFU; 1×10¹¹CFU / g⇒0.665 g.

[0035] B. megaterium: same as above, activity 6.651×10¹ 0 CFU; 1×10¹¹CFU / g⇒0.665 g.

[0036] B. mucilaginosus: same as above, activity 6.651×10¹ 0 CFU; 1×10¹¹CFU / g⇒0.665 g.

[0037] T. harzianum: 7.5 × 10 9 ×4.434=3.3255×10¹ 0 Spores; 1×10¹ 0 Spores / g ⇒ 3.33 g.

[0038] fluorescens: 7.5 × 10 9 ×4.434=3.3255×10¹ 0 CFU; powder 1×10¹¹CFU / g⇒0.333 g.

[0039] The microbial agent should be temporarily stored at 2-8℃ in the dark while waiting to be added, and S4 should be added within 24 hours.

[0040] Preparation of S4 microcapsule mother liquor: Equipment and conditions Jacketed stainless steel mixing tank, effective volume ≥60 L, adjustable from 30–200 rpm, online thermometer and sampling port; vacuum degassing device; deionized water. Completely protected from light; material temperature ≤10℃.

[0041] The solid content of the microcapsule mother liquor was 12% (w / w), i.e., total solids 4.434 kg; total water content was 32.5 L.

[0042] Solid composition: Trehalose 1.717 kg, pullulan 0.343 kg, sodium alginate 0.515 kg, γ-PGA 0.172 kg, maltodextrin 1.030 kg, ascorbic acid 0.034 kg. The 12% solid content refers to the total solid content of the matrix, 4.434 kg. S3 microbial agent is added based on activity, with a mass percentage <0.2%, and does not change the solid content control.

[0043] The jacket was pre-cooled by 10°C for 5 min, and 27.5 L of deionized water was added; another 5.0 L was reserved as pre-dissolving water. Trehalose, maltodextrin, and ascorbic acid were added sequentially at 10°C and 80 rpm, and dissolved completely one by one to obtain a clear sugar phase.

[0044] Subsequently, two pre-slurries were prepared using 5.0 L of pre-dissolved water: Cup A contained 0.343 kg of pullulan, and Cup B contained 0.172 kg of γ-PGA. After thorough dispersion, 0.515 kg of sodium alginate was added in batches to completely wet the mixture. The material temperature was maintained at 10°C, and the stirring speed was adjusted to 100 rpm. Cup A was added to the main tank and stirred for 10 min until completely dissolved. Then, Cup B was added in three equal portions, stirring for 5 min after each addition, until the system was free of visible particles and had a uniform appearance.

[0045] At 10℃, add the calculated amounts of each bacteria from S3 along the liquid surface and continue mixing at 100 rpm with low shear for 10 min to ensure uniform dispersion of the bacterial agent in the mother liquor. Then, perform vacuum degassing, maintaining a negative pressure of −0.06 MPa for 10 min. After releasing the vacuum, allow it to stand for 5 min to eliminate residual microbubbles. The release criteria for the mother liquor are: uniform appearance with no obvious bubble accumulation, solid content of 12.0%±0.5%, pH of 6.5~7.5, conductivity (25℃) ≤1.5 mS / cm, aqueous phase chloride ion mass fraction ≤0.1% (w / w), and short-term activity of not less than 90% of that before mixing 1–2 h after mixing. After passing the inspection, immediately proceed to S5 "low-temperature internal crosslinking + in-situ foaming"; if waiting is required, temporarily store the mother liquor at 2–8℃ in the dark and use it within 24 h.

[0046] S5 low-temperature "internal cross-linking + in-situ foaming" gelation The mother liquor released via S4 was placed in a jacketed reactor, with the material temperature controlled at 10℃ and the stirring speed at 150 rpm. First, 0.343 kg of calcium carbonate was uniformly dispersed into the mother liquor, and stirring was maintained for 5 minutes until no visible particles remained. Separately, a 10% GDL solution was prepared, corresponding to a total GDL volume of 0.275 kg; this solution was added dropwise into the reactor over 15 minutes using a metering pump, maintaining the CaCO3:GDL ratio within the 1:1 to 1:1.5 window, and ensuring the material temperature remained ≤10℃ throughout the process. During the stepwise hydrolysis of GDL, the pH of the system gradually decreases, Ca²⁺ is released endogenously and undergoes internal cross-linking with alginate in the S4 mother liquor. Simultaneously, CO₂ generated from the reaction of CaCO₃ with acid forms pores in situ within the colloid. When the viscosity of the system begins to rise while maintaining good fluidity (generally 3–8 minutes after drop addition), the system is immediately switched to a spray-drop station. The liquid is sprayed through a 1.0 mm nozzle onto a shallow dish coated with PTFE, controlling the drop distance to 10–20 cm and preventing individual drops from merging. After spraying, the system is allowed to stand for 10 minutes to complete initial coagulation. The gelled particles are then thinly spread on a perforated tray and dried at 35°C until the moisture content is ≤8%. During drying, the particles are gently turned every 30 minutes to prevent adhesion and localized over-drying. After drying, the system is sieved to remove lumps and ultrafine powder, yielding 4.434 kg of microcapsule A (dry basis).

[0047] This step does not use any external bath containing polyvalent metal salts. The aqueous phase in direct contact with the live bacteria continuously meets the following requirements: EC ≤ 1.5 mS / cm (25℃) and Cl⁻ ≤ 0.1% (w / w). Key quality control points: Material temperature ≤ 12℃ before spraying; particles should be completely gelled and not collapse within 30 minutes after spraying; finished product appearance is uniform spherical or rounded particles, with a dry and non-sticky feel.

[0048] S6 reversible shell film formation yields microcapsule B Equipment and conditions Roller coating machine or disc coating machine, stainless steel immersion tank, metering spray gun, ambient temperature clean drying room, online pH and thermometer.

[0049] First, prepare 20 L of phytic acid-Fe³⁺ complex solution: Take 18 L of deionized water and dissolve 160 g of sodium phytate at room temperature; separately take 250 g of ferric citrate mother liquor with Fe content of 16% and add it dropwise to the above sodium phytate solution, stir, and adjust the pH to 6.6-7.0 with NaOH and lactic acid, add water to make up to 20 L, and filter to remove bubbles.

[0050] The Fe equivalent is 0.2% (w / w), and the phytate, i.e., sodium phytate, is 0.8% (w / w).

[0051] Microcapsules A were placed in a drum and tumbled at a uniform speed. 4.0 L of complexing solution was required for every 1 kg of microcapsules A. The complexing solution was injected in batches, maintaining constant tumbling to prevent accumulation. The soaked microcapsule A granules were then poured onto a stainless steel sieve to drain for 60 seconds. Subsequently, the drained granules were atomized and sprayed with 25 L of a 0.3% chitosan-lactate solution inside the drum. The distance between the spray gun and the material surface was 30 cm, and the spray rate was 0.8 L / min, until a continuous wet film formed on the granule surface. The granules were then air-dried at room temperature until they were no longer sticky to the touch and could flow freely, and then allowed to stand for 30 minutes to mature.

[0052] After the above treatment, 4.667 kg of microcapsules B (dry weight) were obtained. The quality control requirements were: uniform particle surface, no visible agglomeration or "tears" phenomenon; pH of 1:10 water extract of 6.5-7.5; and reversible destruction of the shell under pH ≤ 6.2 or in the presence of phytase.

[0053] S7 Low-Salt Nutrient Core Weigh out 0.600 kg of potassium sulfate, 0.492 kg of monoammonium phosphate (MAP), and 0.567 kg of urea, and dry mix them in a horizontal ribbon mixer for 8 min to ensure uniform powder composition. Then, use sodium alginate for bonding and gentle curing: prepare 10 L of a 1% sodium alginate solution and disperse 0.12 kg of CaCO3 in it; add the dry mixture to a disc granulator and evenly spray the sodium alginate and calcium carbonate suspension at a rate of 0.7 L / kg. After the particles nucleate and grow to 0.5 mm, atomize and spray in 10 L of a 1% GDL solution, equivalent to 0.10 kg of solid GDL, and continue tumbling for 10 min to complete the gentle curing of the GDL and CaCO3 crosslinking; then dry at ≤30℃ with forced air until the moisture content is ≤10%, sieve to obtain 2 mm particle sizes, and recover and refeed the ultrafine powder.

[0054] The quality and limiting requirements for this step are as follows: dry weight of core particles 15.333 kg; chloride ion (dry weight) Cl⁻≤0.5%; no KCl and NH4Cl are used in the raw materials; the obtained core particles have a particle size of 1-2 mm, and the strength is sufficient for subsequent roller coating and handling without pulverization.

[0055] S8 Three-Phase Layered Granulation Using a drum granulator, 15.333 kg of the core particles obtained in step S7 were loaded into the equipment. The drum speed was set to 30 rpm, and the particles were started to tumble evenly. Then, a transition layer growth process was performed: 68.04 kg of wet S2 matrix, 5.833 kg of biochar, 3.500 kg of zeolite, and 2.333 kg of humate were added sequentially in six small batches, while simultaneously spraying a 1% sodium alginate solution as a cold binder, with a total spray volume of 8.0 L. Throughout the process, the material surface was kept "wet but not liquid-covered," and tumbling continued until the particles grew from 2 mm to 2–3 mm in length, resulting in a dense, uniform appearance and low pulverization rate.

[0056] Based on this, perform the outermost layer roll coating: start the vibrating feeder and evenly add microcapsule B to the surface of the agitated particles in 5 applications; simultaneously, spray the remaining 3.2 L of the aforementioned sodium alginate solution at a low flow rate as a spot binder, controlling the state to be "wet but not sticky," avoiding excessive moisture that could cause microcapsule breakage or softening of the inner layer. Continue rolling coating for 3–5 minutes to ensure that microcapsule B is evenly embedded in the outermost layer of the particles, and the particle surface has a "fine sandy feel without powder shedding."

[0057] Process control requirements: Material temperature ≤30℃; rotation speed should be adjusted to ensure stable granulation without damaging the microcapsules; from this step onwards, no further impregnation, external bathing, or spraying treatments containing polyvalent metal salts are permitted; all sprayed aqueous phases in contact with live bacteria must continuously meet EC≤1.5 mS / cm and Cl⁻≤0.1% (w / w). Once the appearance reaches the state of "2-3 mm pre-granulated + uniformly coated microcapsules B", stop adding liquid and pre-dry at a low airflow rate for 5-10 minutes to stabilize the surface layer, then immediately proceed to S9.

[0058] Granulation section quality inspection: After drying, the particle size distribution is ≥90% (2-4 mm); under magnification, sampling observation shows that the outermost microcapsule B has uniform "point-to-surface" coverage with no exposed areas; the powder drop rate is low and the surface is non-sticky after 3 minutes of circulation in the drum. Batch records are simultaneously improved: the amount of each dry powder fed, the amount of liquid sprayed, the temperature / time curve, the amount of returned material, and the batch pass rate.

[0059] S9 Low-Temperature Drying and Sieving The granulated wet granules are evenly and thinly spread on a perforated tray, with a layer thickness controlled at 25 mm. Drying is carried out using a low-temperature airflow at 35°C, with gentle turning every 20 minutes to ensure even heating and prevent adhesion and wear on the outer microcapsules; drying continues until the finished product moisture content is ≤10%. After drying, the product is first cooled to ≤30°C under clean ambient airflow, and then graded and sieved: particles of 2–4 mm are collected as qualified products; fine powder <2 mm is returned to S8 for regranulation; particles >4 mm are only allowed to undergo short-term edge trimming and polishing under low-speed conditions, and those still unqualified are discarded. The moisture content of the qualified products is quickly checked, and after confirming ≤10%, the entire batch is collected (100 kg of finished product) and transferred to the nitrogen-filled packaging process.

[0060] Example 2 provides a method for preparing a high-efficiency organic fertilizer based on microbial inoculants, applicable to low-nitrogen dryland scenarios. The specific implementation method is as follows: The only differences from Example 1 are steps S3 and S7, as follows: S3 microbial community fine-tuning, adding the free-fixing nitrogen-fixing bacterium *Azotobacter chroococcum*, with a target loading capacity of 5 × 10⁻⁶. 9 CFU / kg.

[0061] Purchase Azotobacter chroococcum = 1 × 10¹¹ CFU / g → 0.222 g.

[0062] The target loading of Bacillus licheniformis was increased from 1.5 × 10¹ 0 Adjusted to 1.0×10¹ 0 CFU / kg, required mass 0.443 g.

[0063] The loading and weighing of the remaining bacterial strains remained unchanged from Example 1: Bacillus subtilis 1.11 g; Bacillus phosphate solubilizer 0.665 g; silicate bacteria 0.665 g; Trichoderma harzianum 3.33 g; and Pseudomonas fluorescens was administered according to the established dosage and dosage in Example 1.

[0064] S7 low-salt nutrient core formula, total nutrients reduced to 4% dry basis. The dry basis weight of the nucleus and granules remains 15.333 kg. The target total nutrient content is set at 4.0% (dry basis), corresponding to a total nutrient weight of 0.613 kg. Following the principle of "low nitrogen promotes synergistic nitrogen fixation," the nutrient content is allocated as follows: N 1.2%, P2O5 1.4%, K2O 1.4% (all on a dry basis), equivalent to 0.184 kg N, 0.215 kg P2O5, and 0.215 kg K2O, respectively. To achieve the above target, low-chlorine raw salts are used: 0.429 kg potassium sulfate (containing 50% K2O, providing 0.215 kg K2O), 0.351 kg monoammonium phosphate (MAP) (containing 61% P2O5 and 12% N, providing 0.215 kg P2O5 and 0.042 kg N), and 0.308 kg urea (containing 46% N, supplementing 0.142 kg N), for a total of 1.089 kg. Except for the nutrient formulation, the remaining inert carrier and solidification process are the same as in Example 1. The chemical nitrogen content is reduced to 1.2% dry basis, which helps to promote the early colonization and nitrogen supply of nitrogen-fixing bacteria in the context of low moisture and low inorganic nitrogen in dry land, and reduces the inhibition of free ammonia on the outer layer of living bacteria and rhizosphere community.

[0065] Comparative Example 1 provides a method for preparing conventional microbial inoculant organic fertilizer. The specific implementation method is as follows: Same as Example 1, the only difference is that in stage S5, instead of using GDL and CaCO3 internal crosslinking + in-situ foaming, a conventional route is followed, using a 2% CaCl2 solution for external crosslinking for 20 min; in stage S6, the same film-forming conditions are maintained.

[0066] Specifically, a 180 L external bath solution with a mass fraction of 2% CaCl2 was prepared in a stainless steel or PP tank, controlled at 25 ℃ and stirred at 100 rpm. Then, the mother liquor from step S4 of Example 1 was connected to a metering pump and continuously sprayed into the external bath solution through a 1.0 mm nozzle at a drop distance of 20 cm, ensuring that the drops did not coalesce. The solution remained in the external bath for 20 minutes from the last drop to complete the external cross-linking, with stirring maintained throughout. The beads were then removed using a stainless steel sieve, washed twice with clean water, and drained for 2 minutes. The wet beads were thinly spread on a tray and dried at a low temperature of 35 ℃ with hot air until the moisture content was ≤8%. After cooling to ≤30 ℃, the solution was sieved to obtain "microcapsule A," which was then subjected to shell film formation treatment under the same conditions as S6 of Example 1.

[0067] Only step S5 is different from that in Example 1; all other steps are the same.

[0068] Evaluation Methods and Comparisons: The following are the unified evaluation methods and judgment indicators.

[0069] 1. Shelf-life viable microbial stability—Test method Finished granules from Examples 1, 2, and Comparative Example 1 were taken respectively, and at least three parallel packages were prepared for each group as test samples. Two storage conditions were set up: ① Normal temperature shelf life: 25℃, protected from light, and relative humidity 60±10%, stored for 12 months; ② Accelerated aging: 40℃, 75%RH, stored for 90 days. After the storage time expired, one parallel package was randomly opened, and samples were quickly taken and tested under clean conditions.

[0070] Detection and Calculation: Weigh 10.0 g of particles into a low-salt sterile diluent, shake thoroughly to homogenize, and perform a 10-fold serial dilution. Perform plate counting on non-selective nutrient agar, making two plates for each dilution, and selecting plates with 30–300 CFU for counting. Calculate the viable cell retention rate.

[0071] 2. Rhizosphere Triggered Release Capability—Testing Method Take the finished granules and place them in a constant-temperature shaker at 25℃ and 60 rpm at a solid-liquid ratio of 2.0 g / 100 mL. Prepare gradient buffer solutions of pH 7.0 and 5.5 with inductively coupled plasma strength, as well as a system containing pH 7.0 and 50 U / L exogenous phytase. Each system should have at least three replicates. Record two types of time points: ① Unsealing initiation time = the time when the outer shell softens and cracks as observed under a stereomicroscope; ② Swelling release time = the time when 90% of the tracer dye is cumulatively released.

[0072] 3. Osmotic stress tolerance—test method A simulated application solution with an EC value of 2.5 mS / cm was prepared using deionized water and kept at a constant temperature of 25°C. Finished product particles were added to the conductivity system at a solid-liquid ratio of 2.0 g / 100 mL and gently shaken for 2 h. Afterward, the particle surface was rinsed with a low-salt sterile diluent, and the CFU / g of the finished product was determined using the standard dilution coating method. The short-term survival rate was calculated against the T0 baseline of the same batch. Simultaneously, the integrity of the microcapsules was assessed: ① The proportion of fine powder <2 mm was determined by sieving; ② ≥100 particles were randomly counted using a stereomicroscope, and the shell breakage / exposure rate was recorded; ③ If an inert tracer control capsule was used, the dye leakage rate within 2 h could be measured simultaneously. ≥3 replicates were set up.

[0073] 4. Field uniformity Randomized block designation was used in the same field, with equal amounts of finished products applied as basal fertilizer as in Examples 1, 2, and Comparative Example 1; observations were conducted 7–14 days post-sowing and at the jointing stage. Emergence rate was calculated by counting 5 fixed points × 2 rows per plot at a fixed length; root system indicators were determined by randomly digging up 10 plants per plot, cleaning the roots, measuring the taproot length, and counting the lateral roots; yield per unit area was calculated by harvesting the effective rows of each plot at maturity, removing edge rows and missing plants, converting to crop standard moisture content, and converting to t·ha⁻¹.

[0074] The specific data for the evaluation are as follows: 1. Shelf-life live bacteria stability 25℃, 12 months

[0075] Table 1 40℃ / 75%RH, accelerated for 90 days

[0076] 2. Root-triggered release ability pH gradient buffer

[0077] Table 3 Exogenous phytase

[0078] Table 4 3. Osmotic stress tolerance

[0079] Table 5 4. Field uniformity

[0080] Table 6 In summary, to verify the effectiveness of the process and structural design of this invention, shelf-life stability, rhizosphere-triggered release, osmotic stress tolerance, and field plot system evaluation were conducted based on Examples 1, 2, and Comparative Example 1. The results show that this invention has the following beneficial effects compared to conventional CaCl2 external crosslinking routes: 1. Long-term preservation: A gelling process of "low-temperature internal cross-linking + in-situ foaming" is used, and a reversible outer shell is constructed using a "phytic acid-Fe³⁺ complex layer + chitosan reinforcement layer," avoiding high-salt external cross-linking and water washing. After 12 months of storage at room temperature (25°C), the viable cell retention rates of Examples 1 and 2 were 78% and 76%, respectively, significantly higher than the 47% of Comparative Example 1; the logarithmic decay slopes were −0.00029 and −0.00033, respectively, compared to −0.00090 for Comparative Example 1. Under accelerated storage at 40°C and 75%RH for 90 days, the retention rates of Examples 1 and 2 were 60% and 58%, respectively, also higher than the 25% of Comparative Example 1.

[0081] 2. Rhizosphere-triggered release: The outer shell thaws under mild acidification or in the presence of phytase, and does not release under non-rhizosphere conditions to avoid early depletion. At pH 7.0, Examples 1 and 2 did not thaw within 60 min, while Comparative Example 1 initiated release in 1.5 min and completed release in 20 min. At pH 5.5, the initiation and completion times of Examples 1 and 2 were 3.0 and 20 min, and 3.5 and 21 min, respectively, exhibiting a "gated release" characteristic. At 50 U / L of phytase, Examples 1 and 2 were triggered to release in 2.0 and 12 min, and 2.5 and 13 min, respectively, while Comparative Example 1 showed almost no phytic acid response.

[0082] 3. Low-salt stress friendly: Throughout S5-S8, the aqueous phase in contact with the bacterial agent was limited to EC ≤ 1.5 mS / cm and Cl⁻ ≤ 0.1% (w / w), and a low-salt nutrient core was constructed using low-chlorine original salt. In the osmotic stress test, the short-term survival rates of Examples 1 and 2 were 90% and 88%, respectively, significantly higher than the 60% of Comparative Example 1; the microcapsule integrity breakage rate was only 1% / 2%, compared to 8% in Comparative Example 1.

[0083] 4. Green and low energy consumption: Single-reactor low-temperature gelation and pore formation followed by low-temperature drying eliminates the need for high-osmotic external bath and water washing, reducing energy consumption and osmotic / thermal stress, protecting the activity of heat-sensitive strains and reducing wastewater burden.

[0084] 5. Industrially controllable: Key window parameters are clearly defined and easy to monitor online, with mother liquor solid content ≈12%, G material ≤12℃, spray concentration and total spray volume, drying endpoint ≤10% moisture, upper limits of EC and Cl⁻, and good consistency within and between batches; the live bacteria and particle size of the batch finished products in the example are stable and reproducible.

[0085] 6. Adaptable to multiple scenarios: Without changing the core processes of S5 to S8, Example 2 adapts to low-nitrogen dryland by incorporating nitrogen-fixing bacteria and reducing the total nutrient content of nuclei and granules to 4%. In field plot trials, Examples 1 and 2 showed emergence rates of 90.2% and 91.5%, respectively, taproot length of 14.3 and 15.1 cm, lateral root number of 24.6 and 26.8 per plant, and yields of 6.47 and 6.60 t·ha⁻¹, respectively, which are 6.1% and 8.2% higher than the 6.10 t·ha⁻¹ of Comparative Example 1, demonstrating higher field consistency and nutrient utilization efficiency.

[0086] It should be particularly noted that the various embodiments listed in this specification and accompanying drawings are intended to illustrate the technical solutions and advantages of the present invention, and not to limit the scope of protection of the present invention. Without departing from the core ideas and technical effects of the present invention, those skilled in the art can make any form of improvement, substitution, combination, or modification to the structural arrangement, process parameters, material selection, control logic, etc., of the described embodiments; any obvious changes based on the same concept should be considered equivalent solutions of the present invention and should be included within the scope of protection defined by the claims of the present invention. The actual scope of protection of the present invention is determined by the appended claims and should be correctly understood in conjunction with the specification and accompanying drawings.

Claims

1. A method for preparing a high-efficiency organic fertilizer based on microbial inoculants, characterized in that, Includes the following steps: S1. Raw material pretreatment: Receive compostable organic substrate and adjust the C / N ratio to 20-25 and the moisture content to 50-60%; S2. Pre-composting: Aerobic fermentation is carried out at 38-45℃ and 55±5% moisture content until GI≥0.8, pile temperature≤40℃, and pH6.5-7.5, followed by cooling to a moisture content of 12-20%. S3. Preparation of microbial agents: Purchase finished microbial agents that meet the requirements for titer and limit of contaminating microorganisms, weigh the microbial agents directly according to the target loading amount, and disperse the powder directly in the S4 microcapsule mother liquor under the condition of ≤10℃. S4. Microcapsule stock solution: Dissolve trehalose, pullulan polysaccharide, sodium alginate, γ-polyglutamic acid, maltodextrin and ascorbic acid at ≤10℃ to form a solution with a solid content of 10-15% based on the total mass of the stock solution, add the bacterial agent described in S3 and mix well; S5. Low-temperature "internal crosslinking + in-situ foaming" gelation: Calcium carbonate micro powder is dispersed in the microcapsule mother liquor described in S4 and gluconate-δ-lactone is added. At ≤12℃, the internal crosslinking of alginate and in-situ foaming of CO2 are completed simultaneously in a single reactor with a molar ratio of CaCO3:GDL of 1:1 to 1:1.

5. Then, it is dried at 30-35℃ until the moisture content is ≤8% to obtain microcapsule particles A. S6. Reversible shell film formation: The microcapsule particles A are immersed in phytic acid-ferric complex solution for 1-3 min, drained, and then coated with chitosan-lactate with a mass fraction of 0.2-0.5% to form a reinforcing layer and dried at room temperature to obtain reversible shell microcapsule particles B; S7. Low-salt nutrient core: Using low-chlorine nitrogen, phosphorus and potassium as nutrient components, the total nutrient mass fraction is 4-8% based on the dry basis of low-salt nutrient core. Starch or sodium alginate is used as a binder. Sodium alginate is gently solidified in the GDL and CaCO3 system, or a cold bonding process is used to obtain 1-2 mm core particles. S8. Three-phase layered granulation: The 1-2 mm core particles obtained in S7 are used as the core to sequentially coat the mature transition layer and the microcapsule particles B are rolled on the outermost layer. Sodium alginate aqueous solution is used for cold bonding during the roll coating to obtain 2-4 mm particles. S9. Low-temperature drying and sieving: Dry at 30-35℃ until the moisture content of the finished product is ≤10%, and sieve to obtain 2-4 mm particle size; In steps S5 to S8, the aqueous phase in direct contact with the bacterial agent satisfies EC ≤ 1.5 mS / cm and Cl⁻ mass fraction ≤ 0.1%; the reversible shell in step S6 unseales and releases live bacteria when pH ≤ 6.2 or in the presence of phytase.

2. The method for preparing a high-efficiency organic fertilizer based on microbial inoculants according to claim 1, characterized in that, The decomposed transition layer in S8 consists of 100 parts by weight of the pre-decomposed matrix of S2, 8-12 parts of biochar, 4-8 parts of zeolite, and 3-6 parts of humate.

3. The method for preparing a high-efficiency organic fertilizer based on microbial inoculants according to claim 1, characterized in that, The mass ratio of the microcapsule mother liquor described in S4 is as follows: trehalose 3-8, pullulan polysaccharide 0.5-1.5, sodium alginate 1.0-2.0, γ-polyglutamic acid 0.3-0.8, maltodextrin 2-5, and ascorbic acid 0.05-0.

2.

4. The method for preparing a high-efficiency organic fertilizer based on microbial inoculants according to claim 1, characterized in that, The calcium carbonate in S5 is a micro powder with a D50 of 5-10 μm.

5. The method for preparing a high-efficiency organic fertilizer based on microbial inoculants according to claim 1, characterized in that, The sodium alginate aqueous solution used for the S8 roller coating has a mass fraction of 0.5-2.0% and is applied by atomized spraying.

6. The method for preparing a high-efficiency organic fertilizer based on microbial inoculants according to claim 1, characterized in that, The microbial agents in S3 include at least four of the following: Bacillus subtilis, Bacillus licheniformis, Bacillus phosphate-solubilizing bacteria, silicate bacteria, Trichoderma, and Pseudomonas aeruginosa.

7. The method for preparing a high-efficiency organic fertilizer based on microbial inoculants according to claim 1, characterized in that, The microbial community is fine-tuned for different scenarios without changing the process sequence and limiting conditions of S5 to S8; in the case of saline soil, the loading of silicate bacteria is increased and the chloride ion content of the finished product is controlled to ≤0.3%; in the case of low nitrogen dry land, free nitrogen-fixing bacteria are added.

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