Slow-release coated microbial agent fertilizer and production method thereof

Abstract

The invention relates to a slow-release coated microbial agent fertilizer and a production method thereof, and belongs to the technical field of coated fertilizers. The fertilizer comprises an inner core layer and a coating layer, wherein the inner core layer consists of urea, diatomite, hydroxyapatite, a microbial agent and nutrient elements; the coating layer is formed by coating liquid formed by reaction of a bio-based polyurethane prepolymer and a siloxane modified cardanol chain extender, and porous calcium borate is added as a modifier. The production method comprises the steps of inner core layer granulation, coating liquid preparation and fluidized bed coating. The microbial agent is effectively protected through the coating layer, the survival rate and colonization ability of the microbial agent are improved, meanwhile, slow release of nutrients is achieved, and the fertilizer requirement rule of crops is matched; the coating layer has the characteristics of biodegradability, high mechanical strength and good hydrophobicity, reduces environmental pollution, improves the soil structure through diatomite and hydroxyapatite, and promotes plant growth. The fertilizer solves the problems of easy inactivation and too fast nutrient release of the traditional microbial fertilizer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coated fertilizers, and particularly relates to a slow-release coated microbial agent fertilizer and a production method thereof. BACKGROUND

[0002] Microbial fertilizers, as an environmentally friendly agricultural input, can improve crop nutrient supply, promote growth, enhance stress resistance, and play a positive role in soil ecosystem health through the life activities of specific functional microorganisms contained therein, and have become an important technical means to achieve sustainable agricultural development. However, traditional microbial fertilizers still face many challenges in practical application, which seriously restricts the stable play of their effects and large-scale promotion. One of the core problems is the survival rate and colonization ability of microbial agents in fertilizers. Microbial agents are extremely sensitive to external environmental factors, and during the processing, storage, transportation of fertilizers and the initial stage after being applied to soil, the number of viable bacteria can easily decrease significantly, making it difficult to achieve the expected function.

[0003] On the other hand, the nutrient release rate of conventional fertilizers is too fast, and often does not match the fertilizer demand law of different growth stages of crops. This not only causes a large amount of nutrient loss and waste, reduces fertilizer utilization rate, but also may cause a series of environmental problems such as water eutrophication and greenhouse gas emission due to leaching or volatilization. Although slow-release fertilizer technology delays the release of nutrients through physical or chemical means, it solves the above problems to some extent, but the existing technology focuses more on the controlled release of chemical nutrients, and there are few comprehensive solutions that can effectively protect and interface the life activities of microbial agents and the nutrient release law.

[0004] Some existing coating technologies, such as using petrochemical-based polyolefins, alkyd resins, etc. as coating materials, can provide a certain physical barrier, but they have problems such as non-biodegradable materials, soil pollution caused by residues, or the need to use a large amount of organic solvents in the coating process, which is contrary to the development concept of green agriculture. In addition, the microporous structure of these coating materials lacks sufficient control precision, either too dense to hinder microbial respiration or too loose to cause the protective function to fail prematurely, making it difficult to achieve an ideal balance between microorganism survival microenvironment construction and nutrient slow release.

[0005] At the same time, the mechanical strength of the coating layer itself is also a common defect. During the processing, packaging, transportation and mechanized fertilization of fertilizer particles, the coating layer is prone to damage, causing the internal microorganisms and nutrients to be exposed prematurely, losing the slow-release and protection effect. Therefore, there is an urgent need in the art to develop a new type of slow-release coated microbial agent fertilizer. SUMMARY

[0006] In view of the above, in order to overcome the defects of the prior art, the present application forms a coating liquid by reacting a bio-based polyurethane prepolymer with a siloxane modified cardanol chain extender, effectively protects the microbial agent and nutrients in the internal core layer, realizes the slow-release function, and the coating liquid is made of renewable resources and has the characteristics of green and biodegradable, reducing the environmental burden.

[0007] In order to achieve the above-mentioned purpose, the following technical scheme is adopted: on the one hand, the present application provides a preparation method of slow-release coated microbial agent fertilizer, comprising the following steps:

[0008] S1. Take the raw materials according to the following mass parts: urea 50-80 parts, diatomite 10-20 parts, hydroxyapatite 5-15 parts, microbial agent 2-8 parts, adhesive 1-5 parts, potassium sulfate 5-15 parts, calcium superphosphate 3-10 parts, calcium nitrate 2-6 parts, magnesium sulfate 1-4 parts, zinc sulfate 0.5-2 parts, wherein the microbial agent is composed of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa and Trichoderma harzianum; the above-mentioned raw materials are added into a double screw mixer, mixed at a speed of 300-500 rpm and a temperature of 25-40℃ for 20-40 min, and then transferred into a disc granulator for granulation, the particle size is controlled to be 2-5 mm, and the internal core layer is obtained;

[0009] S2. Put 1,5-pentanedioic isocyanate and plant-based polyol into a reaction kettle according to the NCO / OH molar ratio of 1.2-2.0:1, add 0.01-0.1% of dibutyltin dilaurate as a catalyst, stir at 60-80℃ for 2-4h under nitrogen protection, and obtain a bio-based polyurethane prepolymer;

[0010] S3. Mix 1,3-bis(ammonia propane alkyl) tetramethyl disiloxane and cardanol glycidyl ether according to the amino group to epoxy group molar ratio of 0.9-1.1:1, add ethyl acetate as a solvent, which is 3-5 times the total mass of the two raw materials, stir at 50-70℃ for 3-5h, and then remove the ethyl acetate by distillation under reduced pressure after the reaction is completed, to obtain a siloxane modified cardanol chain extender monomer;

[0011] S4. Mix the siloxane modified cardanol chain extender monomer and porous calcium borate according to the mass ratio of 100:5-20, stir at a speed of 200-300 rpm for 30-60 min, then add the bio-based polyurethane prepolymer, control the molar ratio of NCO groups in the prepolymer to active hydrogen groups in the chain extender monomer to be 1:0.8-1.2, and react at 40-60℃ for 1-2h to obtain a coating liquid;

[0012] S5. The internal core layer is placed in a fluidized bed coating machine, and the coating liquid is sprayed on the surface of the internal core layer at a dosage of 5-15% of the mass of the internal core layer, and after spraying is completed, drying is carried out at 30-80 DEG C for 2-6h, to obtain the slow-release coated microbial agent fertilizer.

[0013] Further, the porous calcium borate is prepared by the following steps: calcium nitrate and boric acid are dissolved in deionized water at a calcium-boron molar ratio of 1:2-4, to prepare a mixed solution with a total solute mass concentration of 10-16%, and 0.5-2% of the total mass of the mixed solution is added as a template agent, and stirring is carried out until complete dissolution; the mixed solution is transferred into a hydrothermal reaction kettle, and reaction is carried out at 120-180 DEG C for 6-12h, and after natural cooling to room temperature, the precipitate is filtered, washed with deionized water and anhydrous ethanol alternately for 3 times, and then dried at 80-100 DEG C for 6-12h, to obtain the porous calcium borate.

[0014] Further, in the microbial agent, the mass ratio of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa and Trichoderma harzianum is 2-3:1-2:1-2:2-3.

[0015] Further, the total effective viable bacterial count of the microbial agent is >10 7 CFU / g.

[0016] Further, the plant-based polyol is selected from at least one of a soybean oil polyol and a castor oil polyol.

[0017] Further, the binder is selected from at least one of sodium carboxymethyl cellulose and starch.

[0018] Further, the inlet air temperature of the fluidized bed coating machine is 40-60 DEG C, the material temperature is 30-50 DEG C, and the atomization pressure is 0.2-0.5MPa.

[0019] In another aspect, the application provides a slow-release coated microbial agent fertilizer, which is prepared according to the preparation method described above.

[0020] The beneficial effects of the application are:

[0021] The slow-release coated microbial agent fertilizer provided by the application realizes the slow-release function by using the coating liquid formed by the reaction of the bio-based polyurethane prepolymer and the siloxane modified cashew phenol chain extender to effectively protect the microbial agent and nutrients in the internal core layer, and the coating liquid is made of renewable resources and has the characteristics of green and biodegradable, thereby reducing the environmental burden.

[0022] The present application prepares a siloxane modified cardanol glycidyl ether chain extender monomer by reacting 1,3-bis(amino propane) tetramethyl disiloxane with cardanol glycidyl ether, the hydroxyl groups produced by the reaction of the epoxy groups and the amino groups can be used as a chain extender to react with a bio-based polyurethane prepolymer, the siloxane structure in the siloxane modified cardanol glycidyl ether chain extender monomer endows the coating layer with excellent hydrophobicity and chemical stability, while the long-chain alkane structure of cardanol helps to adjust the microporous structure and flexibility of the coating layer, thereby controlling the water and nutrient penetration rate and achieving slow release of nutrients, at the same time, the siloxane groups form a crosslinked structure with the polyurethane network, enhancing the mechanical strength and durability of the coating layer and avoiding damage during transportation or application.

[0023] The present application prepares porous calcium borate by a hydrothermal template method, which has a porous structure and hydrophobicity, and the pores thereof not only provide a microenvironment required for respiration and metabolism of microorganisms, promoting microbial activity, but also can be combined with siloxane modified cardanol glycidyl ether chain extender monomers through coordination, uniformly dispersed in the coating layer, forming additional crosslinking points, further optimizing the pore size distribution and slow release performance of the coating layer, and the porous calcium borate can also release boron and calcium elements to participate in plant metabolism and promote growth and development.

[0024] The coating layer can shield external adverse factors, improve the survival rate and colonization ability of microbial inoculants, and the diatomite and hydroxyapatite in the internal core layer can improve soil structure, provide silicon, calcium and other trace elements, and synergistically act with microbial inoculants to enhance soil fertility and plant stress resistance. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The nutrient release rate of the fertilizer prepared for each embodiment and comparative example of the present application is shown in the line graph;

[0026] Figure 2 The microbial survival rate of the fertilizer prepared for each embodiment and comparative example of the present application after storage is shown in the column graph;

[0027] Figure 3 The mechanical strength determination results of the coating layer of the fertilizer prepared for each embodiment and comparative example of the present application are shown in the column graph.

[0028] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, and are used together with the embodiments of the present application to explain the present application, and do not constitute a limitation on the present application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, and all other embodiments obtained by a person of ordinary skill in the art without creative effort on the basis of the embodiments of the present application shall fall within the scope of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art. In addition, any method and material similar or equivalent to those described herein can be used in the present application. The preferred methods and materials described herein are only for illustration and cannot limit the content of the present application.

[0031] The experimental methods in the following examples are all conventional methods unless otherwise specified. The experimental materials used in the following examples are all purchased from commercial channels unless otherwise specified.

[0032] Among them, Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa, Trichoderma harzianum are purchased from Shandong Zhengxing New Material Co., Ltd.

[0033] Example 1

[0034] A preparation method of a slow-release type coated microbial fertilizer, comprising the following steps:

[0035] S1. Take the raw materials according to the following mass parts: urea 50 parts, diatomite 10 parts, hydroxyapatite 5 parts, microbial inoculant 2 parts, adhesive 1 part, potassium sulfate 5 parts, superphosphate 3 parts, calcium nitrate 2 parts, magnesium sulfate 1 part, zinc sulfate 0.5 part, wherein the microbial inoculant is composed of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa, and Trichoderma harzianum; the above raw materials are added into a double-screw mixer, mixed at a speed of 300 rpm and a temperature of 25℃ for 20 min, and then transferred into a disc granulator for granulation, with the particle size controlled at 2 mm to obtain an internal core layer;

[0036] S2. Put 1,5-pentane diisocyanate and plant-based polyol into a reaction kettle according to a NCO / OH molar ratio of 1.2:1, and add 0.01% of dibutyltin dilaurate based on the total mass as a catalyst, stir at 60℃ for 2h under nitrogen protection to obtain a bio-based polyurethane prepolymer;

[0037] S3. Mix 1,3-bis(ammonia propane alkyl) tetramethyl disiloxane and cardanol glycidyl ether according to an amino group to epoxy group molar ratio of 0.9:1, add ethyl acetate as a solvent, which is 3 times the total mass of the two raw materials, and stir at 50℃ for 3h. After the reaction is completed, remove the ethyl acetate by distillation under reduced pressure to obtain a siloxane modified cardanol chain extender monomer;

[0038] S4. The silicone-modified cardanol chain extender monomer is mixed with the porous calcium borate at a mass ratio of 100:5, stirred at a rotation speed of 200 rpm for 30 min, then the bio-based polyurethane prepolymer is added, the molar ratio of NCO groups in the prepolymer to active hydrogen groups in the chain extender monomer is controlled to be 1:0.8, and reaction is carried out at 40°C for 1 h to obtain a coating liquid;

[0039] S5. The internal core layer is placed in a fluidized bed coating machine, the coating liquid is sprayed on the surface of the internal core layer at a dosage of 5% of the mass of the internal core layer, and after the spraying is completed, drying is carried out at 30°C for 2 h to obtain the slow-release coated microbial inoculant fertilizer.

[0040] The porous calcium borate is prepared by the following steps: calcium nitrate and boric acid are dissolved in deionized water at a calcium-boron molar ratio of 1:2 to prepare a mixed solution with a total solute mass concentration of 10%, and 0.5% of the total mass of the mixed solution is added as a template agent, i.e., sodium dodecyl sulfate, and stirring is carried out until complete dissolution; the mixed solution is transferred into a hydrothermal reaction kettle, reaction is carried out at 120°C for 6 h, and after natural cooling to room temperature, the precipitate is filtered, washed with deionized water and anhydrous ethanol alternately for 3 times, and then dried at 80°C for 6 h to obtain the porous calcium borate.

[0041] In the microbial inoculant, the mass ratio of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa, and Trichoderma harzianum is 2:1:1:2.

[0042] The total effective viable bacterial count of the microbial inoculant is >10 7 CFU / g.

[0043] The plant-based polyol is a soybean oil polyol.

[0044] The binder is sodium carboxymethyl cellulose.

[0045] The inlet air temperature of the fluidized bed coating machine is 40°C, the material temperature is 30°C, and the atomization pressure is 0.2 MPa.

[0046] Example 2:

[0047] A preparation method of a slow-release coated microbial inoculant fertilizer, comprising the following steps:

[0048] S1. The following raw materials are taken by mass parts: urea 80 parts, diatomite 20 parts, hydroxyapatite 15 parts, microbial inoculant 8 parts, binder 5 parts, potassium sulfate 15 parts, superphosphate 10 parts, calcium nitrate 6 parts, magnesium sulfate 4 parts, and zinc sulfate 2 parts, wherein the microbial inoculant is composed of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa, and Trichoderma harzianum; the above raw materials are added into a double-screw mixer, mixed at a rotation speed of 500 rpm and a temperature of 40°C for 40 min, then transferred into a disc granulator for granulation, and the particle size is controlled to be 5 mm to obtain an internal core layer.

[0049] S2. Put 1,5-pentane diisocyanate and plant-based polyol into the reaction kettle according to the NCO / OH molar ratio of 2.0:1, add 0.1% of dibutyltin dilaurate based on the total mass as a catalyst, stir at 80°C for 4h under nitrogen protection, and obtain a bio-based polyurethane prepolymer;

[0050] S3. Mix 1,3-bis(amino propane) tetramethyl disiloxane and cardanol glycidyl ether according to the amino group to epoxy group molar ratio of 1.1:1, add ethyl acetate as a solvent, which is 5 times the total mass of the two raw materials, stir at 70°C for 5h, and remove the ethyl acetate by distillation under reduced pressure after the reaction is completed, to obtain a siloxane modified cardanol chain extender monomer;

[0051] S4. Mix the siloxane modified cardanol chain extender monomer and porous calcium borate according to the mass ratio of 100:20, stir at a speed of 300 rpm for 60 min, then add the bio-based polyurethane prepolymer, control the molar ratio of NCO groups in the prepolymer to active hydrogen groups in the chain extender monomer to be 1:1.2, and react at 60°C for 2h to obtain a coating liquid;

[0052] S5. Place the internal core layer in a fluidized bed coating machine, spray the coating liquid on the surface of the internal core layer at a dosage of 15% of the mass of the internal core layer, and dry at 80°C for 6h after the spraying is completed to obtain the slow-release coated microbial agent fertilizer.

[0053] The porous calcium borate is prepared by the following steps: dissolving calcium nitrate and boric acid in deionized water according to the calcium to boron molar ratio of 1:4, preparing a mixed solution with a total solute mass concentration of 16%, adding 2% of sodium dodecyl sulfate as a template agent based on the total mass of the mixed solution, and stirring until completely dissolved; transfer the mixed solution into a hydrothermal reaction kettle, react at 180°C for 12h, naturally cool to room temperature, filter to obtain a precipitate, wash with deionized water and anhydrous ethanol alternately for 3 times, and then dry at 100°C for 12h to obtain the porous calcium borate.

[0054] In the microbial agent, the mass ratio of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa, and Trichoderma harzianum is 3:2:2:3.

[0055] The total effective viable bacterial count of the microbial agent is >10 7 CFU / g.

[0056] The plant-based polyol is castor oil polyol.

[0057] The binder is starch.

[0058] The inlet air temperature of the fluidized bed coating machine is 60°C, the material temperature is 50°C, and the atomization pressure is 0.5 MPa.

[0059] Example 3:

[0060] A preparation method of a slow-release coated microbial agent fertilizer, comprising the following steps:

[0061] S1. Take raw materials according to the following mass parts: urea 65 parts, diatomite 15 parts, hydroxyapatite 10 parts, microbial agent 5 parts, adhesive 3 parts, potassium sulfate 10 parts, superphosphate 7 parts, calcium nitrate 4 parts, magnesium sulfate 3 parts, zinc sulfate 1 part, wherein the microbial agent is composed of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa, and Trichoderma harzianum; add the above raw materials into a double-screw mixer, mix for 30 min under the condition of a rotation speed of 400 rpm and a temperature of 33℃, and then transfer into a disc granulator to granulate, control the particle size of the granules to be 4 mm, and obtain an internal core layer;

[0062] S2. Put 1,5-pentane diisocyanate and plant-based polyol into a reaction kettle according to an NCO / OH molar ratio of 1.6:1, add dibutyltin dilaurate accounting for 0.06% of the total mass as a catalyst, stir and react at 70℃ for 3h under nitrogen protection, and obtain a bio-based polyurethane prepolymer;

[0063] S3. Mix 1,3-bis(ammonia propane alkyl) tetramethyl disiloxane and cardanol glycidyl ether according to an amino group to epoxy group molar ratio of 1.0:1, add ethyl acetate accounting for 4 times the total mass of the two raw materials as a solvent, stir and react at 60℃ for 4h, remove the ethyl acetate by distillation under reduced pressure after the reaction is completed, and obtain a siloxane modified cardanol chain extender monomer;

[0064] S4. Mix the siloxane modified cardanol chain extender monomer and porous calcium borate according to a mass ratio of 100:12, stir at a rotation speed of 250 rpm for 45 min, then add the bio-based polyurethane prepolymer, control the molar ratio of NCO groups in the prepolymer to active hydrogen groups in the chain extender monomer to be 1:1.0, and react at 50℃ for 1.5h, and obtain a coating liquid;

[0065] S5. Place the internal core layer in a fluidized bed coating machine, spray the coating liquid on the surface of the internal core layer according to an amount of 10% of the mass of the internal core layer, dry at 55℃ for 4h after the spraying is completed, and obtain the slow-release coated microbial agent fertilizer.

[0066] The porous calcium borate is prepared by the following steps: dissolve calcium nitrate and boric acid in deionized water according to a calcium to boron molar ratio of 1:3, prepare a mixed solution with a total solute mass concentration of 13%, add sodium dodecyl sulfate accounting for 1.3% of the total mass of the mixed solution as a template agent, and stir until completely dissolved; transfer the mixed solution into a hydrothermal reaction kettle, react at 150℃ for 9h, naturally cool to room temperature, filter to obtain a precipitate, wash with deionized water and anhydrous ethanol alternately for 3 times, and then dry at 90℃ for 9h to obtain the porous calcium borate.

[0067] The mass ratio of Bacillus subtilis, Lactobacillus plantarum, Pseudomonas aeruginosa and Trichoderma harzianum in the microbial agent is 2.5:1.5:1.5:2.5.

[0068] The total effective viable bacteria number of the microbial agent is >10 7 CFU / g.

[0069] The plant-based polyol is a mixture of soybean oil polyol and castor oil polyol in a mass ratio of 1:1.

[0070] The adhesive is a mixture of sodium carboxymethyl cellulose and starch in a mass ratio of 1:1.

[0071] The inlet air temperature of the fluidized bed coating machine is 50℃, the material temperature is 40℃, and the atomization pressure is 0.4MPa.

[0072] Comparative Example 1:

[0073] In this comparative example, the traditional petrochemical-based polyurethane coating material is used instead of the bio-based polyurethane prepolymer, specifically, in step S2, the plant-based polyol is replaced with an equal molar polyoxypropylene glycol with a molecular weight of 2000, and the other conditions are the same as in Example 3.

[0074] Comparative Example 2:

[0075] In this comparative example, no porous calcium borate is added in step S4, only the siloxane-modified cardanol chain extender monomer is used to react with the bio-based polyurethane prepolymer, and the other conditions are the same as in Example 3.

[0076] Comparative Example 3:

[0077] In this comparative example, the unmodified cardanol chain extender is used instead of the siloxane-modified cardanol chain extender monomer, specifically, in step S3, the cardanol glycidyl ether (which does not contain a siloxane structure in the chain extender) prepared by directly reacting cardanol with epichlorohydrin is used, and the other conditions are the same as in Example 3.

[0078] Result analysis

[0079] According to GB / T 23348-2009 "Slow-release fertilizer Determination of nutrient release rate", the nutrient slow-release performance test is carried out by using a constant-temperature soaking device and a UV-visible spectrophotometer, and the specific steps are as follows: 5.00g of sample is placed in a 100-mesh nylon mesh bag, soaked in 500mL of deionized water, and placed in a constant-temperature condition of 25℃, and samples are taken on the 1st, 3rd, 7th, 14th, 28th and 56th day, respectively, and the nutrient release rate is calculated, and the total nitrogen release rate is used as an indicator, and the results are shown in Figure 1 .

[0080] Figure 1The nitrogen release rates of Examples 1-3 were slow and stable, with a cumulative release rate of 76-80% over 56 days, meeting the slow-release requirements. This indicates that the film layer effectively controls nutrient release and matches the crop nutrient requirements, reducing nutrient loss.

[0081] According to GB / T 20291-2006 "Determination of Effective Living Bacteria in Microbial Fertilizer", the microbial survival rate test was carried out, and the specific steps were as follows: 1.00 g of each sample of the examples and the comparative examples was placed in a constant temperature and humidity incubator, and the conditions were set as follows: temperature 40±2℃, relative humidity 80±5%. On the 60th day, the effective living bacteria number of each sample was determined, and the microbial survival rate was calculated, and the results are shown in Table 4. Figure 2 .

[0082] Figure 2 The microbial survival rate of Examples 1-3 was higher, which was due to the effective protection of the film layer. The film layer shields the external adverse factors and provides a stable microenvironment for the microorganisms, thereby improving the survival rate of the microbial agent during storage and after application.

[0083] According to GB / T 10516-2013 "Determination of Particle Crushing Strength of Nitric Acid Phosphate Fertilizer", the mechanical strength of the film layer was tested by a particle strength tester, and the specific steps were as follows: 50 particles prepared in each example and the comparative example were randomly selected, and the pressure was applied on the instrument until it was broken, and the breaking force was recorded and the average value was calculated, and the results are shown in Table 5. Figure 3 .

[0084] Figure 3 The mechanical strength of Examples 1-3 was higher, because the siloxane groups in the siloxane-modified cardanol chain extender formed a cross-linked structure with the polyurethane network, enhancing the toughness and durability of the film layer; at the same time, the porous calcium borate as a cross-linking point further optimized the structure of the film layer.

[0085] The fertilizer efficiency test was carried out according to the following pot experiment, and the specific steps were as follows: corn seeds were cultivated by sand culture, and when the seedlings grew to the three-leaf-one-heart stage, seedlings with uniform height, healthy growth and no pests and diseases were selected. Ensure that the initial height of the selected seedlings is concentrated in the range of 15±2 cm, and there is no obvious difference in height, stem diameter and other traits. The selected seedlings were transplanted into pots containing an equal amount of base soil, and the initial height, biomass and chlorophyll relative content of each seedling were measured and recorded. The plants were randomly divided into several groups, including the example group, the comparative example group and the blank control group, and each group was set with not less than 3 times of repetition, and the treatment group was applied with 5.00 g of sample per pot, and the control group was not applied. All the pots were placed in an artificial climate chamber under the uniform conditions of 25℃ and 12h / d light, and the other management measures were completely consistent. After 60 days of cultivation, the height, biomass and chlorophyll content of each plant were measured again, and the growth rate of each index was calculated.

[0086] Table 1: Fertilizer efficiency test test result comparison table

[0087] Sample Straw height growth rate (%) Biomass growth rate (%) Chlorophyll growth rate (%) Example 1 34 39 22.5 Example 2 32 38 24.2 Example 3 35 40 25.2 Comparative Example 1 15 18 12 Comparative Example 2 20 25 18 Comparative Example 3 22 28 20 Blank control group 10 12 8

[0088] As can be seen from Table 1, the plant height growth rate, biomass growth rate and chlorophyll growth rate are significantly higher than the comparative example and the blank control group, indicating that the film coating layer of the application not only can release nutrients, but also can enhance soil fertility and plant stress resistance through the synergistic effect of microbial agents and trace elements, thereby improving the utilization rate of fertilizers.

[0089] Although embodiments of the application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the application, and the scope of the application is defined by the appended claims and their equivalents.

[0090] The above describes the application and its embodiments, which are not restrictive, and the embodiments shown in the drawings are only one of the embodiments of the application, and the actual application is not limited thereto. In summary, if a person skilled in the art is inspired by it, without departing from the purpose of the application, without creative design, similar ways and embodiments of the technical solution should belong to the protection scope of the application.

Claims

1. A method for preparing a slow-release coated microbial inoculant fertilizer, characterized by: Comprise the following steps: S1. Take raw materials by mass fraction: urea 50-80 parts, diatomite 10-20 parts, hydroxyapatite 5-15 parts, microbial inoculant 2-8 parts, adhesive 1-5 parts, potassium sulfate 5-15 parts, superphosphate 3-10 parts, calcium nitrate 2-6 parts, magnesium sulfate 1-4 parts, zinc sulfate 0.5-2 parts, wherein the microbial inoculant is composed of bacillus subtilis, lactobacillus plantarum, pseudomonas aeruginosa and trichoderma harzianum; the above raw materials are added into a double screw mixer, mixed at a speed of 300-500 rpm and a temperature of 25-40℃ for 20-40 min, and then transferred into a disc granulator for granulation, with the particle size controlled at 2-5 mm to obtain an internal core layer; S2. Put 1,5-pentane diisocyanate and plant-based polyol into a reaction kettle according to the NCO / OH molar ratio of 1.2-2.0:1, add 0.01-0.1% of dibutyltin dilaurate as a catalyst based on the total mass, and stir at 60-80℃ for 2-4 h under nitrogen protection to obtain a bio-based polyurethane prepolymer; S3. Mix 1,3-bis(ammonia propane alkyl) tetramethyl disiloxane and cardanol glycidyl ether according to the amino group to epoxy group molar ratio of 0.9-1.1:1, add ethyl acetate as a solvent, which is 3-5 times the total mass of the two raw materials, and stir at 50-70℃ for 3-5 h. After the reaction is completed, remove the ethyl acetate by distillation under reduced pressure to obtain a siloxane modified cardanol chain extender monomer; S4. Mix the siloxane modified cardanol chain extender monomer and porous calcium borate according to the mass ratio of 100:5-20, stir at a speed of 200-300 rpm for 30-60 min, then add the bio-based polyurethane prepolymer, control the molar ratio of NCO groups in the prepolymer to active hydrogen groups in the chain extender monomer at 1:0.8-1.2, and react at 40-60℃ for 1-2 h to obtain a coating liquid; S5. Place the internal core layer in a fluidized bed coating machine, spray the coating liquid on the surface of the internal core layer according to the amount of 5-15% of the mass of the internal core layer, and dry at 30-80℃ for 2-6 h after the spraying is completed to obtain the slow-release coated microbial inoculant fertilizer.

2. The method for preparing the slow-release coated microbial inoculant fertilizer according to claim 1, characterized in that: The porous calcium borate is prepared by the following steps: dissolving calcium nitrate and boric acid in deionized water according to the calcium to boron molar ratio of 1:2-4, preparing a mixed solution with a total solute mass concentration of 10-16%, adding 0.5-2% of sodium dodecyl sulfate as a template agent based on the total mass of the mixed solution, and stirring until completely dissolved; transfer the mixed solution into a hydrothermal reaction kettle, react at 120-180℃ for 6-12 h, naturally cool to room temperature, filter to obtain a precipitate, wash with deionized water and anhydrous ethanol alternately for 3 times, and then dry at 80-100℃ for 6-12 h to obtain porous calcium borate.

3. The method for preparing the slow-release coated microbial inoculant fertilizer according to claim 1, characterized in that: In the microbial inoculant, the mass ratio of bacillus subtilis, lactobacillus plantarum, pseudomonas aeruginosa and trichoderma harzianum is 2-3:1-2:1-2:2-3.

4. The method for preparing the slow-release coated microbial inoculant fertilizer according to claim 1, characterized in that: The total effective viable cell number of the microbial agent is >10 7 CFU / g.

5. The method for preparing the slow-release coated microbial inoculant fertilizer according to claim 1, characterized in that: The plant-based polyol is selected from at least one of soybean oil polyol and castor oil polyol.

6. The method for preparing the slow-release coated microbial inoculant fertilizer according to claim 1, characterized in that: The adhesive is selected from at least one of carboxymethyl cellulose sodium and starch.

7. The method for preparing the slow-release coated microbial inoculant fertilizer according to claim 1, characterized in that: The fluidized bed coating machine has an air inlet temperature of 40-60 DEG C, a material temperature of 30-50 DEG C, and an atomization pressure of 0.2-0.5 MPa.

8. A slow release encapsulated microbial inoculant fertilizer characterized by: The preparation method according to any one of claims 1-7.

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