Controlled release fertilizer for promoting crop growth and preparation method thereof

Abstract

The invention belongs to the technical field of sustained and controlled release fertilizers, and particularly relates to a sustained and controlled release fertilizer for promoting crop growth and a preparation method thereof. The preparation method comprises the following steps: firstly, mixing urea with a formaldehyde solution to obtain a mixed solution of urea and formaldehyde, then adding the mixed solution into other uniformly mixed components, regulating and controlling the pH value of the slurry by adding magnesium oxide, and controlling the methylation reaction to be slowly carried out, so that the adhesion among the prepared chemical fertilizer particles is effectively reduced; under the action of a composite catalyst, polyacrylamide and polyvinyl chloride are subjected to an ammonolysis reaction, aniline is further added, and imino groups and benzene rings are introduced to an obtained polymer chain, so that the prepared polymer emulsion coating material has good mechanical properties while having water absorption and retention capabilities.

Description

Technical Field

[0001] The present invention belongs to the technical field of controlled-release fertilizers, and in particular relates to a controlled-release fertilizer for promoting crop growth and a preparation method thereof. Background Art

[0002] Similar to humans and animals, plants also need to absorb the nutrients required for their growth and development from the external environment to maintain their normal life activities. Plants can absorb three elements, carbon, hydrogen, and oxygen, from water and the atmosphere through their roots and leaves, while other mineral nutrients usually need to be obtained from the soil. Therefore, as the substrate for plant growth - soil, it must contain sufficient mineral nutrients to maintain the healthy growth of plants. Plant growth and development require nutrients, but the nutrients contained in the soil itself for plant growth are limited. Therefore, in order to improve the yield and quality of food crops, it is necessary to artificially add exogenous nutrients to the soil. A large number of statistical studies have confirmed that 30 - 50% of the contribution to increasing crop yields comes from chemical fertilizers. Although the use of chemical fertilizers can increase crop yields to a certain extent, as farmers' dependence on chemical fertilizers increases, in order to continuously increase food production, the application rate of chemical fertilizers has been increasing year by year, and the resulting ecological problems have become increasingly prominent. Because, after so much chemical fertilizer is applied to the soil, if it cannot be absorbed and utilized by plants in a timely manner, the remaining fertilizer will cause serious pollution to water bodies, soil, and even the atmosphere. After traditional fertilizers are applied to the soil, only a small part can be absorbed and utilized by plants. Due to the extremely low fertilizer utilization rate, the vast majority of nutrients in the fertilizer cannot be effectively absorbed by plants, which not only causes serious waste of resources but also brings serious environmental problems. In order to obtain the highest yield on a limited cultivated land area, it is necessary to improve the utilization rate of chemical fertilizers. A large number of studies have found that the application of organic fertilizers in combination with inorganic fertilizers during the application of inorganic fertilizers can significantly improve the utilization rate of inorganic fertilizers. This is because after adding organic fertilizers to the soil, the carbon source in the organic fertilizers can be fully utilized and transformed by microorganisms to form new humus substances, thereby improving the soil structure and the fertility quality of the soil, and further promoting the absorption and utilization of inorganic fertilizers by plants.

[0003] A Chinese patent with the application number 201510417523.0 discloses a water-retaining polymer slow-release nitrogen-potassium fertilizer and its preparation method. The steps are as follows: (1) Add potassium hydroxide solution and acrylic acid to a reaction vessel, stir in an ice bath until evenly mixed; then add urea and stir until the urea is completely dissolved; add the initiator potassium persulfate and stir until the potassium persulfate is completely dissolved; then add the cross-linking agent N,N'-methylenebisacrylamide and stir until the cross-linking agent is completely dissolved, and continue to stir for 30 minutes until the solution is evenly mixed; (2) Seal the evenly mixed solution, react at 25-75°C for 2-6.5 hours, granulate, and dry to obtain the water-retaining polymer slow-release nitrogen-potassium fertilizer. Its process is simple and easy to operate. The prepared water-retaining polymer slow-release nitrogen-potassium fertilizer is a chemically synthesized water-retaining and slow-release fertilizer, which can make up for the defects that the nutrient release of the film-coated water-retaining and slow-release fertilizer is limited by the film-coated material and the process is complex, etc. Summary of the Invention

[0004] To solve the above problems, the present invention provides a slow-release and controlled-release fertilizer for promoting crop growth and its preparation method. Under the action of a composite catalyst, polyacrylamide and polyvinyl chloride undergo ammonolysis reaction, and further aniline is added thereto to introduce imino and benzene rings onto the obtained polymer chain, so that the prepared polymer emulsion coating material has the ability of water absorption and water retention while also having good mechanical properties.

[0005] The technical solution of the present invention to solve the above problems is as follows:

[0006] A slow-release and controlled-release fertilizer for promoting crop growth, the fertilizer is externally coated with a polymer emulsion coating, and the fertilizer is composed of the following components in parts by weight: 20-30 parts of organic fertilizer, 20-25 parts of urea, 8-12 parts of superphosphate, 5-10 parts of potassium chloride, 3-6 parts of KOM, 0.2-0.4 parts of ammonium molybdate, 0.5-1 part of boric acid; preferably 28 parts of organic fertilizer, 22 parts of urea, 10 parts of superphosphate, 8 parts of potassium chloride, 5 parts of KOM, 0.3 parts of ammonium molybdate, 0.6 parts of boric acid.

[0007] The preparation process of the polymer emulsion coating material is as follows:

[0008] S1. Add polyacrylamide with ethylene glycol as a solvent, heat and stir to dissolve to obtain a mixed solution for standby; add polyvinyl chloride and a composite catalyst to a reactor and heat to 100-110°C at a heating rate of 5-8°C / min. Among them, the composite catalyst is Al 2 O 3 and CuO are mixed in a weight ratio of 1:2-4, preferably Al 2 O 3 and CuO are mixed in a weight ratio of 1:3; during the heating process, the mixed solution is dropped into it. After the dropping is completed, the temperature is raised to 120-130°C, and after reacting for 6-8 hours, intermediate I is obtained;

[0009] S2. Add the intermediate I obtained in step S1 using tetrahydrofuran as a solvent, heat it to 35 - 45 °C, add copper powder and nickel powder thereto and stir evenly, wherein the weight ratio of copper powder to nickel powder is 1:1.5; continue to raise the temperature to 50 - 55 °C, and add aniline thereto, wherein the addition method of aniline is dropwise addition and it is completed within 10 min; after the operation is completed, raise the temperature to 65 - 70 °C, react for 4 - 6 h, lower the temperature to 30 - 35 °C, add a protonic acid thereto, stir and react for 2 - 4 h, and then perform reduced pressure distillation to obtain the polymer emulsion coating material.

[0010] Further, the organic fertilizer is one or a mixture of bone meal, raw skin powder, rapeseed powder, soybean powder, and fish meal.

[0011] Further, in step S2, the protonic acid is any one of dilute sulfuric acid, dilute hydrochloric acid, and acetic acid.

[0012] A preparation method of a slow - release and controlled - release fertilizer for promoting crop growth is as follows:

[0013] A1. Accurately weigh each component, add urea to the formaldehyde solution to prepare a mixed solution of urea and formaldehyde, mix the other components except urea evenly, add the mixed solution of urea and formaldehyde thereto, heat it in a water bath to 30 - 35 °C, preferably 30 °C, and continuously stir, while adding magnesium oxide to adjust the pH to 7.2, place it at a constant temperature for 40 - 60 min, preferably 50 min, add dilute sulfuric acid dropwise to adjust the pH to 6.0, and let it stand at 40 °C, add magnesium oxide to adjust the pH to 7.2, react at 40 °C for 4 - 6 min, preferably 5 min, granulate and dry to obtain fertilizer granules;

[0014] A2. Pour the fertilizer granules obtained in step A1 into a coating machine, heat the fertilizer to 80 - 90 °C, preferably 85 °C, fix the inclination angle of the coating machine, preferably 45 °, adjust the rotation speed, preferably 50 r / min, make the fertilizer granules rotate freely in the coating machine, turn on the air compressor, put the prepared polymer emulsion coating material into a spray gun, and use the high - pressure atomization method to spray the prepared coating emulsion into the coating machine. During the coating process, heat at intervals, the heating temperature is 55 °C, the spraying time is 15 min, and after cooling, obtain the coated fertilizer.

[0015] The present invention has the following beneficial effects:

[0016] First, urea is mixed with a formaldehyde solution to obtain a mixed solution of urea and formaldehyde, which is then added to other uniformly mixed components. By adding magnesium oxide, the pH of the slurry is regulated to control the slow progress of the methylation reaction, effectively reducing the adhesion between the prepared fertilizer particles. Moreover, through this method, inorganic fertilizers can be effectively filled in the prepared fertilizer granules, effectively restricting the contact between organic fertilizers and inorganic fertilizers and microorganisms in the soil, inhibiting the degradation of microorganisms. As urea is gradually decomposed by microorganisms, the contact area between the organic fertilizer and the soil is increased, so that the prepared fertilizer has certain slow-release properties.

[0017] Furthermore, in the fertilizer prepared in the present invention, a polymer emulsion coating is coated on the outside. Under the action of a composite catalyst, acrylamide and polyvinyl chloride undergo an ammonolysis reaction, and aniline is added thereto to introduce imino groups and benzene rings onto its polymer chain, so that the prepared polymer emulsion coating has good mechanical properties while having the ability to absorb and retain water, ensuring the stability of the coating after water absorption and effectively preventing the occurrence of collapse phenomena. Description of the Drawings

[0018] Figure 1 It is a graph showing the slow-release performance of the prepared fertilizer. Detailed Embodiments

[0019] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present application.

[0020] The polyacrylamide (average Mn 40000) and polyvinyl chloride (low viscosity, Mw ~ 77000) used in the present invention are both purchased from the official website of Aladdin Reagents, and the KOM used is purchased from Anhui Shennong Agricultural Technology Development Co., Ltd.

[0021] Example 1

[0022] A slow-release and controlled-release fertilizer for promoting crop growth, with a polymer emulsion coating on the outside of the fertilizer. The fertilizer is composed of the following components in parts by weight: 20 parts of organic fertilizer, 20 parts of urea, 8 parts of superphosphate, 5 parts of potassium chloride, 3 parts of KOM, 0.2 part of ammonium molybdate, and 0.5 part of boric acid.

[0023] The preparation process of the polymer emulsion coating material is as follows:

[0024] S1. Add 50 parts by weight of polyacrylamide to 65 parts by weight of ethylene glycol as a solvent, heat to 45 °C, stir to dissolve, and set aside the obtained mixture; add 55 parts by weight of polyvinyl chloride and 3 parts by weight of a composite catalyst to a reactor and heat to 100 °C at a heating rate of 5 °C / min. Among them, the composite catalyst is composed of Al 2 O 3 and CuO mixed in a weight ratio of 1:2. During the heating process, dropwise add the mixture. After the addition is completed, raise the temperature to 120 °C and react for 6 h to obtain intermediate I;

[0025] S2. Add intermediate I obtained in step S1 to 60 parts by weight of tetrahydrofuran as a solvent, heat to 35 °C, add 1 part by weight of copper powder and 1.5 parts by weight of nickel powder thereto and stir evenly. Continue to raise the temperature to 50 °C, and add 55 parts by weight of aniline thereto, and complete the dropwise addition within 10 min. After the operation is completed, raise the temperature to 65 °C and react for 4 h. Lower the temperature to 30 °C, add 6 parts by weight of 1 mol / L dilute hydrochloric acid thereto, stir and react for 2 h, and then perform vacuum distillation to obtain the polymer emulsion coating material.

[0026] Among them, the organic fertilizer is composed of bone meal, rapeseed powder, soybean powder, and fish meal mixed in a weight ratio of 1:2:5:2.

[0027] A preparation method of a slow-release and controlled-release fertilizer for promoting crop growth is as follows:

[0028] A1. Accurately weigh each component according to the above parts by weight. Add 20 parts by weight of urea to 65 parts by weight of formaldehyde solution to prepare a mixed solution of urea and formaldehyde. Mix the other components except urea evenly, add the mixed solution of urea and formaldehyde thereto, heat in a water bath to 30 °C and continuously stir, and at the same time add magnesium oxide to adjust the pH to 7.2. Place it at a constant temperature for 40 min, add 1 mol / L dilute sulfuric acid dropwise to adjust the pH to 6.0, and let it stand at 40 °C. Add magnesium oxide to adjust the pH to 7.2 and react at 40 °C for 4 min, granulate and dry to obtain fertilizer particles;

[0029] A2. Pour the fertilizer particles obtained in step A1 into a coating machine, heat the fertilizer to 80 °C, fix the inclination angle of the coating machine at 40 °, adjust the rotation speed to 35 r / min, let the fertilizer particles rotate freely in the coating machine, turn on the air compressor, put the prepared polymer emulsion coating material into the spray gun, and use the high-pressure atomization method to spray the prepared coating emulsion into the coating machine. During the coating process, heat at intervals, the heating temperature is 50 °C, the spraying time is 10 min, and cool to obtain the coated fertilizer.

[0030] Example 2

[0031] Compared with Example 1, the fertilizer composition fractions are different, the preparation conditions are different during the preparation process of the polymer emulsion coating material, and the preparation conditions are different during the preparation process of the sustained-release and controlled-release fertilizer. The remaining steps refer to Example 1.

[0032] A sustained-release and controlled-release fertilizer for promoting crop growth, with a polymer emulsion coating on the outside of the fertilizer. The fertilizer is composed of the following components in parts by weight: 30 parts of organic fertilizer, 25 parts of urea, 12 parts of superphosphate, 10 parts of potassium chloride, 6 parts of KOM, 0.4 part of ammonium molybdate, and 1 part of boric acid.

[0033] During the preparation process of the polymer emulsion coating material:

[0034] In step S1, the composite catalyst is a mixture of Al 2 O 3 and CuO mixed in a weight ratio of 1:4. After adding the composite catalyst, the heating rate is 8 °C / min, and it is heated to 110 °C; during the dropping process of the mixed solution, after the dropping is completed, the temperature is raised to 130 °C and reacted for 8 h;

[0035] In step S2, it is heated to 45 °C before adding copper powder and nickel powder. After adding, the temperature is continuously raised to 55 °C. After the dropping of aniline is completed, the temperature is raised to 70 °C and reacted for 6 h. After the reaction is completed, the temperature is lowered to 35 °C, and dilute hydrochloric acid is added thereto and stirred for 4 h.

[0036] During the preparation process of the sustained-release and controlled-release fertilizer:

[0037] In step A1, it is heated in a water bath to 35 °C, magnesium oxide is added to adjust the pH to 7.2, and it is placed at a constant temperature for 60 min; dilute sulfuric acid is added dropwise thereto to adjust the pH to 6.0, and it is allowed to stand at 40 °C, magnesium oxide is added to adjust the pH to 7.2, and it is reacted at 40 °C for 6 min;

[0038] In step A2, the fertilizer is heated to 90 °C, the inclination angle of the coating machine is fixed at 45 °C, the rotation speed is adjusted to 55 r / min, the intermittent heating temperature during coating is 60 °C, and the spraying time is 20 min.

[0039] Example 3

[0040] Compared with Example 1, the fertilizer composition fractions are different, the preparation conditions are different during the preparation process of the polymer emulsion coating material, and the preparation conditions are different during the preparation process of the sustained-release and controlled-release fertilizer. The remaining steps refer to Example 1.

[0041] A sustained-release and controlled-release fertilizer for promoting crop growth, with a polymer emulsion coating on the outside of the fertilizer. The fertilizer is composed of the following components in parts by weight: 28 parts of organic fertilizer, 22 parts of urea, 10 parts of superphosphate, 8 parts of potassium chloride, 5 parts of KOM, 0.3 part of ammonium molybdate, and 0.6 part of boric acid.

[0042] During the preparation of the polymer emulsion coating material:

[0043] In step S1, the composite catalyst is composed of Al 2 O 3 and CuO mixed in a weight ratio of 1:3. After adding the composite catalyst, the heating rate is 6 °C / min, and it is heated to 105 °C; during the dropping process of the mixed solution, after the dropping is completed, the temperature is raised to 125 °C and the reaction lasts for 8 h;

[0044] In step S2, it is heated to 40 °C before adding copper powder and nickel powder, and the temperature is continuously raised to 50 °C after adding. After the dropping of aniline is completed, the temperature is raised to 70 °C and the reaction lasts for 6 h. After the reaction ends, the temperature is lowered to 30 °C, and dilute hydrochloric acid is added and stirred for 4 h.

[0045] During the preparation of the sustained-release fertilizer:

[0046] In step A1, it is heated in a water bath to 30 °C, magnesium oxide is added to adjust the pH to 7.2, and it is placed at a constant temperature for 50 min; dilute sulfuric acid is dropped into it to adjust the pH to 6.0, and it is left standing at 40 °C. Magnesium oxide is added to adjust the pH to 7.2 and the reaction is carried out at 40 °C for 5 min;

[0047] In step A2, the fertilizer is heated to 85 °C, the inclination angle of the coating machine is fixed at 45 °C, the rotation speed is adjusted to 50 r / min, the intermittent heating temperature during coating is 55 °C, and the spraying time is 15 min.

[0048] Comparative Example 1

[0049] Compared with Example 3, polyvinyl chloride is directly used as the raw material of the polymer emulsion coating material for preparation, and the rest of the preparation process refers to Example 3.

[0050] Comparative Example 2

[0051] Compared with Example 3, polyacrylamide is directly used as the raw material of the polymer emulsion coating material for preparation, and the rest of the preparation process refers to Example 3.

[0052] Comparative Example 3

[0053] Compared with Example 3, the prepared intermediate I is used as the raw material of the polymer emulsion coating material for preparation, and the rest of the preparation process refers to Example 3.

[0054] Comparative Example 4

[0055] Compared with Example 3, polyvinyl chloride, polyacrylamide and aniline are directly mixed as the raw material of the polymer emulsion coating material for preparation, and the rest of the preparation process refers to Example 3.

[0056] The preparation process of the polymer emulsion coating material is as follows: 50 parts by weight of polyacrylamide is added with 65 parts by weight of ethylene glycol as a solvent, heated to 45 °C, stirred and dissolved to obtain a mixed solution, and 55 parts by weight of polyvinyl chloride is added thereto. It is heated to 120 °C at a heating rate of 6 °C / min, reacted for 8 h, the temperature is lowered to 50 °C, 55 parts by weight of aniline is added dropwise thereto, and after the addition is completed, the temperature is raised to 70 °C and reacted for 6 h to obtain the polymer emulsion coating material.

[0057] Related tests

[0058] Test Example 1

[0059] The sustained-release performance of the sustained-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-4 was preliminarily evaluated by a simple water-soluble method. Take 100 sustained-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-4, put them into a small gauze bag, seal it, then put the small bag into a 250 mL wide-mouth bottle, add 200 mL of distilled water, cover and seal, and let it stand. Observe and record the number of easily soluble particles at regular intervals, and take the average value of three parallel samples for each sample. The test results are as Figure 1 shown.

[0060] It can be seen from Figure 1 the results that the sustained-release performances of the coating products prepared with different polymer emulsion coating materials are different. It can be seen from the figure that the sustained-release performances of the coating products prepared in Examples 1-3 are better than those of the coating products prepared in Comparative Examples 1-4, and among them, the performance of Example 3 is the best. By comparing the test data of Example 3 and Comparative Example 4, it is found that when polyvinyl chloride, polyacrylamide and aniline are directly mixed as the polymer emulsion coating material, the sustained-release performance of the prepared coating product is relatively poor. This is because when the three are directly mixed, it may cause uneven distribution, thus affecting the performance of the final coating product. From the test results of Example 3 and Comparative Examples 1-2, it is found that the performance of the coating products obtained by using polyvinyl chloride or polyacrylamide alone is relatively poor, indicating that during the preparation process of the polymer emulsion coating material, the performance of the product obtained after a series of reactions of polyvinyl chloride, polyacrylamide and aniline has been effectively improved. This is because under the action of a catalyst, polyacrylamide and polyvinyl chloride undergo an ammonolysis reaction under the action of a catalyst, causing polyacrylamide and polyvinyl chloride to crosslink with each other, resulting in a significant increase in the sustained-release performance. At the same time, aniline is introduced into the side chain, further ensuring the mechanical properties of the coating.

[0061] Test Example 2

[0062] Accurately weigh a total of 5 portions of the sustained-release fertilizer prepared in Example 3, separately pack them into non-woven fabric bags, bury them about 5 cm below the surface of the air-dried soil collected in the same batch, and maintain the soil humidity at 60%. Place them at room temperature. Take out one non-woven fabric bag respectively after 1, 7, 14, 21, and 28 days, air-dry it, take out the fertilizer granules in the bag, determine the potassium content by ICP, and measure the nitrogen and phosphorus contents with a UV-visible spectrophotometer.

[0063] At the same time, set up a control group, adopt the same test method, calculate the release rates (%) of nitrogen, phosphorus, and potassium in the fertilizers of Example 3 and the control group. The results are shown in Table 1. Among them, the fertilizer in the control group is composed of the following components by weight: 28 parts of organic fertilizer, 22 parts of urea, 10 parts of superphosphate, 8 parts of potassium chloride, 5 parts of KOM, 0.3 parts of ammonium molybdate, and 0.6 parts of boric acid, which are directly mixed.

[0064] Table 1

[0065]

[0066] It can be seen from the test data analysis in Table 1 that the release rate of the sustained-release fertilizer prepared in Example 3 decreased significantly. At the 28th day, the release rate of nitrogen was 66.4%, the release rate of phosphorus was 27.2%, and the release rate of potassium was 42.6%. While for the sustained-release fertilizer prepared in the control group at the 28th day, the release rate of nitrogen was 99.2%, the release rate of phosphorus was 36.8%, and the release rate of potassium was 62.1%. Therefore, the sustained-release fertilizer prepared in Example 3 has good slow-release properties, can improve the utilization efficiency of plant nutrients, and reduce the loss of nutrients.

[0067] Test Example 3

[0068] In order to test the use effect of the fertilizer, sow wheat in the experimental field, and apply the fertilizers prepared in Example 3 and the control group once without topdressing. Record various agronomic matters during the growth process and conduct statistics. The statistical results are shown in Table 2, where the control group refers to the components in Test Example 2 above.

[0069] Table 2

[0070]

[0071] It can be seen from the statistical results in Table 2 that the fertilizer prepared in the control group can quickly provide the nutrient elements required by the crops in the early stage of crop growth, but there is an obvious lack of fertilizer in the middle and late stages of crop growth. The crops show slow growth and small and shriveled grains due to the inability to obtain nutrients in time. While the slow-release fertilizer prepared in Example 3 can provide nutrient elements in a timely manner during each growth cycle of the crops, enabling the crops to grow healthily and well, with a large number of plump grains.

[0072] The long-term over-application of chemical fertilizers will have an impact on the ecological environment of the soil. In order to obtain the highest yield on a limited cultivated land area, it is necessary to improve the utilization rate of chemical fertilizers. In the present invention, an organic / inorganic combined fertilization system is prepared by combining inorganic fertilizers and organic fertilizers. During the application of inorganic fertilizers, organic fertilizers are added. After the addition of organic fertilizers, the carbon source in the organic fertilizers can be fully utilized and transformed by microorganisms to form new humus substances, which can improve the soil structure and the quality of soil fertility, and further promote the absorption and utilization of inorganic fertilizers by plants. During the preparation process, due to the certain viscosity of superphosphate, when it is directly mixed and granulated with other components in the fertilizer raw materials, large-sized particles are easily formed. On the other hand, organic fertilizers themselves have a relatively low specific gravity and low cohesive force and are difficult to granulate, but their adhesiveness can be reduced through the methylation reaction, making it easier to granulate. Therefore, in the preparation process of the present invention, first, urea is mixed with formaldehyde solution to obtain a mixed solution of urea and formaldehyde, and then it is added to other uniformly mixed components. The pH of the slurry is adjusted by adding magnesium oxide to control the slow progress of the methylation reaction. After the reaction, the adhesion between particles can be effectively reduced, and by this method, inorganic fertilizers can be evenly filled in the prepared fertilizer granules, effectively limiting the contact between organic fertilizers, inorganic fertilizers and microorganisms in the soil and inhibiting the degradation of microorganisms. As urea is gradually decomposed by microorganisms, the contact area between organic fertilizers and the soil gradually expands, thus showing the fertilizer effect.

[0073] In order to further achieve the slow / controlled release of fertilizer nutrients, in the present invention, a polymer emulsion coating is coated on the outside of the prepared fertilizer. Existing water-absorbing polymers become lumps by absorbing water and retain water and fertilizer components therein, but existing water-absorbing polymers are difficult to maintain water and fertilizer components for a long time, and the lumps are easily collapsed when pressure is applied. Through research, it is found that polyacrylamide has good water-absorbing performance and is not easily collapsed after absorbing water. Therefore, in the present invention, polyacrylamide is selected as the main raw material of the polymer emulsion coating material. At the same time, polyvinyl chloride with better mechanical properties and controlled release properties is also selected as the main raw material of the polymer emulsion coating material in the present invention. In the present invention, ethylenediamine is used as the solvent, and Al 2 O 3As a composite catalyst, [substance not specified] and CuO cause the ammonolysis reaction between polyacrylamide and polyvinyl chloride. During this process, chemical bonds are formed between the polyacrylamide molecular chain and the polyvinyl chloride molecular chain to obtain intermediate I, which improves the stability of the polymer to a certain extent. Further, under the action of a catalyst, using tetrahydrofuran as a solvent, aniline is added thereto, and under certain conditions, imino groups and benzene rings are introduced onto the intermediate I polymer chain. The imino group has a certain hydrophilicity and, as a polymer emulsion coating material, can improve the water absorption and water retention capacity of the soil. The introduced benzene ring structure is more stable because it has a large π bond and a greater degree of electron delocalization, thus improving the mechanical properties of the polymer and ensuring the stability of the polymer emulsion coating prepared after water absorption and preventing it from collapsing.

[0074] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0075] Although the embodiments of the present application have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present application. The scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A slow-release fertilizer for promoting crop growth, characterized in that: The fertilizer is coated with a polymer latex coating, and the fertilizer is composed of the following components by weight: 20-30 parts of organic fertilizer, 20-25 parts of urea, 8-12 parts of superphosphate, 5-10 parts of potassium chloride, 3-6 parts of KOM, 0.2-0.4 parts of ammonium molybdate, and 0.5-1 parts of boric acid; The preparation process of the polymer emulsion coating material is as follows: S1, adding polyacrylamide with ethylene glycol as solvent, heating and stirring to dissolve to obtain a mixed solution for use; adding polyvinyl chloride and a composite catalyst into a reactor and heating to 100-110°C at a heating rate of 5-8°C / min, adding the mixed solution dropwise thereto during the heating process, and after the addition is completed, raising the temperature to 120-130°C, reacting for 6-8h to obtain an intermediate I; S2. Add the intermediate I obtained in step S1 with tetrahydrofuran as solvent, heat to 35-45°C, add copper powder and nickel powder thereto and stir evenly, continue to increase the temperature to 50-55°C, and add aniline thereto. After the operation is completed, increase the temperature to 65-70°C, react for 4-6h, reduce the temperature to 30-35°C, add protonic acid thereto, stir and react for 2-4h, and then perform reduced pressure distillation to obtain the polymer emulsion coating material.

2. The slow-release fertilizer for promoting crop growth according to claim 1, characterized in that: The organic fertilizer is one or a mixture of bone meal, rawhide meal, rapeseed meal, soybean meal and fish meal.

3. The slow-release fertilizer for promoting crop growth according to claim 1, characterized in that: In step S1, the composite catalyst is a mixture of Al2O3 and CuO in a weight ratio of 1:2-4.

4. The slow-release fertilizer for promoting crop growth according to claim 1, characterized in that: In step S2, the weight ratio of copper powder to nickel powder is 1:1.

5.

5. The slow-release fertilizer for promoting crop growth according to claim 1, characterized in that: In step S2, the protonic acid is any one of dilute sulfuric acid, dilute hydrochloric acid, and acetic acid.

6. The slow-release fertilizer for promoting crop growth according to claim 1, characterized in that: In step S2, aniline is added dropwise, and the addition is completed within 10 minutes.

7. A method for preparing a slow-release fertilizer for promoting crop growth according to any one of claims 1 to 6, characterized in that: The preparation process is as follows: A1. Accurately weigh each component, add urea to the formaldehyde solution to prepare a mixed solution of urea and formaldehyde, mix the weighed components except urea evenly, add the mixed solution of urea and formaldehyde thereto, heat to 30-35° C. in a water bath and stir continuously, add magnesium oxide to adjust the pH to 7.2, place at a constant temperature for 40-60 min, dropwise add dilute sulfuric acid to adjust the pH to 6.0, and let stand at 40° C., add magnesium oxide to adjust the pH to 7.2, react at 40° C. for 4-6 min, granulate, and dry to obtain fertilizer granules; A2. Pour the fertilizer particles obtained in step A1 into a coating machine, heat the fertilizer to 80-90°C, fix the inclination angle of the coating machine, adjust the rotation speed, allow the fertilizer particles to rotate freely in the coating machine, turn on the air compressor, put the prepared polymer emulsion coating material into the spray gun, use high-pressure atomization method, spray the prepared coating emulsion into the coating machine, heat intermittently during the coating process, and obtain the coated fertilizer after cooling.

8. The method for preparing a slow-release fertilizer for promoting crop growth according to claim 7, characterized in that: In step A2, the coating machine drum has an inclination angle of 40°-45°, the rotation speed is adjusted to 35-55 r / min, and the interval heating temperature during coating is 50-60°C.

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