Chitosan grafted polyacrylic acid slow-release fertilizer and preparation method thereof

Abstract

The application relates to the technical field of fertilizers, and discloses a chitosan-grafted polyacrylic acid slow-release fertilizer and a preparation method thereof. The chitosan-grafted polyacrylic acid slow-release fertilizer is obtained by spray drying of a nutrient solution, a carrier dispersion liquid and a calcium chloride aqueous solution; the nutrient solution is obtained by mixing urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, iron sodium ethylenediaminetetraacetate, amino acid and deionized water; the carrier dispersion liquid is obtained by mixing a porous carrier, deionized water and polyoxyethylene sorbitan monooleate; the porous carrier is prepared from sulfonated chitosan powder, deionized water, an acrylic acid neutralizing solution, ammonium persulfate and N,N'-methylenebisacrylamide; and the sulfonated chitosan powder is prepared from formamide, chlorosulfonic acid and chitosan powder. The application can reduce the release rate of nutrients and improve the utilization rate of nutrients.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, specifically to a chitosan-grafted polyacrylic acid slow-release fertilizer and its preparation method. Background Technology

[0002] With the advancement of agricultural modernization, the widespread application of chemical fertilizers has greatly increased crop yields. However, traditional chemical fertilizers suffer from problems such as difficulty in controlling nutrient release rates and low utilization rates. A large amount of nutrients that are not absorbed by crops are easily lost through leaching, volatilization, and other pathways, which not only wastes resources but also causes ecological and environmental problems such as soil compaction and eutrophication of water bodies.

[0003] Patent CN118619784A discloses a humic acid-containing water-soluble fertilizer and its preparation method. The humic acid-containing water-soluble fertilizer comprises the following components: sucrose organic fermented lactic acid solution, organic fulvic acid, mineral-derived humic acid, amide nitrogen, potassium tripolyphosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, potassium nitrate, and water. The preparation method involves mixing, heating, and stirring the components in sequence to obtain the humic acid-containing water-soluble fertilizer. However, the nutrient components of this fertilizer are easily lost, making it difficult for crops to fully utilize them, resulting in resource waste. Summary of the Invention

[0004] The purpose of this invention is to provide a chitosan-grafted polyacrylic acid slow-release fertilizer and its preparation method, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A chitosan-grafted polyacrylic acid slow-release fertilizer is obtained by spray drying a nutrient solution, a carrier dispersion, and a calcium chloride aqueous solution. The nutrient solution is obtained by mixing urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids, and deionized water. The carrier dispersion is obtained by mixing a porous carrier, deionized water, and polyoxyethylene dehydrated sorbitan monooleate. The porous carrier is prepared by sulfonated chitosan powder, deionized water, acrylic acid neutralization solution, ammonium persulfate, and N,N'-methylenebisacrylamide. The sulfonated chitosan powder is prepared by formamide, chlorosulfonic acid, and chitosan powder.

[0006] Furthermore, chitosan has a degree of deacetylation of 90%-95% and a number-average molecular weight of 100,000-500,000 Da.

[0007] Furthermore, the preparation method of the acrylic acid neutralization solution is as follows: Acrylic acid is taken under ice-water bath cooling and neutralized with a sodium hydroxide aqueous solution with a mass fraction of 30%-40% to achieve a neutralization degree of 70%.

[0008] Furthermore, the amino acid is selected from one or more of glycine, lysine, glutamic acid, and aspartic acid.

[0009] A method for preparing a chitosan-grafted polyacrylic acid slow-release fertilizer includes the following steps: (1) Add formamide to the reaction vessel, and slowly add chlorosulfonic acid dropwise under an ice-water bath and a stirring speed of 300-400 rpm, controlling the dropping speed to keep the temperature below 10℃. Then add chitosan powder with a particle size of 100-200 mesh, and continue stirring for 30-40 minutes. Then stir at 400-500 rpm for 3.5-4.5 hours at 68-72℃. After that, pour the reaction product into 5 times its mass of 90-95% ethanol aqueous solution for precipitation, filter to collect the solid, and wash the solid with 70-80% ethanol aqueous solution until the filtrate is neutral. Vacuum dry at 45-55℃ for 10-15 hours, pulverize and pass through a 100-200 mesh sieve to obtain sulfonated chitosan powder. (2) Mix sulfonated chitosan powder and deionized water, stir at 400-600 rpm for 30-50 minutes, then bubble with nitrogen for 30-40 minutes to remove oxygen, add acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide, stir at 200-300 rpm for 5-6 hours at 64-66℃ under nitrogen protection, then wash the resulting gel product with deionized water 2-4 times, freeze dry at -50℃ for 40-48 hours, pulverize and pass through a 100-200 mesh sieve to obtain a porous carrier; (3) Mix urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids and deionized water, and stir at 500-700 rpm for 20-40 minutes to obtain a nutrient solution; mix porous carrier, deionized water and polyoxyethylene dehydrated sorbitan monooleate, and stir at 8000-10000 rpm for 5-7 minutes to obtain a carrier dispersion; slowly add the nutrient solution to the carrier dispersion over 30-50 minutes while stirring at 500-700 rpm, and then slowly add a 4-6% calcium chloride aqueous solution over 15-25 minutes, and continue stirring at 20-25℃ for 1.5-2.5 hours; then spray dry, controlling the inlet air temperature at 145-155℃ and the outlet air temperature at 75-85℃ to obtain chitosan-grafted polyacrylic acid slow-release fertilizer.

[0010] Furthermore, in step (1), the mass ratio of formamide, chlorosulfonic acid and chitosan powder is 100:35-45:9-12.

[0011] Furthermore, in step (2), the mass ratio of sulfonated chitosan powder, deionized water, acrylic acid neutralizing solution, ammonium persulfate and N,N'-methylenebisacrylamide is 10:450-550:85-115:3.0-3.6:0.14-0.18.

[0012] Furthermore, in step (3), the mass ratio of urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, ferric sodium ethylenediaminetetraacetate, amino acids and deionized water is 140-160:45-55:4.5-5.5:2.7-3.3:9-11:190-210.

[0013] Furthermore, in step (3), the mass ratio of the porous carrier, deionized water and polyoxyethylene dehydrated sorbitan monooleate is 28-32:680-720:4.5-5.5.

[0014] Furthermore, in step (3), the mass ratio of nutrient solution, carrier dispersion and calcium chloride aqueous solution is 100:700-900:18-22.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. In this invention, the sulfonyl chloride group in the chlorosulfonic acid molecule undergoes a sulfonation reaction with the hydroxyl and some amino groups on the chitosan chain, thereby introducing strongly hydrophilic and ionic sulfonic acid groups into the chitosan molecular backbone to obtain sulfonated chitosan. Ammonium persulfate decomposes upon heating to generate sulfate radicals, which can abstract hydrogen atoms from the sulfonated chitosan molecular chain, forming a large molecular free radical active center. This active center then initiates the free radical polymerization reaction of acrylic acid monomers, causing polyacrylic acid segments to covalently graft onto the sulfonated chitosan backbone. Simultaneously, the vinyl groups at both ends of the N,N'-methylenebisacrylamide molecule undergo a free radical copolymerization reaction, bonding different sulfonated groups... Chitosan chains and polyacrylic acid chains are linked together to form a three-dimensional covalent network, resulting in a sulfonated chitosan-grafted polyacrylic acid copolymer. A calcium chloride aqueous solution provides calcium ions, which can form ionic bonds with the negatively charged carboxylate and sulfonate ions on the porous carrier, causing ionic cross-linking and aggregation between the porous carrier powders. This encapsulates the nutrient components within the cross-linked network and the porous carrier. The sulfonated chitosan-grafted polyacrylic acid copolymer network provides mechanical strength and integrity, ensuring the stability of the fertilizer during storage and transportation. Furthermore, by blocking the nutrient components, it reduces the nutrient release rate and improves nutrient utilization. Detailed Implementation

[0016] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0017] A chitosan-grafted polyacrylic acid slow-release fertilizer is obtained by spray drying a nutrient solution, a carrier dispersion, and a calcium chloride aqueous solution. The nutrient solution is obtained by mixing urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids, and deionized water. The carrier dispersion is obtained by mixing a porous carrier, deionized water, and polyoxyethylene dehydrated sorbitan monooleate. The porous carrier is prepared by sulfonated chitosan powder, deionized water, acrylic acid neutralization solution, ammonium persulfate, and N,N'-methylenebisacrylamide. The sulfonated chitosan powder is prepared by formamide, chlorosulfonic acid, and chitosan powder.

[0018] For experiments not specifically described in the examples, the procedures and conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagents. In the following examples, glycine is used as an example of amino acid, but the examples are not limited to this.

[0019] Example 1

[0020] (1) Add formamide to the reaction vessel, and slowly add chlorosulfonic acid dropwise under an ice-water bath and a stirring speed of 300 rpm, controlling the dropping speed to keep the temperature below 10°C. Then add chitosan powder with a particle size of 100 mesh, and continue stirring for 30 minutes. Then stir at 400 rpm for 3.5 hours at 68°C. After that, pour the reaction product into a 90% ethanol aqueous solution with a mass fraction of 5 times its mass for precipitation, filter to collect the solid, and wash the solid with a 70% ethanol aqueous solution until the filtrate is neutral. Vacuum dry at 45°C for 10 hours, pulverize and pass through a 100-mesh sieve to obtain sulfonated chitosan powder. The degree of deacetylation of chitosan is 90%, and the number average molecular weight is 100,000 Da. The mass ratio of formamide, chlorosulfonic acid and chitosan powder is 100:35:9.

[0021] (2) Sulfonated chitosan powder and deionized water were mixed and stirred at 400 rpm for 30 minutes. Then nitrogen gas was bubbled through for 30 minutes to remove oxygen. Acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide were added. Under nitrogen protection, the mixture was stirred at 200 rpm at 64°C for 5 hours. The resulting gel product was then washed twice with deionized water and freeze-dried at -50°C for 40 hours. The product was then pulverized and passed through a 100-mesh sieve to obtain a porous carrier.

[0022] The preparation method of the acrylic acid neutralization solution is as follows: Acrylic acid is taken under ice-water bath cooling and neutralized with a 30% sodium hydroxide aqueous solution to a degree of neutralization of 70%. The mass ratio of sulfonated chitosan powder, deionized water, acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide is 10:450:85:3.0:0.14.

[0023] (3) Urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids and deionized water were mixed in a mass ratio of 140:45:4.5:2.7:9:190 and stirred at 500 rpm for 20 minutes to obtain a nutrient solution; porous carrier, deionized water and polyoxyethylene dehydrated sorbitan monooleate were mixed in a mass ratio of 28:680:4.5 and stirred at 8000 rpm for 5 minutes to obtain a carrier dispersion; the nutrient solution was slowly added dropwise to the carrier dispersion over 30 minutes at a stirring speed of 500 rpm, followed by the slow addition of a 4% calcium chloride aqueous solution over 15 minutes, and stirring was continued at 20°C for 1.5 hours; then spray drying was carried out, with the inlet air temperature controlled at 145°C and the outlet air temperature controlled at 75°C to obtain chitosan-grafted polyacrylic acid slow-release fertilizer; the mass ratio of the nutrient solution, carrier dispersion and calcium chloride aqueous solution was 100:700:18.

[0024] Example 2

[0025] (1) Add formamide to the reaction vessel, and slowly add chlorosulfonic acid dropwise under an ice-water bath and a stirring speed of 350 rpm, controlling the dropping speed to keep the temperature below 10°C. Then add chitosan powder with a particle size of 150 mesh, and continue stirring for 35 minutes. Then stir at 70°C and 450 rpm for 4 hours. After that, pour the reaction product into 5 times its mass of a 92.5% ethanol aqueous solution for precipitation, filter to collect the solid, and wash the solid with a 75% ethanol aqueous solution until the filtrate is neutral. Vacuum dry at 50°C for 12.5 hours, pulverize and pass through a 150-mesh sieve to obtain sulfonated chitosan powder. The degree of deacetylation of chitosan is 92%, and the number average molecular weight is 300,000 Da. The mass ratio of formamide, chlorosulfonic acid and chitosan powder is 100:40:10.5.

[0026] (2) Sulfonated chitosan powder and deionized water were mixed and stirred at 500 rpm for 40 minutes. Then, nitrogen gas was bubbled through for 35 minutes to remove oxygen. Acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide were added. Under nitrogen protection, the mixture was stirred at 250 rpm at 65°C for 5.5 hours. The resulting gel product was then washed three times with deionized water and freeze-dried at -50°C for 44 hours. The product was then pulverized and passed through a 150-mesh sieve to obtain a porous carrier.

[0027] The preparation method of the acrylic acid neutralization solution is as follows: Acrylic acid is taken under ice-water bath cooling and neutralized with a 35% sodium hydroxide aqueous solution to a degree of neutralization of 70%. The mass ratio of sulfonated chitosan powder, deionized water, acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide is 10:500:100:3.3:0.16.

[0028] (3) Urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids and deionized water were mixed in a mass ratio of 150:50:5.0:3.0:10:200 and stirred at 600 rpm for 30 minutes to obtain a nutrient solution; porous carrier, deionized water and polyoxyethylene dehydrated sorbitan monooleate were mixed in a mass ratio of 30:700:5.0 and stirred at 9000 rpm for 6 minutes to obtain a carrier dispersion; the nutrient solution was slowly added dropwise to the carrier dispersion over 40 minutes at a stirring speed of 600 rpm, followed by the slow addition of a 5% calcium chloride aqueous solution over 20 minutes, and stirring was continued at 22.5℃ for 2 hours; then spray drying was carried out, with the inlet air temperature controlled at 150℃ and the outlet air temperature controlled at 80℃ to obtain chitosan-grafted polyacrylic acid slow-release fertilizer; the mass ratio of the nutrient solution, carrier dispersion and calcium chloride aqueous solution was 100:800:20.

[0029] Example 3

[0030] (1) Add formamide to the reaction vessel, and slowly add chlorosulfonic acid dropwise under an ice-water bath and a stirring speed of 400 rpm, controlling the dropping speed to keep the temperature below 10°C. Then add chitosan powder with a particle size of 200 mesh, and continue stirring for 40 minutes. Then stir at 72°C and 500 rpm for 4.5 hours. After that, pour the reaction product into 5 times its mass of a 95% ethanol aqueous solution for precipitation, filter to collect the solid, and wash the solid with an 80% ethanol aqueous solution until the filtrate is neutral. Vacuum dry at 55°C for 15 hours, pulverize and pass through a 200-mesh sieve to obtain sulfonated chitosan powder. The degree of deacetylation of chitosan is 95%, and the number average molecular weight is 500,000 Da. The mass ratio of formamide, chlorosulfonic acid and chitosan powder is 100:45:12.

[0031] (2) Sulfonated chitosan powder and deionized water were mixed and stirred at 600 rpm for 50 minutes. Then, nitrogen gas was bubbled through for 40 minutes to remove oxygen. Acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide were added. Under nitrogen protection, the mixture was stirred at 300 rpm at 66°C for 6 hours. The resulting gel product was then washed with deionized water 4 times and freeze-dried at -50°C for 48 hours. The product was then pulverized and passed through a 200-mesh sieve to obtain a porous carrier.

[0032] The preparation method of the acrylic acid neutralization solution is as follows: Acrylic acid is taken under ice-water bath cooling and neutralized with a 40% sodium hydroxide aqueous solution to a degree of neutralization of 70%. The mass ratio of sulfonated chitosan powder, deionized water, acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide is 10:550:115:3.6:0.18.

[0033] (3) Urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids and deionized water were mixed in a mass ratio of 160:55:5.5:3.3:11:210 and stirred at 700 rpm for 40 minutes to obtain a nutrient solution; porous carrier, deionized water and polyoxyethylene dehydrated sorbitan monooleate were mixed in a mass ratio of 32:720:5.5 and stirred at 10000 rpm for 7 minutes to obtain a carrier dispersion; the nutrient solution was slowly added dropwise to the carrier dispersion over 50 minutes at a stirring speed of 700 rpm, followed by the slow addition of a 6% calcium chloride aqueous solution over 25 minutes, and stirring was continued at 25°C for 2.5 hours; then spray drying was carried out, with the inlet air temperature controlled at 155°C and the outlet air temperature controlled at 85°C to obtain chitosan-grafted polyacrylic acid slow-release fertilizer; the mass ratio of the nutrient solution, carrier dispersion and calcium chloride aqueous solution was 100:900:22.

[0034] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the chitosan powder is not sulfonated.

[0035] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that N,N'-methylenebisacrylamide is not added.

[0036] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that no calcium chloride aqueous solution was added.

[0037] Referring to GB / T23348-2009 "Slow-Release Fertilizers", the nutrient release rate of the fertilizer on day 1 and day 7 was tested using the Kjeldahl method. Table 1 below shows the performance analysis results of the embodiments and comparative examples of the present invention.

[0038] Table 1

[0039] Experimental data from the examples and comparative examples show that the calcium chloride aqueous solution in this invention provides calcium ions, which can form ionic bonds with the negatively charged carboxylate and sulfonate ions on the porous carrier, causing ionic cross-linking and aggregation between the porous carrier powders, thus sealing the nutrient components in the cross-linked network and the porous carrier. The sulfonated chitosan-grafted polyacrylic acid copolymer network provides mechanical strength and integrity, ensuring the stability of the fertilizer during storage and transportation. On the other hand, it can reduce the nutrient release rate and improve nutrient utilization by blocking the nutrient components.

[0040] In addition, using a lower amount of N,N'-methylenebisacrylamide may provide space for efficient calcium ion penetration and further ion cross-linking due to the looser covalent cross-linking network formed, thus achieving better nutrient encapsulation and sustained release effects.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A chitosan-grafted polyacrylic acid slow-release fertilizer, characterized in that, The chitosan-grafted polyacrylic acid slow-release fertilizer is obtained by spray drying a nutrient solution, a carrier dispersion, and a calcium chloride aqueous solution. The nutrient solution is obtained by mixing urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids, and deionized water. The carrier dispersion is obtained by mixing a porous carrier, deionized water, and polyoxyethylene dehydrated sorbitan monooleate. The porous carrier is prepared by sulfonated chitosan powder, deionized water, acrylic acid neutralization solution, ammonium persulfate, and N,N'-methylenebisacrylamide. The sulfonated chitosan powder is prepared by formamide, chlorosulfonic acid, and chitosan powder.

2. The chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 1, characterized in that... Chitosan has a degree of deacetylation of 90%-95% and a number-average molecular weight of 100,000-500,000 Da.

3. The chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 1, characterized in that... The preparation method of acrylic acid neutralization solution is as follows: Acrylic acid is taken under ice-water bath cooling and neutralized with a sodium hydroxide aqueous solution with a mass fraction of 30%-40% to achieve a neutralization degree of 70%.

4. The chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 1, characterized in that... The amino acids are selected from one or more of glycine, lysine, glutamic acid, and aspartic acid.

5. A method for preparing a chitosan-grafted polyacrylic acid slow-release fertilizer, applied to the chitosan-grafted polyacrylic acid slow-release fertilizer according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Add formamide to the reaction vessel, and slowly add chlorosulfonic acid dropwise under an ice-water bath and a stirring speed of 300-400 rpm, controlling the dropping speed to keep the temperature below 10℃. Then add chitosan powder with a particle size of 100-200 mesh, and continue stirring for 30-40 minutes. Then stir at 400-500 rpm for 3.5-4.5 hours at 68-72℃. After that, pour the reaction product into 5 times its mass of 90-95% ethanol aqueous solution for precipitation, filter to collect the solid, and wash the solid with 70-80% ethanol aqueous solution until the filtrate is neutral. Vacuum dry at 45-55℃ for 10-15 hours, pulverize and pass through a 100-200 mesh sieve to obtain sulfonated chitosan powder. (2) Mix sulfonated chitosan powder and deionized water, stir at 400-600 rpm for 30-50 minutes, then bubble with nitrogen for 30-40 minutes to remove oxygen, add acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide, stir at 200-300 rpm for 5-6 hours at 64-66℃ under nitrogen protection, then wash the resulting gel product with deionized water 2-4 times, freeze dry at -50℃ for 40-48 hours, pulverize and pass through a 100-200 mesh sieve to obtain a porous carrier; (3) Mix urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, sodium iron ethylenediaminetetraacetate, amino acids and deionized water, and stir at 500-700 rpm for 20-40 minutes to obtain a nutrient solution; mix porous carrier, deionized water and polyoxyethylene dehydrated sorbitan monooleate, and stir at 8000-10000 rpm for 5-7 minutes to obtain a carrier dispersion; slowly add the nutrient solution to the carrier dispersion over 30-50 minutes while stirring at 500-700 rpm, and then slowly add a 4-6% calcium chloride aqueous solution over 15-25 minutes, and continue stirring at 20-25℃ for 1.5-2.5 hours; then spray dry, controlling the inlet air temperature at 145-155℃ and the outlet air temperature at 75-85℃ to obtain chitosan-grafted polyacrylic acid slow-release fertilizer.

6. The method for preparing a chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 5, characterized in that... In step (1), the mass ratio of formamide, chlorosulfonic acid and chitosan powder is 100:35-45:9-12.

7. The method for preparing a chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 5, characterized in that... In step (2), the mass ratio of sulfonated chitosan powder, deionized water, acrylic acid neutralization solution, ammonium persulfate and N,N'-methylenebisacrylamide is 10:450-550:85-115:3.0-3.6:0.14-0.

18.

8. The method for preparing a chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 5, characterized in that... In step (3), the mass ratio of urea, potassium dihydrogen phosphate, zinc sulfate heptahydrate, ferric sodium ethylenediaminetetraacetate, amino acids and deionized water is 140-160:45-55:4.5-5.5:2.7-3.3:9-11:190-210.

9. The method for preparing a chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 5, characterized in that... In step (3), the mass ratio of porous carrier, deionized water and polyoxyethylene dehydrated sorbitan monooleate is 28-32:680-720:4.5-5.

5.

10. The method for preparing a chitosan-grafted polyacrylic acid slow-release fertilizer according to claim 5, characterized in that... In step (3), the mass ratio of nutrient solution, carrier dispersion and calcium chloride aqueous solution is 100:700-900:18-22.

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