Coated fertilizer containing endophyte extract and preparation method thereof

Abstract

The invention discloses an endophyte extract-containing coated fertilizer and a preparation method thereof, the endophyte extract-containing coated fertilizer sequentially comprises a fertilizer, an inner membrane layer on the surface of the fertilizer and a slow-release outer membrane from inside to outside; and the inner membrane layer contains an endophyte extract. The preparation method of the coated fertilizer containing the endophyte extract comprises the following steps: step 1, preparing a polymer, step 2, adding the endophyte extract into the polymer, step 3, putting fertilizer particles into a coating machine, carrying out rotary preheating, adding the polymer containing the endophyte extract into the surface of the preheated fertilizer particles, and carrying out coating treatment to form an inner layer film; and adding a polyol substance and a polyisocyanate substance for reaction to form a slow-release outer membrane.

Description

Technical Field

[0001] The invention belongs to the technical field of coated fertilizers, and in particular relates to a coated fertilizer containing an endophyte extract and a preparation method thereof. Background Art

[0002] Coated fertilizer is a new type of slow-release fertilizer. It takes traditional chemical fertilizer particles as the core and covers the fertilizer surface with a layer of film material to regulate and control the release rate of fertilizer nutrients. It has the effect of improving fertilizer utilization, reducing environmental materials, and achieving long-term effectiveness of fertilizers.

[0003] The controlled release performance of coated fertilizers mainly depends on the film-forming materials, which include stepless coated fertilizers such as sulfur, mineral materials (montmorillonite, zeolite, attapulgite, diatomaceous earth, etc.), fertilizers (gypsum, phosphate, etc.) and biochar, as well as three types of organic polymer materials: natural polymers, organic synthetic polymers (petroleum-based polymers) and biomass-based polymer coating materials. Although inorganic coating materials have the characteristics of wide sources and low prices, due to the poor elasticity and brittleness of the membrane shell, the coated fertilizers mostly release nutrients through a "rupture mechanism", resulting in unsatisfactory controlled release effects.

[0004] Liu et al. developed bio-based elastic polyurethane coated urea fertilizer using waste palm oil. The swelling performance of the material was significantly improved by swelling modification of polyurethane with acrylonitrile, which reduced the nutrient release rate and increased the nutrient release cycle from 50 days to 80 days. Liu et al. used waste soybean oil as raw material, prepared soybean oil-based polyurethane by chemical synthesis technology, and modified soybean oil-based polyurethane with silicone, which greatly improved the hydrophobicity of the film material. When the silicone addition amount reached 20%, the release cycle of the coated fertilizer could reach 70 days, which not only improved the water resistance of the film material, but also extended the fertilizer effect period. Liang et al. prepared castor oil-based polyurethane coated fertilizer by adjusting the hydroxyl / isocyanate molar ratio, which increased the nutrient release life of the controlled-release fertilizer with a 5% coating rate from 20 days to 140 days. Xie et al. used cottonseed oil as raw material, increased the surface roughness of polyurethane and reduced the surface energy of the membrane material, and silanized the coating material, and finally successfully prepared super-hydrophobic bio-based polyurethane coated controlled-release fertilizer. The use of biomass materials from renewable resources as coating materials for controlled-release fertilizers has important practical significance for the research and development of low-cost, environmentally friendly coated controlled-release fertilizers.

[0005] It is generally believed that the release of nutrients is divided into two stages: the first stage is that the external water molecules penetrate into the core fertilizer through the membrane layer and dissolve, increasing the osmotic pressure inside the membrane shell; the second stage is that after the core fertilizer dissolves, the nutrients penetrate into the external environment through the membrane layer for crop absorption. If the membrane shell is brittle, the membrane shell is prone to cracks or ruptures due to increased internal pressure, and the nutrients are quickly released. This release is called the "rupture release mechanism". Therefore, the nutrient release characteristic curve of this type of coated fertilizer is an inverted "L" shape; on the contrary, if the membrane material has good toughness and can withstand the internal pressure, the fertilizer nutrients will be slowly released in a diffusion manner. This method is called the "diffusion mechanism". The nutrient release characteristic curve of this type of coated fertilizer is an "S" shape, which is more in line with the fertilizer requirement of crops.

[0006] Endophyte extract is a substance extracted from plant endophytes. It has multiple biological activities and plays an important role in promoting crop growth, improving crop stress resistance, improving soil properties, and increasing crop yield and quality.

[0007] The prior patent application "A functional controlled-release urea for wheat and its preparation method" (application number: CN202410193121.6) provides, from the inside to the outside, urea particles, a polyurethane film formed by wrapping vegetable oil polyols and isocyanate, a functional substance layer of sprayed endophytic bacteria extract, and a paraffin protective layer. This technology uses paraffin to wrap the functional substance and add it to the polyurethane film on the outer layer of the controlled-release urea, which can reduce the addition loss and the friction loss in the later transportation, and at the same time improve the controlled release effect. Compared with the method of applying the functional substance and urea separately, the controlled-release preparation made by this method can significantly increase wheat yield. However, since the outermost layer is a paraffin layer, paraffin has high requirements for coating technology and is temperature sensitive. If the sealing performance is not good, it will affect its hydrophobic effect and affect the sustained release effect of the functional substance. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a coated fertilizer containing endophytic extract and a preparation method thereof. The endophytic extract is wrapped on the surface of the fertilizer so that the endophytic extract can achieve the purpose of slow and controlled release. Therefore, after the coated fertilizer containing the endophytic extract is applied, it plays the role of promoting plant growth, regulating the amount of flowers and thinning flowers and fruits, rice seed production, preventing and controlling pests, and improving crop yield and quality.

[0009] In order to achieve the above technical objectives, the technical solution implemented by the present invention is:

[0010] As a first aspect of the present invention, there is provided a coated fertilizer containing an endophyte extract, which comprises, from the inside to the outside, a fertilizer, an inner film layer on the surface of the fertilizer, and a slow-release outer film; the inner film layer contains the endophyte extract. Preferably, the weight of the inner film layer accounts for 0.1-1% of the weight of the fertilizer particles, the weight of the slow-release outer film accounts for 1.5-5% of the weight of the fertilizer particles, and the weight of the paraffin layer accounts for 0.1-0.5% of the weight of the fertilizer particles.

[0011] As a second aspect of the present invention, there is provided a method for preparing the coated fertilizer containing the endophyte extract, comprising the following steps:

[0012] Step 1, preparation of polymer: taking 100 parts of water-soluble high molecular polymer by weight, putting it into 10-20 times the weight of water, adding 1-5 parts of glycerol, heating at 50-100° C. for 0.5-3h, and dropping 1-5 parts of polyethylene glycol during the heating process; after cooling to room temperature, adding 5-10 parts of glacial acetic acid and 5-10 parts of anhydrous ethanol, stirring until a viscous liquid is formed to form a polymer;

[0013] Step 2, adding the endophyte extract to the polymer, and mixing them evenly by stirring or other means;

[0014] Step 3, placing the fertilizer granules in a coating machine for rotation, preheating the fertilizer granules to 50-65°C, adding the polymer containing the endophyte extract to the surface of the preheated fertilizer granules for coating treatment to form an inner layer membrane; preheating the paraffin at 60-70°C until it melts, adding the melted paraffin to the fertilizer granules, stirring until uniform, and forming a paraffin layer on the surface of the fertilizer granules; maintaining the temperature at 50-65°C, and then adding polyol substances and polyisocyanate substances to react to form a sustained-release outer membrane.

[0015] Preferably, in step 1, the water-soluble high molecular polymer is selected from one or more mixtures of modified starch, modified cellulose, synthetic water-soluble high polymer, and condensation resin.

[0016] Preferably, in step 3, the fertilizer is selected from a compound fertilizer mixed with one or more components of urea, monoammonium, diammonium, potassium chloride, and potassium sulfate; and the particle size of the fertilizer is 2-5 mm.

[0017] Preferably, in step 1, the preparation of the polymer includes, by weight, taking 100 parts of a water-soluble high molecular polymer, putting it into 10-20 times the mass of water, adding 1-5 parts of glycerol, heating at 50-100° C. for 0.5-3 h, and adding 1-5 parts of polyethylene glycol dropwise during the heating process.

[0018] In step 1, glacial acetic acid provides an acidic environment for the reaction to occur, and anhydrous ethanol serves to increase the solubility of the endophytic bacteria extract in the polymer.

[0019] In step 3, the polymer is added to the surface of the coated fertilizer as a carrier of the endophytic bacteria extract, and the polyurethane film plays a role in slowly releasing the endophytic bacteria extract.

[0020] Endophytic extracts have beneficial functions such as promoting growth and increasing production, but endophytic extracts alone cannot be stably coated on the surface of fertilizers. Polymers are easily soluble in water and have good miscibility with endophytic extracts; polymers have strong adhesion and good film-forming properties, and can effectively adhere to the surface of fertilizers to form a gel coating system on the surface of fertilizers, stably coating endophytic extracts or other components. Therefore, the present invention uses polymers as a medium to coat the endophytic extracts on the surface of fertilizers. The present invention further coats the polymer inner film with a polyurethane outer film to form a water-retaining outer shell, increase the water resistance of the fertilizer, and extend the release period.

[0021] In step 3, polyols and polyisocyanates undergo condensation polymerization, and the polyisocyanate (-NCO) group has a highly unsaturated structure, which determines its high reactivity. When polyisocyanates react with polyols, the -NCO group reacts with the hydroxyl group (-OH) in the polyols to form an urethane bond (-NH-CO-O-), thereby generating a polyurethane material.

[0022] The reaction mechanism of polyisocyanate and polyol can be divided into the following steps:

[0023] (1) Addition reaction: The -N=C=O group in isocyanate reacts with the -OH group in polyol to form an intermediate.

[0024] (2) Rearrangement reaction: The generated intermediate will further undergo internal reaction and rearrange to form carbamate group. Due to the instability of the hydroxyl group on the double bond, this rearrangement process will generate a stable carbamate group, referred to as polyurethane.

[0025] The polyurethane material formed by the reaction of polyisocyanate and polyol has excellent mechanical strength. The film formed on the surface of fertilizer particles can effectively protect the fertilizer from the influence of the external environment, such as rain erosion and soil microbial erosion, which helps to maintain the integrity and stability of the fertilizer and ensure that it releases nutrients at the right time and place.

[0026] Preferably, in step 3, the heating temperature of the fertilizer particles is 50-65° C., and the speed of the coating machine is 20-50 Hz.

[0027] Preferably, in step 3, the weight of the inner film layer accounts for 0.1-1% of the weight of the fertilizer granules, the weight of the slow-release outer film accounts for 1.5-5% of the weight of the fertilizer granules, the coating times are 1-5 times, and the weight of the paraffin accounts for 0.1-0.5% of the weight of the fertilizer granules.

[0028] Preferably, the polyol material is selected from one or a mixture of oligomer polyols, polyether polyols, polyester polyols, bio-based curing agents or isomers thereof.

[0029] Preferably, the polyether polyol is selected from polyoxyethylene polyol, polyoxypropylene diol, polyoxypropylene triol, high-activity polyether triol, and polyether tetraol.

[0030] The polyisocyanate substance is selected from diisocyanate, triisocyanate or one or a mixture of isomers thereof.

[0031] Preferably, the polyisocyanate is selected from polymethylene polyphenyl polyisocyanate (PAPI).

[0032] Preferably, the mass ratio of the polyol substance to the polyisocyanate substance is 1-1.6:1.

[0033] The slow-release outer film is the outer layer, which accounts for 1.5-5% of the weight of the fertilizer particles. Specifically, as the film thickness increases, the release rate of nutrients in the coated fertilizer will decrease. This means that a thicker outer film can slow down the release of nutrients, thereby extending the effective period of the fertilizer and making it more in line with the crop demand curve. In practical applications, a variety of factors should be considered comprehensively to select the appropriate outer film thickness to ensure the best use of the fertilizer.

[0034] The average particle size of the fertilizer granules may be 2-5 mm, preferably 4-5 mm.

[0035] According to the reaction principle, the equivalent ratio of polyisocyanate to polyol should be 1:1. Considering the practical application:

[0036] (1) Excessive polyisocyanate: The resulting polymer usually has higher hardness and strength because the isocyanate groups can continue to react to form more cross-linked structures.

[0037] (2) Equal amounts of polyisocyanate and polyol: Theoretically, the molecular weight of the resulting polymer should be infinite, because each -NCO group can react with one -OH group. At this ratio, the resulting polymer has good elasticity and flexibility.

[0038] (3) Excessive polyols: The resulting polymer usually has lower hardness and strength because the hydroxyl groups do not continue to react. It is rarely used and is mainly used in the preparation of raw rubber, adhesives and certain intermediates that are easy to store.

[0039] If the endophyte extract is wrapped on the surface of the polyurethane outer film in the form of an outer membrane wrapping, since the endophyte extract is easily soluble in water, it will directly dissolve in water when directly exposed to the soil environment and will not have a sustained-release effect.

[0040] The present application adopts membrane wrapping to wrap the endophyte extract on the surface of the fertilizer particles, and then wraps the outside with a polyurethane outer film, which can extend the release period.

[0041] Endophyte extracts are slow-released, and can slowly release endophyte extracts according to the growth needs of crops, avoiding excess or insufficient nutrients caused by one-time application, which affects crop growth. Endophyte extracts continuously release nutrients over a long period of time, extend the fertilizer effect period, reduce nutrient leaching or volatilization, reduce fertilization times and labor costs, and improve agricultural production efficiency.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) In the present application, the endophytic bacteria extract is encapsulated on the surface of the fertilizer particles by a polymer, which is simple to operate, has little loss of the endophytic bacteria extract during the encapsulation process, and can achieve effective encapsulation.

[0044] (2) Wrapping the outside of the endophytic bacteria extract with a paraffin film and a polyurethane outer film can achieve a sustained-release effect of the endophytic bacteria extract and prolong the release period of the endophytic bacteria extract; the experimental results show that the coated fertilizer containing the endophytic bacteria extract prepared by the formula and process of the present invention can significantly improve the parameters such as the stem length, above-ground weight, and single-plant potato weight of sweet potatoes; controlling the release behavior of the endophytic bacteria extract has a significant effect on improving the coordination effect with the inner layer fertilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0046] Figure 1 This is a graph showing the nutrient release rate test results of Example 3.

[0047] Figure 2 This is a graph showing the release rate test results of the endophyte extract in Example 3. DETAILED DESCRIPTION

[0048] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0049] Embodiment 1,

[0050] Paecilomyces variotii SJ1 was deposited in the General Microbiology Center of China Culture Collection Administration (address: No. 3, Yard No. 1, Beichen West Road, Chaoyang District, Beijing) on ​​December 8, 2014, with the deposit number CGMCCNO.10114.

[0051] The method for culturing the Paecilomyces variotii SJ1 strain is as follows: inoculating the strain onto a PDA solid culture medium, culturing it in an incubator at 23-27°C for 6-8 days, transplanting it to a PDA liquid culture medium, culturing it on a rotary shaker at 23-27°C and 170-190 r / min for 3-5 days, fermenting it at 25-28°C and 150-170 r / min, centrifuging and filtering the fermentation liquid to obtain mycelium; washing the cultured mycelium, drying it at 60°C, weighing it, and then crushing it with a high-speed crusher, extracting it with the same volume of ethanol for 24 hours, extracting it three times, stirring and mixing it, ultrasonically vibrating it for 1 hour, vacuum filtering it, collecting the filtrate for later use, and the filtrate is the extract of the Paecilomyces variotii SJ1 strain.

[0052] Example 1.1: Preparation of polymer: 10g polyvinyl alcohol was added to 120g water, and 0.1g glycerol was added. The mixture was heated at 96°C for 1h. During the heating process, 0.2g polyethylene glycol was added dropwise. After cooling to room temperature, 0.5g glacial acetic acid and 0.5g anhydrous ethanol were added. The mixture was stirred until a viscous liquid was formed to form a polymer.

[0053] Preparation of the mixture of endophyte extract and polymer: According to the weight of fertilizer particles, the amount of endophyte extract added is 500 mg / kg, and the amount of polymer added is 10 g / kg, and the mixture is stirred and ultrasonicated to be uniformly mixed.

[0054] Preparation of membrane: Weigh 1kg of urea granules with a particle size of 4-5mm, place them in a coating machine for rotation and heating, preheat the urea granules to 50℃, spray 10g of polymer containing endophyte extract on the surface of urea granules three times, wait for the reaction to end after each spraying before spraying again to form an inner layer membrane. Preheat 1g of paraffin at 70℃ until it melts, add it to the urea granules, stir until uniform, and form a paraffin layer on the surface of urea granules. Keep the temperature of urea granules in the coating machine at 60℃, spray polyol (DH-16) and polymethylene polyphenyl polyisocyanate (PAPI) on the surface of urea granules three times in turn, wait for the reaction to end after each spraying before spraying again to finally form an outer layer membrane. The total mass of polyol and isocyanate is 25g, and the mass ratio is 1.2:1.

[0055] Example 1.2: Weigh 1kg of urea granules with a particle size of 4-5mm, place them in a coating machine for rotation and heating, preheat the urea granules to 50℃, spray the endophytic bacteria extract (addition amount 500mg / kg) on ​​the surface of the urea granules, and wait for the endophytic bacteria extract on the surface of the urea granules to dry. Preheat 1g of paraffin at 70℃ until it melts, add it to the urea granules, stir until uniform, and form a paraffin layer on the surface of the urea granules. Keep the temperature of the urea granules in the coating machine at 60℃, spray polyol (DH-16) and polymethylene polyphenyl polyisocyanate (PAPI) on the surface of the urea granules in three times, and spray the next time after the reaction is completed after each spraying, and finally form an outer film. The total mass of the polyol and isocyanate is 25g, and the mass ratio is 1.2:1.

[0056] Example 1.3: Weigh 1kg of urea granules with a particle size of 4-5mm, place them in a coating machine for rotation and heating, preheat the urea granules to 50℃, preheat 1g of paraffin at 60-70℃ until it melts, add it to the urea granules, stir until uniform, and form a paraffin layer on the surface of the fertilizer granules. Keep the temperature of the urea granules in the coating machine at 60℃, spray polyol (DH-16) and polymethylene polyphenyl polyisocyanate (PAPI) on the surface of the urea granules in three times, and wait for the reaction to end after each spraying before spraying the next time. Preheat the urea granules to 50℃, spray the endophytic bacteria extract (addition amount 500mg / kg) on ​​the surface of the preheated fertilizer granules, and wait for the endophytic bacteria extract on the surface of the urea granules to dry.

[0057] Example 2, Detection method of endophytic bacterial extract

[0058] After pretreatment, the coated urea particles were measured by high performance liquid chromatography (equipped with a fluorescence detector) and quantified by the external standard method.

[0059] Endophyte extract reference: lyophilized powder made by freeze-drying plant endophyte extract.

[0060] Preparation of stock solution: Accurately weigh the freeze-dried powder of endophyte extract and prepare the stock solution with 20% ethanol solution.

[0061] Preparation of standard working solution: Accurately transfer the stock solution into a 10 mL volumetric flask, dilute to the mark with methanol, mix well, and prepare the standard working solution.

[0062] Sample pretreatment: (1) Extraction: Take an appropriate amount of sample and crush it, accurately weigh 1g of the crushed sample into a 50mL centrifuge tube, add 10mL of water, vortex extract for 1min, heat in a water bath at 65℃ for 40min, collect the filtrate after filtration, add 10mL of water to the filter residue, rinse and filter, combine the two filtrates, and wait for purification. (2) Purification: Add 6mL of methanol and 6mL of water to the solid phase extraction column in sequence for activation. After activation, add the sample to be purified, and then add 6mL of water and 6mL of methanol for rinsing respectively. After the solid phase extraction column is blown dry, add 6mL of 5% ammoniated methanol for elution, and collect the eluate in a 10mL test tube, blow dry with nitrogen at 50℃, add 1mL of water, vortex mix for 1min, pass through a 0.22μm organic filter membrane, and wait for detection.

[0063] High performance liquid chromatography reference conditions: chromatographic column: COSMOSIL HILIC 4.6×250 mm, 5 μm (or chromatographic column with equivalent effect); flow rate: 1.0 mL / min; column temperature: 35°C; detection wavelength: excitation wavelength 251 nm, emission wavelength 464 nm; injection volume: 10 μL; mobile phase: 150 mM ammonium acetate solution: acetonitrile = 50:50.

[0064] Calculation of results: The content X of the endophyte extract is expressed in milligrams per kilogram (mg / kg). The results are calculated as follows:

[0065]

[0066] Where: X——the content of endophyte extract in the sample, in milligrams per kilogram (mg / kg);

[0067] A i ——Peak area of ​​characteristic peak of endophyte extract in the sample;

[0068] A s ——Peak area of ​​characteristic peaks of endophyte extract in working solution

[0069] c——Concentration of endophyte extract in working solution, in micrograms per milliliter (μg / mL);

[0070] V——the fixed volume of the sample, in milliliters (mL);

[0071] m – the mass of the sample, in grams (g).

[0072] The calculation result is retained to two decimal places, and the arithmetic mean of the parallel measurement results is taken as the measurement result.

[0073] When the amount of endophyte extract added was 500 mg / kg, the actual results are shown in Table 1:

[0074] Table 1 Results of determination of endophytic bacterial extracts

[0075] Content (mg / kg) 1 2 3 4 5 Example 1.1 492.87 488.40 489.01 487.98 487.72 Example 1.2 166.54 223.06 141.87 259.03 199.36 Example 1.3 80.71 61.03 95.99 51.52 132.83

[0076] The actual detection content of endophyte extracts shows that the polymer prepared in the present invention can wrap endophyte extracts on the surface of fertilizers, and the recovery rate of endophyte extracts is above 97.54%. The recovery rates of endophyte extracts added directly into and outside the polyurethane film are 28.34%-51.81% and 10.30%-26.57%.

[0077] Example 3, nutrient release rate detection method

[0078] The controlled release performance test of the coated controlled release fertilizer adopts the 25°C constant temperature static water culture method. Weigh 12.5g of the sample prepared in Example 1 and put it into a 100-mesh nylon bag, seal it and put it into a plastic container filled with 250mL of distilled water, seal it and put it into a 25°C constant temperature incubator. Urea is determined by the refractive index method to detect the nutrient content in the coated urea culture solution on the 1st, 3rd, 5th, 7th, 10th, 14th, 28th, 42nd, 56th and 60th days. The endophytic extract is determined by the liquid phase method to detect the endophytic extract content in the coated urea culture solution on the 1st, 7th, 14th, 28th, 42nd, 56th and 60th days, and the cumulative nutrient release rate is calculated.

[0079] Initial dissolution rate (%) = cumulative amount of nutrients dissolved in 24 hours / content of the nutrient in the sample × 100.

[0080] Cumulative nutrient release rate: It is expressed as the mass fraction of the sum of the nutrient release amounts in each continuous period within a certain period of time in still water at 25°C to the total amount of the nutrient.

[0081] Nutrient release period: The time required from the start of slow-release nutrient extraction in 25°C still water to the reaching of 80% cumulative nutrient release rate.

[0082] The coated urea containing endophyte extract was determined by 25℃ constant temperature static water culture method. The urea results are as follows Figure 1 As shown, there is no significant difference in the effect of the three treatments on the polyurethane coating in Example 1, and the nutrient release period is about 56 days.

[0083] The results of endophyte extracts were as follows Figure 2 As shown, in Example 1.1, the endophyte extract was added to the polymer and then added to the polyurethane film, and the release period of the endophyte extract was 56 days. In Example 1.2, the endophyte extract was directly added to the polyurethane film, and the release period of the endophyte extract was about 28 days. In Example 1.3, the endophyte extract was added outside the polyurethane film, and the endophyte extract was quickly released in water, and the release period was about 1 day.

[0084] Nutrient release period: The time required from the start of slow-release nutrient extraction in 25°C still water to the reaching of 80% cumulative nutrient release rate.

[0085] Embodiment 4,

[0086] Six treatments were set up, namely blank, urea, polyurethane-coated urea, the coated fertilizer containing endophyte extract in Example 1.1 of the present invention, the coated fertilizer containing endophyte extract inside the membrane in Example 1.2 of the present invention, and the coated fertilizer containing endophyte extract outside the membrane in Example 1.3 of the present invention.

[0087] The study was conducted to investigate the effects on sweet potato growth indices such as stem length, aboveground weight, potato weight, and fruit number.

[0088] Table 1: Sweet potato stem length, aboveground weight, potato weight, and fruit number in Experimental Example 5

[0089] Stem length (cm) Weight on the ground (kg) Single potato weight (g) Number of fruits blank 3.69±0.51 4.67±1.36 426.67±38.21 3.00±1.03 Urea 4.83±0.73 5.11±1.08 483.33±59.54 3.44±0.89 Polyurethane coated urea 6.00±1.01 5.56±1.27 651.67±89.42 3.00±1.18 Example 1.1 6.59±0.89 7.00±0.50 867.22±36.38 3.44±1.05 Example 1.2 6.29±0.49 6.56±1.53 652.78±42.43 3.00±0.78 Example 1.3 6.15±1.23 6.67±1.80 636.11±50.24 2.75±0.54

[0090] The coated fertilizer containing endophyte extract in Example 1.1 of the present invention has excellent performance on the stem length, aboveground weight and single-plant weight of sweet potatoes. It can be seen that controlling the release behavior of endophyte extract has a significant effect on improving the coordination effect with the inner layer fertilizer.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A coated fertilizer containing an endophyte extract, characterized in that: It comprises fertilizer, an inner film layer on the surface of the fertilizer, and a slow-release outer film in order from the inside to the outside; the inner film layer comprises an endophyte extract; The weight of the inner film layer accounts for 0.1-1% of the weight of the fertilizer particles, the weight of the slow-release outer film accounts for 1.5-5% of the weight of the fertilizer particles, and the weight of the paraffin layer accounts for 0.1-0.5% of the weight of the fertilizer particles.

2. A method for preparing a coated fertilizer containing an endophyte extract, characterized in that: The steps include: Step 1, preparation of polymer: taking 100 parts of water-soluble high molecular polymer by weight, putting it into 10-20 times the weight of water, adding 1-5 parts of glycerol, heating at 50-100° C. for 0.5-3h, and dropping 1-5 parts of polyethylene glycol during the heating process; after cooling to room temperature, adding 5-10 parts of glacial acetic acid and 5-10 parts of anhydrous ethanol, stirring until a viscous liquid is formed to form a polymer; Step 2, adding the endophyte extract to the polymer and mixing them evenly; Step 3, placing the fertilizer granules in a coating machine for rotation, preheating the fertilizer granules to 50-65°C, adding the polymer containing the endophyte extract to the surface of the preheated fertilizer granules for coating treatment to form an inner layer membrane; preheating the paraffin at 60-70°C until it melts, adding the melted paraffin to the fertilizer granules, stirring until uniform, and forming a paraffin layer on the surface of the fertilizer granules; maintaining the temperature at 50-65°C, and then adding polyol substances and polyisocyanate substances to react to form a sustained-release outer membrane.

3. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: In step 1, the water-soluble high molecular polymer is selected from one or more mixtures of modified starch, modified cellulose, synthetic water-soluble high polymer, and condensation resin.

4. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: In step 3, the fertilizer is selected from a compound fertilizer mixed with one or more components of urea, monoammonium, diammonium, potassium chloride, and potassium sulfate; the particle size of the fertilizer is 2-5 mm.

5. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: In step 1, the preparation of the polymer includes, by weight, taking 100 parts of a water-soluble high molecular polymer, putting it into 10-20 times the mass of water, adding 1-5 parts of glycerol, heating at 50-100° C. for 0.5-3 h, and dropping 1-5 parts of polyethylene glycol during the heating process.

6. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: In step 3, the fertilizer granules are heated to a temperature of 50-65° C. and the coating machine rotates at a speed of 20-50 Hz.

7. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: The polyol substance is selected from one or a mixture of oligomer polyols, polyether polyols, polyester polyols, bio-based curing agents or isomers thereof; The polyether polyol is selected from polyoxyethylene polyol, polyoxypropylene diol, polyoxypropylene triol, high-activity polyether triol or polyether tetraol.

8. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: The polyisocyanate substance is selected from diisocyanate, triisocyanate or one or a mixture of isomers thereof.

9. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: The polyisocyanate is polymethylene polyphenyl polyisocyanate.

10. The method for preparing the coated fertilizer containing endophyte extract according to claim 2, characterized in that: The mass ratio of polyol substances to polyisocyanate substances is 1-1.6:1.

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