Compound fertilizer with high magnesium content as well as preparation method and application of compound fertilizer

Abstract

The invention discloses a high-magnesium-content compound fertilizer and a preparation method and application thereof, and belongs to the technical field of fertilizer production, the high-magnesium-content compound fertilizer comprises the following raw materials by weight: 20-36 parts of a magnesium fertilizer, 10-14 parts of a nitrogen fertilizer, 7-9 parts of a potassium fertilizer, 7-9 parts of a phosphate fertilizer, 0.1-0.3 part of trace elements, 3-7 parts of a coating material, and 0.1-0.3 part of microcrystalline wax; the preparation method comprises the following steps: putting the magnesium fertilizer, the nitrogen fertilizer, the potassium fertilizer, the phosphorus fertilizer and the trace elements into a rotary drum, preheating to 70-75 DEG C, adding the microcrystalline wax, mixing for 30-40 minutes at the rotating speed of 300-400 r / min, spraying the coating material by using a spray gun in a stirring state, drying the obtained product at 50-60 DEG C to constant weight, and cooling to room temperature to obtain the high-magnesium-content compound fertilizer. The fertilizer prepared by the invention has excellent slow release performance.

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizer production, and in particular relates to a high-magnesium content compound fertilizer and a preparation method and application thereof. Background Art

[0002] Magnesium is one of the essential elements for plant growth and is the only mineral nutrient in the chlorophyll molecule. In addition, it is also an activator of many enzymes such as phosphokinase. Some European scholars even list it as the fourth essential element for plants after nitrogen, phosphorus and potassium. Magnesium deficiency will lead to a decrease in crop yield and quality.

[0003] Patent announcement number CN104211499B discloses a high-phosphorus, high-zinc, high-magnesium liquid compound fertilizer and its preparation method and use method. The patent has high total nutrient content, stable physical and chemical shapes, phosphorus, zinc and magnesium are stably dissolved in the liquid at the same time, no crystallization, precipitation, stratification and other phenomena under high temperature, low temperature and normal temperature conditions, good fluidity, and high nutrient concentration. It is suitable for large-area automated fertilization operations and can significantly improve fertilization efficiency. However, the high-magnesium fertilizer prepared by the patent and the prior art still has the problem of poor slow release performance. Summary of the invention

[0004] In order to solve the problem that the high-magnesium fertilizer prepared by the prior art still has poor slow-release performance, the purpose of the present invention is to provide a high-magnesium content compound fertilizer and a preparation method and application thereof.

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

[0006] In a first aspect, the present invention provides a high-magnesium content compound fertilizer, comprising the following raw materials in parts by weight: 20-36 parts of magnesium fertilizer, 10-14 parts of nitrogen fertilizer, 7-9 parts of potassium fertilizer, 7-9 parts of phosphate fertilizer, 0.1-0.3 parts of trace elements, 3-7 parts of coating material, and 0.1-0.3 parts of microcrystalline wax; the coating material is obtained by cross-linking and mixing gelatinized corn starch, modified humic acid, acrylic acid and a hydrophobic antibacterial monomer; the modified humic acid uses allyltriethoxysilane as a bridge to connect the humic acid with 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid; the hydrophobic antibacterial monomer contains a quaternary ammonium salt group, a long-chain alkyl group and a carbon-carbon double bond.

[0007] Furthermore, the magnesium fertilizer is one or more of magnesium sulfate, magnesium chloride, magnesium oxide and magnesium nitrate mixed in any proportion.

[0008] Furthermore, the nitrogen fertilizer is one or more of urea, ammonium nitrate and ammonium sulfate mixed in any proportion.

[0009] Furthermore, the potash fertilizer is a mixture of one or more of potassium chloride, potassium sulfate and potassium nitrate in any proportion.

[0010] Furthermore, the phosphate fertilizer is one or more of urea phosphate, phosphoric acid, ammonium polyphosphate, sodium hexametaphosphate, potassium metaphosphate, phosphorous acid and potassium tripolyphosphate mixed in any proportion.

[0011] Furthermore, the trace elements are a combination of zinc, manganese and molybdenum compounds in any ratio.

[0012] Further, the coating material is made by the following steps:

[0013] Add corn starch into deionized water and stir at 75°C for 10-20 minutes to obtain gelatinized starch; at 40°C, add alkaline solution to the acrylic acid and hydrophobic antibacterial monomer solution until the pH value is 6, add modified humic acid, gelatinized starch, and deionized water, stir for 40-50 minutes, then add potassium persulfate and N,N'-methylenebisacrylamide, heat to 75°C while stirring at 5°C / min, and perform constant temperature polymerization for 1 hour to obtain a coating material.

[0014] Among them, the alkaline solution is a sodium hydroxide solution with a mass concentration of 10%; the dosage ratio of corn starch to deionized water is 2g:10mL; the dosage ratio of acrylic acid, hydrophobic antibacterial monomer solution, modified humic acid, gelatinized starch, and deionized water is 6g:1.2g:0.8g:2g:20-25mL; the dosage of potassium persulfate is 0.9-1.2 times the mass of N,N'-methylenebisacrylamide; N,N'-methylenebisacrylamide accounts for 1.2% of the total mass; the hydrophobic antibacterial monomer solution is composed of a hydrophobic antibacterial monomer and an ethanol aqueous solution with a volume fraction of 50%, and the dosage ratio of the hydrophobic antibacterial monomer to the 50% ethanol aqueous solution is 2g:10mL.

[0015] Humic acid is an important substance in soil nutrients, which can promote plant growth and improve soil structure; polyacrylic acid polymer is a type of polymer with water absorption and retention functions; starch is a natural polymer compound that is widely available, low in price and can be naturally degraded.

[0016] In the above steps, modified humic acid, gelatinized starch, acrylic acid and hydrophobic antibacterial monomers are cross-linked and mixed with potassium persulfate as an initiator and N,N'-methylenebisacrylamide as a cross-linking agent to obtain a coating material. Modified humic acid contains carbon-carbon double bonds, silicon, sulfur and other elements. The carbon-carbon double bonds can promote the modified humic acid to participate in the polymerization reaction, thereby forming a tighter network structure. In addition, the modified humic acid contains functional groups such as carboxyl and hydroxyl groups, and has strong ion exchange and adsorption capabilities. It can adsorb phosphorus and trace elements to slow down their release rate and achieve a slow-release effect. Silicon can enhance the resistance of crops to environmental stresses such as drought, high temperature, and salinity. Sulfur fertilizer plays an important role in the absorption and utilization of nitrogen by crops. It can promote root nitrogen transport and leaf nitrogen recycling, thereby improving the nitrogen utilization rate of crops. The above two elements can promote the growth of crops.

[0017] The hydrophobic antibacterial monomer contains an acrylic structure, which can participate in the polymerization reaction to form an acrylic polymer. The hydrophobic antibacterial monomer contains a quaternary ammonium salt group and a long-chain alkyl group. The quaternary ammonium salt group can give the fertilizer antibacterial properties, so that the fertilizer can promote crop growth while also playing a bactericidal role, expanding the application scenarios of the fertilizer. Long-chain alkyl groups can improve the hydrophobic properties of the coating material. In areas with high rainfall, fertilizers are easily dissolved and lost quickly due to sufficient water. The presence of long-chain alkyl groups can significantly enhance the hydrophobicity of the coating material and slow down the penetration rate of water, thereby extending the release time of the fertilizer, ensuring that nutrients can be continuously supplied to plants and reducing nutrient loss. In addition, the high concentration of hydrogen ions in acidic soils can easily cause corrosion to the fertilizer coating. The long-chain alkyl chain has good stability and can resist the erosion of the acidic environment to a certain extent, protecting the fertilizer particles from damage.

[0018] Furthermore, the preparation method of modified humic acid is:

[0019] Humic acid and deionized water are added to anhydrous ethanol and stirred to obtain a mixed solution; 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid and allyltriethoxysilane are added to the mixed solution, the temperature is raised to 60-80°C and stirred for 1-2 hours, filtered, washed, centrifuged, and vacuum dried for 20-24 hours to obtain modified humic acid.

[0020] The dosage ratio of humic acid, deionized water, anhydrous ethanol, 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid and allyltriethoxysilane is 10g: 10-20mL: 80-90mL: 4-8g: 0.3-0.5g.

[0021] In the above steps, the silane coupling agent acts as a bridge, and the hydrolyzed silanol groups form bonds with the carboxyl and hydroxyl groups in humic acid and 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid, thereby combining the three to obtain modified humic acid.

[0022] Furthermore, the preparation method of the hydrophobic antibacterial monomer is:

[0023] (2E)-4-(dimethylamino)but-2-enoic acid and 1-bromooctadecane were added into a single-necked flask, followed by addition of hydroquinone and acetone, and the mixture was stirred at 60° C. for 4 h, and the solvent was removed by rotary evaporation. The mixture was washed, filtered, and dried to obtain a hydrophobic antibacterial monomer.

[0024] Among them, the usage ratio of (2E)-4-(dimethylamino)but-2-enoic acid, 1-bromooctadecane, hydroquinone and acetone is 1.3g:4g:1mg:10mL.

[0025] In the above steps, hydroquinone is used as an inhibitor to protect double bonds, and the tertiary amine in (2E)-4-(dimethylamino)but-2-enoic acid reacts with the halogen in 1-bromooctadecane to generate a quaternary ammonium salt group, thereby obtaining a hydrophobic antibacterial monomer, which contains a quaternary ammonium salt group and a long-chain alkyl group.

[0026] In a second aspect, the present invention provides a method for preparing a high magnesium content compound fertilizer, comprising the following steps:

[0027] Magnesium fertilizer, nitrogen fertilizer, potassium fertilizer, phosphate fertilizer and trace elements are placed in a rotating drum, preheated to 70-75°C, microcrystalline wax is added, and mixed for 30-40 minutes at a rotation speed of 300-400r / min. Under stirring, coating material is sprayed with a spray gun. The obtained product is dried to constant weight at 50-60°C and cooled to room temperature to obtain a high magnesium content compound fertilizer.

[0028] In a third aspect, the present invention provides a high-magnesium content compound fertilizer prepared by the above preparation method for use in areas with high rainfall, red-yellow soil and acidic soil.

[0029] Beneficial effects of the present invention:

[0030] 1. The high-magnesium content composite fertilizer prepared by the present invention contains a coating material, which is obtained by cross-linking and mixing gelatinized corn starch, modified humic acid, acrylic acid and hydrophobic antibacterial monomers; the modified humic acid contains carbon-carbon double bonds, silicon, sulfur and other elements, which can improve the sustained release ability of the fertilizer and promote crop growth; the hydrophobic antibacterial monomer contains acrylic acid structure, quaternary ammonium salt group and long-chain alkyl, which can further improve the sustained release ability of the fertilizer and give the fertilizer a bactericidal effect. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Preparation Example 1

[0033] The preparation method of the hydrophobic antibacterial monomer in this preparation example is:

[0034] 1.3 g of (2E)-4-(dimethylamino)but-2-enoic acid and 4 g of 1-bromooctadecane were added to a single-necked flask, followed by 1 mg of hydroquinone and 10 mL of acetone. The mixture was stirred at 60° C. for 4 h, and the solvent was removed by rotary evaporation. The mixture was washed, filtered, and dried to obtain a hydrophobic antibacterial monomer.

[0035] Preparation Example 2

[0036] The preparation method of the modified humic acid in this preparation example is:

[0037] 10 g of humic acid and 10 mL of deionized water were added to 90 mL of anhydrous ethanol and stirred to obtain a mixed solution; 4 g of 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid and 0.3 g of allyltriethoxysilane were added to the mixed solution, the temperature was raised to 60°C and stirred for 1 hour, filtered, washed, centrifuged, and vacuum dried for 20 hours to obtain modified humic acid.

[0038] Preparation Example 3

[0039] The preparation method of the modified humic acid in this preparation example is:

[0040] 10 g of humic acid and 15 mL of deionized water were added to 85 mL of anhydrous ethanol and stirred to obtain a mixed solution; 6 g of 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid and 0.4 g of allyltriethoxysilane were added to the mixed solution, the temperature was raised to 70°C and stirred for 1.5 h, filtered, washed, centrifuged, and vacuum dried for 22 h to obtain modified humic acid.

[0041] Preparation Example 4

[0042] The preparation method of the modified humic acid in this preparation example is:

[0043] 10 g of humic acid and 20 mL of deionized water were added to 80 mL of anhydrous ethanol and stirred to obtain a mixed solution; 8 g of 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid and 0.5 g of allyltriethoxysilane were added to the mixed solution, the temperature was raised to 80°C and stirred for 2 h, filtered, washed, centrifuged, and vacuum dried for 24 h to obtain modified humic acid.

[0044] Example 1

[0045] A high magnesium content composite fertilizer comprises the following raw materials in parts by weight:

[0046] 20 parts of magnesium fertilizer, 10 parts of nitrogen fertilizer, 7 parts of potassium fertilizer, 7 parts of phosphate fertilizer, 0.1 parts of trace elements, 3 parts of coating materials, and 0.1 parts of microcrystalline wax;

[0047] The magnesium fertilizer is magnesium oxide, the nitrogen fertilizer is urea, the potassium fertilizer is potassium sulfate, the phosphate fertilizer is phosphoric acid, and the trace elements are zinc oxide, manganese sulfate, and ammonium molybdate in a mass ratio of 1:1:1.

[0048] The coating material is made by the following steps:

[0049] Corn starch was added into deionized water and stirred at 75°C for 10 minutes to obtain gelatinized starch. At 40°C, alkaline solution was added dropwise into acrylic acid and the hydrophobic antibacterial monomer solution prepared in Preparation Example 1 until the pH value was 6. The modified humic acid prepared in Preparation Example 2, gelatinized starch and deionized water were added. After stirring for 40 minutes, potassium persulfate and N,N'-methylenebisacrylamide were added. The temperature was raised to 75°C while stirring at 5°C / min, and the polymerization reaction was carried out at a constant temperature for 1 hour to obtain a coating material.

[0050] Example 2

[0051] A high magnesium content composite fertilizer comprises the following raw materials in parts by weight:

[0052] 24 parts of magnesium fertilizer, 11 parts of nitrogen fertilizer, 7.5 parts of potassium fertilizer, 7.5 parts of phosphate fertilizer, 0.15 parts of trace elements, 4 parts of coating materials, and 0.15 parts of microcrystalline wax;

[0053] The magnesium fertilizer is magnesium oxide, the nitrogen fertilizer is urea, the potassium fertilizer is potassium sulfate, the phosphate fertilizer is phosphoric acid, and the trace elements are zinc oxide, manganese sulfate, and ammonium molybdate in a mass ratio of 1:1:1.

[0054] The coating material is made by the following steps:

[0055] Corn starch was added into deionized water and stirred at 75°C for 15 minutes to obtain gelatinized starch. At 40°C, alkaline solution was added dropwise into acrylic acid and the hydrophobic antibacterial monomer solution prepared in Preparation Example 1 until the pH value was 6. The modified humic acid prepared in Preparation Example 3, gelatinized starch and deionized water were added. After stirring for 45 minutes, potassium persulfate and N,N'-methylenebisacrylamide were added. The temperature was raised to 75°C while stirring at 5°C / min, and the polymerization reaction was carried out at a constant temperature for 1 hour to obtain a coating material.

[0056] Example 3

[0057] A high magnesium content composite fertilizer comprises the following raw materials in parts by weight:

[0058] 28 parts of magnesium fertilizer, 12 parts of nitrogen fertilizer, 8 parts of potassium fertilizer, 8 parts of phosphate fertilizer, 0.2 parts of trace elements, 5 parts of coating materials, and 0.2 parts of microcrystalline wax;

[0059] The magnesium fertilizer is magnesium oxide, the nitrogen fertilizer is urea, the potassium fertilizer is potassium sulfate, the phosphate fertilizer is phosphoric acid, and the trace elements are zinc oxide, manganese sulfate, and ammonium molybdate in a mass ratio of 1:1:1.

[0060] The coating material is made by the following steps:

[0061] Corn starch was added into deionized water and stirred at 75°C for 20 minutes to obtain gelatinized starch. At 40°C, alkaline solution was added dropwise into acrylic acid and the hydrophobic antibacterial monomer solution prepared in Preparation Example 1 until the pH value was 6. The modified humic acid prepared in Preparation Example 4, gelatinized starch and deionized water were added. After stirring for 50 minutes, potassium persulfate and N,N'-methylenebisacrylamide were added. The temperature was raised to 75°C while stirring at 5°C / min, and the polymerization reaction was carried out at a constant temperature for 1 hour to obtain a coating material.

[0062] Example 4

[0063] Compared with Example 3, the only difference is:

[0064] 32 parts of magnesium fertilizer, 13 parts of nitrogen fertilizer, 8.5 parts of potassium fertilizer, 8.5 parts of phosphate fertilizer, 0.25 parts of trace elements, 6 parts of coating material, and 0.25 parts of microcrystalline wax.

[0065] Example 5

[0066] Compared with Example 3, the only difference is:

[0067] 36 parts of magnesium fertilizer, 14 parts of nitrogen fertilizer, 9 parts of potassium fertilizer, 9 parts of phosphate fertilizer, 0.3 parts of trace elements, 7 parts of coating material, and 0.3 parts of microcrystalline wax.

[0068] Comparative Example 1

[0069] Compared with Example 1, the difference is that no hydrophobic antibacterial monomer is added when preparing the coating material.

[0070] Comparative Example 2

[0071] Compared with Example 1, the difference is that: when preparing the coating material, no hydrophobic antibacterial monomer is added, and the modified humic acid is replaced by humic acid.

[0072] The performance tests were performed on the fertilizers prepared in Examples 1 to 5 and Comparative Examples 1 to 2. The test items were as follows:

[0073] 1. Slow-release experiment of fertilizer: Determine by water dissolution rate method according to GB / T 23348-2009; weigh 10g of fertilizer prepared in Example 1-Example 5 and Comparative Example 1-Comparative Example 2 and put it into a small bag made of 100-mesh nylon mesh, put the small bag into a 250mL glass bottle, add 200mL water, cover and seal, place in a 25°C biochemical constant temperature incubator, take samples at 1, 15, 30, 45, and 65 days, test the nitrogen release amount by automatic analyzer, calculate the cumulative nitrogen release rate, and the calculation formula is as follows: nitrogen release rate=Wn / W, where Wn is the mass fraction of nitrogen release measured on the nth day, and W is the mass fraction of total nitrogen. The test results are shown in Table 1.

[0074] Table 1

[0075]

[0076]

[0077] It can be seen from Table 1 that the dissolution rates of Examples 1 to 5 are lower than those of Comparative Examples 1 and 2 within the same time, indicating that the high magnesium content compound fertilizer prepared by the present invention has a good slow-release effect.

[0078] 2. Bactericidal performance: 2 kg of the fertilizer prepared in Examples 8-10 and Comparative Example 4 was dissolved in 10 L of water. The volume of fertilizer per mu of land was 10 L. Referring to "GB / T17980.19-2000 Guidelines for Field Efficacy Tests of Pesticides (I) Control of Rice Leaf Diseases with Fungicides", the area of ​​each zone was 30 m2, 4 replicates were set, and the pesticide was applied twice, with an interval of 7 days between each application. Investigations were conducted 7 days and 14 days after each application, and the classification was performed according to the relevant data investigation standard. The disease index was statistically calculated and the control effect was calculated. The test results are shown in Table 2.

[0079] Table 2

[0080] project Fertilizer dosage (g / mu) 7-day protective effect after medication (%) 14-day protective effect after medication (%) Example 1 20 79.49 73.68 Example 2 20 81.23 75.39 Example 3 20 81.62 77.51 Example 4 20 82.14 79.26 Example 5 20 83.26 81.42 Comparative Example 1 20 69.15 59.43 Comparative Example 2 20 62.58 57.81

[0081] It can be seen from Table 2 that the post-treatment control effects of Examples 1 to 5 are better than those of Comparative Examples 1 and 2 within the same period of time, indicating that the high magnesium content composite fertilizer prepared by the present invention has good bactericidal performance.

[0082] 3. Weigh 1g of fertilizer, mix with 220mL of mixed matrix (mass ratio of vermiculite: perlite = 7:3) and put into flower pots. Plant 4 cotton seeds in each flower pot, and do 5 parallel tests. The flower pots are placed at room temperature and cultured under sufficient fluorescent light. After 21 days of cultivation, compare the growth of the plants, take out 3 cotton seedlings from each pot and measure their growth indicators, such as plant height, root length, fresh weight, and dry weight. Repeat the test 3 times and take the average value.

[0083] Table 3

[0084] project Plant height / cm Root length / cm Fresh weight / g Dry weight / g Example 1 16.4 8.1 1.2 0.09 Example 2 17.8 8.9 1.4 0.12 Example 3 18.9 9.2 1.9 0.14 Example 4 20.3 9.8 2.1 0.17 Example 5 22.6 10.4 2.9 0.21 Comparative Example 1 14.7 7.5 0.9 0.05 Comparative Example 2 10.6 5.3 0.6 0.03

[0085] As can be seen from Table 3, the plant height, root length, fresh weight and dry weight of the cotton obtained in Examples 1 to 5 are better than those in Comparative Example 1 and Comparative Example 2, indicating that the high magnesium content compound fertilizer prepared by the present invention has a good ability to promote crop growth.

[0086] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0087] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high magnesium content compound fertilizer, characterized in that: The invention comprises the following raw materials in parts by weight: 20-36 parts of magnesium fertilizer, 10-14 parts of nitrogen fertilizer, 7-9 parts of potassium fertilizer, 7-9 parts of phosphate fertilizer, 0.1-0.3 parts of trace elements, 3-7 parts of coating material and 0.1-0.3 parts of microcrystalline wax; the coating material is obtained by cross-linking and polymerization of gelatinized corn starch, modified humic acid, acrylic acid and a hydrophobic antibacterial monomer; the modified humic acid uses allyl triethoxysilane as a bridge to connect the humic acid with 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid; the hydrophobic antibacterial monomer contains a quaternary ammonium salt group, a long-chain alkyl group and a carbon-carbon double bond.

2. A high magnesium content composite fertilizer according to claim 1, characterized in that: The magnesium fertilizer is a mixture of one or more of magnesium sulfate, magnesium chloride, magnesium oxide and magnesium nitrate in any proportion; the nitrogen fertilizer is a mixture of one or more of urea, ammonium nitrate and ammonium sulfate in any proportion; the potassium fertilizer is a mixture of one or more of potassium chloride, potassium sulfate and potassium nitrate in any proportion; the phosphate fertilizer is a mixture of one or more of urea phosphate, phosphoric acid, ammonium polyphosphate, sodium hexametaphosphate, potassium metaphosphate, phosphorous acid and potassium tripolyphosphate in any proportion; the trace elements are a combination of zinc, manganese and molybdenum compounds in any proportion.

3. A high magnesium content composite fertilizer according to claim 1, characterized in that: The coating material is made by the following steps: Add corn starch into deionized water and stir at 75°C for 10-20 minutes to obtain gelatinized starch; at 40°C, add alkaline solution to the acrylic acid and hydrophobic antibacterial monomer solution until the pH value is 6, add modified humic acid, gelatinized starch, and deionized water, stir for 40-50 minutes, then add potassium persulfate and N,N'-methylenebisacrylamide, heat to 75°C while stirring at 5°C / min, and perform constant temperature polymerization for 1 hour to obtain a coating material.

4. A high magnesium content composite fertilizer according to claim 3, characterized in that: The alkaline solution is a sodium hydroxide solution with a mass concentration of 10%; the dosage ratio of corn starch to deionized water is 2g:10mL; the dosage ratio of acrylic acid, hydrophobic antibacterial monomer solution, modified humic acid, gelatinized starch, and deionized water is 6g:1.2g:0.8g:2g:20-25mL; the dosage of potassium persulfate is 0.9-1.2 times the mass of N,N'-methylenebisacrylamide; N,N'-methylenebisacrylamide accounts for 1.2% of the total mass; the hydrophobic antibacterial monomer solution is composed of a hydrophobic antibacterial monomer and an ethanol aqueous solution with a volume fraction of 50%, and the dosage ratio of the hydrophobic antibacterial monomer to the 50% ethanol aqueous solution is 2g:10mL.

5. A high magnesium content composite fertilizer according to claim 3, characterized in that: The preparation method of modified humic acid is: Humic acid and deionized water are added to anhydrous ethanol and stirred to obtain a mixed solution; 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid and allyltriethoxysilane are added to the mixed solution, the temperature is raised to 60-80°C and stirred for 1-2 hours, filtered, washed, centrifuged, and vacuum dried for 20-24 hours to obtain modified humic acid.

6. A high magnesium content compound fertilizer according to claim 5, characterized in that: The dosage ratio of humic acid, deionized water, anhydrous ethanol, 3-[N-tris(hydroxymethyl)methylamine]-2-hydroxypropanesulfonic acid and allyltriethoxysilane is 10g: 10-20mL: 80-90mL: 4-8g: 0.3-0.5g.

7. A high magnesium content composite fertilizer according to claim 3, characterized in that: The preparation method of the hydrophobic antibacterial monomer is as follows: (2E)-4-(dimethylamino)but-2-enoic acid and 1-bromooctadecane were added into a single-necked flask, followed by addition of hydroquinone and acetone, and the mixture was stirred at 60° C. for 4 h, rotary evaporated, washed, filtered, and dried to obtain a hydrophobic antibacterial monomer.

8. A high magnesium content composite fertilizer according to claim 7, characterized in that: The usage ratio of (2E)-4-(dimethylamino)but-2-enoic acid, 1-bromooctadecane, hydroquinone and acetone is 1.3 g:4 g:1 mg:10 mL.

9. The method for preparing a high magnesium content composite fertilizer according to any one of claims 1 to 8, characterized in that: The following steps are involved: Magnesium fertilizer, nitrogen fertilizer, potassium fertilizer, phosphate fertilizer and trace elements are placed in a rotating drum, preheated to 70-75°C, microcrystalline wax is added, and mixed for 30-40 minutes at a rotation speed of 300-400r / min. Under stirring, coating material is sprayed with a spray gun. The obtained product is dried to constant weight at 50-60°C and cooled to room temperature to obtain a high magnesium content compound fertilizer.

10. Use of a high magnesium content compound fertilizer according to any one of claims 1 to 8 in areas with high rainfall, red-yellow soil and acidic soil.

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