Slow-release compound fertilizer and preparation method thereof

Abstract

The invention relates to the field of compound fertilizers, in particular to a slow-release compound fertilizer and a preparation method thereof.The slow-release compound fertilizer is prepared from, by weight, 100 parts of alpha-amino-4-vinyl phenylacetic acid, 0.25-0.35 part of polyethylene glycol 2000 and 1200-1500 parts of modified lignin coated compound fertilizers. A traditional petroleum-based material is replaced, so that dependence of a fertilizer coating material on non-renewable resources is reduced, meanwhile, pollution to soil and water resources can be reduced through preparation of a novel coating material, and meanwhile, based on innovative application of an environment-friendly material, cooperative regulation and control of two technologies are combined, and through a precisely-optimized technological parameter system, the environment-friendly fertilizer is prepared. Efficient slow release, lasting fertilizer efficiency and large-scale stable production of the compound fertilizer are achieved, meanwhile, through comparison verification, the nutrient utilization rate and environmental friendliness are remarkably improved, an efficient and sustainable solution is provided for green agriculture, and wide application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the field of compound fertilizers, and particularly relates to a slow-release compound fertilizer and a preparation method thereof. Background Art

[0002] A slow-release compound fertilizer is a new type of fertilizer that regulates the nutrient release rate through special processes, aiming to extend the fertilizer efficiency, reduce the frequency of fertilization, improve the nutrient utilization rate, and reduce environmental pollution. Traditional compound fertilizers (such as urea, diammonium phosphate, etc.) have a fast nutrient release rate, which is prone to loss, volatilization, or fixation. The slow-release technology delays the nutrient release through physical coating, chemical bonding, or biodegradable materials, which is one of the key directions for the green development of modern agriculture.

[0003] In the prior art, most of the coating materials used in compound fertilizers are petroleum-based coating materials (such as resins, polymers, etc.), which have problems such as non-renewability, high cost, and poor environmental friendliness. Long-term use may exacerbate resource consumption and environmental pollution, and the degradation rate of the coating material does not match the nutrient release demand well, which is prone to excessive nutrient release in the early stage or insufficient release in the later stage, affecting the crop absorption efficiency.

[0004] Therefore, according to the above related technologies, it is urgent to develop a slow-release compound fertilizer and a preparation method thereof. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a slow-release compound fertilizer and a preparation method thereof to solve the problems of poor environmental friendliness of the coating material and unstable slow-release effect in the prior art.

[0006] Based on the above purpose, the present invention provides a slow-release compound fertilizer and a preparation method thereof.

[0007] A slow-release compound fertilizer, comprising the following raw materials in parts by mass: 100 parts by weight of α-amino-4-vinylphenylacetic acid, 0.25 - 0.35 parts by weight of polyethylene glycol 2000, 1200 - 1500 parts by weight of modified lignin-coated compound fertilizer.

[0008] Preferably, a preparation method of a slow-release compound fertilizer, the preparation method is as follows: Step S1: Add clay, urea, monoammonium phosphate, potassium sulfate, magnesium sulfate, borax, and zinc sulfate to a rotary drum mixer in sequence, with a rotation speed of 10 - 20 r / min, stir for 5 - 10 min. After mixing evenly, add it to an extrusion granulator, with a pressure of 10 - 20 MPa, dry, sieve, and the particle diameter is 2 - 4 mm to obtain compound fertilizer particles; Step S2: Add the compound fertilizer particles to a coating machine, heat up to 50 - 70 °C, with a rotation speed of 50 - 70 r / min, add modified lignin and the adhesive gelatin, and run for 5 - 10 min to obtain modified lignin-coated compound fertilizer; Step S3: Add α-amino-4-vinylphenylacetic acid, ammonium persulfate, and polyethylene glycol 2000 into deionized water, stir for 10 - 20 min, add the modified lignin-coated compound fertilizer, heat up to 25 - 35 °C, and react for 14 - 16 h to obtain the slow-release compound fertilizer.

[0009] The modified lignin, as a coating material, is derived from natural plants and has the advantages of renewability, degradability, and low cost. By chemically modifying it to introduce long-chain hydrophobic groups, it is endowed with excellent hydrophobicity and mechanical strength. α-Amino-4-vinylphenylacetic acid, as a functional monomer, undergoes a cross-linking reaction with the hydroxyl and carboxyl groups on the surface of the modified lignin, enhancing the coating density and delaying water penetration. Then, through the hydrophilic regulator polyethylene glycol 2000, the microporous structure is used to regulate the water penetration rate, realizing the gradient release of nutrients, avoiding the problems of rapid nutrient release in the early stage and insufficient nutrients in the later stage, and forming a controllable slow-release barrier through the combination of physical barrier and chemical bonding, thereby precisely regulating the nutrient release rate to match the growth cycle requirements of crops and significantly improving the nutrient utilization rate.

[0010] Preferably, in step S1, the mass ratio of the clay, urea, monoammonium phosphate, potassium sulfate, magnesium sulfate, borax, and zinc sulfate is 1:2 - 4:1.5 - 3:1.3 - 2.5:0.06 - 0.5:0 - 0.1:0 - 0.1.

[0011] Preferably, in step S2, the mass ratio of the compound fertilizer particles, modified lignin, and gelatin is 8 - 12:3 - 5:1.

[0012] Preferably, in step S3, the mass ratio of α-amino-4-vinylphenylacetic acid, ammonium persulfate, polyethylene glycol 2000, and the modified lignin-coated compound fertilizer is 1:0.002 - 0.003:0.0025 - 0.0035:12 - 15.

[0013] Preferably, the preparation steps of the modified lignin in step S2 are as follows: Step A1: Under a nitrogen atmosphere, add tris(2-aminoethyl)amine into a tetrahydrofuran solvent, cool down to -10 - 0 °C, and then add 10-undecenoyl chloride, and stir and react for 10 - 14 h to obtain intermediate 1; Step A2: Under a nitrogen atmosphere, add intermediate 1 and chloromethyloxirane into an N,N-dimethylformamide solvent, then add the catalyst ethyl acetate, heat up to 50 - 60 °C, and stir and react for 5 - 7 h to obtain a quaternary ammonium salt monomer containing an olefin long chain; Step A3: Add lignin into deionized water, heat up to 60 - 80 °C, add an aqueous solution containing ammonium persulfate, activate for 2 - 5 min, add a quaternary ammonium salt monomer containing an olefin long chain, rotate at a speed of 400 - 500 r / min, stir for 3 - 5 h to obtain modified lignin.

[0014] Preferably, in step A1, the mass ratio of tris(2 - aminoethyl)amine to 10 - undecylenoyl chloride is 1:4.8 - 5.2.

[0015] Preferably, in step A2, the mass ratio of intermediate 1, epichlorohydrin, and ethyl acetate is 6.5 - 7.5:1:0.055 - 0.065.

[0016] Preferably, in step A3, the mass ratio of lignin, ammonium persulfate, and the quaternary ammonium salt monomer containing an olefin long chain is 1:0.015 - 0.02:2 - 3.

[0017] Advantages of the present invention: The present invention provides a slow - release compound fertilizer and its preparation method. The present invention uses renewable resources as coating materials to replace traditional petroleum - based materials, thereby reducing the dependence of fertilizer coating materials on non - renewable resources. At the same time, the preparation of new coating materials can reduce the pollution of soil and water resources, meeting the development needs of green agriculture.

[0018] The present invention endows lignin with long - chain hydrophobic groups through chemical modification, combines the synergistic effect of α - amino - 4 - vinylphenylacetic acid and polyethylene glycol 2000 to form a dense and controllable coating structure. This structure realizes the slow - release regulation of nutrients through a hydrophobic barrier and a microporous gradient release mechanism, significantly extending the fertilizer efficiency period to the entire growth period of crops, reducing nutrient loss and volatilization, and improving the nutrient utilization rate of compound fertilizers.

[0019] Based on the innovative application of environmentally friendly materials and the combination of two technologies for synergistic regulation, through a precisely optimized process parameter system, the present invention realizes the high - efficiency slow - release, long - lasting fertilizer efficiency, and large - scale stable production of compound fertilizers. At the same time, through comparative verification, it significantly improves the nutrient utilization rate and environmental friendliness, providing an efficient and sustainable solution for green agriculture. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is the synthesis route diagram of the quaternary ammonium salt monomer containing an olefin long chain in the present invention. Detailed Embodiments

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0023] As Figure 1 shown, the present invention discloses a slow-release compound fertilizer and its preparation method. Modified lignin is used as a coating material, and long-chain hydrophobic groups are introduced through chemical modification. Then, α-amino-4-vinylphenylacetic acid is used as a functional monomer to crosslink with the hydroxyl and carboxyl groups on the surface of the modified lignin, and finally, a slow-release compound fertilizer is obtained.

[0024] Example 1 A preparation method of a slow-release compound fertilizer, comprising the following steps: Step S1: Under a nitrogen atmosphere, add 100 g of tris(2-aminoethyl)amine to 1000 mL of tetrahydrofuran solvent, place it in a circulating ice machine, cool it to -10°C, and then add 480 g of 10-undecenoyl chloride, and stir and react for 10 h to obtain Intermediate 1; Step S2: Under a nitrogen atmosphere, add 650 g of Intermediate 1 and 100 g of chloromethylethylene oxide to 1000 mL of N,N-dimethylformamide solvent, then add 5.5 g of catalyst ethyl acetate, heat it to 50°C, and stir and react for 7 h to obtain a quaternary ammonium salt monomer containing an olefin long chain; Step S3: Add 100 g of lignin to 500 mL of deionized water, heat it to 60 - 80°C, add an aqueous solution containing 1.5 g of ammonium persulfate, activate for 2 min, add 200 g of the quaternary ammonium salt monomer containing an olefin long chain, stir at a rotation speed of 500 r / min for 3 h to obtain modified lignin; Step S4: Add 100 g of clay, 200 g of urea, 150 g of monoammonium phosphate, 130 g of potassium sulfate, and 6 g of magnesium sulfate to a drum mixer in sequence, stir at a rotation speed of 10 r / min for 10 min, mix evenly, then add it to an extrusion granulator, with a pressure of 20 MPa, dry, screen, and the particle diameter is 2 - 4 mm to obtain compound fertilizer particles; Step S5: Add 800 g of compound fertilizer particles to a coating machine, heat it to 50°C, stir at a rotation speed of 70 r / min, add 300 g of modified lignin and 100 g of adhesive gelatin, and run for 10 min to obtain modified lignin-coated compound fertilizer; Step S6: Add 100 g of α-amino-4-vinylphenylacetic acid, 0.2 g of ammonium persulfate, and 0.25 g of polyethylene glycol 2000 to 150 mL of deionized water, stir for 10 min, add 1200 g of modified lignin-coated compound fertilizer, heat it to 25°C, and react for 16 h to obtain a slow-release compound fertilizer.

[0025] Example 2 A preparation method of a slow-release compound fertilizer, comprising the following steps: Step S1: Under a nitrogen atmosphere, add 100 g of tris(2-aminoethyl)amine to 1000 mL of tetrahydrofuran solvent, place it in a circulating ice machine, cool it to -5°C, and then add 500 g of 10-undecylenoyl chloride, and stir and react for 12 h to obtain Intermediate 1; Step S2: Under a nitrogen atmosphere, add 700 g of Intermediate 1 and 100 g of chloromethyl epoxyethane to 1000 mL of N,N-dimethylformamide solvent, then add 6 g of catalyst ethyl acetate, heat it to 55°C, and stir and react for 6 h to obtain a quaternary ammonium salt monomer containing an olefin long chain; Step S3: Add 100 g of lignin to 500 mL of deionized water, heat it to 70°C, add an aqueous solution containing 1.8 g of ammonium persulfate, activate for 3 min, add 250 g of the quaternary ammonium salt monomer containing an olefin long chain, rotate at 450 r / min, and stir for 4 h to obtain modified lignin; Step S4: Add 100 g of clay, 300 g of urea, 200 g of monoammonium phosphate, 200 g of potassium sulfate, 20 g of magnesium sulfate, 5 g of borax, and 5 g of zinc sulfate to a drum mixer in sequence, rotate at 15 r / min, stir for 7 min, mix evenly, then add it to an extrusion granulator, apply a pressure of 15 MPa, dry, sieve, and the particle diameter is 2 - 4 mm to obtain compound fertilizer particles; Step S5: Add 1000 g of the compound fertilizer particles to a coating machine, heat it to 60°C, rotate at 60 r / min, add 400 g of modified lignin and 100 g of adhesive gelatin, and run for 7 min to obtain modified lignin-coated compound fertilizer; Step S6: Add 100 g of α-amino-4-vinylphenylacetic acid, 0.25 g of ammonium persulfate, and 0.3 g of polyethylene glycol 2000 to 150 mL of deionized water, stir for 15 min, add 1300 g of the modified lignin-coated compound fertilizer, heat it to 30°C, and react for 15 h to obtain the slow-release compound fertilizer.

[0026] Example 3 A preparation method of a slow-release compound fertilizer, comprising the following steps: Step S1: Under a nitrogen atmosphere, add 100 g of tris(2-aminoethyl)amine to 1000 mL of tetrahydrofuran solvent, place it in a circulating ice machine, cool it to 0°C, and then add 520 g of 10-undecylenoyl chloride, and stir and react for 14 h to obtain Intermediate 1; Step S2: Under a nitrogen atmosphere, add 750 g of Intermediate 1 and 100 g of chloromethyl epoxyethane to 1000 mL of N,N-dimethylformamide solvent, then add 6.5 g of catalyst ethyl acetate, heat it to 60°C, and stir and react for 5 h to obtain a quaternary ammonium salt monomer containing an olefin long chain; Step S3: Add 100 g of lignin into 500 mL of deionized water, heat up to 60 °C, add an aqueous solution containing 2 g of ammonium persulfate, activate for 5 min, add 300 g of quaternary ammonium salt monomer containing olefin long chain, rotate at 500 r / min, and stir for 3 h to obtain modified lignin; Step S4: Add 100 g of clay, 400 g of urea, 300 g of monoammonium phosphate, 250 g of potassium sulfate, 50 g of magnesium sulfate, 10 g of borax, and 10 g of zinc sulfate into a drum mixer in sequence, rotate at 20 r / min, stir for 50 min, after mixing evenly, add it into an extrusion granulator, with a pressure of 10 MPa, dry, sieve, and the particle diameter is 2 - 4 mm to obtain compound fertilizer granules; Step S5: Add 1200 g of compound fertilizer granules into a coating machine, heat up to 70 °C, rotate at 50 r / min, add 500 g of modified lignin and 100 g of adhesive gelatin, run for 5 min to obtain modified lignin coated compound fertilizer; Step S6: Add 100 g of α - amino - 4 - vinylphenylacetic acid, 0.3 g of ammonium persulfate, and 0.35 g of polyethylene glycol 2000 into 150 mL of deionized water, stir for 20 min, add 1500 g of modified lignin coated compound fertilizer, heat up to 35 °C, and react for 14 h to obtain slow - release compound fertilizer.

[0027] Comparative Example 1: Compared with Example 1, in this comparative example, only "modified lignin" is replaced by "lignin", and the rest of the steps and parameters are the same. This comparative example will not be repeated here, and finally slow - release compound fertilizer is obtained.

[0028] Comparative Example 2: Compared with Example 1, in this comparative example, only "10 - undecenoyl chloride" is replaced by "acryloyl chloride", and the rest of the steps and parameters are the same. This comparative example will not be repeated here, and finally slow - release compound fertilizer is obtained.

[0029] Comparative Example 3: Compared with Example 1, in this comparative example, only "modified lignin" is replaced by "polyethylene resin", and the rest of the steps and parameters are the same. This comparative example will not be repeated here, and finally slow - release compound fertilizer is obtained.

[0030] Comparative Example 4: Compared with Example 1, in this comparative example, the related reaction in Step 6 is not carried out, and the rest of the steps and parameters are the same. This comparative example will not be repeated here, and finally modified lignin coated compound fertilizer is obtained.

[0031] Comparative Example 5: This comparative example is the same as Example 1 except that the mass ratio of compound fertilizer particles, modified lignin, and gelatin in step S5 is adjusted to 15:1:1. The rest of the steps and parameters are the same, and this comparative example will not be repeated here. Finally, modified lignin-coated compound fertilizer is obtained.

[0032] Performance test: Nutrient release rate test: Dissolution rate test in water: 1. Weigh 1 g of the fertilizers of Examples 1-3 and Comparative Examples 1-5 respectively, put them into a 25 mL medical syringe, add 20 mL of ammonia-free high-purity water, seal the syringe with a rubber stopper, collect the filtrate on the first day and measure the total nitrogen content in it, and collect the filtrates from the 2nd to 7th day and the 2nd to 30th day, and measure the total nitrogen content in them. Repeat three times.

[0033] 2. Determination of urea nitrogen content: Catalyzed by CuSO4 and digested by H2SO4; Determination of total nitrogen: Kjeldahl method; The reference Japanese standard is named "Slow-release fertilizers - Test method for dissolution rate", and the number is JIS K 6324:2023.

[0034] Initial dissolution rate: It refers to the amount of nutrients dissolved from the slow-release fertilizer after being soaked in water at 30°C for 24 h; The Japanese standard stipulates that the amount of nutrients dissolved from the slow-release and controlled-release fertilizer within 24 h does not exceed 15%; The calculation formula is as follows:

[0035] Differential dissolution rate: It refers to the daily average amount of nutrients dissolved from the slow-release fertilizer after being cultured at 30°C for 1 week; The Japanese standard stipulates that the differential dissolution rate of nutrients from the slow-release fertilizer after being cultured at 30°C for one week is between 0.25% and 2.5%. The calculation formula is as follows:

[0036] Nutrient cumulative release rate:

[0037] Table 1 Nutrient release rate test data of each example and comparative example

[0038] Mechanical strength test: Compressive strength test: 1. Randomly select 50 compound fertilizer particles from the fertilizers of Examples 1-3 and Comparative Examples 1-5, use the universal material testing machine Instron3365 to apply pressure at a rate of 5 mm / min, and record the maximum pressure (N) when the particles are crushed.

[0039] 2. Calculate the average compressive strength.

[0040] Abrasion resistance test: ASTM D4058-96 "Test Method for Abrasion Resistance of Fertilizer Particles" Randomly select 50 compound fertilizer particles from the fertilizers of Examples 1-3 and Comparative Examples 1-5 respectively. Put the particles into a roller abrasion tester and run it at 30 r / min for 1 hour, then weigh and calculate the mass loss rate.

[0041] Table 2 Mechanical strength test data of each example and comparative example

[0042] Crop absorption efficiency test: 1. Pot experiment: The basic physical and chemical properties of the soil are as follows: maximum water holding capacity 19%, organic matter 0.94%, total nitrogen 0.061%, NH4 + -N 7.65 mg / kg, NO3 - -N 33.11 mg / kg, available phosphorus 3.04 mg / kg, available potassium 106.23 mg / kg, pH 8.09, 7.31 kg of fresh soil per pot, the crop is corn. Take 1000 g of the fertilizers of Examples 1-3 and Comparative Examples 1-5 respectively, apply fertilizer during sowing, and measure the changes in plant height, leaf area and biomass of corn during the two-month growth period; Test for nitrate nitrogen leaching loss in soil: Water sample determination: On the 30th day, collect water samples from the pots, filter them with a 0.45 μm microporous filter membrane, add a drop of saturated mercury oxide to the filtrate, and determine nitrated nitrogen (NO3 - -N) by ultraviolet spectrophotometry; Soil determination: Take the soil on the surface of the pot from 0 to 20 cm, air-dry and grind it, pass through a 1 mm sieve, weigh 10 g of soil, add 40 mL of 1 mol / L KCl for extraction, shake it with a ZP-200 shaker for 30 min, filter, and determine nitrated nitrogen (NO3 - -N) by ultraviolet spectrophotometry.

[0043] Nitrated nitrogen (NO3 - -N) leakage loss formula:

[0044] Table 3 Test data of each example and comparative example

[0045] Data analysis: As can be seen from Table 1, the slow-release compound fertilizer prepared by the present invention has a lower initial dissolution rate, a more stable differential dissolution rate and a nutrient cumulative release rate more suitable for crop requirements; In Comparative Example 1, only ordinary lignin was used, resulting in a significant increase in the initial dissolution rate and out-of-control nutrient release. The reason is that the unmodified lignin did not introduce long-chain hydrophobic groups, and the water penetration was relatively fast, leading to rapid nutrient dissolution. Moreover, the unmodified lignin has a fast degradation rate in the soil and cannot form a sustained-release barrier; In Comparative Example 2, since "10-undecenoyl chloride" was replaced by "acryloyl chloride", the hydrophobicity of the coating film was insufficient, and both the initial dissolution rate and the cumulative release rate were relatively high. The reason is that the short-chain acryloyl chloride cannot form a long-carbon-chain hydrophobic layer, and the water-blocking ability of the coating film is weak. In rainy weather, it is easy to cause accelerated nutrient release. At the same time, the short-chain modified lignin has a fast degradation rate, resulting in a shortened nutrient release period of the compound fertilizer and unable to meet the long-term fertilizer efficiency requirements; In Comparative Example 3, due to the use of polyethylene resin, although the initial dissolution rate was low, the non-degradability led to blocked nutrient release. The reason is that the molecular structure of polyethylene is composed of non-polar carbon-hydrogen chains with extremely low surface energy, which makes it difficult for water molecules to penetrate into the coating film through diffusion, resulting in the inability of soil moisture to effectively contact the internal nutrients. Moreover, the nutrient demand of the previous crops is high, and the nutrient release rate of the fertilizer in Comparative Example 3 cannot meet the demand. At the same time, the chemical properties of polyethylene are extremely stable and it is difficult to be decomposed by microorganisms or degraded by sunlight oxidation in the natural environment. It hinders nutrient release, and the residual polyethylene fragments will gradually accumulate, forming "white pollution", damaging the soil structure and reducing air permeability and water retention; In Comparative Example 4, due to the absence of the final reaction in step S6, the porosity of the coating film was relatively high, and water quickly penetrated to the core fertilizer particles, resulting in out-of-control nutrient release in the early stage. Both the initial dissolution rate and the cumulative release rate far exceeded the standard. The reason is that in Example 1, α-amino-4-vinylphenylacetic acid reacted with the active groups (such as hydroxyl groups and carboxyl groups) on the surface of the modified lignin-coated compound fertilizer to form a dense cross-linked network, enhancing the hydrophobicity and mechanical strength of the coating film. At the same time, polyethylene glycol 2000, as a hydrophilic component, may form a microporous structure on the outer layer, and the gradient release of nutrients is realized by adjusting the water penetration rate; In Comparative Example 5, due to the adjustment of the coating material ratio, the coating film was too thick and the nutrient release was severely delayed. The reason is that the coating material ratio in Comparative Example 5 was unbalanced, resulting in enhanced hydrophobicity and mechanical strength of the coating film, and water could not penetrate into the interior, resulting in slow nutrient release and the crops could not absorb it in time; As can be seen from Table 2, the sustained-release compound fertilizer prepared by the present invention has higher compressive strength and lower wear resistance mass loss rate; In Comparative Example 1, since the lignin was not chemically modified, the coating film structure was loose, the mechanical strength was significantly reduced, and the nutrient release rate was too fast; In Comparative Example 2, since long-chain acyl chloride (10-undecenoyl chloride) was not used and acryloyl chloride was used instead, the modified lignin had insufficient hydrophobicity and the porosity of the coating film increased, resulting in an increase in the initial dissolution rate to 12.69% and a shortening of the nutrient release period; In Comparative Example 3, since degradable materials were not used, although the mechanical strength was high, the coating film was non-degradable, resulting in hindered nutrient release and a high risk of long-term residual pollution; In Comparative Example 4, since the final reaction in Step S6 was not completed, the nutrient release got completely out of control and the crop absorption efficiency decreased significantly; In Comparative Example 5, since the mass ratio of the coating materials was not controlled, the coating film was too thin and unevenly distributed, resulting in a decrease in compressive strength and delayed nutrient release, restricting crop growth; As can be seen from Table 3, the slow-release compound fertilizer prepared by the present invention has a higher crop absorption efficiency; In Comparative Example 1, since lignin was not chemically modified, the coating film structure was loose, resulting in too fast nutrient release in the early stage, insufficient nutrition in the middle stage of the crop, and a significant decrease in growth indicators; In Comparative Example 2, since long-chain acyl chloride was not used and acryloyl chloride was used instead, the modified lignin had insufficient hydrophobicity and the nutrient release rate was unstable, resulting in a lower crop leaf area and biomass than in Example 1; In Comparative Example 3, since degradable materials were not used, the non-degradable coating film led to hindered nutrient release, and the crop biomass was only 76% of that in Example 1, and there was a high risk of long-term residual pollution; In Comparative Example 4, since the final reaction in Step S6 was not completed, the nutrient release got completely out of control, and the plant height and biomass of the crop decreased significantly due to excessive or unbalanced nutrition; In Comparative Example 5, since the mass ratio of the coating materials was not controlled, the too thick coating film led to delayed nutrient release and insufficient nutrition in the early stage of the crop, and both the plant height and biomass were significantly lower than those in Example 1.

[0046] As can be seen from Tables 1-3, the slow-release compound fertilizer prepared by the present invention exhibits excellent nutrient control ability. Through hydrophobicity and controllable degradability, it realizes the release of nutrients on demand, avoids excessive release in the early stage or insufficiency in the later stage. At the same time, the coating film has good mechanical strength and appropriate wear resistance, is suitable for large-scale production and field application, and the present invention realizes the balanced nutrient supply throughout the whole growth period of the crop by precisely regulating the nutrient release.

[0047] Those of ordinary skill in the art should understand that the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the idea of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

[0048] The present invention aims to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A slow-release compound fertilizer, characterized in that, It comprises the following raw materials in parts by weight: 100 parts by weight of α-amino-4-vinylphenylacetic acid, 0.25 - 0.35 parts by weight of polyethylene glycol 2000, and 1200 - 1500 parts by weight of modified lignin-coated compound fertilizer.

2. A preparation method of a slow-release compound fertilizer, characterized in that, The preparation method is as follows: Step S1: Add clay, urea, monoammonium phosphate, potassium sulfate, magnesium sulfate, borax, and zinc sulfate to a rotary drum mixer in sequence, with a rotation speed of 10 - 20 r / min, stir for 5 - 10 min. After mixing evenly, add it to an extrusion granulator, with a pressure of 10 - 20 MPa, dry, sieve, and the particle diameter is 2 - 4 mm to obtain compound fertilizer particles; Step S2: Add the compound fertilizer particles to a coating machine, heat up to 50 - 70 °C, with a rotation speed of 50 - 70 r / min, add modified lignin and the adhesive gelatin, and run for 5 - 10 min to obtain modified lignin-coated compound fertilizer; Step S3: Add α-amino-4-vinylphenylacetic acid, the catalyst ammonium persulfate, and polyethylene glycol 2000 to deionized water, stir for 10 - 20 min, add the modified lignin-coated compound fertilizer, heat up to 25 - 35 °C, and react for 14 - 16 h to obtain a slow-release compound fertilizer.

3. The preparation method of the slow-release compound fertilizer according to claim 2, characterized in that, In Step S1, the mass ratio of the clay, urea, monoammonium phosphate, potassium sulfate, magnesium sulfate, borax, and zinc sulfate is 1:2 - 4:1.5 - 3:1.3 - 2.5:0.06 - 0.5:0 - 0.1:0 - 0.

1.

4. The preparation method of the slow-release compound fertilizer according to claim 2, characterized in that, In Step S2, the mass ratio of the compound fertilizer particles, modified lignin, and gelatin is 8 - 12:3 - 5:

1.

5. The preparation method of the slow-release compound fertilizer according to claim 2, wherein, In Step S3, the mass ratio of α-amino-4-vinylphenylacetic acid, ammonium persulfate, polyethylene glycol 2000, and modified lignin-coated compound fertilizer is 1:0.002 - 0.003:0.0025 - 0.0035:12 - 15.

6. The preparation method of the slow-release compound fertilizer according to claim 2, characterized in that, The preparation steps of the modified lignin in Step S2 are as follows: Step A1: Under a nitrogen atmosphere, add tris(2-aminoethyl)amine to a tetrahydrofuran solvent, cool down to -10 - 0 °C, then add 10-undecenoyl chloride, and stir and react for 10 - 14 h to obtain Intermediate 1; Step A2: Under a nitrogen atmosphere, add Intermediate 1 and epichlorohydrin to an N,N-dimethylformamide solvent, then add the catalyst ethyl acetate, heat up to 50 - 60 °C, and stir and react for 5 - 7 h to obtain a quaternary ammonium salt monomer containing an olefin long chain; Step A3: Add lignin to deionized water, heat up to 60 - 80 °C, add an aqueous solution containing ammonium persulfate, activate for 2 - 5 min, add the quaternary ammonium salt monomer containing an olefin long chain, with a rotation speed of 400 - 500 r / min, and stir for 3 - 5 h to obtain modified lignin.

7. The preparation method of the slow-release compound fertilizer according to claim 6, characterized in that, In Step A1, the mass ratio of tris(2-aminoethyl)amine and 10-undecenoyl chloride is 1:4.8 - 5.

2.

8. The preparation method of the slow-release compound fertilizer according to claim 6, characterized in that, In Step A2, the mass ratio of Intermediate 1, epichlorohydrin, and ethyl acetate is 6.5 - 7.5:1:0.055 - 0.

065.

9. The preparation method of the slow-release compound fertilizer according to claim 6, characterized in that, In Step A3, the mass ratio of lignin, ammonium persulfate, and the quaternary ammonium salt monomer containing an olefin long chain is 1:0.015 - 0.02:2 - 3.

Images