Granular slow-release water-soluble fertilizer and preparation method thereof

Abstract

The invention belongs to the field of pesticide and chemical fertilizers, and particularly discloses a granular slow-release water-soluble fertilizer and a preparation method thereof.The granular slow-release water-soluble fertilizer is prepared from, by weight, 2-5 parts of a slow-release material and 60-70 parts of an element water-soluble fertilizer; wherein the element water-soluble fertilizer comprises liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, ammonium nitrate phosphorus and monoammonium phosphate; the sustained-release material comprises lignin and PLA, and the granular sustained-release water-soluble fertilizer is high in quick-acting property, less in permeation loss and long in drug release time.

Description

Technical Field

[0001] The invention belongs to the field of pesticides and fertilizers, and in particular relates to a granular slow-release water-soluble fertilizer and a preparation method thereof. Background Art

[0002] Water-soluble fertilizer is a water-soluble fertilizer containing a large amount of elements such as nitrogen, phosphorus, and potassium. It has the advantages of complete nutrients, flexible application methods, and fast fertilizer effect. It is suitable for various fertilization systems, such as bottom application, flushing, drip irrigation, sprinkler irrigation, foliar spraying, etc., and can truly realize the integration of water and fertilizer, thereby achieving the effect of saving water, fertilizer, labor and time.

[0003] Since water-soluble fertilizers are fast-acting and difficult to store in the soil for a long time, and crops cannot fully absorb a large amount of nutrients in a short period of time, there will be volatilization loss, osmotic loss, and fixed reaction between fertilizer ions and soil, which will reduce the economic benefits of fertilization. In addition, the current water-soluble fertilizers in my country have relatively backward production processes and unscientific formula concentrations. Some companies simply mix urea with potassium nitrate, potassium sulfate, water-soluble monoammonium phosphate and other raw materials after crushing it. The fertilizers produced often have deliquescence, flatulence, compaction, uneven dyeing, excessive impurities, poor water solubility and other phenomena.

[0004] These common problems of elemental water-soluble fertilizers can be solved by slow-release treatment. Patent CN112250497B discloses a lignin-based modified coating material and its preparation method and application. The coating material is obtained by cross-linking modification and hydrophobic esterification modification of lignin-based materials in sequence. It can improve the physical and chemical properties of soil for a long time and prolong the release time of urea, but the coating rate of this method is low. Patent CN104370627B discloses a slow-release water-soluble fertilizer and its preparation method. The anions and cations of the water-soluble fertilizer are captured simultaneously by ion capture agents, and the dissolved nutrients are collected and enriched and slowly released at the roots of plants, providing microcirculation for plant roots to absorb nutrients, but the ion capture agents may be affected by the soil environment and become ineffective. Summary of the invention

[0005] In order to overcome the problems of low coating rate and susceptibility of slow-release water-soluble fertilizer to soil environment, the present invention prepares granular slow-release water-soluble fertilizer through special slow-release material, which can combine more fertilizers and is not affected by soil environment, thus ensuring the effectiveness of nutrients.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A first aspect of the present invention provides a granular slow-release water-soluble fertilizer, which comprises the following raw materials, by weight: 2-5 parts of slow-release materials and 60-70 parts of elemental water-soluble fertilizer; wherein the elemental water-soluble fertilizer comprises liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, ammonium nitrate phosphate, monoammonium phosphate and a chelating agent; and the slow-release material comprises lignin and PLA.

[0008] In some embodiments, the total content of the liquid ammonia and sulfuric acid in the elemental water-soluble fertilizer is 6-8wt%.

[0009] Preferably, based on 100wt%, the elemental water-soluble fertilizer comprises 5-7wt% liquid ammonia, 14-15wt% phosphorus pentoxide, 0.8-1.6wt% sulfuric acid, 0.1-0.9wt% zinc sulfate, 34-38wt% potassium sulfate, 31-35wt% ammonium nitrate phosphate and 7-10wt% monoammonium phosphate.

[0010] The slow-release water-soluble fertilizer provided by the present invention has sufficient nutrients and a longer release period, can provide nutrients for crops at various growth stages, reduce losses due to leaching and volatilization, improve fertilizer utilization, and reduce environmental pollution caused by excessive fertilization; and the slow-release material provided by the present invention can also avoid the formation of insoluble metal complex salts by metal ions introduced during the production of raw materials and trace elements added in the form of sulfates, reduce the content of water-insoluble matter, make it unaffected by the soil environment, and ensure the effectiveness of the nutrients.

[0011] In some embodiments, the preparation steps of the sustained-release material are as follows:

[0012] S1, dissolving acrylamide, ammonium persulfate and N,N-2-methylacrylamide in deionized water, stirring for 30-60 minutes and then ultrasonicating for 20-40 minutes to obtain prepolymer 1;

[0013] S2, stirring lignin and ethyl acetate evenly, adding vinylbenzyl chloride, ethylene glycol dimethacrylate and azobisisobutyronitrile, stirring at 70-80° C. for 2-4 h, then heating to 85-95° C. for 2-6 h, with a rotation speed of 200-400 rpm, and cooling to room temperature to obtain prepolymer 2;

[0014] S3, adding a molding protective agent to the prepolymer 2 of step S2, stirring at 20-30° C. for 2-6 hours, then heating to 30-50° C., adding anhydrous ferric chloride, stirring for 40-60 minutes, first quenching the reaction with a 40-50wt% ethanol aqueous solution, and then washing with anhydrous ethanol and water for 2-3 times respectively to obtain a prepolymer 3;

[0015] S4, adding the prepolymer 1 of step S1 to the prepolymer 3 of step S3, stirring for 50-70 minutes, and ultrasonicating for 20-40 minutes to obtain the sustained-release material.

[0016] In some embodiments, the mass ratio of acrylamide to N,N-2-methylacrylamide in step S1 is 1:(0.0005-0.0015).

[0017] In some embodiments, the mass ratio of lignin, vinylbenzyl chloride and ethylene glycol dimethacrylate in step S2 is 1:(3.5-4.5):(3.2-4.8).

[0018] The slow-release material prepared by the present invention firstly utilizes the matrix formed after the polymerization of acrylamide to provide a certain rigidity, so that the slow-release particles formed by the fertilizer and the slow-release material will not be easily crushed, thereby extending the shelf life; secondly, the lignin is initially cross-linked with vinylbenzyl chloride and ethylene glycol dimethacrylate, which provides better compatibility and solves the agglomeration phenomenon between lignins; thirdly, the improved compatibility of lignin brings about the problem that the pore size of the slow-release material is too large and single. For this reason, the present application promotes further cross-linking by adding anhydrous ferric chloride, thereby increasing the specific surface area and porosity of the material, reducing the pore size, and converting the -CH2Cl in the initial cross-linking into a rigid methylene cross-linking bridge, thereby stabilizing the micropores; fourthly, the nitroxide group introduced in step S4 can cooperate with the molding protective agent to enhance the binding force between the slow-release material and the fertilizer.

[0019] In some embodiments, the preparation step of the molding protective agent in step S3 is as follows: PLA, glycidyl methacrylate and dichloromethane are stirred at 5-15° C. until dissolved to obtain the molding protective agent.

[0020] In some embodiments, the mass ratio of PLA to glycidyl methacrylate is 1:(0.3-0.5).

[0021] The present invention introduces a molding protective agent containing PLA into the slow-release material. On the one hand, the porous material can bind more fertilizers by strengthening the binding force between the slow-release material and the fertilizer formed by electrostatic interaction and π-π stacking.

[0022] Secondly, the epoxy groups on the glycidyl methacrylate molecules can undergo ring-opening reactions with the hydroxyl groups on the lignin molecules and the two ends of the PLA molecular chain, and graft a large number of methacrylic acid short chains, which is beneficial to enhance the interfacial interaction between lignin and PLA, so that the easy processability of PLA can be effectively reflected;

[0023] Thirdly, the three-dimensional network macromolecular structure and hydrophobic alkane chains formed by the polymerization of acrylamide are intertwined with the PLA molecular chains, destroying the regular arrangement of the original crystalline regions of PLA and forming a stable network structure, thereby giving PLA a toughening effect and avoiding the formation of micropores caused by the breakage of some molecular chains during the granulation and stretching process, so that the sustained-release material can ensure the particle forming rate during roller extrusion.

[0024] In some embodiments, the granular slow-release water-soluble fertilizer is suitable for base application and broadcast application.

[0025] The second aspect of the present invention provides a method for preparing a granular slow-release water-soluble fertilizer, comprising the following steps: firstly mixing and stirring the slow-release material and the elemental water-soluble fertilizer evenly, and then performing roller granulation to obtain the granular slow-release water-soluble fertilizer.

[0026] In some embodiments, the particle size of the granular slow-release water-soluble fertilizer obtained by roller granulation is sieved through a 5-7 mesh sieve.

[0027] Since the present invention eliminates the post-processing of the previous steps in the process of preparing the slow-release material, although the process is simplified and the cost is saved, it contains a certain amount of moisture. The sulfuric acid added to the raw material can increase the reaction heat. The heat released by the reaction of ammonia and sulfuric acid is very large, which can be used to evaporate and remove part of the moisture in the slow-release material, thereby extending the shelf life of the obtained slow-release water-soluble fertilizer; at the same time, the slow-release material and the elemental water-soluble fertilizer can generate a small amount of ammonium polyphosphate fertilizer during the roller granulation process, further increasing the effective duration of the fertilizer.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The granular slow-release water-soluble fertilizer provided by the present invention has sufficient nutrients, a long release period, is not easily affected by the soil environment, and has a high fertilizer utilization rate.

[0030] 2. The slow-release material provided by the present invention is environmentally friendly and biodegradable, can be combined with a large amount of fertilizers, and has a suitable pore size and porosity, can provide a channel for the release of fertilizers, and control the slow-release rate of fertilizers.

[0031] 3. The preparation method of the granular slow-release water-soluble fertilizer provided by the present invention has a simple process, and the forming rate of the granules obtained by roller extrusion is high. DETAILED DESCRIPTION

[0032] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0033] In order to facilitate those skilled in the art to implement the present invention, some raw materials and manufacturers of the embodiments and comparative examples are described as follows:

[0034] PLA was purchased from Nature Works, model 7032D;

[0035] Lignin was purchased from Shandong Longli Biotechnology Co., Ltd.

[0036] Preparation Example 1

[0037] The preparation steps of molding protective agent-A are as follows:

[0038] 20 g of PLA, 8 g of glycidyl methacrylate and 500 mL of dichloromethane were stirred at 10° C. until dissolved to obtain a molding protective agent-A.

[0039] Preparation Example 2

[0040] The preparation steps of molding protective agent-B are as follows:

[0041] The specific steps of this preparation example are the same as those of Preparation Example 1, except that 4 g of glycidyl methacrylate is used.

[0042] Preparation Example 3

[0043] The preparation steps of molding protective agent-C are as follows:

[0044] The specific steps of this preparation example are the same as those of Preparation Example 1, except that 12 g of glycidyl methacrylate is used.

[0045] Preparation Example 4

[0046] The preparation steps of sustained-release material-A are as follows:

[0047] S1, dissolving 71.8 g acrylamide, 0.36 g ammonium persulfate and 0.065 g N,N-2-methylacrylamide in 500 mL deionized water, stirring for 45 min and then ultrasonicating for 30 min to obtain prepolymer 1;

[0048] S2, 1.8 g of lignin was mixed evenly with 100 mL of ethyl acetate, 7.2 g of vinylbenzyl chloride, 7.6 g of ethylene glycol dimethacrylate and 0.8 g of azobisisobutyronitrile were added, and the mixture was stirred at 75° C. for 3 h, and then heated to 90° C. and stirred for 4 h at a speed of 300 rpm. After cooling to room temperature, prepolymer 2 was obtained;

[0049] S3, add 142 mL of molding protective agent-A to the prepolymer 2 of step S2, stir at 25° C. for 4 h, then heat to 40° C., add 9 g of anhydrous ferric chloride, stir for 50 min, quench the reaction with a 45 wt % ethanol aqueous solution until the temperature does not change, then wash with anhydrous ethanol and water for 3 times respectively to obtain prepolymer 3;

[0050] S4. Add the prepolymer 1 of step S1 to the prepolymer 3 of step S3, stir for 60 minutes, and perform ultrasound for 30 minutes to obtain the sustained-release material-A.

[0051] Preparation Example 5

[0052] The preparation steps of sustained-release material-B are as follows:

[0053] The specific steps of this preparation example are the same as those of Preparation Example 4, except that the amount of N,N-2-methylacrylamide used in step S1 is 0.029 g.

[0054] Preparation Example 6

[0055] The preparation steps of sustained-release material-C are as follows:

[0056] The specific steps of this preparation example are the same as those of Preparation Example 4, except that the amount of N,N-2-methylacrylamide used in step S1 is 0.114 g.

[0057] Preparation Example 7

[0058] The preparation steps of sustained-release material-D are as follows:

[0059] The specific implementation of this preparation example is the same as that of Example 4, except that in step S3, the molding protective agent-A is replaced by an equal amount of the molding protective agent-B.

[0060] Preparation Example 8

[0061] The preparation steps of sustained-release material-E are as follows:

[0062] The specific implementation of this preparation example is the same as that of Example 4, except that in step S3, the molding protective agent-A is replaced by an equal amount of molding protective agent-C.

[0063] Example 1

[0064] A granular slow-release water-soluble fertilizer, comprising the following raw materials by weight: 3.5 parts of slow-release material-A and 65 parts of elemental water-soluble fertilizer;

[0065] Wherein, based on 100wt%, the elemental water-soluble fertilizer comprises 6.5wt% liquid ammonia, 14.4wt% phosphorus pentoxide, 1.2wt% sulfuric acid, 0.5wt% zinc sulfate, 35.9wt% potassium sulfate, 32.9wt% ammonium nitrate phosphate and 8.6wt% monoammonium phosphate;

[0066] The preparation steps of the slow-release water-soluble fertilizer in this embodiment are as follows: first, the slow-release material-A, liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, potassium sulfate, ammonium nitrate phosphate and monoammonium phosphate are mixed and stirred evenly, and then roller granulated and passed through a 6-mesh sieve to obtain a granular slow-release water-soluble fertilizer.

[0067] Example 2

[0068] A granular slow-release water-soluble fertilizer, comprising the following raw materials, by weight: 2 parts of slow-release material-A and 60 parts of elemental water-soluble fertilizer;

[0069] Wherein, based on 100wt%, the elemental water-soluble fertilizer comprises 5wt% liquid ammonia, 14wt% phosphorus pentoxide, 1.6wt% sulfuric acid, 0.5wt% zinc sulfate, 38wt% potassium sulfate, 32wt% ammonium nitrate phosphate and 8.9wt% monoammonium phosphate;

[0070] The preparation steps of the slow-release water-soluble fertilizer in this embodiment are as follows: first, the slow-release material-A, liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, potassium sulfate, ammonium nitrate phosphate and monoammonium phosphate are mixed and stirred evenly, and then roller granulated and passed through a 7-mesh sieve to obtain a granular slow-release water-soluble fertilizer.

[0071] Example 3

[0072] A granular slow-release water-soluble fertilizer, comprising the following raw materials, by weight: 5 parts of slow-release material-A and 70 parts of elemental water-soluble fertilizer;

[0073] Wherein, based on 100wt%, the elemental water-soluble fertilizer comprises 7wt% liquid ammonia, 15wt% phosphorus pentoxide, 0.8wt% sulfuric acid, 0.9wt% zinc sulfate, 34wt% potassium sulfate, 32.7wt% ammonium nitrate phosphate and 9.6wt% monoammonium phosphate;

[0074] The preparation steps of the slow-release water-soluble fertilizer in this embodiment are as follows: first, the slow-release material-A, liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, potassium sulfate, ammonium nitrate phosphate and monoammonium phosphate are mixed and stirred evenly, and then roller granulated and passed through a 5-mesh sieve to obtain a granular slow-release water-soluble fertilizer.

[0075] Example 4

[0076] This embodiment provides a granular slow-release water-soluble fertilizer and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the slow-release material-A is replaced by an equal portion of the slow-release material-B.

[0077] Example 5

[0078] This embodiment provides a granular slow-release water-soluble fertilizer and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the slow-release material-A is replaced by an equal portion of the slow-release material-C.

[0079] Example 6

[0080] This embodiment provides a granular slow-release water-soluble fertilizer and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the slow-release material-A is replaced by an equal portion of the slow-release material-D.

[0081] Example 7

[0082] This embodiment provides a granular slow-release water-soluble fertilizer and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the slow-release material-A is replaced by an equal portion of the slow-release material-E.

[0083] Example 8

[0084] A granular slow-release water-soluble fertilizer, comprising the following raw materials, by weight: 3.5 parts of slow-release material-A and 65 parts of elemental water-soluble fertilizer;

[0085] Wherein, based on 100wt%, the elemental water-soluble fertilizer comprises 5wt% liquid ammonia, 14.4wt% phosphorus pentoxide, 0.8wt% sulfuric acid, 0.7wt% zinc sulfate, 36.2wt% potassium sulfate, 33wt% ammonium nitrate phosphate and 9.9wt% monoammonium phosphate;

[0086] The preparation steps of the slow-release water-soluble fertilizer in this embodiment are the same as those in Example 1.

[0087] Example 9

[0088] A granular slow-release water-soluble fertilizer, comprising the following raw materials, by weight: 3.5 parts of slow-release material-A and 65 parts of elemental water-soluble fertilizer;

[0089] Wherein, based on 100wt%, the elemental water-soluble fertilizer comprises 7wt% liquid ammonia, 14.4wt% phosphorus pentoxide, 1.6wt% sulfuric acid, 0.5wt% zinc sulfate, 34.9wt% potassium sulfate, 33wt% ammonium nitrate phosphate and 8.6wt% monoammonium phosphate;

[0090] The preparation steps of the slow-release water-soluble fertilizer in this embodiment are the same as those in Example 1.

[0091] Performance Test:

[0092] 1. Sustained release performance test:

[0093] According to the requirements of GB / T 23348-2009, the sustained-release performance is tested using the 25°C static water dissolution rate method. The specific steps are as follows:

[0094] (1) Weigh 2.0 g of each granular slow-release water-soluble fertilizer prepared in each example, grind it in a mortar, pour it into a beaker and dissolve it in 40 mL of deionized water to obtain the total nitrogen content of 2.0 g of the slow-release water-soluble fertilizer;

[0095] (2) Weigh 2.0 g of each granular slow-release water-soluble fertilizer prepared in each embodiment, place it in a nylon mesh bag with a pore size of 0.15 mm and seal it in a transparent plastic bottle, add 40 mL of deionized water, cover and seal it, place it in a 25°C constant temperature incubator and start timing. After 24 hours, use a 50 mL volumetric flask to completely receive the extract, adjust the volume, shake it well for testing, and add another 40 mL of deionized water to the plastic bottle to continue culturing. Use a Kjeldahl nitrogen analyzer to measure the nitrogen content in the extract after adjusting the volume;

[0096] (3) Repeat the above operation. When the cumulative nitrogen dissolution rate reaches 80% of the total nitrogen content, stop sampling and record the time.

[0097] 2. Encapsulation rate test

[0098] Take 2.0 g of each granular slow-release water-soluble fertilizer prepared in each embodiment, grind it in a mortar, pour it into a beaker and dissolve it in 40 mL of deionized water to obtain the total nitrogen content of 2.0 g of slow-release water-soluble fertilizer, recorded as N1; take 2.0 g of elemental water-soluble fertilizer with the same ratio in each embodiment to obtain the total nitrogen content, recorded as N2; coating rate = (N1 / N2)×100%.

[0099] The results are shown in Table 1.

[0100] Table 1 Performance test results

[0101]

[0102]

[0103] It can be seen from the data in Table 1 that the granular slow-release water-soluble fertilizers provided by the present invention all reach the 28-day cumulative release rate of the slow-release fertilizer specified in GB / T 23348-2009 of no more than 80%, among which the granular slow-release water-soluble fertilizers of Examples 1-3 have a long release time and a high coating rate.

[0104] Compared with Example 1, Examples 4-5 change the amount of N,N-2-methylacrylamide in the sustained-release material, which may result in a larger pore size due to insufficient cross-linking or larger pore size in certain parts due to uneven cross-linking, which is not conducive to extending the sustained-release time and reduces the coating rate to a certain extent.

[0105] Compared with Example 1, Examples 6-7 changed the amount of glycidyl methacrylate in the molding protective agent, which was not conducive to the compatibility of PLA and resulted in a decrease in the coating rate.

[0106] Compared with Example 1, the total content of liquid ammonia and sulfuric acid in the elemental water-soluble fertilizers of Examples 8-9 exceeds the specifically selected range, which is not conducive to the formation of particles in the roller compaction process, thereby reducing the sustained release time and the coating rate.

[0107] The embodiments described above do not impose any form of limitation on the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A granular slow-release water-soluble fertilizer, It is characterized in that The invention comprises the following raw materials by weight: 2-5 parts of slow-release material and 60-70 parts of elemental water-soluble fertilizer; wherein the elemental water-soluble fertilizer comprises liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, ammonium nitrate phosphate and monoammonium phosphate; and the slow-release material comprises lignin and PLA.

2. The granular slow-release water-soluble fertilizer according to claim 1, It is characterized in that The total content of the liquid ammonia and sulfuric acid in the elemental water-soluble fertilizer is 6-8wt%.

3. The granular slow-release water-soluble fertilizer according to claim 1, It is characterized in that The preparation steps of the sustained-release material are as follows: S1, dissolving acrylamide, ammonium persulfate and N,N-2-methylacrylamide in deionized water, stirring for 30-60 minutes and then ultrasonicating for 20-40 minutes to obtain prepolymer 1; S2, stirring lignin and ethyl acetate evenly, adding vinylbenzyl chloride, ethylene glycol dimethacrylate and azobisisobutyronitrile, stirring at 70-80° C. for 2-4 h, then heating to 85-95° C. for 2-6 h, with a rotation speed of 200-400 rpm, and cooling to room temperature to obtain prepolymer 2; S3, adding a molding protective agent to the prepolymer 2 of step S2, stirring at 20-30° C. for 2-6 hours, then heating to 30-50° C., adding anhydrous ferric chloride, stirring for 40-60 minutes, first quenching the reaction with a 40-50wt% ethanol aqueous solution, and then washing with anhydrous ethanol and water for 2-3 times respectively to obtain a prepolymer 3; S4, adding the prepolymer 1 of step S1 to the prepolymer 3 of step S3, stirring for 50-70 minutes, and ultrasonicating for 20-40 minutes to obtain the sustained-release material.

4. The granular slow-release water-soluble fertilizer according to claim 3, It is characterized in that The mass ratio of acrylamide to N,N-2-methylacrylamide in step S1 is 1:(0.0005-0.0015).

5. The granular slow-release water-soluble fertilizer according to claim 3, It is characterized in that In the step S2, the mass ratio of lignin, vinylbenzyl chloride and ethylene glycol dimethacrylate is 1:(3.5-4.5):(3.2-4.8).

6. The granular slow-release water-soluble fertilizer according to claim 3, It is characterized in that The preparation steps of the molding protective agent in step S3 are as follows: PLA, glycidyl methacrylate and dichloromethane are stirred at 5-15° C. until dissolved to obtain the molding protective agent.

7. The granular slow-release water-soluble fertilizer according to claim 6, It is characterized in that The mass ratio of the PLA to glycidyl methacrylate is 1:(0.25-0.55).

8. The granular slow-release water-soluble fertilizer according to claim 1, It is characterized in that The granular slow-release water-soluble fertilizer is suitable for base application and broadcast application.

9. A method for preparing the granular slow-release water-soluble fertilizer according to any one of claims 1 to 8, It is characterized in that The method comprises the following steps: firstly, the slow-release material and the elemental water-soluble fertilizer are mixed and stirred evenly, and then roller-pressed and granulated to obtain the granular slow-release water-soluble fertilizer.

10. The method for preparing the granular slow-release water-soluble fertilizer according to claim 9, It is characterized in that The particle size of the granular slow-release water-soluble fertilizer obtained by roller granulation is sieved through a 5-7 mesh sieve.

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