A bio-compound fertilizer and its preparation method

Abstract

This application discloses a bio-compound fertilizer and its preparation method, belonging to the field of organic fertilizer technology. The bio-compound fertilizer consists of inorganic nutrient components, synergistic components, compound functional microbial agents, and modified coating components. This application prepares a modified coating by blending polyacrylic acid and polyβ-hydroxybutyrate, and adding sodium alginate and nano-silica for modification. This coating can precisely respond to changes in rhizosphere pH and nutrient concentration to regulate nutrient release. This invention can achieve stable retention of live microorganisms and intelligent controlled nutrient release, is suitable for various crops and adverse soil conditions, and solves the pain points of existing products such as live bacteria inactivation and nutrient release imbalance, making it suitable for large-scale agricultural planting.

Description

Technical Field

[0001] This invention relates to the field of organic fertilizer technology, specifically to a bio-compound fertilizer and its preparation method. Background Technology

[0002] With the development of large-scale and intensive agriculture, adverse conditions such as soil salinization, continuous cropping, and acidification are becoming increasingly prominent, severely disrupting the soil micro-ecological balance, reducing crop nutrient absorption efficiency, and hindering the improvement of agricultural yield and quality. Bio-compound fertilizer, as a new type of fertilizer that combines nutrient supply, soil improvement, and micro-ecological regulation, integrates the rapid effectiveness of inorganic nutrients, the soil-improving properties of organic components, and the functionality of microorganisms. It has become an important tool for overcoming soil adverse conditions and promoting green and sustainable agricultural development, and is widely used in the cultivation of various crops such as corn, wheat, peanuts, greenhouse vegetables, and fruit trees.

[0003] However, existing bio-compound fertilizers still face numerous technical bottlenecks in actual production and application, particularly the imperfections in coating technology, which hinders product performance from meeting the core needs of field cultivation. Firstly, the coating materials of existing bio-compound fertilizers mostly employ single polymers or simple blends, lacking targeted modification design. This results in poor adhesion and insufficient structural stability, making the coating prone to damage and detachment during fertilizer storage, transportation, and application. This leads to premature leakage and loss of internal inorganic nutrients, not only wasting nutrients but also causing microbial inactivation due to direct contact between high-salt inorganic nutrients and functional microorganisms. This significantly reduces the survival rate of live bacteria in the field, preventing the effective functioning of microorganisms in promoting growth and preventing disease, resulting in a discrepancy between the actual application effect and the design expectations. Secondly, existing coating technologies struggle to achieve precise control of nutrient release. Most coatings only achieve simple physical isolation and slow release, failing to respond to the dynamic changes in the rhizosphere environment during the crop's growth period. On the one hand, the coating has low sensitivity and poor stability in response to changes in rhizosphere pH. Under adverse conditions such as crop nutrient stress (rhizosphere pH drops to 5.0-5.5) or saline-alkali environment (rhizosphere pH rises to 7.5-8.0), it cannot adjust the nutrient release rate in time, resulting in a mismatch between nutrient supply and crop demand. On the other hand, the coating has a weak ability to sense the concentration of available nitrogen and available phosphorus in the soil, making it difficult to achieve micro-control of nutrient release based on nutrient concentration thresholds. This can easily lead to loss and waste caused by excessively rapid nutrient release, or crop nutrient deficiency caused by excessively slow release.

[0004] Therefore, there is an urgent need to develop a bio-compound fertilizer and its preparation method to improve the nutrient utilization efficiency and overall effectiveness of bio-compound fertilizer. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a bio-compound fertilizer and its preparation method. Using polyacrylic acid and polyβ-hydroxybutyrate as the base coating materials, the fertilizer is modified and optimized by adding sodium alginate and nano-silica. This allows the coating to respond to rhizosphere pH signals and soil nutrient concentrations, synchronizing nutrient release with crop growth stage requirements, reducing nutrient loss from the bio-compound fertilizer, and improving utilization.

[0006] In a first aspect, this application provides a bio-compound fertilizer, which includes inorganic nutrient components, synergistic components, compound functional microbial agents, and modified coating components.

[0007] The inorganic nutrient components include urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer; the synergistic components include decomposed straw, humic acid, chitosan-seaweed extract complex, amino acid chelated trace elements, and EDTA amino acid chelating agent; the compound functional microbial agent includes Bacillus subtilis, Paenibacillus mucilaginosus, Bacillus megaterium, Bacillus licheniformis, and Rhizobium meliloti; the modified coating components include polyacrylic acid, polyβ-hydroxybutyrate, sodium alginate, and nano silica.

[0008] Preferably, the mass ratio of the inorganic nutrient component, the synergistic component, the compound functional microbial agent and the modified coating component is (19-26): (28-32): (0.7-0.9): (42-50).

[0009] Preferably, the mass ratio of urea, monoammonium phosphate, potassium sulfate and calcium magnesium phosphate in the inorganic nutrient components is (35-40):(22-28):(20-24):(12-18); the mass ratio of decomposed straw, humic acid, chitosan-seaweed extract complex, amino acid chelated trace elements and EDTA amino acid chelating agent in the synergistic components is (70-75):(20-22):(3-4):(0.5-1.5):(0.5-1.5).

[0010] Preferably, the organic matter content of the decomposed straw is ≥60%; the biochar is soaked in 1% dilute hydrochloric acid for 2 hours, rinsed with water until neutral, and dried; the amino acid chelated trace elements, including boron, zinc, iron, and manganese, are added in the form of amino acid chelates.

[0011] Preferably, the mass ratio of Bacillus subtilis, Bacillus mucilaginosus, Bacillus megaterium, Bacillus licheniformis, and root nodule-promoting strains in the composite functional microbial agent is (9-11):(4-6):(2-4):(1-3):(0.8-1.2); the total viable count of the composite functional microbial agent is ≥2.0×10⁻⁶. 9 CFU / g.

[0012] Preferably, the viable count of the Bacillus subtilis is ≥1.0 × 10⁻⁶. 8 The bacteria were cultured continuously for three generations in liquid culture media with gradient NaCl concentrations (0.2%-0.8%) and gradient pH (5.0-8.5) to achieve a viable count ≥0.5 × 10⁻⁶ CFU / g. 8 CFU / g; the viable count of the *Bacillus megaterium* is ≥0.3 × 10⁻⁶. 8 CFU / g; the viable count of the *Bacillus licheniformis* is ≥0.2 × 10⁻⁶. 8 CFU / g; the viable count of the root nodule-promoting strain is ≥0.1×10⁻⁶. 8 CFU / g.

[0013] Preferably, the mass ratio of polyacrylic acid, polyβ-hydroxybutyrate, sodium alginate and nano silica in the modified coating component is (47-50):(45-52):(1.0-1.5):(0.2-0.3); the coating thickness formed by the modified coating component is 50-100 μm.

[0014] Secondly, the present invention provides a method for preparing a bio-compound fertilizer, comprising the following steps:

[0015] S1: Urea, monoammonium phosphate, potassium sulfate and calcium magnesium phosphate fertilizer are crushed, mixed evenly, urease inhibitor and buffer are added, and pH is adjusted to obtain inorganic nutrient components; straw is crushed, composting agent is added, moisture content is adjusted, and after high-temperature fermentation and low-temperature activation, it is dried and crushed to obtain synergistic components; each strain is cultured separately to prepare compound functional microbial agents to obtain compound functional microbial agents.

[0016] S2: Mix the pretreated synergistic components and compound functional microbial agents evenly, and then use an extrusion granulation process to obtain core particles after sieving;

[0017] S3: Mix the inorganic nutrient components evenly as coating material, put the above core particles into a fluidized bed coating machine, spray the coating material, add nutrient release regulator, and obtain middle layer coated particles;

[0018] S4: Polyacrylic acid and polyβ-hydroxybutyrate are blended, sodium alginate and nano silica are added, stirred and ultrasonically dispersed to prepare a modified coating material; the middle layer of coated particles are placed into a fluidized bed coating machine, the modified coating material is sprayed on, and after gradient drying and cooling, a bio-compound fertilizer is obtained.

[0019] Preferably, in step S1, the urease inhibitor is hydroquinone, and its mass ratio to the inorganic nutrient component is (0.05-0.1):100; the buffer is sodium bicarbonate, and its mass ratio to the inorganic nutrient component is (0.5-0.7):100; the composting agent is a compound composting microbial agent, which is a mixture of Bacillus subtilis and Trichoderma Pers. at a mass ratio of 1:1, and the mass ratio of the composting agent to the straw is (4-5):100; the moisture content of the straw is adjusted to 60-65%; the high-temperature fermentation temperature is 55-65℃, and the fermentation time is 7-10 days; the low-temperature activation temperature is 35-40℃, and the activation time is 3-5 days; the drying temperature is 45-55℃, and the drying time is 2-3 hours.

[0020] Preferably, in step S2, the mixing temperature is controlled at 25-40℃, and the mixing time is 15-25 min; the extrusion granulation pressure is 0.3-0.5 MPa, and the particle size of the core particles is 2.0-4.0 mm; the sieving uses a 10-20 mesh screen.

[0021] Preferably, in step S3, the air velocity of the fluidized bed coating machine is adjusted to 1.5-2.0 m / s, the coating temperature is controlled at 25-45℃, and the spraying speed of the coating material is 4-6 kg / h; the nutrient release regulator is urea-formaldehyde resin, and the sieving is done using an 8-16 mesh screen.

[0022] Preferably, in step S4, the stirring speed is 300-400 r / min, and the stirring time is 8-12 min; the ultrasonic dispersion power is 180-220 W, and the dispersion time is 4-6 min; during the spraying of the modified coating material, the temperature of the fluidized bed coating machine is 25-45℃, and the spraying speed is 5-7 kg / h; the gradient drying is performed sequentially at 35-40℃ for 1-2 h and at 40-45℃ for 2-3 h.

[0023] Beneficial technical effects:

[0024] This application uses polyacrylic acid and polyβ-hydroxybutyrate as the basic coating materials, and modifies and optimizes them by adding sodium alginate and nano-silica. The hydroxyl and carboxyl groups on the sodium alginate molecular chain can form stable intermolecular hydrogen bonds with polyacrylic acid and polyβ-hydroxybutyrate molecules. On the one hand, this hydrogen bonding crosslinking optimizes the coating molecular network structure, enhances the adhesion of the coating to fertilizer particles, and prevents nutrient loss due to coating damage. On the other hand, it can regulate the dissociation environment of the carboxyl groups in polyacrylic acid, enabling precise and reversible dissociation / association of carboxyl groups even with slight changes in rhizosphere pH, thus strengthening pH control. The sensitivity and stability of the response allow for more precise control of the hydrophilicity / phobicity and porosity of the coating under crop nutrient stress (pH 5.0-5.5) and saline-alkali environments (pH 7.5-8.0). The uniform filling of nano-silica into the pores of the polyacrylic acid and polyβ-hydroxybutyrate blend not only improves the density and structural uniformity of the coating, reducing deviations in the coating degradation rate under complex field conditions and preventing erratic nutrient release, but also acts as a carrier for response sites, adsorbing the carboxyl sites of polyacrylic acid and soil nutrient ions, amplifying the -COO groups after the nutrient ions dissociate from the polyacrylic acid. - The complexation signal allows the coating to precisely regulate the stability of the coating structure by changing the strength of the complexation when the concentration of available nitrogen and available phosphorus in the soil deviates slightly from the crop's required threshold, thereby achieving micro-regulation of nutrient release. Ultimately, the modified coating can stably and accurately regulate the nutrient release rate in the field environment based on changes in rhizosphere pH and nutrient concentration. Attached Figure Description

[0025] Figure 1 A flowchart illustrating the preparation process of a bio-compound fertilizer provided in this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0027] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0028] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. The invention will be further described below with reference to embodiments, but is not limited thereto.

[0029] Example 1

[0030] This embodiment provides a biological compound fertilizer, comprising inorganic nutrient components, synergistic components, compound functional microbial agents, and modified coating components, with a mass ratio of 19:28:0.7:52.3.

[0031] The inorganic nutrient components include urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer, with a mass ratio of 35:22:20:12; the synergistic components include decomposed straw, humic acid, chitosan-seaweed extract complex, amino acid chelated trace elements, and EDTA amino acid chelating agent, with a mass ratio of 70:20:3:0.5:0.5.

[0032] The decomposed straw contains ≥60% organic matter; the biochar is soaked in 1% dilute hydrochloric acid for 2 hours, rinsed with water until neutral, and dried; the amino acid chelated trace elements include amino acid chelated boron, amino acid chelated zinc, amino acid chelated iron, and amino acid chelated manganese, with a mass ratio of 1:3:4:2.

[0033] The mass ratio of Bacillus subtilis, Bacillus mucilaginosus, Bacillus megaterium, Bacillus licheniformis, and root nodule-promoting strains in the compound functional microbial agent is 9:4:2:1:0.8; the total viable count of the compound functional microbial agent is ≥2.0×10⁻⁶. 9 CFU / g, of which the viable count of Bacillus subtilis is ≥1.0×10⁻⁶. 8 CFU / g, viable count of gelatinous Bacillus ≥0.5×10⁻⁶ 8 CFU / g, viable count of Bacillus megaterium ≥ 0.3 × 10⁻⁶ 8 CFU / g, viable count of Bacillus licheniformis ≥0.2×10⁻⁶ 8 CFU / g, viable count of root nodule-promoting bacterial strains ≥0.1×10⁻⁶ 8 CFU / g; The Bacillus subtilis in the compound functional microbial agent was continuously cultured for three generations in liquid culture media with gradient NaCl concentrations of 0.2%, 0.4%, and 0.6% and gradient pH values ​​of 5.0, 6.0, and 7.0 for three generations for directional domestication;

[0034] The mass ratio of polyacrylic acid, polyβ-hydroxybutyrate, sodium alginate, and nano silica in the modified coating component is 47:45:1.0:0.2; the coating thickness formed by the modified coating component is 50 μm.

[0035] like Figure 1 As shown, this embodiment also provides a method for preparing a bio-compound fertilizer, including the following steps:

[0036] S1: Urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer are pulverized, mixed evenly, and urease inhibitor and buffer are added to adjust the pH to 6.5 to obtain inorganic nutrient components; straw is pulverized, composting agent is added, the moisture content is adjusted to 60%, fermented at 55℃ for 7 days and activated at 35℃ for 3 days, dried at 45℃ for 2 hours, and pulverized to obtain synergistic components; each strain is cultured separately to obtain compound functional microbial agents;

[0037] The urease inhibitor is hydroquinone, and its mass ratio to the inorganic nutrient component is 0.05:100; the buffer is sodium bicarbonate, and its mass ratio to the inorganic nutrient component is 0.5:100; the composting agent is a compound composting microbial agent, which is a mixture of Bacillus subtilis and Trichoderma at a mass ratio of 1:1, and the mass ratio of the compound composting microbial agent to straw is 4:100.

[0038] S2: Mix the pretreated synergistic components and compound functional microbial agents at 25°C for 15 min until uniform, then use an extrusion granulation process at 0.3 MPa and sieve through a 10-mesh screen to obtain core particles with a particle size of 2.0 mm.

[0039] S3: Mix the inorganic nutrient components evenly as the coating material, put the above core particles into a fluidized bed coating machine, spray the coating material, add nutrient release regulator, and sieve through an 8-mesh screen to obtain the middle layer coated particles.

[0040] The fluidized bed coating machine has an air velocity of 1.5 m / s, a coating temperature of 25℃, and a coating material spraying speed of 4 kg / h. The nutrient release regulator is urea-formaldehyde resin, and its mass ratio with the coating material is 1:100.

[0041] S4: Polyacrylic acid and polyβ-hydroxybutyrate were blended in the above mass ratio, sodium alginate and nano silica were added, stirred at 300 r / min for 8 min, and ultrasonically dispersed at 180 W for 4 min to prepare modified coating material; the middle layer coated particles were placed in a fluidized bed coating machine, the modified coating material was sprayed on, and after gradient drying and cooling, bio-compound fertilizer was obtained;

[0042] When spraying the modified coating material, the temperature of the fluidized bed coating machine is 25℃ and the spraying speed is 5kg / h; the gradient drying is carried out at 35℃ for 1h and 40℃ for 2h respectively.

[0043] Example 2

[0044] This embodiment provides a bio-compound fertilizer, comprising inorganic nutrient components, synergistic components, compound functional microbial agents, and modified coating components, with a mass ratio of 22.5:30:0.8:46.7;

[0045] The inorganic nutrient components include urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer, with a mass ratio of 37.5:25:22:15; the synergistic components include decomposed straw, humic acid, chitosan-seaweed extract complex, amino acid chelated trace elements, and EDTA amino acid chelating agent, with a mass ratio of 72.5:21:3.5:1.0:1.0.

[0046] The decomposed straw contains ≥60% organic matter; the biochar is soaked in 1% dilute hydrochloric acid for 2 hours, rinsed with water until neutral, and dried; the amino acid chelated trace elements include amino acid chelated boron, amino acid chelated zinc, amino acid chelated iron, and amino acid chelated manganese, with a mass ratio of 1:3:4:2.

[0047] The mass ratio of Bacillus subtilis, Bacillus mucilaginosus, Bacillus megaterium, Bacillus licheniformis, and root nodule-promoting strains in the compound functional microbial agent is 10:5:3:2:1.0; the total viable count of the compound functional microbial agent is ≥2.0×10⁻⁶. 9 CFU / g, of which the viable count of Bacillus subtilis is ≥1.0×10⁻⁶. 8 CFU / g, viable count of gelatinous Bacillus ≥0.5×10⁻⁶ 8 CFU / g, viable count of Bacillus megaterium ≥ 0.3 × 10⁻⁶ 8 CFU / g, viable count of Bacillus licheniformis ≥0.2×10⁻⁶ 8 CFU / g, viable count of root nodule-promoting bacterial strains ≥0.1×10⁻⁶ 8 CFU / g; Bacillus subtilis in the compound functional microbial agent was continuously cultured for three generations in liquid culture media with gradient NaCl concentrations of 0.6%, 0.7%, and 0.8% and gradient pH values ​​of 6.5, 7.5, and 8.5 for three generations for directional domestication;

[0048] The mass ratio of polyacrylic acid, polyβ-hydroxybutyrate, sodium alginate, and nano silica in the modified coating component is 48.5:48.5:1.25:0.25; the coating thickness formed by the modified coating component is 75 μm.

[0049] like Figure 1 As shown, this embodiment also provides a method for preparing a bio-compound fertilizer, including the following steps:

[0050] S1: Urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer are pulverized, mixed evenly, and urease inhibitor and buffer are added to adjust the pH to 7.0 to obtain inorganic nutrient components; straw is pulverized, composting agent is added, and the moisture content is adjusted to 62.5%. It is then fermented at 60℃ for 8.5 days and activated at 37.5℃ for 4 days, dried at 50℃ for 2.5 hours, and pulverized to obtain synergistic components; each strain is cultured separately to obtain a compound functional microbial agent;

[0051] The urease inhibitor is hydroquinone, with a mass ratio of 0.075:100 to the inorganic nutrient components; the buffer is sodium bicarbonate, with a mass ratio of 0.6:100 to the inorganic nutrient components; and the composting agent is a compound composting microbial agent, which is a mixture of Bacillus subtilis and Trichoderma at a mass ratio of 1:1, with a mass ratio of 4.5:100 to the straw.

[0052] S2: The pretreated synergistic components and compound functional microbial agents were mixed at 32.5℃ for 20 min, and then extruded and granulated at 0.4 MPa. The mixture was then sieved through a 15-mesh sieve to obtain core particles with a particle size of 3.0 mm.

[0053] S3: Mix the inorganic nutrient components evenly as the coating material, put the above core particles into a fluidized bed coating machine, spray the coating material, add nutrient release regulator, and sieve with a 12-mesh sieve to obtain the middle layer coated particles.

[0054] The fluidized bed coating machine has an air speed of 1.75 m / s, a coating temperature of 35℃, and a coating material spraying speed of 5 kg / h. The nutrient release regulator is urea-formaldehyde resin, and its mass ratio with the coating material is 1:100.

[0055] S4: Polyacrylic acid and polyβ-hydroxybutyrate were blended in the above mass ratio, sodium alginate and nano silica were added, stirred at 350 r / min for 10 min, and ultrasonically dispersed at 200 W for 5 min to prepare modified coating material; the middle layer coated particles were placed in a fluidized bed coating machine, the modified coating material was sprayed on, and after gradient drying and cooling, bio-compound fertilizer was obtained;

[0056] When spraying the modified coating material, the temperature of the fluidized bed coating machine is 35℃ and the spraying speed is 6kg / h; the gradient drying is carried out at 37.5℃ for 1.5h and 42.5℃ for 2.5h respectively.

[0057] Example 3

[0058] This embodiment provides a bio-compound fertilizer, comprising inorganic nutrient components, synergistic components, compound functional microbial agents, and modified coating components, with a mass ratio of 26:32:0.9:41.1;

[0059] The inorganic nutrient components include urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer, with a mass ratio of 40:28:24:18; the synergistic components include decomposed straw, humic acid, chitosan-seaweed extract complex, amino acid chelated trace elements, and EDTA amino acid chelating agent, with a mass ratio of 75:22:4:1.5:1.5.

[0060] The decomposed straw contains ≥60% organic matter; the biochar is soaked in 1% dilute hydrochloric acid for 2 hours, rinsed with water until neutral, and dried; the amino acid chelated trace elements include amino acid chelated boron, amino acid chelated zinc, amino acid chelated iron, and amino acid chelated manganese, with a mass ratio of 1:3:4:2.

[0061] The mass ratio of Bacillus subtilis, Bacillus mucilaginosus, Bacillus megaterium, Bacillus licheniformis, and root nodule-promoting strains in the compound functional microbial agent is 11:6:4:3:1.2; the total viable count of the compound functional microbial agent is ≥2.0×10⁻⁶. 9 CFU / g, of which the viable count of Bacillus subtilis is ≥1.0×10⁻⁶. 8 CFU / g, viable count of gelatinous Bacillus ≥0.5×10⁻⁶ 8 CFU / g, viable count of Bacillus megaterium ≥ 0.3 × 10⁻⁶ 8 CFU / g, viable count of Bacillus licheniformis ≥0.2×10⁻⁶ 8 CFU / g, viable count of root nodule-promoting bacterial strains ≥0.1×10⁻⁶ 8 CFU / g; The Bacillus subtilis in the compound functional microbial agent was continuously cultured for three generations in liquid culture media with gradient NaCl concentrations of 0.5%, 0.6%, and 0.7% and gradient pH values ​​of 5.5, 6.5, and 7.5 for three generations for directional domestication;

[0062] The mass ratio of polyacrylic acid, polyβ-hydroxybutyrate, sodium alginate, and nano silica in the modified coating component is 50:52:1.5:0.3; the coating thickness formed by the modified coating component is 100 μm.

[0063] like Figure 1 As shown, this embodiment also provides a method for preparing a bio-compound fertilizer, including the following steps:

[0064] S1: Urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer are pulverized, mixed evenly, and urease inhibitor and buffer are added to adjust the pH to 7.5 to obtain inorganic nutrient components; straw is pulverized, composting agent is added, the moisture content is adjusted to 65%, fermented at 65℃ for 10 days and activated at 40℃ for 5 days, dried at 55℃ for 3 hours, and pulverized to obtain synergistic components; each strain is cultured separately to obtain compound functional microbial agents;

[0065] The urease inhibitor is hydroquinone, and its mass ratio to the inorganic nutrient component is 0.1:100; the buffer is sodium bicarbonate, and its mass ratio to the inorganic nutrient component is 0.7:100; the composting agent is a compound composting microbial agent, which is a mixture of Bacillus subtilis and Trichoderma at a mass ratio of 1:1, and the mass ratio of the compound composting microbial agent to straw is 5:100.

[0066] S2: The pretreated synergistic components and compound functional microbial agents are mixed at 40℃ for 25 min, and then extruded and granulated at 0.5 MPa. The granules are then sieved through a 20-mesh screen to obtain core particles with a particle size of 4.0 mm.

[0067] S3: Mix the inorganic nutrient components evenly as coating material, put the above core particles into a fluidized bed coating machine, spray the coating material, add nutrient release regulator, and obtain middle layer coated particles;

[0068] The fluidized bed coating machine has an air velocity of 2.0 m / s, a coating temperature of 45℃, and a coating material spraying speed of 6 kg / h. The nutrient release regulator is urea-formaldehyde resin, and its mass ratio with the coating material is 1:100.

[0069] S4: Polyacrylic acid and polyβ-hydroxybutyrate were blended in the above mass ratio, sodium alginate and nano silica were added, stirred at 400 r / min for 12 min, and ultrasonically dispersed at 220 W for 6 min to prepare modified coating material; the middle layer coated particles were placed in a fluidized bed coating machine, the modified coating material was sprayed on, and after gradient drying and cooling, bio-compound fertilizer was obtained;

[0070] When spraying the modified coating material, the temperature of the fluidized bed coating machine is 45℃ and the spraying speed is 7kg / h; the gradient drying is carried out at 40℃ for 2h and at 45℃ for 3h.

[0071] Comparative Example 1

[0072] This comparative example provides a bio-compound fertilizer and its preparation method. The difference from Example 1 is that the modified coating component lacks nano-silica and only contains polyacrylic acid, polyβ-hydroxybutyrate and sodium alginate, with a mass ratio of 49.5:49.5:1.25. Other process parameters and operating steps are the same as in Example 1.

[0073] Comparative Example 2

[0074] This comparative example provides a bio-compound fertilizer and its preparation method. The difference from Example 1 is that sodium alginate is missing in the modified coating component, and it only contains polyacrylic acid, polyβ-hydroxybutyrate and nano silica in a mass ratio of 49.5:49.5:0.5. Other process parameters and operating steps are the same as in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a bio-compound fertilizer and its preparation method. The difference from Example 1 is that the modified coating component contains only polyacrylic acid and polyβ-hydroxybutyrate, with a mass ratio of 1:1. Other process parameters and operating steps are the same as in Example 1.

[0077] The bio-compound fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 of this application were tested and compared in terms of viable bacteria retention rate (%), nutrient release rate at pH=5.0-5.5, nutrient release rate at pH=7.5-8.0, and coating damage rate (%). The results are shown in Table 1.

[0078] Test method:

[0079] Viable bacterial retention rate: The plate count method was used to determine the total number of viable bacteria for each sample at the time of preparation (0 days), after 30 days of storage at room temperature, and after 60 days of storage at room temperature. The viable bacterial retention rate was calculated (retention rate = number of viable bacteria after storage / initial number of viable bacteria × 100%). Three parallel experiments were set up for each sample, and the average value was taken.

[0080] Coating damage rate: Simulating field transportation and irrigation environment, the sample was placed in a shaker (200r / min) and shaken for 30min, then sprayed with clean water for 10min. The percentage of particles with damaged coating was counted. Three parallel tests were set up for each sample, and the average value was taken.

[0081] pH-Nutrient Dual Response Performance Test: Simulate crop nutrient stress environments (pH=5.0-5.5), saline-alkali environments (pH=7.5-8.0), and neutral environments (pH=6.5-7.0), respectively. Place each sample in the corresponding pH buffer solution and incubate at a constant temperature of 25℃ for 72h. Measure the release rates of nitrogen (N), phosphorus (P2O5), and potassium (K2O) at different time points (24h, 48h, 72h), calculate the total nutrient release rate over 72h, and set up 3 parallel experiments for each sample, taking the average value.

[0082] Table 1 Performance test results of the bio-compound fertilizers prepared in the examples and comparative examples

[0083]

[0084] The bio-compound fertilizer prepared in Examples 1-3 of this invention uses polyacrylic acid and polyβ-hydroxybutyrate as the basic coating materials, and is modified and optimized by adding sodium alginate and nano-silica. The hydroxyl and carboxyl groups on the sodium alginate molecular chain can form stable intermolecular hydrogen bonds with polyacrylic acid and polyβ-hydroxybutyrate molecules. On the one hand, this hydrogen bonding crosslinking optimizes the coating molecular network structure, enhances the adhesion of the coating to fertilizer particles, and prevents nutrient loss due to coating damage. On the other hand, it can regulate the dissociation environment of the carboxyl groups in polyacrylic acid, enabling precise and reversible dissociation of the carboxyl groups even with slight changes in rhizosphere pH. The association enhances the sensitivity and stability of pH response, allowing for more precise control of hydrophilicity / phobicity and porosity of the coating under crop nutrient stress (pH 5.0-5.5) and saline-alkali environments (pH 7.5-8.0). Nano-silica uniformly fills the pores of the polyacrylic acid and polyβ-hydroxybutyrate blend system, not only improving the density and structural uniformity of the coating and reducing deviations in the coating degradation rate under complex field conditions, thus avoiding sudden changes in nutrient release, but also serving as a carrier for response sites. It adsorbs the carboxyl sites of polyacrylic acid and soil nutrient ions, amplifying the -COO groups after the nutrient ions dissociate from the polyacrylic acid. - The complexation signal allows the coating to precisely regulate the stability of the coating structure by changing the strength of the complexation when the concentration of available nitrogen and available phosphorus in the soil deviates slightly from the crop's required threshold, thereby achieving micro-regulation of nutrient release. Ultimately, the modified coating can stably and accurately regulate the nutrient release rate in the field environment based on changes in rhizosphere pH and nutrient concentration.

[0085] Among them, the comparative examples, lacking one or two key modifying components such as sodium alginate and nano silica, could not form hydrogen bond cross-linking and pore filling effects, nor could they amplify response signals. As a result, they lost their precise pH-nutrient dual-response capability, leading to insufficient membrane adhesion, high breakage rate, and large fluctuations in nutrient release rate. Ultimately, all comparative examples showed low viable bacterial retention rate, poor membrane stability, and poor nutrient release regulation.

[0086] It should be understood that the above are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, other modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A bio-complex fertilizer, characterized by, It includes inorganic nutrient components, synergistic components, compound functional microbial agents, and modified coating components; The inorganic nutrient components include urea, monoammonium phosphate, potassium sulfate, and calcium magnesium phosphate fertilizer; the synergistic components include decomposed straw, humic acid, chitosan-seaweed extract complex, amino acid chelated trace elements, and EDTA amino acid chelating agent; the composite functional microbial agent includes Bacillus subtilis, Bacillus lentigines, Bacillus megaterium, Bacillus licheniformis, and root nodule-promoting strains; the modified coating components include polyacrylic acid, polyβ-hydroxybutyrate, sodium alginate, and nano-silica.

2. The bio-composite fertilizer according to claim 1, characterized in that, The mass ratio of the inorganic nutrient component, the synergistic component, the compound functional microbial agent and the modified coating component is (19-26): (28-32): (0.7-0.9): (42-50).

3. The bio-composite fertilizer according to claim 1, characterized in that, The mass ratio of urea, monoammonium phosphate, potassium sulfate and calcium magnesium phosphate in the inorganic nutrient components is (35-40):(22-28):(20-24):(12-18); the mass ratio of decomposed straw, humic acid, chitosan-seaweed extract complex, amino acid chelated trace elements and EDTA amino acid chelating agent in the synergistic components is (70-75):(20-22):(3-4):(0.5-1.5):(0.5-1.5).

4. The bio-composite fertilizer according to claim 1, characterized in that, The mass ratio of Bacillus subtilis, Paenibacillus mucilaginosus, Bacillus megaterium, Bacillus licheniformis and rhizobium promoting strain in the complex functional microbial agent is (9-11):(4-6):(2-4):(1-3):(0.8-1.2); the total viable bacterial count of the complex functional microbial agent is ≥10 9 CFU / g; the Bacillus subtilis in the complex functional microbial agent is continuously cultured for 3 generations of directional domestication in a liquid culture medium with gradient NaCl concentration of 0.2%-0.8% and gradient pH of 5.0-8.

5.

5. The bio-composite fertilizer according to claim 1, characterized in that, The mass ratio of polyacrylic acid, polyβ-hydroxybutyrate, sodium alginate and nano silica in the modified coating component is (47-50):(45-52):(1.0-1.5):(0.2-0.3); the coating thickness formed by the modified coating component is 50-100 μm.

6. A method of producing the bio-complex fertilizer according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Crush urea, monoammonium phosphate, potassium sulfate and calcium magnesium phosphate fertilizer, mix them evenly, add urease inhibitor and buffer, adjust the pH to obtain inorganic nutrient components. The straw is crushed, a composting agent is added, the moisture content is adjusted, and after high-temperature fermentation and low-temperature activation, it is dried and crushed to obtain the synergistic component. Each strain was cultured separately to prepare a compound functional microbial agent, thus obtaining the compound functional microbial agent; S2: Mix the pretreated synergistic components and compound functional microbial agents evenly, and then use an extrusion granulation process to obtain core particles after sieving; S3: Mix the inorganic nutrient components evenly as coating material, put the above core particles into a fluidized bed coating machine, spray the coating material, add nutrient release regulator, and obtain middle layer coated particles; S4: Polyacrylic acid and polyβ-hydroxybutyrate are blended, sodium alginate and nano silica are added, stirred and ultrasonically dispersed to prepare a modified coating material; the middle layer of coated particles are placed into a fluidized bed coating machine, the modified coating material is sprayed on, and after gradient drying and cooling, a bio-compound fertilizer is obtained.

7. The method for preparing a bio-compound fertilizer according to claim 6, characterized in that, In step S1, the urease inhibitor is hydroquinone, and its mass ratio to the inorganic nutrient component is (0.05-0.1):100; the buffer is sodium bicarbonate, and its mass ratio to the inorganic nutrient component is (0.5-0.7):100; the composting agent is a compound composting microbial agent, which is a mixture of Bacillus subtilis and Trichoderma at a mass ratio of 1:1, and the mass ratio of the composting agent to the straw is (4-5):100; the moisture content is adjusted to 60-65%; the high-temperature fermentation temperature is 55-65℃, and the fermentation time is 7-10 days; the low-temperature activation temperature is 35-40℃, and the activation time is 3-5 days; the drying temperature is 45-55℃, and the drying time is 2-3 hours.

8. The method of claim 6, wherein the bio-complex fertilizer is prepared by the steps of: In step S2, the mixing temperature is controlled at 25-40℃, and the mixing time is 15-25 min; the extrusion granulation pressure is 0.3-0.5 MPa, and the particle size of the core particles is 2.0-4.0 mm; the sieving uses a 10-20 mesh screen. ​ 9. The method of claim 6, wherein the bio-complex fertilizer is prepared by the steps of: In S3, the air speed of the fluidized bed coating machine is adjusted to 1.5-2.0 m / s, the coating temperature is controlled at 25-45℃, and the spraying speed of the coating material is 4-6 kg / h; the nutrient release regulator is urea-formaldehyde resin. ​ 10. The method of claim 6, wherein the bio-complex fertilizer is prepared by the steps of: In step S4, the stirring speed is 300-400 r / min, and the stirring time is 8-12 min; the ultrasonic dispersion power is 180-220 W, and the dispersion time is 4-6 min; during the spraying of the modified coating material, the temperature of the fluidized bed coating machine is 25-45℃, and the spraying speed is 5-7 kg / h; the gradient drying is performed sequentially at 35-40℃ for 1-2 h and at 40-45℃ for 2-3 h. ​

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