High utilization rate organic nitrogen fertilizer and preparation method thereof

Abstract

The application relates to the technical field of organic nitrogen fertilizer, and discloses a high-utilization organic nitrogen fertilizer and a preparation method thereof. The organic nitrogen fertilizer comprises core fertilizer particles and a coating layer, the coating layer is prepared from a coating liquid, and the core fertilizer particles comprise 40-50 parts of high-nitrogen organic raw material, 8-12 parts of a phosphorus source, 5-10 parts of a potassium source, 3-5 parts of a water-retaining agent and 2-5 parts of a binder. The obtained organic nitrogen fertilizer comprises core fertilizer particles and a coating layer. The nitrogen is slowly and stably released according to the crop demand through the coating layer, nitrogen loss and volatilization are significantly reduced, and the nitrogen utilization rate is improved. In addition, the core fertilizer is prepared by compounding the high-nitrogen organic raw material and the inorganic phosphorus and potassium source, organic and inorganic cooperation is realized, nutrients are comprehensive and release is coordinated, and the nutrient demand of crops in the whole growth period is met.

Description

Technical Field

[0001] This invention relates to the field of organic nitrogen fertilizer technology, and more specifically, to a highly efficient organic nitrogen fertilizer and its preparation method. Background Technology

[0002] Nitrogen is a key nutrient element essential for crop growth. Although traditional chemical nitrogen fertilizers (such as urea) can quickly replenish nitrogen, their utilization rate is generally low (usually only 30%-50%). Most nitrogen is lost through ammonia volatilization, nitrification-denitrification, and leaching, which not only wastes resources and increases production costs, but also leads to a series of environmental problems such as soil acidification, water eutrophication, and greenhouse gas emissions.

[0003] Organic nitrogen fertilizers (such as livestock and poultry manure and oilseed cake) are valued for their comprehensive nutrients and soil-improving properties. However, they generally suffer from unstable nitrogen release, mineralization rates highly dependent on environmental factors, and low readily available nitrogen content, making it difficult to meet the concentrated nitrogen requirements of crops during critical growth stages. Current technologies often employ physical or chemical methods to prepare slow-release nitrogen fertilizers to improve utilization, but most are still based on synthetic polymer coatings (such as polyolefins), which pose risks of high cost, poor degradation, and secondary pollution. Other technologies attempt to simply mix organic fertilizers with microbial agents, but in complex field environments, the colonization of functional microbial communities is difficult, their activity is not long-lasting, and the synergistic effect is unstable.

[0004] Therefore, providing an organic nitrogen fertilizer that can achieve slow, on-demand nitrogen release and promote nutrient absorption and soil health through biological processes, as well as its preparation method, is of great practical significance. Summary of the Invention

[0005] In view of this, the present invention proposes a highly efficient organic nitrogen fertilizer and its preparation method, aiming to solve at least one of the problems in the current background technology.

[0006] This invention proposes a high-utilization organic nitrogen fertilizer, which includes core fertilizer particles and a coating layer; The coating layer is prepared from a coating liquid; The core fertilizer granules consist of 40-50 parts of high-nitrogen organic raw materials, 8-12 parts of phosphorus source, 5-10 parts of potassium source, 3-5 parts of water-retaining agent, and 2-5 parts of binder.

[0007] Preferably, the high-nitrogen organic raw material is a mixture of fermented and decomposed soybean meal, peanut cake, fish meal and livestock and poultry manure; the mass ratio of the fermented and decomposed soybean meal, peanut cake, fish meal and livestock and poultry manure is 2-3:1-2:1-2:2-4.

[0008] Preferably, the phosphorus source is a mixture of bone meal, calcium phosphate and calcium dihydrogen phosphate, wherein the mass ratio of bone meal, calcium phosphate and calcium dihydrogen phosphate is 1:1:1; the potassium source is a mixture of potassium sulfate, potassium chloride and potassium humate, wherein the mass ratio of potassium sulfate, potassium chloride and potassium humate is 2-3:2-3:1.

[0009] Preferably, the water-retaining agent is a compound of polyglutamic acid and acrylamide-potassium acrylate copolymer, with a mass ratio of 1:2-3, wherein the molecular weight of polyglutamic acid is 100-200 kDa.

[0010] Preferably, the binder is a mixture of sodium carboxymethyl cellulose and starch phosphate, wherein the mass ratio of sodium carboxymethyl cellulose to starch phosphate is 1:1-2.

[0011] Preferably, the preparation method of the coating liquid includes the following steps: Sodium alginate, chitosan and citric acid were pretreated; Pretreated sodium alginate was mixed with chitosan to obtain the first mixture; Glycerin was added to the first mixture for a second mixing to obtain a second mixture; The pretreated citric acid was mixed with the second mixture, and after mixing, it was cooled and matured. Finally, it was filtered to obtain the coating solution.

[0012] Preferably, the mass ratio of sodium alginate, chitosan, citric acid and glycerol is 3-6:2-4:1-1.5:1-3.

[0013] This invention also provides a method for preparing the high-utilization organic nitrogen fertilizer described in the above technical solution, comprising the following steps: The high-nitrogen organic raw materials are crushed, then mixed with phosphorus source, potassium source, water-retaining agent and binder, and 10%-15% water of the total mass of raw materials is added. The mixture is stirred at 200-300 r / min for 20-30 min to obtain the mixture. The mixture is granulated to obtain core fertilizer granules. Sodium alginate, chitosan, glycerol, and citric acid were weighed according to the mass fractions to prepare the coating solution; The core fertilizer granules are placed in a fluidized bed coating machine and preheated to 30-40°C. Then, the coating liquid is sprayed evenly onto the surface of the core fertilizer granules. After coating, the granules are dried at 40-50°C for 1-2 hours and cooled to room temperature to obtain a high-utilization organic nitrogen fertilizer.

[0014] Preferably, the granulation process specifically involves feeding the mixture into a granulator, adjusting the granulator's tilt angle to 30-40° and rotation speed to 30-50 r / min, drying the granulated material at 60-80°C until the moisture content is ≤8%, and then screening for particles with a diameter of 2-4 mm.

[0015] Preferably, the coating liquid is uniformly coated on the surface of the core fertilizer particles by spraying, with a spraying pressure of 0.3-0.5 MPa and a droplet size of 50-100 μm.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The organic nitrogen fertilizer obtained by this invention includes core fertilizer granules and a coating layer. Through the coating layer, this invention achieves slow and stable release of nitrogen according to crop needs, significantly reducing nitrogen loss and volatilization, and improving nitrogen utilization. In addition, the core fertilizer of this invention uses high-nitrogen organic raw materials and inorganic phosphorus and potassium sources to achieve organic-inorganic synergy, providing comprehensive and coordinated nutrient release to meet the nutritional needs of crops throughout their entire growth period. Detailed Implementation

[0017] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0018] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0019] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0020] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0021] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0022] This invention provides a high-utilization organic nitrogen fertilizer, which includes core fertilizer particles and a coating layer; The coating layer is prepared from a coating liquid; The core fertilizer granules consist of 40-50 parts of high-nitrogen organic raw materials, 8-12 parts of phosphorus source, 5-10 parts of potassium source, 3-5 parts of water-retaining agent, and 2-5 parts of binder.

[0023] In this invention, the high-nitrogen organic raw material is a mixture of fermented and decomposed soybean meal, peanut cake, fish meal and livestock and poultry manure; the mass ratio of the fermented and decomposed soybean meal, peanut cake, fish meal and livestock and poultry manure is 2-3:1-2:1-2:2-4.

[0024] This invention uses high-nitrogen organic raw materials as the core nitrogen source, providing the organic nitrogen required for crop growth, while also being rich in nutrients such as amino acids, peptides, and organic matter. Fermentation and composting treatment eliminates harmful substances (such as pathogens and insect eggs) in the raw materials and reduces the initial rate of ammonia volatilization. Specifically, soybean meal and peanut cake provide slow-release organic nitrogen with a long nitrogen release period; fishmeal is rich in high-quality protein and trace elements (zinc, iron, etc.), which can enhance crop stress resistance; livestock and poultry manure supplements organic matter, improves soil aggregate structure, and promotes microbial activity, achieving the dual effect of soil nourishment and nitrogen supply. After mixing and proportioning, the matching degree between the nitrogen release rate and the nitrogen requirements of crops during their growth stages is improved, avoiding the problem of nitrogen release being too fast or too slow from a single raw material. In this invention, the phosphorus source is preferably a mixture of bone meal, calcium phosphate and calcium dihydrogen phosphate, and the mass ratio of bone meal, calcium phosphate and calcium dihydrogen phosphate is preferably 1:1:1; the potassium source is preferably a mixture of potassium sulfate, potassium chloride and potassium humate, and the mass ratio of potassium sulfate, potassium chloride and potassium humate is preferably 2-3:2-3:1.

[0025] This invention supplements crops with phosphorus sources needed for growth, participating in photosynthesis, energy metabolism, and cell wall synthesis; three phosphorus sources form a synergistic system of slow-release and fast-acting phosphorus. Specifically: bone meal is a natural slow-release phosphorus source with a long release period, suitable for the phosphorus needs of crops in the middle and late stages; calcium phosphate and calcium dihydrogen phosphate are fast-acting phosphorus sources, which can quickly meet the phosphorus needs of crops during key stages such as seedling and jointing stages; after the three are combined, the phosphorus utilization rate can be significantly improved compared with a single phosphorus source, avoiding waste caused by phosphorus fixation, and at the same time alleviating the problems of crop stunting, flower and fruit drop caused by soil phosphorus deficiency.

[0026] This invention supplements potassium by providing a potassium source, enhancing crop resistance to lodging and pests, promoting the transport of photosynthetic products and fruit enlargement; potassium humate also improves soil and enhances crop efficiency. Specifically: potassium sulfate and potassium chloride provide readily available potassium to meet the needs of rapid crop growth, while controlling chloride ion content within a safe range (suitable for most crops); the humic acid in potassium humate chelates free potassium ions in the soil, reducing leaching losses, and simultaneously improving soil aeration and water retention; the combination of these three components significantly improves potassium utilization and enhances crop stress resistance.

[0027] In this invention, the water-retaining agent is preferably a compound of polyglutamic acid and acrylamide-potassium acrylate copolymer, with a mass ratio preferably of 1:2-3, wherein the molecular weight of polyglutamic acid is preferably 100-200 kDa.

[0028] This invention also adds a water-retaining agent to adsorb and lock in soil moisture and nutrients, reducing water evaporation and nutrient leaching, while promoting crop root absorption. Acrylamide-potassium acrylate copolymer has a strong water adsorption capacity, which can quickly improve the soil's water retention capacity. Polyglutamic acid has biocompatibility, which can promote crop root growth and enhance the root's absorption efficiency of nitrogen, phosphorus, and potassium. At the same time, it can be used as organic nutrients after degradation. After compounding, the soil water holding capacity can be significantly improved, nutrient leaching loss can be reduced, and the fresh weight of crop roots can be increased.

[0029] In this invention, the binder is preferably a mixture of sodium carboxymethyl cellulose and starch phosphate, and the mass ratio of sodium carboxymethyl cellulose to starch phosphate is preferably 1:1-2. This invention uses a binder to improve the adhesion of the mixture, ensuring smooth granulation and enhancing the mechanical strength and stability of the core particles. Specifically: sodium carboxymethyl cellulose has good water solubility and strong binding force, which can improve the granule formation rate; starch phosphate has both binding and biodegradability, avoiding residual pollution, while also enhancing the water resistance of the particles and preventing disintegration upon contact with water in the field; after compounding, the compressive strength of the core particles is improved, and the storage stability is good at low moisture content, with no obvious clumping.

[0030] In this invention, the method for preparing the coating liquid of the coating layer includes the following steps: Sodium alginate, chitosan and citric acid were pretreated; Pretreated sodium alginate and chitosan were mixed and stirred at room temperature for 30-50 minutes to obtain the first mixture; Add glycerin to the first mixture, heat to 40-50℃ and stir for 40-60 minutes to carry out a second mixing, to obtain the second mixture; The pretreated citric acid is mixed with the second mixture and stirred for 40-60 minutes. After mixing, the mixture is cooled to 25-30°C and aged for 1-2 hours. Finally, it is filtered to obtain the coating solution.

[0031] Specifically, the pretreatment involves selecting sodium alginate with a viscosity of 200-300 mPa·s (2% aqueous solution, 25℃), screening it through a 100-mesh sieve, drying it at a constant temperature of 60℃ for 2 hours, and pulverizing it to a particle size ≤0.05mm; selecting chitosan with a degree of deacetylation ≥85%, soaking and washing it twice (30 minutes each time) in a 50% ethanol aqueous solution, vacuum drying it at 50℃ for 3 hours until the moisture content is ≤5%, pulverizing it, and then screening it through a 120-mesh sieve. Crush citric acid to a particle size ≤0.1mm and mix it with deionized water at a mass ratio of 1:5.

[0032] In this invention, the preferred mass ratio of sodium alginate, chitosan, citric acid and glycerol is 3-6:2-4:1-1.5:1-3.

[0033] This invention uses a coating solution with specific components to prepare a coating layer. Sodium alginate in the coating solution forms a gel network structure, serving as the basic framework of the coating layer and preventing the rapid release of nutrients from the core fertilizer. It is biodegradable and environmentally friendly. Specifically: the sodium alginate gel layer is pH-responsive, slowly degrading in slightly acidic soil environments to achieve on-demand nutrient release; its hydrophilicity ensures soil moisture penetration to the core particles, preventing fertilizer drying and inactivation; and when used alone, the nitrogen release cycle is longer than without a coating layer.

[0034] Chitosan enhances the mechanical strength and stability of the coating layer, inhibits the rapid decomposition of core fertilizers by soil microorganisms, and also has a certain antibacterial effect. Specifically, chitosan and sodium alginate form an interpenetrating network structure, increasing the elongation at break of the coating layer and preventing it from falling off during transportation or field operations; its antibacterial properties reduce the ineffective consumption of nitrogen by pathogens in the soil, while promoting the growth of beneficial microorganisms; when combined with sodium alginate, the degradation cycle of the coating layer is adapted to the crop growth period, leaving no residual pollution.

[0035] This invention uses citric acid as a crosslinking agent to promote the formation of hydrogen and ionic bonds between sodium alginate and chitosan molecules, optimizing the density of the gel structure. Adjusting the pH of the coating solution enhances the bonding force between the coating layer and the core particles. The crosslinked gel layer exhibits reduced porosity and decreased nitrogen volatilization loss. Adjusting the pH to 5.5-6.5 strengthens the affinity between the coating solution and the core particle surface, resulting in uniform coating without localized leakage.

[0036] Furthermore, this invention uses glycerol as a plasticizer to improve the flexibility of the coating layer, preventing cracking caused by temperature changes or mechanical impact; it also enhances the fluidity of the coating liquid, facilitating spray coating. Specifically, glycerol lowers the glass transition temperature of the coating layer, maintaining good flexibility within the range of -5℃ to 40℃, and reducing the cracking rate; simultaneously, it reduces the viscosity of the coating liquid, resulting in uniform droplet size (50-100μm) during spraying, and a coating layer thickness deviation ≤0.1mm.

[0037] This invention also provides a method for preparing the high-utilization organic nitrogen fertilizer described in the above technical solution, comprising the following steps: The high-nitrogen organic raw materials are crushed, then mixed with phosphorus source, potassium source, water-retaining agent and binder, and 10%-15% water of the total mass of raw materials is added. The mixture is stirred at 200-300 r / min for 20-30 min to obtain the mixture. The mixture is granulated to obtain core fertilizer granules. Sodium alginate, chitosan, glycerol, and citric acid were weighed according to the mass fractions to prepare the coating solution; The core fertilizer granules are placed in a fluidized bed coating machine and preheated to 30-40°C. Then, the coating liquid is sprayed evenly onto the surface of the core fertilizer granules. After coating, the granules are dried at 40-50°C for 1-2 hours and cooled to room temperature to obtain a high-utilization organic nitrogen fertilizer.

[0038] In this invention, the granulation is preferably carried out by feeding the mixture into a granulator, adjusting the granulator tilt angle to 30-40° and the rotation speed to 30-50 r / min, drying the granulated material at 60-80°C until the moisture content is ≤8%, and screening the particles with a particle size of 2-4 mm.

[0039] In this invention, the coating liquid is uniformly coated onto the surface of the core fertilizer particles by spraying. The spraying pressure is preferably 0.3-0.5 MPa, and the droplet size is preferably 50-100 μm. Example 1 (1) Raw material preparation: Prepare 25 parts of fermented and decomposed soybean meal, 10 parts of peanut cake, 10 parts of fish meal, 30 parts of livestock and poultry manure, 4 parts of bone meal, 4 parts of calcium phosphate, 4 parts of calcium dihydrogen phosphate, 3 parts of potassium sulfate, 3 parts of potassium chloride, 1.5 parts of potassium humate, 1 part of polyglutamic acid, 2 parts of acrylamide-potassium acrylate copolymer, 1 part of sodium carboxymethyl cellulose, 1 part of starch phosphate, 3 parts of sodium alginate, 2 parts of chitosan, 1 part of citric acid, and 1 part of glycerol; (2) Crush the high-nitrogen organic raw materials to a particle size ≤0.1mm, add them together with phosphorus source, potassium source, water-retaining agent and binder to a mixer, add water of 10% of the total mass of raw materials, stir at 200r / min speed for 30min to obtain a mixture; send the mixture to a granulator, adjust the granulator tilt angle to 30° and the speed to 30r / min, after granulation, dry at 60℃ to a moisture content of 7%, and screen out core fertilizer particles with a particle size of 2-3mm; (3) Sodium alginate and chitosan were pulverized to a particle size ≤0.05mm, and citric acid was dissolved in 5 times the mass of deionized water to complete the pretreatment; the pretreated sodium alginate and chitosan were added to a mixing vessel and stirred at room temperature for 30min to obtain the first mixture; glycerol was added to the first mixture, and the temperature was raised to 40℃ and stirred for 60min to obtain the second mixture; the pretreated citric acid solution was slowly added to the second mixture and stirred for 40min, then cooled to 25℃ and aged for 1h, and filtered with a 200-mesh filter to obtain the coating solution; (4) Place the core fertilizer granules into a fluidized bed coating machine, preheat to 30°C, and spray the coating liquid evenly onto the surface of the core granules with a spray pressure of 0.3 MPa and a droplet size of 50-70 μm. After coating, dry at 40°C for 2 hours and cool to room temperature to obtain a high-utilization organic nitrogen fertilizer.

[0040] Example 2 (1) Prepare raw materials: Prepare 30 parts of fermented and decomposed soybean meal, 15 parts of peanut cake, 12 parts of fish meal, 35 parts of livestock and poultry manure, 4 parts of bone meal, 4 parts of calcium phosphate, 4 parts of calcium dihydrogen phosphate, 4 parts of potassium sulfate, 4 parts of potassium chloride, 2 parts of potassium humate, 1.5 parts of polyglutamic acid, 3.5 parts of acrylamide-potassium acrylate copolymer, 1.5 parts of sodium carboxymethyl cellulose, 2.5 parts of starch phosphate, 5 parts of sodium alginate, 3 parts of chitosan, 1.2 parts of citric acid, and 2 parts of glycerol.

[0041] (2) Crush the high-nitrogen organic raw materials to a particle size ≤0.1mm, mix them with other core components, add water at 12% of the total mass of the raw materials, and stir at 250r / min for 25min; then send the mixture into a granulator, adjust the tilt angle to 35° and the rotation speed to 40r / min for granulation, and dry it at 70℃ to a moisture content of 6% after granulation, and screen the core fertilizer particles with a particle size of 3-4mm.

[0042] (3) Sodium alginate and chitosan were pulverized and pretreated. Citric acid was dissolved in 5 times the mass of deionized water. The pretreated sodium alginate and chitosan were stirred at room temperature for 40 min to obtain the first mixture. Glycerin was added and the temperature was raised to 45℃ and stirred for 50 min to obtain the second mixture. Citric acid solution was added and stirred for 50 min. The temperature was lowered to 28℃ and matured for 1.5 h. The coating solution was filtered through a 200-mesh filter to obtain the coating solution.

[0043] (4) Preheat the core particles to 35°C, and spray the coating liquid evenly onto the surface of the core particles with a spray pressure of 0.4 MPa and a droplet size of 70-90 μm. After coating, dry at 45°C for 1.5 h and cool to room temperature to obtain a high-utilization organic nitrogen fertilizer.

[0044] Example 3 (1) Prepare raw materials: Prepare 30 parts of fermented and decomposed soybean meal, 12 parts of peanut cake, 12 parts of fish meal, 40 parts of livestock and poultry manure, 4 parts of bone meal, 4 parts of calcium phosphate, 4 parts of calcium dihydrogen phosphate, 6 parts of potassium sulfate, 6 parts of potassium chloride, 3 parts of potassium humate, 2 parts of polyglutamic acid, 4 parts of acrylamide-potassium acrylate copolymer, 2 parts of sodium carboxymethyl cellulose, 3 parts of starch phosphate, 6 parts of sodium alginate, 4 parts of chitosan, 1.5 parts of citric acid, and 3 parts of glycerol; (2) Crush the high-nitrogen organic raw materials to a particle size ≤0.1mm, mix them with the remaining core components, add 15% water of the total mass of the raw materials, stir at 300r / min for 20min; granulate with a granulator tilt angle of 40° and a rotation speed of 50r / min, dry at 80℃ to a moisture content of 5%, and screen core fertilizer particles with a particle size of 2-4mm.

[0045] (3) Sodium alginate and chitosan were pulverized and pretreated. Citric acid was dissolved in 5 times the mass of deionized water. The two were stirred at room temperature for 50 min to obtain the first mixture. Glycerin was added and heated to 50℃ and stirred for 40 min to obtain the second mixture. Citric acid solution was added and stirred for 60 min. The mixture was cooled to 30℃ and aged for 2 h. The coating solution was filtered through a 200-mesh filter.

[0046] (4) Preheat the core particles to 40°C, and spray the coating liquid evenly onto the surface of the core particles with parameters of spray pressure 0.5MPa and droplet size 90-100μm. After coating, dry at 50°C for 1 hour and cool to room temperature to obtain a high-utilization organic nitrogen fertilizer.

[0047] Performance testing (1) Nitrogen utilization rate test Test subjects: The organic nitrogen fertilizer obtained in Examples 1-3 and conventional urea were used as control groups; Test crop: Wheat (variety: Jimai 44); Experimental conditions: Experimental field area 10m² 2 / group, 3 replicates; soil type: loam; basic fertility: organic matter 1.5%, available nitrogen 80mg / kg, available phosphorus 20mg / kg, available potassium 120mg / kg; fertilizer application rate: pure nitrogen 15kg / mu, applied as a single basal application; other field management (watering, weeding, pest and disease control) remained consistent. Test steps: At the wheat maturity stage, measure the dry weight and grain yield of each group of plants; collect aboveground parts of plants and soil samples from 0-20cm, and use the Kjeldahl method to determine the cumulative nitrogen in plants and the residual nitrogen in the soil; calculate the nitrogen use efficiency according to the formula: nitrogen use efficiency = (cumulative nitrogen in plants / nitrogen application rate) × 100%.

[0048] (2) Nitrogen slow-release performance test Test method: The soil culture method was adopted. 5g of fertilizer sample was weighed and mixed with 200g of air-dried soil (passed through a 2mm sieve), and placed in a culture box. The soil moisture content was adjusted to 60% of the field capacity and placed in a constant temperature incubator at 25℃. Samples were taken on the 7th, 14th, 28th, 42nd, 60th and 90th days of culture. The available nitrogen content in the soil was determined by the alkaline hydrolysis diffusion method, and the cumulative nitrogen release rate was calculated.

[0049] (3) Particle physical property testing Compressive strength: Using a particle strength tester, 20 particles were randomly selected, and the compressive strength of each particle was measured. The average value was then taken.

[0050] Water resistance: Weigh 10g of the product and place it in 50mL of deionized water. Soak at room temperature for 24h, observe the particle disintegration, and calculate the percentage of undisintegrated particles (mass of undisintegrated particles / total mass of sample × 100%).

[0051] (4) Soil improvement effect test Test indicators: After wheat harvest, soil organic matter content, soil bulk density, and soil microbial biomass carbon (MBC) were measured.

[0052] Test methods: Organic matter content was measured using the potassium dichromate volumetric method, soil bulk density was measured using the ring sampler method, and MBC was measured using the chloroform fumigation extraction method.

[0053] The test results are shown in Table 1. Table 1 Performance Test Results

[0054] As shown in Table 1, the nitrogen utilization rate of the organic nitrogen fertilizers obtained in Examples 1-3 was significantly higher than that of the control group. From the slow-release curve, the nitrogen release rate of the organic nitrogen fertilizers obtained in the examples was only 18.7%-22.3% in the early stage (7 days), which avoided nitrogen loss caused by the rapid release of urea in the early stage; the cumulative release rate in the later stage (90 days) reached 89.2%-91.5%, which could continuously meet the nitrogen requirements of crops throughout the entire growth period and solve the problem of insufficient release of ordinary organic fertilizers in the later stage.

[0055] Furthermore, the compressive strength of the organic nitrogen fertilizers obtained in Examples 1-3 is 16.8-19.2 N / particle, and the proportion of undisintegrated particles after 24 hours of water resistance is ≥92.5%. Based on this, it can be seen that the organic nitrogen fertilizer particles obtained by the present invention have a stable particle structure, can withstand the mechanical impact of transportation and field operations, and are not easily disintegrated in the soil, thus ensuring the slow-release effect.

[0056] Furthermore, the organic nitrogen fertilizer obtained in Examples 1-3 of this invention can significantly increase the soil organic matter content, reduce soil bulk density, and increase soil microbial biomass carbon compared to the control group. Based on this, it can be seen that the organic components and coating layer degradation products in the organic nitrogen fertilizer obtained by this invention can effectively improve soil structure and promote soil microbial activity, thus having a synergistic effect of fertilization and soil nourishment.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-utilization organic nitrogen fertilizer, characterized in that, The organic nitrogen fertilizer includes core fertilizer particles and a coating layer; The coating layer is prepared from a coating liquid; The core fertilizer granules consist of 40-50 parts of high-nitrogen organic raw materials, 8-12 parts of phosphorus source, 5-10 parts of potassium source, 3-5 parts of water-retaining agent, and 2-5 parts of binder.

2. The high-utilization organic nitrogen fertilizer according to claim 1, characterized in that, The high-nitrogen organic raw material is a mixture of fermented and decomposed soybean meal, peanut cake, fish meal and livestock and poultry manure; the mass ratio of the fermented and decomposed soybean meal, peanut cake, fish meal and livestock and poultry manure is 2-3:1-2:1-2:2-4.

3. The high-utilization organic nitrogen fertilizer according to claim 1, characterized in that, The phosphorus source is a mixture of bone meal, calcium phosphate, and calcium dihydrogen phosphate, wherein the mass ratio of bone meal, calcium phosphate, and calcium dihydrogen phosphate is 1:1:1; the potassium source is a mixture of potassium sulfate, potassium chloride, and potassium humate, wherein the mass ratio of potassium sulfate, potassium chloride, and potassium humate is 2-3:2-3:

1.

4. The high-utilization organic nitrogen fertilizer according to claim 1, characterized in that, The water-retaining agent is a compound of polyglutamic acid and acrylamide-potassium acrylate copolymer, with a mass ratio of 1:2-3, wherein the molecular weight of polyglutamic acid is 100-200kDa.

5. The high-utilization organic nitrogen fertilizer according to claim 1, characterized in that, The binder is a mixture of sodium carboxymethyl cellulose and starch phosphate, wherein the mass ratio of sodium carboxymethyl cellulose to starch phosphate is 1:1-2.

6. The high-utilization organic nitrogen fertilizer according to claim 1, characterized in that, The preparation method of the coating liquid includes the following steps: Sodium alginate, chitosan and citric acid were pretreated; Pretreated sodium alginate was mixed with chitosan to obtain the first mixture; Glycerin was added to the first mixture for a second mixing to obtain a second mixture; The pretreated citric acid was mixed with the second mixture, and after mixing, it was cooled and matured. Finally, it was filtered to obtain the coating solution.

7. The high-utilization organic nitrogen fertilizer according to claim 6, characterized in that, The mass ratio of sodium alginate, chitosan, citric acid and glycerol is 3-6:2-4:1-1.5:1-3.

8. A method for preparing a high-utilization organic nitrogen fertilizer according to any one of claims 1-7, characterized in that, Includes the following steps: The high-nitrogen organic raw materials are crushed, then mixed with phosphorus source, potassium source, water-retaining agent and binder, and 10%-15% water of the total mass of raw materials is added. The mixture is stirred at 200-300 r / min for 20-30 min to obtain the mixture. The mixture is granulated to obtain core fertilizer granules. Sodium alginate, chitosan, glycerol, and citric acid were weighed according to the mass fractions to prepare the coating solution; The core fertilizer granules are placed in a fluidized bed coating machine and preheated to 30-40°C. Then, the coating liquid is sprayed evenly onto the surface of the core fertilizer granules. After coating, the granules are dried at 40-50°C for 1-2 hours and cooled to room temperature to obtain a high-utilization organic nitrogen fertilizer.

9. The method for preparing high-utilization organic nitrogen fertilizer according to claim 8, characterized in that, The granulation process specifically involves feeding the mixture into a granulator, adjusting the granulator's tilt angle to 30-40° and rotation speed to 30-50 r / min, drying the granulated material at 60-80℃ until the moisture content is ≤8%, and then screening the particles with a diameter of 2-4 mm.

10. The method for preparing a high-utilization organic nitrogen fertilizer according to claim 8, characterized in that, The coating liquid is uniformly coated onto the surface of the core fertilizer particles by spraying, with a spraying pressure of 0.3-0.5 MPa and a droplet size of 50-100 μm.

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