Preparation method of compound fertilizer with water and fertilizer retention and salt and alkali resistance functions

Abstract

The invention relates to the field of fertilizers, in particular to a preparation method of a compound fertilizer with water and fertilizer retention and salt and alkali resistance functions, which comprises the following steps: step 1, preparing aminated starch; step 2, preparing N-acryloyl glycyl chloride; step 3, preparing a starch / acryloyl glycinamide compound; step 4, weighing the starch / acryloyl glycinamide compound, adding the compound into deionized water, then adding acrylic acid and acrylamide, and carrying out copolymerization to obtain coating layer feed liquid; and step 5, spraying the coating layer feed liquid on the surfaces of the fertilizer particle cores in a spraying manner to obtain the compound fertilizer. According to the compound fertilizer prepared by the invention, a coated compound fertilizer is prepared by taking a fertilizer particle inner core as an inner core and taking a material prepared from modified starch as a coating layer. The compound fertilizer prepared by the invention has relatively strong water and fertilizer retention and slow release properties, and can play a relatively strong salt and alkali resistance function.

Description

Technical Field

[0001] The invention relates to the field of fertilizers, and in particular to a method for preparing a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistance functions. Background Art

[0002] Water and nutrient conservation is a key technology in agricultural production, aimed at improving soil moisture and nutrient retention to meet crop growth needs. Traditional methods typically increase soil water absorption by adding materials such as agro-forestry water-retaining agents or polyacrylamide. However, these materials have limited water absorption and reabsorption capacity. Furthermore, in water-scarce conditions, the water-retaining materials may compete with crops for water, limiting crop growth.

[0003] In order to solve the problems existing in traditional water and fertilizer conservation methods, some researchers have begun to try to use bio-sourced macromolecular materials to improve fertilizer conservation capacity. These bio-sourced macromolecular materials usually have groups such as hydroxyl and carboxyl groups, which can enhance the fertilizer conservation capacity of the material. In addition, these materials also have super strong water absorption capacity, which can improve the water conservation capacity of the soil. However, there are some problems and limitations with current water and fertilizer conservation materials. First, the water absorption and reabsorption times of agricultural and forestry water-retaining agents or polyacrylamide used in traditional water and fertilizer conservation methods are limited, making it difficult to meet the water needs of crops. Secondly, these materials may compete with crops for water under water-scarce conditions, resulting in restricted crop growth. In addition, existing bio-sourced macromolecular materials still have certain limitations in terms of fertilizer conservation capacity, and their performance needs to be further improved. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a new water-retaining, fertilizer-retaining, salt-alkali-resistant compound fertilizer technology package to overcome the problems and limitations existing in the prior art, improve the soil's water retention capacity and the crop's stress resistance, and improve the growth and yield of crops.

[0005] The purpose of the present invention is achieved by adopting the following technical solutions:

[0006] A method for preparing a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistant functions comprises the following steps:

[0007] Step 1: Weigh corn starch and dimethyl sulfoxide, mix them, heat and stir until a uniform mixture is formed, then add the aminosilane solution, continue to keep warm and stir for 1-2 hours, then cool to room temperature, discharge into anhydrous ethanol, centrifuge, wash and dry to obtain amino starch;

[0008] Step 2, weighing N-acryloylglycine and thionyl chloride, mixing, using nitrogen as a protective gas, heating and reflux treatment, after the reaction is completed, distilling off the solvent to obtain N-acryloylglycine chloride;

[0009] Step 3: Weigh the amino starch, add it to deionized water for gelatinization, add triethylamine dropwise, then add N-acryloylglycine chloride, stir thoroughly at room temperature for 3-5 hours, and then remove water under reduced pressure to obtain a starch / acryloylglycine amide complex;

[0010] Step 4: Weigh the starch / acryloylglycine amide complex and add it to deionized water. After heating and stirring until uniform, add acrylic acid and acrylamide, introduce nitrogen as a protective gas, add a thermal initiator, keep the temperature and stir to react for 1-2 hours, then add a photoinitiator and a crosslinking agent, and treat under ultraviolet light for 10-20 minutes to obtain a coating layer liquid;

[0011] Step 5: On the compound fertilizer production line, the coating layer liquid is sprayed on the surface of the fertilizer particle core by spraying, and after drying, a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistant functions is obtained.

[0012] Preferably, in step 1, the temperature for heating and stirring is 80-90°C.

[0013] Preferably, in step 1, the mass ratio of corn starch, dimethyl sulfoxide and aminosilane solution is 1:60-80:20-40.

[0014] Preferably, in step 1, the aminosilane solution is obtained by mixing KH-550 and deionized water in a mass ratio of 1:8-12.

[0015] Preferably, in step 2, the mass ratio of N-acryloylglycine to thionyl chloride is 1:5-10.

[0016] Preferably, in step 2, the reflux temperature is 75-85° C., and the reflux time is 4-6 h.

[0017] Preferably, in step 3, the gelatinization temperature is 60-70° C., and the gelatinization time is 0.5-1 h.

[0018] Preferably, in step 3, the mass ratio of amination starch, N-acryloylglycine chloride, triethylamine and deionized water is 1:0.28-0.56:0.01-0.05:40-60.

[0019] Preferably, in step 4, the mass ratio of starch / acryloylglycineamide complex, acrylic acid, acrylamide and deionized water is 1:0.3-0.6:0.8-1.6:40-60.

[0020] Preferably, in step 4, the reaction temperature is 60-70° C., the thermal initiator is one of sodium persulfate, ammonium persulfate, and potassium persulfate, and the amount of the thermal initiator added is 2%-6% of the mass of the starch / acryloylglycineamide complex.

[0021] Preferably, in step 4, the photoinitiator is benzoin diethyl ether or benzoin dimethyl ether, and the added amount is 1.5%-3% of the mass of the starch / acryloylglycinamide complex.

[0022] Preferably, in step 4, the cross-linking agent is N,N-methylenebisacrylamide, and the added amount is 2%-4% of the mass of the starch / acryloylglycineamide complex.

[0023] Preferably, in step 5, the inner core of the fertilizer granules is nitrogen, phosphorus and potassium fertilizers, and the mass ratio of nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer is 150-170:180-200:35-55; wherein the nitrogen fertilizer is one or more of urea, ammonium nitrate and calcium ammonium nitrate; the phosphorus fertilizer is one or more of monoammonium phosphate or diammonium phosphate; and the potassium fertilizer is one or more of potassium chloride or potassium sulfate.

[0024] Preferably, in step 5, the particle size of the inner core of the fertilizer particles is 3.1-4.8 mm.

[0025] Preferably, in step 5, the spraying thickness is 0.3-0.8 mm.

[0026] The beneficial effects of the present invention are:

[0027] The present invention prepares a composite fertilizer comprising a fertilizer granule core as the inner core and a material prepared from modified starch as the coating layer, thereby producing a coated composite fertilizer. The composite fertilizer prepared by the present invention has strong water and fertilizer retention and slow release properties, and can provide strong salt and alkali resistance.

[0028] 2. The preparation process of the composite fertilizer coating of the present invention includes the following steps: first, treating corn starch with aminosilane to obtain amino starch; then combining the starch with the prepared N-acryloylglycine chloride; the acyl chloride group combines with the amino group to form an amide, thereby obtaining a starch / acryloylglycine amide complex; and then using the starch / acryloylglycine amide complex as a monomer, initiating crosslinking copolymerization with acrylic acid and acrylamide to finally prepare the coating material.

[0029] 3. The coating layer of the compound fertilizer prepared by the present invention introduces a variety of carboxylic acid, amide and other groups, which has strong water and fertilizer retention properties, and also has good salt-removal and salt-alkali resistance, thereby improving the soil's water retention capacity and crop resistance, and improving crop growth and yield. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships, without substantially changing the technical content, should also be regarded as the scope of the present invention.

[0031] In order to better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0032] The corn starch used in the embodiment of the present invention has a purity of ≥98%, a water content of ≤14%, and an acidity of ≤1.8.

[0033] The present invention will be further described below with reference to the following examples.

[0034] Example 1

[0035] A method for preparing a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistant functions comprises the following steps:

[0036] Step 1, weigh corn starch and dimethyl sulfoxide, mix them, heat them to 85 ° C and stir them until a uniform mixture is formed, then mix KH-550 and deionized water in a mass ratio of 1:10 to obtain an aminosilane solution, add it to the mixture, the mass ratio of corn starch, dimethyl sulfoxide and aminosilane solution is 1:70:30, continue to keep warm and stir for 1.5 hours, then cool to room temperature, discharge into anhydrous ethanol, centrifuge, wash and dry to obtain amino starch;

[0037] Step 2, weighing N-acryloylglycine and thionyl chloride, mixing at a mass ratio of N-acryloylglycine to thionyl chloride of 1:8, using nitrogen as a protective gas, heating to 80° C., and reflux for 5 hours. After the reaction is completed, distilling off the solvent to obtain N-acryloylglycine chloride;

[0038] Step 3, weighing ammoniated starch, adding it to deionized water, and gelatinizing it at 65° C. for 0.8 h, adding a small amount of triethylamine dropwise, and then adding N-acryloylglycine chloride, the mass ratio of ammoniated starch, N-acryloylglycine chloride, triethylamine and deionized water is 1:0.42:0.03:50, stirring thoroughly at room temperature for 4 h, and then removing water under reduced pressure to obtain N-acryloylglycine amide / starch complex;

[0039] Step 4, weighing N-acryloylglycine amide / starch complex and adding it to deionized water, heating to 65 ° C and stirring until uniform, then adding acrylic acid and acrylamide, the mass ratio of starch / acryloylglycine amide complex, acrylic acid, acrylamide and deionized water is 1:0.4:1.2:50, passing nitrogen as a protective gas, adding sodium persulfate, the addition amount is 4% of the mass of the starch / acryloylglycine amide complex, keeping warm and stirring for 1.5 hours, then adding benzoin diethyl ether, the addition amount is 2.5% of the mass of the starch / acryloylglycine amide complex, and adding N,N-methylenebisacrylamide, the addition amount is 3% of the mass of the starch / acryloylglycine amide complex, and treating under ultraviolet light for 15 minutes to obtain a coating layer liquid;

[0040] Step 5: On a compound fertilizer production line, urea, monoammonium phosphate, and potassium chloride are prepared in a mass ratio of 160:190:45 to prepare a fertilizer particle core with a particle size of 3.1 mm. The coating layer liquid is sprayed on the surface of the fertilizer particle core by spraying. The spraying thickness is 0.5 mm. After drying, a compound fertilizer with water-retaining, fertilizer-retaining, and salt-alkali-resistant functions is obtained.

[0041] Example 2

[0042] A method for preparing a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistant functions comprises the following steps:

[0043] Step 1, weigh corn starch and dimethyl sulfoxide, mix them, heat them to 80°C and stir them until a uniform mixture is formed, then mix KH-550 and deionized water in a mass ratio of 1:8 to obtain an aminosilane solution, add it to the mixture, and add the mass ratio of corn starch, dimethyl sulfoxide and aminosilane solution to the mixture in a ratio of 1:60:20. Continue to keep warm and stir for 1 hour, then cool to room temperature, discharge the material into anhydrous ethanol, centrifuge, wash and dry to obtain amino starch;

[0044] Step 2, weighing N-acryloylglycine and thionyl chloride, mixing at a mass ratio of N-acryloylglycine to thionyl chloride of 1:5, using nitrogen as a protective gas, heating to 75° C., and reflux for 4 hours. After the reaction is completed, distilling off the solvent to obtain N-acryloylglycine chloride;

[0045] Step 3, weighing ammoniated starch, adding it to deionized water, and gelatinizing it at 60° C. for 0.5 h, adding a small amount of triethylamine dropwise, and then adding N-acryloylglycine chloride, the mass ratio of ammoniated starch, N-acryloylglycine chloride, triethylamine and deionized water is 1:0.28:0.01:40, stirring thoroughly at room temperature for 3 h, and then removing water under reduced pressure to obtain N-acryloylglycine amide / starch complex;

[0046] Step 4, weighing N-acryloylglycine amide / starch complex and adding it to deionized water, heating to 60°C and stirring until uniform, then adding acrylic acid and acrylamide, the mass ratio of starch / acryloylglycine amide complex, acrylic acid, acrylamide and deionized water is 1:0.3:0.8:40, passing nitrogen as a protective gas, adding ammonium persulfate, the addition amount is 2% of the mass of the starch / acryloylglycine amide complex, keeping warm and stirring for 1 hour, then adding benzoin dimethyl ether, the addition amount is 1.5% of the mass of the starch / acryloylglycine amide complex, and adding N,N-methylenebisacrylamide, the addition amount is 2% of the mass of the starch / acryloylglycine amide complex, and treating under ultraviolet light for 10 minutes to obtain a coating layer liquid;

[0047] Step 5: On a compound fertilizer production line, ammonium nitrate, monoammonium phosphate, and potassium sulfate are prepared in a mass ratio of 150:180:35 to prepare a fertilizer particle core with a particle size of 3.6 mm. The coating layer liquid is sprayed on the surface of the fertilizer particle core by spraying, and the spraying thickness is 0.3 mm. After drying, a compound fertilizer with water-retaining, fertilizer-retaining, and salt-alkali-resistant functions is obtained.

[0048] Example 3

[0049] A method for preparing a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistant functions comprises the following steps:

[0050] Step 1, weigh corn starch and dimethyl sulfoxide, mix them, heat them to 90°C and stir them until a uniform mixture is formed, then mix KH-550 and deionized water in a mass ratio of 1:12 to obtain an aminosilane solution, add it to the mixture, and add the mass ratio of corn starch, dimethyl sulfoxide and aminosilane solution to 1:80:40. Continue to keep warm and stir for 2 hours, then cool to room temperature, discharge the material into anhydrous ethanol, centrifuge, wash and dry to obtain amino starch;

[0051] Step 2, weighing N-acryloylglycine and thionyl chloride, mixing at a mass ratio of N-acryloylglycine to thionyl chloride of 1:10, using nitrogen as a protective gas, heating to 85° C., and reflux for 6 hours. After the reaction is completed, distilling off the solvent to obtain N-acryloylglycine chloride;

[0052] Step 3, weighing ammoniated starch, adding it to deionized water, and gelatinizing it at 70° C. for 1 hour, adding a small amount of triethylamine dropwise, and then adding N-acryloylglycine chloride, the mass ratio of ammoniated starch, N-acryloylglycine chloride, triethylamine and deionized water is 1:0.56:0.05:60, stirring thoroughly at room temperature for 5 hours, and then removing water under reduced pressure to obtain N-acryloylglycine amide / starch complex;

[0053] Step 4, weighing N-acryloylglycine amide / starch complex and adding it to deionized water, heating to 70°C and stirring until uniform, then adding acrylic acid and acrylamide, the mass ratio of starch / acryloylglycine amide complex, acrylic acid, acrylamide and deionized water is 1:0.6:1.6:60, passing nitrogen as a protective gas, adding potassium persulfate, the addition amount is 6% of the mass of the starch / acryloylglycine amide complex, keeping warm and stirring for 2 hours, then adding benzoin diethyl ether, the addition amount is 3% of the mass of the starch / acryloylglycine amide complex, and adding N,N-methylenebisacrylamide, the addition amount is 4% of the mass of the starch / acryloylglycine amide complex, and treating under ultraviolet light for 20 minutes to obtain a coating layer liquid;

[0054] Step 5: On a compound fertilizer production line, urea, diammonium phosphate, and potassium chloride are prepared in a mass ratio of 170:200:55 to prepare a fertilizer particle core with a particle size of 4.8 mm. The coating layer liquid is sprayed on the surface of the fertilizer particle core by spraying. The spraying thickness is 0.8 mm. After drying, a compound fertilizer with water-retaining, fertilizer-retaining, and salt-alkali-resistant functions is obtained.

[0055] Comparative Example 1

[0056] A method for preparing a compound fertilizer, which differs from Example 1 in that the N-acryloylglycine amide / starch complex in the preparation process is replaced with corn starch, that is, the preparation steps include:

[0057] Step 1, weighing corn starch, adding it to deionized water, and gelatinizing it at 65° C. for 0.8 h, then adding acrylic acid and acrylamide, the mass ratio of corn starch, acrylic acid, acrylamide and deionized water is 1:0.4:1.2:50, passing nitrogen as a protective gas, adding sodium persulfate in an amount of 4% of the mass of the corn starch, keeping the temperature and stirring for 1.5 h, then adding benzoin diethyl ether in an amount of 2.5% of the mass of the corn starch, and adding N,N-methylenebisacrylamide in an amount of 3% of the mass of the corn starch, and treating under ultraviolet light for 15 min to obtain a coating layer liquid;

[0058] Step 2: On a compound fertilizer production line, urea, monoammonium phosphate, and potassium chloride are prepared in a mass ratio of 160:190:45 to prepare a fertilizer particle core with a particle size of 3.1 mm. The coating layer liquid is sprayed on the surface of the fertilizer particle core by spraying, and the spraying thickness is 0.5 mm. After drying, a compound fertilizer with water-retaining, fertilizer-retaining, and salt-alkali-resistant functions is obtained.

[0059] Comparative Example 2

[0060] A method for preparing a compound fertilizer, which differs from Example 1 in that the N-acryloylglycine amide / starch complex in the preparation process is replaced with amino starch, that is, the preparation steps include:

[0061] Step 1, preparing amino starch (preparation is the same as in Example 1);

[0062] Step 2: Weighing amino starch, adding it to deionized water, and gelatinizing it at 65° C. for 0.8 h, then adding acrylic acid and acrylamide, the mass ratio of amino starch, acrylic acid, acrylamide and deionized water is 1:0.4:1.2:50, introducing nitrogen as a protective gas, adding sodium persulfate in an amount of 4% of the mass of the amino starch, keeping the temperature and stirring for 1.5 h, then adding benzoin diethyl ether in an amount of 2.5% of the mass of the amino starch, and adding N,N-methylenebisacrylamide in an amount of 3% of the mass of the amino starch, and treating under ultraviolet light for 15 min to obtain a coating layer liquid;

[0063] Step 3: On a compound fertilizer production line, urea, monoammonium phosphate, and potassium chloride are prepared in a mass ratio of 160:190:45 to prepare a fertilizer particle core with a particle size of 3.1 mm. The coating layer liquid is sprayed on the surface of the fertilizer particle core by spraying. The spraying thickness is 0.5 mm. After drying, a compound fertilizer with water-retaining, fertilizer-retaining, and salt-alkali-resistant functions is obtained.

[0064] Comparative Example 3

[0065] A method for preparing a compound fertilizer, which differs from Example 1 in that the N-acryloylglycine amide / starch complex in the preparation process is replaced with a mixture of starch and N-acryloylglycine, and the mass ratio of starch to N-acryloylglycine is 1:0.42. That is, the preparation steps include:

[0066] Step 1, weighing corn starch and N-acryloylglycine, adding them to deionized water and gelatinizing them at 65° C. for 0.8 h, then adding acrylic acid and acrylamide, the mass ratio of corn starch, N-acryloylglycine, acrylic acid, acrylamide and deionized water is 1:0.42:0.4:1.2:50, passing nitrogen as a protective gas, adding sodium persulfate in an amount of 4% of the mass of the corn starch, keeping the temperature and stirring for 1.5 h, then adding benzoin diethyl ether in an amount of 2.5% of the mass of the corn starch and adding N,N-methylenebisacrylamide in an amount of 3% of the mass of the corn starch, and treating under ultraviolet light for 15 min to obtain a coating layer liquid;

[0067] Step 2: On a compound fertilizer production line, urea, monoammonium phosphate, and potassium chloride are prepared in a mass ratio of 160:190:45 to prepare a fertilizer particle core with a particle size of 3.1 mm. The coating layer liquid is sprayed on the surface of the fertilizer particle core by spraying, and the spraying thickness is 0.5 mm. After drying, a compound fertilizer with water-retaining, fertilizer-retaining, and salt-alkali-resistant functions is obtained.

[0068] Experimental example

[0069] The effects of the fertilizers prepared in the examples and comparative examples on the yield of rapeseed in saline-alkali land were determined through field experiments.

[0070] The rapeseed variety used was Zhongyouza 501. The experiment was conducted in Binzhou City, Shandong Province. Each experimental plot covered one mu (approximately 1 mu). Basic soil properties were as follows: pH 7.81, organic matter content 2.31%, available nitrogen 187.5 mg / kg, available phosphorus 22.4 mg / kg, available potassium 285.1 mg / kg, and total salt content 0.088%. The rapeseed was planted on April 5, 2023, and harvested on September 3, 2023. Aside from fertilization, all other field management practices, including sowing, irrigation, and weeding, were identical across treatments.

[0071] The emergence rate was tested 7 days after planting; the content of water-stable large aggregates (particle size > 0.25 mm) was randomly tested using a wet screening method (30 times / min, 30 min); the yield was calculated from the yield of all rapeseed after harvesting; the yield increase rate was based on Comparative Example 1 as the benchmark, compared with the yield increase ratio of Comparative Example 1.

[0072] The test results are shown in Table 1.

[0073] Table 1 Performance of rapeseed planted in different ways

[0074]

[0075] As can be seen from Table 1, rapeseed planted using the compound fertilizer prepared in Example 1 of the present invention performed better in saline-alkali soil, with a seedling emergence rate of 97.3%, a water-stable macroaggregate content of 45.3%, and a yield of 237.6 kg / mu, a yield increase of 23.6% compared to the control. This indicates that the compound fertilizer prepared in Example 1 of the present invention can improve soil water retention and crop stress resistance, thereby further improving crop growth and yield.

[0076] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0077] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistant functions, It is characterized in that The following steps are involved: Step 1, weigh corn starch and dimethyl sulfoxide, mix them, heat and stir until a uniform mixed solution is formed, then add the aminosilane solution, continue to keep warm and stir for 1-2 hours, then cool to room temperature, discharge into anhydrous ethanol, centrifuge, wash and dry to obtain amino starch; Step 2, weighing N-acryloylglycine and thionyl chloride, mixing, using nitrogen as a protective gas, heating and reflux treatment, after the reaction is completed, distilling off the solvent to obtain N-acryloylglycine chloride; Step 3, weighing the amino starch, adding it to deionized water for gelatinization, adding triethylamine dropwise, and then adding N-acryloylglycyl chloride, stirring well at room temperature for 3-5 hours, and then removing water under reduced pressure to obtain a starch / acryloylglycylamide complex; Step 4, weighing starch / acryloyl glycinamide complex and adding it to deionized water, heating and stirring until uniform, then adding acrylic acid and acrylamide, introducing nitrogen as protective gas, adding thermal initiator, stirring and reacting for 1-2 hours at a temperature of keeping warm, then adding photoinitiator and crosslinking agent, treating under ultraviolet light irradiation for 10-20 minutes, and obtaining coating layer liquid; Step 5: In the compound fertilizer production line, the coating layer liquid is sprayed on the inner core surface of the fertilizer particles by spraying, and after drying, a compound fertilizer with water-retaining, fertilizer-retaining and salt-alkali-resistant functions is obtained.

2. A method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In the step 1, the temperature of heating and stirring is 80-90° C.; the mass ratio of corn starch, dimethyl sulfoxide and aminosilane solution is 1:60-80:20-40.

3. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In the step 1, the aminosilane solution is obtained by mixing KH-550 and deionized water in a mass ratio of 1:8-12.

4. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In the step 2, the mass ratio of N-acryloylglycine to thionyl chloride is 1:5-10; the reflux temperature is 75-85° C., and the reflux time is 4-6 h.

5. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In step 3, the gelatinization temperature is 60-70° C., and the gelatinization time is 0.5-1 h.

6. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In the step 3, the mass ratio of the amination starch, N-acryloylglycyl chloride, triethylamine and deionized water is 1:0.28-0.56:0.01-0.05:40-60.

7. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In the step 4, the mass ratio of the starch / acryloylglycinamide complex, acrylic acid, acrylamide and deionized water is 1:0.3-0.6:0.8-1.6:40-60.

8. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In the step 4, the reaction temperature is 60-70° C., the thermal initiator is one of sodium persulfate, ammonium persulfate, and potassium persulfate, and the amount of the thermal initiator added is 2%-6% of the mass of the starch / acryloyl glycinamide complex; the photoinitiator is benzoin diethyl ether or benzoin dimethyl ether, and the amount added is 1.5%-3% of the mass of the starch / acryloyl glycinamide complex; the cross-linking agent is N,N-methylenebisacrylamide, and the amount added is 2%-4% of the mass of the starch / acryloyl glycinamide complex.

9. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistant functions according to claim 1, It is characterized in that In step 5, the inner core of the fertilizer particles is nitrogen, phosphorus and potassium fertilizers, and the mass ratio of nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer is 150-170:180-200:35-55; wherein the nitrogen fertilizer is one or more of urea, ammonium nitrate and calcium ammonium nitrate; the phosphorus fertilizer is one or more of monoammonium phosphate or diammonium phosphate; and the potassium fertilizer is one or more of potassium chloride or potassium sulfate.

10. The method for preparing a compound fertilizer having water-retaining, fertilizer-retaining and salt-alkali-resistance functions according to claim 1, It is characterized in that In step 5, the particle size of the inner core of the fertilizer particles is 3.1-4.8 mm; and the spraying thickness is 0.3-0.8 mm.

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