Composite material coated slow-release nitrogen fertilizer and preparation method thereof

Abstract

The invention discloses a composite material coated slow-release nitrogen fertilizer and a preparation method thereof, and the composite material coated slow-release nitrogen fertilizer is prepared by the following steps: successively cross-linking polyvinyl alcohol, gelatinized corn starch, borax and maleic acid to form a basic skeleton, taking glycerol as a plasticizer, adding humic acid-vermiculite with water-retaining, fertilizer-retaining and yield-increasing functions, and uniformly stirring to obtain a mixture; then adding sodium lignin sulfonate as a dispersing agent, so that the sodium lignin sulfonate is uniformly dispersed on the cross-linked skeleton; and mixing the uniformly stirred coating solution and the nitrogen fertilizer in a disc granulator according to a certain weight ratio, carrying out full rolling coating in the disc granulation, and carrying out blast constant-temperature drying until the weight is constant so as to obtain the nitrogen fertilizer. The slow-release nitrogen fertilizer prepared by the invention has the advantages of slow release property, biodegradation function, easily available raw materials, low cost and capability of increasing yield and improving physicochemical properties of soil, the slow-release nitrogen fertilizer developed by coating the novel composite slow-release material has the effects of environmental friendliness, water retention, fertilizer conservation and yield increase, and the fertilizer efficiency and the utilization rate of the soil can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural fertilizer coating, discloses a slow-release nitrogen fertilizer coated with a composite material and a preparation method thereof, and particularly discloses a slow-release nitrogen fertilizer coated with a composite material of polyvinyl alcohol starch-humic acid vermiculite and a preparation method thereof. Background Art

[0002] In agricultural production, the method of nitrogen fertilizer application largely determines grain yield, and different nitrogen fertilizer types influence application methods. As the most widely used traditional nitrogen fertilizer, its application often leads to nitrogen loss and environmental pollution. For example, ammonia volatilization and rainwater leaching damage soil structure, reduce its ability to retain water and fertilizer, and increase other greenhouse emissions from rice paddies. Furthermore, frequent topdressing is required, increasing labor costs. To overcome these issues, slow-release nitrogen fertilizer research and application technology have emerged. These precisely controlled nitrogen release synchronizes fertilizer application with crop growth needs, reducing nitrogen surplus in the soil, improving nitrogen fertilizer utilization, reducing environmental pollution, and boosting crop yields. In the early development of slow-release nitrogen fertilizer technology, the main method was low-cost sulfur coating. However, due to its poor slow-release effect and the potential for sulfur contamination, it has gradually been replaced by other coating technologies. Currently available slow-release nitrogen fertilizers are difficult to implement on a large scale due to their high cost and the difficulty of degrading the coating materials. Therefore, the development of environmentally friendly, efficient, and cost-effective slow-release / controlled-release fertilizers is of great significance for promoting the sustainable development of agriculture in my country.

[0003] Polyvinyl alcohol (PVA) is a water-soluble polymer material with good film-forming properties and high adhesion, and compared with other types of polymer materials, polyvinyl alcohol has the characteristics of stable physical and chemical properties and biodegradability in soil. Both polyvinyl alcohol molecules and starch molecules contain free hydroxyl groups, and when combined, they can be used to prepare materials with good performance and environmental protection. Starch is a natural high-molecular organic compound with a wide range of sources and low prices. Polyvinyl alcohol-starch, as a biodegradable material, is often used as an environmentally friendly coating material. Humic acid is a high-molecular organic matter with a variety of active functional groups, and compared with other types of organic materials, humic acid has the characteristics of stable physical and chemical properties and biodegradability in soil. Humic acid molecules and metal ions can exchange, adsorb, complex, chelate, etc., and when combined, they can be used to prepare materials with good performance and environmental protection. Studies have shown that humic acid and its derivatives are one of the biodegradable materials that are currently attracting much attention and have broad application prospects. Vermiculite is a layered silicate mineral with exchangeable cations (such as Ca 2+ Mg 2+Vermiculite powder is a highly versatile and versatile material that can be used in a wide variety of soils, including soil-based fertilizers, fertilizers, and other fertilizers. It can also rapidly expand to 6-20 times its original volume upon heating. This unique expansibility makes it physically and chemically stable and biodegradable in the soil. Vermiculite powder's high water absorption and cation exchange capacity (CEC) enable it to retain and slowly release water and nutrients required by plants, demonstrating excellent performance in soil improvement and fertilizer slow-release. Humic acid and vermiculite can form complexes through cationic bridging, surface adsorption, or intercalation, improving soil conditions and promoting yield increases.

[0004] Therefore, the industry is in urgent need of a slow-release nitrogen fertilizer developed by coating a polyvinyl alcohol starch-humic acid vermiculite composite material to achieve the effect of precise slow-controlled release of nitrogen fertilizer. Summary of the Invention

[0005] In view of the above shortcomings, the present invention slowly releases conventional urea-coated composite materials to achieve the purpose of soil water and fertilizer retention and soil structure improvement, thereby reducing nitrogen fertilizer leaching and volatilization losses, reducing greenhouse gas emissions and environmental pollution, improving soil fertility, and achieving high rice yields. In order to solve the above technical problems, the present invention is achieved through the following technical means:

[0006] The present invention first discloses a method for preparing a composite material-coated slow-release nitrogen fertilizer, comprising:

[0007] (1) Dissolve 6.0 g of polyvinyl alcohol in 70 g of deionized water, stir at 200-250 rpm for 1 h, and heat to 90° C. Then, add gelatinized starch, 0.1 g of borax, and 3.0 ml of glycerol in sequence and continue heating and stirring to obtain a first mixed solution for use;

[0008] (2) adding 1.0 g of maleic acid to the first mixed solution with stirring, and continuing stirring at 500-600 rpm for 1 h under heating conditions of 60-70° C. to obtain a second mixed solution;

[0009] (3) dissolving the vermiculite-humic acid film in the second mixed solution and stirring, adding 0.5 g of sodium lignin sulfonate, stirring and mixing at room temperature, and ultrasonicating to obtain a polyvinyl alcohol starch-vermiculite humic acid coating solution;

[0010] (4) Urea was first added into a disc granulator, and then polyvinyl alcohol starch-vermiculite humic acid coating solution was added and mixed. The speed and temperature of the disc granulator were set, and the mixture was dried at a constant temperature to a constant weight, thereby obtaining a slow-release nitrogen fertilizer coated with a composite material having a coating thickness of 0.15 mm.

[0011] Furthermore, the gelatinized starch in step (1) is prepared by the following method:

[0012] 4.0 g corn starch was mixed with 80.0 ml deionized water, heated in a constant temperature water bath at 85° C. for gelatinization, and stirred at 500-600 rpm for 0.5 h to obtain gelatinized starch.

[0013] Furthermore, the conditions for continuing heating and stirring in step (1) are:

[0014] Continue stirring at 60°C and 500-600 rpm for 2 h.

[0015] Furthermore, the vermiculite-humic acid film in step (3) is prepared by the following method:

[0016] (3.1) 20 g of vermiculite powder was acidified by adding 200 ml of a 3.6% hydrochloric acid solution. After drying, the mixture was mixed with 200 ml of a 1% sodium chloride solution and ultrasonically treated. The mixture was centrifuged and allowed to stand for 2 h. The lower precipitate was separated and dried in a constant temperature forced air oven to constant weight to obtain the modified vermiculite.

[0017] (3.2) Modified vermiculite and humic acid were mixed and dissolved in deionized water. The mixture was ultrasonically treated at a power of 200-220W for 10-15 minutes to obtain a soil dispersion. The soil dispersion was then vacuum filtered through a cellulose nitrate membrane with a pore size of 0.45μm. The mixture was dried in a constant temperature forced air oven to a constant weight. The mixture was separated from the filter membrane to obtain a vermiculite-humic acid membrane for later use.

[0018] Furthermore, the vermiculite powder in step (3.1) has a particle size of ≥150 mesh; the ultrasonic treatment power is 200-220w, and the ultrasonic treatment time is 20-30min; the centrifugal speed is 3000-4000rpm, and the centrifugal time is 10-15mi; and the constant temperature blast oven is 105°C.

[0019] Furthermore, in step (3.2), the amount of modified vermiculite and humic acid is 0.6 g, the amount of deionized water is 50 ml, and the oven temperature is 20-25°C.

[0020] Furthermore, in step (3), the room temperature is 20-25° C., the stirring speed is 1000 rpm, and the stirring time is 1 hour; the ultrasonic power is 120-150 W, and the ultrasonic treatment time is 15-20 minutes.

[0021] Furthermore, the urea particle size in step (4) is 3.5 mm to 4.00 mm; and the mass ratio of the polyvinyl alcohol starch-vermiculite humic acid coating solution to urea is 2:1.

[0022] Furthermore, in step (4), the rotation speed of the disc granulator is 30-40 rpm and the temperature is 55°C.

[0023] The present invention also discloses a slow-release nitrogen fertilizer coated with a composite material prepared according to any of the above preparation methods.

[0024] The polyvinyl alcohol starch-humic acid vermiculite coating material prepared by the present invention has the following advantages:

[0025] (1) Good biodegradability and environmental friendliness: Starch can be decomposed by microorganisms in the natural environment, and PVA can increase the degradation rate of starch after cross-linking. Both naturally decompose in soil or water, which is in line with the green development of coating materials.

[0026] (2) Good film-forming properties: PVA makes up for the brittleness of starch, starch enhances the rigidity of PVA, and the two cross-link to form a durable composite film.

[0027] (3) Low cost and resource renewability: Compared with the urea polyurethane coating materials commonly used on the market, this raw material is easy to obtain and has a lower cost, is simpler to process, and can be promoted and applied on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the cumulative release curve of nitrogen in slow-release nitrogen fertilizer;

[0029] Figure 2 This is a comparison chart of the yield of slow-release nitrogen fertilizer and conventional nitrogen fertilizer;

[0030] Figure 3 This is a graph of total nitrogen content in soil at different periods for the experimental group with slow-release nitrogen fertilizer and the control group with conventional nitrogen fertilizer;

[0031] Figure 4 This is a property diagram of the slow-release nitrogen fertilizer coated with the composite material prepared in the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. Unless otherwise specified, the materials, reagents, etc. used in the following examples are all commercially available.

[0034] Example 1

[0035] A method for preparing a composite material-coated slow-release nitrogen fertilizer comprises:

[0036] (1) 20 g of vermiculite powder with a particle size of ≥150 mesh was added to 200 ml of a 3.6% hydrochloric acid solution for acidification and drying, and then 200 ml of a 1% sodium chloride solution was added and mixed and ultrasonicated at a power of 200 W for 30 min; then the mixture was centrifuged at 3000 rpm for 15 min, allowed to stand, and the lower precipitate was separated and removed, and dried in a constant temperature blast oven at 105° C. to constant weight to obtain modified vermiculite;

[0037] (2) 0.6 g of modified vermiculite and 0.6 g of humic acid with a particle size of ≥120 mesh were mixed, dissolved in 50 ml of deionized water, and ultrasonically treated at a power of 200 W for 15 min to obtain a soil dispersion. The soil dispersion was then vacuum filtered through a nitrocellulose membrane with a pore size of 0.45 μm, dried in a constant temperature forced air oven at 20°C to constant weight, and then separated from the filter membrane to obtain a vermiculite-humic acid membrane;

[0038] (3) 4.0 g corn starch was mixed with 80.0 ml deionized water, stirred at 500 rpm in a constant temperature water bath at 85 °C for 0.5 h, and heated for gelatinization to obtain gelatinized starch;

[0039] (4) 6 g of polyvinyl alcohol (brand 1799) was dissolved in 70 g of deionized water, heated at 90°C for dissolution, and stirred at 200 rpm for 1 h. Then, gelatinized starch was added and stirred at 200 rpm for 1 h. 0.1 g of borax and 3.0 ml of glycerol were added in sequence and stirred at 60°C and 500-600 rpm for 2 h to obtain a first mixed solution.

[0040] (5) Add 1.0 g of maleic acid to the first mixed solution, and continue stirring at 60° C. and 600 rpm for 1 h to obtain a second mixed solution;

[0041] (6) dissolving the vermiculite-humic acid film in the second mixed solution and stirring, adding 0.5 g of sodium lignin sulfonate, stirring at 20° C. and 1000 rpm for 1 h, and ultrasonicating at 120 W for 20 min to obtain a polyvinyl alcohol starch-vermiculite humic acid coating solution;

[0042] (7) The polyvinyl alcohol starch-vermiculite humic acid coating solution was mixed with 3.5 mm nitrogen fertilizer in a mass ratio of 2:1. The nitrogen fertilizer was first added into the disc granulator and then the polyvinyl alcohol starch-vermiculite humic acid coating solution was added. The disc granulator speed was set to 30 rpm and the rotary blast drying temperature was set to 55 °C. The slow-release nitrogen fertilizer coated with the composite material with a coating thickness of 0.15 mm was obtained. The mixture was placed in a sealed bag, labeled, and stored in a desiccator for later use.

[0043] Example 1

[0044] A method for preparing a composite material-coated slow-release nitrogen fertilizer comprises:

[0045] (1) 20 g of vermiculite powder with a particle size of ≥150 mesh was added to 200 ml of a 3.6% hydrochloric acid solution for acidification and drying, and then 200 ml of a 1% sodium chloride solution was added and mixed and ultrasonically treated at a power of 220 W for 20 min; then centrifuged at 4000 rpm for 10 min, allowed to stand, and the lower precipitate was separated and removed, and dried in a constant temperature blast oven at 105° C. to constant weight to obtain modified vermiculite;

[0046] (2) 0.6 g of modified vermiculite and 0.6 g of humic acid with a particle size of ≥120 mesh were mixed, dissolved in 50 ml of deionized water, and ultrasonically treated at a power of 220 W for 10 min to obtain a soil dispersion. The soil dispersion was then vacuum filtered through a nitrocellulose membrane with a pore size of 0.45 μm, dried in a constant temperature forced air oven at 25°C to constant weight, and then separated from the filter membrane to obtain a vermiculite-humic acid membrane;

[0047] (3) 4.0 g corn starch was mixed with 80.0 ml deionized water, stirred at 600 rpm in a constant temperature water bath at 85 °C for 0.5 h, and heated for gelatinization to obtain gelatinized starch;

[0048] (4) 6 g of polyvinyl alcohol (brand 1799) was dissolved in 70 g of deionized water, heated at 90°C to dissolve, and stirred at 250 rpm for 1 h. Then, gelatinized starch was added and stirred at 250 rpm for 1 h. 0.1 g of borax and 3.0 ml of glycerol were added in sequence and stirred at 60°C and 600 rpm for 2 h to obtain a first mixed solution.

[0049] (5) Add 1.0 g of maleic acid to the first mixed solution, and continue stirring at 70°C and 500 rpm for 1 h to obtain a second mixed solution;

[0050] (6) dissolving the vermiculite-humic acid film in the second mixed solution and stirring, adding 0.5 g of sodium lignin sulfonate, stirring at 25 ° C and 1000 rpm for 1 hour, and ultrasonicating at 150 W for 15 minutes to obtain a polyvinyl alcohol starch-vermiculite humic acid coating solution;

[0051] (7) The polyvinyl alcohol starch-vermiculite humic acid coating solution was mixed with 4.00 mm nitrogen fertilizer in a mass ratio of 2:1. The nitrogen fertilizer was first added into the disc granulator and then the polyvinyl alcohol starch-vermiculite humic acid coating solution was added. The disc granulator speed was set to 40 rpm and the rotary blast drying temperature was set to 55 °C. The slow-release nitrogen fertilizer coated with the composite material with a coating thickness of 0.15 mm was obtained. The mixture was placed in a sealed bag, labeled, and stored in a desiccator for later use.

[0052] Example 1

[0053] A method for preparing a composite material-coated slow-release nitrogen fertilizer comprises:

[0054] (1) 20 g of vermiculite powder with a particle size of ≥150 mesh was added to 200 ml of a 3.6% hydrochloric acid solution for acidification and drying, and then 200 ml of a 1% sodium chloride solution was added and mixed and ultrasonically treated at a power of 210 W for 25 min; then centrifuged at 3500 rpm for 13 min, allowed to stand, and the lower precipitate was separated and removed, and dried in a constant temperature blast oven at 105° C. to constant weight to obtain modified vermiculite;

[0055] (2) 0.6 g of modified vermiculite and 0.6 g of humic acid with a particle size of ≥120 mesh were mixed, dissolved in 50 ml of deionized water, and ultrasonically treated at a power of 210 W for 13 min to obtain a soil dispersion. The soil dispersion was then vacuum filtered through a nitrocellulose membrane with a pore size of 0.45 μm, dried in a constant temperature forced air oven at 23°C to constant weight, and then separated from the filter membrane to obtain a vermiculite-humic acid membrane;

[0056] (3) 4.0 g corn starch was mixed with 80.0 ml deionized water, stirred at 550 rpm in a constant temperature water bath at 85 °C for 0.5 h, and heated to gelatinize to obtain gelatinized starch;

[0057] (4) 6 g of polyvinyl alcohol (brand 1799) was dissolved in 70 g of deionized water, heated at 90°C to dissolve, and stirred at 230 rpm for 1 h. Then, gelatinized starch was added and stirred at 230 rpm for 1 h. 0.1 g of borax and 3.0 ml of glycerol were added in sequence and stirred at 60°C and 550 rpm for 2 h to obtain a first mixed solution.

[0058] (5) Add 1.0 g of maleic acid to the first mixed solution, and continue stirring at 65°C and 550 rpm for 1 h to obtain a second mixed solution;

[0059] (6) dissolving the vermiculite-humic acid film in the second mixed solution and stirring, adding 0.5 g of sodium lignin sulfonate, stirring at 23 ° C and 1000 rpm for 1 hour, and ultrasonicating at 130 W for 17 minutes to obtain a polyvinyl alcohol starch-vermiculite humic acid coating solution;

[0060] (7) The polyvinyl alcohol starch-vermiculite humic acid coating solution was mixed with 3.5 mm nitrogen fertilizer in a mass ratio of 2:1. The nitrogen fertilizer was first added into the disc granulator and then the polyvinyl alcohol starch-vermiculite humic acid coating solution was added. The disc granulator speed was set to 35 rpm and the rotary blast drying temperature was set to 55 °C. The slow-release nitrogen fertilizer coated with the composite material with a coating thickness of 0.15 mm was obtained. The mixture was placed in a sealed bag, labeled, and stored in a desiccator for later use.

[0061] Test example

[0062] 1. Test materials

[0063] The experiment was conducted in 2023 and 2024 at the Rice Research Institute Experimental Base of Sichuan Agricultural University, Wenjiang District, Chengdu, Sichuan Province (30°70′N, 103°83′E). The experimental field had sandy loam soil in the topsoil layer (0-20 cm) with a total nitrogen content of 1.65 g / kg, organic matter of 19.67 g / kg, alkaline-hydrolyzable nitrogen of 113.92 mg / kg, available phosphorus of 28.19 mg / kg, and available potassium of 89.88 mg / kg. The test variety was "Chuankangyou 6308," a three-line indica hybrid rice variety provided by Sichuan Agricultural University with a full growth period of 148-153.9 days. The polyvinyl alcohol starch-humic acid vermiculite coating solution was evenly spread on a glass plate and rolled with an extrusion rod coater. The rod coater specifications were 50μm, 100μm, 150μm, and 200μm. The resulting film thicknesses were 0.05mm, 0.10mm, 0.15mm, and 0.20mm. After the film dried to a constant weight, the polyvinyl alcohol starch slow-release film with water and fertilizer retention and controlled release properties was obtained. The water absorption rate of the film was measured, and the water and fertilizer retention and controlled release properties of the film thicknesses of 0.05mm, 0.10mm, 0.15mm, and 0.20mm were determined; the thickness of the slow-release coating was then determined.

[0064] 2. Experimental treatment

[0065] 2.1 Comparative test of membrane water absorption and coating thickness

[0066] Take 1g of each square starch-polyvinyl alcohol film with a thickness of 0.05mm, 0.10mm, 0.15mm, and 0.20mm, weigh it W0, and place it in a beaker filled with deionized water to fully absorb water. After the film swells at room temperature for 24 hours, it is spread on a mesh to remove the water on the surface of the film, and then weighed on an analytical balance, record it as W1. Let M represent the water absorption rate in deionized water and salt water, then:

[0067]

[0068] Where: M-water absorption (%); W0-weight of the film before water absorption (g); W1-weight of the film after water absorption (g).

[0069] 2.2 Soil leaching test

[0070] A PVC tube with an inner diameter of 6 cm and a height of 20 cm was used for the soil column leaching test. The lower end of the tube was first blocked with cotton wool and sealed with gauze. 25 g of quartz sand was added to the bottom of the PVC tube. 100 g of air-dried soil, previously sieved through a 2 mm sieve, was then added. 6 g of standard urea and a slow-release nitrogen fertilizer (the nitrogen content was consistent with that of standard urea fertilizer) were then added. 100 g of air-dried soil was then added, and finally, 25 g of quartz sand was added to cover the tube. At the beginning of the experiment, 100 mL of deionized water was added to the sand column until the soil column reached saturation and no deionized water leaked from the bottle opening. The tube was sealed and incubated at room temperature for 24 hours. The soil column was then leached with 150 mL of deionized water via drip irrigation. The sand column was leached with 150 mL of deionized water every five days for a total of 11 leaching cycles, with the experiment repeated twice.

[0071] 2.3 Soil nutrient release and yield comparison test

[0072] The experiment adopted a single-factor completely randomized block design with two treatments: the control group (T1) with conventional nitrogen fertilizer and the experimental group (T2) with slow-release nitrogen fertilizer. The experiment was repeated three times and the plot area was 10m×11m=110m. 2 Rice was sown on April 18 and transplanted on May 20, with a row spacing of 33.3 cm × 16.7 cm, and single seedlings were planted. Each plot was separated by a 40 cm ridge and wrapped with plastic film. Fertilizer and water management were consistent, and pest and disease control was carried out. Each plot was applied with 150 kg / hm2 of N. -2 , the amount of phosphate fertilizer applied is equivalent to P2O575 kg / hm -2 , potassium fertilizer application rate is equivalent to K2O 120kg / hm -2 Phosphorus and potassium fertilizers are applied as basal fertilizers at one time. Conventional nitrogen fertilizer is applied in a ratio of basal fertilizer: tillering fertilizer: ear fertilizer = 3:3:4. Base fertilizer is applied 1 day before transplanting, tillering fertilizer is applied 7 days after transplanting, and ear fertilizer is applied in equal amounts when the plant has 4 leaves and 2 leaves respectively. Slow-release nitrogen fertilizer is applied as basal fertilizer at one time.

[0073] 3. Measurement items and result analysis

[0074] 3.1 Determination of membrane water absorption and membrane thickness:

[0075] After the membranes swelled for 24 hours, they were spread on a screen to remove surface water until no more surface water evaporated, and then weighed on a balance. The results are shown in Table 1. The optimal 24-hour water absorption rate for a 0.15 mm membrane thickness was 20%-25%, indicating an optimal rate of water ingress and optimal nitrogen fertilizer dissolution and release. However, other treatments with excessively high water absorption rates were detrimental to nitrogen fertilizer nutrient release.

[0076] Table 1 Water absorption rate of different coating thicknesses and determination of the optimal coating thickness

[0077]

[0078]

[0079] 3.2 Release rate of slow-release nitrogen fertilizer:

[0080] After collecting the leachate from the soil leaching experiment, the total volume of the leachate was weighed with a measuring cylinder, and a small amount of leachate was taken with a pipette to determine its total nitrogen content using the Kjeldahl method. Figure 1 As shown in the figure, urea released almost all of its nitrogen on the 20th day, reaching 82.47%. On the 52nd day, the slow-release nitrogen fertilizer released nearly 80% of its nitrogen. This indicates that the slow-release nitrogen fertilizer coated using the method described in this patent affects the total nitrogen release rate in the soil column, reducing the release rate of the nitrogen fertilizer and demonstrating a significant slow-release effect.

[0081] 3.3 Rice production:

[0082] Harvest 10m in each plot at maturity 2 The yield was calculated based on the actual area, excluding the plants in the edge rows. The grain moisture was measured with a grain moisture meter (PM-8188-A, Kett Electric Laboratory, Tokyo, Japan), and the actual yield was converted based on the standard moisture content of 13.5%. Figure 2 As shown, the rice yield of the slow-release nitrogen fertilizer coated by the method involved in this patent is significantly higher than the rice yield obtained by conventional urea at the same nitrogen application rate.

[0083] 3.4 Soil nitrogen content:

[0084] Sampling was carried out at the tillering stage, jointing stage, booting stage and maturity stage respectively. 0-20cm soil samples were collected using the diagonal 5-point sampling method and mixed evenly. After the soil samples were brought back to the laboratory, plant debris and gravel were manually picked up. They were naturally air-dried in a pollution-free room, ground, and sieved through 20 mesh and 100 mesh sieves respectively for the determination of total nitrogen content in the soil. The test results are as follows: Figure 3 As shown. In the early tillering stage, because the release rate of slow-release nitrogen fertilizer is lower than that of conventional urea, the total nitrogen content in the soil treated with the slow-release nitrogen fertilizer coated by the patent method is lower than that treated with conventional urea. However, at other stages, it is higher than that of conventional urea at the same nitrogen application rate, indicating that the slow-release nitrogen fertilizer has a good fertilizer retention effect.

[0085] It should be noted that, in this document, terms such as "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0086] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite material-coated slow-release nitrogen fertilizer, comprising: (1) Dissolve 6 g of polyvinyl alcohol in 70 g of deionized water, stir at 200-250 rpm for 1 h, and heat to 90° C. Then, add gelatinized starch, 0.1 g of borax, and 3.0 ml of glycerol in sequence and continue heating and stirring to obtain a first mixed solution for use; (2) adding 1.0 g of maleic acid to the first mixed solution with stirring, and continuing stirring at 500-600 rpm for 1 h under heating conditions of 60-70° C. to obtain a second mixed solution; (3) dissolving the vermiculite-humic acid film in the second mixed solution and stirring, adding 0.5 g of sodium lignin sulfonate, stirring and mixing at room temperature, and ultrasonicating to obtain a polyvinyl alcohol starch-vermiculite humic acid coating solution; (4) Urea was first added into a disc granulator, and then polyvinyl alcohol starch-vermiculite humic acid coating solution was added and mixed. The speed and temperature of the disc granulator were set, and the mixture was dried at a constant temperature to a constant weight, thereby obtaining a slow-release nitrogen fertilizer coated with a composite material having a coating thickness of 0.15 mm.

2. The preparation method according to claim 1, wherein: The gelatinized starch in step (1) is prepared by the following method: 4.0 g corn starch was mixed with 80.0 ml deionized water, heated in a constant temperature water bath at 85° C. for gelatinization, and stirred at 500-600 rpm for 0.5 h to obtain gelatinized starch.

3. The preparation method according to claim 1, wherein: The conditions for continuing heating and stirring in step (1) are: Continue stirring at 60°C and 500-600 rpm for 2 h.

4. The preparation method according to claim 1, wherein: The vermiculite-humic acid film in step (3) is prepared by the following method: (3.1) 20 g of vermiculite powder was acidified by adding 200 ml of a 3.6% hydrochloric acid solution. After drying, the mixture was mixed with 200 ml of a 1% sodium chloride solution and ultrasonically treated. The mixture was centrifuged and allowed to stand for 2 h. The lower precipitate was separated and dried in a constant temperature forced air oven to constant weight to obtain the modified vermiculite. (3.2) Modified vermiculite and humic acid were mixed and dissolved in deionized water. The mixture was ultrasonically treated at a power of 200-220W for 10-15 minutes to obtain a soil dispersion. The soil dispersion was then vacuum filtered through a cellulose nitrate membrane with a pore size of 0.45μm. The mixture was dried in a constant temperature forced air oven to a constant weight. The mixture was separated from the filter membrane to obtain a vermiculite-humic acid membrane for later use.

5. The preparation method according to claim 3, wherein: The vermiculite powder in step (3.1) has a particle size of ≥150 mesh; the ultrasonic treatment power is 200-220w, and the ultrasonic treatment time is 20-30min; The centrifugal speed is 3000-4000 rpm, the centrifugal time is 10-15 min; the constant temperature of the blast oven is 105°C.

6. The preparation method according to claim 3, wherein: In step (3.2), the amount of modified vermiculite and humic acid is 0.6 g, and the amount of deionized water is 50 ml; The oven temperature is 20-25°C.

7. The preparation method according to claim 1, wherein: In step (3), the room temperature is 20-25° C., the stirring speed is 1000 rpm, and the stirring time is 1 h; The ultrasonic power is 120-150w, and the ultrasonic treatment time is 15-20min.

8. The preparation method according to claim 1, wherein: The urea particle size in step (4) is 3.5 mm to 4.00 mm; The mass ratio of the polyvinyl alcohol starch-vermiculite humic acid coating solution to urea is 2:

1.

9. The preparation method according to claim 1, wherein: The rotation speed of the disc granulator in step (4) is 30-40 rpm and the temperature is 55°C.

10. A slow-release nitrogen fertilizer coated with a composite material prepared according to the preparation method of any one of claims 1 to 9.

Images