A biodegradable granular fertilizer substrate for lemons and its preparation and application method

Abstract

The invention discloses a biodegradable granular fertilizer substrate for lemon and its preparation and application method, belonging to the technical field of agricultural materials; it is characterized in that, by weight, it is composed as follows, including: 20-52 parts of castor oil, 8-18 parts of solvent, 2-5 parts of self-made aminopropyl oligosiloxane, 15-24 parts of hexamethylene diisocyanate, and 16-24 parts of n-propylamine modified polyvinyl alcohol. The substrate of the present application, by introducing oligosiloxane and modified polyvinyl alcohol, under the synergistic improvement of the two, after the substrate coating fertilizer of the present application, it can be a long-term slow-release fertilizer for more than 120 days; the fruit growth cycle of lemon is long, and after the substrate coating fertilizer of the present application, the full cycle of lemon fruit growth can be completely covered; not only the input of labor is reduced, but also the production efficiency is improved; and the substrate fully improves the utilization efficiency of granular fertilizer, reduces the amount of fertilizer and the frequency of fertilization, and improves the production efficiency in the lemon planting process.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural materials, and specifically relates to a biodegradable granular fertilizer substrate for lemons and a preparation method thereof. Background Art

[0002] With the development of contemporary social economy and the improvement of human living standards, people's awareness of health and environmental protection has gradually increased, and the demand for healthy food has increased day by day, and has gradually formed an industrial scale. Lemon is a fruit with extremely high health, nutritional and medicinal value recognized by the world, and is rich in vitamins; lemon is a fruit that can be eaten fresh or processed, and as an important natural flavor and food and industrial raw material, it is widely used in food, medicine, cosmetics, daily chemical and other industries.

[0003] From an agricultural perspective, the fertilization structure is unreasonable. Crops require different nutrients to grow. Blindly applying fertilizers will only increase production costs and environmental pollution, especially when it comes to lemon cultivation. Lemons are evergreen plants. They can bloom and bear fruit at any time of the year, and the process from bud formation, flowering to fruit ripening lasts 120 to 180 days. During the entire growth cycle, fertilizers need to be released continuously.

[0004] At present, some fruit farmers use a large amount of unreasonable fertilizers in pursuit of agricultural output, which easily causes soil compaction, acidification, and excessive nitrate ions in lemon orchards, ultimately causing lemon quality to decline and water eutrophication. In order to overcome the negative effects of excessive fertilization, the prior art includes, for example, the Chinese invention patent with publication number CN115124391B: a controllable biodegradable large-particle fertilizer substrate and its preparation method and application, wherein the substrate comprises the following components in parts by weight: 28-63 parts of starch, 7-35 parts of polyvinyl alcohol, 2-7 parts of metal salts, 14-26 parts of citric acid, 1-3 parts of sodium hydroxide, 15-30 parts of glycerol, and 0-10 parts of deionized water.

[0005] The prior art uses a modified starch to increase the hydrophobicity and mechanical properties of the controllable biodegradable large-particle fertilizer substrate; the fertilizer fertility can be slowly released, but in actual application, the starch is easily affected by bacteria in the planting soil and degraded. Although it can be biodegraded, the nutrient release rate is generally fast, which cannot meet the fertilization needs of the complete growth cycle during lemon planting; and after the microorganisms begin to decompose the starch, the disintegration speed will become faster and faster, and it will eventually be completely released within a faster time period; which may lead to nutrient deficiency in the late growth stage of lemons.

[0006] Although the above-mentioned existing technologies have achieved the effect of green biodegradation, in the face of lemon cultivation, a substrate with a longer sustained-release period is obviously required; therefore, it is urgent to introduce new process technologies to solve the above problems and seek more feasible solutions. Summary of the invention

[0007] In order to solve the defects existing in the above technical scheme, the purpose of the present invention is to provide a biodegradable granular fertilizer substrate for lemons and a preparation and application method thereof; the purpose of the present invention can be achieved by the following technical scheme: a biodegradable granular fertilizer substrate for lemons, comprising, by weight: 20-52 parts of castor oil, 8-18 parts of solvent, 2-5 parts of homemade aminopropyl oligosiloxane, 15-24 parts of hexamethylene diisocyanate, and 16-24 parts of n-propylamine-modified polyvinyl alcohol.

[0008] Further, the solvent is N,N-dimethylformamide;

[0009] Furthermore, the biodegradable granular fertilizer substrate for lemons includes, by weight: 35 parts of castor oil, 13 parts of solvent, 3 parts of homemade aminopropyl oligosiloxane, 20 parts of hexamethylene diisocyanate, and 18 parts of n-propylamine-modified polyvinyl alcohol.

[0010] The preparation method of the self-made aminopropyl oligosiloxane is as follows: deionized water, propanol, and acetonitrile are added to a reaction container, followed by the addition of a catalyst tetraethylammonium hydroxide and (3-aminopropyl)triethoxysilane, followed by heating to 50 degrees Celsius, stirring the mixed solution, and fully reacting for 24 hours. After the stirring reaction is completed, the mixture is cooled to room temperature, and the solvent is removed by vacuum rotary evaporation to obtain a white solid product, the self-made aminopropyl oligosiloxane;

[0011] Furthermore, the concentration of the catalyst tetraethylammonium hydroxide is 25wt%.

[0012] The preparation method of n-propylamine-modified polyvinyl alcohol is as follows: dimethyl sulfoxide and polyvinyl alcohol are added to a reaction container, and then the reaction container is placed in an oil bath at 90 degrees Celsius and magnetically stirred; after being fully stirred, the obtained mixed solution is cooled to 20 degrees Celsius, and then N,N'-carbonyldiimidazole is quickly added to the reaction container and vigorously stirred for 4 hours; then, n-propylamine is slowly dripped into the vigorously stirred mixed solution, and after the dripping is completed, stirring is continued for 24 hours; then ammonia water is dripped into the solution, and the mixture after the reaction is continued to be stirred for 2 hours; finally, the mixed solution is heated to 40 degrees Celsius, and at this temperature, a diluted HCl aqueous solution is dripped; a precipitate product is precipitated immediately; the precipitate product is collected, dissolved in dimethyl sulfoxide, and added to the diluted HCl aqueous solution again, and the washing is repeated 3 times, the precipitate is collected by centrifugation, and finally the product is freeze-dried, so as to prepare n-propylamine-modified polyvinyl alcohol in the form of white powder;

[0013] Furthermore, during the preparation process, the pH of the diluted HCl aqueous solution added dropwise is 5-6.

[0014] A biodegradable granular fertilizer substrate for lemons and a preparation method thereof: the entire preparation process needs to ensure that the reaction is carried out under the protection of a nitrogen atmosphere, firstly, castor oil and a solvent N, N-dimethylformamide are mixed, then hexamethylene diisocyanate and a self-made aminopropyl oligosiloxane are weighed and added to a reaction container; then 1-2 drops of dibutyltin dilaurate are added as a catalyst, and magnetic stirring is continued; during the stirring process, the temperature of the reaction system is controlled at 70 degrees Celsius, and the reaction system is observed during the stirring process, and the viscosity of the reaction system is adjusted by dripping the solvent N, N-dimethylformamide to prevent the reaction system from solidifying; after reacting for 2.5 hours, the temperature of the reaction system is reduced to 50 degrees Celsius, then polyvinyl alcohol modified with n-propylamine is added, and the reaction is continued for 5 hours until the isocyanate group reacts completely; after the reaction is completed, the prepared product is placed in a vacuum drying oven, and dried to a constant weight at 80 degrees Celsius, so as to prepare a biodegradable granular fertilizer substrate for lemons.

[0015] Among them, during the preparation process, the content of isocyanate groups needs to be tested to determine the extent of the prepolymerization reaction;

[0016] Furthermore, a chemical analysis method, toluene-di-n-butylamine titration method, is used to measure the content of isocyanate groups during the reaction to determine the extent of the reaction.

[0017] The present invention has the beneficial effects:

[0018] 1. The present invention improves the hydrophobicity of the polyurethane substrate by introducing self-made aminopropyl oligosiloxane into the polyurethane molecular chain during the preparation and synthesis of the polyurethane substrate; the introduced oligosiloxane has the characteristic of low surface energy, and when preparing the film, it will migrate and aggregate to the surface, thereby reducing the flatness of the substrate surface, thereby increasing the contact angle and reducing the water absorption rate of the substrate; and it has an active group amino group, which can improve the thermal stability of the substrate, and in the specific application process, the performance of the substrate can be more stable;

[0019] 2. The present invention introduces n-propylamine to modify polyvinyl alcohol in the substrate. The n-propylamine has a shorter carbon chain length, which increases the van der Waals force between molecules, and can improve the mechanical properties of the polyurethane substrate, thereby having excellent mechanical properties of high strength and high toughness; and after alkylation modification, the dispersibility of polyvinyl alcohol can be significantly improved; the dispersion is more uniform, which can also indirectly increase the mechanical strength;

[0020] 3. The self-made aminopropyl oligosiloxane and n-propylamine-modified polyvinyl alcohol introduced in this application both have low molecular weights and can be naturally degraded in the soil, which is green and environmentally friendly;

[0021] 4. The substrate of the present application, by introducing oligosiloxane and modified polyvinyl alcohol, under the synergistic improvement effect of the two, after the substrate of the present application is coated with fertilizer, it can release fertilizer for a long time for more than 120 days; lemon has a long fruiting growth cycle, and after the substrate of the present application is coated with fertilizer, it can completely cover the entire growth cycle of lemon fruit; not only does it reduce labor input and improve production efficiency; but the substrate also fully improves the utilization efficiency of granular fertilizers, reduces the amount and frequency of fertilization, and improves production efficiency during lemon planting. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment, and the illustrative embodiments of the present invention and its description are only used to explain the present invention, and are not used as limitation of the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper limit and the lower limit of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the range is also included in the present invention. The upper limit and lower limit of these smaller ranges can be independently included or excluded in the scope.

[0023] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0024] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0025] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0026] The "parts" indicated in the following examples are all parts by weight.

[0027] Example 1

[0028] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 20 parts of castor oil, 8 parts of solvent, 2 parts of self-made aminopropyl oligosiloxane, 15 parts of hexamethylene diisocyanate, and 16 parts of n-propylamine-modified polyvinyl alcohol;

[0029] Wherein, the solvent is N,N-dimethylformamide;

[0030] Among them, castor oil was purchased from Shanghai Zhongshen New Material Technology Co., Ltd., and the molecular weight of castor oil was tested to be 932, hydroxyl value ≥155mgKOH / g, acid value ≤1.2mgKOH / g, and moisture ≤0.08%;

[0031] Among them, hexamethylene diisocyanate was purchased from Shandong Dengnuo New Materials Technology Co., Ltd., CAS No.: 822-06-0;

[0032] Among them, polyvinyl alcohol was purchased from Beijing Wantuming Technology Co., Ltd. with the product number: Polyvinyl alcohol 2488.

[0033] Preparation and synthesis method of homemade aminopropyl oligosiloxane: add 16ml of deionized water, 8ml of propanol, 4ml of acetonitrile, 0.4ml of 25wt% tetraethylammonium hydroxide, and 36g of (3-aminopropyl)triethoxysilane into a 100ml round-bottom flask, then stir the mixed solution at 50 degrees Celsius and react for 24 hours. After the stirring reaction is completed, cool to room temperature and remove the solvent by reduced pressure rotary evaporation to prepare a white solid product homemade aminopropyl oligosiloxane.

[0034] Preparation and synthesis method of n-propylamine modified polyvinyl alcohol: in a reaction container, add 120 ml of dimethyl sulfoxide and 3 g of polyvinyl alcohol, then place the reaction container in a 90 degree Celsius oil bath and perform magnetic stirring; after fully stirring, cool the obtained mixed solution to 20 degrees Celsius, then quickly add 6 g of N,N'-carbonyldiimidazole to the reaction container, and vigorously stir for 4 hours; then, slowly drip 4 g of n-propylamine into the vigorously stirred mixed solution, and after the dripping is complete, continue to stir for 24 hours; then drip ammonia water into the solution, and continue to stir the reacted mixture for 2 hours; finally, heat the mixed solution to 40 degrees Celsius, and at this temperature, drip a diluted HCl aqueous solution with a pH of 5-6; collect the precipitated product, dissolve it in dimethyl sulfoxide; then add it again into the diluted HCl aqueous solution, repeat washing 3 times, collect the precipitate by centrifugation, and finally freeze-dry the product to prepare n-propylamine modified polyvinyl alcohol in the form of white powder.

[0035] A biodegradable granular fertilizer substrate for lemons and a preparation method thereof: during the entire preparation process, the reaction needs to be carried out under the protection of a nitrogen atmosphere. First, 20 parts by weight of castor oil and 8 parts by weight of a solvent N,N-dimethylformamide are mixed, and then 15 parts by weight of hexamethylene diisocyanate and 2 parts by weight of a homemade aminopropyl oligosiloxane are weighed and added to a reaction container; then 1-2 drops of dibutyltin dilaurate are added as a catalyst; the temperature of the reaction system is raised to 70 degrees Celsius, and magnetic stirring is performed, and the magnetic speed is set to 400r / min; during the stirring process, the reaction system needs to be observed, and N , N-dimethylformamide is used to adjust the viscosity of the reaction system to prevent the system from solidifying. After the reaction for 2.5 hours, the prepolymerization stage is terminated; the temperature of the reaction system is lowered to 50 degrees Celsius, and then 16 parts by weight of n-propylamine-modified polyvinyl alcohol is added to continue the chain extension reaction for 5 hours; during the reaction, the toluene-di-n-butylamine titration method is used to determine the content of isocyanate groups during the reaction to determine the extent of the reaction; until the isocyanate groups react completely; after the reaction is completed, the prepared product is placed in a vacuum drying oven and dried to constant weight at 80 degrees Celsius to prepare a biodegradable granular fertilizer substrate for lemons.

[0036] Example 2

[0037] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 28 parts of castor oil, 10 parts of solvent, 2 parts of self-made aminopropyl oligosiloxane, 18 parts of hexamethylene diisocyanate, and 17 parts of n-propylamine-modified polyvinyl alcohol;

[0038] Wherein, the solvent is N,N-dimethylformamide;

[0039] Among them, in Example 2, the preparation method of the homemade aminopropyl oligosiloxane, the preparation method of n-propylamine-modified polyvinyl alcohol, and the preparation method of the biodegradable granular fertilizer substrate for lemon are all the same as those in Example 1.

[0040] Example 3

[0041] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 35 parts of castor oil, 13 parts of solvent, 3 parts of self-made aminopropyl oligosiloxane, 20 parts of hexamethylene diisocyanate, and 18 parts of n-propylamine-modified polyvinyl alcohol;

[0042] Wherein, the solvent is N,N-dimethylformamide;

[0043] Among them, in Example 3, the preparation method of the homemade aminopropyl oligosiloxane, the preparation method of n-propylamine-modified polyvinyl alcohol, and the preparation method of the biodegradable granular fertilizer substrate for lemon are all the same as those in Example 1.

[0044] Example 4

[0045] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 46 parts of castor oil, 16 parts of solvent, 4 parts of self-made aminopropyl oligosiloxane, 22 parts of hexamethylene diisocyanate, and 21 parts of n-propylamine-modified polyvinyl alcohol;

[0046] Wherein, the solvent is N,N-dimethylformamide;

[0047] Among them, in Example 4, the preparation method of the homemade aminopropyl oligosiloxane, the preparation method of n-propylamine-modified polyvinyl alcohol, and the preparation method of the biodegradable granular fertilizer substrate for lemon are all the same as those in Example 1.

[0048] Example 5

[0049] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 52 parts of castor oil, 18 parts of solvent, 5 parts of self-made aminopropyl oligosiloxane, 24 parts of hexamethylene diisocyanate, and 24 parts of n-propylamine-modified polyvinyl alcohol;

[0050] Wherein, the solvent is N,N-dimethylformamide;

[0051] Among them, in Example 5, the preparation method of the homemade aminopropyl oligosiloxane, the preparation method of n-propylamine-modified polyvinyl alcohol, and the preparation method of the biodegradable granular fertilizer substrate for lemon are all the same as those in Example 1.

[0052] Comparative Example 1

[0053] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 35 parts of castor oil, 13 parts of solvent, 20 parts of hexamethylene diisocyanate, and 18 parts of n-propylamine-modified polyvinyl alcohol;

[0054] Wherein, the solvent is N,N-dimethylformamide;

[0055] This comparative example 1 is based on Example 3, except that the homemade aminopropyl oligosiloxane is not added to the formula components of the comparative example 1; and the method for preparing the biodegradable granular fertilizer substrate for lemons is also improved accordingly.

[0056] Comparative Example 2

[0057] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 35 parts of castor oil, 13 parts of solvent, 3 parts of self-made aminopropyl oligosiloxane, 20 parts of hexamethylene diisocyanate, and 18 parts of polyvinyl alcohol;

[0058] Wherein, the solvent is N,N-dimethylformamide;

[0059] This comparative example 2 is based on Example 3, except that, in the formula components of the comparative example 2, polyvinyl alcohol of the same weight without any modification is used; and the method for preparing the biodegradable granular fertilizer substrate for lemons is also improved accordingly.

[0060] Comparative Example 3

[0061] A biodegradable granular fertilizer substrate for lemons, comprising, by weight: 35 parts of castor oil, 13 parts of solvent, 20 parts of hexamethylene diisocyanate, and 18 parts of polyvinyl alcohol;

[0062] Wherein, the solvent is N,N-dimethylformamide;

[0063] This comparative example 3 is based on Example 3, except that, in the formula components of the comparative example 3, no self-made aminopropyl oligosiloxane is added, and the same weight of polyvinyl alcohol without any modification is used; and the method for preparing the biodegradable granular fertilizer substrate for lemons is also improved accordingly.

[0064] Comparative Example 4

[0065] A controllable biodegradable large-particle fertilizer substrate, the preparation method of which refers to the patent publication number CN115124391A.

[0066] An application method of a biodegradable granular fertilizer substrate for lemons: step S1, weighing granular fertilizer, placing it in a coating machine, setting the speed of the coating machine to 60 rpm, the temperature to 70 degrees Celsius, and preheating for 10 minutes;

[0067] Step S2, spraying the biodegradable granular fertilizer substrate for lemons evenly on the surface of the granular fertilizer through the spray port of the coating machine, and continuously blowing hot air until the surface is dry;

[0068] Step S3, then transfer it to a 60 degree Celsius forced air drying oven for drying, and after drying to constant weight, weigh the mass of the granular fertilizer before and after coating, and maintain the total mass after coating at 118%-122% of that before coating; that is, a biodegradable coated slow-release granular fertilizer for lemons is prepared.

[0069] Furthermore, the granular fertilizer in step S1 is any one of urea granular fertilizer, nitrogen, phosphorus and potassium granular fertilizer, and medium and trace element granular fertilizer.

[0070] Test example

[0071] Mechanical properties test: Referring to GB / T 30693-2014, the water contact angle of the substrates prepared in Examples 1-5 and Comparative Examples 1-4 was tested; and corresponding mechanical properties tests were performed, including tensile strength and elongation at break. The test results are shown in Table 1;

[0072] Table 1

[0073]

[0074] Release rate test: refer to the slow-release fertilizer, the national standard GB / T 23348-2009 "Slow-release fertilizer", and measure the release rate and degradation rate of the fertilizer coated on the prepared substrate; the substrate can be coated with urea granular fertilizer, nitrogen, phosphorus and potassium granular fertilizer, and medium and trace element granular fertilizer;

[0075] In the specific implementation, this test example will prepare the substrate-coated urea granules, weigh the urea granules prepared by the substrates prepared in Examples 1-5 and Comparative Examples 1-4, 10 g each; soak in a glass bottle with 250 ml of distilled water, and then culture at 25 degrees Celsius, and measure the urea dissolution release rate of each example at 1d, 14d, 28d, 60d, and 120d respectively; the test results are shown in Table 2.

[0076] Table 2 Urea dissolution release rate of each case (%)

[0077]

[0078] Degradation rate test: adopt the above-mentioned application method of the biodegradable granular fertilizer substrate for lemon, replace the granular fertilizer in step S1 with frosted glass balls of uniform size to obtain coated glass beads; weigh 20g of the coated glass beads prepared in each example and place them in a plastic mesh bag with a pore size smaller than that of the frosted glass balls; bury the mesh bag in the soil to a depth of 10cm at the same time; and water the buried position every 5d; dig out the mesh bag every 30d, wash and dry it, and then weigh the mass of the remaining coated glass beads, so that the cumulative degradation rate can be calculated. The test results are shown in Table 3.

[0079] Table 3 Cumulative degradation rate of each case (%)

[0080]

[0081] Comprehensive performance analysis: From the mechanical property test data in Table 1, it can be seen that Examples 1-5 all have a contact angle greater than 90° and have excellent hydrophobicity; Comparative Example 1 does not incorporate the self-made aminopropyl oligosiloxane, and Comparative Example 2 adds polyvinyl alcohol without any modification; the mechanical properties of both have declined to a large extent, among which the contact angle of Comparative Example 1 declines more, while the tensile strength and elongation at break of Comparative Example 2 decline more; the possible reason is that the self-made aminopropyl oligosiloxane is introduced into the polyurethane molecular chain, which improves the hydrophobicity of the polyurethane substrate; the introduced oligosiloxane has the characteristics of low surface energy, and when preparing the film, it will migrate and aggregate to the surface, thereby reducing the flatness of the substrate surface, thereby increasing the contact angle; and the introduction of n-propylamine-modified polyvinyl alcohol into the substrate, the n-propylamine carbon chain length is relatively short, which increases the van der Waals force between molecules, and can improve the mechanical properties of the polyurethane substrate, thereby having excellent mechanical properties of high strength and high toughness; After alkylation modification, the dispersibility of polyvinyl alcohol can be significantly improved; the dispersion is more uniform, which can also indirectly increase the mechanical strength.

[0082] It can be seen from the urea dissolution release rate test data in Table 2 that in the present embodiments 1-5, the urea dissolution release rate is about 80% after 120 days of cultivation; after 120 days, there is still 20% of the fertilizer available for release. After the substrate of the present application is coated with urea granular fertilizer, the fertilizer can be released for a long time for more than 120 days; the fruit growth cycle of lemon is long, lasting 120 to 180 days. After the substrate of the present application is coated with fertilizer, the whole cycle of lemon fruit growth can be completely covered; while the contact angles of comparative examples 1-3 are all less than 90°, and the mechanical properties are significantly different from those of embodiments 1-5 of the present application, so that at 120 days, the urea dissolution release rates of comparative examples 1-3 are all about 90%; it is impossible to support the whole lemon growth process;

[0083] After the substrates of Examples 1-5 of the present application are coated with urea granular fertilizers, they are placed in water. The water first slowly penetrates into the core of the urea granular fertilizers, dissolves the fertilizer nutrients, and forms a local saturated solution. Under the action of pressure difference and concentration difference, the nutrients are gradually released outward through the polymer membrane until the nutrients are completely released.

[0084] In the prior art adopted in Comparative Example 4, after water penetrates into the fertilizer core from the surface material channel, urea dissolves and forms a high osmotic pressure. However, the substrate of the prior art has insufficient mechanical properties and elasticity, and ruptures under high pressure, causing the internal urea solution to flow out quickly; and as biodegradation proceeds, the release efficiency in the later stage gradually accelerates.

[0085] It can be seen from the cumulative degradation rate data in Table 3 that the prior art of comparative example 4 has excellent biodegradation efficiency, and the degradation is basically completed at 60 days; and the technical solution selected in the present application needs to have a longer sustained release time in order to ensure that the lemon growth cycle can be covered; in the soil, they can also be naturally degraded, and the homemade aminopropyl oligosiloxane and n-propylamine modified polyvinyl alcohol both have low molecular weights; neither will remain in the soil for a long time and can be biodegraded.

[0086] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A biodegradable granular fertilizer substrate for lemons, characterized in that: The composition is as follows, by weight: 20-52 parts of castor oil, 8-18 parts of solvent, 2-5 parts of self-made aminopropyl oligosiloxane, 15-24 parts of hexamethylene diisocyanate, and 16-24 parts of n-propylamine-modified polyvinyl alcohol; The solvent is N,N-dimethylformamide; The preparation method of the self-made aminopropyl oligosiloxane is as follows: deionized water, propanol, and acetonitrile are added into a reaction container, and then a catalyst tetraethylammonium hydroxide and (3-aminopropyl)triethoxysilane are added, and then the temperature is raised to 50 degrees Celsius, and the mixed solution is stirred and fully reacted for 24 hours. After the stirring reaction is completed, the mixture is cooled to room temperature, and the solvent is removed by vacuum rotary evaporation to prepare the self-made aminopropyl oligosiloxane; The preparation method of n-propylamine-modified polyvinyl alcohol comprises the following steps: adding dimethyl sulfoxide and polyvinyl alcohol to a reaction container, and then placing the reaction container in an oil bath at 90 degrees Celsius and stirring with a magnetic force; after being fully and evenly stirred, cooling the obtained mixed solution to 20 degrees Celsius, and then quickly adding N,N'-carbonyldiimidazole to the reaction container and stirring vigorously for 4 hours; then slowly dripping n-propylamine into the mixed solution after being stirred vigorously, and after the dripping is complete, continuing to stir for 24 hours; then dripping ammonia water into the solution, and continuing to stir the mixture after the reaction for 2 hours; finally heating the mixed solution to 40 degrees Celsius, and dripping HCl aqueous solution; a precipitate product will be precipitated immediately; collecting the precipitate product, dissolving it in dimethyl sulfoxide, and adding it again into the HCl aqueous solution, repeating the washing for 3 times, collecting the precipitate by centrifugation, and finally freeze-drying the product to prepare n-propylamine-modified polyvinyl alcohol.

2. The biodegradable granular fertilizer substrate for lemon according to claim 1, characterized in that: The composition is as follows by weight: 35 parts of castor oil, 13 parts of N,N-dimethylformamide, 3 parts of self-made aminopropyl oligosiloxane, 20 parts of hexamethylene diisocyanate, and 18 parts of n-propylamine-modified polyvinyl alcohol.

3. The biodegradable granular fertilizer substrate for lemon as claimed in claim 1, characterized in that: The concentration of the catalyst tetraethylammonium hydroxide in the preparation process of the homemade aminopropyl oligosiloxane is 25wt%.

4. The biodegradable granular fertilizer substrate for lemon as claimed in claim 1, characterized in that: The pH of the HCl aqueous solution during the preparation of the n-propylamine-modified polyvinyl alcohol is 5-6.

5. A method for preparing a biodegradable granular fertilizer substrate for lemon as claimed in any one of claims 1 to 2, characterized in that: The preparation method comprises the following steps: firstly, mixing castor oil and solvent N,N-dimethylformamide, then weighing hexamethylene diisocyanate and self-made aminopropyl oligosiloxane, and adding the mixture into a reaction container; then adding 1-2 drops of dibutyltin dilaurate as a catalyst, and continuing magnetic stirring; during the stirring process, controlling the temperature of the reaction system at 70 degrees Celsius, observing the reaction system during the stirring process, and adjusting the viscosity of the reaction system by dropping solvent N,N-dimethylformamide to prevent the reaction system from solidifying; after reacting for 2.5 hours, lowering the temperature of the reaction system to 50 degrees Celsius, then adding polyvinyl alcohol modified with n-propylamine, and continuing the reaction for 5 hours until the isocyanate group reacts completely; after the reaction is completed, placing the prepared product in a vacuum drying oven, and drying it to a constant weight at 80 degrees Celsius, so as to prepare a biodegradable granular fertilizer substrate for lemons.

6. The method for preparing a biodegradable granular fertilizer substrate for lemon as claimed in claim 5, characterized in that: The preparation reaction process needs to be carried out under the protection of nitrogen atmosphere.

7. The application method of a biodegradable granular fertilizer substrate for lemon as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: Step S1, weighing granular fertilizer, placing it in a coating machine, setting the speed of the coating machine to 60 rpm, the temperature to 70 degrees Celsius, and preheating for 10 minutes; Step S2, spraying the biodegradable granular fertilizer substrate for lemons evenly on the surface of the granular fertilizer through the spray port of the coating machine, and continuously blowing hot air until the surface is dry; Step S3, then transfer it to a 60 degree Celsius forced air drying oven for drying, and after drying to constant weight, weigh the mass of the granular fertilizer before and after coating, and maintain the total mass after coating at 118%-122% of that before coating; that is, a biodegradable coated slow-release granular fertilizer for lemons is prepared.

8. The application method of the biodegradable granular fertilizer substrate for lemon as claimed in claim 7, characterized in that: The granular fertilizer in step S1 is any one of urea granular fertilizer, nitrogen, phosphorus and potassium granular fertilizer, and medium and trace element granular fertilizer.

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