Liquid vegetable oil film coated slow-release fertilizer and preparation method thereof

Abstract

The invention relates to the field of slow-release fertilizers, and discloses a liquid vegetable oil film coated slow-release fertilizer, which is prepared from the following raw materials in parts by mass: 50 to 70 parts of urea, 20 to 30 parts of diammonium phosphate, 10 to 20 parts of potassium sulfate, 10 to 15 parts of rapeseed oil, 1 to 3 parts of beewax, 0.5 to 1 part of food-grade lecithin, 5 to 10 parts of humic acid, 2 to 5 parts of seaweed extract, 0.5 to 2 parts of microbial agent, 0.01 to 0.1 part of plant growth regulator and 0.1 to 0.3 part of antioxidant. Through a coating system with natural components such as the rapeseed oil, the beewax and the lecithin as cores, full biodegradability of a fertilizer coating material is achieved, the problems of soil pollution and micro-plastic residues caused by traditional petroleum-based polymer coating are effectively solved, and the rapeseed oil serving as a main coating material can be decomposed into harmless substances by microorganisms in soil.

Description

Technical Field

[0001] The invention relates to the technical field of slow-release fertilizers, in particular to a slow-release fertilizer coated with a liquid vegetable oil film and a preparation method thereof. Background Art

[0002] In agricultural production, the rational application of fertilizers plays a vital role in ensuring crop growth and improving crop yield and quality. However, the current fertilizer application process faces severe challenges. On the one hand, with the increase in agricultural scale and intensification, the use of fertilizers has increased significantly. But at the same time, serious nutrient loss has become a prominent problem. Due to factors such as rainwater erosion and soil leaching, a large amount of nitrogen, phosphorus, potassium and other nutrients enter the surrounding water bodies or deep soil layers without being fully absorbed and utilized by crops, which not only causes a huge waste of resources and makes the actual utilization rate of fertilizers at a low level for a long time, but also causes a series of environmental problems, such as eutrophication of water bodies, excessive reproduction of algae, destruction of water ecological balance, and a threat to the sustainable development of the agricultural ecological environment.

[0003] In order to deal with the problem of fertilizer nutrient loss, traditional slow-release fertilizer technology came into being, among which solid polymer coating technology is the most widely used. However, this technology has many disadvantages. The solid polymer coating has poor biodegradability and is difficult to decompose naturally in the soil. Long-term accumulation will change the physical structure of the soil, affect the soil's air permeability and water permeability, and hinder the normal growth and respiration of crop roots. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a liquid plant oil film-coated slow-release fertilizer and a preparation method thereof, which solves the problem that the solid polymer coating technology in the traditional slow-release fertilizer technology has poor biodegradability, is difficult to decompose naturally in the soil, and long-term accumulation will change the physical structure of the soil, affect soil ventilation and permeability, and hinder the growth and respiration of crop roots.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A liquid vegetable oil film-coated slow-release fertilizer comprises the following raw materials, measured by weight: 50-70 parts of urea, 20-30 parts of diammonium phosphate, 10-20 parts of potassium sulfate, 10-15 parts of rapeseed oil, 1-3 parts of beeswax, 0.5-1 part of food-grade lecithin, 5-10 parts of humic acid, 2-5 parts of seaweed extract, 0.5-2 parts of microbial agent, 0.01-0.1 parts of plant growth regulator and 0.1-0.3 parts of antioxidant.

[0006] Preferably, the microbial agent is a phosphate-solubilizing bacteria, and the number of viable bacteria is ≥ 1×10 8 CFU / g.

[0007] Preferably, the plant growth regulator is indolebutyric acid.

[0008] Preferably, the particle sizes of the urea, diammonium phosphate, and potassium sulfate are all 2 - 4 mm.

[0009] Preferably, the antioxidant is vitamin E.

[0010] Preferably, a preparation method of a slow - release fertilizer coated with a liquid vegetable oil film comprises the following steps: S1. Pretreatment of the basic fertilizer: Mix and stir urea, diammonium phosphate, and potassium sulfate, perform surface treatment on the mixed particles to form an activation layer, and simultaneously crush humic acid to a suitable particle size. S2. Preparation of the coating solution: Add rapeseed oil to a reaction vessel, stir and heat up, add beeswax and lecithin in stages and control the temperature for stirring, then add seaweed extract and antioxidant and stir, and finally add microbial inoculum and plant growth regulator for dispersion treatment. S3. Composite coating process: Mix the pretreated basic fertilizer with humic acid, and perform multi - stage coating using a fluidized bed device. Different coating solutions are used in different stages, and secondary curing treatment is carried out after coating. S4. Post - treatment and environmental protection control: Adsorb the drying waste gas, and separate the finished product to control the particle size distribution.

[0011] Preferably, in the S1 step, a ribbon blender is used for stirring, the stirring speed is 120 - 180 revolutions per minute, the stirring time is 20 - 30 minutes, the plasma treatment power is 100 - 300 W, the treatment time is 30 - 60 seconds, argon is used as the working gas, the air pressure is controlled at 10 - 30 Pa, and the humic acid is crushed by a jet mill to a particle size ≤50 μm.

[0012] Preferably, in the S2 step, the reaction vessel is a jacketed reaction kettle, the stirring speed of rapeseed oil is 80 - 120 revolutions per minute, heat up to 60 - 70 °C, after adding beeswax, heat up to 75 - 85 °C and maintain for 30 - 40 minutes, when adding lecithin, the temperature drops to 50 - 60 °C and stir for 20 - 30 minutes, after adding seaweed extract and antioxidant, maintain the temperature at 40 - 50 °C and stir for 15 - 20 minutes, the frequency of the ultrasonic disperser is 20 - 40 kHz, the power density is 0.5 - 1.5 W / cm 2 , and the treatment time is 5 - 10 minutes.

[0013] Preferably, in the S3 step, the composite coating process specifically comprises the following steps: The first-stage coating: After mixing the pretreated basic fertilizer and humic acid in a mass ratio of 10:1 in a rotary drum mixer, it is fed into a fluidized bed device. The particles are fluidized at a fluidization wind speed of 2 - 3 m / s, and a coating liquid composed of rapeseed oil and beeswax is sprayed through a peristaltic pump connected to a fan-shaped nozzle. The temperature in the fluidized bed is controlled at 40 - 50 °C to achieve the construction of the nutrient-controlled release core layer; The second-stage coating: Maintain the operation of the fluidized bed device, switch to a coating liquid composed of lecithin and seaweed extract, adjust the fluidization wind speed to 1.5 - 2.5 m / s, and lower the temperature to 30 - 40 °C to form a biocompatible intermediate transition layer; The third-stage coating: Finally, spray a coating liquid composed of microbial inoculum and plant growth regulator, further lower the fluidization wind speed to 1 - 2 m / s, and maintain the temperature at 25 - 35 °C to construct a biologically active surface structure; Secondary curing: After the coating is completed, the fertilizer particles are placed in an environment with a humidity of 60 - 70% and a temperature of 45 - 55 °C and left standing for 4 - 6 hours, and an alternating electric field with an electric field strength of 5 - 10 kV / m and a frequency of 50 - 100 Hz is applied.

[0014] Preferably, in the step S4, the drying waste gas is treated by an activated carbon fiber adsorption device with an adsorption efficiency of ≥95%. The activated carbon fiber adsorption device is equipped with an on-line VOC detector, and when the adsorption capacity reaches 80%, the standby module is automatically switched. The finished product is separated by an air classifier, and the particle size distribution is controlled at 2.5 - 3.5 mm.

[0015] The present invention provides a slow-release fertilizer coated with a liquid vegetable oil film and its preparation method. It has the following beneficial effects: 1. The present invention realizes the full biodegradability of the fertilizer coating material through a coating system with natural components such as rapeseed oil, beeswax, and lecithin, effectively solving the soil pollution and microplastic residue problems brought by traditional petroleum-based polymer coatings. Rapeseed oil, as the main coating material, can be decomposed by microorganisms into harmless substances in the soil, and its degradation products can also provide organic matter for the soil. Beeswax avoids the risk of soil acidification caused by sulfur coating when adjusting the membrane permeability. It not only conforms to the development trend of green agriculture but also prolongs the storage stability through antioxidants, ensuring no secondary pollution during the production and use processes.

[0016] 2. The slow-release fertilizer of the present invention contains urea, diammonium phosphate, and potassium sulfate. The basic fertilizer provides the main nutrients of nitrogen, phosphorus, and potassium, and at the same time, various components such as humic acid, seaweed extract, and microbial inoculum are added. These components act synergistically to form a slow-release system, which can continuously and stably provide nutrients for plants, avoid the rapid loss and waste of nutrients, significantly prolong the fertilizer efficiency period, and improve the fertilizer utilization rate.

[0017] 3. Through the adjustment of beeswax dosage and the optimization of process parameters, the present invention can precisely control the fertilizer release rate and functional characteristics, thereby covering the full-scenario requirements from quick-acting to long-acting, and from field to protected agriculture.

[0018] 4. The present invention forms a gradient structure through multi-stage coating in a fluidized bed. The coating liquids and process parameters at different stages construct a nutrient-controlled release core layer, a biocompatible intermediate transition layer, and a bioactive surface layer, realizing the controllable release of nutrients. The secondary curing treatment makes the coating layer denser and harder, improving the integrity and uniformity of the coating.

[0019] 4. The present invention efficiently treats the drying exhaust gas through an activated carbon fiber adsorption device, and is equipped with an on-line VOC detector to ensure the continuous and stable operation of the exhaust gas treatment system, achieving zero environmental emissions. After being separated by an air classifier, the particle size of the finished product is precisely controlled, improving the product uniformity, making the fertilizer particles have better fluidity and more uniform application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic flow chart of a preparation method of a slow-release fertilizer coated with a liquid vegetable oil film according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] Please refer to the attached Figure 1 , an embodiment of the present invention provides a slow-release fertilizer coated with a liquid vegetable oil film, including raw materials of the following components, by mass: 50-70 parts of urea, 20-30 parts of diammonium phosphate, 10-20 parts of potassium sulfate, 10-15 parts of rapeseed oil, 1-3 parts of beeswax, 0.5-1 part of food-grade lecithin, 5-10 parts of humic acid, 2-5 parts of seaweed extract, 0.5-2 parts of microbial inoculum, 0.01-0.1 part of plant growth regulator, and 0.1-0.3 part of antioxidant.

[0023] Specifically, urea: provides nitrogen nutrition for plants, and after treatment, it can better combine with the coating to assist in the slow release of fertilizers.

[0024] Diammonium phosphate: can provide phosphorus and ammonium nitrogen, and can promote root development and improve the utilization rate of phosphate fertilizer in combination with humic acid.

[0025] Potassium sulfate: is a source of potassium, and cooperates with other basic fertilizers to build a stable fertilizer core.

[0026] Rapeseed oil: A natural vegetable oil used to form a coating film to delay nutrient release, environmentally friendly and biodegradable.

[0027] Beeswax: Can regulate the permeability of the coating film, cooperate with rapeseed oil to enhance the strength of the coating film, and make the slow-release effect of the fertilizer better.

[0028] Food-grade lecithin: As a surfactant, it promotes the uniform formation of the coating film and can also provide nutrients for microorganisms.

[0029] Humic acid: Can adsorb nutrients to form a slow-release environment, chelate metal ions and promote the proliferation of beneficial microorganisms.

[0030] Seaweed extract: Contains polysaccharides to enhance the flexibility of the coating film, and the natural plant growth regulators it contains can promote root development and improve the stress resistance of crops.

[0031] Phosphate-solubilizing bacteria agent: Can secrete organic acids to dissolve the insoluble phosphorus in the soil and cooperate with the coating film to delay nutrient release.

[0032] Indolebutyric acid: A plant growth regulator that can promote root growth and enhance the fertilizer efficiency together with the bacteria agent.

[0033] Vitamin E: As an antioxidant, it inhibits the oxidative rancidity of rapeseed oil and ensures the storage stability of the fertilizer.

[0034] The microbial bacteria agent is phosphate-solubilizing bacteria, and the viable bacteria count ≥ 1×10 8 CFU / g; the plant growth regulator is indolebutyric acid; the particle sizes of urea, diammonium phosphate and potassium sulfate are all 2 - 4 mm; the antioxidant is vitamin E.

[0035] Specifically, the phosphate-solubilizing bacteria are used to decompose soil phosphorus for plant absorption and promote root development, indolebutyric acid is used to regulate plant growth and enhance the nutrient absorption capacity, the 2 - 4 mm urea, diammonium phosphate and potassium sulfate particles are used to cooperate with the coating film process to achieve nutrient slow release, and vitamin E is used to ensure the stability of the coating material and extend the fertilizer efficiency period.

[0036] A preparation method of a slow-release fertilizer coated with a liquid vegetable oil film includes the following steps: S1. Pretreatment of basic fertilizer: Mix and stir urea, diammonium phosphate and potassium sulfate, perform surface treatment on the mixed particles to form an activation layer, and at the same time crush humic acid to a suitable particle size; S2. Preparation of coating liquid: Add rapeseed oil to the reaction vessel and stir to heat up, add beeswax and lecithin in stages and control the temperature to stir, then add seaweed extract and antioxidant and stir, and finally add the microbial bacteria agent and plant growth regulator for dispersion treatment; S3. Composite coating process: Mix the pretreated basic fertilizer with humic acid, and perform multi-stage coating using a fluidized bed device. Different coating liquids are used in different stages, and secondary curing treatment is carried out after coating. S4. Post-treatment and environmental protection control: Adsorb the drying waste gas, and separate the finished products to control the particle size distribution.

[0037] Specifically, the basic fertilizer pretreatment step is used to mix nitrogen, phosphorus, and potassium fertilizers and perform surface activation treatment, while crushing humic acid to improve the slow-release performance; the coating liquid preparation step is used to mix natural materials such as rapeseed oil, beeswax, and lecithin and synergistic components in stages to form a stable emulsion system; the composite coating process step is used to form a gradient structure through multi-stage fluidized bed coating and perform secondary curing to achieve controllable nutrient release; the post-treatment and environmental protection control step is used for waste gas purification and particle size grading to ensure environmental compliance and improve the uniformity of the finished products.

[0038] In step S1, a spiral ribbon mixer is used for stirring, the stirring speed is 120 - 180 revolutions per minute, the stirring time is 20 - 30 minutes, the plasma treatment power is 100 - 300 W, the treatment time is 30 - 60 seconds, argon is used as the working gas, the air pressure is controlled at 10 - 30 Pa, and the humic acid is crushed by a jet mill to a particle size ≤ 50 μm.

[0039] Specifically, using a spiral ribbon mixer to stir at a speed of 120 - 180 revolutions per minute for 20 - 30 minutes can fully mix urea, diammonium phosphate, and potassium sulfate, ensuring uniform nutrient distribution in the basic fertilizer. Then, using a plasma with a power of 100 - 300 W, with argon as the working gas, treating the mixed particles at an air pressure of 10 - 30 Pa for 30 - 60 seconds can form a hydrophilic activation layer on the particle surface, enhancing the binding force with the subsequent coating materials. At the same time, crushing the humic acid to a particle size ≤ 50 μm by a jet mill greatly increases its specific surface area, enabling it to better adsorb on the surface of fertilizer particles to optimize the nutrient slow-release microenvironment, and can also effectively improve the soil's fertilizer and water retention capacity, comprehensively enhancing the quality and effect of the fertilizer.

[0040] In step S2, the reaction vessel is a jacketed reactor, the stirring speed of rapeseed oil is 80 - 120 revolutions per minute, the temperature is raised to 60 - 70 °C, after adding beeswax, the temperature is raised to 75 - 85 °C and maintained for 30 - 40 minutes, when adding lecithin, the temperature is lowered to 50 - 60 °C and stirred for 20 - 30 minutes, after adding seaweed extract and antioxidant, the temperature is maintained at 40 - 50 °C and stirred for 15 - 20 minutes, the frequency of the ultrasonic disperser is 20 - 40 kHz, and the power density is 0.5 - 1.5 W / cm 2 , and the treatment time is 5 - 10 minutes.

[0041] Specifically, a jacketed reactor is selected as the reaction vessel to provide a stable environment for the reaction. Rapeseed oil is stirred at 80 - 120 revolutions per minute and heated to 60 - 70 °C to prepare for the subsequent component mixing; after adding beeswax, it is heated to 75 - 85 °C and maintained for 30 - 40 minutes to promote the full fusion of beeswax and rapeseed oil; when adding lecithin, the temperature is lowered to 50 - 60 °C and stirred for 20 - 30 minutes to ensure the uniform dispersion of lecithin. After adding seaweed extract and antioxidant, it is stirred at 40 - 50 °C for 15 - 20 minutes to promote the full mixing of each component. Finally, it is treated with an ultrasonic disperser with a frequency of 20 - 40 kHz and a power density of 0.5 - 1.5 W / cm 2 for 5 - 10 minutes to further refine and homogenize each component, form a stable and excellent - performance system for the coating liquid, ensure the smooth progress of the subsequent coating process and the coating quality, and enhance the comprehensive performance of the slow - release fertilizer.

[0042] In step S3, the composite coating process specifically includes the following steps: The first - stage coating: After mixing the pretreated basic fertilizer and humic acid in a mass ratio of 10:1 in a drum mixer, it is fed into a fluidized - bed device. The particles are fluidized at a fluidization air velocity of 2 - 3 m / s, and the coating liquid composed of rapeseed oil and beeswax is sprayed through a peristaltic pump connected to a fan - shaped nozzle. The temperature in the fluidized bed is controlled at 40 - 50 °C to realize the construction of the nutrient - controlled - release core layer; The second - stage coating: Maintain the operation of the fluidized - bed device, switch to the coating liquid composed of lecithin and seaweed extract, adjust the fluidization air velocity to 1.5 - 2.5 m / s, and lower the temperature to 30 - 40 °C to form a biocompatible intermediate transition layer; The third - stage coating: Finally, spray the coating liquid composed of microbial inoculum and plant growth regulator, further lower the fluidization air velocity to 1 - 2 m / s, and maintain the temperature at 25 - 35 °C to construct a biologically active surface structure; Secondary curing: After the coating is completed, the fertilizer particles are placed in an environment with a humidity of 60 - 70% and a temperature of 45 - 55 °C and left standing for 4 - 6 hours, and an alternating electric field with an electric - field intensity of 5 - 10 kV / m and a frequency of 50 - 100 Hz is applied.

[0043] Specifically, first, the pre-treated basic fertilizer and humic acid are fully mixed in a drum mixer at a mass ratio of 10:1 and then fed into a fluidized bed device. The particles are in a good fluidized state at a fluidization wind speed of 2 - 3 m / s. Meanwhile, at a temperature of 40 - 50 °C, a coating liquid composed of rapeseed oil and beeswax is sprayed through a peristaltic pump connected to a fan-shaped nozzle to construct a nutrient-controlled release core layer. The coating formed by rapeseed oil and beeswax has a certain density, which can effectively slow down the release rate of fertilizer nutrients, enabling the fertilizer to continuously and stably supply nutrients to plants in the soil, avoiding the rapid loss and waste of nutrients, and significantly extending the fertilizer efficiency period. In addition, the construction of this core layer can also improve the anti-leaching ability of the fertilizer, reduce nutrient loss caused by factors such as rain erosion, and improve the utilization rate of the fertilizer.

[0044] Next, the operation of the fluidized bed device is maintained, and the coating liquid composed of lecithin and seaweed extract is switched. At this time, the fluidization wind speed is adjusted to 1.5 - 2.5 m / s, and the temperature is lowered to 30 - 40 °C to form a biocompatible intermediate transition layer. Lecithin has good emulsifying and dispersing properties, which can evenly distribute the seaweed extract in the coating. The seaweed extract is rich in various nutrients and bioactive components required for plant growth, such as amino acids, vitamins, and plant hormones. This intermediate transition layer can not only enhance the binding force between the coating and the fertilizer particles and the subsequent surface layer, making the entire coating structure more stable, but also provide a relatively mild and friendly microenvironment for plant roots, promoting the growth and development of plant roots and improving the plant's ability to absorb nutrients. At the same time, the seaweed extract also has a certain role in regulating stress resistance, helping plants better cope with adverse environments such as drought and salinity.

[0045] Finally, a coating liquid composed of microbial inoculum and plant growth regulator is sprayed. At this time, the fluidization wind speed is further reduced to 1 - 2 m / s, and the temperature is maintained at 25 - 35 °C to construct a biologically active surface structure. The beneficial microorganisms in the microbial inoculum can colonize and reproduce in the soil, form a symbiotic relationship with plant roots, and participate in the transformation and cycling process of nutrients in the soil. For example, phosphate-solubilizing bacteria can convert insoluble phosphorus in the soil into available phosphorus that plants can absorb, improving the availability of soil phosphorus; nitrogen-fixing bacteria can fix nitrogen in the air and provide an additional nitrogen source for plants.

[0046] After film coating is completed, the fertilizer granules are placed in an environment with a humidity of 60 - 70% and a temperature of 45 - 55°C and left standing for 4 - 6 hours, and an alternating electric field with an electric field intensity of 5 - 10 kV / m and a frequency of 50 - 100 Hz is applied for secondary curing. Under such specific temperature, humidity and electric field conditions, further cross-linking and polymerization reactions will occur between the molecules in the film coating material, making the film coating layer denser and harder, enhancing the mechanical strength and wear resistance of the film coating. At the same time, the action of the electric field can also promote the combination of the film coating material and the surface of the fertilizer granules, improving the integrity and uniformity of the film coating.

[0047] In step S4, the drying waste gas is treated by an activated carbon fiber adsorption device with an adsorption efficiency ≥ 95%. The activated carbon fiber adsorption device is equipped with an on-line VOC detector. When the adsorption capacity reaches 80%, the standby module is automatically switched. The finished product is separated by an air classifier, and the particle size distribution is controlled within 2.5 - 3.5 mm.

[0048] Specifically, the drying waste gas is treated by an activated carbon fiber adsorption device to achieve deep purification of pollutants such as VOCs through a high adsorption rate of ≥ 95%. The equipped on-line VOC detector monitors the adsorption status in real time. When the adsorption capacity reaches 80%, the standby module is automatically switched to ensure the continuous and stable operation of the waste gas treatment system, effectively avoiding production interruption and achieving zero environmental emissions. After the finished product is separated by an air classifier, the particle size is accurately controlled within 2.5 - 3.5 mm, significantly improving the product uniformity, making the fertilizer granules have better fluidity and more uniform application.

[0049] The following is an introduction in combination with specific embodiments: Example 1 Raw material ratio: 60 parts of urea, 25 parts of diammonium phosphate, 15 parts of potassium sulfate 12 parts of rapeseed oil, 2 parts of beeswax, 0.8 part of lecithin 8 parts of humic acid, 3 parts of seaweed extract Microbial inoculant (phosphate-solubilizing bacteria, 1×10 8 CFU / g) 1 part Plant growth regulator (indolebutyric acid) 0.05 part Antioxidant (vitamin E) 0.2 part Preparation process: Pretreatment of basic fertilizer: Stir with a spiral ribbon mixer at 150 revolutions per minute for 25 minutes, plasma treatment (200 W, argon, 20 Pa) for 45 seconds, and crush humic acid to 30 μm.

[0050] Coating liquid preparation: Rapeseed oil is heated to 65°C at 100 revolutions per minute, and after adding beeswax, it is heated to 80°C and maintained for 35 minutes. Lecithin is stirred for 25 minutes at 55°C, and seaweed extract + vitamin E is stirred for 18 minutes at 45°C. Ultrasonic dispersion (30 kHz, 1 W / cm 2 ) for 8 minutes.

[0051] Compound coating: First stage: Fluidization air velocity is 2.5 m / s, temperature is 45°C, rapeseed oil + beeswax coating; Second stage: Fluidization air velocity is 2 m / s, temperature is 35°C, lecithin + seaweed extract coating; Third stage: Fluidization air velocity is 1.5 m / s, temperature is 30°C, microbial inoculant + indolebutyric acid coating; Secondary curing: Static for 5 hours at humidity of 65% and temperature of 50°C, alternating electric field (8 kV / m, 75 Hz); Post-treatment: Activated carbon fiber adsorbs VOC (efficiency 97%), and the finished product particle size is 3.0 ± 0.2 mm.

[0052] Example 2 The difference between this example and Example 1 above is that: 70 parts of urea, 20 parts of diammonium phosphate, 10 parts of potassium sulfate 15 parts of rapeseed oil, 3 parts of beeswax, 10 parts of humic acid Plasma treatment power is 300 W; The beeswax stage of the coating liquid is heated to 85°C; The electric field strength for secondary curing is 10 kV / m.

[0053] Example 3 The difference between this example and Example 1 above is that: 50 parts of urea, 30 parts of diammonium phosphate, 20 parts of potassium sulfate; 10 parts of rapeseed oil, 1 part of beeswax; 5 parts of humic acid, 5 parts of seaweed extract; Plasma treatment power is 100 W; The temperature of the beeswax stage of the coating liquid is 75°C; For secondary curing, the humidity is 60% and the temperature is 45°C.

[0054] Table 1 shows the comparison of the slow-release fertilizers in each example for agricultural requirements Extended description of key parameters Controlled release period: Example 1: Stable release is achieved through 2 parts of beeswax, adapting to the growth cycle of conventional crops; Example 2: By using 3 parts of beeswax + cross-linking with an enhanced electric field, the nutrient release rate is delayed; Example 3: By using 1 part of beeswax + highly active humic acid, the initial nutrient release is accelerated.

[0055] Among them, by adjusting the dosage of beeswax and optimizing the process parameters, the fertilizer release rate and functional characteristics can be precisely controlled, so as to cover the full-scenario requirements from quick-acting to long-acting, from field crops to protected agriculture.

[0056] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A slow-release fertilizer coated with a liquid vegetable oil film, characterized in that, Raw materials comprising the following components, by mass parts: 50 - 70 parts of urea, 20 - 30 parts of diammonium phosphate, 10 - 20 parts of potassium sulfate, 10 - 15 parts of rapeseed oil, 1 - 3 parts of beeswax, 0.5 - 1 part of food-grade lecithin, 5 - 10 parts of humic acid, 2 - 5 parts of seaweed extract, 0.5 - 2 parts of microbial inoculum, 0.01 - 0.1 part of plant growth regulator, 0.1 - 0.3 part of antioxidant.

2. The slow-release fertilizer coated with a liquid vegetable oil film according to claim 1, wherein, The microbial inoculant is phosphate-solubilizing bacteria, and the viable count ≥ 1×10 8 CFU / g.

3. The slow-release fertilizer coated with a liquid vegetable oil film according to claim 1, wherein, The plant growth regulator is indolebutyric acid.

4. The slow-release fertilizer coated with a liquid vegetable oil film according to claim 1, characterized in that, The particle sizes of the urea, diammonium phosphate and potassium sulfate are all 2 - 4 mm.

5. The slow-release fertilizer coated with a liquid vegetable oil film according to claim 1, characterized in that, The antioxidant is vitamin E.

6. A preparation method of a slow-release fertilizer coated with a liquid vegetable oil film, characterized in that, For a slow-release fertilizer coated with a liquid vegetable oil film according to any one of claims 1 - 5, it comprises the following steps: S1. Pretreatment of the basic fertilizer, mixing and stirring urea, diammonium phosphate and potassium sulfate, performing surface treatment on the mixed particles to form an activation layer, and at the same time crushing the humic acid to a suitable particle size; S2. Preparation of the coating solution, adding rapeseed oil to a reaction vessel, stirring and heating up, adding beeswax and lecithin in stages and controlling the temperature for stirring, then adding the seaweed extract and antioxidant for stirring, and finally adding the microbial inoculum and plant growth regulator for dispersion treatment; S3. Composite coating process, mixing the pretreated basic fertilizer with humic acid, performing multi-stage coating using a fluidized bed device, using different coating solutions at different stages, and performing secondary curing treatment after coating; S4. Post-treatment and environmental protection control, performing adsorption treatment on the drying exhaust gas, and separating the finished product to control the particle size distribution.

7. The preparation method of a slow-release fertilizer coated with a liquid vegetable oil film according to claim 6, characterized in that, In the S1 step, a ribbon blender is used for stirring, the stirring speed is 120 - 180 revolutions per minute, the stirring time is 20 - 30 minutes, the plasma treatment power is 100 - 300 W, the treatment time is 30 - 60 seconds, argon is used as the working gas, the air pressure is controlled at 10 - 30 Pa, and the humic acid is crushed by a jet mill to a particle size ≤ 50 μm.

8. The preparation method of a slow-release fertilizer coated with a liquid vegetable oil film according to claim 6, characterized in that, In the S2 step, the reaction vessel is a jacketed reaction kettle, the stirring speed of the rapeseed oil is 80 - 120 revolutions per minute, heating up to 60 - 70 °C, heating up to 75 - 85 °C after adding beeswax and maintaining for 30 - 40 minutes, the temperature drops to 50 - 60 °C when adding lecithin and stirring for 20 - 30 minutes, maintaining the temperature at 40 - 50 °C and stirring for 15 - 20 minutes after adding the seaweed extract and antioxidant, the frequency of the ultrasonic disperser is 20 - 40 kHz, the power density is 0.5 - 1.5 W / cm², and the treatment time is 5 - 10 minutes.

9. The preparation method of a slow-release fertilizer coated with a liquid vegetable oil film according to claim 6, characterized in that, In the S3 step, the composite coating process specifically comprises the following steps: First-stage coating, after mixing the pretreated basic fertilizer and humic acid in a mass ratio of 10:1 in a drum mixer, feeding them into a fluidized bed device, fluidizing the particles at a fluidization wind speed of 2 - 3 m / s, spraying the coating solution composed of rapeseed oil and beeswax through a peristaltic pump connected to a fan-shaped nozzle, and controlling the temperature in the fluidized bed at 40 - 50 °C to realize the construction of the nutrient-controlled release core layer; In the second stage, coating is carried out to maintain the operation of the fluidized bed device. The coating liquid composed of lecithin and seaweed extract is switched, the fluidization air velocity is adjusted to 1.5 - 2.5 m / s, and the temperature is reduced to 30 - 40 °C to form a biocompatible intermediate transition layer; In the third stage, coating is carried out and finally the coating liquid composed of microbial inoculum and plant growth regulator is sprayed. The fluidization air velocity is further reduced to 1 - 2 m / s, and the temperature is maintained at 25 - 35 °C to construct a biologically active surface structure; Secondary curing: After the coating is completed, the fertilizer particles are placed in an environment with a humidity of 60 - 70% and a temperature of 45 - 55 °C and left standing for 4 - 6 hours, and an alternating electric field with an electric field strength of 5 - 10 kV / m and a frequency of 50 - 100 Hz is applied.

10. The preparation method of a slow-release fertilizer coated with a liquid vegetable oil film according to claim 6, characterized in that, In the step S4, the drying waste gas is treated by an activated carbon fiber adsorption device with an adsorption efficiency ≥ 95%. The activated carbon fiber adsorption device is equipped with an on-line VOC detector, and when the adsorption capacity reaches 80%, the standby module is automatically switched. The finished product is separated by an air classifier, and the particle size distribution is controlled at 2.5 - 3.5 mm.

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