Nanoscale slow-release synergist, preparation method thereof and nanoscale slow-release synergistic fertilizer

Abstract

The application belongs to the field of fertilizers, and particularly relates to a preparation method of a nano slow-release synergist, which comprises the following steps: S1, preparing a nano matrix: taking a nano porous material as a carrier, and loading medium and trace elements to obtain the nano matrix; S2, preparing a hydrophobic nano matrix: performing surface hydrophobic modification on the nano matrix obtained in step S1 by using a silane coupling agent to obtain the hydrophobic nano matrix; S3, preparing a complexed nano matrix: complexing medium and trace elements on the surface of the hydrophobic nano matrix obtained in step S2 to obtain the complexed nano matrix; and S4, preparing the nano slow-release synergist: coating a polymer coating layer on the surface of the complexed nano matrix obtained in step S3 to obtain the nano slow-release synergist. The prepared nano slow-release synergist can supply medium and trace elements required by crops in the whole growth cycle of the crops, and has a good promoting effect on the improvement of the yield and quality of the crops.

Description

Technical Field

[0001] This invention relates to the field of fertilizers, specifically to a nano-slow-release synergist, its preparation method, and a nano-slow-release synergist fertilizer. Background Technology

[0002] As an essential production material in agricultural production, fertilizers are being studied in an increasingly in-depth and refined manner. The requirements are not only that fertilizers can better promote crop growth, improve crop quality, and have high utilization rates, but also that they are friendly to the soil environment.

[0003] Throughout the entire growth cycle of crops, the demand for fertilizer nutrients follows certain patterns. In order to improve fertilizer utilization and meet the nutrient requirements of crops throughout their entire growth cycle, the concept of nutrient slow release has been proposed, and slow-release fertilizers have been developed. Most existing slow-release fertilizers are designed to slow the release of nitrogen, the nutrient element most easily lost, while others are designed to slow the release of macronutrients such as phosphorus and potassium, in order to provide nitrogen, phosphorus, and potassium nutrients that can meet the needs of crops throughout their entire growth cycle.

[0004] A growing body of research indicates that micronutrients play a vital role in crop growth. By participating in various processes of crop metabolism, they influence photosynthesis, nutrient synthesis, hormone regulation, and other aspects, thereby affecting crop yield, quality, and disease resistance. For many crops, micronutrient deficiencies can directly lead to severe yield reduction, serious quality defects, or severe pest and disease outbreaks. For example, boron deficiency can cause rapeseed to "flower but not bear fruit," cotton to "bud but not flower," wheat to "not heading," and peanuts to "shell but no kernel." Calcium deficiency can cause bitter pit, cork disease, pitted spot disease, heart rot, water core disease, and fruit cracking in fruit trees.

[0005] Similar to nitrogen, phosphorus, and potassium, the demand for micronutrients in crops follows certain patterns throughout their growth cycle. Moreover, the deficiency of micronutrients has a more pronounced negative impact on crop growth at any stage. However, there is very little research on the slow release of micronutrients in current technologies. The few micronutrients with slow-release effects are only provided through solid wastes with slow nutrient release (such as steel slag, fly ash, and phosphogypsum). These solid wastes not only have low nutrient content and are difficult to apply, but their nutrient release patterns are also uncontrollable. They may not release nutrients for a long time or have a short slow-release period, which cannot adequately meet the demand for micronutrients in crops throughout their growth cycle.

[0006] Therefore, there is a need to develop a fertilizer enhancer that can achieve a stable supply of micronutrients throughout the entire growth cycle of crops. Summary of the Invention

[0007] The first objective of this invention is to provide a method for preparing a nano-slow-release synergist, which can produce a nano-slow-release synergist that can stably supply the micronutrients required for crop growth throughout the entire crop growth cycle, thus greatly promoting the improvement of crop yield and quality.

[0008] A second objective of this invention is to provide a nano-sustained-release synergist prepared by the above-described preparation method.

[0009] The third objective of this invention is to provide a nano-slow-release synergistic fertilizer containing the aforementioned nano-slow-release synergist, which can achieve the effects of increasing crop yield and improving crop quality through the application of the nano-slow-release synergistic fertilizer.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing a nano-sustained-release synergist includes the following steps:

[0012] S1 Preparation of nanomatrix: Nanomatrix was prepared by loading trace elements onto nanoporous materials as carriers.

[0013] S2 Preparation of hydrophobic nanomatrix: The nanomatrix obtained in step S1 is surface-modified with a silane coupling agent to prepare a hydrophobic nanomatrix; the silane coupling agent is 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane.

[0014] S3 Preparation of complexed nanomatrix: Trace elements are complexed on the surface of the hydrophobic nanomatrix obtained in step S2 to prepare a complexed nanomatrix;

[0015] S4 Preparation of Nano-Slow-Release Synergist: The complex nano-matrix obtained in step S3 is coated with a polymer coating layer to obtain a nano-slow-release synergist; the polymer coating layer includes the following components in parts by weight: 70-80 parts of lignin-based epoxy resin, 10-20 parts of waterborne polyurethane, and 10-20 parts of trace elements.

[0016] The nano-slow-release synergist of this invention, through structural design, achieves a three-layer structure from the inside out: "nano-supported layer - metal complex layer - polymer coating layer". During use, as the fertilization time progresses, the outermost polymer coating layer structure is destroyed, and the trace elements mixed in the polymer coating layer are released first, and this release process can continue for a period of time. Subsequently, when the polymer coating layer is completely destroyed, the trace elements in the metal complex layer inside it begin to be released. Similarly, this release process can also continue for a certain period of time. During the release of the trace elements in the metal complex layer, the hydrophobic layer is gradually destroyed. Only when the hydrophobic layer is destroyed to a certain extent does the trace elements loaded inside the nanoporous material begin to be released slowly.

[0017] In other words, this application not only achieves the slow release of micronutrients through a three-layer structure of "nano-supported layer - metal complex layer - polymer coating layer", but also ensures that the micronutrients are not released directly and completely in each layer, but are released slowly, thus ensuring that the micronutrients can be stably released for crop absorption throughout the entire growth cycle of the crop.

[0018] In the design process, the main purpose of this invention is to provide a stable and continuous supply of micronutrients to crops throughout their entire growth cycle. It takes into account factors such as cost, ease of production, positive effects on the soil environment, and positive effects on macronutrient fertilizers.

[0019] Among them, using nanoporous materials as the matrix not only takes into account their porous characteristics to load trace elements and achieve their slow release, but also considers that nanomaterials can effectively promote soil aggregate structure in the soil, and can promote the release of phosphorus through competitive adsorption with macro-element phosphorus in the soil, thereby improving the utilization rate of phosphorus. At the same time, the porosity of nanoporous materials can also promote the improvement of soil water retention and heat preservation properties, and provide soil microorganisms with a stable microenvironment to ensure their effective reproduction.

[0020] However, in practical applications, nanomaterials are prone to aggregation. Therefore, in order to ensure good dispersibility and stability of nanoporous materials in soil and fertilizers, this invention modifies the surface of the nano-matrix loaded with trace elements to prevent aggregation between nanomaterials and to prevent the nano-matrix loaded with trace elements from absorbing water and swelling during subsequent processing and storage, thus preventing the loss of trace elements. On this basis, in order to achieve the purpose of long-term sustained release of trace elements, this invention limits the coupling agent used in the hydrophobic modification of the nano-matrix. A silane coupling agent with a strong metal complexing group (thiol group) is selected for hydrophobic modification, so that a large number of metal complexing groups are introduced on the surface of the nano-matrix during hydrophobic modification. Then, through complexation, the metal trace elements are loaded on the surface of the hydrophobically modified nano-matrix, forming another sustained release of trace elements.

[0021] Considering that the complexed nanomatrix prepared above is still difficult to release throughout the entire growth cycle of crops, this invention designs a polymer coating on the surface of the complexed nanomatrix. At the same time, taking into account both cost and coating effect, this invention selects lignin-based epoxy resin as the main component of the polymer coating layer, and combines it with a certain amount of waterborne polyurethane. This ensures the coating effect of the coating layer and achieves a good slow release of the internally coated components.

[0022] This invention also adds a certain amount of micronutrients to the coating layer, which ensures that micronutrients are released as the coating layer is destroyed after fertilization, so as to achieve the release throughout the entire growth cycle. In addition, adding micronutrients to the coating layer also promotes the destruction of the coating layer to a certain extent, avoiding the situation of micronutrient deficiency during the crop growth period due to an excessively long slow release period.

[0023] Preferably, the nanoporous material in step S1 is selected from at least one of nano-montmorillonite, nano-bentonite, nano-silica, intercalated modified nano-montmorillonite, or intercalated modified nano-bentonite. Among them, intercalated modified nano-montmorillonite or intercalated modified nano-bentonite has a greater adsorption capacity for trace elements.

[0024] Preferably, the trace elements in steps S1, S3, and S4 are selected from at least one of calcium, magnesium, iron, manganese, molybdenum, copper, zinc, and cobalt. The selection of metallic trace elements allows them to better bind to the hydrophobic modified layer through complexation, thus achieving effective slow release. In other embodiments, the trace elements in this application can also be non-metallic elements such as boron and silicon. In particular, the trace elements in steps S1 and S4 can be either metallic or non-metallic. Of course, in practice, the selection of trace elements also needs to consider the specific crop variety to which they are applied.

[0025] Furthermore, the specific operation method of step S1 includes: dispersing the nanoporous material in water to form a uniform dispersion A, dissolving the water-soluble trace element salt in water to form an aqueous solution A, slowly adding the aqueous solution A to the dispersion A under stirring, stirring for 2-6 hours, letting it stand for 20-24 hours, filtering and drying to obtain the nano matrix;

[0026] The weight ratio of the nanoporous material to the trace element salt satisfies: m(porous material):m(metal ion) = 0.8 to 2:1, preferably 1.5:1.

[0027] Furthermore, the specific operation method of step S2 includes: dispersing the nano-matrix in water to form a uniform dispersion B; dissolving the silane coupling agent in ethanol to form an alcohol solution, wherein the volume ratio of the silane coupling agent to ethanol is 0.1 to 0.5:1, preferably 0.8:1; slowly adding the alcohol solution dropwise to the dispersion B under stirring, and stirring the reaction for 3 to 5 hours; wherein the mass ratio of the silane coupling agent to the nano-matrix is ​​1 to 2:1, preferably 1.5:1.

[0028] Furthermore, the specific operation method of step S3 includes: dissolving the water-soluble trace element salt in water to form an aqueous solution B, directly adding the aqueous solution B dropwise to the product of step S2 to carry out the reaction, the reaction time is 4-6 hours, the reaction temperature is 60-80℃; after the reaction is completed, precipitate for 10-20 hours, filter, and dry at 120℃ to constant weight;

[0029] The addition amount of trace element salts satisfies the following ratio: n(metal ion):n(silane coupling agent) = 1~2:1, preferably 1.5:1. That is, the molar ratio of metal ion to silane coupling agent is 1~2:1.

[0030] Furthermore, the preparation method of the lignin-based epoxy resin in step S4 is as follows:

[0031] Alkali lignin pretreatment: Weigh alkali lignin, dissolve it in 1 mol / L NaOH solution, filter to remove insoluble matter, adjust the pH of the solution to 2 with 1 mol / L hydrochloric acid, filter, wash with distilled water until neutral, and dry at 40℃ for later use; The alkali lignin in this application is papermaking waste in papermaking black liquor.

[0032] Synthesis of lignin-based epoxy resin: Weigh the pretreated alkali lignin, add 20% NaOH solution as solvent and catalyst, add epichlorohydrin at room temperature, stir, heat to 80℃, react for 3 hours and then cool to room temperature for later use.

[0033] The mass ratio of pretreated alkali lignin to epichlorohydrin is 1:10 to 12, preferably 1:12, and the volume ratio (m / V) of alkali lignin to 20% sodium hydroxide solution is 5 ml: 1 g.

[0034] Furthermore, the operation method of step S4 includes:

[0035] Preparation of the spraying solution: Weigh the components of the polymer coating layer according to the proportions, namely lignin-based epoxy resin, waterborne polyurethane and trace elements; weigh the curing agent and diluent and mix them evenly to prepare the spraying solution.

[0036] Preparation of nano-slow-release synergist: The complexed nano matrix prepared in step S3 is fluidized in a fluidization device and heated to 90-120°C. Then, the spraying liquid is sprayed onto the surface of the fluidized complexed nano matrix in several times until the surface is cured to form nano-slow-release synergist; the amount of polymer coating layer is 2.5-4.5% of the weight of complexed nano matrix.

[0037] In step S4, the curing agent is selected from at least one of T-31, diethylenetriamine, or maleic anhydride; the diluent is selected from methanol or acetone; the amount of curing agent is 5-10% by weight of the lignin-based epoxy resin; the amount of diluent is 15% to 30% by weight of the lignin-based epoxy resin.

[0038] This invention also provides a nano-controlled-release synergist, prepared by the above-described method. The nano-controlled-release synergist of this invention is a solid powder with a particle size in the micrometer range.

[0039] The present invention also provides a nano-slow-release synergistic fertilizer, comprising 5% to 15% by weight of the nano-slow-release synergist prepared by the above preparation method.

[0040] Specifically, the nano-slow-release synergistic fertilizer of the present invention can be prepared by mixing nano-slow-release synergists with inorganic and / or organic fertilizer raw materials and then granulating them; or it can be prepared by directly mixing nano-slow-release synergists into organic fertilizer.

[0041] The beneficial effects of this invention are:

[0042] 1. The nano-slow-release synergist of the present invention has a good effect on slow-release of micronutrients, which can ensure the effective supply of micronutrients throughout the entire growth period, thereby ensuring the improvement of crop yield and quality.

[0043] 2. The nano-slow-release synergist of the present invention, when applied to soil, allows for effective dispersion of the nanomaterials in the soil without aggregation due to hydrophobic modification. This fully leverages the role of the nanomaterials in the soil, including: improving soil aggregate structure and enhancing soil fertility and water retention through the introduction of nanoporous materials and polymer materials; achieving adsorption and passivation of heavy metals through nanoporous materials; simultaneously, the nanomaterials can enhance phosphorus availability through competitive adsorption, improving the utilization rate of phosphorus and even nitrogen, phosphorus, and potassium elements in fertilizers; furthermore, the microenvironment provided by the nanoporous materials ensures increased soil microbial activity, promoting soil microenvironment improvement. In summary, the nano-slow-release synergist of the present invention is of significant importance in promoting soil environmental improvement and protecting against non-point source pollution. Attached Figure Description

[0044] Figure 1 The cumulative nutrient release curves of calcium in the nano-sustained-release synergists of each embodiment are shown.

[0045] Figure 2 The cumulative nutrient release curves of magnesium in the nano-slow-release synergists of each embodiment are shown.

[0046] Figure 3 The cumulative nutrient release curves of zinc in the nano-slow-release synergists of each embodiment are shown. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents used, or any products for which the manufacturer is not specified, are all commercially available conventional products. All features disclosed in this specification, except for mutually exclusive features and / or steps, may be combined in any manner.

[0048] The following embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way.

[0049] In the following examples and comparative examples, "parts" refers to parts by mass.

[0050] The waterborne polyurethane described in the following examples and comparative examples was purchased from Shenzhen Yoshida Chemical Co., Ltd., and its polyurethane content was 32%. The amount of waterborne polyurethane in the following examples and comparative examples refers to the amount of pure polyurethane, that is, it was converted during the weighing process.

[0051] The lignin-based epoxy resins in the following examples and comparative examples were all prepared by the following method:

[0052] Alkali lignin pretreatment: Weigh alkali lignin, dissolve it in 1 mol / L NaOH solution, filter to remove insoluble matter, adjust the pH of the solution to 2 with 1 mol / L hydrochloric acid, filter, wash with distilled water until neutral, and dry at 40℃ for later use.

[0053] Synthesis of lignin-based epoxy resin: Weigh the pretreated alkali lignin, add 20% NaOH solution as solvent and catalyst, add epichlorohydrin at room temperature, stir, heat to 80℃, react for 3 hours and then cool to room temperature for later use.

[0054] The mass ratio of pretreated alkali lignin to epichlorohydrin is 1:12, and the volume ratio of alkali lignin to 20% sodium hydroxide solution is 5ml:1g.

[0055] Example 1

[0056] This embodiment provides a method for preparing a nano-sustained-release synergist, comprising the following steps:

[0057] S1 Preparation of nano-matrix: 1000g of nano-montmorillonite was dispersed in 1L of water to form a uniform dispersion A; water-soluble trace element salts were dissolved in water to form an aqueous solution A (the amount of water used was such that the solid was completely dissolved without precipitation); the aqueous solution A was slowly added to the dispersion A while stirring, stirred for 4h, allowed to stand for 24h, filtered, and dried (80℃) to constant weight to obtain the nano-matrix;

[0058] The weight ratio of nano-montmorillonite and trace element salts satisfies: m(porous material): m(metal ion) = 1.5:1.

[0059] S2 Preparation of hydrophobic nanomatrix: The nanomatrix obtained in step S1 is dispersed in 1.5L of water to form a uniform dispersion B; 3-mercaptopropyltrimethoxysilane is dissolved in ethanol to form an alcohol solution, the volume ratio of silane coupling agent to ethanol is 0.8:1, and the above alcohol solution is slowly added dropwise to dispersion B under stirring, and the reaction is stirred for 5h.

[0060] The mass ratio of 3-mercaptopropyltrimethoxysilane to the nanomatrix is ​​1.5:1.

[0061] S3 Preparation of complex nanomatrix: Dissolve water-soluble trace element salts in water to form aqueous solution B (the amount of water is such that the solid is completely dissolved without precipitation). Add aqueous solution B dropwise directly to the product of step S2 to carry out the reaction. The reaction time is 6 hours and the reaction temperature is 80°C. After the reaction is completed, precipitate for 20 hours, filter, and dry at 120°C to constant weight.

[0062] The addition amount of trace element salts satisfies the following ratio: n(metal ion):n(3-mercaptopropyltrimethoxysilane) = 1.5:1.

[0063] S4 is used to prepare nano-sustained-release synergists:

[0064] Preparation of the spraying solution: Weigh the components of the polymer coating layer (70 parts of lignin-based epoxy resin, 20 parts of waterborne polyurethane, and 10 parts of trace elements) according to the proportions; weigh the curing agent diethylenetriamine (10% of the weight of lignin-based epoxy resin) and the diluent methanol (15% of the weight of lignin-based epoxy resin), and mix them evenly to prepare the spraying solution.

[0065] Preparation of nano-slow-release synergist: The complex nano matrix prepared in step S3 is fluidized in a fluidization device and heated to 100°C. Then, the spraying liquid is sprayed onto the surface of the fluidized complex nano matrix in three parts until the surface is solidified to form nano-slow-release synergist.

[0066] The amount of polymer coating is 3% of the weight of the complexed nanomatrix.

[0067] In this embodiment, the trace elements in steps S1, S3, and S4 are all calcium, magnesium, and zinc, and are all provided by water-soluble calcium chloride, magnesium chloride, and zinc sulfate. The weight ratio of each component satisfies: m(Ca 2+ ):m(Mg 2+ ):m(Zn 2+ = 5:2:0.1.

[0068] The nano-sustained-release synergist prepared in this embodiment is designated as ZG1.

[0069] Example 2

[0070] This embodiment provides a nano-sustained-release synergist, the preparation method of which differs from that of Example 1 in that:

[0071] In step S4, the polymer coating layer consists of 80 parts of lignin-based epoxy resin, 10 parts of waterborne polyurethane, and 10 parts of trace elements.

[0072] The nano-sustained-release synergist prepared in this embodiment is designated as ZG2.

[0073] Comparative Example 1

[0074] This comparative example provides a mixture of trace elements, prepared by directly mixing calcium chloride, magnesium chloride, and zinc sulfate, wherein the weight ratio of each component satisfies: m(Ca 2+ ):m(Mg 2+ ):m(Zn 2+ = 5:2:0.1.

[0075] The micro- and trace element mixture prepared in this comparative example is denoted as DK1.

[0076] Experimental Example 1: Nutrient Release Pattern

[0077] Referring to the static water extraction method of the national standard "Slow-Release Fertilizers" (GB T 23348-2009), the cumulative release patterns of various nutrients in the nano-slow-release synergists prepared in each example were determined; specifically:

[0078] First, the total calcium, total magnesium and total zinc contents in the nano-sustained-release synergist were determined according to the determination methods in GB / T19203-2003 and GB / T14540.4-2003, respectively.

[0079] Subsequently, the nano-sustained-release synergist was extracted at 25°C, and the calcium, magnesium, and zinc contents in aqueous solutions sampled at different time points were determined according to GB 11905-1989 for the detection of calcium and magnesium in water and GBT 7472-1987 for the detection of zinc in water. Data changes were recorded, and change curves were plotted as follows: Figures 1-3 .

[0080] from Figures 1-3 It can be seen that the slow-release synergists prepared in Examples 1 and 2 can both guarantee a slow-release period of more than 90 days for micronutrients, and maintain a continuous and slow release of nutrients throughout the entire slow-release period, which can supply the crop's continuous demand for nutrients throughout the entire growth cycle.

[0081] Experiment Example 2 Field Trial

[0082] Experimental location: Yunyang Town, Jingyang County, Xianyang City, Shaanxi Province

[0083] Experiment time: 2020

[0084] Experimental crop: Provençal fruit tomato

[0085] Experimental fertilizers: The slow-release synergists from Examples 1 and 2 were added to the same basic compound fertilizer at a dosage of 10% and granulated together to prepare compound fertilizers containing trace elements, which were denoted as ZG1 and ZG2, respectively. At the same time, the untreated trace element mixture DK1 was also added to the same basic compound fertilizer at a dosage of 10% and granulated together to prepare compound fertilizer containing trace elements, which was denoted as DK1. The above basic compound fertilizer was a 15-15-15 sulfur-based compound fertilizer.

[0086] Experimental treatments: Four treatments were set up, applying compound fertilizers ZG1, ZG2, and DK1 respectively, as well as a blank control group (the compound fertilizer was a compound fertilizer without trace elements); each treatment was set up with 3 replicates;

[0087] The experiment was designed as a randomized block design, with each cell corresponding to an area of ​​60m². 2 The compound fertilizer for each treatment was applied as base fertilizer and organic fertilizer together with 40 kg / mu before transplanting. All other fertilization operations and field operations were exactly the same in each plot.

[0088] During harvest, the yield of marketable fruit, the percentage of marketable fruit, and the sugar content of tomatoes in each plot were measured. The percentage of marketable fruit was calculated as the ratio of the weight of harvested marketable fruit to the total weight of fruit. Marketable fruit refers to fruit that does not meet the requirements for smoothness and gloss, such as cracked fruit and diseased fruit.

[0089] The results obtained after data processing are shown in Table 1:

[0090] Table 1. Results data for tomatoes under each treatment.

[0091] experimental group Marketable fruit yield (kg / mu) Marketable fruit rate / % Sugar content / % Blank group 10085 81.5％ 3.9 DK1 11010 89.6％ 4.2 ZG1 13010 96.1％ 4.6 ZG2 13081 96.7％ 4.6

[0092] The above results indicate that the application of compound fertilizer containing the nano-slow-release synergist of this application significantly improved the marketable fruit rate, marketable fruit yield, and sugar content of tomatoes.

[0093] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A method for preparing a nano-sustained-release synergist, characterized in that, Includes the following steps: S1 Preparation of nanomatrix: Nanomatrix was prepared by loading trace elements onto nanoporous materials as carriers. S2 Preparation of hydrophobic nanomatrix: The nanomatrix obtained in step S1 is modified with a silane coupling agent to obtain a hydrophobic nanomatrix; the silane coupling agent is 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane. S3 Preparation of complexed nanomatrix: Trace elements are complexed on the surface of the hydrophobic nanomatrix obtained in step S2 to prepare a complexed nanomatrix; S4 Preparation of nano-slow-release synergist: The complex nano-matrix obtained in step S3 is coated with a polymer coating layer to obtain the nano-slow-release synergist; the polymer coating layer comprises the following components in parts by weight: 70-80 parts of lignin-based epoxy resin, 10-20 parts of waterborne polyurethane, and 10-20 parts of trace elements. The nanoporous material in step S1 is selected from at least one of nano-montmorillonite, nano-bentonite, nano-silica, intercalated modified nano-montmorillonite, or intercalated modified nano-bentonite. The trace elements mentioned in steps S1, S3 and S4 are all selected from at least one of calcium, magnesium, iron, manganese, molybdenum, copper, zinc and cobalt; The specific operation method of step S1 includes: dispersing the nanoporous material in water to form a uniform dispersion A, dissolving the water-soluble trace element salt in water to form an aqueous solution A, slowly adding the aqueous solution A to the dispersion A while stirring, stirring for 2-6 hours, letting it stand for 20-24 hours, filtering and drying to obtain the nano matrix; the weight ratio of the nanoporous material and the trace element salt satisfies: m(porous material):m(metal ion) = 0.8~2:1; The specific operation method of step S2 includes: dispersing the nano-matrix in water to form a uniform dispersion B; dissolving the silane coupling agent in ethanol to form an alcohol solution, wherein the volume ratio of the silane coupling agent to the ethanol is 0.1~0.5:1; slowly adding the alcohol solution dropwise to the dispersion B under stirring; and stirring the reaction for 3~5 hours; wherein the mass ratio of the silane coupling agent to the nano-matrix is ​​1~2:

1. The specific operation method of step S3 includes: dissolving the water-soluble trace element salt in water to form an aqueous solution B, directly adding the aqueous solution B dropwise to the product of step S2 to carry out the reaction, the reaction time is 4-6 hours, the reaction temperature is 60-80℃; after the reaction is completed, precipitate for 10-20 hours, filter, and dry at 120℃ to constant weight; the amount of trace element salt added satisfies: n(metal ion):n(silane coupling agent) = 1~2:1; Step S4 includes the following steps: preparing the spraying liquid: weighing each component of the polymer coating layer according to the proportion; weighing the curing agent and diluent and mixing them evenly to prepare the spraying liquid; preparing the nano-slow-release synergist: fluidizing the complexed nano matrix prepared in step S3 in a fluidization device and heating it to 90~120℃, then spraying the spraying liquid onto the surface of the fluidized complexed nano matrix in several times until the surface is cured to form the nano-slow-release synergist; the amount of the polymer coating layer is 2.5~4.5% of the weight of the complexed nano matrix.

2. The method for preparing the nano-sustained-release synergist according to claim 1, characterized in that, The preparation method of lignin-based epoxy resin in step S4 includes: Alkali lignin pretreatment: Weigh alkali lignin, dissolve it in 1 mol / L NaOH solution, filter to remove insoluble matter, adjust the pH of the solution to 2 with 1 mol / L hydrochloric acid, filter, wash with distilled water until neutral, and dry at 40℃ for later use. Synthesis of lignin-based epoxy resin: Weigh the pretreated alkali lignin, add 20% NaOH solution as solvent and catalyst, add epichlorohydrin at room temperature, stir, heat to 80℃, react for 3 hours, and then cool to room temperature for later use. The mass ratio of pretreated alkali lignin to epichlorohydrin is 1:10~12, and the volume ratio of alkali lignin to 20% sodium hydroxide solution is 5ml:1g.

3. The method for preparing the nano-sustained-release synergist according to claim 1, characterized in that, The curing agent is selected from at least one of T-31, diethylenetriamine, or maleic anhydride; the diluent is selected from methanol or acetone; the amount of the curing agent is 5-10% by weight of the lignin-based epoxy resin; the amount of the diluent is 15% to 30% by weight of the lignin-based epoxy resin.

4. A nano-sustained-release synergist, characterized in that, It is prepared by the method described in any one of claims 1 to 3.

5. A nano-slow-release synergistic fertilizer, characterized in that, The nano-sustained-release synergist is prepared by any of the methods described in claims 1 to 3, comprising 5% to 15% by weight.

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