Special three-level controlled-release nitrogen blended fertilizer for rice and preparation method thereof

Abstract

The invention relates to a special three-stage controlled-release nitrogen blended fertilizer for rice and a preparation method thereof, and belongs to the technical field of fertilizers. The preparation method comprises the following steps: heating and stirring montmorillonite and a hydrochloric acid aqueous solution, filtering, washing, drying, soaking in a urea solution, adjusting the pH value, stirring and mixing, carrying out suction filtration, and freeze-drying to obtain composite particles; preheating deionized water, adding polyvinyl alcohol, stirring and mixing, cooling, adding absolute ethyl alcohol and glycerol, uniformly mixing, heating, spraying on the surfaces of the composite particles, and drying to obtain an intermediate; uniformly mixing lysine and an ethanol solution, adding 3, 4-dihydroxybenzaldehyde, heating, stirring, primarily drying, adding the intermediate, stirring at constant temperature, carrying out vacuum drying to obtain a controlled-release nitrogen fertilizer, adding a basic fertilizer, and mixing to obtain the controlled-release nitrogen fertilizer. The slow-release fertilizer has environmental responsiveness and biodegradability in an adsorption coating manner, the dissolution rate of urea is greatly reduced, and three-stage controlled release of nitrogen elements is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of fertilizers, and relates to a special three-stage controlled-release nitrogen blended fertilizer for rice and a preparation method thereof. Background Art

[0002] During the rice planting process, the application of slow-release fertilizers mainly involves several key stages. In the initial stage, namely the rice seedling raising period, the application of slow-release fertilizers can ensure that the seedlings obtain continuous nutrition and thus grow healthily. Subsequently, in the initial stage when the rice is transplanted to a new environment, the slow-release fertilizers continuously release nutrients to help the rice quickly adapt and enhance its disease resistance and growth momentum. When the rice enters the tillering and jointing stages, the demand for nutrients increases significantly, and the slow-release fertilizers provide sufficient nutrients at this time to ensure the smooth growth of the rice and achieve high yields. Finally, in the mature stage of the rice, the slow-release fertilizers continue to provide the required nutrients to assist the rice in completing the filling process, thereby improving the quality and yield of the paddy rice.

[0003] As a natural mineral, montmorillonite, with its unique layered structure and adsorption properties, can effectively adsorb and fix the nitrogen element in nitrogen fertilizers, thereby realizing the slow release of nitrogen. This not only meets the continuous nutritional needs during the rice growth process but also significantly improves the utilization rate of fertilizers and reduces the loss of nitrogen and environmental pollution. However, the adsorption between montmorillonite and nitrogen is physical adsorption, and its interaction force is weak, which easily leads to the rapid desorption of nitrogen under high-temperature, high-humidity or water conditions, thus affecting the controlled-release effect. Summary of the Invention

[0004] The purpose of the present invention is to provide a special three-stage controlled-release nitrogen blended fertilizer for rice and a preparation method thereof. In the present invention, montmorillonite treated with hydrochloric acid is used as a carrier to adsorb urea, and polyvinyl alcohol forms a dense water-soluble film on the surface of the composite particles. Finally, a Schiff base structure formed by lysine and 3,4-dihydroxybenzaldehyde forms a three-dimensional cross-linked network on the surface of the intermediate, enhancing the mechanical strength and water resistance of the coating layer, making the slow-release fertilizer have both environmental responsiveness and biodegradability, greatly reducing the dissolution rate of urea, and realizing the three-stage controlled release of nitrogen elements.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice includes the following steps:

[0007] 1) After heating and stirring montmorillonite and an aqueous hydrochloric acid solution, filtering, washing, and drying, pretreated montmorillonite is obtained;

[0008] 2) The pretreated montmorillonite is immersed in a urea solution, the pH value is adjusted, and then stirring and mixing are carried out. After suction filtration and freeze-drying, composite particles are obtained;

[0009] 3) After preheating deionized water, add polyvinyl alcohol and stir to mix, then cool down the temperature, add anhydrous ethanol and glycerol and mix evenly. After heating up the temperature, spray it on the surface of the composite particles, and after drying, obtain the intermediate;

[0010] 4) After mixing lysine and ethanol solution evenly, add 3,4-dihydroxybenzaldehyde and stir by heating. After preliminary drying, add the intermediate and stir at a constant temperature, then carry out vacuum drying to obtain the controlled-release nitrogen fertilizer. After adding and mixing with the basic fertilizer, it is obtained.

[0011] As a preferred technical solution of the present invention, in step 1), the heating and stirring is carried out at a temperature of 40-50 °C for 45-60 min. The washing is carried out with pure water until the surface is neutral. The drying is carried out at 110-120 °C for 1.0-1.5 h.

[0012] As a preferred technical solution of the present invention, in step 1), the mass ratio of the montmorillonite to the hydrochloric acid aqueous solution is 10-13:40-50. The concentration of the hydrochloric acid aqueous solution is 5-8 wt%. After the montmorillonite is activated by hydrochloric acid, its own adsorption performance can be effectively improved.

[0013] As a preferred technical solution of the present invention, in step 2), the pH value is adjusted to 7-8. The stirring and mixing is carried out at a rotation speed of 300-500 rpm for 2-3 h.

[0014] As a preferred technical solution of the present invention, in step 2), the dosage ratio of the pretreated montmorillonite to the urea solution is 3 g:60-65 mL. The urea solution is formed by mixing urea and deionized water according to a mass ratio of 12-18:100. Attapulgite forms a stable complex with urea through physical interception, hydrogen bond bonding and ion exchange.

[0015] As a preferred technical solution of the present invention, in step 3), the preheating temperature is 80 °C. The stirring and mixing is carried out at a temperature of 80-90 °C and a rotation speed of 500-800 rpm for 1.5-2.0 h. The cooling and temperature reduction is to reduce the temperature to 40 °C. The heating and temperature increase is to heat to a temperature of 45 °C. The drying is carried out at 60 °C until constant weight.

[0016] As a preferred technical solution of the present invention, in step 3), the mass ratio of the polyvinyl alcohol, deionized water, anhydrous ethanol, glycerol and the composite particles is 5-6:30-38:5-6:1.5-2.0:30-32.

[0017] As a preferred technical solution of the present invention, in step 4), the heating and stirring is carried out by adjusting the pH to 5.5 - 6.0 with acetic acid and stirring at a temperature of 50 - 60 °C for 2 - 3 h. The constant temperature stirring is carried out by stirring at 40 °C for 20 - 30 min. The initial drying is carried out by drying at a temperature of 50 °C until the water content is 20 wt%. The vacuum drying is carried out by drying at 70 °C to constant weight.

[0018] As a preferred technical solution of the present invention, in step 4), the mass ratio of lysine, ethanol solution, 3,4 - dihydroxybenzaldehyde and the intermediate is 2 - 3:25 - 30:1.3 - 1.6:21 - 24; the ethanol solution is composed of ethanol and deionized water mixed in a volume ratio of 7:3.

[0019] As a preferred technical solution of the present invention, in step 4), the mass ratio of the controlled - release nitrogen fertilizer and the basic fertilizer is 1.8 - 2.3:1.0 - 1.2. The basic fertilizer is composed of potassium nitrate, triple superphosphate and metal salt mixed in a mass ratio of 30 - 35:13 - 15:0.2 - 0.5. The metal salt is one or more of magnesium salt, iron salt, zinc salt and selenium salt.

[0020] A special - use three - stage controlled - release nitrogen blended fertilizer for rice prepared by the above - mentioned preparation method.

[0021] Advantages of the present invention:

[0022] In the present invention, montmorillonite treated with hydrochloric acid is used as a carrier to adsorb urea, a dense water - soluble film is formed on the surface of the composite particles with polyvinyl alcohol, and finally a three - dimensional cross - linked network is formed on the surface of the intermediate by the Schiff base structure formed by lysine and 3,4 - dihydroxybenzaldehyde, enhancing the mechanical strength and water resistance of the coating layer, making the slow - release fertilizer have both environmental responsiveness and biodegradability, greatly reducing the urea dissolution rate, and realizing the three - stage controlled release of nitrogen elements. Specific embodiments

[0023] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the specific embodiments, structures, features and their effects of the present invention in combination with examples. The polyvinyl alcohol used in the specific embodiments is polyvinyl alcohol 1788.

[0024] Example 1

[0025] A preparation method of a special - use three - stage controlled - release nitrogen blended fertilizer for rice includes the following steps:

[0026] 1) Stir montmorillonite and hydrochloric acid aqueous solution at 40 °C for 45 min, filter to obtain the solid, wash it with pure water until the surface is neutral, and dry it at 110 °C for 1.0 h to obtain pretreated montmorillonite; wherein, the mass ratio of the montmorillonite to the hydrochloric acid aqueous solution is 10:40; the concentration of the hydrochloric acid aqueous solution is 5 wt%;

[0027] 2) Immerse the pretreated montmorillonite in the urea solution, adjust the pH value to 7, stir at 300 rpm for 2 h, filter by suction, and freeze-dry to obtain composite particles; wherein, the dosage ratio of the pretreated montmorillonite to the urea solution is 3 g:60 mL; the urea solution is composed of urea and deionized water mixed according to the mass ratio of 12:100;

[0028] 3) After preheating deionized water to 80 °C, add polyvinyl alcohol and stir at 80 °C and 500 rpm for 1.5 h, cool down to 40 °C, add anhydrous ethanol and glycerol and mix well, heat up to 45 °C and spray it on the surface of the composite particles, and dry at 60 °C to constant weight to obtain the intermediate; wherein, the mass ratio of the polyvinyl alcohol, deionized water, anhydrous ethanol, glycerol and the composite particles is 5:30:5:1.5:30;

[0029] 4) Mix lysine and ethanol solution well, add 3,4-dihydroxybenzaldehyde, adjust the pH to 5.5 with acetic acid, stir at 50 °C for 2 h, dry at 50 °C until the water content is 20 wt%, add the intermediate and stir at 40 °C for 20 min, and then dry at 70 °C to constant weight to obtain the controlled-release nitrogen fertilizer. After adding and mixing with the basic fertilizer, it is obtained; wherein, the mass ratio of the lysine, ethanol solution, 3,4-dihydroxybenzaldehyde and the intermediate is 2:25:1.3:21; the ethanol solution is composed of ethanol and deionized water mixed according to the volume ratio of 7:3; the mass ratio of the controlled-release nitrogen fertilizer to the basic fertilizer is 1.8:1.0; the basic fertilizer is composed of potassium nitrate, triple superphosphate and metal salt mixed according to the mass ratio of 30:13:0.2; the metal salt is composed of magnesium sulfate, ferric sulfate and ammonium zinc sulfate mixed according to the mass ratio of 1:1:1.

[0030] Example 2

[0031] A preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice comprises the following steps:

[0032] 1) Stir montmorillonite and hydrochloric acid aqueous solution at 43 °C for 50 min, filter to obtain the solid, wash it with pure water until the surface is neutral, and dry it at 115 °C for 1.5 h to obtain pretreated montmorillonite; wherein, the mass ratio of the montmorillonite to the hydrochloric acid aqueous solution is 11:43; the concentration of the hydrochloric acid aqueous solution is 6 wt%;

[0033] 2) Immerse the pretreated montmorillonite in the urea solution. After adjusting the pH value to 7.3, stir at a speed of 360 rpm for 2.5 h, perform suction filtration, and then conduct freeze-drying to obtain composite particles. Among them, the dosage ratio of the pretreated montmorillonite to the urea solution is 3 g: 62 mL; the urea solution is prepared by mixing urea and deionized water according to a mass ratio of 14: 100;

[0034] 3) After preheating the deionized water to 80 °C, add polyvinyl alcohol and stir at a temperature of 83 °C and a speed of 600 rpm for 1.5 h. Cool down to 40 °C, add anhydrous ethanol and glycerol and mix well. Heat up to 45 °C and then spray it on the surface of the composite particles, and dry at 60 °C until constant weight to obtain an intermediate. Among them, the mass ratio of polyvinyl alcohol, deionized water, anhydrous ethanol, glycerol and the composite particles is 5.3: 33: 5.3: 1.7: 31;

[0035] 4) After mixing lysine and the ethanol solution, add 3,4-dihydroxybenzaldehyde, adjust the pH to 5.7 with acetic acid, stir at a temperature of 53 °C for 2.5 h, dry at a temperature of 50 °C until the water content is 20 wt%, add the intermediate and stir at 40 °C for 25 min, and then dry at 70 °C until constant weight to obtain the controlled-release nitrogen fertilizer. After adding and mixing with the basic fertilizer, it is obtained. Among them, the mass ratio of lysine, the ethanol solution, 3,4-dihydroxybenzaldehyde and the intermediate is 2.3: 27: 1.4: 22; the ethanol solution is prepared by mixing ethanol and deionized water according to a volume ratio of 7: 3; the mass ratio of the controlled-release nitrogen fertilizer to the basic fertilizer is 2: 1.05; the basic fertilizer is composed of potassium nitrate, triple superphosphate and metal salt according to a mass ratio of 32: 13.5: 0.3; the metal salt is composed of magnesium sulfate, ferric sulfate and ammonium zinc sulfate according to a mass ratio of 1: 1: 1.

[0036] Example 3

[0037] A preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice comprises the following steps:

[0038] 1) Stir the montmorillonite and the hydrochloric acid aqueous solution at a temperature of 47 °C for 55 min, filter to obtain the solid, wash it with pure water until the surface is neutral, and dry at 115 °C for 1.5 h to obtain the pretreated montmorillonite. Among them, the mass ratio of the montmorillonite to the hydrochloric acid aqueous solution is 12: 47; the concentration of the hydrochloric acid aqueous solution is 7 wt%;

[0039] 2) Immerse the pretreated montmorillonite in the urea solution. After adjusting the pH value to 7.7, stir at a speed of 430 rpm for 2.5 h, perform suction filtration, and then conduct freeze-drying to obtain composite particles. Among them, the dosage ratio of the pretreated montmorillonite to the urea solution is 3 g: 65 mL; the urea solution is prepared by mixing urea and deionized water according to a mass ratio of 16: 100;

[0040] 3) After preheating deionized water to 80 °C, add polyvinyl alcohol and stir at 87 °C and 700 rpm for 1.8 h. Cool down to 40 °C, add anhydrous ethanol and glycerol and mix well. Heat up to 45 °C and spray it on the surface of the composite particles, and dry at 60 °C to constant weight to obtain an intermediate; wherein, the mass ratio of polyvinyl alcohol, deionized water, anhydrous ethanol, glycerol and composite particles is 5.5:35:5.5:1.8:31.5;

[0041] 4) After mixing lysine and ethanol solution, add 3,4-dihydroxybenzaldehyde and adjust the pH to 5.8 with acetic acid, stir at 57 °C for 2.5 h, dry at 50 °C until the water content is 20 wt%, add the intermediate and stir at 40 °C for 25 min, and then dry at 70 °C to constant weight to obtain the controlled-release nitrogen fertilizer. After adding and mixing with the basic fertilizer, it is obtained; wherein, the mass ratio of lysine, ethanol solution, 3,4-dihydroxybenzaldehyde and intermediate is 2.7:28:1.5:23; the ethanol solution is composed of ethanol and deionized water mixed according to a volume ratio of 7:3; the mass ratio of the controlled-release nitrogen fertilizer and the basic fertilizer is 2.1:1.15; the basic fertilizer is composed of potassium nitrate, triple superphosphate and metal salt mixed according to a mass ratio of 33:14.5:0.4; the metal salt is composed of magnesium sulfate, ferric sulfate and ammonium zinc sulfate mixed according to a mass ratio of 1:1:1.

[0042] Example 4

[0043] A preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice comprises the following steps:

[0044] 1) Stir montmorillonite and hydrochloric acid aqueous solution at 50 °C for 60 min, filter to obtain the solid, wash it with pure water until the surface is neutral, and dry at 120 °C for 1.5 h to obtain pretreated montmorillonite; wherein, the mass ratio of montmorillonite and hydrochloric acid aqueous solution is 13:50; the concentration of the hydrochloric acid aqueous solution is 8 wt%;

[0045] 2) Immerse the pretreated montmorillonite in the urea solution, adjust the pH value to 8, stir at 500 rpm for 3 h, filter by suction, and freeze-dry to obtain composite particles; wherein, the dosage ratio of the pretreated montmorillonite and the urea solution is 3 g:65 mL; the urea solution is composed of urea and deionized water mixed according to a mass ratio of 18:100;

[0046] 3) After preheating deionized water to 80 °C, add polyvinyl alcohol and stir at 90 °C and 800 rpm for 2.0 h. Cool down to 40 °C, add anhydrous ethanol and glycerol and mix well. Heat up to 45 °C and spray it on the surface of the composite particles, and dry at 60 °C to constant weight to obtain an intermediate; wherein, the mass ratio of polyvinyl alcohol, deionized water, anhydrous ethanol, glycerol and composite particles is 6:38:6:2.0:32;

[0047] 4) After mixing lysine and ethanol solution, add 3,4-dihydroxybenzaldehyde, adjust the pH to 6.0 with acetic acid, stir at 60 °C for 3 h, dry at 50 °C until the water content is 20 wt%, add the intermediate, stir at 40 °C for 30 min, and then dry at 70 °C to constant weight to obtain the controlled-release nitrogen fertilizer. After adding and mixing with the basic fertilizer, it is obtained; wherein, the mass ratio of lysine, ethanol solution, 3,4-dihydroxybenzaldehyde and the intermediate is 3:30:1.6:24; the ethanol solution is composed of ethanol and deionized water mixed in a volume ratio of 7:3; the mass ratio of the controlled-release nitrogen fertilizer and the basic fertilizer is 2.3:1.2; the basic fertilizer is composed of potassium nitrate, triple superphosphate and metal salt mixed in a mass ratio of 35:15:0.5; the metal salt is composed of magnesium sulfate, ferric sulfate and ammonium zinc sulfate mixed in a mass ratio of 1:1:1.

[0048] Comparative Example 1

[0049] Compared with Example 3, the difference in Comparative Example 1 is that step 1) is not carried out, montmorillonite is used instead of pretreated montmorillonite, and the other components, preparation steps and parameters are the same.

[0050] Comparative Example 2

[0051] Compared with Example 3, the difference in Comparative Example 2 is that step 2) is not carried out, pretreated montmorillonite is used instead of the composite particles, and the other components, preparation steps and parameters are the same.

[0052] Comparative Example 3

[0053] Compared with Example 3, the difference in Comparative Example 3 is that threonine is used instead of lysine, and the other components, preparation steps and parameters are the same.

[0054] Comparative Example 4

[0055] Compared with Example 3, the difference in Comparative Example 4 is that lysine is not used, and the other components, preparation steps and parameters are the same.

[0056] Comparative Example 5

[0057] Compared with Example 3, the difference in Comparative Example 5 is that 3,4-dihydroxybenzaldehyde is not used, and the other components, preparation steps and parameters are the same.

[0058] The controlled-release nitrogen fertilizers prepared in Examples 1-4 and Comparative Examples 1-5 were respectively subjected to the following performance tests, and the test results are shown in Table 1.

[0059] Water dissolution experiment: According to the standard of GB / T23348-2009, it is measured by the water dissolution rate method. Respectively take 10 grams of slow-release fertilizer, soak them in 250 grams of pure water respectively, and place them in an incubator at 28°C. Measure the dissolution rate of urea on the 7th day and the 60th day respectively. Dissolution rate (%) = mass of urea dissolved on the Nth day / total initial urea mass * 100%;

[0060] Table 1 Dissolution rate (%)

[0061]

[0062]

[0063] It can be seen from the test results in Table 1 that compared with Comparative Examples 1-6, the slow-release fertilizers prepared by the present invention have a significant slow-release effect.

[0064] From the test results in Table 1 and the analysis in combination with the comparison between Examples 1-4 and Comparative Examples 1-5, this is because montmorillonite treated with hydrochloric acid in the present invention is used as a carrier to adsorb urea, and polyvinyl alcohol is used to form a dense water-soluble film on the surface of the composite particles. The physical barrier delays the penetration of water and the diffusion of urea to achieve urea slow release. Finally, the Schiff base structure formed by lysine and 3,4-dihydroxybenzaldehyde forms a three-dimensional cross-linked network on the surface of the intermediate, enhancing the mechanical strength and water resistance of the coating layer, making the slow-release fertilizer have both environmental adaptability and biodegradability. The Schiff base structure is a dynamic covalent bond that can be slowly broken under the action of water or microorganisms to achieve "self-repair" or "responsive release". The cross-linked network fills the micropore defects of the polyvinyl alcohol film layer, reducing the water penetration rate and further decreasing the urea dissolution rate; while the diamino lysine significantly increases the grafting rate of dihydroxybenzaldehyde. The benzene ring structure on dihydroxybenzaldehyde promotes the formation of a more dense structure. One end of the aldehyde group of dihydroxybenzaldehyde forms a chemical bond connection with the amino group of lysine, and the other end of the dihydroxy group can form a hydrogen bond physical force with the carboxyl group of lysine, further improving the structural density and greatly improving the urea slow-release effect.

[0065] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any indirect modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a special three - stage controlled - release nitrogen blended fertilizer for rice, characterized in that, It includes the following steps: 1) After heating and stirring montmorillonite and hydrochloric acid aqueous solution, filtering, washing, and drying, pretreated montmorillonite is obtained; 2) The pretreated montmorillonite is soaked in urea solution, the pH value is adjusted, then stirred and mixed, suction filtered, and freeze-dried to obtain composite particles; 3) After preheating deionized water, adding polyvinyl alcohol and stirring and mixing, cooling down, adding anhydrous ethanol and glycerol and mixing evenly, heating up and spraying on the surface of the composite particles, and drying to obtain an intermediate; 4) Lysine and ethanol solution are mixed evenly, 3,4-dihydroxybenzaldehyde is added and heated and stirred, after preliminary drying, the intermediate is added and stirred at a constant temperature, and then vacuum dried to obtain controlled-release nitrogen fertilizer. After adding and mixing with basic fertilizer, it is obtained.

2. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 1), the heating and stirring is carried out at a temperature of 40 - 50 °C for 45 - 60 min; the washing is with pure water until the surface is neutral; the drying is at 110 - 120 °C for 1.0 - 1.5 h.

3. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 1), the mass ratio of the montmorillonite to the hydrochloric acid aqueous solution is 10 - 13:40 - 50; the concentration of the hydrochloric acid aqueous solution is 5 - 8 wt%.

4. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 2), the pH value is adjusted to 7 - 8; the stirring and mixing is carried out at a rotation speed of 300 - 500 rpm for 2 - 3 h.

5. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 2), the dosage ratio of the pretreated montmorillonite to the urea solution is 3 g:60 - 65 mL; the urea solution is composed of urea and deionized water mixed according to a mass ratio of 12 - 18:

100.

6. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 3), the preheating temperature is 80 °C; the stirring and mixing is carried out at a temperature of 80 - 90 °C and a rotation speed of 500 - 800 rpm for 1.5 - 2.0 h; the cooling down is to cool to 40 °C; the heating up is to heat to 45 °C; the drying is at 60 °C until constant weight.

7. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 3), the mass ratio of the polyvinyl alcohol, deionized water, anhydrous ethanol, glycerol and the composite particles is 5 - 6:30 - 38:5 - 6:1.5 - 2.0:30 - 32.

8. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 4), the heating and stirring is carried out by adjusting the pH to 5.5 - 6.0 with acetic acid and stirring at a temperature of 50 - 60 °C for 2 - 3 h; the constant temperature stirring is at 40 °C for 20 - 30 min; the preliminary drying is at 50 °C until the water content is 20 wt%; the vacuum drying is at 70 °C until constant weight.

9. The preparation method of a special three-stage controlled-release nitrogen blended fertilizer for rice according to claim 1, characterized in that: In step 4), the mass ratio of the lysine, ethanol solution, 3,4-dihydroxybenzaldehyde and the intermediate is 2 - 3:25 - 30:1.3 - 1.6:21 - 24; the ethanol solution is composed of ethanol and deionized water mixed according to a volume ratio of 7:3; the mass ratio of the controlled-release nitrogen fertilizer to the basic fertilizer is 1.8 - 2.3:1.0 - 1.2; the basic fertilizer is composed of potassium nitrate, triple superphosphate and metal salt mixed according to a mass ratio of 30 - 35:13 - 15:0.2 - 0.5; the metal salt is one or more of magnesium salt, iron salt, zinc salt and selenium salt.

10. A special three-stage controlled-release nitrogen blended fertilizer for rice prepared by the preparation method according to any one of claims 1 to 9.

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