Method for preparing nitrogen fertilizer by using industrial urea modified humic acid and method for preparing special slow-release fertilizer for alkaline soil

Abstract

The invention discloses a method for preparing a nitrogen fertilizer by using industrial urea modified humic acid and a method for preparing a slow-release fertilizer special for alkaline soil, and belongs to the technical field of fertilizer mixers.The method comprises the following steps that S3, low-temperature chemical crosslinking is conducted, adding epoxy chloropropane accounting for 30% of the mass of the humic acid, and reacting under the conditions that the temperature is 60 DEG C and the pH is 8-9 to obtain a low-temperature chemical cross-linked humic acid-urea core; s4, photocatalytic reaction: adding 0.05% of TiO2 / graphene composite photocatalyst into a reaction system obtained in the step S3, and adjusting the pH value to 4-5; and reacting at room temperature for 2-4 hours under the irradiation of visible light with the wavelength of 300-400nm to form the photoresponse type artificial humic acid-urea compound. According to the invention, the humic acid can be prevented from being modified by using industrial urea at high temperature, the generation of biuret is thoroughly eliminated, and the nitrogen release rate is positively correlated with the illumination intensity.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of fertilizer mixtures, in particular to a method for preparing nitrogen fertilizer by modifying humic acid with industrial urea and a method for preparing special slow-release fertilizer for alkaline soil. BACKGROUND

[0002] In agricultural production, efficient utilization of nitrogen fertilizer has been a key problem that has plagued the sustainable development of agriculture, especially in alkaline soil environments, nitrogen loss is particularly serious. Urea, as the most important nitrogen fertilizer, is easily hydrolyzed under the catalysis of urease after being applied to soil, producing ammonia volatilization, resulting in low nitrogen utilization rate, less than 35%, and causing environmental pollution. According to research, in alkaline soil, ammonia volatilization loss of urea can be as high as 40-50%, which seriously restricts the economic benefits and ecological safety of agricultural production.

[0003] In traditional compound fertilizers, humic acid and urea are physically mixed, and the two are spatially separated and function independently: urea provides nitrogen; humic acid improves soil and stimulates growth, which will cause the following problems: humic acid is dispersed in the soil and is easily fixed or mineralized, and the improvement effect is limited and short-lived. By chemical modification (such as condensation, grafting), urea molecules are connected to the humic acid macromolecular skeleton by covalent bonds or strong hydrogen bonds to form a "humic acid-urea" complex (HA-Urea), which realizes: spatially close combination: nitrogen source "anchored" on the humic acid carrier; synchronous regulation of release: nitrogen release is regulated by the humic acid degradation / enzymatic process; humic acid can activate phosphorus, potassium and trace elements in the soil. After modification, multiple nutrients are supplied in the rhizosphere, improving overall fertilizer efficiency. To solve this problem, existing technologies mainly focus on the following directions:

[0004] The first method is physical embedding technology. By embedding urea in sodium alginate, starch, chitosan and other natural polymer materials, microcapsules or particles are formed to delay the release of urea. However, such materials have poor stability under alkaline conditions, and the molecular chain is easily dissociated, leading to rapid disintegration of the embedding structure, which cannot effectively control the release of urea, making it difficult to meet the long-acting slow-release requirements in alkaline soil environments.

[0005] The second method is high-temperature condensation: urea and humic acid are reacted at 80-100°C to form HA-Urea complex. This process easily leads to the condensation of urea itself to generate toxic by-products, biuret, which often exceeds the national standard (≤1.5%) and significantly inhibits seed germination and seedling growth. The reason for using high temperature is that the melting point of urea is about 132-135°C, which means that at 140°C, urea is completely in a liquid state and can better penetrate into the pore structure of A-HA. At higher temperatures, molecular motion is accelerated, which can accelerate the diffusion process after urea melting, thus achieving the desired penetration effect faster.

[0006] The third method is to add urease inhibitors. Commercial inhibitors such as NBPT (N-(n-butyl) thiophosphoryl triamide) are directly mixed with urea to slow down urea hydrolysis by inhibiting urease activity. This method has some effect, but has the disadvantages of high cost, short duration, and susceptibility to environmental factors, and single reliance on chemical inhibitors makes it difficult to achieve precise matching of nitrogen release and crop demand.

[0007] Melting penetration method: urea is melted at a temperature above 132°C and then penetrated into the pores of humic acid. This method has high energy consumption, and high temperatures increase the risk of biuret formation, while also potentially damaging the active structure of humic acid. Both biuret and urea are easily soluble in water, while the target product (modified humic acid) may be partially soluble in water or form a colloid. Washing limitations: when washing with water or ethanol, unreacted urea can be washed away, but the already formed biuret will coexist with the product in the aqueous phase or be adsorbed on the solid surface, making it difficult to completely remove by simple washing.

[0008] The existing technology has obvious limitations in addressing the problem of efficient utilization of nitrogen in alkaline soils, therefore, there is an urgent need to develop a new type of slow-release fertilizer preparation technology that can effectively inhibit ammonia volatilization (target inhibition rate > 70%) and has environmental responsiveness and controllable cost, to meet the dual needs of precision fertilization and green development in modern agriculture.

[0009] When using urea-modified humic acid (HA-Urea complex) to replace part of the free urea and humic acid, the nitrogen release mechanism changes fundamentally: chemical bond slow release: urea is combined with humic acid through amide bonds (-CONH-) or hydrogen bonds, which requires soil microorganisms or enzymes to release ammonium nitrogen, significantly delaying the release rate of nitrogen; reducing ammonia volatilization: humic acid itself can adsorb NH4 + and inhibit urease activity, and this effect is stronger after modification; improving soil retention: humic acid-urea complex is affinity to soil colloids and is not easily leached with water. SUMMARY

[0010] As described in the prior art above, one of the purposes of the present application is to provide a method for preparing nitrogen fertilizer by modifying humic acid with industrial urea, which can avoid modifying humic acid with industrial urea at high temperature, completely eliminate the formation of biuret, and realize the synchronization of nitrogen release rate with the peak of crop nitrogen absorption.

[0011] The second purpose of the present application is to provide a method for preparing a slow-release fertilizer special for alkaline soil, which prevents the initial loss of unmodified free urea and is special for alkaline soil fertilizer.

[0012] The purposes of the present application are achieved by the following technical solutions:

[0013] A method for preparing nitrogen fertilizer by modifying humic acid with industrial urea, comprising the following method steps:

[0014] S1, fractionally extracting artificial humic acid by a pH continuous dissolution method to obtain a high-aromaticity A-HA3-4 component;

[0015] S2, dissolving the A-HA3-4 in a buffer solution with a pH of 4-5 to prepare a 0.5% humic acid solution;

[0016] S3, low-temperature chemical crosslinking: adding 0.25% urea derivatives and 30% epoxy chloropropane based on the mass of humic acid to the humic acid solution, and reacting at 60°C and pH 8-9 for 2 hours to obtain a low-temperature chemically crosslinked humic acid-urea inner core (HA-U-EPI);

[0017] S4, photocatalytic reaction: adding 0.05% TiO2 / graphene composite photocatalyst to the reaction system obtained in step S3 and adjusting the pH back to 4-5; under 300-400 nm visible light irradiation, reacting at room temperature (25°C) for 2-4 hours to form a light-responsive artificial humic acid-urea composite; mixing A-HA3-4 and urea at a mass ratio of 1:1;

[0018] S5, obtaining a light-responsive artificial humic acid-urea composite by centrifugal separation and freeze-drying, wherein the light-responsive artificial humic acid-urea composite is used for preparing nitrogen fertilizer.

[0019] Further, in step S3, the urea derivative is N-hydroxymethyl urea.

[0020] Further, the mass ratio of TiO2 to graphene in the TiO2 / graphene composite photocatalyst is 1:1-3, and the TiO2 is anatase phase.

[0021] Further, the light-responsive artificial humic acid-urea complex can degrade residual pesticides in the soil, and the residual amount of organophosphorus pesticides in the soil is reduced by 15-25%.

[0022] Further, in step S1, the aromaticity index of the high aromaticity A-HA3-4 component is 0.7-0.9.

[0023] Further, the light-responsive artificial humic acid-urea complex has a biuret content of less than 0.5%.

[0024] The second purpose of the application is achieved by the following technical scheme:

[0025] A method for preparing a special slow-release fertilizer for alkaline soil, comprising the following steps:

[0026] T1, intermediate layer wrapping: dispersing the low-temperature chemically cross-linked humic acid-urea core (HA-U-EPI) in a humic acid solution containing a benzoquinone compound, forming a urease inhibition layer on the surface of the core by electrostatic adsorption, and controlling the thickness of the urease inhibition layer to be 50-100 nm;

[0027] T2, outer layer modification: immersing the microspheres coated with the urease inhibition layer in an acrylamide-acrylic acid copolymer P(AM-co-AA) solution, using layer-by-layer self-assembly technology to construct 3-5 layers of polymer outer layer, and finally cross-linking with glutaraldehyde to enhance the structural stability;

[0028] T3, post-treatment: freeze-drying the product obtained in step S3 to obtain the special slow-release fertilizer particles for alkaline soil with a particle size of 150-250 μm.

[0029] Further, the benzoquinone compound is selected from at least one of benzoquinone, chlorobenzoquinone, and hydroxybenzoquinone, and the addition amount is 0.5-2.0% of the mass of humic acid, which is used to synergistically inhibit the activity of urease with humic acid, and the inhibition rate is ≥75%.

[0030] Further, the molecular weight of the acrylamide-acrylic acid copolymer is 50-200 thousand, the molar ratio of acrylamide to acrylic acid is (7:3)-(9:1), and the solution concentration is 0.5-2.0 wt%.

[0031] Compared with the prior art, the application has the following advantages:

[0032] (1) The application provides a method for preparing nitrogen fertilizer by modifying humic acid with industrial urea, which uses N-hydroxymethyl urea instead of industrial urea, and the --NH2 of which has been protected by --CH2OH, the activity of which is controllable and will not cause self-condensation; at 60 DEG C, it can be efficiently reacted with the --COOH / --OH of humic acid to form stable ether bonds ( --C --O --C --) and amide bonds ( --CONH --), completely avoiding the urea self-condensation path caused by high temperature, and eliminating the formation of biuret from the source. In the traditional method, urea is easy to self-condense to form biuret at 80-100 DEG C. Using the method of chemical bonding, such as using epichlorohydrin as a crosslinking agent, it can be carried out under milder conditions, which usually includes lower temperature and shorter reaction time, avoiding the generation of by-products; low temperature conditions reduce unnecessary side reactions, such as the formation of biuret, and the content of biuret is <0.5% (far lower than the industry standard of 1.5%). Epichlorohydrin reacts with the --COOH / --OH of humic acid and the --NH2 of urea at the same time, forming a double connection of stable ether bonds and amide bonds, and the crosslinking degree is high. A new mechanism of "photocatalytic assisted molecular assembly" is proposed, and the TiO2 / graphene composite photocatalyst generates active oxygen (·OH) under visible light, ·OH attacks the free radical sites generated on the surface of humic acid, and covalent grafting occurs with the catalyst, realizing in-situ chemical anchoring of the catalyst, non-physical adsorption, and the firmness is improved by more than 3 times. In addition, a stimulation-inhibition reverse response system is constructed, which is light response: light intensity↑ → ROS↑ → humic acid network oxidative degradation → nitrogen release↑, which is more suitable for the heat demand rhythm of plant photosynthesis. Photocatalytic degradation of organophosphorus pesticides has the function of soil remediation.

[0033] (2) The application provides a method for preparing a slow-release fertilizer special for alkaline soil, which adopts an intermediate layer wrapping: dispersing the low-temperature chemically crosslinked humic acid-urea core (HA-U-EPI) in a humic acid solution containing a benzoquinone compound, forming a urease inhibition layer on the surface of the core through electrostatic adsorption, controlling the thickness of the urease inhibition layer to be 50-100 nm, inhibiting the contact of urease with urea, preventing the initial loss of unmodified free urea, and controlling the cumulative release rate of nitrogen in 30 days to be 40-60%, thereby significantly prolonging the fertilizer efficiency; the microspheres coated with the urease inhibition layer are immersed in a polyacrylamide-polyacrylic acid copolymer P(AM-co-AA) solution, a 3-5 layer polymer outer layer is constructed by using layer-by-layer self-assembly technology, and finally glutaraldehyde is used for crosslinking treatment, so as to enhance the structural stability, and the method is more suitable for the demand of alkaline soil. Due to the following mechanism: pH response: pH↑ (alkaline) → P(AM-co-AA) ionization ( --COO - ) → hydrogen bond network densification → urea release↓, the ammonia volatilization inhibition rate in alkaline soil is >70%. DETAILED DESCRIPTION

[0034] Hereinafter, the present application will be further described in conjunction with specific embodiments. It should be noted that the following described embodiments or technical features can be combined arbitrarily to form new embodiments.

[0035] Embodiment 1

[0036] The present embodiment provides a method for preparing nitrogen fertilizer by modifying humic acid with industrial urea, a method for preparing nitrogen fertilizer by modifying humic acid with industrial urea, comprising the following method steps:

[0037] S1, using eucalyptus leaves as raw material, artificial humic acid (A-HS) is obtained by hydrothermal humification at 200℃ for 24h, and the artificial humic acid is fractionally extracted by pH continuous dissolution method to obtain high aromaticity A-HA3-4 component, and the aromaticity index of the high aromaticity A-HA3-4 component is 0.7;

[0038] S2, dissolving A-HA3-4 in a buffer solution with pH 4.5 to prepare a 0.5% humic acid solution;

[0039] S3, low-temperature chemical crosslinking: adding 0.25% urea derivative N-hydroxymethyl urea and 30% epoxy chloropropane based on the mass of humic acid into the humic acid solution, and reacting at 60℃ and pH 8.5 for 2 hours to obtain a low-temperature chemically crosslinked humic acid-urea inner core (HA-U-EPI);

[0040] S4, photocatalytic reaction: adding 0.05% TiO2 / graphene composite photocatalyst into the reaction system obtained in step S3, adjusting the pH back to 5, the mass ratio of TiO2 to graphene in the TiO2 / graphene composite photocatalyst is 1:2, and the TiO2 is anatase phase; under 300nm visible light irradiation, reacting at room temperature (25℃) for 3 hours, λ=365 nm, 120 mW / cm², so that the catalyst is firmly anchored on the surface of HA-U-EPI through a light-induced free radical grafting mechanism, forming a light-responsive artificial humic acid-urea composite; mixing A-HA3-4 and urea at a mass ratio of 1:1;

[0041] S5, obtaining the light-responsive artificial humic acid-urea composite by centrifugal separation and freeze-drying, and the light-responsive artificial humic acid-urea composite is used for preparing nitrogen fertilizer.

[0042] Detection: the biuret content is 0.38%, and the photocatalytic degradation efficiency of methyl parathion pesticide reaches 21%.

[0043] Embodiment 2

[0044] The present embodiment provides a method for preparing nitrogen fertilizer by modifying humic acid with industrial urea, comprising the following method steps:

[0045] S1, obtaining high aromaticity A-HA3-4 component by pH continuous dissolution method for grading extraction of artificial humic acid, the aromaticity index of the high aromaticity A-HA3-4 component is 0.8;

[0046] S2, dissolving A-HA3-4 in a buffer solution with pH 4 to prepare a 0.5% humic acid solution;

[0047] S3, low-temperature chemical crosslinking: adding 0.25% urea derivative and 30% epoxy chloropropane based on the mass of humic acid to the humic acid solution, and reacting at 60°C and pH 8 for 3 hours to obtain a low-temperature chemically crosslinked humic acid-urea inner core (HA-U-EPI);

[0048] S4, photocatalytic reaction: adding 0.05% TiO2 / graphene composite photocatalyst to the reaction system obtained in step S3, adjusting the pH back to 4, the mass ratio of TiO2 to graphene in the TiO2 / graphene composite photocatalyst is 1:1; under 360nm visible light irradiation, reacting at room temperature (25°C) for 2 hours to form a light-responsive artificial humic acid-urea composite; mixing A-HA3-4 and urea at a mass ratio of 1:1;

[0049] S5, obtaining the light-responsive artificial humic acid-urea composite by centrifugal separation and freeze-drying, and using the light-responsive artificial humic acid-urea composite to prepare nitrogen fertilizer.

[0050] Detection: biuret content is 0.26%, and the photocatalytic degradation efficiency of methyl parathion is 15%.

[0051] Example 3

[0052] The embodiment provides a method for preparing nitrogen fertilizer by modifying humic acid with industrial urea, comprising the following method steps:

[0053] S1, obtaining high aromaticity A-HA3-4 component by pH continuous dissolution method for grading extraction of artificial humic acid, the aromaticity index of the high aromaticity A-HA3-4 component is 0.9;

[0054] S2, dissolving A-HA3-4 in a buffer solution with pH 5 to prepare a 0.5% humic acid solution;

[0055] S3, low-temperature chemical crosslinking: adding 0.25% urea derivative and 30% epoxy chloropropane (EPI) based on the mass of humic acid to the humic acid solution, and reacting at 60°C and pH 9 for 4 hours to obtain a low-temperature chemically crosslinked humic acid-urea inner core (HA-U-EPI);

[0056] S4, photocatalytic reaction: 0.05% TiO2 / graphene composite photocatalyst was added to the reaction system obtained in step S3, the pH was adjusted back to 4.5, the mass ratio of TiO2 to graphene in the TiO2 / graphene composite photocatalyst was 1:3; under 400 nm visible light irradiation, the reaction was carried out at room temperature (25℃) for 3 hours to form a light-responsive artificial humic acid-urea complex; A-HA3-4 was mixed with urea at a mass ratio of 1:1;

[0057] S5, the light-responsive artificial humic acid-urea complex was obtained by centrifugal separation and freeze-drying, and the light-responsive artificial humic acid-urea complex was used for preparing nitrogen fertilizer.

[0058] Detection: biuret content 0.18%, photocatalytic degradation of pesticide methyl parathion efficiency reached 25%.

[0059] Example 4

[0060] A method for preparing a special slow-release fertilizer for alkaline soil, comprising the following steps:

[0061] T1, intermediate layer wrapping: the low-temperature chemically cross-linked humic acid-urea core (HA-U-EPI) was dispersed in a humic acid solution containing a benzoquinone compound, and a urease inhibition layer was formed on the surface of the core by electrostatic adsorption, and the thickness of the urease inhibition layer was controlled to be 80 nm;

[0062] T2, outer layer modification: the microspheres coated with the urease inhibition layer were immersed in an acrylamide-acrylic acid copolymer P(AM-co-AA) solution, and a three-layer polymer outer layer was constructed by using layer-by-layer self-assembly technology, and finally glutaraldehyde was used for cross-linking treatment to enhance the structural stability;

[0063] T3, post-treatment: the product obtained in step S3 was freeze-dried to obtain alkaline soil special slow-release fertilizer particles with a particle size of 250 μm.

[0064] In this embodiment, the benzoquinone compound benzoquinone is used to synergistically inhibit the activity of urease with humic acid, and the inhibition rate is ≥75%.

[0065] In this embodiment, the molecular weight of the acrylamide-acrylic acid copolymer is 50,000, the molar ratio of acrylamide to acrylic acid is 7:3, and the solution concentration is 2.0 wt%.

[0066] Example 5

[0067] A method for preparing a special slow-release fertilizer for alkaline soil, comprising the following steps:

[0068] T1, intermediate layer wrapping: the low-temperature chemical cross-linked humic acid-urea inner core (HA-U-EPI) is dispersed in a humic acid solution containing chloranil, and a urease inhibition layer is formed on the surface of the inner core by electrostatic adsorption, and the thickness of the urease inhibition layer is controlled to be 50 nm;

[0069] T2, outer layer modification: the microspheres coated with the urease inhibition layer are immersed in an acrylamide-acrylic acid copolymer P(AM-co-AA) solution, and a 4-layer polymer outer layer is constructed by using layer-by-layer self-assembly technology, and finally glutaraldehyde is used for cross-linking treatment to enhance the structural stability;

[0070] T3, post-processing: the product obtained in step S3 is freeze-dried to obtain a basic soil special slow-release fertilizer particle with a particle size of 150 μm.

[0071] In this embodiment, the quinone compound chloranil is used to cooperate with humic acid to inhibit urease activity, and the inhibition rate is ≥75%.

[0072] In this embodiment, the molecular weight of the acrylamide-acrylic acid copolymer is 100,000, the molar ratio of acrylamide to acrylic acid is 9:1, and the solution concentration is 0.5 wt%.

[0073] Example 6

[0074] A method for preparing a basic soil special slow-release fertilizer, comprising the following steps:

[0075] T1, intermediate layer wrapping: the low-temperature chemical cross-linked humic acid-urea inner core (HA-U-EPI) is dispersed in a humic acid solution containing chloranil, and a urease inhibition layer is formed on the surface of the inner core by electrostatic adsorption, and the thickness of the urease inhibition layer is controlled to be 50 nm;

[0076] T2, outer layer modification: the microspheres coated with the urease inhibition layer are immersed in an acrylamide-acrylic acid copolymer P(AM-co-AA) solution, and a 4-layer polymer outer layer is constructed by using layer-by-layer self-assembly technology, and finally glutaraldehyde is used for cross-linking treatment to enhance the structural stability;

[0077] T3, post-processing: the product obtained in step S3 is freeze-dried to obtain a basic soil special slow-release fertilizer particle with a particle size of 150 μm.

[0078] In this embodiment, the quinone compound is selected from hydroxyquinone, which is used to cooperate with humic acid to inhibit urease activity, and the inhibition rate is ≥75%.

[0079] In this embodiment, the molecular weight of the acrylamide-acrylic acid copolymer is 200,000, the molar ratio of acrylamide to acrylic acid is 7:3, and the solution concentration is 1.0 wt%.

[0080] Test: in the soil with pH=8.5, the urease activity inhibition rate is 78%, and the nitrogen release rate is decreased by 52% compared with the control.

[0081] The above embodiments are only preferred embodiments of the present application, and cannot be used to limit the protection scope of the present application. Any non-essential changes and replacements made by those skilled in the art on the basis of the present application shall fall within the protection scope of the present application.

Claims

1. A method for preparing nitrogen fertilizer using industrial urea-modified humic acid, characterized by, The method comprises the following steps: S1. Using eucalyptus leaves as raw materials, artificial humic acid is obtained by hydrothermal humification at 200 DEG C for 24 hours, and the artificial humic acid is fractionally extracted by a pH continuous dissolution method to obtain a high-aromaticity A-HA3-4 component; S2. The A-HA3-4 is dissolved in a buffer solution with a pH of 4-5 to prepare a 0.5% humic acid solution; S3. Low-temperature chemical crosslinking: 0.25% urea derivatives and 30% epoxy chloropropane based on the mass of the humic acid are added to the humic acid solution, and the solution is reacted at 60 DEG C and a pH of 8-9 for 2 hours to obtain a low-temperature chemically crosslinked humic acid-urea core; S4. Photocatalytic reaction: 0.05% TiO2 / graphene composite photocatalyst is added to the reaction system obtained in step S3, and the pH is adjusted back to 4-5; under the irradiation of 300-400 nm visible light at room temperature, the reaction is carried out for 2-4 hours to form a light-responsive artificial humic acid-urea composite; the A-HA3-4 and urea are mixed at a mass ratio of 1:1; S5. The light-responsive artificial humic acid-urea composite is obtained by centrifugal separation and freeze-drying, and the light-responsive artificial humic acid-urea composite is used for preparing nitrogen fertilizer.

2. The method for preparing nitrogen fertilizer using industrial urea modified humic acid according to claim 1, characterized in that, In step S3, the urea derivative is N-hydroxymethyl urea.

3. The method for preparing nitrogen fertilizer using industrial urea modified humic acid according to claim 1, characterized in that, In the TiO2 / graphene composite photocatalyst, the mass ratio of TiO2 to graphene is 1:1-3, and the TiO2 is in an anatase phase.

4. The method for preparing nitrogen fertilizer using industrial urea modified humic acid according to claim 3, characterized in that, The light-responsive artificial humic acid-urea composite can degrade residual pesticides in soil, and the residual amount of organophosphorus pesticides in the soil is reduced by 15-25%.

5. The method for preparing nitrogen fertilizer using industrial urea modified humic acid according to claim 1, characterized in that, In step S1, the aromaticity index of the high-aromaticity A-HA3-4 component is 0.7-0.

9.

6. The method for preparing nitrogen fertilizer using industrial urea modified humic acid according to claim 1, characterized in that, The content of biuret in the light-responsive artificial humic acid-urea composite is less than 0.5%.

7. A method of preparing a slow release fertilizer specific to alkaline soil, characterized in that, The method comprises the following steps: T1. Intermediate layer wrapping: the low-temperature chemically crosslinked humic acid-urea core is dispersed in a humic acid solution containing a benzoquinone compound, and a urease inhibition layer is formed on the surface of the core by electrostatic adsorption, and the thickness of the urease inhibition layer is controlled to be 50-100 nm; T2. Outer layer modification: the microspheres coated with the urease inhibition layer are immersed in an acrylamide-acrylic acid copolymer solution, and 3-5 layers of polymer outer layers are constructed by using a layer-by-layer self-assembly technique, and finally glutaraldehyde is used for crosslinking treatment to enhance the structural stability; T3. Post-treatment: the product obtained in step S3 is freeze-dried to obtain the alkaline soil special slow-release fertilizer particles with a particle size of 150-250 μm.

8. A process for the preparation of slow release special fertilizer for alkaline soil as claimed in claim 7, wherein, The benzoquinone compound is selected from at least one of benzoquinone, chlorobenzoquinone and hydroxybenzoquinone, and the addition amount is 0.5-2.0% of the mass of the humic acid, which is used to inhibit the activity of urease in cooperation with the humic acid, and the inhibition rate is ≥75%.

9. A process for the preparation of slow release special fertilizer for alkaline soil as claimed in claim 7, wherein the said process is characterized by, The molecular weight of the acrylamide-acrylic acid copolymer is 50,000-200,000, the molar ratio of acrylamide to acrylic acid is (7:3)-(9:1), and the solution concentration is 0.5-2.0 wt%.