A preparation method and application of value-added compound fertilizer

Abstract

The invention discloses a preparation method and application of a value-added compound fertilizer, belonging to the technical field of fertilizers. Modified humic acid, inorganic fertilizer particles and a composite bacterial agent are prepared into a fertilizer core material, methionine grafted modified chitosan, polyvinyl alcohol, industrial starch, tributyl citrate and water are mixed into a coating liquid, the fertilizer core material is transferred to a coating machine, and the coating liquid is sprayed for coating to prepare the value-added compound fertilizer; bacillus subtilis and bacillus amyloliquefaciens are added to the value-added compound fertilizer, which can inhibit the growth and reproduction of pathogens and pests in the soil and enhance the stress resistance of corn; after the humic acid is modified by formaldehyde, it is helpful to increase the number of hydroxyl groups in the humic acid, thereby increasing the adsorption effect of the modified humic acid, reducing the leaching loss of inorganic fertilizers, and improving the slow-release effect of the value-added compound fertilizer; under the coating effect of the coating liquid, the slow-release effect of the value-added compound fertilizer is further improved, thereby helping to increase the corn yield.

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizers, and in particular relates to a preparation method of a value-added compound fertilizer and application thereof. Background Art

[0002] Compound fertilizer is a kind of fertilizer containing two or more nutrients of nitrogen, phosphorus and potassium. It has the advantages of high nutrient content, few by-products and good physical properties. Its main raw materials include ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium chloride, urea, potassium sulfate, potassium chloride, ammonium phosphate, etc. The nutrients exist in granular form, which is convenient for storage and application, and is especially suitable for mechanized fertilization.

[0003] The main functions of compound fertilizers include balanced fertilization, improving fertilizer utilization rate, and promoting high and stable yields of crops. Value-added compound fertilizers are made on the basis of traditional compound fertilizers by adding humic acid, biological agents, organic fertilizers, etc., and by improving the raw material ratio and process technology. Compared with traditional compound fertilizers, value-added compound fertilizers can more comprehensively and fully meet the multi-faceted needs of crop growth, and their slow-release properties can generally be improved by coating.

[0004] The Chinese patent with patent number CN103626598B discloses functional chitosan biological slow-release fertilizer and its preparation method, and determines the chitosan film material formula with fertilizer nutrient release characteristics similar to crop absorption law, which has significant nutrient slow-release effect, can inhibit nitrogen volatilization, and has high fertilizer utilization rate. However, the amino group in chitosan can inhibit bacterial activity by combining with negative electrons. In addition to pathogenic microorganisms such as Staphylococcus aureus and Escherichia coli, it also has an antibacterial effect on microorganisms used for soil improvement such as Bacillus subtilis. Therefore, chitosan as a coating material will reduce the activity of the bacterial agent in the value-added compound fertilizer, thereby reducing the effect of the bacterial agent. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for preparing a value-added compound fertilizer to solve the problem that the activity of the bacterial agent in the value-added compound fertilizer is inhibited by chitosan; the second purpose is to provide an application of the value-added compound fertilizer in corn planting.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a value-added compound fertilizer comprises the following steps:

[0008] Step 1: Evenly mix the modified humic acid, inorganic fertilizer particles and composite bacterial agent in a mass ratio of 1:1:0.3-0.4, and use a granulator to prepare a fertilizer core material with a particle diameter of 2-2.5 mm;

[0009] Step 2: Evenly mix methionine grafted modified chitosan, polyvinyl alcohol, industrial starch, tributyl citrate and water in a mass ratio of 6-8:6-8:20-30:2-3:100-120 to obtain a coating solution;

[0010] Step 3: Transfer the fertilizer core material to the coating machine, spray the coating liquid onto the surface of the fertilizer core material at 40-60r / min and 20-30°C, the mass ratio of the fertilizer core material to the coating liquid is 20:3-4, after the coating liquid is sprayed, the coating machine continues to work for 8-12 minutes, take out the particles and ventilate and dry them for 8-12 hours, completing the preparation method of the value-added compound fertilizer and obtaining the value-added compound fertilizer.

[0011] Furthermore, the methionine grafted modified chitosan is prepared by the following steps:

[0012] Step 1: L-methionine and deionized water are added to a reactor, stirred at 25-30° C. and 200-500 r / min for 10-20 min, then di(trichloromethyl)carbonate is dissolved in tetrahydrofuran, added to the reactor under the protection of nitrogen, heated to 55-60° C. and stirred for 120-150 min, the liquid after the reaction is distilled under reduced pressure to 2-5% of the original volume, the remaining liquid is recrystallized with 10 times the volume of n-hexane, and dried to obtain a powdered oxazolidinedione compound monomer; the reaction process is as follows:

[0013]

[0014] Furthermore, the usage ratio of L-methionine, deionized water, bis(trichloromethyl) carbonate and tetrahydrofuran is 2.5-2.6 g:100 mL:1.6-1.8 g:10 mL.

[0015] Step 2: Carboxymethyl chitosan and dimethyl sulfoxide are added to a reactor and stirred to mix, and then an oxazolidinedione compound monomer is added to the reactor under nitrogen protection, and the reaction is stirred for 3-4 hours at 20-25° C. and 200-500 r / min. The amino groups on the carboxymethyl chitosan initiate the ring opening and polymerization of the oxazolidinedione compound monomer, thereby grafting the methionine side chain. The reaction solution after the reaction is precipitated with anhydrous ethanol, and the precipitate is collected and vacuum dried at 40-50° C. to obtain methionine-grafted modified chitosan;

[0016] Furthermore, the usage ratio of carboxymethyl chitosan, dimethyl sulfoxide and oxazolidinedione compound monomer is 1-1.2 g:100 mL:5-6 g.

[0017] Further, the inorganic fertilizer particles are prepared by the following steps:

[0018] Superphosphate, potassium dihydrogen phosphate, potassium chloride, urea, diatomaceous earth and attapulgite are mixed evenly, then transferred to a granulator, sprayed with 35-40% ethylene glycol aqueous solution by mass fraction, and inorganic fertilizer particles with a diameter of 0.4-0.8 mm are prepared by wet granulation.

[0019] The mass ratio of superphosphate, potassium dihydrogen phosphate, potassium chloride, urea, diatomaceous earth, attapulgite and 35-40wt% ethylene glycol aqueous solution is 1:1:1:4:0.6-0.8:0.6-0.8:0.3-0.4.

[0020] Further, the modified humic acid is prepared by the following steps:

[0021] The humic acid is stirred and dispersed with deionized water and then transferred to a reactor. Then, a phosphoric acid aqueous solution with a mass fraction of 6-8wt% is used to adjust the pH value to 3.5±0.1. Then, a formaldehyde aqueous solution with a mass fraction of 25-30% is added to the reactor. The reaction is carried out at 90-95° C. for 50-60 minutes. The pH value is adjusted to 2.0±0.1 with a phosphoric acid aqueous solution with a mass fraction of 6-8wt%, filtered, and the retained reaction product is ventilated and dried to obtain modified humic acid.

[0022] Furthermore, the usage ratio of humic acid, deionized water and formaldehyde aqueous solution is 2-3 g:100 mL:0.8-1 g.

[0023] Furthermore, the composite bacterial agent is prepared by the following steps:

[0024] The Bacillus subtilis powder, the Bacillus amyloliquefaciens powder and water are uniformly mixed in a dosage ratio of 3-5:2-4:5-9 to obtain a composite bacterial solution; the composite bacterial solution is adsorbed by biochar, and ventilated and dried to obtain a composite bacterial agent;

[0025] Furthermore, the number of viable microorganisms in the composite bacterial agent is ≥ 8×10 10 CFU / g.

[0026] The composite prepared value-added compound fertilizer can be applied to corn planting.

[0027] Beneficial effects of the present invention:

[0028] The value-added compound fertilizer prepared by the preparation method of the present invention is added with bacillus subtilis and bacillus amyloliquefaciens, which can inhibit the growth and reproduction of pathogens and pests in the soil, improve the pH value of the soil, and enhance the stress resistance of corn; after the humic acid is modified by formaldehyde, it is helpful to increase the number of hydroxyl groups in the humic acid, thereby increasing the adsorption effect of the modified humic acid, reducing the leaching loss of inorganic fertilizers, and improving the slow-release effect of the value-added compound fertilizer; under the coating effect of the coating liquid, the slow-release effect of the value-added compound fertilizer is further improved, thereby helping to increase the corn yield.

[0029] The preparation method of the present invention modifies ordinary carboxymethyl chitosan to prepare methionine grafted modified chitosan and apply it to the coating liquid; methionine and di(trichloromethyl) carbonate react to form oxazolidinedione compound monomers, and the amino groups on the carboxymethyl chitosan trigger the ring opening and polymerization of the oxazolidinedione compound monomers, thereby grafting the methionine side chain, and the methylthio group has negative charge, thereby balancing the positive charge of the amino group, reducing its inhibitory effect on the bacillus agent, and helping to be applied to the coating material of the value-added compound fertilizer containing the agent. The methionine grafted modified chitosan can be naturally degraded, and the decomposed methionine can provide a slow-release sulfur source for corn growth, further improving the corn yield. DETAILED DESCRIPTION

[0030] 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.

[0031] Example 1

[0032] This embodiment provides a method for preparing a value-added compound fertilizer, comprising the following steps:

[0033] Step 1: 20 kg of humic acid was stirred and dispersed with 1000 L of deionized water and then transferred to a reactor, and then the pH value was adjusted to 3.5±0.1 with a 6 wt % phosphoric acid aqueous solution, and then 8 kg of a 25 wt % formaldehyde aqueous solution was added to the reactor, and the reaction was carried out at 90° C. for 50 min, and the pH value was adjusted to 2.0±0.1 with a 6 wt % phosphoric acid aqueous solution, filtered, and the retained reaction product was ventilated and dried to obtain modified humic acid;

[0034] 5 kg of superphosphate, 5 kg of potassium dihydrogen phosphate, 5 kg of potassium chloride, 20 kg of urea, 3 kg of diatomaceous earth and 2 kg of attapulgite were mixed evenly, and then transferred to a granulator, sprayed with 1.5 kg of 35% by mass ethylene glycol aqueous solution, and inorganic fertilizer particles with a diameter of 0.4 mm were prepared by wet granulation;

[0035] 3 kg of Bacillus subtilis powder, 2 kg of Bacillus amyloliquefaciens powder and 5 kg of water were mixed evenly to obtain a composite bacterial solution, which was adsorbed with biochar and dried through ventilation to obtain a microbial viable count of ≥ 8 × 10 10 CFU / g of composite bacterial agent;

[0036] 10 kg of modified humic acid, 10 kg of inorganic fertilizer granules and 3 kg of composite bacterial agent were mixed evenly, and a fertilizer core material with a particle diameter of 2 mm was prepared by a granulator.

[0037] Step 2: 25 kg of L-methionine and 1000 L of deionized water are added to a reactor, stirred at 25° C. and 200 r / min for 10 min, and then 16 kg of di(trichloromethyl)carbonate is dissolved in 100 L of tetrahydrofuran, added to the reactor under the protection of nitrogen, heated to 55° C. and continued to stir for 120 min, the liquid after the reaction is distilled under reduced pressure to 2% of the original volume, the remaining liquid is recrystallized with 10 times the volume of n-hexane, and the crystalline product is dried to obtain a powdery oxazolidinedione compound monomer;

[0038] 2 kg of carboxymethyl chitosan and 200 L of dimethyl sulfoxide were added to a reactor and stirred to mix, and then 10 kg of oxazolidinedione compound monomer was added to the reactor under nitrogen protection, and the reaction was stirred at 20° C. and 200 r / min for 3 h, and the amino groups on the carboxymethyl chitosan initiated the ring opening and polymerization of the oxazolidinedione compound monomer, thereby grafting methionine side chains, and the reaction solution after the reaction was precipitated with anhydrous ethanol, and the precipitate was collected and vacuum dried at 40° C. to obtain methionine grafted modified chitosan;

[0039] 0.6 kg of methionine grafted modified chitosan, 0.6 kg of polyvinyl alcohol, 2 kg of industrial starch, 0.2 kg of tributyl citrate and 10 kg of water were mixed evenly to obtain a coating solution.

[0040] Step 3: Transfer 20kg of fertilizer core material to the coating machine, spray 3kg of coating liquid onto the surface of the fertilizer core material at 40r / min and 20°C, and continue to work the coating machine for 8min after the coating liquid is sprayed. Take out the particles and ventilate and dry them for 8h, thus completing the preparation method of value-added compound fertilizer and obtaining value-added compound fertilizer.

[0041] Example 2

[0042] This embodiment provides a method for preparing a value-added compound fertilizer, comprising the following steps:

[0043] Step 1: 25 kg of humic acid was stirred and dispersed with 1000 L of deionized water and then transferred to a reactor, and then the pH value was adjusted to 3.5±0.1 with a 7 wt % phosphoric acid aqueous solution, and then 9 kg of a 28 wt % formaldehyde aqueous solution was added to the reactor, and the reaction was kept warm at 93° C. for 55 min, and the pH value was adjusted to 2.0±0.1 with a 7 wt % phosphoric acid aqueous solution, filtered, and the intercepted reaction product was ventilated and dried to obtain modified humic acid;

[0044] 5 kg of superphosphate, 5 kg of potassium dihydrogen phosphate, 5 kg of potassium chloride, 20 kg of urea, 3.5 kg of diatomaceous earth and 3 kg of attapulgite were mixed evenly, and then transferred to a granulator, sprayed with 1.8 kg of 38% by mass ethylene glycol aqueous solution, and inorganic fertilizer particles with a diameter of 0.6 mm were prepared by wet granulation;

[0045] 4 kg of Bacillus subtilis powder, 3 kg of Bacillus amyloliquefaciens powder and 7 kg of water were mixed evenly to obtain a composite bacterial solution, which was adsorbed with biochar and dried through ventilation to obtain a microbial viable count of ≥ 8 × 10 10 CFU / g of composite bacterial agent;

[0046] 10 kg of modified humic acid, 10 kg of inorganic fertilizer granules and 3.5 kg of composite bacterial agent were mixed evenly, and a fertilizer core material with a particle diameter of 2.2 mm was prepared by a granulator.

[0047] Step 2: 25.5 kg of L-methionine and 1000 L of deionized water were added to a reactor, stirred at 28° C. and 350 r / min for 15 min, and then 17 kg of di(trichloromethyl)carbonate was dissolved in 100 L of tetrahydrofuran, added to the reactor under the protection of nitrogen, heated to 58° C. and continued to stir for 135 min, and the liquid after the reaction was distilled under reduced pressure to 4% of the original volume, and the remaining liquid was recrystallized with 10 times the volume of n-hexane, and the crystalline product was dried to obtain a powdery oxazolidinedione compound monomer;

[0048] 2.2 kg of carboxymethyl chitosan and 200 L of dimethyl sulfoxide were added to a reactor and stirred to mix, and then 11 kg of oxazolidinedione compound monomer was added to the reactor under nitrogen protection, and the reaction was stirred at 22° C. and 350 r / min for 3.5 hours, and the amino groups on the carboxymethyl chitosan initiated the ring opening and polymerization of the oxazolidinedione compound monomer, thereby grafting methionine side chains, and the reaction solution after the reaction was precipitated with anhydrous ethanol, and the precipitate was collected and vacuum dried at 45° C. to obtain methionine grafted modified chitosan;

[0049] 0.7 kg of methionine grafted modified chitosan, 0.7 kg of polyvinyl alcohol, 2.5 kg of industrial starch, 0.25 kg of tributyl citrate and 11 kg of water were mixed evenly to obtain a coating solution.

[0050] Step 3: Transfer 20 kg of fertilizer core material to the coating machine, spray 3.5 kg of coating liquid onto the surface of the fertilizer core material at 50 r / min and 25°C, and continue to work the coating machine for 10 minutes after the coating liquid is sprayed. Take out the particles and ventilate and dry them for 10 hours, completing the preparation method of value-added compound fertilizer and obtaining value-added compound fertilizer.

[0051] Example 3

[0052] This embodiment provides a method for preparing a value-added compound fertilizer, comprising the following steps:

[0053] Step 1: 30 kg of humic acid was stirred and dispersed with 1000 L of deionized water and then transferred to a reactor, and then the pH value was adjusted to 3.5±0.1 with an 8 wt % phosphoric acid aqueous solution, and then 10 kg of a 30 wt % formaldehyde aqueous solution was added to the reactor, and the reaction was carried out at 95° C. for 60 min, and the pH value was adjusted to 2.0±0.1 with an 8 wt % phosphoric acid aqueous solution, filtered, and the retained reaction product was ventilated and dried to obtain modified humic acid;

[0054] 5 kg of superphosphate, 5 kg of potassium dihydrogen phosphate, 5 kg of potassium chloride, 20 kg of urea, 4 kg of diatomaceous earth and 4 kg of attapulgite were mixed evenly, and then transferred to a granulator, sprayed with 2 kg of 40% by mass ethylene glycol aqueous solution, and inorganic fertilizer particles with a diameter of 0.8 mm were prepared by wet granulation;

[0055] 5 kg of Bacillus subtilis powder, 4 kg of Bacillus amyloliquefaciens powder and 9 kg of water were mixed evenly to obtain a composite bacterial solution, which was adsorbed with biochar and dried through ventilation to obtain a microbial viable count of ≥ 8 × 10 10 CFU / g of composite bacterial agent;

[0056] 10 kg of modified humic acid, 10 kg of inorganic fertilizer granules and 4 kg of composite bacterial agent were mixed evenly, and a fertilizer core material with a particle diameter of 2.5 mm was prepared by a granulator.

[0057] Step 2: 26 kg of L-methionine and 1000 L of deionized water are added to a reactor, stirred at 30° C. and 500 r / min for 20 min, and then 18 kg of di(trichloromethyl)carbonate is dissolved in 100 L of tetrahydrofuran, added to the reactor under the protection of nitrogen, heated to 60° C. and continued to stir for 150 min, and the liquid after the reaction is distilled under reduced pressure to 5% of the original volume, and the remaining liquid is recrystallized with 10 times the volume of n-hexane, and the crystalline product is dried to obtain a powdery oxazolidinedione compound monomer;

[0058] 2.4 kg of carboxymethyl chitosan and 200 L of dimethyl sulfoxide were added to a reactor and stirred and mixed, and then 12 kg of oxazolidinedione compound monomer was added to the reactor under nitrogen protection, and the reaction was stirred at 25° C. and 500 r / min for 4 hours, and the amino groups on the carboxymethyl chitosan initiated the ring opening and polymerization of the oxazolidinedione compound monomer, thereby grafting methionine side chains, and the reaction solution after the reaction was precipitated with anhydrous ethanol, and the precipitate was collected and vacuum dried at 50° C. to obtain methionine grafted modified chitosan;

[0059] 0.8 kg of methionine grafted modified chitosan, 0.8 kg of polyvinyl alcohol, 3 kg of industrial starch, 0.3 kg of tributyl citrate and 12 kg of water were mixed evenly to obtain a coating solution.

[0060] Step 3: Transfer 20kg of fertilizer core material to the coating machine, spray 4kg of coating liquid onto the surface of the fertilizer core material at 60r / min and 30°C, and continue to work the coating machine for 12min after the coating liquid is sprayed. Take out the particles and ventilate and dry them for 12h, completing the preparation method of value-added compound fertilizer and obtaining value-added compound fertilizer.

[0061] Comparative Example 1: Based on Example 3, the humic acid used in the fertilizer core material in step 1 is not modified, and the other steps remain unchanged to prepare a value-added compound fertilizer.

[0062] Comparative Example 2: Based on Example 3, in step 2, carboxymethyl chitosan was directly used instead of methylthioamino acid grafted modified chitosan, and the other steps remained unchanged to prepare a value-added compound fertilizer.

[0063] In the embodiments and comparative examples, humic acid was purchased from Shanxi Jiayou Humic Acid Technology Co., Ltd.; Bacillus subtilis powder and carboxymethyl chitosan were purchased from Hubei Mingtuo Biotechnology Co., Ltd.; Bacillus amyloliquefaciens powder was purchased from Hubei Jiufenglong Chemical Co., Ltd.; polyvinyl alcohol was Wanwei brand polyvinyl alcohol 2488 purchased from Henan Huide Chemical Products Co., Ltd.; and industrial starch was modified cassava starch purchased from Jiangsu Baoshijia Biotechnology Co., Ltd.

[0064] Using the chitosan grafted with methylthioamino acid in Examples 1 to 3 and the carboxymethyl chitosan in Comparative Example 2 as test substances, different test substances were dissolved in deionized water to form a solution with a mass fraction of 1%, and then mixed with ordinary broth culture medium to make the mass concentration of the test substance 0.1%;

[0065] 1 mL of activated Bacillus subtilis solution (10 7 CFU / mL) were inoculated in 50mL of different culture media (with the culture medium without the test substance added as the blank control), cultured at 30°C and 100r / min for 24h, and counted according to the dilution plate counting method in GB 4789.2-1994 to obtain the inhibition rate of different test substances. Inhibition rate (%) = (l gN-l gM) / l gN×100, where N is the number of Bacillus subtilis in the blank control (unit CFU / mL), and M is the number of Bacillus subtilis in the culture medium with the test substance added (unit CFU / mL). The results are shown in Table 1:

[0066] Table 1

[0067] project Example 1 Example 2 Example 3 Comparative Example 2 Antibacterial rate (%) 5.5 6.2 7.7 61.4

[0068] It can be seen from Table 1 that the antibacterial effect of the modified methionine grafted chitosan on Bacillus subtilis is effectively reduced.

[0069] Performance tests were performed on Example 1-Example 3 and Comparative Example 1-Comparative Example 2. From June to October 2023, corn of the variety "Yanyu 601" was used as the test crop in the test field in Lixin County, Anhui Province, with a row spacing of about 60 cm and a plant spacing of about 25 cm. The same planting area and field management were used, and the value-added compound fertilizers in Example 1-Example 2 and Comparative Example 1-Comparative Example 2 were respectively applied as base fertilizers, with a fertilizer application rate of 50 kg / mu, and the treatment without base fertilizer was used as a blank group. After harvesting corn, the relevant test data are shown in Table 2, where the calculation method of corn yield is per mu yield (kg) = per mu ear number × ear number / kg number of grains.

[0070] Table 2

[0071] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Seedling rate (%) 84 83 84 79 81 Soil pH 7.2 7.2 7.3 7.3 7.6 Corn yield (kg / mu) 623.7 605.4 612.9 552.3 524.2

[0072] It can be seen from Table 1 that the use of the value-added compound fertilizer in the embodiment as base fertilizer is helpful to increase corn yield. Comparative Example 1 shows that humic acid can improve the slow-release effect of the value-added compound fertilizer after modification, thereby improving fertilizer efficiency; Comparative Example 2 shows that after carboxymethyl chitosan is modified with methionine, the inhibitory effect on beneficial microorganisms in the soil is reduced, which helps to improve the soil pH value and can significantly increase the yield of corn.

[0073] It should be noted that, in this article, terms such as "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes 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 apparatus.

[0074] 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 method for preparing a value-added compound fertilizer, characterized in that: The steps include: Step 1: Evenly mix the modified humic acid, inorganic fertilizer particles and composite bacterial agent in a mass ratio of 1:1:0.3-0.4, and use a granulator to prepare a fertilizer core material with a particle diameter of 2-2.5 mm; Step 2: Evenly mix methionine grafted modified chitosan, polyvinyl alcohol, industrial starch, tributyl citrate and water in a mass ratio of 6-8:6-8:20-30:2-3:100-120 to obtain a coating solution; Step 3: Transfer the fertilizer core material to a coating machine, spray the coating liquid onto the surface of the fertilizer core material at 40-60r / min and 20-30°C, and continue the coating machine to work for 8-12 minutes after the spraying is completed. Take out the particles and ventilate and dry them for 8-12 hours, thereby completing the preparation method of the value-added compound fertilizer and obtaining the value-added compound fertilizer; the mass ratio of the fertilizer core material to the coating liquid is 20:3-4; The methionine grafted modified chitosan is prepared by the following steps: Carboxymethyl chitosan and dimethyl sulfoxide are added to a reaction kettle and stirred to mix, and an oxazolidinedione compound monomer is added to the reaction kettle under nitrogen protection, and the reaction is stirred at 20-25° C. and 200-500 r / min for 3-4 hours, and the reaction solution is precipitated with anhydrous ethanol, and the precipitate is collected and vacuum dried at 40-50° C. to obtain methionine grafted modified chitosan; The oxazolidinedione compound monomer is prepared by the following steps: L-methionine and deionized water are added to a reactor, stirred at 25-30°C and 200-500r / min for 10-20min, di(trichloromethyl)carbonate is dissolved in tetrahydrofuran under the protection of nitrogen and added to the reactor, stirred at 55-60°C for 120-150min, the liquid after the reaction is distilled under reduced pressure to 2-5% of the original volume, the remaining liquid is recrystallized with 10 times the volume of n-hexane, and dried to obtain an oxazolidinedione compound monomer.

2. The method for preparing a value-added compound fertilizer according to claim 1, characterized in that: The usage ratio of the carboxymethyl chitosan, dimethyl sulfoxide and oxazolidinedione compound monomer is 1-1.2 g:100 mL:5-6 g.

3. The method for preparing a value-added compound fertilizer according to claim 1, characterized in that: The usage ratio of the L-methionine, deionized water, bis(trichloromethyl) carbonate and tetrahydrofuran is 2.5-2.6 g:100 mL:1.6-1.8 g:10 mL.

4. The method for preparing a value-added compound fertilizer according to claim 1, characterized in that: The inorganic fertilizer particles are prepared by the following steps: Superphosphate, potassium dihydrogen phosphate, potassium chloride, urea, diatomaceous earth and attapulgite are mixed evenly, then transferred to a granulator, sprayed with a 35-40wt% ethylene glycol aqueous solution, and wet granulated to prepare inorganic fertilizer particles with a diameter of 0.4-0.8mm.

5. The method for preparing a value-added compound fertilizer according to claim 4, characterized in that: The mass ratio of the superphosphate, potassium dihydrogen phosphate, potassium chloride, urea, diatomaceous earth, attapulgite and 35-40wt% ethylene glycol aqueous solution is 1:1:1:4:0.6-0.8:0.6-0.8:0.3-0.

4.

6. The method for preparing a value-added compound fertilizer according to claim 1, characterized in that: The modified humic acid is prepared by the following steps: The humic acid is stirred and dispersed with deionized water and then transferred to a reactor. The pH value is adjusted to 3.5±0.1 with a 6-8wt% phosphoric acid aqueous solution, and then a 25-30wt% formaldehyde aqueous solution is added. The mixture is kept warm at 90-95°C for 50-60 minutes, and the pH value is adjusted to 2.0±0.1 with a 6-8wt% phosphoric acid aqueous solution. The mixture is filtered, and the retained reaction product is dried to obtain modified humic acid.

7. The method for preparing a value-added compound fertilizer according to claim 6, characterized in that: The dosage ratio of the humic acid, deionized water and formaldehyde aqueous solution is 2-3 g:100 mL:0.8-1 g.

8. The method for preparing a value-added compound fertilizer according to claim 1, characterized in that: The composite bacterial agent is prepared by the following steps: The Bacillus subtilis powder, Bacillus amyloliquefaciens powder and water were mixed evenly in a dosage ratio of 3-5:2-4:5-9, and the composite bacterial solution was adsorbed with biochar, ventilated and dried to obtain a microbial viable count of ≥8×10 10 CFU / g compound bacterial agent.

9. Use of the value-added compound fertilizer prepared according to the preparation method according to any one of claims 1 to 8 in corn planting.

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